Laminating oriented polyethylene film

Abstract

To provide a stretched polyethylene film for lamination that has high recyclability and excellent heat resistance.SOLUTION: Provided is a stretched polyethylene film for lamination that is characterized by containing a polyethylene (A) having a weight average molecular weight (Mw) measured by gel permeation chromatography of 70,000 to 250,000 and a ratio of molecular weights of 10,000 or less of 8 wt.% or less, and a density measured according to JIS K6922-1 (year of 1997) of 945 to 980 kg / m3, and exhibiting at least one peak in the range of 135°C or higher in the endothermic curve measured by differential scanning calorimetry.

Description

[Technical Field]

[0001] The present invention relates to a stretched polyethylene film for lamination. [Background technology]

[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 (for example, polypropylene film, polyester film, polyamide film) are widely used as packaging materials (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 building 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, packaging materials made from the same resin materials, formed by laminating oriented polyethylene film and unoriented polyethylene film, have been proposed (e.g., 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. This necessitates a lower heat-sealing temperature, which may result in insufficient heat-sealing strength.

[0005] Furthermore, ultra-high molecular weight polyethylene films have been proposed as polyethylene films with excellent rigidity, heat resistance, and strength (for example, Patent Document 4). However, the ultra-high molecular weight polyethylene films have poor melt-mixability with ordinary polyethylene, and when subjected to material recycling, uneven dispersion and melting occur, resulting in a significant loss of quality in the recycled resin, which has been an issue. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-104525 [Patent Document 2] Japanese Patent Application Publication No. 2019-171860 [Patent Document 3] Japanese Patent Application Publication No. 2019-529165 [Patent Document 4] Japanese Patent Application Laid-Open No. 1994-262679 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a stretched polyethylene film for lamination which is highly recyclable and has excellent heat resistance. [Means for solving the problem]

[0008] As a result of extensive research aimed at solving the above problems, the present inventors have found that a specific stretched polyethylene film exhibits excellent recyclability and heat resistance, leading to the completion of the present invention.

[0009] That is, the present invention relates to a polymer having a weight average molecular weight (Mw) of 70,000 to 250,000 as measured by gel permeation chromatography, a proportion of molecular weights of 10,000 or less of 5% by weight or less, and a density of 945 to 980 kg / m as measured by JIS K6922-1 (1997). 3The present invention relates to a stretched polyethylene film for lamination, which contains polyethylene (A) and exhibits at least one peak in the range of 135°C or higher in an endothermic curve measured by differential scanning calorimetry.

[0010] The present invention also provides a stretched polyethylene film for lamination having a density of 880 to 940 kg / m on at least one surface thereof. 3 The present invention relates to a laminate film having an ethylene polymer film formed thereon.

[0011] The present invention also relates to a method for producing a biaxially oriented film, in which the oriented polyethylene film for lamination is further stretched in the transverse direction.

[0012] The present invention also relates to recycled polyethylene pellets comprising a film containing the stretched polyethylene film for lamination. [Effects of the Invention]

[0013] The stretched polyethylene film for lamination of the present invention has high heat resistance and is useful as a substrate for laminate films for packaging foods, beverages, pharmaceuticals, etc. Furthermore, since the laminate film obtained is composed mostly of polyethylene-based materials, it has excellent recyclability and can reduce the environmental load. DETAILED DESCRIPTION OF THE INVENTION

[0014] The stretched polyethylene film for lamination, which is one embodiment of the present invention, will be described in detail below.

[0015] The polyethylene (A) constituting the present invention has a weight average molecular weight (Mw) measured by gel permeation chromatography of 70,000 to 250,000, preferably 100,000 to 200,000, and more preferably 100,000 to 150,000. If Mw is less than 70,000, the strength of the stretched film for lamination will be low, and the seal strength of the resulting laminate film will be insufficient. If Mw exceeds 250,000, the melt extrudability in material recycling will be poor and the performance of the resulting recycled resin will be deteriorated, which is undesirable.

[0016] The polyethylene (A) constituting the present invention has a proportion of molecules having a molecular weight of 10,000 or less as measured by gel permeation chromatography of 8% by weight or less, preferably 6% by weight or less, and more preferably 4% by weight or less. If this proportion exceeds 8% by weight, the heat resistance of the stretched film deteriorates, and the heat-sealed appearance of the laminated film deteriorates, which is undesirable. This is presumably because the molecular chains are relaxed by molecules with low molecular weight during the stretching process, resulting in insufficient orientation of the polyethylene crystals.

[0017] The polyethylene (A) constituting the present invention has a density of 945 to 980 kg / m as measured according to JIS K6922-1 (1997). 3 The density is 945 kg / m 3 If it is less than 980 kg / m, the heat resistance of the oriented polyethylene film for lamination will deteriorate, which is not preferable. 3 Polyethylene with a density above this is difficult to produce industrially.

[0018] Such polyethylene (A) can be obtained by homopolymerizing ethylene or copolymerizing ethylene with a small amount of an 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 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.

[0019] The polyethylene (A) constituting the present invention preferably contains 5 to 100 ppm of organic peroxides and their decomposition products. This results in a stretched laminate film with a high peak temperature in the endothermic curve measured by a differential scanning calorimeter, and further improved heat resistance. If the content exceeds 100 ppm, it may be difficult to control the appearance of the stretched polyethylene film.

[0020] 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)hexyne-3, and α,α'-bis(t-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-hexylperoxybenzoate, t-butylperoxy-m-toluylbenzoate, and t-butylperoxy-m-toluylbenzoate. peroxy esters such as α,α'-bis(t-butylperoxy)diisophthalate, and peroxy ketals 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, dialkyl peroxides, particularly α,α'-bis(t-butylperoxy)diisopropylbenzene and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, are preferred.

[0021] The polyethylene (A) constituting the present invention may contain additives typically used in polyolefins, such as antioxidants, lubricants, neutralizing agents, antiblocking agents, surfactants, and slip agents, as needed.

[0022] The polyethylene (A) of the present invention may also contain 0.01 to 10% by weight of an ethylene-α-olefin copolymer (B) having 0.15 or more long-chain branches per 1,000 carbon atoms in the main chain in a fraction having an Mn of 100,000 or more when fractionated by molecular weight. In this case, the proportion of polyethylene (A) is 90 to 99.99% by weight. Adding the ethylene-α-olefin copolymer (B) in this proportion is preferred because it improves the formability and transparency of the stretched polyethylene film for lamination.

[0023] The ethylene-α-olefin copolymer (B) is produced using a metallocene catalyst. The metallocene catalyst used contains a metallocene complex, an activating cocatalyst, and, if necessary, an organoaluminum compound as constituent components, and it is preferable to copolymerize the macromonomer, ethylene, and an olefin having 3 to 6 carbon atoms simultaneously with the synthesis of the macromonomer. The macromonomer is an olefin polymer having a vinyl group at its terminal, and is an ethylene copolymer having a vinyl group at its terminal, obtained by copolymerizing ethylene with an olefin having 3 to 6 carbon atoms.

[0024] The stretched polyethylene film for lamination of the present invention 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 stretched polyethylene film for lamination of the present invention to exhibit high heat resistance. If the endothermic curve peak of the stretched polyethylene film is less than 135°C, the laminate film obtained by lamination processing will have insufficient heat resistance and will not have good heat-sealing properties, which is undesirable.

[0025] The thickness of the stretched polyethylene film for lamination is preferably 10 μm to 200 μm, more preferably 12 μm to 100 μm, and even more preferably 14 μm to 50 μm. Within these ranges, a laminate film having desirable heat seal strength can be obtained.

[0026] As a method for producing the stretched film for lamination, roll rolling is preferred because the stretched polyethylene film for lamination has excellent heat resistance.

[0027] Roll calendering refers to a molding method in which a polyethylene sheet delivered from a T-die or the like is rolled between two or more rolls to form a film having a predetermined thickness. Suitable roll calendering methods include the polishing roll method used in T-die extrusion molding and calendaring. Examples of calendaring devices include a two-roll in-line calendar, a three-roll in-line calendar, a four-roll in-line calendar, an S-calender, a reverse L-calender, a Z-calender, and a diagonal Z-calender.

[0028] The number of times of rolling may be one or more, but rolling more than one time is preferred because the strength and heat resistance of the stretched polyethylene film for lamination are improved by rolling it multiple times.

[0029] The temperature of the polyethylene sheet subjected to the roll rolling is preferably 110°C to 150°C, more preferably 115°C to 140°C, and even more preferably 120°C to 135°C, from the viewpoint of the heat resistance of the stretched polyethylene film for lamination.

[0030] The stretched polyethylene film for lamination of the present invention can be further stretched in the transverse direction to produce a biaxially stretched film. As a method for transverse stretching, a tenter method is preferred.

[0031] The stretched polyethylene film for lamination may be subjected to any suitable surface treatment to enhance the adhesiveness of the laminate film, such as corona treatment, flame treatment, and plasma treatment.

[0032] The stretched polyethylene film for lamination may be subjected to vapor deposition treatment of aluminum, alumina, silicon dioxide, etc., or 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.

[0033] The stretched polyethylene film for lamination of the present invention can be used to obtain a laminate film by laminating an ethylene polymer film to at least one surface thereof.

[0034] The thickness of the ethylene polymer film is preferably 5 μm to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 μm to 120 μm. Within this range, a laminate film with excellent heat-sealing properties can be obtained.

[0035] The ethylene polymer may be a homopolymer of ethylene or a copolymer of ethylene and a monomer copolymerizable with ethylene. Examples of the ethylene polymer 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 of their excellent heat-sealability of the laminate film.

[0036] The production methods for high-density polyethylene and ethylene-α-olefin copolymers are not particularly limited, and examples include high-, medium-, and low-pressure ionic polymerization methods 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, Nipolon-L, and Nipolon-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. High-pressure low-density polyethylene can be produced by high-pressure radical polymerization. Such resins can be conveniently selected from commercially available products, such as those commercially available from Tosoh Corporation under the trade name Petrothene. Ethylene-vinyl acetate copolymers can be produced by known methods such as high-pressure radical polymerization, solution polymerization, and emulsion polymerization. Such resins can be conveniently selected from commercially available products. For example, ethylene-vinyl acetate copolymers are commercially available from Tosoh Corporation under the trade name Ultrathene.

[0037] The density of the ethylene polymer is preferably 880 kg / m 3 ~940kg / m 3 and more preferably 890 kg / m 3 ~930kg / m 3 and most preferably 895 kg / m 3 ~925kg / 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).

[0038] 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 in such a range are advantageous in that they have excellent formability when producing an ethylene polymer film.

[0039] The melting point of the ethylene polymer is preferably 80° C. to 130° C., more preferably 800° C. to 120° C. The melting point of the ethylene polymer can be measured using a measuring device DSC6220 (manufactured by Seiko Instruments Inc.) by increasing the temperature from an initial temperature of 30° C. to 230° C. at a temperature increase rate of 10° C. / min and a temperature decrease rate of 10° C. / min.

[0040] The ethylene-based polymer film may further contain any appropriate additive as necessary. The ethylene-based polymer film may also contain a tackifier. By forming an ethylene-based polymer film containing a tackifier, a laminate film with excellent heat-sealing properties can be obtained.

[0041] Examples of the tackifier 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, and copolymer hydrogenated petroleum resins, as well as 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. Among these tackifiers, tackifiers consisting of at least one selected from the group consisting of petroleum resins, terpene resins, and rosin resins are preferred from the viewpoint of improving adhesion.

[0042] The tackifier preferably has a softening point measured by the ring and ball method in the range of 90° C. to 140° C., more preferably 100° C. to 135° C., and even more preferably 105° C. to 130° C. When the softening point is within the above range, there is little blocking of the film after molding, and the adhesive strength retention in a low-temperature environment is favorable.

[0043] The tackifier may be commercially available. Specific examples of petroleum resins include (trade names) Arkon P100, Arkon P125, Arkon P140, Arkon M90, Arkon M115, and Arkon M135 (all manufactured by Arakawa Chemical Industries, Ltd.), Imave S110 and Imave P125 (all manufactured by Idemitsu Kosan Co., Ltd.), and T-REZ RC115 and T-REZ HA125 (all manufactured by JXTG Nippon Oil & Energy Corporation). Examples of rosin-based resins include Pine Crystal KE-311 (manufactured by Arakawa Chemical Industries, Ltd.). Examples of terpene-based resins include YS Resin PX1150 and YS Resin PX1150N (manufactured by Yasuhara Chemical Co., Ltd.).

[0044] The content of the tackifier is preferably 1 to 30 parts by weight, more preferably 5 to 40 parts by weight, relative to 100 parts by weight of the ethylene polymer constituting the ethylene polymer film. Within this range, a laminate film with excellent heat-sealing properties can be obtained.

[0045] Examples of other additives include additives commonly used in polyolefins, such as antioxidants, lubricants, neutralizing agents, antiblocking agents, surfactants, and slip agents; thermoplastic resins such as other polyolefins; and the like.

[0046] The laminate film can be produced by laminating an ethylene polymer film to at least one surface of the stretched polyethylene film for lamination of the present invention, or to the adhesive layer surface of a stretched polyethylene film for lamination provided with an adhesive layer such as an anchor coating agent. Examples of such methods include various extrusion lamination methods such as single lamination, tandem lamination, sandwich lamination, and coextrusion 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°C to 350°C, and the surface temperature of the cooling roll is preferably in the range of 10°C to 50°C. During extrusion lamination, ozone gas may be sprayed to obtain good adhesion. In this case, the temperature of the ethylene polymer extruded from the die is preferably 200°C or higher. The amount of ozone gas to be treated is determined based on the amount of ozone gas per meter of the film made of the resin composition for extrusion lamination of the present invention extruded from the die. 2 It is preferable that the amount is 0.5 mg or more per unit area.

[0047] The adhesive layer is not particularly limited, but examples thereof include polyurethane adhesives, isocyanate adhesives, polyethyleneimine adhesives, polybutadiene adhesives, acrylic adhesives, and epoxy adhesives. The polyurethane adhesive or isocyanate adhesive is preferably an adhesive composed of at least one polyol component having at least two hydroxyl groups in the molecule and at least one polyisocyanate component and / or diisocyanate having at least two isocyanate groups in the 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'-diisocyanatodiphenylmethane, 1,5-diisocyanatonaphthalene, 4,4'-diisocyanatodicyclohexylmethane, 1,4-diisocyanatobenzene, and / or 2,4- or 2,6-diisocyanatotoluene, and aliphatic and alicyclic diisocyanates such as 1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3-diisocyanatocyclopentane, 1,4-diisocyanatocyclohexane, and 1-isocyanato-3,3,5-trimethyl-3 or -5-isocyanatomethanecyclohexane. The polyisocyanate component can be produced from these diisocyanate monomers. Such anchor coating agents can be appropriately selected from commercially available products, and polyurethane-based adhesives such as Nipponlan 3228, available from Tosoh Corporation, and polyethyleneimine-based adhesives such as Toyobine, available from Tosoh Corporation, are commercially available.

[0048] The thickness of the adhesive layer is preferably 0.01 μm 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 is preferably 0.5 μm 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 recyclability and adhesiveness can be obtained.

[0049] The laminate film of the present invention has excellent recyclability because it is mostly made of polyethylene-based materials. Recycling methods include material recycling, in which the laminate film is melt-kneaded to obtain pellets, and chemical recycling, in which the laminate film is thermally decomposed to obtain low-molecular-weight hydrocarbons. Material recycling is particularly preferred because of its low cost and low energy requirements. In other words, the pellets obtained by recycling are composed of the laminate film of the present invention. Here, these pellets are also referred to as recycled polyethylene pellets of the present invention.

[0050] The melt-kneading device for the stretched polyethylene film for lamination is not particularly limited as long as it can uniformly disperse the stretched polyethylene film for lamination, and can be produced using a commonly used resin kneading device. For example, recycled pellets can be obtained using kneading devices such as a single-screw extruder, twin-screw extruder, multi-screw extruder, Banbury mixer, pressure kneader, rotating roll, and internal mixer. Among these, a twin-screw extruder is more preferred because of its excellent dispersibility and continuous productivity.

[0051] When kneading is performed using a twin-screw extruder, the screw rotation speed is not particularly limited, but is preferably 50 rpm to 3000 rpm, more preferably 300 rpm to 3000 rpm. A screw rotation speed of 50 rpm or more is preferred because the dispersibility of the mixed components is improved and the resulting resin has excellent physical properties, while a screw rotation speed of 3000 rpm or less is preferred because the resin does not deteriorate due to excessive shear heat generation, and the resulting resin has excellent physical properties.

[0052] When an extruder is used in the kneading step, a resin composition kneaded in the extruder, preferably a resin composition kneaded under the high-speed shear conditions of 50 rpm to 3000 rpm, can be used as a raw material. In addition, a molded article obtained by extrusion molding in the extruder as is can be used as a molded product.

[0053] Furthermore, the recycled polyethylene pellets of the present invention may contain antistatic agents, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antioxidants, antiblocking agents, flow improvers, mold release agents, flame retardants, colorants, inorganic neutralizing agents, hydrochloric acid absorbers, filler conductive agents, chain extenders, hydrolysis inhibitors, and the like, as long as the effects of the present invention are not impaired. [Example]

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. All parts and percentages are based on weight unless otherwise specified. The evaluation methods used in the examples and comparative examples are as follows.

[0055] <Differential scanning calorimetry> Using a differential scanning calorimeter (DSC) (DSC6220, manufactured by SII Nanotechnology, Inc.), the sample was heated from 0°C to 230°C at a rate of 10°C / min (first scan), and the endothermic peak of the first scan was measured. The sample weight of the stretched polyethylene film for lamination was 6 mg.

[0056] <Melt mass flow rate> Measurement was carried out using a melt indexer (manufactured by Takara Kogyo Co., Ltd.) based on JIS K6924-1 (under conditions of 190°C and a load of 2160 g).

[0057] <density> Measurements were made in accordance with JIS K6922-1 (1997).

[0058] <Molecular weight> The molecular weight was measured using a GPC system (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 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 with a known molecular weight. 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.

[0059] <Long chain branching> The number of long chain branches per 1000 carbon atoms was determined by measuring the carbon nuclear magnetic resonance (C-NMR) spectrum of the polymer using a Bruker AVANCE600 nuclear magnetic resonance spectrometer, and calculating the number of long chain branches per 1000 carbon atoms in the polymer using the following calculation method. The measurement temperature was set to 130°C, and a mixed solution of 1,2-dichlorobenzene / 1,2-dichlorobenzene-d4 = 75 / 25 (volume ratio) was used as the solvent.

[0060] <How to calculate the number of long chain branches (LCB)> In an NMR spectrum processed with a Gaussian window function, the sum of the peak areas of all peaks with peak tops between 5 and 50 ppm was set to 1000, and the number of long-chain branches (the number of branches with 7 or more carbon atoms) was determined from the peak area of ​​the peak derived from a methine carbon bonded to a branch with 7 or more carbon atoms. Under these measurement conditions, the number of long-chain branches (the number of branches with 7 or more carbon atoms) was determined from the peak area of ​​the peak with its top near 38.22 to 38.27 ppm. The peak area of ​​the peak was defined as the signal area ranging from the chemical shift of the valley between the adjacent peak on the high magnetic field side to the chemical shift of the valley between the adjacent peak on the low magnetic field side. Under these measurement conditions, the peak derived from a methine carbon bonded to a hexyl branch was at 38.21 ppm in the measurement of an ethylene-1-octene copolymer.

[0061] <Heat seal appearance> The laminate 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 0.3 MPa, and a sealing time of 8 seconds, and then air-cooled, and the appearance of the laminate films was evaluated. Laminate films with significant shrinkage and poor appearance were marked with "x", and films with minimal shrinkage and good appearance were marked with "o".

[0062] <Recyclability> The stretched polyethylene film for lamination and the ethylene polymer film obtained in the examples were pulverized and melt-kneaded using a twin-screw extruder (manufactured by Technovel, product name ULTnano25TW) with a screw diameter of 25 mm at a resin temperature of 160°C and a screw rotation speed of 300 rpm to obtain strands. The smoothness of the obtained strands was evaluated, and smooth strands were considered to have excellent recyclability.

[0063] [Example 1] [Preparation of organically modified clay] A 1-liter flask was charged with 300 ml of industrial alcohol (Equinene F-3, manufactured by Japan Alcohol Sales Co., Ltd.) and 300 ml of distilled water. 15.0 g of concentrated hydrochloric acid and 63.7 g (120 mmol) of dioleylmethylamine ((C18H35)2(CH3)N, manufactured by Lion Specialty Chemicals Co., Ltd., product name Lipomin MO) were added, heated to 45°C, and 100 g of synthetic hectorite (Laponite RD, manufactured by BYK) was dispersed in the flask. The mixture was then heated to 60°C and stirred for 1 hour while maintaining the temperature. The resulting 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.

[0064] [Preparation of polymerization catalyst] After replacing the air in a 300 mL flask equipped with a thermometer and reflux condenser with nitrogen, 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, and 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 (solids content: 12.0 wt%).

[0065] [Production of polyethylene powder (A1)] A 2-L autoclave was charged with 1.2 L of hexane, 1.0 mL of 20% triisobutylaluminum, and 200 mg (corresponding to 24 mg of solids) of the catalyst suspension obtained in [Preparation of polymerization catalyst], and after heating to 85°C, an ethylene / hydrogen mixed gas was continuously fed 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 powder (A1).

[0066] The resulting polyethylene powder (A1) 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%, and a density of 950 kg / m 3 It was.

[0067] The obtained polyethylene powder (A1) was melt-kneaded using a twin-screw extruder (manufactured by Technovel, trade name ULTnano25TW) with a screw diameter of 25 mm at a resin temperature of 160°C and a screw rotation speed of 300 rpm to obtain polyethylene pellets (A1).

[0068] Polyethylene pellets (A1) were compression molded using a compression molding machine AWFA.50 (manufactured by Shinto Metal Industry Co., Ltd.) and a mold of 150 mm x 150 mm x 0.2 mm under the following conditions: heating temperature 200°C, cooling temperature 25°C, primary pressure 0.1 MPa x 3 minutes, secondary pressure 10 MPa x 3 minutes, and cooling pressure 10 MPa x 3 minutes, to produce a sheet with a thickness of 0.2 mm.

[0069] The obtained sheet was heated in the compression molding machine at a temperature of 140°C and a pressure of 0.1 MPa for 3 minutes, and then roll-formed by passing it through an 8-inch test roll (manufactured by Kansai Roll Co., Ltd.) 10 times at a roll temperature of 130°C, a rotation speed of 20 rpm, and a roll clearance of 0.1 mm to obtain a stretched polyethylene film for lamination. Differential scanning calorimetry was performed using the obtained stretched polyethylene film for lamination.

[0070] In addition, stretched polyethylene film for lamination and ethylene-based polymer film, ethylene-1-hexene copolymer (manufactured by Tosoh Corporation, trade name "Nipolon ZZF230-1", MFR: 2g / 10min, density: 920kg / m) 3 The laminated film was then bonded to a 50 μm-thick ethylene-1-hexene copolymer film obtained by film molding using an inflation molding machine (Placo Co., Ltd.) using a urethane adhesive (a mixture of Mitsui Chemicals' Takelac A3210 and Takenate A3072). The heat-sealed appearance of the resulting laminated film was evaluated. The evaluation results are shown in Table 1.

[0071] Furthermore, the recyclability was evaluated using 20% ​​by weight of stretched polyethylene film for lamination and 80% by weight of the above ethylene-1-hexene copolymer film.

[0072] [Example 2] Polyethylene pellets (A2) were obtained in the same manner as in Example 1, except that 50 ppm of organic peroxide (Perhexa C, manufactured by NOF Corporation) was added to the polyethylene powder (A1). Using the polyethylene pellets (A2), a stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0073] [Example 3] A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 2, except that the temperature of the sheet fed to the 8-inch test roll was 120° C. The evaluation results are shown in Table 1.

[0074] [Example 4] [Preparation of denatured clay] A 1-liter flask was charged with 300 mL of industrial alcohol (trade name: Equinene F-3, manufactured by Japan Alcohol Sales Co., Ltd.) and 300 mL of distilled water. 18.8 g of concentrated hydrochloric acid and 49.1 g (120 mmol) of dimethylhexacosylamine (MeN(C26H53), synthesized by conventional methods) were added, and the mixture was heated to 45 ° C. to disperse 100 g of synthetic hectorite (trade name: Laponite RDS, manufactured by Rockwood Additives). The mixture was then heated to 60 ° C. and stirred for 1 hour while maintaining the 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 140 g of organically modified clay. This organically modified clay was then jet-milled to a median diameter of 14 μm.

[0075] [Preparation of polymerization catalyst] After replacing the air in a 300 mL flask equipped with a thermometer and reflux condenser with nitrogen, 25.0 g of the organically modified clay obtained in [Preparation of Modified Clay] and 108 mL of hexane were added, followed by 0.4406 g of dimethylsilylene(cyclopentadienyl)(2,4,7-trimethyl-1-indenyl)zirconium dichloride and 142 mL of 20% triisobutylaluminum, and stirring for 3 hours at 60°C. After cooling to 45°C, the supernatant was removed and washed five times with 200 mL of hexane, and 200 mL of hexane was added to obtain a catalyst suspension (solids content: 12.0 wt%).

[0076] [Production of ethylene-α-olefin copolymer (B)] A 2-L autoclave was charged with 1.2 L of hexane, 1.0 mL of 20% triisobutylaluminum, and 75 mg (equivalent to 9.0 mg of solids) of the catalyst suspension obtained in [Preparation of Polymerization Catalyst]. After heating to 80°C, 8.3 g of 1-butene was added, and an ethylene / hydrogen mixed gas was continuously fed so that the partial pressure reached 0.85 MPa (hydrogen concentration in the ethylene / hydrogen mixed gas: 850 ppm). After 90 minutes, the pressure was released, and the slurry was filtered and dried to obtain an ethylene-1-butene copolymer powder. The density of the resulting polymer was 941 kg / m 3 The number of long chain branches was 0.30 per 1000 carbon atoms in the main chain.

[0077] A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 2, except that polyethylene powder (A3) consisting of 95% by weight of polyethylene powder (A) and 5% by weight of ethylene-1-butene copolymer powder as the ethylene-α-olefin copolymer (B) was used instead of polyethylene powder (A). The evaluation results are shown in Table 1.

[0078] [Comparative Example 1] Instead of the polyethylene pellets (A1), polyethylene pellets (A4) (manufactured by Tosoh Corporation, Nipolonhard 5700, density 954 kg / m) with a weight average molecular weight of 122,000 and a proportion of components with a molecular weight of 10,000 or less of 10.2% were used. 3 A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 1, except that the oriented polyethylene film for lamination was used. The evaluation results are shown in Table 1, and the heat resistance of the stretched polyethylene film for lamination was poor.

[0079] Comparative Example 2 Instead of the polyethylene pellets (A), polyethylene pellets (A5) (manufactured by Tosoh Corporation, Nipolonhard 7300A, density 952 kg / m) with a weight average molecular weight of 250,000 and a proportion of components with a molecular weight of 10,000 or less of 26.1% were used. 3A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 1, except that the oriented polyethylene film for lamination was used. The evaluation results are shown in Table 1, and the heat resistance of the stretched polyethylene film for lamination was poor.

[0080] Comparative Example 3 Instead of polyethylene powder (A1), a weight average molecular weight of 2 million, a molecular weight of 10,000 or less of 0%, and a density of 938 kg / m 3 A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 1, except that the ultra-high molecular weight polyethylene powder (A6) was used. The evaluation results are shown in Table 1, and the recyclability of the laminate film was poor.

[0081] Comparative Example 4 A stretched polyethylene film for lamination and a laminate film were obtained in the same manner as in Example 1, except that a biaxial stretching device (manufactured by Toyo Seiki Seisakusho, Ltd., product name: EX10-B) was used to tenter stretch the film to a stretching ratio of 4 at 130°C. The evaluation results are shown in Table 1, and the heat resistance of the stretched polyethylene film for lamination was poor.

[0082] [Table 1]

Claims

1. The weight average molecular weight (Mw) measured by gel permeation chromatography is 70,000 to 150,000, and the proportion of molecular weights of 10,000 or less is 6% by weight or less. The density measured according to JIS K6922-1 (1997) is 945 to 980 kg / m ３ and in an endothermic curve measured by differential scanning calorimetry, all peaks, including one peak, or at least a main peak, are present in the range of 135°C or higher.

2. 2. The stretched polyethylene film for lamination according to claim 1, wherein the polyethylene (A) contains 5 to 100 ppm of organic peroxides and their decomposition products.

3. 3. The stretched polyethylene film for lamination according to claim 1, wherein the polyethylene composition comprises 90 to 99.99% by weight of polyethylene (A) and 0.01 to 10% by weight of an ethylene-α-olefin copolymer (B) having 0.15 or more long chain branches per 1,000 carbon atoms in the main chain in a fraction having an Mn of 100,000 or more when fractionated by molecular weight.

4. The stretched polyethylene film for lamination according to any one of claims 1 to 3 has a density of 880 to 940 kg / m on at least one surface thereof. ３ A laminate film having an ethylene polymer film formed thereon.

5. A method for producing a biaxially oriented film, comprising further stretching the oriented polyethylene film for lamination according to any one of claims 1 to 3 in the transverse direction.

6. A recycled polyethylene pellet comprising the film of claims 1 to 4.

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