Polyethylene composition and biaxially stretched polyethylene film

Abstract

Provided is a polyethylene composition useful for biaxially stretched polyethylene films having high heat resistance and excellent machine-direction and transverse-direction mechanical strength.　This polyethylene composition (C) comprises: polyethylene (A) which has a weight-average molecular weight (Mw) determined by gel permeation chromatography of 50,000-200,000, the content of components each having a molecular weight of 10,000 or less being 8 mass% or less, and which has a density measured in accordance with JIS K6922-1 (1997) of 945-980 kg / m3; and polyethylene (B) having a density measured in accordance with JIS K6922-1 (1997) of 940-965 kg / m3 and a weight-average molecular weight (Mw) determined by gel permeation chromatography of 220,000-5,000,000.

Description

Polyethylene composition and biaxially oriented polyethylene film

[0001] The present invention relates to a polyethylene composition and a biaxially oriented polyethylene film.

[0002] Polyethylene films are used as packaging materials because they have moderate flexibility, excellent transparency, moisture resistance, chemical resistance, etc., and are inexpensive.

[0003] However, polyethylene film has low rigidity, impact resistance, heat resistance, etc., and there are applications in which it cannot be used alone. To solve these problems, laminate films obtained by laminating polyethylene film with other resin films (e.g., polypropylene film, polyester film, polyamide film) are widely used as packaging materials (see, for example, Patent Document 1).

[0004] Meanwhile, in recent years, social issues such as waste plastics have been attracting attention, and with the growing demand for a recycling-oriented society, there is a demand for improved recyclability of packaging materials. Packaging materials made from a combination of films of different materials, such as those described above, have the problem of being difficult to recycle through material recycling, chemical recycling, and other methods. In response to this issue, packaging materials made from the same resin materials, formed by laminating oriented polyethylene film and unoriented polyethylene film, have been proposed (see, for example, Patent Documents 2 and 3). The oriented polyethylene film is used to complement the mechanical properties of the unoriented polyethylene film and to prevent resin adhesion to the seal bar during heat sealing. However, even such oriented polyethylene film does not have the same mechanical properties as biaxially oriented polyamide film or biaxially oriented polyester film, and shrinkage is particularly severe in the heat-sealed areas, requiring a lower heat-sealing temperature, which may result in insufficient heat-sealing strength. Monoaxially oriented polyethylene film has also been proposed as a polyethylene film with excellent heat resistance (see, for example, Patent Document 4). However, uniaxially stretched films have the problem of being inferior in mechanical properties in the direction perpendicular to the stretching direction and prone to tearing.

[0005] Japanese Patent Publication No. 2005-104525 Japanese Patent Publication No. 2019-171860 Japanese Patent Publication No. 2019-529165 Japanese Patent Publication No. 2022-142174

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a biaxially oriented polyethylene film that has high heat resistance and excellent mechanical strength in both the longitudinal and transverse directions, and a polyethylene composition that is a raw material for the film.

[0007] As a result of extensive research aimed at solving the above problems, the present inventors have found that a specific biaxially oriented polyethylene film exhibits excellent heat resistance and mechanical properties, leading to the completion of the present invention.

[0008] That is, the respective aspects of the present invention are the following [1] to [4]: ​​[1] A polymer having a weight average molecular weight (Mw) of 50,000 to 200,000 as measured by gel permeation chromatography, with the proportion of molecular weights of 10,000 or less being 8% by mass or less, and a density of 945 to 980 kg / m as measured according to JIS K6922-1 (1997). ３ and a density measured according to JIS K6922-1 (1997) of 940 to 965 kg / m ３ and 10 to 70 parts by mass of polyethylene (B) having a weight-average molecular weight (Mw) of 220,000 to 5,000,000 as measured by gel permeation chromatography (the total of (A) and (B) being 100 parts by mass). [2] A biaxially oriented polyethylene film comprising the polyethylene composition according to [1], wherein the endothermic curve measured by a differential scanning calorimeter exhibits at least one peak at 135°C or higher. [3] The biaxially oriented polyethylene film according to [2], having breaking strengths of 200 MPa or higher in both the MD and TD directions. [4] A method for producing a biaxially oriented polyethylene film, comprising stretching a film or sheet comprising the polyethylene composition according to [1] at a stretching temperature of 100 to 135°C to a stretch ratio of 1.5 to 10 in the MD direction and 1.5 to 10 in the TD direction.

[0009] The polyethylene composition of the present invention is useful as a raw material for biaxially oriented polyethylene films, and the resulting biaxially oriented polyethylene films have excellent heat resistance and mechanical properties and are useful as substrates for laminate films for packaging foods, beverages, pharmaceuticals, etc. Furthermore, since the resulting laminate films are composed mostly of polyethylene-based materials, they have excellent recyclability and can reduce the environmental load.

[0010] The polyethylene composition and biaxially oriented polyethylene film, which are one embodiment of the present invention, will be described in detail below.

[0011] The polyethylene composition (C) according to one embodiment of the present invention has a weight average molecular weight (Mw) of 50,000 to 200,000, with the proportion of molecular weights of 10,000 or less being 8% by mass or less, as measured by gel permeation chromatography, and a density of 945 to 980 kg / m, as measured in accordance with JIS K6922-1 (1997). ３ and polyethylene (A) having a density of 940 to 965 kg / m as measured according to JIS K6922-1 (1997). ３ and a weight average molecular weight (Mw) of 220,000 to 5,000,000 as measured by gel permeation chromatography.

[0012] The polyethylene (A) has a weight average molecular weight (Mw) measured by gel permeation chromatography of 50,000 to 200,000, preferably 100,000 to 200,000, and more preferably 100,000 to 150,000. Mw of less than 50,000 is undesirable because the film breaks during stretching. Mw of more than 200,000 is undesirable because the extrusion load during melt extrusion increases.

[0013] The proportion of polyethylene (A) having a molecular weight of 10,000 or less as measured by gel permeation chromatography is 8% by mass or less, preferably 6% by mass or less, and more preferably 4% by mass or less. If this proportion exceeds 8% by mass, the heat resistance of the stretched film deteriorates, and the heat-sealed appearance deteriorates, which is undesirable.

[0014] The polyethylene (A) has a density of 945 to 980 kg / m as measured according to JIS K6922-1 (1997). ３and preferably 945 to 960 kg / m ３ The density is 945 kg / m ３ If the density is less than 980 kg / m, the heat resistance of the stretched film will be deteriorated, which is not preferable. ３ Polyethylene exceeding this limit is difficult to produce industrially.

[0015] Such polyethylene (A) can be obtained by homopolymerizing ethylene or copolymerizing ethylene with a small amount of an α-olefin. For the polymerization, a Ziegler catalyst comprising a solid catalyst component containing magnesium and titanium and an organoaluminum compound, a metallocene catalyst comprising an organic transition metal compound containing a cyclopentadienyl derivative and a compound and / or an organic metal compound that reacts with the organic transition metal compound to form an ionic complex, or a vanadium-based catalyst can be used. Metallocene catalysts and vanadium-based catalysts are preferred because they make it easy to control the proportion of molecular weights of 10,000 or less. For example, polyethylene (A) can be produced by a production method such as a slurry method, a solution method, or a gas-phase method. The method for producing polyethylene (A) is not particularly limited, but a slurry method or a solution method is preferred because it makes it easy to control the proportion of molecular weights of 10,000 or less.

[0016] The polyethylene (B) has a density of 940 to 965 kg / m as measured according to JIS K6922-1 (1997). ３ The density is 940 kg / m ３ If it is less than 965 kg / m, the heat resistance of the oriented polyethylene film for lamination will be deteriorated, which is not preferable. ３ Polyethylene with a density above this is difficult to produce industrially.

[0017] The polyethylene (B) has a weight average molecular weight (Mw) measured by gel permeation chromatography of 220,000 to 5,000,000, preferably 220,000 to 3,000,000, more preferably 220,000 to 700,000, and even more preferably 220,000 to 300,000. Mw less than 220,000 is undesirable because the film breaks during stretching. Mw greater than 5,000,000 is undesirable because dispersibility with polyethylene (A) deteriorates.

[0018] The proportion of polyethylene (B) having a molecular weight of 10,000 or less as measured by gel permeation chromatography is preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 10% by mass or less, and most preferably 7% by mass or less, from the viewpoints of the heat resistance and heat-sealed appearance of the stretched film.

[0019] Such polyethylene (B) can be obtained by homopolymerizing ethylene or copolymerizing ethylene with a small amount of an α-olefin. For the polymerization, a Ziegler catalyst comprising a solid catalyst component containing magnesium and titanium and an organoaluminum compound, a metallocene catalyst comprising an organotransition metal compound containing a cyclopentadienyl derivative and a compound and / or organometallic compound that reacts with the organotransition metal compound to form an ionic complex, a vanadium-based catalyst, or the like can be used.

[0020] In the polyethylene composition (C), the mixing ratio of the polyethylene (A) to the polyethylene (B) is 30 to 90 parts by mass of the polyethylene (A) and 10 to 70 parts by mass of the polyethylene (B), preferably 90 to 50 parts by mass of the polyethylene (A) and 10 to 50 parts by mass of the polyethylene (B), and more preferably 90 to 70 parts by mass of the polyethylene (A) and 10 to 30 parts by mass of the polyethylene (B). Here, the total of (A) and (B) is 100 parts by mass. By including 30 to 90 parts by mass of the polyethylene (A), when a biaxially stretched polyethylene film is formed, film breakage during stretching can be suppressed while maintaining heat resistance.

[0021] The polyethylenes (A) and (B) and the polyethylene composition (C) may contain additives that are typically used in polyolefins, such as antioxidants, lubricants, neutralizing agents, antiblocking agents, surfactants and slip agents, as necessary.

[0022] The biaxially oriented polyethylene film of one embodiment of the present invention comprises the polyethylene composition (C) and exhibits at least one peak in the range of 135°C or higher in an endothermic curve measured by differential scanning calorimetry. This allows the biaxially oriented polyethylene film to exhibit high heat resistance. If the endothermic curve peak of the biaxially oriented polyethylene film is less than 135°C, the heat resistance of the film will be insufficient, and the appearance of the film will be deteriorated due to heat shrinkage caused by heat sealing, which is not preferred.

[0023] The biaxially oriented polyethylene film preferably has a breaking strength of 200 MPa or more in both the MD and TD directions.

[0024] Biaxially stretched films can be obtained by biaxially stretching in the machine direction (MD direction) and transverse direction (TD direction) within the above ranges using various known methods, such as a tubular method or a tenter method. In the case of the tenter method, the method for producing a raw film is not particularly limited, and examples include a method in which a film to be stretched is obtained by extrusion molding such as known inflation molding or T-die casting, and then stretched. Alternatively, a sheet obtained by press molding can be used as the raw film. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. Among these methods, biaxially stretched polyethylene films obtained by the tenter method are preferred.

[0025] The stretching ratio in the MD direction is generally 1.5 to 10 times, preferably 1.5 to 8 times, and the stretching ratio in the TD direction is generally 1.5 to 10 times, preferably 1.5 to 8 times.

[0026] The stretching temperature is 100 to 135°C, preferably 110 to 130°C, from the viewpoint of stretchability and heat resistance.

[0027] After biaxial stretching, the film may be heat set at a temperature in the range of 80 to 140° C. depending on the application.

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Parts and percentages are based on mass unless otherwise specified. Evaluation methods in the examples and comparative examples are as follows.

[0029] <Differential Scanning Calorimetry> Using a differential scanning calorimeter (DSC) (DSC6220 (trade name) manufactured by SII Nanotechnology Inc.), the temperature was raised from 0°C to 230°C at a heating rate of 10°C / min (first scan), and the endothermic peak of the first scan was measured. The sample weight of the biaxially stretched polyethylene film was 3 mg.

[0030] <Melt Mass Flow Rate> The melt mass flow rate was measured using a melt indexer (manufactured by Takara Kogyo Co., Ltd.) in accordance with JIS K6924-1 (under conditions of 190° C. and a load of 2160 g).

[0031] <Density> Measured in accordance with JIS K6922-1 (1997).

[0032] <Molecular Weight> The molecular weight was measured using a GPC apparatus (HLC (registered trademark)-8121GPC / HT (trade name) manufactured by Tosoh Corporation) and a column (TSKgel (registered trademark) GMHhr-H (20) HT (trade name) manufactured by Tosoh Corporation) with the column temperature set to 140°C and 1,2,4-trichlorobenzene as the eluent. The measurement sample was prepared at a concentration of 1.0 mg / ml, and 0.3 ml was injected for measurement. The molecular weight calibration curve was calibrated using a polystyrene sample of known molecular weight (manufactured by Tosoh Corporation; the molecular weight was expressed as a PE-converted molecular weight using a Q factor). From the chromatogram obtained as a result of the measurement, the weight-average molecular weight Mw and the proportion of components with a molecular weight of 10,000 or less were calculated.

[0033] <Melt extrudability> Melt kneading was carried out at 200°C and 60 rpm using a single screw extruder (manufactured by Toyo Seiki Seisakusho, (trade name) Labo Plastomill (registered trademark) single screw extruder 2D25S). When the extrusion load became high and melt kneading was not possible under the above conditions, the melt extrudability was judged to be poor and marked with x, and when melt kneading was possible, marked with o.

[0034] <Stretchability> The appearance of the biaxially stretched films obtained in the examples was evaluated, and poor stretchability and the film having broken parts were rated as x, and excellent stretchability and the film having no broken parts were rated as o.

[0035] <Breaking Strength> The breaking strength of a dumbbell piece (ATMS-1822) was measured at 25° C. and 300 mm / min using an RTE-1210 (trade name, manufactured by Orientec Co., Ltd.).

[0036] <Heat-sealed appearance> The biaxially stretched films obtained in the examples were heat-sealed using a heat-sealing tester TP-701B (manufactured by Tester Sangyo Co., Ltd.) at a set temperature of 130°C, double-sided heating, an air pressure of 0.2 MPa, and a sealing time of 1 second, followed by air cooling, and the appearance of the biaxially stretched polyethylene film was evaluated. A rating of × was given when the laminate film had significant shrinkage and poor appearance, and a rating of ◯ was given when the shrinkage was small and the appearance was good.

[0037] <Heat shrinkage rate> The biaxially stretched films obtained in the examples were heat-sealed using a heat seal tester TP-701B (manufactured by Tester Sangyo Co., Ltd.) at a set temperature of 130°C, double-sided heating, an air pressure of 0.2 MPa, and a sealing time of 1 second, followed by air cooling. The heat shrinkage rate was calculated from the film length before heat sealing and the length after heat sealing according to the following formula.

[0038] Heat shrinkage rate = (film length before heat sealing - film length after heat sealing) / (film length before heat sealing) Example 1 Preparation of organically modified clay In a 1-liter flask were placed 300 ml of industrial alcohol (manufactured by Japan Alcohol Sales Co., Ltd., (trade name) Ekinen (registered trademark) F-3) and 300 ml of distilled water, and 15.0 g of concentrated hydrochloric acid and dioleylmethylamine ((C １８ H ３５ ) ２ (CH ３ ) N, 63.7 g (120 mmol) of (trade name) Lipomin (registered trademark) MO (manufactured by Lion Specialty Chemicals Co., Ltd.) was added, heated to 45 ° C, and 100 g of synthetic hectorite (trade name Laponite RD, manufactured by BYK Corporation) was dispersed therein, and the mixture was then heated to 60 ° C and stirred for 1 hour while maintaining that temperature. The slurry was filtered, washed twice with 600 ml of water at 60 ° C, and dried in a dryer at 85 ° C for 12 hours to obtain 130 g of organically modified clay. This organically modified clay was then jet milled to a median diameter of 15 μm.

[0039] [Preparation of polymerization catalyst] A 300 mL flask equipped with a thermometer and a reflux condenser was purged with nitrogen, and then 25.0 g of the organically modified clay obtained in [Preparation of organically modified clay] and 108 mL of hexane were added, followed by the addition of 0.392 g (1 mmol) of bis(indenyl)zirconium dichloride and 142 mL of 20% triisobutylaluminum, followed by stirring for 3 hours at 60° C. After cooling to room temperature, the supernatant was removed and washed twice with 220 mL of hexane, and then 220 mL of hexane was added to obtain a catalyst suspension (solid mass content: 12.0 mass%).

[0040] [Production of polyethylene (A1) powder] 1.2 L of hexane, 1.0 mL of 20% triisobutylaluminum, and 200 mg (corresponding to 24 mg of solid content) of the catalyst suspension obtained in [Preparation of polymerization catalyst] were added to a 2 L autoclave, and after heating to 85° C., an ethylene / hydrogen mixed gas was continuously supplied so that the partial pressure became 0.90 MPa (hydrogen concentration in the ethylene / hydrogen mixed gas: 450 ppm). After 90 minutes, the pressure was released, and the slurry was filtered and dried to obtain polyethylene (A1) powder.

[0041] The obtained polyethylene (A1) powder had a weight average molecular weight of 111,000, a proportion of components with a molecular weight of 10,000 or less of 3.4% by mass, and a density of 950 kg / m ３ It was.

[0042] The obtained polyethylene (A1) powder was melt-kneaded using a twin-screw extruder (manufactured by Technovel, trade name ULTnano25TW) having a screw diameter of 25 mm under conditions of a resin temperature of 160°C and a screw rotation speed of 300 rpm, to obtain polyethylene (A1) pellets.

[0043] As the polyethylene (B), a commercially available polyethylene resin (B1) (Nipolon Hard (registered trademark) 8D01A, manufactured by Tosoh Corporation) was used.

[0044] [Preparation of Polyethylene Composition (C1)] 280 g of polyethylene (A1) pellets and 120 g of polyethylene (B1) were dry-blended and then melt-kneaded at 200°C using a single-screw extruder (manufactured by Toyo Seiki Seisakusho, Ltd., (trade name) Labo Plastomill (registered trademark) single-screw extruder 2D25S) to obtain polyethylene composition (C1). The MFR of composition (C1) was 0.44 g / 10 min. At this time, the screw rotation speed was set to 60 rpm, and melt extrudability was evaluated. The results are shown in Table 1.

[0045] Using the polyethylene composition (C1), a compression molding machine AWFA.50 (manufactured by Shinto Metal Industry Co., Ltd.) and a 150 mm × 150 mm × 0.1 mm mold was used to perform compression molding under the conditions of a heating temperature of 230°C, a cooling temperature of 25°C, a primary pressure of 0.1 MPa × 4 minutes, a secondary pressure of 20 MPa × 4 minutes, and a cooling pressure of 20 MPa × 4 minutes to produce a sheet having a thickness of 0.1 mm.

[0046] The prepared sheet was simultaneously biaxially stretched using a biaxial stretching device (manufactured by Toyo Seiki Seisakusho, Ltd., (trade name) EX10-B) at a stretching temperature of 120°C, an MD stretch ratio of 2, a TD stretch ratio of 2, and a stretching speed of 500 mm / min, and air-cooled after stretching to obtain a biaxially stretched film. Differential scanning calorimetry was performed using the obtained biaxially stretched film. Furthermore, the heat seal appearance, heat shrinkage rate, and breaking strength were evaluated. The evaluation results are shown in Table 1.

[0047] [Example 2] A biaxially stretched film was obtained in the same manner as in Example 1, except that a commercially available polyethylene resin (B2) (Nipolon Hard (registered trademark) 8900, manufactured by Tosoh Corporation) was used as the polyethylene (B). The evaluation results are shown in Table 1.

[0048] [Example 3] The hydrogen concentration in the production of polyethylene powder was adjusted to have a weight average molecular weight of 131,000, a proportion of components with a molecular weight of 10,000 or less of 1.5%, and a density of 951 kg / m ３ A biaxially stretched film was obtained in the same manner as in Example 2, except that polyethylene powder (A2) having the formula (I) was used as polyethylene (A). The evaluation results are shown in Table 1.

[0049] [Example 4] A biaxially stretched film was obtained in the same manner as in Example 1, except that a commercially available polyethylene resin (B3) (Nipolon Hard (registered trademark) 7300A, manufactured by Tosoh Corporation) was used as the polyethylene (B). The evaluation results are shown in Table 1.

[0050] [Example 5] Polyethylene (B) was produced by two-stage polymerization in which the polymerization of component (X1) was followed by the polymerization of component (Y1) as follows: a polyethylene having a weight-average molecular weight of 270,000, a proportion of components with a molecular weight of 10,000 or less of 6%, and a density of 946 kg / m ３ A biaxially stretched film was obtained in the same manner as in Example 1, except that polyethylene (B4) of 100% was used. The evaluation results are shown in Table 1.

[0051] [Production of Polyethylene (B4)] Production of Component (X1) To a 10-liter autoclave were added 6 liters of hexane, 5.5 ml of a 20 wt % hexane solution of triisobutylaluminum, and 2.50 g (corresponding to a solid content of 310 mg) of the suspension of the production catalyst obtained in Preparation Example 1, and the temperature was raised to 60°C. Ethylene was then continuously supplied so that the ethylene partial pressure could be maintained at 0.80 MPa, and slurry polymerization was carried out for 2 hours.

[0052] Production of Component (Y1) and Ethylene-Based Resin (B4) After polymerizing the component (X1), ethylene was continuously supplied so as to maintain the ethylene partial pressure at 0.50 MPa at 60°C, and hydrogen was further added intermittently so that the hydrogen concentration in the gas phase of the autoclave became 4,500 ppm. This resulted in slurry polymerization for 8 hours to polymerize the component (Y1), thereby producing an ethylene-based resin (B4) powder.

[0053] The obtained polyethylene (B4) powder was melt-kneaded using a twin-screw extruder (manufactured by Technovel, trade name ULTnano25TW) having a screw diameter of 25 mm at a resin temperature of 160°C and a screw rotation speed of 300 rpm to obtain polyethylene (B4) pellets.

[0054] [Example 6] Polyethylene (B) was produced by two-stage polymerization in which the polymerization of component (X2) was followed by the polymerization of component (Y2) as follows: a polyethylene having a weight-average molecular weight of 680,000, a proportion of components with a molecular weight of 10,000 or less of 7 mass%, and a density of 945 kg / m ３ A biaxially stretched film was obtained in the same manner as in Example 1, except that polyethylene (B5) of 100% was used. The evaluation results are shown in Table 1.

[0055] [Production of Polyethylene (B5)] Production of Component (X2) A 10-liter autoclave was charged with 6 liters of hexane, 5.5 ml of a 20 wt % hexane solution of triisobutylaluminum, and 2.50 g (corresponding to a solid content of 310 mg) of the suspension of the production catalyst obtained in Preparation Example 1, and the temperature was raised to 60°C. Ethylene was then continuously supplied so that the ethylene partial pressure could be maintained at 0.80 MPa, and slurry polymerization was carried out for 1 hour.

[0056] Production of Component (Y2) and Ethylene-Based Resin (B5) After polymerizing the component (X2), ethylene was continuously supplied so as to maintain the ethylene partial pressure at 0.87 MPa at 60°C, and hydrogen was further added intermittently so that the hydrogen concentration in the gas phase of the autoclave became 4,500 ppm. This slurry polymerization was carried out for 4 hours to polymerize the component (Y2), thereby producing an ethylene-based resin (B5).

[0057] Polyethylene (B5) pellets were obtained in the same manner as in Example 5, except that polyethylene powder (B5) was used instead of polyethylene powder (B4). [Example 7] A biaxially stretched film was obtained in the same manner as in Example 2, except that the polyethylene (A1) pellets were 90% by mass and the polyethylene (B2) was 10% by mass. The evaluation results are shown in Table 1. [Example 8] A biaxially stretched film was obtained in the same manner as in Example 2, except that the polyethylene (A1) pellets were 50% by mass and the polyethylene (B2) was 50% by mass. The evaluation results are shown in Table 1.

[0058] A biaxially stretched polyethylene film was obtained in the same manner as in Example 1, except that polyethylene (A1) pellets were used instead of the polyethylene composition (C1). The evaluation results are shown in Table 1, but the stretched polyethylene film broke during stretching and could not be produced.

[0059] Comparative Example 2 A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that polyethylene (B1) was used instead of polyethylene composition (C1). The evaluation results are shown in Table 1, and the melt extrudability was poor.

[0060] Comparative Example 3 A biaxially oriented polyethylene film was obtained in the same manner as in Example 1, except that a commercially available polyethylene resin (A3) (Nipolon Hard (registered trademark) 5700, manufactured by Tosoh Corporation) was used as the polyethylene (A). The evaluation results are shown in Table 1, and the heat resistance of the film was poor.

[0061] Comparative Example 4 A biaxially stretched polyethylene film was obtained in the same manner as in Example 1, except that a commercially available polyethylene resin (B6) (Nipolonhard (registered trademark) 6000, manufactured by Tosoh Corporation) was used as the polyethylene (B). The evaluation results are shown in Table 1, but the stretched polyethylene film broke during stretching and could not be formed into a film.

[0062]

[0063] While the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0064] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2024-024088 filed on February 20, 2024 are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. The weight average molecular weight (Mw) measured by gel permeation chromatography is 50,000 to 200,000, and the proportion of molecular weights of 10,000 or less is 8% by mass or less, and the density measured according to JIS K6922-1 (1997) is 945 to 980 kg / m ３ and a density measured according to JIS K6922-1 (1997) of 940 to 965 kg / m ３ and 10 to 70 parts by mass (the total of (A) and (B) is 100 parts by mass) of polyethylene (B) having a weight average molecular weight (Mw) of 220,000 to 5,000,000 as measured by gel permeation chromatography.

2. The polyethylene composition (C) according to claim 1, wherein the proportion of polyethylene (B) having a molecular weight of 10,000 or less as measured by gel permeation chromatography is 20% by mass or less.

3. A biaxially oriented polyethylene film comprising the polyethylene composition according to claim 1 or 2, which has at least one peak at 135°C or higher in an endothermic curve measured with a differential scanning calorimeter.

4. The biaxially oriented polyethylene film according to claim 3, having a breaking strength of 200 MPa or more in both the MD and TD directions.

5. A method for producing a biaxially oriented polyethylene film, comprising stretching a film or sheet made from the polyethylene composition according to claim 1 or 2 at a stretching temperature of 100 to 135°C to a stretching ratio of 1.5 to 10 times in the MD direction and 1.5 to 10 times in the TD direction.

Images