Stretched polyethylene film for lamination

Abstract

To provide a polyethylene laminate that is highly recyclable, has excellent physical properties such as rigidity, strength, and impact resistance, and is excellent in heat sealability and transparency.SOLUTION: A stretched polyethylene film for lamination is composed of a polyethylene composition (X) that contains 90-99.5 wt.% of a polyethylene (A) having weight average molecular weight (Mw), measured by gel permeation chromatography, of 90,000-250,000 and density, measured by JIS K6922-1 (1997), of 945-980 kg / m3 and 0.5-10 wt.% of a propylene polymer (B) having lower viscosity than that of the polyethylene (A).SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

[0003] However, polyethylene films have low rigidity, impact resistance, heat resistance, etc., and there are also applications where they cannot be used alone. To solve such problems, laminated films obtained by laminating a polyethylene film and other resin films (for example, polypropylene films, polyester films, polyamide films) are widely used as packaging materials (see, for example, Patent Document 1).

[0004] On the other hand, in recent years, social problems such as waste plastics have attracted attention, and with the increasing demand for building a recycling-oriented society, improvement of the recyclability of packaging materials is required. Packaging materials combining different types of material films as described above have problems such as being difficult to recycle by material recycling, chemical recycling, etc. In contrast, as packaging materials composed of the same type of resin material, packaging materials formed by laminating a stretched polyethylene film and an unstretched polyethylene film have been proposed (see, for example, Patent Documents 2 and 3). The stretched polyethylene film is used to supplement the mechanical properties of the unstretched polyethylene film and to suppress the adhesion of resin to the sealing bar when heat-sealed. However, even this stretched polyethylene film does not have mechanical properties as good as those of biaxially stretched polyamide films and biaxially stretched polyester films, and particularly, the shrinkage of the heat-sealed portion is severe, so it is necessary to lower the heat-sealing temperature, and there is a possibility that the heat-sealing strength may be insufficient.

[0005] Furthermore, ultra-high molecular weight polyethylene film has been proposed as a polyethylene film with excellent rigidity, heat resistance, and strength (see, for example, Patent Document 4). However, ultra-high molecular weight polyethylene film has poor melt-mixability with general polyethylene, and when subjected to material recycling, dispersion and melting irregularities occur, which significantly impairs the quality of the recycled resin. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-104525 [Patent Document 2] Japanese Patent Publication No. 2019-171860 [Patent Document 3] Japanese Patent Publication No. 2019-529165 [Patent Document 4] Japanese Patent Publication No. 1994-262679 [Overview of the project] [Problems that the invention aims to solve]

[0007] This invention was made to solve the above-mentioned problems, and its objective is to provide a stretched polyethylene film for lamination that is excellent in recyclability and heat resistance, and also has good transparency. [Means for solving the problem]

[0008] As a result of diligent research to solve the aforementioned problems, the inventors discovered that a specific stretched polyethylene film exhibits excellent recyclability, heat resistance, and transparency, and thus completed the present invention.

[0009] In other words, the various embodiments of the present invention are as follows [1] to

[10] . [1] A stretched polyethylene film for lamination comprising a polyethylene composition (X) containing 90-99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000-250,000 as measured by gel permeation chromatography and a density of 945-980 kg / m3 as measured by JIS K6922-1 (1997), and 0.5-10% by weight of a propylene polymer (B) with a lower viscosity than polyethylene (A). [2] The stretched polyethylene film for lamination described in [1] above, wherein polyethylene (A) has a molecular weight of 10,000 or less, as measured by gel permeation chromatography, of 8% by weight or less. [3] The stretched polyethylene film for lamination according to [1] or [2] above, wherein the melting point of the propylene polymer (B) is 20°C or more higher than that of polyethylene (A). [4] A stretched polyethylene film for lamination according to any one of [1] to [3] above, wherein a propylene polymer (B) is dispersed in a continuous phase of polyethylene (A), and the ratio of the major axis to the minor axis of the dispersed phase (aspect ratio) is 3 or more. [5] A stretched polyethylene film for lamination according to any of [1] to [4] above, wherein polyethylene (A) contains 5 to 100 ppm of organic peroxides and their decomposition products. [6] A stretched polyethylene film for lamination according to any one of [1] to [5] above, wherein the polyethylene composition (X) further comprises 0.01 to 10 parts by weight of an ethylene-α-olefin copolymer (C) having 0.15 or more long-chain branches per 1,000 carbon atoms in the fraction having a molecular weight of 100,000 or more after molecular weight fractionation. [7] A laminate film having an ethylene polymer film with a density of 880 to 940 kg / m3 on at least one side of the stretched polyethylene film for lamination described in any of [1] to [6] above. [8] A method for producing a stretched polyethylene film for lamination according to any of [1] to [6] above, comprising the following steps (1) and (2). (1) A process to produce a stretchable polyethylene film by extruding a polyethylene composition (X) containing 90% to 99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000 to 250,000 as measured by gel permeation chromatography and a density of 945 to 980 kg / m3 as measured by JIS K6922-1 (1997), and 0.5% to 10% by weight of a propylene polymer (B) with a lower viscosity than polyethylene (A), under conditions where the extrusion temperature is above the melting point of the propylene polymer (B) and the ratio of die lip clearance (L) to film thickness (T) (L / T) is 8 or more. (2) A process to produce stretched polyethylene film for lamination by stretching the stretchable polyethylene film produced in step (1) by 2 to 10 times in the mechanical direction of the film at a temperature from 110°C to below the melting point of the propylene polymer (B). [9] A method for producing a stretched polyethylene film for lamination according to [8] above, further comprising the following step (3). (3) A step of further stretching the stretched polyethylene film for lamination manufactured in step (2) in a direction perpendicular to the direction of the machine.

[10] Recycled polyethylene pellets obtained by melt-molding a stretched polyethylene film for lamination as described in any of [1] to [6] above. [Effects of the Invention]

[0010] One embodiment of the present invention, a stretched polyethylene film for lamination, has high heat resistance and is useful as a base material for laminate films used in packaging for food, beverages, pharmaceuticals, etc. Furthermore, since the resulting laminate film is composed mostly of polyethylene-based materials, it offers excellent recyclability and reduces environmental impact.

[0011] According to the present invention, a laminate film with excellent heat resistance, resulting in superior film appearance and heat sealability, can be provided. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below.

[0013] One embodiment of the present invention is a stretched polyethylene film for lamination, comprising a polyethylene composition (X) containing 90% to 99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000 to 250,000 as measured by gel permeation chromatography and a density of 945 to 980 kg / m3 as measured by JIS K6922-1 (1997), and 0.5% to 10% by weight of a propylene-based polymer (B) with a lower viscosity than polyethylene (A).

[0014] Polyethylene (A) has a weight-average molecular weight (Mw) of 90,000 to 250,000, preferably 100,000 to 200,000, and more preferably 100,000 to 150,000, as measured by gel permeation chromatography. If the Mw is less than 90,000, it is undesirable because the stretchability deteriorates, and if the Mw exceeds 250,000, it is undesirable because the melt extrudeability in material recycling is poor and the performance of the resulting recycled resin deteriorates.

[0015] Furthermore, it is preferable that polyethylene (A) has a molecular weight of 10,000 or less, measured by gel permeation chromatography, that the proportion of such molecules is preferably 8% by weight or less, more preferably 6% by weight or less, and particularly preferably 4% by weight or less, because this improves the heat resistance of the stretched film and improves the heat-seal appearance of the laminate film. This is presumed to be because, during the stretching process, molecules with low molecular weight relax the molecular chains, resulting in insufficient orientation of the polyethylene crystals.

[0016] Furthermore, polyethylene (A) has a density of 945-980 kg / m³ as measured according to JIS K6922-1 (1997). A density of less than 945 kg / m³ is undesirable because it worsens the heat resistance of stretched polyethylene film for lamination, and polyethylene with a density exceeding 980 kg / m³ is difficult to produce industrially.

[0017] Such polyethylene (A) can be obtained by homopolymerizing ethylene or copolymerizing ethylene with a small amount of α-olefin. For the polymerization, generally, a Ziegler catalyst composed of a solid catalyst component containing magnesium and titanium and an organoaluminum compound, a metallocene catalyst composed of an organotransition metal compound containing a cyclopentadienyl derivative and a compound and / or an organometallic compound that reacts with it to form an ionic complex, a vanadium-based catalyst, etc. can be used. Metallocene catalysts and vanadium-based catalysts are preferred because they are easy to control the proportion of a molecular weight of 10,000 or less. For example, it can be produced by production methods such as a slurry method, a solution method, a gas phase method, etc. Further, the production method of polyethylene (A) is not particularly limited, but a slurry method or a solution method is preferred because it is easy to control the proportion of a molecular weight of 10,000 or less.

[0018] The above-mentioned ethylene and α-olefin are produced from petroleum-derived naphtha, bio-derived naphtha, or naphtha obtained by recycling plastics.

[0019] The propylene-based polymer (B) is not particularly limited as long as it is a polymer containing 50 mol% or more of propylene, and examples thereof include a propylene homopolymer, or a random copolymer, block copolymer, graft copolymer of propylene and an α-olefin other than propylene such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. These propylene-based polymers may be used alone or in combination of two or more.

[0020] Such propylene-based polymers (B) are sold under the trade names Prime Polypro from Prime Polymer Co., Ltd., Polyfine, Novatec PP from Nippon Polypropylene Corporation, Wintec, Noblen, Exlene from Sumitomo Chemical Co., Ltd., Polypropylene, Quoria TM from San Allomer Co., Ltd., etc.

[0021] If the viscosity of the propylene polymer (B) is lower than that of polyethylene (A), the stretchability of the polyethylene film is improved, and a film with excellent transparency can be obtained. When the viscosity of polyethylene (A) is high and the viscosity of the propylene polymer (B) is low, extrusion molding at a temperature above the melting point of the propylene polymer (B) forms a dispersed phase in which the propylene polymer (B) is dispersed in the continuous phase of polyethylene (A), and it becomes easy to increase the ratio of the major axis to the minor axis (aspect ratio) of the dispersed propylene polymer (B) phase. An aspect ratio of 3 or higher is preferable because it provides excellent stretchability and improves the transparency of the stretched polyethylene film.

[0022] The ratio of polyethylene (A) to propylene polymer (B) is preferably 90% to 99.5% by weight for polyethylene (A) and 0.5% to 10% by weight for propylene polymer (B), and more preferably 92% to 99% by weight for polyethylene (A) and 1% to 8% by weight for propylene polymer (B). Most preferably 94% to 98% by weight for polyethylene (A) and 2% to 6% by weight for propylene polymer (B). If polyethylene (A) is less than 90% by weight, the strength of the stretched film for lamination decreases, which is undesirable, and if it exceeds 99.5% by weight, the effect of improving transparency is small, which is also undesirable. The total blending ratio of (A) and (B) should be 100% by weight.

[0023] Polyethylene (A) is preferable because it contains 5 to 100 ppm of organic peroxides and their decomposition products, resulting in a higher peak temperature in the endothermic curve measured by a differential scanning calorimetry device for stretched polyethylene film, and thus a stretched laminate film with further improved heat resistance can be obtained.

[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)hexine-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 hydroxybenzoates 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.

[0025] The polyethylene composition (X) may also contain additives commonly used in polyolefins, such as antioxidants, lubricants, neutralizing agents, anti-blocking agents, surfactants, and slip agents, as needed.

[0026] The polyethylene composition (X) may also contain 0.01 to 10 parts by weight of an ethylene-α-olefin copolymer (C) having 0.15 or more long-chain branches per 1,000 carbon atoms in the fraction with a molecular weight of 100,000 or more after molecular weight fractionation. Adding the ethylene-α-olefin copolymer (C) in this proportion is preferable because it improves the moldability and transparency of the stretched polyethylene film for lamination.

[0027] The above-mentioned ethylene-α-olefin copolymer (C) is produced using a metallocene catalyst. The metallocene catalyst used preferably comprises a metallocene complex, an activating co-catalyst, and, if necessary, an organoaluminum compound, and performs copolymerization of the macromonomer with ethylene and an olefin having 3 to 6 carbon atoms simultaneously with the synthesis of the macromonomer. A macromonomer is an olefin polymer having vinyl groups at its ends, and is an ethylene copolymer having vinyl groups at its ends obtained by copolymerizing ethylene with an olefin having 3 to 6 carbon atoms.

[0028] The thickness of the stretched polyethylene film for lamination is preferably 10 to 200 μm, more preferably 12 to 100 μm, and even more preferably 14 to 50 μm. Within this range, a laminate film with desirable heat seal strength can be obtained.

[0029] The above-mentioned method for manufacturing stretched film for lamination is not particularly limited, and examples include obtaining a stretched film by known extrusion molding methods such as inflation molding or T-die casting, and then stretching it by methods such as the tenter method or roll rolling.

[0030] A method for manufacturing a stretched film for lamination, according to one aspect of the present invention, includes the following steps (1) and (2). (1) A process to produce a stretchable polyethylene film by extruding a polyethylene composition (X) containing 90 to 99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000 to 250,000 as measured by gel permeation chromatography and a density of 945 to 980 kg / m3 as measured by JIS K6922-1 (1997), and 0.5 to 10% by weight of a propylene polymer (B) with a lower viscosity than polyethylene (A), under conditions where the melting point is above that of the propylene polymer (B) and the ratio of die lip clearance (L) to film thickness (T) (L / T) is 8 or more. (2) A process to produce a stretched film for lamination by stretching the stretchable polyethylene film produced in step (1) by 2 to 10 times in the mechanical direction of the film at a temperature from 110°C to below the melting point of the propylene polymer (B).

[0031] In step (1), the stretchable polyethylene film is preferably produced by extruding the polyethylene composition (X) at a temperature above the melting point of the propylene polymer (B) and with a die lip clearance (L) to film thickness (T) ratio (L / T) of 8 or more, because this increases the aspect ratio of the propylene polymer (B) phase. The lip clearance (L) is preferably 1.5 mm to 5 mm, and the thickness of the resulting stretchable film is preferably 0.07 mm to 0.6 mm.

[0032] In step (2), the stretching temperature is preferably between 110°C and below the melting point of the propylene polymer. Below 110°C, the tensile stress of the polyethylene film for stretching may be too high, making stretching impossible. On the other hand, if the temperature exceeds the melting point of the propylene polymer, the aspect ratio of the propylene polymer (B) phase may decrease, potentially worsening the stretchability and transparency.

[0033] Roll rolling is a molding method in which a polyethylene sheet dispensed from a T-die or the like is rolled between two or more rolls to form a film of a predetermined thickness. Suitable roll rolling methods include the polishing roll method used in T-die extrusion molding and calendering. Examples of calendering equipment include two-roll series calenders, three-roll series calenders, four-roll series calenders, S-type calenders, inverted L-type calenders, Z-type calenders, and oblique Z-type calenders.

[0034] The stretching process may be performed once or multiple times, but stretching multiple times is preferable because it improves the strength and heat resistance of the stretched polyethylene film for lamination.

[0035] In a method for manufacturing a stretched film for lamination according to one aspect of the present invention, the following step (3) may be further included in addition to the above steps (1) and (2). (3) A step of further stretching the stretched polyethylene film for lamination manufactured in step (2) in a direction perpendicular to the direction of the machine.

[0036] A biaxially oriented film can be manufactured by further stretching a polyethylene stretched film for lamination in a direction perpendicular to the machine direction. The tenter method is preferred as the method for stretching perpendicular to the machine direction.

[0037] The stretched polyethylene film for lamination described above may be subjected to any appropriate surface treatment to enhance the adhesion of the laminate film. Examples of surface treatments include corona treatment, flame treatment, and plasma treatment.

[0038] Furthermore, the polyethylene stretched film for lamination may be treated with vapor deposition of aluminum, alumina, silicon dioxide, etc., or it 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.

[0039] Furthermore, the polyethylene stretched film for lamination may be obtained by co-extruding a polyethylene composition (X) with an ethylene-vinyl alcohol copolymer or polyamide, or a polyester with a gas barrier resin such as polyvinyl alcohol or polyvinylidene chloride.

[0040] One embodiment of the present invention is a polyethylene stretched film for lamination, which has an ethylene polymer film on at least one side thereof.

[0041] The thickness of the ethylene 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.

[0042] The above-mentioned 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. Of these, high-pressure low-density polyethylene, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid ester copolymer are preferred because they exhibit excellent heat-sealability of the laminate film.

[0043] 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, Philips 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. 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 as ethylene-vinyl acetate copolymer, it is commercially available from Tosoh Corporation under the trade name Ultracene.

[0044] The above-mentioned ethylene-based polymer films are manufactured from petroleum-derived naphtha, bio-derived naphtha, or naphtha obtained from recycled plastics.

[0045] The density of the ethylene polymer is preferably 880-940 kg / m³, more preferably 890-930 kg / m³, and most preferably 895-925 kg / m³. 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).

[0046] 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 1.0 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.

[0047] 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.

[0048] 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.

[0049] 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, and copolymerized 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 versions 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.

[0050] The above-mentioned tackifier is preferably one whose softening point, as measured by the ring-and-sphere method, is 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 less blocking of the film after molding, and the adhesive strength is well maintained in low-temperature environments.

[0051] The tackifiers mentioned above can be commercially available. Specifically, examples of petroleum resins include (product names) 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 KE-311 (manufactured by Arakawa Chemical Industries, Ltd.), etc. Examples of terpene-based resins include YS Resin PX1150, YS Resin PX1150N (both manufactured by Yasuhara Chemical Co., Ltd.), etc.

[0052] The content ratio of the tackifier is preferably 1 to 30 parts by weight, and more preferably 5 to 40 parts by weight, per 100 parts by weight of the ethylene polymer constituting the ethylene polymer film. Within this range, a laminate film with excellent heat sealability can be obtained.

[0053] Other additives include, for example, additives commonly used in polyolefins such as antioxidants, lubricants, neutralizing agents, anti-blocking agents, surfactants, and slip agents; and thermoplastic resins such as other polyolefins.

[0054] The above-mentioned laminate film can be manufactured by laminating an ethylene polymer film onto at least one surface of the above-mentioned stretched polyethylene film for lamination, or onto the adhesive layer surface of a stretched polyethylene film for lamination 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°C to 350°C, and the surface temperature of the cooling roll is preferably in the range of 10°C 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. Furthermore, the amount of ozone gas to be processed is preferably 0.5 mg or more per 1 m2 of film made of the extrusion lamination resin composition extruded from the die.

[0055] 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 / or 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 are available from Tosoh Corporation under the product name Nipponan 3228, and polyethyleneimine-based adhesives are available from Tosoh Corporation under the product name Toyovine.

[0056] The thickness of the adhesive layer is preferably 0.01 to 2.0 μm, 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, 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 adhesion can be obtained.

[0057] Laminated films are highly recyclable because they are mostly composed of polyethylene-based materials. Recycling methods include material recycling, which involves melting and kneading the laminated film to obtain pellets, and chemical recycling, which involves thermally decomposing the laminated film to obtain low-molecular-weight hydrocarbons. Material recycling is particularly preferred due to its low cost and energy consumption.

[0058] There are no particular restrictions on the melt-kneading apparatus for stretched polyethylene film for lamination, as long as the stretched polyethylene film for lamination can be uniformly dispersed, and it can be manufactured using commonly used resin kneading apparatus. For example, recycled pellets can be obtained using kneading apparatus such as a single-screw extruder, twin-screw extruder, multi-screw extruder, Banbury mixer, pressure kneader, rotary roll, or internal mixer. Among these, a twin-screw extruder is more preferable due to its excellent dispersibility and continuous production capabilities.

[0059] When kneading with a twin-screw extruder, the screw rotation speed is not particularly limited, but it is preferable to knead at 50 rpm to 3000 rpm, and more preferably at 300 rpm to 3000 rpm. A screw rotation speed of 50 rpm or higher is preferable because it improves the dispersibility of each mixed component and results in a resin with excellent physical properties. A screw rotation speed of 3000 rpm or lower is also preferable because it prevents deterioration of the resin due to excessive shear heat, resulting in a resin with excellent physical properties.

[0060] When an extruder is used in the kneading process, the resin composition kneaded in the extruder, preferably the resin composition kneaded under the high-speed shearing conditions of 50 rpm to 3000 rpm, can be used as the raw material. Alternatively, the molded body obtained by extruding it directly in the extruder can be used as the molded product.

[0061] Furthermore, recycled polyethylene pellets, which are one embodiment of the present invention, are obtained by melt-molding the above-mentioned stretched polyethylene film for lamination. Recycled polyethylene pellets may also contain antistatic agents, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antioxidants, blocking inhibitors, flow improvers, release agents, flame retardants, colorants, inorganic neutralizing agents, hydrochloric acid absorbers, filler conductive agents, chain length extenders, hydrolysis inhibitors, and the like, to the extent that they do not impair the effects of the present invention. [Examples]

[0062] 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 weight unless otherwise specified. The evaluation methods in the examples and comparative examples are as follows. <Melting point> Measurements were taken in accordance with JIS K7122 (1987). <Viscosity> Using a cone-disk rheometer (manufactured by Rheometrics, product name: SR2000), the storage modulus G' (Pa) and loss modulus G'' (Pa) were determined at a temperature of 190°C and an angular velocity ω = 1 (s-1), and the complex viscosity (η*) was calculated using the following formula.

[0063] η*=(G'2+G''2)1 / 2 / ω <density> Measurements were taken in accordance with JIS K6922-1 (1997). <Molecular weight> Molecular weight was measured using a GPC instrument (HLC-8121GPC / HT, manufactured by Tosoh Corporation) and a column (TSKgel GMHhr-H(20)HT, manufactured by Tosoh Corporation), 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 chromatograms obtained from the measurements, the weight-average molecular weight Mw and the percentage of components with a molecular weight of 10,000 or less were calculated. <Long chain branching> The number of long-chain branches per 1000 carbon atoms was determined by measuring the carbon nuclear magnetic resonance (13C-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 method described below. The measurement temperature was set to 130°C, and a mixture of 1,2-dichlorobenzene / 1,2-dichlorobenzene-d4 = 75 / 25 (volume ratio) was used as the solvent. <Method for calculating the number of long chain branches (LCBs)> In NMR spectra 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. The number of long-chain branches (number of branches with 7 or more carbon atoms) was determined from the peak area of ​​the peak originating from the methine carbon to which branches with 7 or more carbon atoms are bonded. Under these measurement conditions, the number of long-chain branches (number of branches with 7 or more carbon atoms) was determined from the peak area of ​​the peak with peak tops around 38.22 to 38.27 ppm. The peak area of ​​the said peak was calculated by taking the valley between it and adjacent peaks on the high-field side. The signal area was defined as the area from the chemical shift to the chemical shift of the trough between adjacent peaks on the low magnetic field side. Under these measurement conditions, the peak top position of the peak originating from the methine carbon bonded to the hexyl branch was 38.21 ppm in the measurement of ethylene-1-octene copolymer. <Hayes> The haze of stretched polyethylene film for lamination was measured using a haze meter (NDH-300A, manufactured by Nippon Denshoku Industries Co., Ltd.). <Aspect Ratio> The stretched polyethylene film obtained in the example was cooled with liquid nitrogen, then fractured in the direction of film flow. The cross-section was observed with a scanning electron microscope (Keyence Corporation, product name VE-9800), and the major and minor axes of the dispersed phase were measured. <Heat seal appearance> The laminate films obtained in the examples were heat-sealed using a heat seal tester TP-701B (manufactured by Tester Sangyo Co., Ltd.) at a set temperature of 130°C, heating on both sides, an air pressure of 0.2 MPa, and a sealing time of 1 second. After air cooling, the shrinkage rate of the heat-sealed laminate film was evaluated visually. The shrinkage rate was calculated as ((film width before heat sealing mm) - (film width after heat sealing mm)) ÷ (film width before heat sealing mm) × 100. A smaller shrinkage rate was considered to indicate a superior heat-sealed appearance. <Recyclability> The stretched polyethylene film and ethylene polymer film for lamination obtained in the examples were crushed and melt-kneaded using a twin-screw extruder with a screw diameter of 25 mm (Technovel product name ULTnano25TW) at a resin temperature of 160°C and a screw rotation speed of 300 rpm to obtain strands. The surface of the obtained strands was visually inspected, and if no protruding foreign matter was observed, it was judged to have excellent recyclability (○), and if there were a significant number of protruding foreign matter, it was judged to have poor recyclability (×). If a small amount of such foreign matter was observed, it was judged (△). [Example 1] [Preparation of organically modified clay] 300 ml of industrial alcohol (manufactured by Nippon Alcohol Sales Co., Ltd., product name: Ekinen F-3) and 300 ml of distilled water were placed in a 1 liter flask. 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 M2O) were added. After heating to 45°C, 100 g of synthetic hectorite (manufactured by BYK, product name: Laponite RD) was dispersed in the mixture. The temperature was then raised to 60°C and the mixture was 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 130 g of organically modified clay. This organically modified clay was pulverized using a jet mill to a median diameter of 15 μm. [Preparation of polymerization catalyst] After purging a 300 mL flask equipped with a thermometer and reflux tubing 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 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%). [Manufacturing of polyethylene powder (A1)] 1.2 L of hexane and 1.0 mL of 20% triisobutylaluminum were added to a 2 L autoclave, along with 200 mg (equivalent to 24 mg of solids) of the catalyst suspension obtained in [Preparation of Polymerization Catalyst]. The temperature was raised to 85°C, and 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 (A1). The obtained polyethylene powder (A1) had a weight-average molecular weight of 111,000, a content of 3.4% by weight of components with a molecular weight of 10,000 or less, and a density of 950 kg / m3. [Manufacturing of polyethylene composition (X1)] 50 ppm of organic peroxide (Perhexa C, manufactured by NOF Corporation) was added to the obtained polyethylene powder (A1), and the mixture was melt-kneaded using a twin-screw extruder with a screw diameter of 25 mm (Technovel Co., Ltd., product name ULTnano25TW) at a resin temperature of 150°C and a screw rotation speed of 100 rpm to obtain polyethylene pellets (A1).

[0064] The obtained polyethylene pellets (A1) were mixed with 97% by weight of Novatec FB3B (hereinafter sometimes referred to as PP-1), a propylene polymer manufactured by Nippon Polypropylene, as a 97% by weight. The mixture was then melt-kneaded using a twin-screw extruder (Technovel, product name ULTnano25TW) with a screw diameter of 25 mm at a resin temperature of 220°C and a screw rotation speed of 300 rpm to obtain polyethylene composition pellets (X1). [Manufacturing of stretched polyethylene film] Next, polyethylene composition pellets (X1) were formed into a film using an inflation molding machine equipped with an extruder having a screw diameter of 50 mm. The extrusion temperature was 220°C, the die lip clearance (L) was 3 mm, and the thickness of the resulting stretchable polyethylene film was 100 μm.

[0065] The obtained polyethylene film was uniaxially stretched at 120°C using a tenter stretcher (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name EX10-B) to a stretching ratio of 3 times, thereby obtaining a stretched polyethylene film for lamination. [Manufacturing and evaluation of laminate films] Furthermore, a laminate film was obtained by bonding a stretched polyethylene film for lamination with a 50 μm thick ethylene-1-hexene copolymer film, which was obtained by film forming using an inflation molding machine (Placo Co., Ltd.) with ethylene-1-hexene copolymer (manufactured by Tosoh Corporation, trade name "Nipolon ZZF230-1", MFR: 2 g / 10 min, density: 920 kg / m3) as an ethylene-based polymer film, via a urethane adhesive (a mixture of trade names "Takelac A3210" and "Takenate A3072" manufactured by Mitsui Chemicals, Ltd.). The heat-sealed appearance of the obtained laminate film was evaluated. The evaluation results are shown in Table 1.

[0066] Furthermore, the recyclability was evaluated using 20% ​​by weight of stretched polyethylene film for lamination and 80% by weight of the above-mentioned ethylene-1-hexene copolymer film. [Example 2] A laminate film was obtained in the same manner as in Example 1, except that polyethylene pellets (A1) accounted for 93% by weight and PP-1 as a propylene polymer accounted for 7% by weight. The evaluation results are shown in Table 1. [Example 3] A laminate film was obtained in the same manner as in Example 1, except that an organic peroxide was not added to the polyethylene powder (A1). The evaluation results are shown in Table 1. [Example 4] [Preparation of modified clay] 300 mL of industrial alcohol (Ekinen F-3, manufactured by Nippon Alcohol Sales Co., Ltd.) and 300 mL of distilled water were placed in a 1 L flask. 18.8 g of concentrated hydrochloric acid and 49.1 g (120 mmol) of dimethylhexacosylamine (Me2N(C26H53), synthesized by conventional methods) were added. The mixture was heated to 45°C to disperse 100 g of synthetic hectorite (Laponite RDS, manufactured by Rockwood Additives). 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 using a jet mill to a median diameter of 14 μm. [Preparation of polymerization catalyst] After purging a 300 mL flask equipped with a thermometer and reflux tubing with nitrogen, 25.0 g of the organically modified clay obtained in [Preparation of Modified Clay] and 108 mL of hexane were added. Then, 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). [Production of ethylene-α-olefin copolymer (C)] In a 2 L autoclave, 1.2 L of hexane and 1.0 mL of 20% triisobutylaluminum were added, along with 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 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 dried to obtain 58.5 g of ethylene-1-butene copolymer powder. The density of the obtained polymer was 941 kg / m³. The number of long-chain branches was 0.30 per 1000 carbon atoms in the main chain.

[0067] To 100 parts by weight of the polyethylene composition pellet (X1) used in Example 1, 5 parts by weight of ethylene-1-butene copolymer powder was added. Using a twin-screw extruder with a screw diameter of 25 mm (Technovel product name ULTnano25TW), the mixture was melt-kneaded at a resin temperature of 150°C and a screw rotation speed of 100 rpm to obtain polyethylene composition pellet (X2). Film, stretching, and lamination molding using polyethylene composition pellet (X2) were carried out in the same manner as in Example 1 to obtain a laminated film. The evaluation results are shown in Table 1. [Example 5] A laminate film was obtained in the same manner as in Example 1, except that the hydrogen concentration in the polyethylene powder production was adjusted to obtain polyethylene powder (A2) with a weight-average molecular weight of 131,000, a component content of 1.5% by weight with a molecular weight of 10,000 or less, and a density of 950 kg / m3. The evaluation results are shown in Table 1. [Example 6] A laminate film was obtained in the same manner as in Example 1, except that polyethylene pellets (manufactured by Tosoh Corporation, trade name Nipolon Hard 5700, hereinafter sometimes referred to as A3) with a weight-average molecular weight of 122,000, a component content of 10.2% by weight with a molecular weight of 10,000 or less, and a density of 954 kg / m3 were used instead of polyethylene pellets (A1). [Comparative Example 1] A laminate film was obtained in the same manner as in Example 1, except that polyethylene pellets (A1) were used at 100% by weight instead of polyethylene composition pellets (X1), which consisted of 97% by weight polyethylene pellets (A1) and 3% by weight propylene polymer (PP-1). The evaluation results are shown in Table 1, but the seal appearance and transparency were inferior. [Comparative Example 2] A laminate film was obtained in the same manner as in Example 1, except that polyethylene pellets (manufactured by Tosoh Corporation, trade name Nipolon Hard 7300A, sometimes referred to as A4 below) with a weight-average molecular weight of 260,000, a component content of 26.1% with a molecular weight of 10,000 or less, and a density of 952 kg / m3 were used instead of polyethylene pellets (A1). The evaluation results are shown in Table 1, but the seal appearance was significantly inferior. [Comparative Example 3] A laminate film was obtained in the same manner as in Example 1, except that polyethylene pellets (manufactured by Tosoh Corporation, trade name Nipolon Hard 4000, sometimes referred to as A5 below) with a weight-average molecular weight of 88,000, a component content of 18.7% by weight with a molecular weight of 10,000 or less, and a density of 960 kg / m3 were used instead of polyethylene pellets (A1). The evaluation results are shown in Table 1, but the stretchability was poor and a homogeneous film could not be obtained. [Comparative Example 4] A laminate film was obtained in the same manner as in Example 1, except that Nippon Polypropylene Co., Ltd.'s product name EG6D (hereinafter sometimes referred to as PP-2) was used as the propylene polymer instead of Nippon Polypropylene Co., Ltd.'s product name Novatec FB3B (hereinafter sometimes referred to as PP-1). The evaluation results are shown in Table 1, but the transparency and seal appearance were insufficient due to the high viscosity of PP and the small aspect ratio. [Comparative Example 5] A laminate film was obtained in the same manner as in Example 1, except that polyethylene composition pellets (X1) consisting of 97% polyethylene pellets (A1) and 3% propylene polymer (PP-1) were replaced with polyethylene composition pellets consisting of 88% polyethylene pellets (A1) and 12% propylene polymer (PP-1) by weight. The evaluation results are shown in Table 1, but the seal appearance and transparency were inferior.

[0068] [Table 1]

Claims

1. A stretched polyethylene film for lamination comprising a polyethylene composition (X) containing 90 to 99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000 to 250,000 as measured by gel permeation chromatography and a density of 945 to 980 kg / m³ as measured by JIS K6922-1 (1997), and 0.5 to 10% by weight of a propylene polymer (B) with a lower viscosity than polyethylene (A).

2. The stretched polyethylene film for lamination according to claim 1, wherein the polyethylene (A) has a molecular weight of 10,000 or less, as measured by gel permeation chromatography, of 8% by weight or less.

3. The stretched polyethylene film for lamination according to claim 1, wherein the melting point of the propylene polymer (B) is 20°C or more higher than that of polyethylene (A).

4. The stretched polyethylene film for lamination according to claim 1, wherein a propylene polymer (B) is dispersed in a continuous phase of polyethylene (A) to form a dispersed phase, and the ratio of the major axis to the minor axis (aspect ratio) of the dispersed phase is 3 or more.

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

6. The stretched polyethylene film for lamination according to claim 1, wherein the polyethylene composition (X) further comprises 0.01 to 10 parts by weight of an ethylene-α-olefin copolymer (C) having 0.15 or more long-chain branches per 1,000 carbon atoms in the fraction having a molecular weight of 100,000 or more after molecular weight fractionation.

7. A laminate film comprising an ethylene polymer film having a density of 880 to 940 kg / m³ on at least one side of a stretched polyethylene film for lamination according to any one of claims 1 to 6.

8. A method for producing a stretched polyethylene film for lamination according to any one of claims 1 to 6, comprising the following steps (1) and (2). (1) A step to produce a stretchable polyethylene film by extruding a polyethylene composition (X) containing 90% to 99.5% by weight of polyethylene (A), which has a weight-average molecular weight (Mw) of 90,000 to 250,000 as measured by gel permeation chromatography and a density of 945 to 980 kg / m³ as measured by JIS K6922-1 (1997), and 0.5% to 10% by weight of a propylene polymer (B) with lower viscosity than polyethylene (A), under conditions where the melting point is above that of the propylene polymer (B) and the ratio of die lip clearance (L) to film thickness (T) (L / T) is 8 or more. (2) A step to produce stretched polyethylene film for lamination by stretching the stretchable polyethylene film produced in step (1) by 2 to 10 times in the mechanical direction of the film at a temperature from 110°C to below the melting point of the propylene polymer (B).

9. A method for producing a stretched polyethylene film for lamination according to claim 8, further comprising the following step (3). (3) A step of further stretching the stretched polyethylene film for lamination manufactured in step (2) in a direction perpendicular to the direction of the machine.

10. A recycled polyethylene pellet obtained by melt-molding a stretched polyethylene film for lamination according to any one of claims 1 to 6.

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