Stretched films, laminates and packaging

Abstract

A stretched film comprising a polyethylene-based resin composition satisfying requirements (1)-(3). (1) The melt flow rate (190°C, 2.16 kgw) is 0.01-2.0 g / 10min. (2) The density is 935-970 kg / m 3 <sp / >. (3) The ratio I21 / I2 between a melt index (I21: 190°C, 21.6 kgw) and a melt index (I2:190°C, 2.16 kgw) is 80 or more.

Description

[Technical field]

[0001] The present invention relates to a stretched film, a laminate, and a package. [Background technology]

[0002] In recent years, against the background of environmental problems, laws regarding the disposal of various plastics have been enacted, and the need for recycling packaging materials has also increased, leading to the study of various recyclable packaging materials (see, for example, Patent Documents 1 and 2). Among these, mono-material materials (e.g., ALL PE) made of a single material have attracted attention as recyclable packaging materials.

[0003] General packaging materials use films made of various resins as the base material, but the properties required for an all-PE base material include rigidity, low shrinkage, and strength. From the standpoint of rigidity and low shrinkage, high-density polyethylene (HDPE) is suitable as a resin, but the problem with HDPE is that its longitudinal tear strength is very weak. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6716764 [Patent Document 2] JP 2020-121455 A Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above-mentioned conventional techniques, an object of the present invention is to provide a film that can be used as a base material for packaging materials, which has an excellent balance of rigidity, low shrinkage, and longitudinal tear strength. [Means for solving the problem]

[0006] Means for Solving the Problems The present inventors have conducted intensive research in view of the above problems and have found that the above problems can be solved by a stretched film made of a polyethylene resin composition having specific physical properties, thereby completing the present invention.

[0007] The stretched film of the present invention is characterized by being made of a polyethylene resin composition that satisfies the following requirements (1) to (3): (1) a melt flow rate (190°C, 2.16 kg load) of 0.01 g / 10 min to 2.0 g / 10 min; (2) a density of 935 kg / m 3 More than 970kg / m 3 (3) Melt index (I 21 : 190℃, 21.6kg load) and melt index (I 2 : 190℃, 2.16kg load) 21 / I 2 is 80 or more. Effect of the Invention

[0008] The stretched film of the present invention has an excellent balance of rigidity, low shrinkage, and longitudinal tear strength, and therefore can be suitably used as a recyclable packaging material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below. The stretched film of the present invention is made of a polyethylene resin composition (hereinafter, simply referred to as "resin composition") that satisfies the following requirements (1) to (3): (1) The melt flow rate (MFR: 190°C, 2.16 kg load) is 0.01 g / 10 min or more and 2.0 g / 10 min or less. (2) The density is 935 kg / m 3 More than 970kg / m 3 (3) Melt index (I 21 : 190℃, 21.6kg load) and melt index (I 2 : 190℃, 2.16kg load) 21 / I 2 is 80 or more.

[0010] [Resin composition] <Requirement (1)> The lower limit of the MFR (190°C, 2.16 kg load) of the resin composition is usually 0.01 g / 10 min or more, preferably 0.02 g / 10 min or more, and the upper limit is usually 2.0 g / 10 min or less, preferably 1.5 g / 10 min or less, more preferably 1.0 g / 10 min or less. By having the MFR of the resin composition within the above range, strength and extrudability are obtained.

[0011] <Requirement (2)> The lower limit of the density of the resin composition is usually 935 kg / m 3 More than 938kg / m 3 More preferably, 940 kg / m 3 The upper limit is usually 970 kg / m 3 Less than or equal to 968 kg / m 3 Less than or equal to 965 kg / m 3 The density of the resin composition is within the above range, so that the resin composition can obtain rigidity and strength. The density is a value measured in accordance with JIS K7112 (density gradient tube method).

[0012] <Requirement (3)> The melt index (I 21 : 190℃, 21.6kg load) and melt index (I 2 : 190℃, 2.16kg load) 21 / I 2 The lower limit of I of the resin composition is usually 80 or more, preferably 100 or more, more preferably 120 or more, and the upper limit is preferably 300 or less, more preferably 250 or less. 21 / I 2 When the content is within the above range, strength and extrudability are obtained.

[0013] Melt Index I 21 is a value measured at 190℃ under a load of 21.6 kg in accordance with JIS K7210. Melt index I 2is a value measured at 190°C under a load of 2.16 kg in accordance with JIS K7210.

[0014] <Composition> The resin composition is not particularly limited as long as it is a polyethylene-based resin composition that satisfies the above requirements (1) to (3), but the polyethylene-based polymer as a resin component contained in the resin composition may be a homopolymer of ethylene or an ethylene-based copolymer of ethylene and other monomers. As the ethylene-based copolymer, a copolymer of ethylene and an α-olefin having 3 or more carbon atoms (ethylene-α-olefin copolymer) is particularly preferable. Specific examples of the α-olefin in the ethylene-α-olefin copolymer include propylene, butene, 1-octene, and 1-hexene. Such a copolymer can be produced using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. In addition to the copolymer of ethylene and an α-olefin, other low-density polyethylene may be used as the resin component. In the present invention, one or a combination of two or more polyethylenes that satisfy each of the above characteristics can be selected from commercially available polyethylene resins and used as the resin component. As a polyethylene-based resin containing an ethylene-α-olefin copolymer, a linear low-density polyethylene can be mentioned.

[0015] The polyethylene polymer may contain structural units derived from one or more types of biomass-derived monomers (ethylene). The same type of monomer constituting the polymer may be only biomass-derived monomers, or may be both biomass-derived monomers and fossil fuel-derived monomers. A biomass-derived monomer is a monomer made from any renewable natural raw material or its residue, such as a plant-derived or animal-derived monomer, including fungi, yeast, algae, and bacteria, and has a carbon content of 1×10 14C isotope. -12 The biomass carbon concentration (pMC) measured in accordance with ASTM D6866 is about 100 (pMC). The biomass-derived monomer (ethylene) can be obtained, for example, by a conventionally known method.

[0016] It is preferable from the viewpoint of reducing the environmental load that the polyethylene polymer contains a structural unit derived from a biomass-derived monomer. If the polymer production conditions such as the polymerization catalyst and polymerization temperature are the same, even if the raw olefin contains a biomass-derived olefin, the 14C isotope can be reduced by 1×10 -12 Other than the proportion of ethylene oxide in the polymer, the molecular structure is the same as that of polyethylene polymers made from fossil fuel-derived monomers. Therefore, the performance of these polymers is said to be the same.

[0017] In the resin composition, the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution; Mw / Mn) measured by gel permeation chromatography (GPC) is preferably more than 20, more preferably 21 or more, and particularly preferably 22 or more. There is no particular upper limit, but it is preferably 50 or less, more preferably 48 or less. When the Mw / Mn of the resin composition is in the above-mentioned range, a stretched film having excellent tear strength can be obtained.

[0018] The resin composition may contain, as necessary, at least one of various additives that are typically added to polyolefin resin compositions, such as a weather stabilizer, a heat stabilizer, an antistatic agent, an anti-fogging agent, an anti-blocking agent, a slip agent, a lubricant, a pigment, a dripping agent, and a nucleating agent, so long as the additive does not impair the object of the present invention.

[0019] [Stretched film] The stretched film of the present invention is characterized by comprising the polyethylene resin composition of the present invention described above. The stretched film of the present invention may be a uniaxially stretched film or a biaxially stretched film.

[0020] The stretching ratio of the stretched film of the present invention is preferably 2.0 times or more, more preferably 2.5 times or more, particularly preferably 3.0 times or more, and most preferably 3.1 times or more. The upper limit of the stretching ratio is not particularly limited, but is preferably 60 times or less, more preferably 50 times or less. By having the stretching ratio within the above range, rigidity and strength can be obtained.

[0021] The thickness of the stretched film of the present invention may be appropriately set depending on various applications, but in general, the lower limit is preferably 5 μm or more, more preferably 10 μm or more, and the upper limit is preferably 150 μm or less, more preferably 100 μm or less. By having the thickness of the stretched film within the above range, a balance between rigidity and strength as a packaging material can be achieved.

[0022] The method for producing the stretched film of the present invention is not particularly limited, and examples thereof include a method in which a film (raw film to be stretched) obtained by a known melt extrusion molding method is stretched.

[0023] Methods for stretching the raw material include simultaneous or sequential biaxial stretching in the longitudinal and transverse directions using a tenter method, simultaneous biaxial stretching in the longitudinal and transverse directions using a tubular method, and uniaxial stretching in the film flow direction by using a difference in the rotation speed ratio of two or more rolls.

[0024] In the uniaxial stretching, it is preferable to unwind the raw sheet into a roll stretching machine, preheat it with a preheating roll, and then uniaxially stretch it in the MD direction (take-up speed direction). From the viewpoint of increasing production efficiency, it is preferable to preheat the raw sheet and then immediately uniaxially stretch it in the MD direction. In the present invention, uniaxial stretching means stretching in a uniaxial direction, but it may be stretched in a direction different from the uniaxial direction to the extent that the effect of the present invention is not impaired. This is because, depending on the stretching equipment used, even if it is intended to be stretched in a uniaxial direction, it may be substantially stretched in a direction different from the uniaxial direction.

[0025] The stretched film may be annealed, if necessary, by contacting the stretched sheet with a heated roll.

[0026] The stretched film of the present invention preferably has an elastic modulus in the MD direction of more than 1600 MPa, more preferably 1700 MPa or more. The upper limit of the elastic modulus is not particularly limited, but in reality, it is 7000 MPa or less. The elastic modulus in the MD direction in the above-mentioned range ensures the rigidity of the film.

[0027] [Laminate] The laminate of the present invention is characterized by including a layer made of the above-mentioned stretched film of the present invention. The laminate of the present invention may have a plurality of layers made of the above-mentioned stretched film of the present invention. The above-mentioned stretched film of the present invention is preferably used as a substrate in the laminate. Other layers in the laminate of the present invention can be appropriately adopted depending on the application.

[0028] The laminate of the present invention can be produced by known methods, such as coextrusion molding of one or more thermoplastic resins, extrusion lamination, dry lamination, and thermal lamination.

[0029] [Packaging] The package of the present invention is characterized by including a layer made of the stretched film of the present invention described above. For example, the package of the present invention can be obtained by forming the laminate of the present invention described above into a bag-shaped container, filling it with a packaged item (content) for various uses, and heat sealing it. EXAMPLES

[0030] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way. In the following examples, MFR, melt index, density, molecular weight distribution (Mw / Mn), elastic modulus, tear strength and heat shrinkage were measured as follows.

[0031] <Melt flow rate (MFR: [g / 10min])> The measurements were performed in accordance with JIS K7210 at 190°C and a load of 2.16 kg (kgf).

[0032] <Melt index> Melt Index I 21 The melt index I was measured at 190°C and a load of 21.6 kg in accordance with JIS K7210. 2 The melt index ratio I was calculated based on the measurement at 190°C and a load of 2.16 kg in accordance with JIS K7210. 21 / I 2 was calculated.

[0033] <Density [kg / m 3 ]> In accordance with JIS K7112, the strand obtained during melt index measurement was heat treated at 100°C for 1 hour and then allowed to stand at room temperature for 1 hour, after which the melt index was measured by the density gradient tube method.

[0034] <Molecular weight distribution (Mw / Mn)> The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) are values ​​calculated in terms of polystyrene measured by gel permeation chromatography (GPC). The measuring device and conditions are as follows. The molecular weight was calculated based on a conversion method using a calibration curve prepared using commercially available monodisperse polystyrene. Apparatus: Gel permeation chromatograph Alliance GP2000 type (Waters), Analysis equipment: Empower2 (Waters), Column: TSKgel GMH6-HT x 2 + TSKgel GMH6-HTL x 2 (7.5 mm I.D. x 30 cm, Tosoh Corporation), Column temperature: 140°C, Mobile phase: o-dichlorobenzene (containing 0.025% BHT), Detector: differential refractometer (RI), flow rate: 1.0 mL / min, Injection volume: 400μL, Sampling time interval: 1s, Column calibration: monodisperse polystyrene (Tosoh Corporation), Molecular weight conversion: Old EPR conversion / calibration method that takes viscosity into account.

[0035] <Elasticity modulus> A dumbbell of a size conforming to JIS K6781 was punched out from the film to prepare a test specimen, and the direction punched parallel to the film's take-off direction was defined as MD (machine direction). The test specimen was set in the air chuck of a universal material testing machine, and a tensile test was performed with a chuck distance of 80 mm and a tensile speed of 200 mm / min. The slope of the initial stress against the displacement was defined as the elastic modulus.

[0036] <Tear strength> The Elmendorf tear strength was measured in accordance with JIS K 7128-2 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The MD direction is defined as the direction in which the cut is made in the direction in which the film is taken off.

[0037] <Heat shrinkage rate> The stretched film was cut into strips of 10 mm width x 100 mm length, and the longitudinal direction was set as the take-off direction (MD). The cut film was placed in an air oven heated to 100°C and heated for 15 minutes, and the length of the film was confirmed. The heat shrinkage was calculated as follows. Heat shrinkage rate [%] = (100 mm - length after heating mm) / 100 mm x 100

[0038] [Example 1] As a polyethylene resin composition, the MFR is 0.04g / 10min and the density is 952kg / m 3 , I 21 / I 2 Using Prime Polymer's "Hi-Zex 7000F" with a molecular weight of 178 and Mw / Mn of 42, the material was melt-kneaded at 200°C in an extruder, and then a raw film with a thickness of 125 μm was produced using an inflation molding machine. This raw film was uniaxially stretched at a stretch ratio of 5 times while being heated to 115°C using a heating roll, to obtain a uniaxially stretched film with a thickness of 25 μm. The elastic modulus, tear strength, and heat shrinkage of the obtained stretched film were measured. The results are shown in Table 1.

[0039] [Example 2] The polyethylene resin composition has an MFR of 0.1 g / 10 min and a density of 950 kg / m 3, I 21 / I 2 A stretched film was obtained and evaluated in the same manner as in Example 1, except that "Hi-Zex 6300M" manufactured by Prime Polymer Co., Ltd., having a molecular weight of 222 and an Mw / Mn ratio of 27 was used. The results are shown in Table 1.

[0040] [Example 3] As a polyethylene resin composition, the MFR is 0.09g / 10min and the density is 954kg / m 3 , I 21 / I 2 A stretched film was obtained and evaluated in the same manner as in Example 1, except that "Hi-Zex GE100" manufactured by Prime Polymer Co., Ltd., with a molecular weight of 167 and a molecular weight / molecular weight of 31 was used, and the raw film was heated to 120° C. with a heating roll. The results are shown in Table 1.

[0041] [Comparative Example 1] As a polyethylene resin composition, the MFR is 0.04g / 10min and the density is 952kg / m 3 , I 21 / I 2 Using Prime Polymer's "Hi-Zex 7000F" with a modulus of elasticity of 178 and Mw / Mn of 42, air-cooled inflation molding was carried out under the following conditions using an inflation molding machine to produce a 40μm thick film (unstretched). The elastic modulus and tear strength of the resulting unstretched film were measured. Since this was an unstretched film, the heat shrinkage rate was not measured. The results are shown in Table 1.

[0042] <Film molding conditions> Molding machine: Modern Machinery 65mmφ inflation molding machine Die: 125mmφ (diameter), 4.0mm (lip width) Molding temperature: 190℃ Extrusion rate: 50kg / h Take-off speed: 20.5m / min

[0043] [Comparative Example 2] The polyethylene resin composition has an MFR of 1.1 g / 10 min and a density of 950 kg / m3 , I 21 / I 2 An unstretched film was produced and evaluated in the same manner as in Comparative Example 1, except that "Hi-Zex 3300F" manufactured by Prime Polymer Co., Ltd., which has a molecular weight of 32 and an Mw / Mn ratio of 6, was used. The results are shown in Table 1.

[0044] [Comparative Example 3] As a polyethylene resin composition, the MFR is 0.75 g / 10 min and the density is 926 kg / m 3 , I 21 / I 2 An unstretched film was produced and evaluated in the same manner as in Comparative Example 1, except that "Evolue SP3010" manufactured by Prime Polymer Co., Ltd., which has a molecular weight of 31 and a Mw / Mn of 11, was used. The results are shown in Table 1.

[0045] [Comparative Example 4] The polyethylene resin composition has an MFR of 1.1 g / 10 min and a density of 950 kg / m 3 , I 21 / I 2 A stretched film was obtained and evaluated in the same manner as in Example 1, except that "Hi-Zex 3300F" manufactured by Prime Polymer Co., Ltd., having a molecular weight of 32 and an Mw / Mn ratio of 6 was used. The results are shown in Table 1.

[0046] [Comparative Example 5] As a polyethylene resin composition, the MFR is 0.75 g / 10 min and the density is 926 kg / m 3 , I 21 / I 2 A stretched film was obtained and evaluated in the same manner as in Example 1, except that "Evolue SP3010" manufactured by Prime Polymer Co., Ltd., which has a molecular weight of 31 and a Mw / Mn of 11, was used. The results are shown in Table 1.

[0047] [Table 1]

Claims

1. A uniaxially stretched film having a stretch ratio of 3.1 times or more, which is made of a polyethylene resin composition that satisfies the following requirements (1) to (3): (1) a melt flow rate (190°C, 2.16 kg load) of 0.01 g / 10 min or more and 2.0 g / 10 min or less; (2) a density of 935 kg / m 3 More than 970kg / m 3 (3) the melt index (I 21 : 190°C, 21.6 kg load) and melt index (I 2 : 190°C, 2.16 kg load) 21 / I 2 is 80 or more.

2. 2. The uniaxially stretched film according to claim 1, wherein the polyethylene resin composition has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (molecular weight distribution; Mw / Mn) measured by gel permeation chromatography (GPC) of more than 20.

3. 2. The uniaxially stretched film according to claim 1, having an elastic modulus in the MD direction of more than 1600 MPa.

4. A laminate comprising a layer made of the uniaxially stretched film according to any one of claims 1 to 3.

5. A packaging material comprising a layer of the uniaxially stretched film according to any one of claims 1 to 3.

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