Biaxially stretched film and method for producing the same

Abstract

This biaxially stretched film has a layer obtained from a material containing an ethylene-based polymer. The ethylene-based polymer has a melt flow rate (MFR) of 0.01-5.0 g / 10 min, a density of at least 941 kg / m3 but less than 970 kg / m3, and a melt tension of 31-250 mN. The ratio, Mw / Mn, between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the ethylene-based polymer is 6.1 or more, Mw and Mn being measured by gel permeation chromatography (GPC).

Description

Biaxially stretched film and method for producing same

[0001] The present disclosure relates to biaxially oriented films and methods for making the same.

[0002] In recent years, in consideration of environmental issues, laws regarding the disposal of various plastics have been enacted. There is also a growing need for recycling packaging materials. Therefore, various recyclable packaging materials have been studied (see, for example, Patent Documents 1 and 2). For example, packaging materials made of a single material (monomaterial packaging materials) have attracted attention as recyclable packaging materials, and specifically, polyethylene-based monomaterial packaging materials have been studied.

[0003] Japanese Patent No. 6716764 Japanese Patent Application Laid-Open No. 2020-121455

[0004] Common packaging materials have a substrate made of a film made of various resins. Polyethylene-based monomaterial packaging materials have a polyethylene-based substrate. Properties required for a polyethylene-based substrate include rigidity, low shrinkage, and strength. One method for improving strength is to stretch the film; for example, biaxially stretched films tend to have superior strength to uniaxially stretched films. Furthermore, from the standpoint of rigidity and low shrinkage, high-density polyethylene (HDPE) is a suitable polymer for the polyethylene-based substrate. However, biaxial stretching of high-density polyethylene films generally tends to be difficult.

[0005] An object of the present disclosure is to provide a polyethylene-based biaxially stretched film that has an excellent balance of rigidity, low shrinkage, and strength, and a method for producing the same.

[0006] One embodiment of the biaxially stretched film of the present disclosure is a biaxially stretched film having a layer obtained from a material containing an ethylene-based polymer, the ethylene-based polymer having a melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, a melt flow rate (MFR) of 941 kg / m ... 3 More than 970kg / m 3The biaxially stretched film of the present disclosure has a density of less than 1000 MPa, a melt tension of 31 to 250 mN, and a value of Mw / Mn, which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), measured by gel permeation chromatography (GPC), of 6.1 or greater. Another embodiment of the biaxially stretched film of the present disclosure is a biaxially stretched film obtained from a material containing an ethylene-based polymer, having a tensile modulus in the MD direction of 1,000 MPa or greater, a tensile modulus in the TD direction of 1,500 MPa or greater, a dart impact of 100 g or greater, a heat shrinkage in the MD direction of 15% or less, and a heat shrinkage in the TD direction of 15% or less. One embodiment of a method for producing a biaxially stretched film of the present disclosure has a melt flow rate (MFR) of 0.01 g / 10 min or greater and 5.0 g / 10 min or less, and a melt flow rate of 941 kg / m 3 More than 970kg / m 3 the method includes the steps of preparing a material containing an ethylene polymer having a density of less than 1000 kJ / cm, a melt tension of 31 to 250 mN, and an Mw / Mn of 6.1 or greater; forming a film using at least the material; and biaxially stretching the film.

[0007] According to the present disclosure, it is possible to provide a polyethylene-based biaxially stretched film having an excellent balance of rigidity, low shrinkage, and strength, and a method for producing the same.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail. Each component described in this specification may be used singly or in combination. In this specification, the term "polymer" may be used without any particular distinction between homopolymers and copolymers. That is, the term "polymer" is used to refer to both homopolymers and copolymers. Generally, a thick film is referred to as a "sheet" and a thin film is referred to as a "film" to distinguish between sheets and films. However, in this specification, sheets and films are referred to as "films" without any particular distinction based on thickness.

[0009] In this specification, the numerical range n1 to n2 means n1 or more and n2 or less. Here, n1 and n2 are any numbers that satisfy n1 < n2. For example, "1 to 10" means 1 or more and 10 or less. In this specification, when multiple lower limit values ​​and multiple upper limit values ​​are listed for a certain element, a numerical range formed by combining a value arbitrarily selected from the listed lower limit value and a value arbitrarily selected from the listed upper limit value is also considered to be listed.

[0010] In this specification, an ethylene-based polymer may have a structural unit derived from a biomass-derived monomer (e.g., ethylene, α-olefin). Furthermore, a propylene-based polymer may have a structural unit derived from a biomass-derived monomer (e.g., propylene, α-olefin). The monomers constituting the polymer may be biomass-derived monomers only, or may contain both biomass-derived monomers and fossil fuel-derived monomers. The same type of monomers constituting the polymer may be biomass-derived monomers only, or may contain both biomass-derived monomers and fossil fuel-derived monomers. A biomass-derived monomer is a monomer obtained from any renewable natural raw material or residue thereof, such as a plant-derived or animal-derived material, including fungi, yeast, algae, and bacteria, and has a carbon isotope of 1×10 -12 The biomass-derived monomer contains about 100 carbon atoms and has a biomass carbon concentration (pMC) measured in accordance with ASTM D6866. The biomass-derived monomer can be obtained, for example, by a conventionally known method.

[0011] It is preferable that the polymer has a structural unit derived from a biomass-derived monomer from the viewpoint of reducing the environmental load (mainly reducing greenhouse gas emissions). If the polymer production conditions, such as the polymerization catalyst, polymerization process, and polymerization temperature, are the same, the molecular structure of the polymer obtained from the raw material monomer containing the biomass-derived monomer will have a 14C isotope concentration of 1×10 -14 ~1 x 10 -12 The molecular structure of the polymer obtained from raw material monomers containing only fossil fuel-derived monomers is equivalent to that of the polymer obtained from raw material monomers containing only fossil fuel-derived monomers, except that the ratio of the monomers is about the same. Therefore, the performance of these polymers is also considered to be equivalent.

[0012] In this specification, an ethylene-based polymer may have a structural unit derived from a chemically recycled monomer (e.g., ethylene, α-olefin). Furthermore, a propylene-based polymer may have a structural unit derived from a chemically recycled monomer (e.g., propylene, α-olefin). The monomers constituting the polymer may consist solely of chemically recycled monomers, or may contain a chemically recycled monomer and a non-chemically recycled, fossil fuel-derived monomer and / or a biomass-derived monomer. The same type of monomers constituting the polymer may consist solely of chemically recycled monomers, or may contain a chemically recycled monomer and a non-chemically recycled, fossil fuel-derived monomer and / or a biomass-derived monomer. Chemically recycled monomers can be obtained, for example, by a conventionally known method. Chemically recycled monomers are monomers obtained by depolymerizing or pyrolyzing a polymer contained in waste plastics or the like back into monomer units such as ethylene or propylene, as well as monomers obtained using such monomers as raw materials.

[0013] It is preferable that the polymer has structural units derived from chemically recycled monomers from the viewpoint of reducing environmental impact (mainly reducing waste). If the polymer production conditions, such as the polymerization catalyst, polymerization process, and polymerization temperature, are equivalent, the molecular structure of the polymer obtained from raw material monomers containing chemically recycled monomers is equivalent to the molecular structure of the polymer obtained from raw material monomers containing only non-chemically recycled fossil fuel-derived monomers. Therefore, the performance of these polymers is also considered to be equivalent.

[0014] [Biaxially oriented film] The biaxially oriented film of the first aspect of the present disclosure is obtained from a material containing an ethylene-based polymer, and has a tensile modulus in the MD direction of 1,000 MPa or more, a tensile modulus in the TD direction of 1,500 MPa or more, a dart impact of 100 g or more, a heat shrinkage rate in the MD direction of 15% or less, and a heat shrinkage rate in the TD direction of 15% or less.

[0015] A biaxially stretched film according to a second aspect of the present disclosure is a biaxially stretched film having a layer obtained from a material containing an ethylene-based polymer, the ethylene-based polymer having a melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, and a melt flow rate (MFR) of 941 kg / m 3 More than 970kg / m 3 a density of less than 1000 kJ / cm; a melt tension of 31 to 250 mN; and a molecular weight distribution (Mw / Mn) of 6.1 or greater.

[0016] When describing matters common to the biaxially stretched film of the first embodiment and the biaxially stretched film of the second embodiment, or when no particular distinction is made between the biaxially stretched film of the first embodiment and the biaxially stretched film of the second embodiment, they are also referred to as "the biaxially stretched film of the present disclosure."

[0017] The biaxially stretched film of the present disclosure has an excellent balance of rigidity, strength, and low shrinkage. Therefore, the biaxially stretched film can be suitably used as a substrate for constituting a recyclable packaging material. In this specification, the tensile modulus is an index of the rigidity of the film, and the dart impact is an index of the strength of the film.

[0018] In this specification, the MD direction means the direction of resin flow during film formation (when producing a resin film), i.e., the direction in which the film is taken up, the longitudinal direction, and the TD direction means the direction approximately perpendicular to the MD direction, the transverse direction.

[0019] The tensile modulus in the MD direction of the biaxially stretched film of the first embodiment is 1,000 MPa or more, preferably 1,250 MPa or more, more preferably 1,500 MPa or more, even more preferably 1,600 MPa or more, even more preferably 1,700 MPa or more, and particularly preferably 2,000 MPa or more. Such a biaxially stretched film has excellent rigidity. The upper limit of the tensile modulus in the MD direction is not particularly limited. The tensile modulus in the MD direction may be, for example, 7,000 MPa or less, 6,000 MPa or less, or 5,000 MPa or less. The tensile modulus in the MD direction may be, for example, 1,000 to 7,000 MPa.

[0020] The tensile modulus in the TD direction of the biaxially stretched film of the first embodiment is 1,500 MPa or more, preferably 1,700 MPa or more, and more preferably 2,000 MPa or more. Such a biaxially stretched film has excellent rigidity. The upper limit of the tensile modulus in the TD direction is not particularly limited. The tensile modulus in the TD direction may be, for example, 12,000 MPa or less, 10,000 MPa or less, or 9,000 MPa or less. The tensile modulus in the TD direction may be, for example, 1,500 to 12,000 MPa. Details of the conditions for measuring the tensile modulus are described in the Examples section.

[0021] The tensile modulus of the biaxially stretched film can be adjusted, for example, by the density of the ethylene polymer constituting the biaxially stretched film. 3 Films formed from materials containing high-density ethylene polymers, such as the above-mentioned ethylene polymers, tend to have a high tensile modulus. The tensile modulus of a biaxially stretched film can be adjusted, for example, by the stretch ratio.

[0022] The dart impact of the biaxially stretched film of the first embodiment is 100 g or more, preferably 130 g or more, more preferably 150 g or more, even more preferably 200 g or more, even more preferably 240 g or more, particularly preferably 280 g or more, and particularly preferably 400 g or more. In one embodiment, the dart impact is, for example, 500 g or more, or 600 g or more. Such biaxially stretched films have excellent strength. The upper limit of the dart impact is not particularly limited. The dart impact may be, for example, 2,000 g or less, 1,500 g or less, or 1,200 g or less. The dart impact may be, for example, 100 to 2,000 g, or 200 to 2,000 g. The dart impact is measured in accordance with ASTM D1709 Method A. Details of the measurement conditions are described in the Examples section.

[0023] The dart impact of the film can be improved, for example, by biaxial stretching.

[0024] The heat shrinkage rate in the MD direction of the biaxially stretched film of the first embodiment is 15% or less, preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and particularly preferably 6.5% or less. Such a biaxially stretched film has excellent low shrinkage properties. The heat shrinkage rate in the MD direction is, for example, 0% or more.

[0025] The heat shrinkage in the TD direction of the biaxially stretched film of the first embodiment is 15% or less, preferably 14% or less, more preferably 12% or less, and even more preferably 10% or less. In one embodiment, the heat shrinkage in the TD direction is, for example, 8% or less, or 6.5% or less. Such a biaxially stretched film has excellent low shrinkage properties. The heat shrinkage in the TD direction is, for example, 0% or more.

[0026] In this specification, the heat shrinkage of a biaxially stretched film is calculated as follows. A biaxially stretched film is cut into a strip of 10 mm width x 100 mm length to obtain a test specimen. A test specimen whose longitudinal direction (the length direction) is parallel to the MD direction of the film is referred to as an MD test specimen. A test specimen whose longitudinal direction (the length direction) is parallel to the TD direction of the film is referred to as a TD test specimen. Each test specimen is placed in an air oven at 120°C and heated for 15 minutes, and the length of the test specimen is confirmed. The heat shrinkage is calculated as follows.

[0027] Heat shrinkage rate (%) in MD direction of biaxially stretched film = {length of MD test piece before heating (100 mm) - length of MD test piece after heating (mm)} / 100 mm x 100 Heat shrinkage rate (%) in TD direction of biaxially stretched film = {length of TD test piece before heating (100 mm) - length of TD test piece after heating (mm)} / 100 mm x 100

[0028] The heat shrinkage rate of the biaxially stretched film can be adjusted, for example, by the density of the ethylene polymer constituting the biaxially stretched film. 3 Films formed from materials containing high-density ethylene polymers such as the above-mentioned ethylene polymers tend to have small heat shrinkage. The heat shrinkage of a biaxially stretched film can be kept low, for example, by performing heat setting at an appropriate temperature after stretching the film.

[0029] The tear strength in the MD direction of the biaxially stretched film of the first embodiment is preferably 1 N or less, more preferably 0.5 N or less. The tear strength in the TD direction of the biaxially stretched film of the first embodiment is preferably 1 N or less, more preferably 0.5 N or less. Such a biaxially stretched film has excellent ease of cutting. The tear strength in the MD direction and the TD direction of the biaxially stretched film of the first embodiment may be, for example, 0.01 N or more. The tear strength is measured by the Elmendorf tear method in accordance with JIS K 7128-2. Details of the measurement conditions are described in the Examples section.

[0030] The tear strength of a film can be reduced by, for example, biaxial stretching, and can be adjusted by the stretching ratio in the MD and TD directions. The tear strength of a biaxially stretched film tends to decrease by increasing the stretching ratio or by making the film thinner.

[0031] The total haze of the biaxially stretched film of the first embodiment is preferably 50% or less, more preferably 40% or less, even more preferably 30% or less, even more preferably 25% or less, and particularly preferably 20% or less. The lower limit of the total haze of the biaxially stretched film of the first embodiment is not particularly limited. The total haze of the biaxially stretched film of the first embodiment may be, for example, 1% or more, or 3% or more. The total haze may be, for example, 1% or more and 50% or less. The total haze is measured in accordance with JIS K 7136. Details of the measurement conditions are described in the Examples section.

[0032] The thickness of the biaxially stretched film of the present disclosure is preferably 5 μm or more, more preferably 10 μm or more, and is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 70 μm or less, and particularly preferably 50 μm or less, for example, 5 to 150 μm. A stretched film having such a thickness has an excellent balance of rigidity and strength as a substrate for, for example, a packaging material.

[0033] The biaxially stretched film of the present disclosure can be obtained, for example, by preparing a material containing an ethylene polymer, forming a film having at least a layer made of the material using the material by a known method (hereinafter also referred to as a "raw film"), and then biaxially stretching the raw film. The raw film can be obtained, for example, by a melt extrusion molding method such as a T-die casting method or an inflation molding method, and T-die casting is preferred from the viewpoint of ease of producing a raw film having the thickness required for biaxial stretching.

[0034] The biaxial stretching method includes various known methods, such as a method of simultaneously or sequentially biaxially stretching in the machine and transverse directions by a tenter method (flat method) and a method of simultaneously biaxially stretching in the machine and transverse directions by a tubular method, and the method of using a tenter method is preferred from the viewpoint that a film having the above-mentioned physical properties can be more easily obtained. A sequential biaxial stretching method in which a raw film is stretched in the machine direction by a heated roll and then the obtained stretched film is stretched in the transverse direction by a tenter is more preferred.

[0035] In the case of the tenter method, a sequential biaxial stretching method is preferred, and a biaxially stretched film is obtained, for example, by stretching an original film in the MD direction (longitudinal direction) at a temperature range of 90 to 135° C., and then stretching the resulting stretched film in the TD direction (transverse direction) at a temperature range of 90 to 140° C. After biaxial stretching, a heat setting treatment may be carried out, for example, at a temperature range of 80 to 140° C., if desired, from the viewpoint of further reducing the heat shrinkage rate.

[0036] With regard to the stretching ratio, from the viewpoints of ease of cutting and productivity, the stretching ratios in the MD and TD directions are each independently preferably 2 times or more, more preferably 3 times or more, and may be 4 times or more, and preferably 14 times or less, more preferably 12 times or less, and even more preferably 10 times or less, and may be 7 times or less, for example, 2 to 14 times. In one embodiment, the stretching ratio in the MD direction is preferably 3 to 7 times, and the stretching ratio in the TD direction is preferably 4 to 10 times. Specifically, a sequential biaxial stretching method is preferred in which a raw film is stretched 3 to 7 times in the MD direction using a heated roll, and then the resulting stretched film is stretched 4 to 10 times in the TD direction using a tenter.

[0037] The biaxially stretched film may be subjected to an annealing treatment, if necessary, by, for example, bringing the biaxially stretched film into contact with a roll adjusted to a predetermined temperature.

[0038] The surface of the biaxially stretched film may be subjected to a surface activation treatment, for example, corona treatment, flame treatment, plasma treatment, or undercoat treatment, in order to improve printability or adhesion to other layers.

[0039] The biaxially stretched film of the present disclosure can be used in a variety of applications, for example, as a substrate for packaging materials, and particularly as a substrate for polyethylene-based monomaterial packaging materials.

[0040] [Material] The biaxially stretched film of the present disclosure has, for example, a layer obtained from a material containing an ethylene-based polymer described below. The biaxially stretched film of the present disclosure may be, for example, a multilayer stretched film having a layer obtained from a material containing an ethylene-based polymer described below.

[0041] <Ethylene-based polymer> In this specification, an ethylene-based polymer refers to a polymer in which the ratio (content ratio) of ethylene-derived structural units to the total content of structural units derived from polymerizable monomers is more than 50 mol%. In the ethylene-based polymer, the content ratio of ethylene-derived structural units is preferably 51 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, still more preferably 80 mol% or more, particularly preferably 90 mol% or more, and particularly preferably 95 mol% or more. In this specification, the content ratio of each structural unit in the polymer is measured by nuclear magnetic resonance spectroscopy (NMR method).

[0042] The ethylene-based polymer may be a homopolymer of ethylene or a copolymer of ethylene and another polymerizable monomer (hereinafter also referred to as an "ethylene-based copolymer"). Examples of the other polymerizable monomer include α-olefins having 3 or more carbon atoms. A preferred example of the ethylene-based copolymer is a copolymer of ethylene and an α-olefin having 3 or more carbon atoms (hereinafter also referred to as an "ethylene-α-olefin copolymer").

[0043] In the ethylene copolymer, the number of carbon atoms in the α-olefin is preferably 3 to 20, more preferably 3 to 10, even more preferably 3 to 8, and particularly preferably 3 to 6. Examples of the α-olefin include linear α-olefins such as propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-octadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene; and branched α-olefins such as 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4-ethyl-1-hexene, and 3-ethyl-1-hexene. Among these, from the viewpoint of copolymerizability with ethylene, linear α-olefins are preferred, and propylene, 1-butene, 1-hexene, and 1-octene are more preferred. The ethylene / α-olefin copolymer may have one type or two or more types of structural units derived from α-olefins.

[0044] Examples of ethylene polymers include high density polyethylene (HDPE) and low density polyethylene. The density of high density polyethylene is usually 941 kg / m 3 More than 970kg / m 3 The density of low density polyethylene is usually less than 941 kg / m 3 less than 940 kg / m 3 or less, more preferably 935 kg / m 3 is usually 900 kg / m or less 3 or more, preferably 910 kg / m 3 More preferably, 920 kg / m 3 or more, for example, 900 kg / m 3 More than 941kg / m 3The high density polyethylene and the low density polyethylene may both be commercially available products. The high density polyethylene may be an ethylene homopolymer or an ethylene-α-olefin copolymer (particularly preferably an ethylene-α-olefin copolymer having 3 to 6 carbon atoms). The low density polyethylene may be an ethylene homopolymer (for example, high-pressure low density polyethylene) or an ethylene-α-olefin copolymer (particularly preferably an ethylene-α-olefin copolymer having 3 to 6 carbon atoms).

[0045] The ethylene polymer contained in the material may be, for example, one or more types of high-density polyethylene, or a mixture of one or more types of high-density polyethylene and one or more types of low-density polyethylene.

[0046] From the viewpoint of more easily achieving the above-mentioned effects, the content of high-density polyethylene in the above material is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 85% by mass or more.

[0047] In the above-mentioned mixture of high-density polyethylene and low-density polyethylene, the content of high-density polyethylene is preferably 50 to 99.9% by mass, more preferably 60 to 99% by mass, and even more preferably 70 to 99% by mass, and the content of low-density polyethylene is preferably 0.1 to 50% by mass, more preferably 1 to 40% by mass, and even more preferably 1 to 30% by mass.

[0048] The ethylene-based polymer may have a structural unit derived from a biomass-derived monomer (e.g., ethylene, α-olefin). The ethylene-based polymer may have a structural unit derived from a chemically recycled monomer (e.g., ethylene, α-olefin).

[0049] From the viewpoint of more easily exhibiting the above-mentioned effects, the content of the ethylene polymer in the material is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0050] From the viewpoint of making it easier to obtain a film having the above-described physical properties, the ethylene polymer preferably satisfies any one or more of the requirements (A1) to (A3) described below, and more preferably satisfies all of the requirements (A1) to (A3). The ethylene polymer preferably further satisfies the requirement (A4) described below in addition to any one or more of the requirements (A1) to (A3). The biaxially stretched film of the second aspect has a layer obtained from a material containing an ethylene polymer that satisfies all of the requirements (A1) to (A4). By using such an ethylene polymer, for example, it is possible to form a film that has excellent biaxial stretchability despite having a high density.

[0051] The ethylene polymer preferably satisfies one or more of the requirements (A1) to (A3) described below and further satisfies one or more of the requirements (A5) to (A6) described below, and more preferably satisfies all of the requirements (A1) to (A3) and all of the requirements (A5) to (A6). The ethylene polymer preferably satisfies one or more of the requirements (A1) to (A3) and further satisfies the requirement (A4) described below and further satisfies one or more of the requirements (A5) to (A6). The biaxially stretched film of the second embodiment preferably has a layer obtained from a material containing an ethylene polymer that satisfies all of the requirements (A1) to (A4) and one or more of the requirements (A5) to (A6).

[0052] When the ethylene-based polymer is a mixture of two or more types, the term "ethylene-based polymer" in the following description of each requirement means the mixture of ethylene-based polymers. That is, when the material contains two or more types of ethylene-based polymers, the mixture of two or more types of ethylene-based polymers preferably satisfies any one or more of the requirements (A1) to (A3), more preferably satisfies all of the requirements (A1) to (A3), and further preferably satisfies the requirement (A4) in addition to any one or more of the requirements (A1) to (A3).

[0053] Furthermore, when the material contains two or more types of ethylene-based polymers, it is preferable that the mixture of two or more types of ethylene-based polymers satisfies one or more of the requirements (A1) to (A3) and further satisfies one or more of the requirements (A5) to (A6), it is more preferable that the mixture satisfies all of the requirements (A1) to (A3) and all of the requirements (A5) to (A6), and it is also preferable that the mixture further satisfies the requirement (A4) in addition to one or more of the requirements (A1) to (A3), and further satisfies one or more of the requirements (A5) to (A6).

[0054] (Requirement (A1): MFR) The melt flow rate (MFR) of the ethylene polymer is preferably 0.01 g / 10 min or more and 5.0 g / 10 min or less. The MFR is more preferably 4.0 g / 10 min or less, even more preferably 3.0 g / 10 min or less, still more preferably 2.0 g / 10 min or less, particularly preferably 1.5 g / 10 min or less, and especially preferably 1.2 g / 10 min or less. In one embodiment, the MFR is, for example, 1.0 g / 10 min or less, less than 1.0 g / 10 min, 0.8 g / 10 min or less, less than 0.8 g / 10 min, 0.5 g / 10 min or less, less than 0.5 g / 10 min, or 0.4 g / 10 min or less. In another embodiment, the MFR is 0.01 to 1.0 g / 10 min. The MFR is more preferably 0.02 g / 10 min or more, even more preferably 0.04 g / 10 min or more, and even more preferably 0.1 g / 10 min or more. Another embodiment is one in which the MFR is 0.5 g / 10 min or more. Another embodiment is one in which the MFR is 0.5 to 1.2 g / 10 min.

[0055] Biaxial stretching of films made of high-density polyethylene generally tends to be difficult. For example, in sequential biaxial stretching, a film is stretched in the MD direction and then in the TD direction, during which the film temperature often drops. Therefore, when stretching the film in the TD direction, the film tends to tear easily in the MD direction, making stretching difficult. In contrast, ethylene polymers having an MFR equal to or less than the above upper limit tend to be able to form films with excellent biaxial stretchability even when they have a high density. This is presumably because ethylene polymers having an MFR equal to or less than the above upper limit contain a large amount of high-molecular-weight polymer components, and therefore the film is less likely to tear even when stretched in the TD direction after being stretched in the MD direction and then cooled. Therefore, such films tend to have excellent sequential biaxial stretchability by a continuous tenter method. Ethylene polymers having an MFR equal to or greater than the above lower limit tend to have excellent extrusion moldability.

[0056] The MFR of an ethylene polymer is measured in accordance with JIS K 7210 under conditions of a temperature of 190° C. and a load of 2.16 kg (kgf).

[0057] The MFR of an ethylene-based polymer tends to depend on the molecular weight; the smaller the MFR, the larger the molecular weight, and the larger the MFR, the smaller the molecular weight. The molecular weight of an ethylene-based polymer can be adjusted by the composition ratio of hydrogen to ethylene (hydrogen / ethylene) in the polymerization system. Therefore, the MFR of an ethylene-based polymer can be increased by increasing the hydrogen / ethylene ratio in the polymerization reaction when producing the ethylene-based polymer, and can be decreased by decreasing the hydrogen / ethylene ratio. The MFR of an ethylene-based polymer can also be adjusted by changing the polymerization temperature.

[0058] (Requirement (A2): Density) The density of the ethylene polymer is preferably 941 kg / m 3 More than 970kg / m 3 The density is more preferably less than 943 kg / m 3 More preferably, 945 kg / m 3 More preferably, 946 kg / m 3The density is more preferably 965 kg / m or more. 3 More preferably, 960 kg / m or less 3 Particularly preferably 956 kg / m or less 3 Density is 941 to 956 kg / m or less. 3 In one embodiment, a biaxially stretched film having a layer formed from a material containing an ethylene polymer having a density equal to or higher than the above lower limit tends to be excellent in rigidity and low shrinkage. A film having a layer formed from a material containing an ethylene polymer having a density equal to or lower than the above upper limit tends to be excellent in biaxial stretchability.

[0059] The density of the ethylene polymer is measured by the density gradient tube method using the strand obtained when measuring the MFR in accordance with JIS K 7112. Details of the measurement conditions are described in the Examples section.

[0060] The density of an ethylene-based polymer depends on, for example, the content ratio of structural units derived from α-olefins having 3 or more carbon atoms (hereinafter also referred to as "α-olefin content"). The density tends to be higher as the α-olefin content is lower, and the density tends to be lower as the α-olefin content is higher.

[0061] (Requirement (A3): Melt tension) The melt tension of the ethylene polymer is preferably 31 to 250 mN. That is, the melt tension is preferably 31 mN or more and 250 mN or less. The melt tension is more preferably 35 mN or more, 40 mN or more, or 45 mN or more. Another embodiment is that the melt tension is 61 mN or more, 80 mN or more, or 90 mN or more. The melt tension is more preferably 240 mN or less, even more preferably 230 mN or less, still more preferably 200 mN or less, and particularly preferably 170 mN or less. Another embodiment is that the melt tension is 120 mN or less. Another embodiment is that the melt tension is 35 to 120 mN or 40 to 120 mN.

[0062] Biaxial stretching of films made of high-density polyethylene generally tends to be difficult. For example, in sequential biaxial stretching, a film is stretched in the MD direction and then in the TD direction, during which the film temperature often drops. Therefore, when stretching the film in the TD direction, the film tends to tear easily in the MD direction, making stretching difficult. In contrast, ethylene polymers having a melt tension equal to or greater than the lower limit tend to be able to form films with excellent biaxial stretchability, even when they have a high density. This is presumably because ethylene polymers having a melt tension equal to or greater than the lower limit contain many molecules (so-called tie molecules) in the amorphous portion that straddle one crystalline portion and another crystalline portion, which can prevent the film from tearing in the MD direction when stretched in the TD direction. Furthermore, ethylene polymers having a melt tension equal to or greater than the lower limit are presumably able to prevent film sagging during film formation. Therefore, such films tend to have excellent sequential biaxial stretchability when formed using a continuous tenter method. An ethylene polymer having a melt tension of the above upper limit or less tends to be able to form a film having excellent transparency.

[0063] The melt tension of the ethylene polymer is measured at a resin temperature of 190°C, and the details of the measurement method are described in the Examples section.

[0064] The melt tension of the ethylene polymer can be adjusted, for example, by the MFR, molecular weight, or molecular weight distribution (Mw / Mn) of the ethylene polymer. For example, the melt tension can be increased by increasing the molecular weight distribution.

[0065] (Requirement (A4): Mw / Mn) The Mw / Mn of the ethylene polymer is preferably 6.1 or more, more preferably 7 or more, and even more preferably 8 or more. In one embodiment, the Mw / Mn is 10 or more, 15 or more, or 20 or more. The upper limit of the Mw / Mn of the ethylene polymer is not particularly limited. The Mw / Mn of the ethylene polymer may be, for example, 50 or less, or 45 or less. In another embodiment, the Mw / Mn is 12 or less. The Mw / Mn of the ethylene polymer is, for example, 6.1 or more and 50 or less, or 7 or more and 50 or less. In another embodiment, the Mw / Mn is 7 or more and 12 or less.

[0066] Ethylene polymers having an Mw / Mn ratio equal to or greater than the above lower limit tend to be able to form films with excellent biaxial stretchability because they contain high-molecular-weight polymer components. This is presumably because the presence of a large number of tie molecules derived from the high-molecular-weight polymer components prevents the film from tearing in the MD direction or other directions when stretched in the TD direction. This is also presumably because the presence of a large number of high-molecular-weight polymer components increases the melt tension, thereby preventing film sagging during film formation. Ethylene polymers having an Mw / Mn ratio equal to or less than the above upper limit tend to be able to form films with excellent transparency.

[0067] Mw / Mn is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), each measured by gel permeation chromatography (GPC), and is the molecular weight distribution. Mw and Mn are values ​​converted into polyethylene equivalents. Details of the measuring device and measuring conditions are as described in the Examples section. In addition, the molecular weight is calculated based on a calibration curve prepared using commercially available monodisperse polystyrene and a conversion method.

[0068] The Mw / Mn of the ethylene polymer can be increased, for example, by producing the ethylene polymer by a multistage polymerization process or by mixing two or more ethylene polymers having different average molecular weights.

[0069] The ethylene polymer can be produced using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. The ethylene polymer may also be produced by a continuous multi-stage polymerization process using multiple polymerization reactors. A commercially available ethylene polymer may be used. For example, a polyethylene satisfying the above-mentioned requirements may be selected from commercially available polyethylenes.

[0070] (Requirement (A5): Semi-melting temperature range) The semi-melting temperature range of the ethylene polymer is preferably 5.5°C or higher, more preferably 6.0°C or higher, and even more preferably 6.5°C or higher. In one embodiment, the semi-melting temperature range is 7.0°C or higher or 7.5°C or higher. An ethylene polymer having such a semi-melting temperature range is less likely to break during stretching or melt sagging, and tends to be able to be stably stretched in the TD direction after being stretched in the MD direction, for example.

[0071] The upper limit of the semi-melting temperature range of the ethylene polymer is not particularly limited. The semi-melting temperature range of the ethylene polymer is preferably 50° C. or less, more preferably 40° C. or less, even more preferably 30° C. or less, and particularly preferably 25° C. or less. An ethylene polymer having such a semi-melting temperature range tends to have excellent heat resistance and rigidity.

[0072] The semi-melting temperature range of the ethylene polymer is, for example, 5.5 to 50°C.

[0073] The semi-melting temperature range is the temperature (T) at which the ratio of the heat of fusion to the total heat of fusion of the entire ethylene polymer obtained by differential scanning calorimetry (DSC) is 30%, where ΔH is the total heat of fusion of the entire ethylene polymer. 30 ) and the temperature at which the ratio becomes 70% (T 70 ) and the difference (T 70 -T 30 The details of the measurement conditions are described in the Examples section.

[0074] (Requirement (A6): I 21 / I2) I 21 / I2 is the melt index (I 21 It is the ratio of the melt index (I: 190°C, 21.6 kg load) to the melt index (I: 190°C, 2.16 kg load).21 and I2 are measured at a temperature of 190°C in accordance with JIS K 7210.

[0075] Ethylene polymer I 21 Although there is no particular limitation to / I2, it is preferably 35 to 300. 21 / I2 is more preferably 37 or more, and even more preferably 40 or more. 21 The ethylene polymer having the above I tends to have excellent moldability. 21 / I2 is more preferably 250 or less, even more preferably 200 or less, even more preferably 150 or less, and particularly preferably 100 or less. 21 In one embodiment, / I2 is 70 or less. 21 An ethylene polymer having I tends to have excellent transparency. 21 In one embodiment, / I2 is 40 to 70.

[0076] The ethylene polymer has, for example, an MFR of 0.5 to 1.2 g / 10 min, a melt tension of 40 to 120 mN, an Mw / Mn ratio of 7 to 12, and 21 / I2 is 40 to 70.

[0077] The ethylene polymer has, for example, a melt tension of 40 to 120 mN and an Mw / Mn ratio of 7 to 12, and 21 / I2 is 40 to 70.

[0078] The ethylene polymer has, for example, Mw / Mn of 7 to 12 and 21 In one embodiment, / I2 is 40 to 70.

[0079] <Other Polymers> The above material may further contain a polymer other than an ethylene-based polymer (hereinafter also referred to as "other polymer"). Examples of other polymers include thermoplastic resins other than ethylene-based polymers. Examples of thermoplastic resins include olefin-based polymers other than ethylene-based polymers, (meth)acrylic resins, polyvinyl chloride, polystyrene, polyester, polyamide, polyimide, polyacetal, polyvinyl alcohol, polyacrylonitrile, and polycarbonate.

[0080] Among these other polymers, olefin polymers are preferred. Examples of olefin polymers include propylene polymers, butene polymers, 4-methyl-1-pentene polymers, 3-methyl-1-butene polymers, and hexene polymers, with propylene polymers being preferred. Materials containing a propylene polymer together with an ethylene polymer tend to provide excellent adhesion of the raw film to the chill roll during raw film formation before stretching, and the resulting raw film tends to have high surface smoothness (small surface irregularities). Therefore, the resulting biaxially stretched film tends to have excellent appearance.

[0081] In this specification, a propylene-based polymer refers to a polymer in which the proportion of propylene-derived structural units relative to the total content of structural units derived from polymerizable monomers (content ratio) is greater than 50 mol %. In the propylene-based polymer, the content ratio of propylene-derived structural units is preferably 51 mol % or more, more preferably 60 mol % or more, even more preferably 70 mol % or more, still more preferably 80 mol % or more, particularly preferably 90 mol % or more, and particularly preferably 95 mol % or more.

[0082] The propylene-based polymer may be a homopolymer of propylene, or a copolymer of propylene and another polymerizable monomer (hereinafter also referred to as a "propylene-based copolymer"). Examples of the other polymerizable monomer include α-olefins having two or more carbon atoms (excluding propylene). A preferred example of the propylene-based copolymer is a copolymer of propylene and an α-olefin having two or more carbon atoms (hereinafter also referred to as a "propylene-α-olefin copolymer").

[0083] In the propylene-based copolymer, the number of carbon atoms in the α-olefin is preferably 2 to 20, more preferably 2 to 10, even more preferably 2 to 8, and particularly preferably 2 to 6. Examples of α-olefins other than propylene include linear α-olefins such as ethylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-octadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene; and branched α-olefins such as 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4-ethyl-1-hexene, and 3-ethyl-1-hexene. Among these, from the viewpoint of copolymerizability with propylene, linear α-olefins are preferred, and ethylene, 1-butene, 1-hexene, and 1-octene are more preferred. The propylene-α-olefin copolymer may have one or more structural units derived from α-olefins other than propylene.

[0084] The propylene copolymer may be a propylene random copolymer or a propylene block copolymer. Specific examples of the propylene copolymer include a propylene-ethylene copolymer, a propylene-1-butene copolymer, and a propylene-ethylene-1-butene copolymer.

[0085] The melt flow rate (MFR) of the propylene polymer is preferably 0.01 to 100 g / 10 min, more preferably 0.1 to 50 g / 10 min, still more preferably 0.5 to 30 g / 10 min, and particularly preferably 1 to 10 g / 10 min. The MFR of the propylene polymer is measured in accordance with JIS K 7210 under conditions of a temperature of 230°C and a load of 2.16 kg (kgf).

[0086] The propylene-based polymer may have a structural unit derived from a biomass-derived monomer (e.g., propylene, α-olefin). The propylene-based polymer may have a structural unit derived from a chemically recycled monomer (e.g., propylene, α-olefin).

[0087] When the material contains other polymers, the content of the ethylene polymer is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 90 parts by mass or more, and is preferably 99.9 parts by mass or less, more preferably 99 parts by mass or less, for example, 50 to 99.9 parts by mass, relative to 100 parts by mass of the total content of the ethylene polymer and other polymers. When the material contains other polymers, the content of the other polymer is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, for example, 0.1 to 50 parts by mass, relative to 100 parts by mass of the total content of the ethylene polymer and other polymers. The other polymer is preferably a propylene polymer.

[0088] <Additives> The material may contain additives that can be added to general polyolefin resin compositions. Examples of additives include nucleating agents, weather stabilizers, heat stabilizers, antistatic agents, antifogging agents, antiblocking agents, slip agents, lubricants, pigments, anti-dripping agents, and nucleating agents.

[0089] The content of the additive in the material is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the ethylene polymer.

[0090] The material containing an ethylene polymer can be prepared by a conventionally known method. For example, the material may be prepared by mixing the above-mentioned components by dry blending, or may be prepared by dry blending followed by melt kneading and, if necessary, granulation. Examples of dry blending methods include methods using a Henschel mixer, a tumbler blender, or a V-blender. Examples of melt kneading methods include methods using a single-screw extruder, a multi-screw extruder, or a Banbury mixer.

[0091] <Multilayer Stretched Film> The biaxially stretched film of the present disclosure may be a multilayer stretched film having at least one layer made of a material containing an ethylene-based polymer (hereinafter also referred to as an "ethylene-based polymer material") that satisfies the above-mentioned requirements, and the thickness ratio of each layer is not particularly limited. The number of layers in the multilayer stretched film may be, for example, 2 to 11, 3 to 9, 3 to 7, or 3 to 5.

[0092] The structure of the multilayer stretched film is not particularly limited, but examples include the following structures (1a) to (6a): In the structures below, for example, the expression "ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene-based polymer material" means a multilayer stretched film having, in this order in the lamination direction, a layer formed from an ethylene-based polymer material, a layer formed from low-density polyethylene or high-density polyethylene, and a layer formed from an ethylene-based polymer material. (1a) Ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene-based polymer material (2a) Ethylene-based polymer material / low-density polyethylene or high-density polyethylene / low-density polyethylene or high-density polyethylene (3a) Low-density polyethylene or high-density polyethylene / ethylene-based polymer material / low-density polyethylene or high-density polyethylene (4a) Low-density polyethylene or high-density polyethylene / ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene-based polymer material / low-density polyethylene or high-density polyethylene (5a) Ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene-based polymer material (6a) Ethylene-based polymer material / low-density polyethylene or high-density polyethylene / ethylene ...

[0093] The method for producing the biaxially stretched film of the present disclosure is not particularly limited, and examples thereof include a method of stretching a film (raw material) obtained by a known melt extrusion molding method. The film (raw material) may be a multilayer film. The method for producing the multilayer film (raw material) is not particularly limited, and examples thereof include a co-extrusion molding method.

[0094] [Laminate] The laminate of the present disclosure has a layer made of the biaxially stretched film of the present disclosure. The laminate of the present disclosure may have a plurality of layers made of the biaxially stretched film. The laminate of the present disclosure can be suitably used, for example, as a packaging material.

[0095] The configuration of the laminate of the present disclosure is not particularly limited, and examples thereof include the following configurations (1b) to (10b). In the following configurations, "PE laminate" means that an ethylene resin is laminated by extrusion lamination. "Biaxially stretched film" means the biaxially stretched film of the present disclosure. "Unstretched HDPE film" means an unstretched high-density polyethylene film.

[0096] In the following configurations, for example, the expression "biaxially oriented film / adhesive / unstretched HDPE film / adhesive / unstretched low-density polyethylene film" means a laminate having, in this order in the stacking direction, a biaxially oriented film, an adhesive layer, an unstretched HDPE film, an adhesive layer, and an unstretched low-density polyethylene film.

[0097] (1b) Biaxially oriented film / adhesive / unstretched HDPE film / adhesive / unstretched low-density polyethylene film (2b) Biaxially oriented film / PE laminate (3b) Biaxially oriented film / PE laminate / unstretched low-density polyethylene film (4b) Biaxially oriented film / adhesive / PE laminate / unstretched low-density polyethylene film (5b) Biaxially oriented film / PE laminate / unstretched HDPE film / adhesive / unstretched low-density polyethylene film (6b) Biaxially oriented film / adhesive / PE laminate / unstretched HDPE film / adhesive / unstretched low-density polyethylene film (7b) Biaxially oriented film / adhesive / unstretched low-density polyethylene film / adhesive / unstretched low-density polyethylene film (8b) Biaxially oriented film / adhesive / unstretched low-density polyethylene film / adhesive / biaxially oriented film / PE laminate (9b) Biaxially oriented film / adhesive / unstretched HDPE film / PE laminate (10b) Biaxially oriented film / adhesive / unstretched HDPE film / PE laminate / unstretched low-density polyethylene film

[0098] Various additional functions can be imparted to the biaxially stretched film of the present disclosure and / or the above-mentioned laminated film by the following methods. Examples include co-extrusion with a barrier resin (e.g., ethylene-vinyl alcohol copolymer (EVOH), nylon (Ny), etc.) or an adhesive resin (e.g., Admer), or coating the surface (e.g., vapor-deposited film, etc.). The vapor-deposited film may be, for example, a film made of metal or a film made of inorganic oxide.

[0099] Examples of metals constituting the metal vapor deposition film include aluminum, chromium, tin, nickel, copper, silver, gold, and platinum. Examples of inorganic oxides include aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, and barium oxide.

[0100] The laminate of the present disclosure preferably has the biaxially stretched film as a substrate. The laminate of the present disclosure may have the biaxially stretched film as a substrate and a sealant layer. Such a laminate is suitable as a packaging material. The sealant layer contains, for example, a thermoplastic resin as a main component. Examples of thermoplastic resins include polyolefins such as polyethylene and polypropylene. The main component refers to a component whose content in the layer is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0101] The sealant layer may be a non-stretched film or a stretched film.

[0102] The laminate of the present disclosure may be produced, for example, by bonding the biaxially stretched film of the present disclosure and a sealant film corresponding to the sealant layer together by a lamination process using an adhesive, or by extrusion lamination using an adhesive resin composition.

[0103] The laminate of the present disclosure may have the biaxially oriented film as a substrate and a sealant layer containing polyethylene as a main component. Such a laminate is suitable as a polyethylene-based mono-material packaging material.

[0104] The laminate of the present disclosure may be a packaging material. For example, a bag-shaped container having an opening can be produced by heat-sealing the packaging material. After filling the bag-shaped container with an item to be packaged (contents) for various uses, the opening can be heat-sealed to obtain a package.

[0105] [Aspects of the present disclosure] The present disclosure relates to, for example, the following [1] to

[16] . [1] A biaxially stretched film having a layer obtained from a material containing an ethylene-based polymer, wherein the ethylene-based polymer has a melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, a melt flow rate (MFR) of 941 kg / m ... 3 More than 970kg / m 3A biaxially stretched film having a density of less than 100 mN and a melt tension of 31 to 250 mN, wherein the ethylene polymer has a ratio Mw / Mn, which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), measured by gel permeation chromatography (GPC), of 6.1 or more. [2] The biaxially stretched film according to [1] above, wherein the material further contains a propylene polymer, and the content of the ethylene polymer is 50 to 99 parts by mass and the content of the propylene polymer is 1 to 50 parts by mass, where the total content of the ethylene polymer and the propylene polymer in the material is 100 parts by mass. [3] The biaxially stretched film according to [2] above, wherein the propylene polymer contains at least one selected from the group consisting of a propylene homopolymer and a random copolymer of propylene and an α-olefin having 2 to 8 carbon atoms (excluding propylene). [4] The biaxially stretched film according to any one of [1] to [3] above, having a stretch ratio in the MD direction of 2 or more and a stretch ratio in the TD direction of 2 or more. [5] The biaxially stretched film is obtained from a material containing an ethylene-based polymer, has a tensile modulus in the MD direction of 1,000 MPa or more, a tensile modulus in the TD direction of 1,500 MPa or more, a dart impact of 100 g or more, and a heat shrinkage in the MD direction of 15% or less and a heat shrinkage in the TD direction of 15% or less. [6] The biaxially stretched film according to [5] above, having tear strengths in the MD direction and TD direction of 1 N or less, each measured by the Elmendorf tear method. [7] The biaxially stretched film according to [5] or [6] above, having a total haze of 50% or less. [8] A laminate having a layer made of the biaxially stretched film according to any one of [1] to [7] above. [9] A packaging material having a layer made of the biaxially stretched film according to any one of [1] to [7].

[10] A melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, and a melt flow rate of 941 kg / m 3 More than 970kg / m 3A method for producing a biaxially stretched film, comprising the steps of preparing a material containing an ethylene polymer having a density of less than 1000 kJ / cm and a melt tension of 31 to 250 mN, and having a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 6.1 or more, as measured by gel permeation chromatography (GPC), where Mw / Mn is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), as measured by gel permeation chromatography (GPC), of 6.1 or more, forming a film using at least the material, and biaxially stretching the film.

[11] A method for producing a biaxially stretched film according to

[10] above, wherein the film is formed using at least the material by a T-die casting method.

[12] A method for producing a biaxially stretched film according to

[10] or

[11] above, wherein the film is biaxially stretched at a stretch ratio of 2 or more in the MD direction and a stretch ratio of 2 or more in the TD direction.

[13] A method for producing a biaxially stretched film according to any one of

[10] to

[12] above, wherein the film is sequentially biaxially stretched by a tenter method.

[14] The method for producing a biaxially stretched film according to any one of

[10] to

[13] above, wherein the production method is carried out continuously.

[15] The method for producing a biaxially stretched film according to any one of

[10] to

[14] above, wherein the material further contains a propylene-based polymer, and the content of the ethylene-based polymer is 50 to 99 parts by mass and the content of the propylene-based polymer is 1 to 50 parts by mass, where the total content of the ethylene-based polymer and the propylene-based polymer in the material is 100 parts by mass.

[16] The method for producing a biaxially stretched film according to

[15] above, wherein the material contains, as the propylene-based polymer, at least one selected from the group consisting of a propylene homopolymer and a random copolymer of propylene and an α-olefin having 2 to 8 carbon atoms (excluding propylene).

[0106] The biaxially stretched film of the present disclosure will be described in more detail below based on examples, but the biaxially stretched film of the present disclosure is not limited to the following examples. In the following examples, reference examples, and comparative examples, "parts" means "parts by mass."

[0107] [Polymer] The polymers used in the following Examples, Reference Examples, and Comparative Examples are described below. <Ethylene-based polymer> Ethylene-based polymer A: Hi-Zex 7000F, manufactured by Prime Polymer, MFR: 0.04 g / 10 min, density: 952 kg / m 3 , Melt tension: 226 mN, Mw / Mn: 42, Semi-melting temperature range: 7.4 ° C., I 21 / I2: 178 Ethylene-based polymer B: Hi-Zex GE100, manufactured by Prime Polymer, MFR: 0.09 g / 10 min, density: 954 kg / m 3 , melt tension: 161 mN, Mw / Mn: 41, semi-melting temperature range: 6.5°C Ethylene polymer C: Hi-Zex GE200, manufactured by Prime Polymer, MFR: 0.19 g / 10 min, density: 952 kg / m 3 , melt tension: 131 mN, Mw / Mn: 23, semi-melting temperature range: 7.1°C Ethylene polymer D: Hi-Zex GE300, manufactured by Prime Polymer, MFR: 1.0 g / 10 min, density: 947 kg / m 3 , Melt tension: 51 mN, Mw / Mn: 8.6, Semi-melting temperature range: 12.3 ° C, I 21 / I2: 58 Ethylene-based polymer E: Hi-Zex 5000SF, manufactured by Prime Polymer, MFR: 0.69 g / 10 min, density: 955 kg / m 3 , melt tension: 54 mN, Mw / Mn: 9.7, semi-melting temperature range: 6.9°C Ethylene polymer F: Hi-Zex GE410, manufactured by Prime Polymer, MFR: 1.3 g / 10 min, density: 952 kg / m 3 , melt tension: 35 mN, Mw / Mn: 6.1, semi-melting temperature range: 5.7°C Ethylene polymer G: Evolue H SP4505, manufactured by Prime Polymer, MFR: 0.4 g / 10 min, density: 944 kg / m 3 , melt tension: 60 mN, Mw / Mn: 6.0 Ethylene-based polymer H: Hi-Zex 3300F, manufactured by Prime Polymer, MFR: 1.1 g / 10 min, density: 950 kg / m 3 , Melt tension: 28 mN, Mw / Mn: 6.2, Semi-melting temperature range: 6.4 ° C, I 21 / I2: 32 Ethylene polymer I: Evolue SP3022, manufactured by Prime Polymer, MFR: 1.6 g / 10 min, density: 927 kg / m 3, melt tension: 65 mN, Mw / Mn: 8.5 Ethylene-based polymer J: Hi-Zex 3600F, manufactured by Prime Polymer, MFR: 1.0 g / 10 min, density: 958 kg / m 3 , melt tension: 30 mN, Mw / Mn: 6.3, and the like. Each of the ethylene-based polymers A to J has a ratio (content ratio) of the content of ethylene-derived structural units to the total content of structural units derived from polymerizable monomers of 51 mol % or more. <Propylene-based polymers> Propylene-based polymer A: Prime Polypro F327, manufactured by Prime Polymer, random polypropylene Propylene-based polymer A has a ratio (content ratio) of the content of propylene-derived structural units to the total content of structural units derived from polymerizable monomers of 51 mol % or more.

[0108] [Measurement Methods] In the following examples and comparative examples, melt flow rate (MFR), density, melt tension, molecular weight distribution (Mw / Mn), half-melting temperature range, melt index ratio (I 21 / I2), tensile modulus, dart impact, heat shrinkage, tear strength and total haze were measured as follows.

[0109] <Melt Flow Rate (MFR)> The melt flow rate (MFR, unit: g / 10 min) of an ethylene polymer was measured in accordance with JIS K 7210 under conditions of a temperature of 190°C and a load of 2.16 kg (kgf).

[0110] <Density> In accordance with JIS K 7112, the density (unit: kg / m) of the strand obtained during the measurement of MFR was measured at 23°C by a density gradient tube method. 3 ) was measured.

[0111] <Melt Tension> The melt tension was determined by measuring the stress when the molten filament was stretched at a constant speed. A capillary rheometer, Capillograph 1B (manufactured by Toyo Seiki Seisakusho, Ltd.), was used to measure the stress. The measurement conditions were: resin temperature: 190°C, melting time: 6 minutes, barrel diameter: 9.55 mmφ, extrusion speed: 15 mm / min, take-up speed: 24 m / min (if the molten filament breaks, the take-up speed is reduced by 5 m / min increments), nozzle diameter: 2.095 mmφ, and nozzle length: 8 mm.

[0112] <Molecular Weight Distribution (Mw / Mn)> The weight average molecular weight (Mw) and number average molecular weight (Mn) of each polymer were measured by gel permeation chromatography (GPC), and calculations were performed in polyethylene equivalent terms. The molecular weight distribution (Mw / Mn) was calculated from the obtained Mw and Mn. The GPC measurement conditions were as follows: (Measurement conditions) Measurement apparatus: Gel permeation chromatograph GPC / HT type (manufactured by Tosoh) Analysis software: Data processing software Empower3 (manufactured by Waters) Column: 2 x TSKgel GMH6-HT + 2 x TSKgel GMH6-HTL (both 7.5 mm inner diameter x 30 cm length, manufactured by Tosoh) Column temperature: 140°C Mobile phase: o-dichlorobenzene (containing 0.025% by mass of BHT) Detector: Differential refractometer Flow rate: 1.0 mL / min Sample concentration: 0.1% (w / v) Injection volume: 400 μL Sampling time interval: 0.5 seconds Column calibration: Monodisperse polystyrene (manufactured by Tosoh) Molecular weight conversion: Polyethylene conversion / general calibration method

[0113] <Semi-melting temperature range> DSC measurement was carried out on an ethylene polymer as follows. Using a differential scanning calorimeter, an ethylene polymer sample was heated in a nitrogen atmosphere from -30°C to 230°C at a rate of 10°C / min, held at 230°C for 10 minutes, then cooled to -30°C at a rate of 10°C / min, and held at -30°C for 1 minute. The sample was then heated to 230°C at a rate of 10°C / min. The semi-melting temperature range is the temperature (T 30 ) and the temperature at which the ratio becomes 70% (T70 ) and the difference (T 70 -T 30 Specifically, in the DSC curve during the second temperature rise, a baseline was drawn in the region from 20°C to 150°C, the value of the baseline was subtracted from the DSC curve, the remaining area was taken as the total heat of fusion (ΔH), and the difference between the temperatures at which the area became 30% and 70% was calculated.

[0114] <Melt index ratio (I 21 / I2)> In accordance with JIS K 7210, the melt index (I 21 The melt index (I2, unit: g / 10 min) of the ethylene polymer was measured in accordance with JIS K 7210 under the conditions of a temperature of 190°C and a load of 2.16 kg (kgf). From these, the melt index ratio (I 21 / I2) was calculated.

[0115] <Tensile Modulus> Dumbbell shapes of a size conforming to JIS K 6781 were punched out from the stretched films obtained in the Examples, Reference Examples, or Comparative Examples to obtain test specimens. Test specimens obtained by punching out the dumbbells so that their longitudinal direction was parallel to the MD direction (take-up direction) of the stretched film are referred to as MD test specimens, and the tensile modulus obtained using the MD test specimens is the tensile modulus in the MD direction. Test specimens obtained by punching out the dumbbells so that their longitudinal direction was perpendicular to the MD direction of the stretched film are referred to as TD test specimens, and the tensile modulus obtained using the TD test specimens is the tensile modulus in the TD direction. Each test specimen was set in the air chuck of a universal testing machine, and a tensile test was performed under the conditions of a temperature of 23°C, a chuck distance of 80 mm, and a tensile speed of 200 mm / min. A stress-strain curve was obtained by plotting strain on the horizontal axis and stress (MPa) on the vertical axis. In this stress-strain curve, the average value of the slope of the tangent line in the strain range of 1 to 3% was taken as the tensile modulus.

[0116] Dart Impact (Dart Impact Strength) Dart impact was measured under the following conditions according to ASTM D1709 Method A. The test specimen was clamped using an air clamp, and a hemispherical dart was dropped from a certain height. The load at which the test specimen broke 50% was read from the graph. The number of drops per level was 10.

[0117] <Heat shrinkage> The stretched film was cut into strips of 10 mm width x 100 mm length to obtain MD test pieces and TD test pieces. Each test piece was placed in an air oven at 120°C and heated for 15 minutes, and the length of the test piece was confirmed. The heat shrinkage in the MD direction and the TD direction was calculated based on the above formula.

[0118] <Tear Strength> The tear strength of a stretched film was measured by the Elmendorf tear method using an Elmendorf tear tester (manufactured by Toyo Seiki Seisakusho) at a temperature of 23° C. in accordance with JIS K 7128. The tear strength in the MD direction was determined when a cut was made along the MD direction of the stretched film, and the tear strength in the TD direction was determined when a cut was made along the TD direction of the stretched film.

[0119] <Total Haze> Total haze was measured in accordance with JIS K 7136 using a haze meter.

[0120] <Chill roll adhesion and film appearance> A state in which the film was uniformly adhered to the chill roll in the TD direction and no polka dots due to poor adhesion to the chill roll were marked as "A", and a state in which the film was not partially adhered to the chill roll in the TD direction and polka dots were partially formed in the non-adhered areas was marked as "B".

[0121] Example 1 Ethylene-based polymer A (Hi-Zex 7000F manufactured by Prime Polymer) was melt-kneaded at 250°C in an extruder, and then a raw film having a thickness of 800 μm was produced in a sheet forming machine. This raw film was uniaxially stretched in the machine direction (MD direction) at a stretch ratio of 5 while heated with a roll at 134°C, to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched in the transverse direction (TD direction) at a stretch ratio of 7 while heated with a tenter at 136°C. The physical properties of the obtained biaxially stretched film were measured. The results are shown in Table 1. In Example 1, continuous biaxial stretching was possible.

[0122] Examples 2 to 10 and Comparative Examples 1 to 4 Biaxially stretched films were produced in the same manner as in Example 1, except that one or more conditions selected from the polymer used, the stretch ratio, and the stretching temperature were changed as shown in Table 1. In Examples 2 to 10 and Comparative Example 3, continuous biaxial stretching was possible. In Comparative Examples 1, 2, and 4, continuous biaxial stretching was not possible. In Example 7, a mixture of 70 parts of ethylene polymer A and 30 parts of propylene polymer A was used as the material. In Comparative Example 4, a mixture of 85 parts of ethylene polymer J and 15 parts of propylene polymer A was used as the material.

[0123] Reference Example 1 Ethylene-based polymer A ("Hi-Zex 7000F" manufactured by Prime Polymer) was melt-kneaded at 250°C in an extruder, and then a raw film having a thickness of 250 μm was produced using an inflation molding machine. This raw film was uniaxially stretched in the machine direction (MD direction) at a stretch ratio of 5 times while being heated with a roll at 120°C, to obtain a uniaxially stretched film. The physical properties of the obtained uniaxially stretched film were measured. The results are shown in Table 1. In Reference Example 1, continuous uniaxial stretching was possible.

[0124]

Claims

1. A biaxially stretched film having a layer obtained from a material containing an ethylene-based polymer, the ethylene-based polymer having a melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, and a melt flow rate of 941 kg / m 3 More than 970kg / m 3 and a melt tension of 31 to 250 mN, wherein the ethylene-based polymer has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), Mw / Mn, which is measured by gel permeation chromatography (GPC), of 6.1 or more.

2. The biaxially stretched film according to claim 1, wherein the material further contains a propylene-based polymer, and the content of the ethylene-based polymer is 50 to 99 parts by mass and the content of the propylene-based polymer is 1 to 50 parts by mass, when the total content of the ethylene-based polymer and the propylene-based polymer in the material is 100 parts by mass.

3. The biaxially stretched film according to claim 2, wherein the material contains, as the propylene-based polymer, at least one selected from the group consisting of propylene homopolymers and random copolymers of propylene and α-olefins having 2 to 8 carbon atoms (excluding propylene).

4. The biaxially stretched film according to claim 1, wherein the stretching ratio in the MD direction is 2 times or more and the stretching ratio in the TD direction is 2 times or more.

5. A biaxially oriented film obtained from a material containing an ethylene-based polymer, having a tensile modulus in the MD direction of 1,000 MPa or more, a tensile modulus in the TD direction of 1,500 MPa or more, a dart impact of 100 g or more, a heat shrinkage rate in the MD direction of 15% or less, and a heat shrinkage rate in the TD direction of 15% or less.

6. The biaxially oriented film according to claim 5, wherein the tear strength in the MD direction and the tear strength in the TD direction, as measured by the Elmendorf tear method, are each independently 1 N or less.

7. The biaxially oriented film of claim 5, having a total haze of 50% or less.

8. A laminate having a layer made of the biaxially stretched film according to any one of claims 1 to 7.

9. A packaging material having a layer of the biaxially oriented film according to any one of claims 1 to 7.

10. Melt flow rate (MFR) of 0.01 g / 10 min or more and 5.0 g / 10 min or less, 941 kg / m 3 More than 970kg / m 3 The method for producing a biaxially stretched film includes the steps of: preparing a material containing an ethylene-based polymer having a density of less than 100 μm and a melt tension of 31 to 250 mN, and having a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) of 6.1 or more, as measured by gel permeation chromatography (GPC); forming a film using at least the material; and biaxially stretching the film.

11. The method for producing a biaxially stretched film according to claim 10, wherein the film is formed by a T-die casting method using at least the material.

12. The method for producing a biaxially stretched film according to claim 10, wherein the film is biaxially stretched under conditions in which the stretching ratio in the MD direction is 2 times or more and the stretching ratio in the TD direction is 2 times or more.

13. The method for producing a biaxially stretched film according to claim 10, wherein the film is sequentially biaxially stretched by a tenter method.

14. The method for producing a biaxially stretched film according to claim 10, wherein the production method is carried out continuously.

15. The method for producing a biaxially stretched film according to any one of claims 10 to 14, wherein the material further contains a propylene-based polymer, and when the total content of the ethylene-based polymer and the propylene-based polymer in the material is taken as 100 parts by mass, the content of the ethylene-based polymer is 50 to 99 parts by mass and the content of the propylene-based polymer is 1 to 50 parts by mass.

16. The method for producing a biaxially stretched film according to claim 15, wherein the material contains, as the propylene-based polymer, at least one selected from the group consisting of propylene homopolymers and random copolymers of propylene and α-olefins having 2 to 8 carbon atoms (excluding propylene).

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