Stretched polyethylene film, packaging material, and food packaging body

Abstract

A stretched polyethylene film which comprises a high-density polyethylene layer 1 (101), a medium-density polyethylene layer (102), and a high-density polyethylene layer 2 (103) in this order, and which, when a first differential scanning calorimetry (1stRun) and a second differential scanning calorimetry (2ndRun) are continued using a differential scanning calorimeter, has a DSC curve 1 obtained by the first differential scanning calorimetry (1stRun) and a DSC curve 2 obtained by the second differential scanning calorimetry (2ndRun), and the DSC curve 2 obtained by the second differential scanning calorimetry (2ndRun) is a DSC curve 3 obtained by the second differential scanning calorimetry (2ndRun). An endothermic peak (A) is observed in the range of 10-160 DEG C inclusive, the heat of fusion ([Delta] Hm) of the endothermic peak (A) is 110-162 J / g inclusive, and a first differential scanning calorimetry (1stRun) includes a step in which the temperature is increased from-50 DEG C to 200 DEG C at a temperature increase rate of 10 DEG C / min, an isothermal step in which the temperature is held at 200 DEG C for 10 minutes, and a step in which the temperature is decreased from 200 DEG C to-50 DEG C at a temperature decrease rate of 10 DEG C / min. The second differential scanning calorimetry (2ndRun) comprises a process of raising the temperature from-50 DEG C to 200 DEG C at a temperature raising speed of 10 DEG C / min.

Description

Technical Field

[0001] The invention relates to a stretched polyethylene film, a packaging material and a food packaging body. Background Art

[0002] In the field of packaging films, attempts to improve various performances by improving the raw materials used, layer structures, etc. are known.

[0003] Patent document 1 discloses a laminated film comprising a substrate layer and a heat-sealing layer, wherein the stiffness strength in the TD direction measured under the conditions of a loop length of 50 mm and a pressing length of 10 mm is greater than 70 mN, and the polyethylene content is greater than 90% by mass. It is also recorded that the laminated film can be recycled and can fully ensure the self-supporting property of a self-supporting bag.

[0004] Patent document 2 discloses a polyethylene laminate for packaging materials, which comprises at least a stretched polyethylene film, an adhesive layer, and a heat-sealable polyethylene layer, wherein the adhesive layer comprises a solvent-free adhesive, and the stretched polyethylene film comprises at least one of a high-density polyethylene (HDPE) and a medium-density polyethylene (MDPE). Patent document 2 also records that the polyethylene laminate for packaging materials can significantly reduce the load on the environment and has high printability and strength.

[0005] Patent document 3 discloses a polyethylene co-extruded film comprising a polyethylene film substrate and a polyethylene film layer, wherein the polyethylene film substrate is an electron beam irradiated layer comprising polyethylene, a light stabilizer and a cross-linking agent, the polyethylene film layer comprises polyethylene, and the surface opposite to the surface provided with the polyethylene film substrate has heat sealability, and records that the polyethylene co-extruded film can suppress deterioration over time and further improves heat resistance and strength.

[0006] Patent document 4 describes a multilayer film, which is stacked in sequence: a gas barrier layer formed by coating a dispersion containing an inorganic layered compound and a water-soluble polymer on at least one surface of a substrate layer composed of a thermoplastic resin; a covering layer containing a cationic resin and a resin having a hydroxyl group; an adhesive layer; and a sealant layer, and describes that the multilayer film has excellent heat sealing properties and gas barrier properties.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2022-053864

[0010] Patent Document 2: Japanese Patent Application Publication No. 2022-079510

[0011] Patent Document 3: Japanese Patent Application Publication No. 2018-008455

[0012] Patent Document 4: Japanese Patent Application Publication No. 2009-241359 Summary of the invention

[0013] Problems to be solved by the invention

[0014] In recent years, packaging films have received serious attention from society due to the increase in environmental awareness, especially the issue of marine plastic pollution. In addition, the recycling of packaging films is now more required than ever before. In other words, it is increasingly required to design and manufacture packaging films in consideration of "ease of recycling".

[0015] Most packaging films so far have achieved the desired effects (strength, gas barrier properties, etc.) by laminating multiple raw materials. For example, the multilayer film described in Patent Document 4 has at least four layers: a gas barrier layer, a cover layer, an adhesive layer, and a sealant layer. However, laminating multiple raw materials makes it difficult to recycle.

[0016] From the viewpoint of making the packaging film easy to recycle, for example, it is conceivable to make the packaging film have the simplest possible layer structure.

[0017] From the perspective of simplifying the layer structure, in the extreme case, it is considered to make the packaging film a "single layer". In addition, even if it is not made into a single layer, as a whole, there are examples such as Patent Documents 1 to 3 that consider the ease of recycling as a multilayer structure in which a single material is mixed at a high content.

[0018] The inventors of the present application conducted preliminary research on various properties required of packaging films using polyethylene films, which are relatively inexpensive and commonly used packaging materials. The results of the research revealed that polyethylene "single-layer" films have poor flexibility.

[0019] The present invention provides a stretched polyethylene film having improved flexibility and a packaging material composed of such a stretched polyethylene film.

[0020] Means for solving problems

[0021] [1] A stretched polyethylene film comprising

[0022] High density polyethylene layer 1;

[0023] a medium density polyethylene layer; and

[0024] High density polyethylene layer 2,

[0025] When the first differential scanning calorimetry (1st Run) and the second differential scanning calorimetry (2nd Run) are continuously performed using a differential scanning calorimeter, in the DSC curve 1 obtained by the first differential scanning calorimetry, an endothermic peak A is observed in the range of 10°C to 160°C, and the melting heat (ΔH m ) is 110 J / g or more and 162 J / g or less, the first differential scanning calorimetry (1stRun) includes 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min, and the second differential scanning calorimetry (2ndRun) includes a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

[0026] [2] The stretched polyethylene film according to [1], wherein the density of the medium-density polyethylene layer measured in accordance with JIS K 7112:1999 is 910 kg / m 3 Above 935kg / m 3 the following.

[0027] [3] The stretched polyethylene film according to [1] or [2], wherein the amorphous thickness determined from a peak at a diffraction angle 2θ in the MD direction within a range of 0.2 to 0.4° as measured by small angle X-ray scattering (SAXS) is less than 12.5 nm.

[0028] [4] A stretched polyethylene film as described in any one of [1] to [3], wherein, when the entire stretched polyethylene film is set to 100 mass%, the total amount of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 in the stretched polyethylene film is 25 mass% to 85 mass%.

[0029] [5] The stretched polyethylene film according to any one of [1] to [4], wherein the density of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is 940 kg / m 3 Above 970kg / m 3 the following.

[0030] [6] The stretched polyethylene film as described in any one of [1] to [5], wherein the MFR of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with ASTM D1238 at 190°C and a load of 2.16 kg is each not less than 0.01 g / 10 min and not more than 20 g / 10 min.

[0031] [7] The stretched polyethylene film as described in any one of [1] to [6], wherein the MFR of the medium density polyethylene layer measured according to ASTM D1238 at 190°C and a load of 2.16 kg is 0.01 g / 10 min or more and 20 g / 10 min or less.

[0032] [8] A stretched polyethylene film as described in any one of [1] to [7], wherein in the stretched polyethylene film, the full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° in the MD direction determined by small-angle X-ray scattering (SAXS) is 0.21° or less.

[0033] [9] The stretched polyethylene film according to any one of [1] to [8], wherein the haze per sheet of the stretched polyethylene film measured in accordance with JIS K 7136:2000 is 16.0% or less.

[0034]

[10] A stretched polyethylene film as described in any one of [1] to [9], wherein the tensile modulus T2 of the stretched polyethylene film in the TD direction is greater than 700 MPa, measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min.

[0035]

[11] A stretched polyethylene film as described in any one of [1] to

[10] , wherein the total value of the tensile elastic modulus T1 in the MD direction and the tensile elastic modulus T2 in the TD direction of the stretched polyethylene film, measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min, is 1500 MPa to 2900 MPa.

[0036]

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

[11] , wherein the heat shrinkage in the MD direction of the stretched polyethylene film when heated at 100°C for 15 minutes according to JIS C2151:2019 is 6.0% or less.

[0037]

[13] The stretched polyethylene film according to any one of [1] to

[12] , wherein the heat shrinkage in the MD direction of the stretched polyethylene film when heated at 120°C for 15 minutes according to JIS C2151:2019 is 25.0% or less.

[0038]

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

[13] , wherein at least one surface of the stretched polyethylene film is a corona-treated surface.

[0039]

[15] A stretched polyethylene film as described in any one of [1] to

[14] , wherein the lamination strength in the MD direction of the stretched polyethylene film, measured in accordance with JIS Z 0238:1998 using a tensile testing machine under the conditions of T-peeling and a crosshead speed of 300 mm / min, is 0.7 N / 15 mm or more and 10.0 N / 15 mm or less.

[0040]

[16] A stretched polyethylene film as described in any one of [1] to

[15] , wherein the number of pinholes in the stretched polyethylene film is 2500 / m as measured by 3000 bending tests at a bending angle of 440 degrees and a bending speed of 40 times / min at -30°C using a Gelbo flex tester. 2 the following.

[0041]

[17] A stretched polyethylene film as described in any one of [1] to

[16] , wherein the tear strength in the MD direction of the stretched polyethylene film measured using a light load tear tester under the conditions of test piece size: MD direction: 63.5 mm, TD direction: 50.0 mm, pendulum weight: 96.09 g, tear length: 12.7 mm, pendulum lifting angle: 90° is 100 mN or more and 600 mN or less.

[0042]

[18] The stretched polyethylene film according to any one of [1] to

[17] , wherein the overall thickness of the stretched polyethylene film is 10 μm to 100 μm.

[0043]

[19] The stretched polyethylene film according to any one of [1] to

[18] , which is a food packaging film.

[0044]

[20] A packaging material using the stretched polyethylene film according to any one of [1] to

[19] .

[0045]

[21] A food package, comprising:

[0046]

[20] the packaging material; and

[0047] Food in the aforementioned packaging materials.

[0048] Effects of the Invention

[0049] According to the present invention, a stretched polyethylene film having improved flexibility can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] [ Figure 1 ] is a cross-sectional view schematically showing an example of the structure of a stretched polyethylene film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] Hereinafter, embodiments of the present invention will be described using the drawings. It should be noted that, in the present specification, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0052] <Stretched Polyethylene Film>

[0053] The stretched polyethylene film (100) involved in the present embodiment sequentially comprises a high-density polyethylene layer 1 (101), a medium-density polyethylene layer (102), and a high-density polyethylene layer 2 (103). When a first differential scanning calorimetry (1st Run) and a second differential scanning calorimetry (2nd Run) are continuously performed using a differential scanning calorimeter, in a DSC curve 1 obtained by the first differential scanning calorimetry, an endothermic peak A is observed in the range of 10°C to 160°C, and the heat of fusion (ΔH m ) is 110 J / g or more and 162 J / g or less, the first differential scanning calorimetry (1stRun) includes 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min, and the second differential scanning calorimetry (2ndRun) includes a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

[0054] According to the research of the inventors of the present application, it is found that by forming a three-layer structure including a high-density polyethylene layer 1, a medium-density polyethylene layer, and a high-density polyethylene layer 2 in this order, and by making the melting heat (ΔH) of the endothermic peak A observed in the range of 10°C to 160°C in the DSC curve obtained by differential scanning calorimetry of a stretched polyethylene film m ) is within the above range, thereby being able to improve the softness.

[0055] It should be noted that, in this specification, flexibility refers to the properties represented by puncture resistance, bending resistance, and tear strength, and can be evaluated by the performance balance of puncture resistance, bending resistance, and tear strength. In addition, in this specification, so-called flexibility means that the film is soft and not easy to break or tear.

[0056] In the stretched polyethylene film of the present embodiment, from the viewpoint of further suppressing uneven thickness of the stretched polyethylene film, the heat of fusion (ΔH m ) is 110 J / g or more, preferably 120 J / g or more, more preferably 130 J / g or more, further preferably 140 J / g or more, further preferably 145 J / g or more, further preferably 150 J / g or more, and is 162 J / g or less, preferably 160 J / g or less.

[0057] The heat of fusion (ΔH) of the endothermic peak A in the DSC curve obtained by differential scanning calorimetry is m ) was determined as follows.

[0058] A test piece of about 5.0 mg was cut out from the stretched polyethylene film. Next, the test piece was subjected to a first differential scanning calorimetry (1st Run) and a second differential scanning calorimetry (2nd Run) under a nitrogen flow using a differential scanning calorimeter, wherein the first differential scanning calorimetry (1st Run) included 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min, and the second differential scanning calorimetry (2nd Run) included a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

[0059] In the DSC curve 1 obtained by the first differential scanning calorimetry, the heat of fusion (ΔH m )(J / g). Here, the heat of the endothermic peak A is calculated by finding the area enclosed by the melting endothermic curve including the endothermic peak A and the baseline. The baseline is obtained by differentiating the Heat Flow with time before and after the endothermic peak A to display the Deriv.Heat Flow, and is set as a line connecting the point where the change of Deriv.Heat Flow starts (i.e., the point where the flat region of Deriv.Heat Flow ends) and the point where the change of Deriv.Heat Flow ends (i.e., the point where Deriv.Heat Flow enters the flat region).

[0060] When a plurality of endothermic peaks are observed in the range of 10° C. to 160° C., the maximum peak is defined as endothermic peak A.

[0061] Next, the materials constituting the stretched polyethylene film will be described.

[0062] In the stretched polyethylene film according to the present embodiment, from the viewpoint of making the amorphous thickness of the stretched polyethylene film below a predetermined value and further improving the flexibility of the stretched polyethylene film, the density of the medium-density polyethylene layer measured in accordance with JIS K 7112:1999 is preferably 910 kg / m 3 More preferably 913 kg / m 3 More preferably, 915 kg / m 3 Above, preferably 935kg / m 3 Below, more preferably 933kg / m3 Below, more preferably 932kg / m 3 Below, more preferably 930kg / m 3 Below, more preferably 928kg / m 3 Below, more preferably 925kg / m 3 Below, more preferably 922kg / m 3 Below, more preferably 920kg / m 3 In addition, in the stretched polyethylene film according to the present embodiment, from the viewpoint of further improving the performance balance between flexibility and thermal dimensional stability, the density of the medium-density polyethylene layer measured in accordance with JIS K 7112:1999 is preferably 917 kg / m 3 More preferably 918 kg / m 3 above.

[0063] According to the stretched polyethylene film according to the present embodiment, the flexibility can be further improved by adopting a three-layer structure in which a medium-density polyethylene layer is sandwiched between high-density polyethylene layers 1 and 2 and by setting the density of the medium-density polyethylene layer within the above range.

[0064] From the viewpoint of making the amorphous thickness of the stretched polyethylene film below a predetermined value and further improving the flexibility, the density of the medium-density polyethylene constituting the medium-density polyethylene layer as measured in accordance with JIS K7112:1999 is preferably 910 kg / m 3 More preferably 913 kg / m 3 More preferably, 915 kg / m 3 Above, preferably 935kg / m 3 Below, more preferably 933kg / m 3 Below, more preferably 932kg / m 3 Below, more preferably 930kg / m 3 Below, more preferably 928kg / m 3 Below, more preferably 925kg / m 3 Below, more preferably 922kg / m 3 Below, more preferably 920kg / m 3 the following.

[0065] From the viewpoint of further improving processability, the melt flow rate (MFR) of the medium density polyethylene layer measured according to ASTM D1238 at 190°C and a load of 2.16 kg is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.5 g / 10 min or more, further preferably 1.0 g / 10 min or more, and from the viewpoint of further improving the stiffness of the stretched polyethylene film while maintaining the tear resistance of the stretched polyethylene film, it is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, further preferably 5 g / 10 min or less, further preferably 4 g / 10 min or less, further preferably 3 g / 10 min or less.

[0066] From the viewpoint of improving heat resistance and stiffness while maintaining processability and adhesion, the melting point of the medium density polyethylene layer measured by differential scanning calorimetry (DSC) is preferably above 110°C, more preferably above 115°C. In addition, from the viewpoint of improving adhesion while maintaining heat resistance, it is preferably below 135°C, more preferably below 130°C, further preferably below 128°C, and further preferably below 125°C.

[0067] From the viewpoint of further improving processability, the melt flow rate (MFR) of the medium density polyethylene constituting the medium density polyethylene layer, measured in accordance with ASTM D1238 at 190°C and a load of 2.16 kg, is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.5 g / 10 min or more, further preferably 1.0 g / 10 min or more, and from the viewpoint of further improving the stiffness of the stretched polyethylene film while maintaining the tear resistance of the stretched polyethylene film, it is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, further preferably 5 g / 10 min or less, further preferably 4 g / 10 min or less, further preferably 3 g / 10 min or less.

[0068] From the viewpoint of improving heat resistance and stiffness while maintaining processability and adhesion, the melting point of the medium density polyethylene constituting the medium density polyethylene layer, as measured by differential scanning calorimetry (DSC), is preferably above 110°C, more preferably above 115°C. Furthermore, from the viewpoint of improving adhesion while maintaining heat resistance, it is preferably below 135°C, more preferably below 130°C, further preferably below 128°C, and further preferably below 125°C.

[0069] When two or more polyethylenes are used as the polyethylene constituting the medium density polyethylene layer, the density, MFR and melting point of the medium density polyethylene layer can be measured using a mixture obtained by melt blending two or more polyethylenes using a known method. The melting point of the medium density polyethylene layer can be the peak temperature of the maximum melting peak.

[0070] From the viewpoint that the non-crystalline thickness of the stretched polyethylene film is below the specified value, further improves flexibility, relative to the medium density polyethylene layer as a whole, the content of the medium density polyethylene in the medium density polyethylene layer is preferably more than 80 mass %, more preferably more than 85 mass %, more preferably more than 90 mass %, more preferably more than 95 mass %, more preferably more than 98 mass %. The upper limit of the content of the medium density polyethylene in the medium density polyethylene layer is not limited, for example, is below 100 mass %.

[0071] In the stretched polyethylene film involved in the present embodiment, from the viewpoint of further improving the performance balance of transparency, rigidity, heat resistance, slippage, thermal fusion strength and flexibility, the total amount of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 is preferably 25 mass% or more, more preferably 30 mass% or more, further preferably 35 mass% or more, further preferably 40 mass% or more, and further preferably 45 mass% or more, relative to the entire stretched polyethylene film. In addition, from the viewpoint of making the amorphous thickness of the stretched polyethylene film below a specified value and further improving the flexibility of the stretched polyethylene film, it is preferably 85 mass% or less, more preferably 83 mass% or less, further preferably 80 mass% or less, further preferably 70 mass% or less, further preferably 65 mass% or less, and further preferably 60 mass% or less.

[0072] In the stretched polyethylene film of this embodiment, the high-density polyethylene layer 1 and the high-density polyethylene layer 2 can be formed using the same material or different materials. When using different materials, the following composition of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 is preferably satisfied.

[0073] From the viewpoint of further improving the performance balance of transparency, rigidity, heat resistance, slidability and heat-welding strength, the content of high-density polyethylene in high-density polyethylene layer 1 and high-density polyethylene layer 2 is preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and more preferably 98% by mass or more, relative to the entirety of each high-density polyethylene layer 1 and high-density polyethylene layer 2. The upper limit of the content of high-density polyethylene in high-density polyethylene layer 1 and high-density polyethylene layer 2 is not limited, for example, each is 100% by mass or less.

[0074] From the viewpoint of achieving a better balance of various properties such as heat resistance, transparency, mechanical properties, and rigidity, the density of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is preferably 940 kg / m 3 More preferably 943 kg / m 3 More preferably, 945 kg / m 3 In addition, from the viewpoint of achieving a better balance between flexibility and rigidity, 970 kg / m 3 Below, more preferably 968kg / m 3 Below, more preferably 965kg / m 3 Below, more preferably 960kg / m 3 Below, more preferably 955kg / m 3 Below, more preferably 950kg / m 3 the following.

[0075] From the viewpoint of achieving a better balance of various properties such as heat resistance, transparency, mechanical properties, and rigidity, the density of the high-density polyethylene constituting the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is preferably 940 kg / m 3 More preferably 943 kg / m 3 More preferably, 945 kg / m 3 In addition, from the viewpoint of achieving a better balance between flexibility and rigidity, 970 kg / m 3 Below, more preferably 968kg / m 3 Below, more preferably 965kg / m 3 Below, more preferably 960kg / m 3 Below, more preferably 955kg / m 3 Below, more preferably 950kg / m 3 the following.

[0076] From the viewpoint of further improving fluidity and moldability, the melt flow rate (MFR) of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured under the conditions of 190°C and a load of 2.16 kg in accordance with ASTM D1238 is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.5 g / 10 min or more, and further preferably 1.0 g / 10 min or more. From the viewpoint of further improving the tear resistance of the stretched polyethylene film while improving the stiffness of the stretched polyethylene film, it is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, further preferably 5 g / 10 min or less, further preferably 3 g / 10 min or less, further preferably 2 g / 10 min or less, and further preferably 1.5 g / 10 min or less.

[0077] From the viewpoint of further improving fluidity and moldability, the melt flow rate (MFR) of the high-density polyethylene constituting the high-density polyethylene layer 1 and the high-density polyethylene layer 2, as measured according to ASTM D1238 at 190°C and a load of 2.16 kg, is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, further preferably 0.5 g / 10 min or more, and further preferably 1.0 g / 10 min or more. From the viewpoint of further improving the stiffness of the stretched polyethylene film while maintaining the tear resistance of the stretched polyethylene film, it is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, further preferably 5 g / 10 min or less, further preferably 3 g / 10 min or less, further preferably 2 g / 10 min or less, and further preferably 1.5 g / 10 min or less.

[0078] From the viewpoint of further improving the balance among thermal dimensional stability, heat resistance, mechanical properties, rigidity, bag-making properties, fluidity and moldability, the melting points of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 as measured by a differential scanning calorimeter (DSC) are each preferably 120°C or higher, more preferably 125°C or higher, and are further preferably 135°C or lower, more preferably 133°C or lower, and further preferably 130°C or lower.

[0079] From the viewpoint of further improving the balance among thermal dimensional stability, heat resistance, mechanical properties, rigidity, bag making properties, fluidity and formability, the melting points of the high-density polyethylene constituting the high-density polyethylene layer 1 and the high-density polyethylene layer 2 as measured by a differential scanning calorimeter (DSC) are preferably 120°C or higher, more preferably 125°C or higher, and are preferably 135°C or lower, more preferably 133°C or lower, and further preferably 130°C or lower.

[0080] When two or more polyethylenes are used as the polyethylene constituting the high-density polyethylene layer, the density, MFR and melting point of the high-density polyethylene layer can be measured values ​​obtained by melt-blending two or more polyethylenes using a known method. The melting point of the high-density polyethylene layer can be the peak temperature of the maximum melting peak.

[0081] It is preferred that at least one surface of the stretched polyethylene film of the present embodiment is a corona-treated surface (a surface modified by corona discharge irradiation). By making at least one surface of the stretched polyethylene film of the present embodiment a corona-treated surface, the printing properties, coating properties, and lamination properties with other films of the stretched polyethylene film of the present embodiment can be further improved.

[0082] The high-density polyethylene layer 1, high-density polyethylene layer 2 and medium-density polyethylene layer may contain various additives within the scope of not impairing the purpose of the present invention. As additives, heat stabilizers, weathering stabilizers, antioxidants, ultraviolet absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, inorganic or organic fillers, etc. can be cited.

[0083] From the viewpoint of further improving the balance of transparency, rigidity, heat resistance, slidability and thermal fusion strength, the thickness of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 17 μm or less, more preferably 15 μm or less, further preferably 10 μm or less, and further preferably 7 μm or less.

[0084] The thicknesses of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 may be the same or different, but are preferably the same from the viewpoint of making the mechanical strength of the stretched polyethylene film uniform on the high-density polyethylene layer 1 side and the high-density polyethylene layer 2 side.

[0085] From the viewpoint of improving the flexibility of the stretched polyethylene film, the thickness of the medium-density polyethylene layer is preferably 2 μm or more, more preferably 3 μm or more, further preferably 5 μm or more, further preferably 8 μm or more, and is preferably 30 μm or less, more preferably 25 μm or less, further preferably 20 μm or less, further preferably 15 μm or less, further preferably 13 μm or less, further preferably 11 μm or less.

[0086] From the viewpoint of maintaining the tear property of the stretched polyethylene film and further improving the mechanical strength, the overall thickness of the stretched polyethylene film is preferably 10 μm or more, more preferably 13 μm or more, and further preferably 15 μm or more. Furthermore, from the viewpoint of further improving the tear property, handleability, formability, bag-making suitability, lightness, etc. of the stretched polyethylene film, the thickness is preferably 100 μm or less, more preferably 70 μm or less, further preferably 50 μm or less, further preferably 40 μm or less, further preferably 30 μm or less, and further preferably 25 μm or less.

[0087] Next, the physical properties of the stretched polyethylene film will be described.

[0088] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving the balance among the thermal dimensional stability, formability, mechanical properties, transparency, bag making properties, handleability and packaging suitability of the stretched polyethylene film, the tensile elastic modulus T1 in the MD direction of the stretched polyethylene film measured under the conditions of a measuring temperature of 23±2°C, 50±5%RH and a tensile speed of 5 mm / min in accordance with JIS K7127:1999 using a tensile testing machine is preferably 800 MPa or more, more preferably 850 MPa or more, further preferably 900 MPa or more, further preferably 950 MPa or more, further preferably 1000 MPa or more, further preferably 1050 MPa or more, further preferably 1100 MPa or more, further preferably 1200 MPa or more, and from the viewpoint of further improving the balance among the thermal dimensional stability, bag making properties and packaging suitability of the stretched polyethylene film, it is preferably 1500 MPa or less, more preferably 1450 MPa or less, further preferably 1400 MPa or less, further preferably 1350 MPa or less.

[0089] From the viewpoint of further improving the balance among the formability, mechanical properties, transparency, bag making properties, handleability and packaging suitability of the stretched polyethylene film, the tensile elastic modulus T2 in the TD direction of the stretched polyethylene film is preferably 700 MPa or more, more preferably 750 MPa or more, further preferably 800 MPa or more, further preferably 850 MPa or more, further preferably 900 MPa or more, further preferably 920 MPa or more, further preferably 925 MPa or more. Furthermore, from the viewpoint of further improving the balance among the bag making properties and packaging suitability of the stretched polyethylene film, it is preferably 1400 MPa or less, more preferably 1300 MPa or less, further preferably 1200 MPa or less, further preferably 1180 MPa or less, further preferably 1150 MPa or less, further preferably 1130 MPa or less.

[0090] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving the performance balance among transparency, rigidity, heat resistance, heat fusion strength, and thermal dimensional stability, and further improving the stiffness of the stretched polyethylene film, the following JIS K7127: 1999. The total value of the tensile elastic modulus T1 in the MD direction and the tensile elastic modulus T2 in the TD direction of the stretched polyethylene film, measured using a tensile testing machine under the conditions of a measuring temperature of 23±2°C, 50±5% RH and a stretching speed of 5 mm / min, is preferably 1500 MPa or more, more preferably 1600 MPa or more, further preferably 1700 MPa or more, further preferably 1800 MPa or more, further preferably 1900 MPa or more, further preferably 2000 MPa or more, further preferably 2050 MPa or more. In addition, from the viewpoint of preventing failures such as cutting from occurring during the molding of the stretched polyethylene film, facilitating continuous stretch molding of the film and further improving industrial continuous productivity, it is preferably 2900 MPa or less, more preferably 2800 MPa or less, further preferably 2700 MPa or less, further preferably 2600 MPa or less, further preferably 2500 MPa or less, further preferably 2400 MPa or less.

[0091] Such tensile modulus is a substitute value for quantitatively measuring the stiffness of the film, and can be adjusted by, for example, adjusting the types and content ratios of the high-density polyethylene layer 1, the high-density polyethylene layer 2 and the medium-density polyethylene layer contained in the stretched polyethylene film, the thickness of the stretched polyethylene film, the stretching ratio, etc.

[0092] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving the transparency of the stretched polyethylene film, the haze per stretched polyethylene film measured in accordance with JIS K 7136: 2000 is preferably 16.0% or less, more preferably 15.8% or less, further preferably 15.5% or less, further preferably 15.3% or less, further preferably 15.0% or less. The lower limit of the haze per stretched polyethylene film is not limited, and may be, for example, 0.1% or more, 1.0% or more, 3.0% or more, or 5.0% or more.

[0093] In the stretched polyethylene film involved in the present embodiment, from the viewpoint of improving the flexibility of the stretched polyethylene film, the amorphous thickness determined by small-angle X-ray scattering (SAXS) from the peak in the range of 0.2 to 0.4° at the diffraction angle 2θ in the MD direction is preferably less than 12.5 nm, more preferably 12.4 nm or less, further preferably 12.2 nm or less, further preferably 12.0 nm or less, further preferably 11.7 nm or less, and further preferably 11.5 nm or less. The lower limit of the amorphous thickness determined by small-angle X-ray scattering (SAXS) from the peak in the range of 0.2 to 0.4° at the diffraction angle 2θ in the MD direction is not limited, and is, for example, 9.0 nm or more, 9.5 nm or more, 10.0 nm or more, 10.5 nm or more, or 11.0 nm or more.

[0094] Such amorphous thickness can be adjusted by adjusting the types and content ratios of the high-density polyethylene layer 1, high-density polyethylene layer 2 and medium-density polyethylene layer contained in the stretched polyethylene film, the thickness of the stretched polyethylene film, the stretching ratio, etc.

[0095] According to the stretched polyethylene film involved in this embodiment, the flexibility of the stretched polyethylene film can be further improved by setting it as a three-layer structure in which the medium density polyethylene layer is sandwiched by the high density polyethylene layer 1 and the high density polyethylene layer 2, and making the amorphous thickness of the stretched polyethylene film below the above upper limit.

[0096] In the stretched polyethylene film of the present embodiment, from the viewpoint of increasing the crystallinity of the surface layer of the stretched polyethylene film, thereby suppressing the formation of a fragile layer and making the slip property further good, the full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° at the diffraction angle 2θ in the MD direction determined by small angle X-ray scattering (SAXS) is preferably 0.21° or less, more preferably 0.20° or less, further preferably 0.19° or less, and further preferably 0.18° or less. From the viewpoint of further improving film forming properties, bag forming processability, lamination strength, and thermal dimensional stability, the full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° at the diffraction angle 2θ in the MD direction of the stretched polyethylene film is preferably 0.05° or more, more preferably 0.10° or more, further preferably 0.13° or more, further preferably 0.15° or more, further preferably 0.16° or more, and further preferably 0.17° or more.

[0097] The full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° diffraction angle 2θ in the MD direction determined by small-angle X-ray scattering (SAXS) can be adjusted, for example, by adjusting the types and content ratios of the high-density polyethylene layer 1, the high-density polyethylene layer 2 and the medium-density polyethylene layer contained in the stretched polyethylene film, the thickness of the stretched polyethylene film, the stretching ratio, etc.

[0098] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving thermal dimensional stability and bag-making properties, the heat shrinkage rate in the MD direction of the stretched polyethylene film when heated at 100°C for 15 minutes is preferably 6.0% or less, more preferably 5.5% or less, further preferably 5.0% or less, further preferably 4.5% or less, further preferably 4.3% or less, further preferably 4.1% or less, further preferably 4.0% or less, and can be 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, or 2.5% or more.

[0099] In addition, the heat shrinkage rate of the stretched polyethylene film can be measured in accordance with JIS C2151:2019.

[0100] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving thermal dimensional stability and bag-making properties, the heat shrinkage rate in the MD direction of the stretched polyethylene film when heated at 120°C for 15 minutes is preferably 25.0% or less, more preferably 23.0% or less, further preferably 22.5% or less, further preferably 22.0% or less, further preferably 21.0% or less, further preferably 20.0% or less, and can be 1.0% or more, 3.0% or more, 5.0% or more, 10.0% or more, or 15.0% or more.

[0101] When at least one side of the stretched polyethylene film is a corona-untreated side, from the viewpoint of further improving heat resistance, the heat-welding strength when the corona-untreated side of the stretched polyethylene film is bonded and heat-welded at 140° C. is preferably 4.0 N / 15 mm or less, more preferably 3.8 N / 15 mm or less. The lower limit of the heat-welding strength is not limited, and is, for example, 0.1 N / 15 mm or more.

[0102] The thermal weld strength was measured as follows.

[0103] The corona untreated surfaces of two stretched polyethylene films cut to a width of 15 mm were heat-fused to each other under the conditions of 140°C, a pressure of 2.0 kgf, and a sealing time of 1.0 second to obtain a laminated film. Next, the two stretched polyethylene films were peeled off under the conditions of 90° peeling, a peeling speed of 300 mm / min, and stretching in the MD direction using the laminated film cut to a width of 15 mm, and the peel strength at this time was set as the heat-fusion strength (N / 15 mm).

[0104] In the stretched polyethylene film of the present embodiment, from the viewpoint of further improving the balance between adhesion and easy opening properties, the lamination strength measured in accordance with JIS Z 0238:1998 is preferably 0.7 N / 15 mm or more, more preferably 0.8 N / 15 mm or more, and is preferably 10.0 N / 15 mm or less, more preferably 5.0 N / 15 mm or less, further preferably 3.0 N / 15 mm or less, and further preferably 2.0 N / 15 mm or less.

[0105] In addition, the lamination strength was measured as follows.

[0106] A test piece of 297 cm×210 cm was cut out from the stretched polyethylene film, and the corona-treated surface of the test piece was bonded to the corona-treated surface of a 50 μm-thick cast LLDPE film whose one surface was corona-treated using an ester adhesive, and then aged at 40° C. for 3 days. Next, a test piece of 15 mm width was cut out, and the peel strength when peeled in the MD direction under the conditions of a peel angle of 90°, a chuck distance of 100 mm, and a crosshead speed of 300 mm / min was determined using a tensile tester in accordance with JIS Z 0238:1998, and was defined as the lamination strength.

[0107] In the stretched polyethylene film of this embodiment, the static friction coefficient (tanθ) of the surface of the stretched polyethylene film measured by a sliding tester is preferably greater than 0.20, more preferably greater than 0.25, and is preferably less than 0.65, more preferably less than 0.60, further preferably less than 0.55, and further preferably less than 0.50.

[0108] When either the high-density polyethylene layer 1 or the high-density polyethylene layer 2 of the stretched polyethylene film is corona treated, the static friction coefficient (tanθ) of the stretched polyethylene film surface can be measured between the treated surfaces, between the untreated surfaces, or between the treated surface and the untreated surface.

[0109] Especially from the aspect that can further improve the operability of stretched polyethylene film, the static friction coefficient (tanθ) of the surface of the corona untreated side is preferably within the above range. The static friction coefficient (tanθ) of the surface of the corona untreated side of the stretched polyethylene film is preferably 0.20 or more, more preferably 0.25 or more, and preferably 0.65 or less, more preferably 0.60 or less, further preferably 0.55 or less, further preferably 0.50 or less.

[0110] The static friction coefficient (tan θ) of the surface of the stretched polyethylene film on the side of the corona-untreated surface was measured by the following method.

[0111] Prepare two stretched polyethylene films cut into a size of 50 mm × 75 mm (hereinafter referred to as stretched polyethylene films 1 and 2), and fix one of the stretched polyethylene films 1 to an inclined plate with the corona untreated side facing upward. Next, a friction body whose bottom surface (size is 41 mm × 26 mm) is made of brass and is fixed to the center of the surface of the other stretched polyethylene film 2 opposite to the corona untreated side, and a weight is installed on the friction body in such a way that the mass applied from the friction body to the stretched polyethylene film 2 becomes 150 g. Next, overlap the surfaces of the corona untreated sides of the two stretched polyethylene films 1 and 2. Next, tilt the inclined plate at a speed of 1° / sec, and calculate the value of tanθ based on the angle θ when the upper stretched polyethylene film 2 slides out.

[0112] When measuring the static friction coefficient (tanθ) of the corona treated surface, the static friction coefficient (tanθ) of the corona untreated surface is measured by replacing the corona untreated surface with the corona treated surface in the above-mentioned method for measuring the static friction coefficient (tanθ).

[0113] In the stretched polyethylene film of the present embodiment, from the viewpoint of further suppressing the rupture of the packaging body, the puncture strength from the corona-treated surface to the corona-untreated surface measured under the conditions of 23±2°C and 50±5%RH in accordance with JIS Z1707:1997 is preferably 2.5N or more, more preferably 3.0N or more, further preferably 4.0N or more, further preferably 4.3N or more, and is preferably 8.0N or less, more preferably 7.8N or less, further preferably 7.5N or less, further preferably 7.3N or less, further preferably 7.0N or less, further preferably 6.5N or less, further preferably 6.0N or less, further preferably 5.5N or less, further preferably 5.0N or less.

[0114] From the viewpoint of further improving film-forming property and bag-making processability, the tear strength in the MD direction of the stretched polyethylene film, measured using a light-load tear tester under the condition of a check weight mass of 96.09 g, is preferably 100 mN or more, more preferably 150 mN or more, further preferably 180 mN or more, further preferably 200 mN or more, further preferably 230 mN or more, further preferably 250 mN or more. Furthermore, from the viewpoint of further improving the tear property while maintaining the heat-sealing property and stiffness of the stretched polyethylene film, it is preferably 600 mN or less, more preferably 580 mN or less, further preferably 550 mN or less, further preferably 530 mN or less, further preferably 500 mN or less, further preferably 490 mN or less, further preferably 450 mN or less.

[0115] In order to realize such tear strength, the density, thickness, etc. of each of the high-density polyethylene layer 1, the high-density polyethylene layer 2, and the medium-density polyethylene layer included in the stretched polyethylene film may be appropriately adjusted.

[0116] In addition, the tear strength in the MD direction was measured as follows.

[0117] A test piece with a length of 63.5 mm in the MD direction and 50 mm in the TD direction was cut out from the stretched polyethylene film. The tear strength (mN) in the MD direction was measured for one of the test pieces using a light load tear tester under the conditions of pendulum weight: 96.09 g, tear length: 12.7 mm, and pendulum lifting angle: 90°.

[0118] As the light-load tear tester, for example, a Model-D tester manufactured by Toyo Seiki Seisaku-sho, Ltd. can be used.

[0119] In the stretched polyethylene film of this embodiment, the number of pinholes generated in the stretched polyethylene film is preferably 2500 / m, as measured by 3000 bending tests using a Gelbo flex tester at a bending angle of 440 degrees, a bending speed of 40 times / min, and an atmosphere of -30°C. 2 Below, more preferably 2300 pieces / m 2 Below, more preferably 2200 pieces / m 2 Below, more preferably 2100 pieces / m 2 Below, more preferably 2000 pieces / m 2 the following.

[0120] The lower limit of the number of pinholes generated in the stretched polyethylene film is not limited, but is, for example, 100 pinholes / m. 2 Above, can be 300 pieces / m 2 Above, can be 500 pieces / m 2 Above, can be 800 pieces / m2 Above, can be 1000 pieces / m 2 above.

[0121] The number of pinholes generated is an index of the bending resistance of the stretched polyethylene film of the present embodiment. The smaller the number of pinholes generated, the better the bending resistance.

[0122] By setting the number of pinholes generated in the stretched polyethylene film to be within the above range, the generation of pinholes due to bending during low-temperature filling or low-temperature transportation can be further suppressed.

[0123] In addition, as a Gelbo flex tester, for example, a tester manufactured by Tester Sangyo Co., Ltd. can be used.

[0124] <Identification of high-density polyethylene layer and medium-density polyethylene layer>

[0125] Whether the stretched polyethylene film of the present embodiment includes the high-density polyethylene layer 1 , the medium-density polyethylene layer, and the high-density polyethylene layer 2 can be determined, for example, by cutting a cross section of the stretched polyethylene film and measuring the melting point of each layer.

[0126] The melting points of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 are, for example, in the range of 130° C. to 140° C., and the melting point of the medium-density polyethylene layer is, for example, in the range of 110° C. to 129° C.

[0127] <Method for producing stretched polyethylene film>

[0128] From the viewpoint of further improving the oriented crystallinity and the mechanical strength, the stretched polyethylene film of the present embodiment is stretched along a single axis or a double axis. From the viewpoint of further improving the productivity, it is preferably stretched uniaxially. In addition, by uniaxially stretching along the MD direction, the tensile elastic modulus T1 in the MD direction can be further improved.

[0129] The stretched polyethylene film can be obtained, for example, by the following method: a high-density polyethylene resin for forming a high-density polyethylene layer 1, a medium-density polyethylene resin for forming a medium-density polyethylene layer, and a high-density polyethylene resin for forming a high-density polyethylene layer 2 are co-extruded into a film in this order, and the obtained film is stretched by a known stretching film manufacturing method such as a uniaxial stretching method, a simultaneous biaxial stretching method, or a sequential biaxial stretching method.

[0130] As molding device and molding conditions, there are no particular limitations, and molding devices and molding conditions known in the past can be adopted. As molding device, T-die extruder, multi-layer T-die extruder, inflation molding machine or multi-layer inflation molding machine etc. can be used.

[0131] The conditions of the uniaxial stretching method and the biaxial stretching method can adopt, for example, the manufacturing conditions of the known stretched polyethylene film. More specifically, in the case of the uniaxial stretching method, for example, the longitudinal stretching temperature is in the range of 100°C to 145°C, and the longitudinal stretching ratio is in the range of 4.5 to 6 times. In the sequential biaxial stretching method, for example, the longitudinal stretching temperature is in the range of 100°C to 145°C, the longitudinal stretching ratio is in the range of 4.5 to 6 times, the transverse stretching temperature is in the range of 110°C to 160°C, and the transverse stretching ratio is in the range of 9 to 11 times.

[0132] <Applications of Stretch Polyethylene Film / Packaging Materials / Food Packaging>

[0133] Specifically, the stretched polyethylene film of the present embodiment can be suitably used as a film for food packaging.

[0134] Furthermore, the stretched polyethylene film of the present embodiment can be suitably used as a packaging material.

[0135] When forming a packaging material, the stretched polyethylene film of the present embodiment can be used alone to form the packaging material, or other layers can be stacked to form the packaging material. Other layers include a substrate layer, a coating layer, an adhesive layer, a heat-sealing layer, etc. It should be noted that, from the perspective of ease of recycling, when these layers are stacked, they are preferably formed from a polyethylene resin.

[0136] The packaging material of the present embodiment can be suitably used in a food package. The food package is used, for example, to package food, and specifically includes: the packaging material of the present embodiment; and the food in the packaging material.

[0137] Depending on the application, only a part of the food package may be constituted by the packaging material of the present embodiment, or substantially the entire food package may be constituted by the packaging material of the present embodiment.

[0138] The method for producing a food package from a stretched polyethylene film or packaging material is not particularly limited, and any method known in the field of packaging materials and packaging bodies, such as heat sealing or fusing, can be used as appropriate.

[0139] The stretched polyethylene film of this embodiment is preferably used for food packaging that requires good flexibility. The food packaging may be in the form of a gas-palm bag or a stand-up bag (bag packaging). These forms are preferred from the perspective of being able to provide good flexibility.

[0140] When a food packaging body (packaging bag, etc.) is formed of the stretched polyethylene film and packaging material of the present embodiment, it is preferred that the corona-treated surface is the inner surface side and the corona-untreated surface is the outer surface side.

[0141] In addition, when other layers are stacked on the stretched polyethylene film as mentioned above, it is preferably stacked on the corona treated surface side. That is, when the laminate using the stretched polyethylene film of the present embodiment is used for food packaging (packaging bag, etc.), the stretched polyethylene film side of the present embodiment preferably becomes the outermost layer of the food packaging.

[0142] The food packaged in the food package is not limited, and examples thereof include baked cakes, rice cakes, snacks, rice seasonings, and cereal powders.

[0143] The embodiments of the present invention have been described above, but these are examples of the present invention, and various configurations other than the above can be adopted. In addition, the present invention is not limited to the above-mentioned embodiments, and modifications and improvements within the scope of achieving the purpose of the present invention are included in the present invention.

[0144] Example

[0145] <Raw materials>

[0146] The raw materials used in Examples and Comparative Examples are shown below.

[0147] The density was measured in accordance with JIS K 7112: 1999. The MFR was measured in accordance with ASTM D1238 under the conditions of 190° C. and a load of 2.16 kg. The melting point was measured using a differential scanning calorimeter (DSC).

[0148] (High Density Polyethylene)

[0149] High-density polyethylene (HDPE1): Density: 949kg / m 3 , MFR: 1.1g / 10min, melting point: 130℃

[0150] (Medium Density Polyethylene)

[0151] Medium density polyethylene (MDPE1): Density: 916kg / m 3 , MFR: 2.3g / 10min, melting point: 116℃

[0152] Medium density polyethylene (MDPE2): Density: 918kg / m 3 , MFR: 3.8g / 10min, melting point: 116℃

[0153] Medium density polyethylene (MDPE3): Density: 923kg / m 3 , MFR: 1.5g / 10min, melting point: 121℃

[0154] Medium density polyethylene (MDPE4): Density: 925kg / m 3 , MFR: 1.9g / 10min, melting point: 122℃

[0155] Medium density polyethylene (MDPE5): Density: 937kg / m 3 , MFR: 1.8g / 10min, melting point: 127℃

[0156] Medium density polyethylene (MDPE6): Density: 942kg / m 3 , MFR: 2.9g / 10min, melting point: 127℃

[0157] <Manufacturing of stretched polyethylene film>

[0158] [Examples 1 to 3 and Comparative Example 1]

[0159] With the coordination shown in Table 1, the high-density polyethylene, medium-density polyethylene, and high-density polyethylene of the embodiment and the comparative example are subjected to T-die extrusion molding in a film-like manner in sequence, and after obtaining the cast sheet, the cast sheet is subjected to uniaxial stretching. Then, the high-density polyethylene layer 2 sides of the cast sheet after uniaxial stretching are subjected to corona treatment to make the stretched polyethylene film of each example. Extrusion conditions and uniaxial stretching conditions are shown below.

[0160] Multilayer extrusion machine: Multilayer T-die extruder (L / D=27, manufactured by Screw Seiki Co., Ltd.)

[0161] Extrusion setting temperature: 230℃, processing speed: 25m / min

[0162] Longitudinal stretching temperature: 110~130℃

[0163] Longitudinal stretch ratio: 5 times

[0164] The following evaluations were performed on the obtained stretched polyethylene films of the respective examples. The obtained results are shown in Table 1, respectively.

[0165] <Small-angle X-ray scattering (SAXS) measurement of stretched polyethylene film>

[0166] In each example of the stretched polyethylene film, the MD direction of the film was set as the up-down direction, the TD direction was set as the left-right direction, and the film was set in the following apparatus in such a way that the angle between the X-ray source direction and the film surface was perpendicular. Small-angle X-ray scattering (SAXS) measurement was performed using the following apparatus and conditions.

[0167] Device: Made by RIGAKU Co., Ltd., product name: Ultima IV (small angle scattering attachment system)

[0168] X-ray incident direction: film normal direction

[0169] X-ray wavelength: 0.15418nm

[0170] Optical unit specifications:

[0171] 1. Select a slit for the optical system; use 0.03mm (=1 st . Slit)

[0172] 2.DS; anti-scattering slit 1.00mm (=2 nd . Slit)

[0173] 3. Incident side Soller slit; 5° using flexible optical system

[0174] 4.1 st .~2 nd .Slit distance: 70mm

[0175] 5.2 nd .~Distance between samples: 98mm

[0176] 6. Vacuum path length: 100mm (in front of the light receiving slit box, set on a dedicated table)

[0177] 7.RS, SS; scattering slit 0.20mm, light receiving slit 0.10mm

[0178] 8. Camera length: 285mm

[0179] 9. Cable slit on the light receiving side; 5° using flexible optical system

[0180] 10. Monochromation: None (monochromatization on the incident side by multilayer mirror)

[0181] 11. Detector: RIGAKU scintillation detector (HV: 762V) (one-dimensional)

[0182] X-ray irradiation conditions:

[0183] A. Scan axis: 2theta

[0184] B. Determination method: Continuous

[0185] C. Scanning start angle: 0.1°

[0186] D. Scan end angle: 1.0°

[0187] E. Sampling width: 0.02°

[0188] F. Scanning speed: 0.5° / min

[0189] G. Voltage and current: 40kV-40mA

[0190] H. Number of sample stacks: To obtain sufficient scattering intensity, the samples were stacked to a thickness of about 0.5 mm while keeping their orientations aligned.

[0191] The X-ray scattering pattern obtained under the above measurement conditions is corrected for air scattering of the detector to obtain the SAXS spectrum I(q). The diffraction angle θ is calculated according to formula (1) using the magnitude of the scattering vector from the peak of the long crystal period in the SAXS spectrum I(q), and the long crystal period (d) is calculated by substituting it into Bragg's formula (2).

[0192] q=4πsinθ / λ (1)

[0193] θ: diffraction angle

[0194] q: the magnitude of the scattering vector

[0195] λ: X-ray wavelength

[0196] 2dsinθ=λ (2)

[0197] d: Long crystallization period

[0198] θ: diffraction angle

[0199] λ: X-ray wavelength

[0200] In addition, with reference to the structural analysis of crystalline polymer materials based on the scattering method in NICHIAS Technology Times (2014) No. 2 No. 365, the SAXS spectrum I (q) was Fourier transformed using the following (3), thereby calculating the electron density correlation function γ (r). γ (r) has a special property that can be directly used for structural characterization. As structural information, the amorphous thickness (da) of each example of the stretched polyethylene film obtained was calculated. In addition, r represents distance (nm).

[0201] [Mathematical formula 1]

[0202]

[0203] In addition, the difference between the long crystal period (d) and the amorphous thickness is calculated as the crystal thickness (dc). In addition, using X-ray analysis software PDXL-2 (RIGAKU), the full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° for the diffraction angle 2θ in the MD direction is calculated. Specifically, air scattering is removed from the SAXS spectrum I (q) obtained above. For the obtained value, the above-mentioned software is used to separate it into crystalline scattering and amorphous scattering, and the peak fitting result of the crystalline scattering based on the following (analysis conditions) is calculated. The full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° for the diffraction angle 2θ in the MD direction is calculated.

[0204] (Analysis conditions)

[0205] Fitting peak shape: Split-type quasi-Voigt function

[0206] Crystallite size distribution type: Lorenz model

[0207] <Differential Scanning Calorimetry>

[0208] A test piece of about 5.0 mg was cut out from the stretched polyethylene film of each example. Next, the test piece was subjected to a first differential scanning calorimetry (1st Run) and a second differential scanning calorimetry (2nd Run) under a nitrogen flow using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments). The first differential scanning calorimetry (1st Run) included 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min. The second differential scanning calorimetry (2nd Run) included a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

[0209] The heat of fusion (ΔH) was determined from the endothermic peak A observed in the range of 10°C to 160°C in the DSC curve 1 obtained by the first differential scanning calorimetry. m )(J / g).

[0210] <Haze>

[0211] The haze of each stretched polyethylene film of each example was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries, Ltd.) in accordance with JIS K7136:2000.

[0212] <Tensile elastic modulus>

[0213] A test piece of 15 mm x 15 cm was cut from the stretched polyethylene film of each example. Next, the tensile elastic modulus T1 in the MD direction and the tensile elastic modulus T2 in the TD direction of the test piece were measured using a tensile testing machine manufactured by Orientec in accordance with JIS K7127:1999 at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min. Based on the obtained values, the total value of T1 and T2 was calculated.

[0214] <Heat shrinkage ratio in MD direction of stretched polyethylene film at 100°C>

[0215] The heat shrinkage rate in the MD direction of the stretched polyethylene film at 100° C. is measured in accordance with JIS C2151:2019.

[0216] A 10 cm × 10 cm test piece was cut out from the stretched polyethylene film of each example. Next, the test piece was heated at 100°C for 15 minutes. At this time, the test piece was hung in a hot air circulation thermostatic bath (manufactured by ADVANTEC, product name: DRM620DE) without applying force and heated. Next, the test piece was cooled to room temperature and the length of the test piece was measured. The length of the test piece in the MD direction after the heat treatment was set as MD 100 [cm], through 100×(10-MD 100 ) / 10 to calculate the heat shrinkage rate [%] in the MD direction. The above measurement was performed three times, and the average value of the obtained measured values ​​was adopted as the heat shrinkage rate of the stretched polyethylene film at 100°C.

[0217] <Heat shrinkage ratio in MD direction of stretched polyethylene film at 120°C>

[0218] The heat shrinkage rate in the MD direction of the stretched polyethylene film at 120° C. is measured in accordance with JIS C2151:2019.

[0219] A 10 cm × 10 cm test piece was cut out from the stretched polyethylene film of each example. Next, the test piece was heated at 120°C for 15 minutes. At this time, the test piece was hung in a hot air circulation thermostatic bath (manufactured by ADVANTEC, product name: DRM620DE) without applying force and heated. Next, after the test piece was cooled to room temperature, the length of the test piece was measured. The length of the test piece in the MD direction after the heat treatment was set as MD 120 [cm], through 100×(10-MD 120 ) / 10 to calculate the heat shrinkage rate [%] in the MD direction. The above measurement was performed three times, and the average value of the obtained measured values ​​was adopted as the heat shrinkage rate of the stretched polyethylene film at 120°C.

[0220] <Static friction coefficient>

[0221] Prepare 2 stretched polyethylene films of each example cut into a size of 50 mm × 75 mm (hereinafter referred to as stretched polyethylene films 1 and 2), and fix one of the stretched polyethylene films 1 to an inclined plate with the corona untreated side facing upward. Next, a friction body whose bottom surface (size is 41 mm × 26 mm) is made of brass and is fixed to the center of the surface of the other stretched polyethylene film 2 opposite to the corona untreated side, and a weight is installed on the friction body in such a way that the mass applied from the friction body to the stretched polyethylene film 2 becomes 150 g. Next, overlap the surfaces of the corona untreated side of the two stretched polyethylene films 1 and 2. Next, tilt the inclined plate at a speed of 1° / sec, and calculate the value of tanθ based on the angle θ when the upper stretched polyethylene film 2 slides out, as the static friction coefficient of the surface of the corona untreated side.

[0222] <Heat-welding strength>

[0223] The corona untreated surfaces of two stretched polyethylene films of each example cut into 15 mm width were heat-fused at 140°C, a pressure of 2.0 kgf, and a sealing time of 1.0 second to obtain a laminated film. Next, the obtained laminated film was cut into 15 mm width, and the two stretched polyethylene films were peeled off under the conditions of 90° peeling, a peeling speed of 300 mm / min, and stretching in the MD direction, and the peel strength at this time was taken as the heat fusion strength (N / 15 mm).

[0224] <Lamination Strength>

[0225] A test piece of 297 cm×210 cm was cut out from the stretched polyethylene film of each example, and the corona-treated side of the test piece was bonded to the corona-treated side of a 50 μm thick cast LLDPE film (TUX FCS#50 manufactured by Mitsui Chemicals Tohcello) with one side corona-treated using an ester adhesive (TAKELAC A310 / TAKENATE A3 / ethyl acetate manufactured by Mitsui Chemicals) = 12 / 1 / 7, and aged at 40°C for 3 days. Next, the test piece was cut into a 15 mm width, and peeled in the MD direction using a tensile tester (Tensilon Universal Tester RTC-1225 manufactured by Orientec) in accordance with JIS Z 0238:1998 under the conditions of a peel angle of 90°, a chuck distance of 100 mm, and a crosshead speed of 300 mm / min. The peel strength at this time was determined as the lamination strength.

[0226] <Puncture Strength>

[0227] As an index of flexibility, the puncture strength was measured as follows.

[0228] A test piece with a width of 60 mm and a length of 200 to 300 mm was cut out from the stretched polyethylene film of each example. Next, the puncture strength (N) from the corona treated surface to the corona untreated surface was measured using Tensilon RTC-1225 manufactured by Orientec in accordance with JIS Z1707:1997 at 23±2°C and 50±5%RH.

[0229] <Bending resistance>

[0230] As an index of flexibility, the bending resistance was evaluated as follows.

[0231] A test piece of 297 cm × 210 cm was cut out from the stretched polyethylene film of each example, and a bending test was performed 3000 times at a bending angle of 440 degrees and a bending speed of 40 times / min in an atmosphere of -30°C using a Gelbo flex tester (manufactured by Tester Sangyo Co., Ltd.). Bags were then made using the test pieces after the bending test, and the number of pinholes generated was measured using Ageless sealing test liquid manufactured by Mitsubishi Gas Chemical.

[0232] <Tear strength>

[0233] As an index of flexibility, tear strength was measured as follows.

[0234] A test piece having a length of 63.5 mm in the MD direction and 50 mm in the TD direction was cut out from the stretched polyethylene film of each example. The tear strength (mN) in the MD direction was measured for one of the test pieces using a light load tear tester (manufactured by Toyo Seiki Seisaku-sho, Ltd., Model-D) under the conditions of pendulum weight: 96.09 g, tear length: 12.7 mm, and pendulum lifting angle: 90°.

[0235] The flexibility of the stretched polyethylene film was evaluated according to the following criteria.

[0236] (Benchmark)

[0237] A (good): Satisfies all of the following (i) to (iii)

[0238] B (poor): One or more of the following items (i) to (iii) are not satisfied

[0239] (i) The puncture strength is 2.5N or more.

[0240] (ii) Bending resistance (number of pinholes) 2500 pinholes / m 2 the following.

[0241] (iii) The tear strength in the MD direction is 100 mN or more.

[0242] [Table 1]

[0243]

[0244] When the stretched polyethylene film of the example is used, a food packaging film having improved flexibility (performance balance of puncture strength, bending resistance, and tear strength) can be obtained.

[0245] This application claims priority based on Japanese patent applications No. 2022-157678, No. 2022-157993, and No. 2022-157996, filed on September 30, 2022, the disclosures of which are incorporated herein in their entirety.

[0246] The present invention can also take the following aspects.

[0247] [1a] A stretched polyethylene film comprising, in sequence

[0248] High density polyethylene layer 1;

[0249] a medium density polyethylene layer; and

[0250] High density polyethylene layer 2,

[0251] The density of the medium-density polyethylene layer measured in accordance with JIS K 7112:1999 is 910 kg / m 3 Above 935kg / m 3 the following.

[0252] [2a] The stretched polyethylene film as described in [1a], wherein, when the entire stretched polyethylene film is set to 100 mass%, the total amount of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 in the stretched polyethylene film is 25 mass% to 85 mass%.

[0253] [3a] The stretched polyethylene film according to [1a] or [2a], wherein the density of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is 940 kg / m 3 Above 970kg / m 3 the following.

[0254] [4a] A stretched polyethylene film as described in any one of [1a] to [3a], wherein the MFR of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with ASTM D1238 at 190°C and a load of 2.16 kg is each not less than 0.01 g / 10 min and not more than 20 g / 10 min.

[0255] [5a] A stretched polyethylene film as described in any one of [1a] to [4a], wherein the MFR of the medium-density polyethylene layer measured according to ASTM D1238 at 190°C and a load of 2.16 kg is at least 0.01 g / 10 min and no more than 20 g / 10 min.

[0256] [6a] A stretched polyethylene film as described in any one of [1a] to [5a], wherein in the stretched polyethylene film, the full width at half maximum (FWHM) of the peak in the range of 0.2 to 0.4° in the MD direction determined by small-angle X-ray scattering (SAXS) is less than 0.20°.

[0257] [7a] The stretched polyethylene film according to any one of [1a] to [6a], wherein in the stretched polyethylene film, when a first differential scanning calorimetry (1st Run) and a second differential scanning calorimetry (2nd Run) are continuously performed using a differential scanning calorimeter, in a DSC curve 1 obtained by the first differential scanning calorimetry, an endothermic peak A is observed in the range of 10°C to 160°C, and the heat of fusion (ΔH m ) is 110 J / g or more and 162 J / g or less, the first differential scanning calorimetry (1stRun) includes 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min, and the second differential scanning calorimetry (2ndRun) includes a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

[0258] [8a] The stretched polyethylene film according to any one of [1a] to [7a], wherein the haze per one sheet of the stretched polyethylene film measured in accordance with JIS K 7136:2000 is 16.0% or less.

[0259] [9a] A stretched polyethylene film as described in any one of [1a] to [8a], wherein the total value of the tensile elastic modulus T1 in the MD direction and the tensile elastic modulus T2 in the TD direction of the stretched polyethylene film, measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min, is 1600 MPa to 2900 MPa.

[0260] [10a] The stretched polyethylene film according to any one of [1a] to [9a], wherein the heat shrinkage in the MD direction of the stretched polyethylene film when heated at 100°C for 15 minutes according to JIS C2151:2019 is 5.5% or less.

[0261] [11a] The stretched polyethylene film according to any one of [1a] to [10a], wherein the heat shrinkage in the MD direction of the stretched polyethylene film when heated at 120°C for 15 minutes according to JIS C2151:2019 is 25.0% or less.

[0262] [12a] The stretched polyethylene film according to any one of [1a] to [11a], wherein at least one surface of the stretched polyethylene film is a corona-treated surface.

[0263] [13a] The stretched polyethylene film according to any one of [1a] to [12a], wherein

[0264] At least one surface of the stretched polyethylene film is a corona-untreated surface,

[0265] When heat-sealed at 140° C. so that the corona-untreated surfaces of the stretched polyethylene films are bonded to each other, the heat fusion strength is 4.0 N / 15 mm or less.

[0266] [14a] A stretched polyethylene film as described in any one of [1a] to [13a], wherein the lamination strength in the MD direction of the stretched polyethylene film, measured in accordance with JIS Z 0238:1998 using a tensile testing machine under the conditions of T-peeling and a crosshead speed of 300 mm / min, is 0.7 N / 15 mm or more and 10.0 N / 15 mm or less.

[0267] [15a] The stretched polyethylene film according to any one of [1a] to [14a], wherein the overall thickness of the stretched polyethylene film is 10 μm to 100 μm.

[0268] [16a] The stretched polyethylene film according to any one of [1a] to [15a], which is a film for food packaging.

[0269] [17a] A packaging material using the stretched polyethylene film according to any one of [1a] to [16a].

[0270] [18a] A food package, comprising:

[0271] [17a] the packaging material; and

[0272] Food in the aforementioned packaging materials.

[0273] The present invention can also adopt the following aspects.

[0274] [1b] A stretched polyethylene film comprising

[0275] High density polyethylene layer 1;

[0276] a medium density polyethylene layer; and

[0277] High density polyethylene layer 2,

[0278] The amorphous thickness determined by small-angle X-ray scattering (SAXS) measurement from a peak at a diffraction angle 2θ in the MD direction within a range of 0.2 to 0.4° was less than 12.5 nm.

[0279] [2b] A stretched polyethylene film as described in [1b], wherein the tensile modulus T2 of the stretched polyethylene film in the TD direction is greater than 920 MPa, measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5% RH, and a stretching speed of 5 mm / min.

[0280] [3b] The stretched polyethylene film according to [1b] or [2b], wherein the density of the medium-density polyethylene layer measured in accordance with JIS K7112:1999 is 910 kg / m 3 Above and less than 940kg / m 3 .

[0281] [4b] A stretched polyethylene film as described in any one of [1b] to [3b], wherein, when the entire stretched polyethylene film is set to 100 mass%, the total amount of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 in the stretched polyethylene film is not less than 25 mass% and not more than 85 mass%.

[0282] [5b] The stretched polyethylene film according to any one of [1b] to [4b], wherein the density of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is 940 kg / m 3 Above 970kg / m 3 the following.

[0283] [6b] The stretched polyethylene film according to any one of [1b] to [5b], wherein the haze per one sheet of the stretched polyethylene film measured in accordance with JIS K 7136:2000 is 16.0% or less.

[0284] [7b] A stretched polyethylene film as described in any one of [1b] to [6b], wherein the total value of the tensile elastic modulus T1 in the MD direction and the tensile elastic modulus T2 in the TD direction of the stretched polyethylene film, measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min, is 1500 MPa to 2900 MPa.

[0285] [8b] The stretched polyethylene film according to any one of [1b] to [7b], wherein the heat shrinkage in the MD direction of the stretched polyethylene film when heated at 100°C for 15 minutes according to JIS C2151:2019 is 6.0% or less.

[0286] [9b] The stretched polyethylene film according to any one of [1b] to [8b], wherein at least one surface of the stretched polyethylene film is a corona-treated surface.

[0287] [10b] The stretched polyethylene film according to any one of [1b] to [9b], wherein

[0288] At least one surface of the stretched polyethylene film is a corona-untreated surface,

[0289] When heat-sealed at 140° C. in such a manner that the corona-untreated surfaces of the stretched polyethylene films are bonded together, the heat fusion strength is 4.0 N / 15 mm or less.

[0290] [11b] The stretched polyethylene film according to any one of [1b] to [10b], wherein the overall thickness of the stretched polyethylene film is 10 μm to 100 μm.

[0291] [12b] The stretched polyethylene film according to any one of [1b] to [11b], which is a film for food packaging.

[0292] [13b] A packaging material using the stretched polyethylene film according to any one of [1b] to [12b].

[0293] [14b] A food packaging body comprising:

[0294] [13b] The packaging material described in; and the food contained in the aforementioned packaging material.

[0295] Description of Reference Numerals 100 stretched polyethylene film 101 high density polyethylene layer 1102 medium density polyethylene layer 103 high density polyethylene layer 2

Claims

1. A stretched polyethylene film comprising High density polyethylene layer 1; a medium density polyethylene layer; and High density polyethylene layer 2, When the first differential scanning calorimetry (1st Run) and the second differential scanning calorimetry (2nd Run) are continuously performed using a differential scanning calorimeter, in the DSC curve 1 obtained by the first differential scanning calorimetry, an endothermic peak A is observed in the range of 10°C to 160°C, and the melting heat (ΔH m ) is 110 J / g or more and 162 J / g or less, the first differential scanning calorimetry (1stRun) includes 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 10 minutes, and a process of cooling from 200°C to -50°C at a cooling rate of 10°C / min, and the second differential scanning calorimetry (2ndRun) includes a process of heating from -50°C to 200°C at a heating rate of 10°C / min.

2. The stretched polyethylene film according to claim 1, wherein The density of the medium-density polyethylene layer measured according to JIS K 7112:1999 is 910 kg / m 3 Above 935kg / m 3 the following.

3. The stretched polyethylene film according to claim 1 or 2, wherein the amorphous thickness determined from a peak at a diffraction angle 2θ in the MD direction within a range of 0.2 to 0.4° as measured by small angle X-ray scattering (SAXS) is less than 12.5 nm.

4. The stretched polyethylene film according to any one of claims 1 to 3, wherein When the entirety of the stretched polyethylene film is taken as 100 mass %, the total amount of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 in the stretched polyethylene film is 25 mass % or more and 85 mass % or less.

5. The stretched polyethylene film according to any one of claims 1 to 4, wherein The density of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with JIS K 7112:1999 is 940 kg / m 3 Above 970kg / m 3 the following.

6. The stretched polyethylene film according to any one of claims 1 to 5, wherein The MFR of the high-density polyethylene layer 1 and the high-density polyethylene layer 2 measured in accordance with ASTM D1238 under the conditions of 190° C. and a load of 2.16 kg is each 0.01 g / 10 min or more and 20 g / 10 min or less.

7. The stretched polyethylene film according to any one of claims 1 to 6, wherein The MFR of the medium-density polyethylene layer measured under the conditions of 190° C. and a load of 2.16 kg in accordance with ASTM D1238 is 0.01 g / 10 min or more and 20 g / 10 min or less.

8. The stretched polyethylene film according to any one of claims 1 to 7, wherein In the stretched polyethylene film, the full width at half maximum (FWHM) of a peak having a diffraction angle 2θ in the MD direction within a range of 0.2 to 0.4° determined by small-angle X-ray scattering (SAXS) measurement is 0.21° or less.

9. The stretched polyethylene film according to any one of claims 1 to 8, wherein In the stretched polyethylene film, a haze per one sheet of the stretched polyethylene film measured in accordance with JIS K 7136:2000 is 16.0% or less.

10. The stretched polyethylene film according to any one of claims 1 to 9, wherein The stretched polyethylene film has a tensile modulus T2 in the TD direction of 700 MPa or more, measured using a tensile testing machine at a measuring temperature of 23±2° C., 50±5% RH, and a stretching speed of 5 mm / min in accordance with JIS K7127:1999.

11. The stretched polyethylene film according to any one of claims 1 to 10, wherein The total value of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction of the stretched polyethylene film measured in accordance with JIS K7127:1999 using a tensile testing machine at a measuring temperature of 23±2°C, 50±5%RH, and a stretching speed of 5 mm / min is 1500 MPa to 2900 MPa.

12. The stretched polyethylene film according to any one of claims 1 to 11, wherein The heat shrinkage rate of the stretched polyethylene film in the MD direction when subjected to heat treatment at 100° C. for 15 minutes in accordance with JIS C2151:2019 is 6.0% or less.

13. The stretched polyethylene film according to any one of claims 1 to 12, wherein The heat shrinkage of the stretched polyethylene film in the MD direction when subjected to heat treatment at 120° C. for 15 minutes in accordance with JIS C2151:2019 is 25.0% or less.

14. The stretched polyethylene film according to any one of claims 1 to 13, wherein At least one surface of the stretched polyethylene film is a corona-treated surface.

15. The stretched polyethylene film according to any one of claims 1 to 14, wherein The lamination strength of the stretched polyethylene film in the MD direction, measured in accordance with JIS Z 0238:1998 using a tensile tester under conditions of T-peeling and a crosshead speed of 300 mm / min, is 0.7 N / 15 mm or more and 10.0 N / 15 mm or less.

16. The stretched polyethylene film according to any one of claims 1 to 15, wherein The number of pinholes generated in the stretched polyethylene film was 2500 / m as measured by 3000 bending tests at a bending angle of 440 degrees and a bending speed of 40 times / min in an atmosphere of -30°C using a Gelbo flex tester. 2 the following.

17. The stretched polyethylene film according to any one of claims 1 to 16, wherein The tear strength of the stretched polyethylene film in the MD direction measured using a light load tear tester under the following conditions: test piece size: MD direction: 63.5 mm, TD direction: 50.0 mm, pendulum weight: 96.09 g, tear length: 12.7 mm, pendulum lifting angle: 90°, is 100 mN to 600 mN.

18. The stretched polyethylene film according to any one of claims 1 to 17, wherein The overall thickness of the stretched polyethylene film is 10 μm or more and 100 μm or less.

19. The stretched polyethylene film according to any one of claims 1 to 18, which is a food packaging film.

20. A packaging material using the stretched polyethylene film according to any one of claims 1 to 19.

21. A food package, comprising: The packaging material of claim 20; and The food in the packaging material.

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