Polyethylene resin and stretched polyethylene film

Abstract

Provided are a stretched polyethylene film having excellent heat resistance and a polyethylene resin used as a raw material therefor and having excellent melt extrudability.　A polyethylene resin (A) having a proportion of molecular weights, measured by gel permeation chromatography, of 3000 or less of 2-15 mass%, a proportion of molecular weights of 3000-30,000 of 25 mass% or less, a density of 940-970 kg / m3, and a melt mass flow rate (MFR) of 0.1-5.0 g / 10 min.

Description

Polyethylene resin and stretched polyethylene film

[0001] This invention relates to polyethylene resin and stretched polyethylene film.

[0002] In recent years, social issues such as plastic waste have attracted attention, and along with the growing demand for the creation of a circular economy, there is a need to improve the recyclability of packaging materials. Conventional packaging materials that combine dissimilar material films have the problem of being difficult to recycle through material recycling, chemical recycling, etc. In response to this, a packaging material formed by laminating stretched polyethylene film and unstretched polyethylene film has been proposed as a packaging material composed of the same type of resin material (for example, Patent Document 1).

[0003] Stretched polyethylene film is used to suppress resin adhesion to sealing bars during heat sealing. However, stretched polyethylene film has inferior heat resistance compared to conventionally used stretched polyamide film and stretched polyester film, which can cause shrinkage due to heating during heat sealing, potentially degrading the appearance of the packaging. Patent document 2 proposes a polyethylene film with excellent heat resistance. However, the proposed polyethylene has few low molecular weight components, and there is a need to improve the productivity of the film, which is reduced due to limitations in extrusion amount caused by the high resin pressure during molding.

[0004] Japanese Patent Publication No. 2019-171860 Japanese Patent Publication No. 2022-142174

[0005] The present invention was made to solve the above-mentioned problems, and its objective is to provide a stretchable polyethylene film with excellent heat resistance and a polyethylene composition with excellent melt extrusion properties that serves as a raw material for the film.

[0006] As a result of diligent research to solve the aforementioned problems, the present inventors have found that a specific stretched polyethylene film exhibits excellent heat resistance and melt extrusion properties, and have completed the present invention. Specifically, the embodiments of the present invention are as follows [1] to [7].

[0007] [1] The proportion of molecules with a molecular weight of 3,000 or less measured by gel permeation chromatography is 2 to 15% by mass, the proportion of molecules with a molecular weight of 3,000 or more but 30,000 or less is 25% by mass or less, and the density measured according to JIS K6922-1 (1997) is 940 to 970 kg / m³. ３ [1] A polyethylene resin (A) having a melt mass flow rate (MFR) of 0.1 to 5.0 g / 10 min measured according to JIS K6924-1 (under the conditions of 190°C and 2160 g load). [2] A polyethylene composition (A) according to [1], comprising 3 to 10 parts by mass of an ethylene-α-olefin copolymer (D) having a weight-average molecular weight (Mw) of 100,000 to 200,000 and a molecular weight of 100,000 or more after molecular weight fractionation, with 0.15 or more long-chain branches per 1,000 carbon atoms in the main chain in the fraction, per 100 parts by mass of polyethylene resin (A). [3] A polyethylene resin (A) according to [1] or [2], comprising 5 to 100 ppm or less of organic peroxides and their decomposition products. [4] The weight-average molecular weight (Mw) measured by gel permeation chromatography is 70,000 to 250,000, the proportion of molecules with a molecular weight of 3,000 to 30,000 measured by gel permeation chromatography is 25% by mass or less, and the density measured according to JIS K6922-1 (1997) is 940 to 970 kg / m³. ３ A polyethylene resin (A) according to any one of [1] to [3], comprising polyethylene (B) and polyethylene (C) having a weight-average molecular weight (Mw) of 1,000 to 20,000 as measured by gel permeation chromatography. [5] A polyethylene resin (A) according to [4], wherein polyethylene (B) is 85 to 97% by mass and polyethylene (C) is 3 to 15% by mass. [6] A stretched polyethylene film made of the polyethylene resin (A) according to any one of [1] to [5], wherein at least one peak in the endothermic curve measured by differential scanning calorimetry is 135°C or higher. [7] A laminate film having an ethylene-based polymer film on at least one side of the stretched polyethylene film according to [6].

[0008] The polyethylene resin of the present invention is useful as a raw material for stretched polyethylene film, exhibits excellent melt extrusion properties during molding, and the resulting stretched polyethylene film has excellent heat resistance and is useful as a base material for laminate film.

[0009] Polyethylene resin (A) according to one aspect of the present invention has a molecular weight of 3,000 or less measured by gel permeation chromatography of 2 to 15% by mass, a molecular weight of 3,000 or more measured by 30,000 or less measured by 25% by mass or less, and a density of 940 to 970 kg / m³ measured according to JIS K6922-1 (1997). ３ The MFR is 0.1 to 5.0 g / 10 min. The polyethylene resin (A) has a molecular weight of 3,000 or less measured by gel permeation chromatography of 2 to 15% by mass, preferably 4 to 10% by mass, and more preferably 6 to 10% by mass. When it is 2% by mass or more, melt extrudeability is good, and when it is 15% by mass or less, the heat resistance of the stretched polyethylene film is good. The polyethylene resin (A) has a molecular weight of 3,000 or more and 30,000 or less measured by gel permeation chromatography of 25% by mass or less, preferably 23% by mass or less, more preferably 21% by mass or less, and most preferably 18% by mass or less. When it is 25% by mass or less, the heat resistance of the stretched polyethylene film is good.

[0010] Polyethylene composition (A) has a density of 940–970 kg / m³ as measured according to JIS K6922-1 (1997). ３ The coefficient of gravity is preferably 945 to 960 kg / m³. ３ It is 940 kg / m ３ Based on the above, the heat resistance of the stretched polyethylene film is good, at 970 kg / m². ３The following polyethylenes are easy to produce industrially. Polyethylene composition (A) has an MFR of 0.1 to 5.0 g / 10 min, preferably 0.4 to 3.0 g / 10 min, and more preferably 0.4 to 2.0 g / 10 min, measured under JIS K6924-1 conditions (190°C, 2160 g load). At 0.3 g / 10 min or higher, melt extrudeability is good, and at 5.0 g / 10 min or lower, film stretchability is good. Polyethylene resin (A) is obtained by homopolymerizing ethylene or copolymerizing ethylene with a small amount of α-olefin. For polymerization, a Ziegler catalyst consisting of a solid catalyst component containing magnesium and titanium and an organoaluminum compound, a metallocene catalyst consisting of an organotransition metal compound containing a cyclopentadienyl derivative and a compound that reacts with it to form an ionic complex and / or an organometallic compound, a vanadium-based catalyst, etc. are generally used, and metallocene catalysts and vanadium-based catalysts are preferred because it is easy to control the proportion of molecules with a molecular weight of 30,000 or less.

[0011] The metallocene catalyst preferably comprises one metallocene complex, an activating co-catalyst, and optionally an organoaluminum compound as constituent components, and is copolymerized with ethylene and an olefin having 3 to 6 carbon atoms. The metallocene complex of the metallocene catalyst is preferably a non-crosslinked bis(indenyl)zirconium complex, a non-crosslinked bis(cyclopentadienyl)zirconium complex, a crosslinked bis(cyclopentadienyl)zirconium complex, a crosslinked bis(indenyl)zirconium complex, a crosslinked (cyclopentadienyl)(indenyl)zirconium complex, a crosslinked (cyclopentadienyl)(fluorenyl)zirconium complex, or a crosslinked (indenyl)(fluorenyl)zirconium complex.

[0012] Specific examples of metallocene complexes include, for example, bis(indenyl)zirconium dichloride, dimethylsilanediylbis(cyclopentadienyl)zirconium dichloride, dimethylsilanediyl(cyclopentadienyl)(indenyl)zirconium dichloride, dimethylsilanediyl(cyclopentadienyl)(2-methylindenyl)zirconium dichloride, dimethylsilanediyl(cyclopentadienyl)(4,7-dimethylindenyl)zirconium dichloride, dimethylsilanediyl(cyclopentadienyl)(2,4,7-trimethylindenyl)zirconium dichloride, and diphenylmethylene(1-cyclopentadienyl). Examples of dichlorides such as (9-fluorenyl)zirconium dichloride, diphenylmethylene (1-cyclopentadienyl)(2,7-di-t-butyl-9-fluorenyl)zirconium dichloride, and isopropylidene (1-cyclopentadienyl)(2,7-di-t-butyl-9-fluorenylzirconium dichloride, as well as dimethyl, diethyl, dihydro, diphenyl, and dibenzyl derivatives of the above transition metal compounds, can be cited. Compounds in which the zirconium atom of the above transition metal compounds is substituted with a titanium atom or a hafnium atom can also be cited, but are not limited to these. One or more of these may be used.

[0013] The activating co-catalyst used as a component of the metallocene catalyst is a compound that plays a role in converting the metallocene complex, or the reaction product of the metallocene complex and an organoaluminum compound, into an active species capable of polymerizing olefins. Preferably, it is a compound that generates a cationic compound from the metallocene complex, and the generated cationic compound acts as a polymerization active species capable of polymerizing olefins. The activating co-catalyst is a compound that, after forming a polymerization active species, weakly coordinates to or interacts with the generated cationic compound, but does not directly react with the active species.

[0014] Specific examples of activation co-catalysts include alkylaluminoxanes such as methylaluminoxane, silica gel-supported alkylaluminoxanes, tris(fluorinated aryl)borons such as tris(pentafluorophenyl)boron, tetrakis(fluorinated aryl)boron salts such as N,N-dimethylammonium-tetrakis(pentafluorophenyl)boron, boron compounds, silica gel supports thereof, clay minerals, and clay minerals treated with organic compounds. However, it is preferable to use clay minerals treated with organic compounds among these activation co-catalysts because it is easier to control the proportion of molecules with a molecular weight of 3,000 or less. When using clay minerals treated with organic compounds as activation co-catalysts, it is preferable to use clay minerals belonging to the smectite group, with specific examples including montmorillonite, byderite, saponite, and hectorite. It is also possible to use a mixture of multiple of these clay minerals.

[0015] Organic compound treatment refers to the introduction of organic ions between clay mineral layers to form an ion complex. Examples of organic compounds used in organic compound treatment include alkylammonium salts such as N,N-dimethyl-n-octadecylamine hydrochloride, N,N-dimethyl-n-eicosylamine hydrochloride, N,N-dimethyl-n-docosylamine hydrochloride, N,N-dimethyloleylamine hydrochloride, N,N-dimethylbehenylamine hydrochloride, N-methyl-bis(n-octadecyl)amine hydrochloride, N-methyl-bis(n-eicosyl)amine hydrochloride, N-methyl-dioleylamine hydrochloride, N-methyl-dibehenylamine hydrochloride, and N,N-dimethylaniline hydrochloride. There are no particular restrictions on the method of preparing the metallocene catalyst, such as a method of reacting a metallocene complex with an activation co-catalyst. Furthermore, during the preparation of the metallocene catalyst, alkylaluminum such as triethylaluminum or triisobutylaluminum may be used as needed to activate the metallocene complex or remove impurities from the solvent.

[0016] When producing the ethylene polymer (A), the polymerization temperature is preferably 20 to 120°C, and more preferably in the range of 60 to 120°C. The polymerization time is preferably in the range of 10 seconds to 20 hours, and the polymerization pressure is preferably in the range of atmospheric pressure to 300 MPa. The polymerizable monomers are ethylene and α-olefins having 3 to 6 carbon atoms, and the supply ratio of ethylene to α-olefins having 3 to 6 carbon atoms is preferably 0 to 0.2, more preferably 0 to 0.15 (molar ratio). It is also possible to adjust the molecular weight using hydrogen during polymerization. The amount of hydrogen used in this case can be determined by the polymerization method, which can be carried out by slurry method, solution method, gas phase method, etc. Furthermore, the method for producing polyethylene is not particularly limited, but the slurry method or solution method is preferred because it is easier to control the proportion of molecular weights between 3,000 and 30,000.

[0017] Polymerization can be carried out by batch, semi-continuous, or continuous methods, and it is particularly preferable to carry out the polymerization in two or more stages by changing the polymerization conditions in order to control the amount of each molecular weight component. When polyethylene resin (A) is produced by multi-stage polymerization of two or more stages, polymers with different molecular weights are produced in each stage, but the order is arbitrary. Furthermore, in the present invention, there are no particular restrictions on the molecular weight of the polymer produced in each stage as long as the conditions for obtaining polyethylene resin (A) are met, but for example, in the case of three-stage polymerization in which molecular weight components with a molecular weight of 3,000 or less are polymerized in the first polymerizer, molecular weight components with a molecular weight of 3,000 or more and 30,000 or more are polymerized in the second polymerizer, and molecular weight components with a molecular weight of 30,000 or more are polymerized in the third polymerizer, the molecular weight of the polymer polymerized in the first polymerizer is preferably 500 to 3,000, the polymerization temperature is preferably 70°C to 80°C, and the hydrogen / ethylene (molar ratio) is preferably 0.04 to 0.1 (hydrogen concentration: 4% to 10%), more preferably 0.04 to 0.05 (hydrogen concentration: 4% to 5%).

[0018] The molecular weight of the polymer polymerized in the second polymerizer is preferably 4,000 to 10,000, the polymerization temperature is preferably 70°C to 75°C, and the hydrogen / ethylene (molar ratio) is 0.005 to 0.01 (hydrogen concentration: 5,000 ppm to 10,000 ppm), preferably 0.0001 to 0.0005 (hydrogen concentration: 100 ppm to 500 ppm). The molecular weight of the polymer polymerized in the third polymerizer is preferably 70,000 to 150,000, the polymerization temperature is preferably 80°C to 90°C, and the hydrogen / ethylene (molar ratio) is 0.0001 to 0.002 (hydrogen concentration: 100 ppm to 2,000 ppm), preferably 0.0001 to 0.0005 (hydrogen concentration: 100 ppm to 500 ppm).

[0019] The polyethylene resin (A) may be a single polyethylene or a composition comprising two or more types of polyethylene. The polyethylene resin (A) has a weight average molecular weight (Mw) measured by gel permeation chromatography of 70,000 to 250,000, a proportion of molecular weight of 3,000 to 30,000 measured by gel permeation chromatography of 25% by mass or less, and a density measured in accordance with JIS K6922-1 (1997) of 940 to 970 kg / m ３ and may comprise polyethylene (B) having the above-described characteristics and polyethylene (C) having a weight average molecular weight (Mw) measured by gel permeation chromatography of 1,000 to 20,000.

[0020] Polyethylene (B) has a weight average molecular weight (Mw) measured by gel permeation chromatography of 70,000 to 250,000, preferably 100,000 to 200,000, more preferably 100,000 to 150,000. When Mw is 70,000 or more, the stretchability of the film is good, and when Mw is 250,000 or less, the melt extrudability is excellent. In polyethylene (B), the proportion of components with a molecular weight of 3,000 to 30,000 measured by gel permeation chromatography is 25% by mass or less, preferably 17% by mass or less, more preferably 14% by mass or less. When the proportion is 25% by mass or less, the heat resistance of the stretched polyethylene film becomes favorable. Polyethylene (B) has a density measured in accordance with JIS K6922-1 (1997) of 940 to 970 kg / m ３ , preferably 945 to 960 kg / m ３It is 940 kg / m ３ Based on the above, the heat resistance of the stretched polyethylene film is good, at 970 kg / m². ３ The following polyethylenes are easy to produce industrially.

[0021] Polyethylene (B) is obtained as a homopolymer of ethylene, or by copolymerizing ethylene with a small amount of α-olefin. For polymerization, Ziegler catalysts consisting of a solid catalyst component containing magnesium and titanium and an organoaluminum compound, metallocene catalysts consisting of an organotransition metal compound containing a cyclopentadienyl derivative and a compound that reacts with it to form an ionic complex and / or an organometallic compound, vanadium-based catalysts, etc., can be used, and metallocene catalysts and vanadium-based catalysts are preferred because it is easy to control the proportion of molecular weights of 30,000 or less. For example, it can be produced by manufacturing methods such as slurry methods, solution methods, and gas phase methods. Furthermore, the method for producing polyethylene is not particularly limited, but slurry methods or solution methods are preferred because it is easy to control the proportion of molecular weights of 3,000 to 30,000 or less. Polyethylene (C) has a weight-average molecular weight (Mw) of 1,000 to 20,000, preferably 1,000 to 10,000, as measured by gel permeation chromatography. When it is 1,000 or more, smoke generation during molding is suppressed, and when it is 20,000 or less, it has excellent melt extrudeability.

[0022] It is preferable that polyethylene (C) shows at least one peak in the range of 115°C or higher in the endothermic curve measured by differential scanning calorimetry. If at least one peak is shown, the stretched film has excellent heat resistance. From the viewpoint of heat resistance and melt extrusion properties of the stretched film, the ratio of polyethylene (B) to polyethylene (C) in polyethylene resin (A) is preferably 85 to 97% by mass of (B) and 3 to 15% by mass of (C), more preferably 85 to 95% by mass of (B) and 5 to 15% by mass of (C), and most preferably 90 to 95% by mass of (B) and 5 to 10% by mass of (C). The total of (B) and (C) is 100% by mass.

[0023] A polyethylene resin composition according to one aspect of the present invention can be obtained by conventionally known methods, such as mixing with a Henschel mixer, V-blender, ribbon blender, tumbler blender, etc., or by further melt-kneading a mixture obtained by such methods with a single-screw extruder, twin-screw extruder, kneader, Banbury mixer, etc., and then granulating it. The polyethylene resin (A) preferably contains 5 to 100 ppm of organic peroxides and their decomposition products. At 5 ppm or more, the heat resistance of the stretched polyethylene film is further improved, and at 100 ppm or less, the appearance of the stretched polyethylene film is good.

[0024] Examples of organic peroxides include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyn-3, α,α'-bis(t-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-hexylperoxybenzoate, t-butylperoxy-m-toluylbenzoate, and t-butylperoxy. Examples include peroxyesters such as α,α'-bis(t-butylperoxy)isophthalate and bis(t-butylperoxy)isophthalate, and peroxyketals such as 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, and n-butyl-4,4-bis(t-butylperoxy)valerate. Among these, dialkylperoxides are particularly preferred, especially α,α'-bis(t-butylperoxy)diisopropylbenzene and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3. Organic peroxides may decompose in the composition and exist as decomposition products.

[0025] The polyethylene resin (A) may optionally have added thereto additives normally used for polyolefins, such as antioxidants, lubricants, neutralizers, anti-blocking agents, surfactants, slip agents and nucleating agents. The polyethylene resin (A) may also contain 3 to 10 parts by mass of an ethylene / α-olefin copolymer (D) per 100 parts by mass of the total polyethylene resin (A), wherein the ethylene / α-olefin copolymer (D) has a weight average molecular weight (Mw) of 100,000 to 200,000, and has 0.15 or more long-chain branches per 1000 main chain carbon atoms in a fraction having a molecular weight of 100,000 or more after molecular weight fractionation. Addition of the ethylene / α-olefin copolymer (D) in this proportion is preferable because it improves the transparency of the stretched polyethylene film without impairing the heat resistance thereof.

[0026] The above ethylene / α-olefin copolymer (D) is produced using a metallocene catalyst. The metallocene catalyst used comprises a metallocene complex, an activating co-catalyst, and optionally an organoaluminum compound as constituent components, and it is preferable that copolymerization of the macromonomer, ethylene and an olefin having 3 to 6 carbon atoms is performed simultaneously with the synthesis of the macromonomer. A macromonomer is an olefin polymer having a vinyl group at the terminal, and is an ethylene copolymer having a vinyl group at the terminal obtained by copolymerizing ethylene and an olefin having 3 to 6 carbon atoms.

[0027] An oriented polyethylene film according to one aspect of the present invention is made of polyethylene resin (A) and exhibits at least one peak in the range of 135°C or higher in the endothermic curve measured by differential scanning calorimetry. This results in good heat resistance of the oriented polyethylene film of the present invention. The thickness of the oriented polyethylene film is preferably 10 to 200 μm, more preferably 12 to 100 μm, and even more preferably 14 to 50 μm. Within this range, an oriented polyethylene film with desirable mechanical strength can be obtained. The oriented polyethylene film can be a multilayer oriented polyethylene film including at least one layer made of polyethylene composition (C). For example, it can be a three-layer oriented film consisting of a layer containing polyethylene composition (C), a medium-density polyethylene layer, and a high-density polyethylene layer from the outside in. By using such a configuration, the stretchability of the film can be improved. Furthermore, the strength and heat resistance of the oriented polyethylene film can be improved.

[0028] The method for manufacturing the stretched film for lamination described above is not particularly limited, and examples include obtaining a stretchable film by known extrusion molding methods such as inflation molding or T-die casting, and then stretching it by the tenter method or roll rolling molding. The stretching temperature by the tenter method or roll rolling molding is preferably 110 to 140°C. At temperatures above 110°C, the tensile stress of the stretched polyethylene film is low and stretching is easy, and at temperatures below 140°C, the appearance of the stretched polyethylene film is good.

[0029] Roll rolling molding refers to a molding method in which a polyethylene sheet discharged from a T-die or the like between two or more rolls is rolled to mold a film having a predetermined thickness. As the roll rolling molding, a polishing roll method used in T-die extrusion molding and calender molding are suitably used. Examples of calender molding equipment include two-in-line calenders, three-in-line calenders, four-in-line calenders, S-type calenders, inverted L-type calenders, Z-type calenders, and oblique Z-type calenders. The number of stretching operations may be one or multiple; however, setting the number of stretching operations to multiple is preferable because it improves the strength and heat resistance of the stretched polyethylene film. A biaxially stretched film can be produced by further stretching the stretched polyethylene film in the transverse direction. As a transverse stretching method, the tenter method is preferable. After transverse stretching, heat setting may be performed in a temperature range of 80 to 140°C depending on the application.

[0030] The above stretched polyethylene film may be subjected to any appropriate surface treatment in order to improve the adhesiveness of the laminated film. Examples of the surface treatment include corona treatment, flame treatment, plasma treatment, and the like. Furthermore, the stretched polyethylene film may be subjected to vapor deposition treatment of aluminum, alumina, silicon dioxide or the like, and may be coated with a gas barrier resin such as polyvinyl alcohol or polyvinylidene chloride, or a material in which a layered filler is dispersed in a gas barrier resin.

[0031] A laminate film according to one aspect of the present invention has an ethylene-based polymer film on at least one side of a stretched polyethylene film. The thickness of the ethylene-based polymer film is preferably 5 to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 to 120 μm. Within this range, a laminate film with excellent heat-sealability can be obtained. The ethylene-based polymer may be a homopolymer of ethylene, or a copolymer of ethylene and monomers copolymerizable with ethylene. Examples of ethylene-based polymers include high-density polyethylene, ethylene-α-olefin copolymer, high-pressure low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-unsaturated carboxylic acid copolymer, ethylene-unsaturated carboxylic acid ester copolymer, ethylene-carbon monoxide copolymer, and ethylene-styrene copolymer. Among these, high-pressure low-density polyethylene, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid ester copolymer are preferred because they provide excellent heat-sealability for the laminate film.

[0032] The method for producing high-density polyethylene and ethylene-α-olefin copolymers is not particularly limited, and examples include high, medium, and low-pressure ionic polymerization using Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. Such resins can be conveniently selected from commercially available products. For example, they are commercially available from Tosoh Corporation under the trade names Nipolon Hard (registered trademark), Nipolon (registered trademark)-L, and Nipolon (registered trademark)-Z. Examples of α-olefins constituting ethylene-α-olefin copolymers include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. A high-pressure method for producing low-density polyethylene can be exemplified by high-pressure radical polymerization. Such resins can be conveniently selected from commercially available products, and for example, they are commercially available from Tosoh Corporation under the trade name Petrocene. Known production methods for ethylene-vinyl acetate copolymers include high-pressure radical polymerization, solution polymerization, and emulsion polymerization. Such resins can be conveniently selected from commercially available products, and are sold by Tosoh Corporation under the trade name UltraCen (registered trademark) as an ethylene-vinyl acetate copolymer.

[0033] The density of the ethylene polymer is preferably 880 to 940 kg / m³. ３ More preferably, 890 to 930 kg / m ３ The most preferred value is 895 to 925 kg / m ３ Within this range, a laminate film with excellent heat-seal appearance can be obtained. The density of the ethylene polymer is measured in accordance with JIS K6922-1 (1997). The melt flow rate of the ethylene polymer is preferably 0.1 to 30 g / 10 min, more preferably 0.5 to 25 g / 10 min, and even more preferably 1 to 20 g / 10 min. Ethylene polymers having a melt flow rate within this range are advantageous in that they have excellent moldability when manufacturing ethylene polymer films.

[0034] The melting point of the ethylene polymer is preferably 80 to 130°C, and more preferably 80 to 120°C. The melting point of the ethylene polymer can be measured using a measuring instrument DSC6220 (manufactured by Seiko Instruments Corporation) by raising the temperature from a starting temperature of 30°C to 230°C at a heating rate of 10°C / min and a cooling rate of 10°C / min. The ethylene polymer film may further contain any suitable additives as needed. The ethylene polymer film may also contain a tackifier. By forming an ethylene polymer film containing a tackifier, a laminate film with excellent heat sealability can be obtained.

[0035] Examples of the above-mentioned tackifiers include petroleum resins such as aliphatic petroleum resins, aliphatic hydrogenated petroleum resins, aromatic petroleum resins, aromatic hydrogenated petroleum resins, alicyclic petroleum resins, alicyclic hydrogenated petroleum resins, copolymerized hydrogenated petroleum resins, coumarone resins, styrene resins, and natural resin-based tackifiers such as rosin resins, methyl ester resins, glycerin ester resins, pentaerythritol ester resins, terpene resins, and modified products thereof. Of these tackifiers, a tackifier consisting of at least one selected from the group consisting of petroleum resins, terpene resins, and rosin resins is preferred from the viewpoint of improving adhesion.

[0036] The tackifier described above preferably has a softening point measured by the ring-sphere method in the range of 90 to 140°C, more preferably 100 to 135°C, and even more preferably 105 to 130°C. When the softening point is within the above range, there is less blocking of the film after molding, and the adhesive strength retention in low-temperature environments is favorable. The tackifier described above can be a commercially available product. Specifically, examples of petroleum resins include Alcon® P100, Alcon P125, Alcon P140, Alcon M90, Alcon M115, Alcon M135 (all manufactured by Arakawa Chemical Industries, Ltd.), iMarb® S110, iMarb P125 (both manufactured by Idemitsu Kosan Co., Ltd.), T-REZ® RC115, T-REZ HA125 (both manufactured by JXTG Energy Corporation), etc. Examples of rosin-based resins include Pine Crystal (registered trademark) KE-311 (manufactured by Arakawa Chemical Industries, Ltd.). Examples of terpene-based resins include YS Resin PX1150 and YS Resin PX1150N (both manufactured by Yasuhara Chemical Co., Ltd.).

[0037] The content ratio of the tackifier is preferably 1 to 30 parts by mass, and more preferably 5 to 40 parts by mass, per 100 parts by mass of the ethylene polymer constituting the ethylene polymer film. Within this range, a laminate film with excellent heat sealability can be obtained. Other additives include, for example, additives commonly used in polyolefins such as antioxidants, lubricants, neutralizing agents, anti-blocking agents, surfactants, and slip agents, as well as thermoplastic resins such as other polyolefins.

[0038] The above-mentioned laminate film can be manufactured by laminating an ethylene polymer film onto at least one surface of a stretched polyethylene film, or onto the surface of an adhesive layer of a stretched polyethylene film that has an adhesive layer such as an anchor coating agent. Examples of such methods include various extrusion lamination processes such as single lamination, tandem lamination, sandwich lamination, and co-extrusion lamination, as well as dry lamination. In the extrusion lamination method, the processing temperature of the ethylene polymer is preferably in the range of 200 to 350°C, and the surface temperature of the cooling roll is preferably in the range of 10 to 50°C. When subjecting to extrusion lamination, ozone gas may be blown to obtain good adhesion. In that case, the temperature of the ethylene polymer extruded from the die is preferably 200°C or higher. The amount of ozone gas to be processed is 1 m of film made of the extrusion lamination resin composition of the present invention extruded from the die. ２ It is preferable that the amount is 0.5 mg or more per unit.

[0039] The above adhesive layer is not particularly limited, but examples include polyurethane adhesives, isocyanate adhesives, polyethyleneimine adhesives, polybutadiene adhesives, acrylic adhesives, and epoxy adhesives. The polyurethane adhesive or isocyanate adhesive is preferably composed of at least one polyol component having at least two hydroxyl groups in its molecule and at least one polyisocyanate component and / or diisocyanate having at least two isocyanate groups in its molecule. The polyol component can be appropriately selected from polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, and the like. Examples of diisocyanates include aromatic diisocyanates such as 4,4'-, 2,4'-, and 2,2'-diisocyanate diphenylmethane, 1,5-diisocyanate naphthalene, 4,4'-diisocyanate dicyclohexylmethane, 1,4-diisocyanate benzene, and 2,4- or 2,6-diisocyanate toluene; and aliphatic and alicyclic diisocyanates such as 1,6-diisocyanate hexane, 1,10-diisocyanate decane, 1,3-diisocyanate cyclopentane, 1,4-diisocyanate cyclohexane, and 1-isocyanate-3,3,5-trimethyl-3 or -5-isocyanate methanecyclohexane. Polyisocyanate components can be produced from these diisocyanate monomers. Such anchor coating agents can be selected from commercially available products as appropriate. Polyurethane-based adhesives such as Nipponran (registered trademark) 3228 from Tosoh Corporation and polyethyleneimine-based adhesives such as Toyovine (registered trademark) from Tosoh Corporation are commercially available.

[0040] The thickness of the adhesive layer is preferably 0.01 to 2.0 μm or less, more preferably 0.01 to 1 μm, and most preferably 0.01 to 0.5 μm in the case of extrusion lamination, and preferably 0.5 to 5.0 μm or less, more preferably 0.8 to 3 μm, and most preferably 0.8 to 2 μm in the case of dry lamination. Within these ranges, a laminate film with excellent adhesive properties can be obtained. The laminate film can be used as a packaging laminate film for food, beverages, pharmaceuticals, etc.

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way by these examples. Parts and percentages are based on mass unless otherwise specified. The evaluation methods in the examples and comparative examples are as follows.

[0042] <Melt Mass Flow Rate (MFR)> Measured using a melt indexer (manufactured by Takara Kogyo) in accordance with JIS K6924-1 (under conditions of 190°C and 2160g load). <Density> Measured in accordance with JIS K6922-1 (1997).

[0043] <Molecular Weight> Molecular weight was measured using a GPC instrument (Tosoh Corporation (product name) HLC®-8121GPC / HT) and a column (Tosoh Corporation (product name) TSKgel® GMHhr-H(20)HT), with the column temperature set to 140°C and 1,2,4-trichlorobenzene as the eluent. The 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 polystyrene samples with known molecular weights. From the chromatogram obtained from the measurement results, the weight-average molecular weight Mw and the molecular weight component percentages were calculated.

[0044] <Melting Extrusion Properties> Melting and kneading were performed using a twin-screw extruder (manufactured by Japan Steel Works, product name TEX30-SS-42BW-5V) at an extrusion temperature of 230°C, a screw rotation speed of 100 rpm, and a feed rate of 5 kg / h. The resin pressure during melt molding was measured. The resin pressure was 44 kgf / cm². ２ The following is A, 45-50 kgf / cm² ２ B, 51 kgf / cm２ Let's call the above C.

[0045] <Differential Scanning Calorimetry> A differential scanning calorimeter (DSC) (Hitachi High-Tech Science, product name DSC7000X) was used to heat the sample from 20°C to 230°C at a heating rate of 10°C / min (1st scan), and the endothermic peak of the 1st scan was measured. The sample amount of stretched polyethylene film was 3 mg.

[0046] <Heat Shrinkage Rate> The laminate film obtained in the example was heat-sealed using a heat seal tester (Tester Industries Co., Ltd., product name TP-701B) at a set temperature of 130°C, heating on both sides, air pressure of 0.2 MPa, and sealing time of 1 second, and then air-cooled. The heat shrinkage rate was calculated from the film length before and after heat sealing based on the following formula: Heat shrinkage rate = (film length before heat sealing - film length after heat sealing) / (film length before heat sealing)

[0047] [Example 1] [Preparation of organically modified clay] Put 300 ml of industrial alcohol (manufactured by Nippon Alcohol Sales Co., Ltd., (product name) Ekinen F-3) and 300 ml of distilled water into a 1 liter flask, and add 15.0 g of concentrated hydrochloric acid and dioleylmethylamine ((C) １８ H ３５ ) ２ (CH ３ 63.7 g (120 mmol) of (product name) Lipomin M2O, manufactured by Lion Specialty Chemicals Co., Ltd. was added and heated to 45°C. Then, 100 g of synthetic hectorite (product name) Laponite RD, manufactured by BYK, was dispersed in the mixture, and the temperature was raised to 60°C and stirred for 1 hour while maintaining that temperature. After filtering off the slurry, it was washed twice with 600 ml of water at 60°C and dried in an oven at 85°C for 12 hours to obtain 130 g of organically modified clay. This organically modified clay was pulverized with a jet mill to a median diameter of 15 μm.

[0048] [Preparation of polymerization catalyst] A 300 mL flask equipped with a thermometer and reflux tubing was purged with nitrogen. Then, 25.0 g of the organically modified clay obtained in [Preparation of organically modified clay] and 108 mL of hexane were added. Next, 0.392 g (1 mmol) of bis(indenyl) zirconium dichloride and 142 mL of 20% triisobutylaluminum were added, and the mixture was stirred at 60°C for 3 hours. After cooling to room temperature, the supernatant was removed, washed twice with 220 mL of hexane, and then 220 mL of hexane was added to obtain a catalyst suspension (solid weight: 12.0 wt%).

[0049] [Production of Polyethylene Powder (B1)] 1.2 L of hexane and 1.0 mL of 20% triisobutylaluminum were added to a 2 L autoclave. 200 mg (equivalent to 24 mg of solids) of the catalyst suspension obtained in [Preparation of Polymerization Catalyst] was added. After heating to 85°C, an ethylene / hydrogen mixed gas was continuously supplied to maintain a partial pressure of 0.90 MPa (hydrogen concentration in the ethylene / hydrogen mixed gas: 450 ppm). After 90 minutes, the pressure was removed, the slurry was filtered off, and then dried to obtain polyethylene powder (B1). The obtained polyethylene powder (B1) had a weight-average molecular weight of 111,000, a component ratio of 15% consisting of molecules with a molecular weight of 3,000 to 30,000 or less, and a density of 952 kg / m³. ３ The obtained polyethylene powder was melt-kneaded using a twin-screw extruder with a screw diameter of 25 mm (Technovel product name ULTnano25TW) under conditions of resin temperature of 160°C and screw rotation speed of 300 rpm to obtain polyethylene pellets (B1).

[0050] [Preparation of Polyethylene (A1)] 95% by mass of polyethylene pellets (B1) and polyethylene (C1) (manufactured by Mitsui Chemicals, high wax 100P, density 950 kg / m³) ３The endothermic curve measured by differential scanning calorimetry shows a single peak at 117°C. After dry blending 5% by mass of the material, the mixture was melt-kneaded using a twin-screw extruder (manufactured by Japan Steel Works, product name TEX30-SS-42BW-5V) at an extrusion temperature of 230°C, a screw rotation speed of 100 rpm, and a feed rate of 5 kg / h to obtain polyethylene pellets (A1). The MFR of polyethylene pellets (A1) was 1.2 g / 10 min. At this time, the resin pressure was measured and the melt extrudeability was evaluated. The results are shown in Table 1. Using polyethylene pellets (A1), compression molding was performed using a compression molding machine AWFA.50 (manufactured by Shinto Metal Industries Co., Ltd.) and a mold of 150 mm × 150 mm × 0.1 mm under the conditions of heating temperature 230°C, cooling temperature 25°C, primary pressure 0.1 MPa × 4 min, secondary pressure 20 MPa × 4 min, and cooling pressure 20 MPa × 4 min to produce a sheet with a thickness of 0.15 mm. The prepared sheet was uniaxially stretched using a biaxial stretching machine (manufactured by Toyo Seiki Seisakusho, product name EX10-B) at a stretching temperature of 125°C, a stretching ratio of 5 times, and a stretching speed of 100 mm / min. After stretching, it was air-cooled to obtain a stretched film. Differential scanning calorimetry was performed using the obtained stretched film. In addition, as a stretched polyethylene film for lamination and an ethylene-1-hexene copolymer film (manufactured by Tosoh Corporation, product name "Nipolon ZZF230", MFR: 2 g / 10 min, density: 920 kg / m³) was used. ３ A 50 μm thick ethylene-1-hexene copolymer film, obtained by film forming using an inflation molding machine (manufactured by Placo Co., Ltd.) with a melting point of 120°C, was bonded to a laminate film via a urethane adhesive (a mixture of Mitsui Chemicals' trade names "Takelac® A3210" and "Takenate® A3072"). The thermal shrinkage rate of the obtained laminate film was evaluated. The evaluation results are shown in Table 1.

[0051] [Example 2] Polyethylene pellets (A2) were obtained in the same manner as in Example 1, except that 50 ppm of an organic peroxide (Perhexa C, manufactured by NOF Corporation) was added to the polyethylene pellets. Using polyethylene pellets (A2), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0052] [Example 3] [Preparation of Modified Clay] Put 300 mL of industrial alcohol (manufactured by Nippon Alcohol Sales Co., Ltd. (product name) Ekinen F-3) and 300 mL of distilled water into a 1 L flask, add 18.8 g of concentrated hydrochloric acid and dimethylhexacosylamine (Me ２ N(C) ２６ H ５３ 49.1 g (120 mmol) of synthetic hectorite (synthesized by conventional methods) was added, and the mixture was heated to 45°C to disperse 100 g of synthetic hectorite (Rockwood Additionals (trade name) Laponite RDS). The mixture was then heated to 60°C and stirred for 1 hour while maintaining that temperature. After filtering the slurry, it was washed twice with 600 mL of 60°C water and dried in an oven at 85°C for 12 hours to obtain 140 g of organically modified clay. This organically modified clay was pulverized with a jet mill to a median diameter of 14 μm.

[0053] [Preparation of polymerization catalyst] A 300 mL flask equipped with a thermometer and reflux tubing was purged with nitrogen. Then, 25.0 g of the organically modified clay obtained in [Preparation of modified clay] and 108 mL of hexane were added. Next, 0.4406 g of dimethylsilylene (cyclopentadienyl) (2,4,7-trimethyl-1-indenyl) zirconium dichloride and 142 mL of 20% triisobutylaluminum were added, and the mixture was stirred at 60°C for 3 hours. After cooling to 45°C, the supernatant was removed, washed five times with 200 mL of hexane, and then 200 mL of hexane was added to obtain a catalyst suspension (solid weight: 12.0% by weight).

[0054] [Production of Ethylene-α-Olefin Copolymer (D)] 1.2 L of hexane and 1.0 mL of 20% triisobutylaluminum were added to a 2 L autoclave. 75 mg (equivalent to 9.0 mg of solids) of the catalyst suspension obtained in [Preparation of Polymerization Catalyst] was added. After raising the temperature to 80°C, 8.3 g of 1-butene was added, and an ethylene / hydrogen mixed gas was continuously supplied to maintain a partial pressure of 0.85 MPa (hydrogen concentration in the ethylene / hydrogen mixed gas: 850 ppm). After 90 minutes, the pressure was removed, the slurry was filtered off, and the mixture was dried to obtain ethylene-1-butene copolymer powder. The density of the obtained polymer was 941 kg / m³. ３The long-chain branching number was 0.30 per 1000 carbon atoms in the main chain, and the weight-average molecular weight (Mw) was 130,000. Polyethylene pellets (A3) were obtained in the same manner as in Example 2, except that 5 parts by mass of the obtained ethylene-1-butene copolymer powder was added to 100 parts by mass of polyethylene resin (A). Using the polyethylene pellets (A3), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0055] [Example 4] Polyethylene pellets (A4) were obtained in the same manner as in Example 2, except that polyethylene pellets (B1) were changed to 90% by mass and polyethylene (C1) to 10% by mass. Using polyethylene pellets (A4), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0056] [Example 5] Polyethylene pellets (A5) were obtained in the same manner as in Example 2, except that polyethylene pellets (B1) were changed to 85% by mass and polyethylene (C1) to 15% by mass. Using polyethylene pellets (A5), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0057] [Example 6] Polyethylene (C2) was used instead of polyethylene (C1) (Mitsui Chemicals, High Wax 400P, density 980 kg / m³). ３ Polyethylene pellets (A6) were obtained in the same manner as in Example 4, except that a single peak at 128°C was observed in the endothermic curve measured by differential scanning calorimetry. Using polyethylene pellets (A6), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0058] [Example 7] Polyethylene (C3) was used instead of polyethylene (C1) (Mitsui Chemicals, High Wax 200P, density 970 kg / m³). ３Polyethylene pellets (A7) were obtained in the same manner as in Example 4, except that a single peak at 124°C was observed in the endothermic curve measured by differential scanning calorimetry. Using polyethylene pellets (A7), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0059] [Example 8] Polyethylene (C4) was used instead of polyethylene (C1) (Mitsui Chemicals, High Wax 800P, Density 970 kg / m³). ３ Polyethylene pellets (A8) were obtained in the same manner as in Example 4, except that a single peak at 130°C was observed in the endothermic curve measured by differential scanning calorimetry. Using polyethylene pellets (A8), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0060] [Example 9] As polyethylene pellets (B), 68% by mass of polyethylene pellets (B1) and high-density polyethylene (B2) (Tosoh, Nipolon Hard 8900, density 952 kg / m³) ３ Polyethylene pellets (A9) were obtained in the same manner as in Example 4, except that the dry blend pellets were changed to 22% by mass. The polyethylene composition pellets (A9) obtained at this time had a weight-average molecular weight of 180,000, a component ratio of 14% with a molecular weight of 3,000 to 30,000 or less, and a density of 952 kg / m³. ３ Using polyethylene pellets (A9), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0061] [Example 10] A laminate film was obtained in the same manner as in Example 9, except that a biaxially oriented film was obtained by uniaxially stretching the film and then further stretching it 5 times at 130° in a direction perpendicular to the stretching direction. The evaluation results are shown in Table 1.

[0062] [Comparative Example 1] A stretched polyethylene film and a laminate film were obtained in the same manner as in Example 2, except that polyethylene (B1) was used instead of polyethylene composition (A2). The evaluation results are shown in Table 2. A stretched polyethylene film and a laminate film were obtained. The evaluation results are shown in Table 2. The melt extrudeability was poor.

[0063] [Comparative Example 2] Polyethylene (C3) is used instead of polyethylene (C1) (Tosoh Corporation, Nipolon Hard 1000, density 964 kg / m³). ３ Polyethylene pellets (A10) were obtained in the same manner as in Example 4, except that a single peak at 130°C was observed in the endothermic curve measured by differential scanning calorimetry. Using polyethylene pellets (A10), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2. The melt extrudeability was poor.

[0064] [Comparative Example 3] Polyethylene pellets (A11) were obtained in the same manner as in Example 2, except that polyethylene pellets (B1) were changed to 70% by mass and polyethylene (C1) to 30% by mass. Using polyethylene pellets (A11), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2. The stretchability of the film was poor, making it difficult to produce a stretched film.

[0065] [Comparative Example 4] Polyethylene pellets (A12) were obtained in the same manner as in Example 5, except that polyethylene pellets (B1) were changed to 70% by mass and polyethylene (C2) to 30% by mass. Using polyethylene pellets (A12), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2. The heat resistance of the stretched film was poor.

[0066] [Comparative Example 5] Polyethylene pellets (A13) were obtained in the same manner as in Example 8, except that polyethylene CB1) was not added, and the composition was 75% by mass of polyethylene pellets (B1) and 25% by mass of high-density polyethylene (B2). Using polyethylene pellets (A13), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2, but the melt extrudeability was poor.

[0067] [Comparative Example 6] Instead of polyethylene (B1), polyethylene (B3) (manufactured by Tosoh, Nipolon Hard 5700, density 954 kg / m³) is used. ３ Polyethylene pellets (A14) were obtained in the same manner as in Example 4, except that a weight-average molecular weight of 122,000 and a component proportion of 29% with a molecular weight of 3,000 to 30,000 or less were used. Using polyethylene pellets (A14), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2, but the heat resistance of the stretched film was poor.

[0068] [Comparative Example 7] Polyethylene pellets (A15) were obtained in the same manner as in Example 4, except that polyethylene (B2) was used instead of polyethylene (B1). Using polyethylene pellets (A15), stretched polyethylene film and laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 2, and the melt extrudeability was poor.

[0069] [Comparative Example 8] Polyethylene pellets (A16) were obtained in the same manner as in Example 4, except that polyethylene (C3) was used instead of polyethylene (B1). The film had poor stretchability, making it difficult to produce a stretched film.

[0070]

[0071]

[0072] Furthermore, the entire contents of the claims, description, and abstract of Japanese Patent Application No. 2025-048642, filed on March 24, 2025, and Japanese Patent Application No. 2025-181121, filed on October 27, 2025, are incorporated herein by reference as disclosure of the specification of the present invention.

Claims

1. The proportion of molecules with a molecular weight of 3,000 or less measured by gel permeation chromatography is 2 to 15% by mass, the proportion of molecules with a molecular weight of 3,000 to 30,000 is 25% by mass or less, and the density measured according to JIS K6922-1 (1997) is 940 to 970 kg / m³. ３ Polyethylene resin (A) having a melt mass flow rate (MFR) of 0.1 to 5.0 g / 10 min, measured according to JIS K6924-1 (under conditions of 190°C and 2160 g load).

2. The polyethylene composition (A) according to claim 1, comprising 3 to 10 parts by mass of an ethylene-α-olefin copolymer (D) having a weight-average molecular weight (Mw) of 100,000 to 200,000 and a molecular weight of 100,000 or more after molecular weight fractionation, with long-chain branches of 0.15 or more per 1,000 carbon atoms in the main chain in the fraction, per 100 parts by mass of polyethylene resin (A).

3. The polyethylene resin (A) according to claim 1, wherein the polyethylene resin (A) contains 5 to 100 ppm or less of an organic peroxide and its decomposition products.

4. The weight-average molecular weight (Mw) measured by gel permeation chromatography is between 70,000 and 250,000, the proportion of molecules with a molecular weight of 3,000 to 30,000 measured by gel permeation chromatography is 25% by mass or less, and the density measured according to JIS K6922-1 (1997) is 940 to 970 kg / m³. ３ The polyethylene resin (A) according to claim 1, comprising polyethylene (B) and polyethylene (C) having a weight-average molecular weight (Mw) of 1,000 to 20,000 as measured by gel permeation chromatography.

5. The polyethylene resin (A) according to claim 4, wherein polyethylene (B) is 85 to 97% by mass and polyethylene (C) is 3 to 15% by mass.

6. A stretched polyethylene film made of polyethylene resin (A) according to any one of claims 1 to 5, wherein at least one peak in the endothermic curve measured by a differential scanning calorimetry device is 135°C or higher.

7. A laminate film having an ethylene polymer film on at least one side of the stretched polyethylene film according to claim 6.

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