Laminated film

Abstract

To provide a laminate film which can be easily opened without causing lid tearing or the like when opened as a lid member when used as a lid material for a container or the like.SOLUTION: There is provided a laminate film having a heat seal layer and at least one or more support layers, wherein for elongation at break A1 and breaking strength B1 before heat sealing and elongation at break A2 and breaking strength B2 after heat sealing overlap with a polyethylene terephthalate film at a seal temperature of 200°C, a seal pressure of 0.2 MPa and a sealing time of 1 second, followed by peeling off the polyethylene terephthalate film, A1 / A2 is 2.5 or less and B1 / B2 is 3.0 or less in both a longitudinal direction and a width direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a laminated film having excellent openability. [Background technology]

[0002] The primary purpose of packaging is to protect its contents, and it is crucial that it is not easily opened against external forces during transportation and display. On the other hand, it is also required to be easy to open, without the lid tearing or other damage occurring during use.

[0003] In recent years, with the increasing elderly population and the rise of individual meals, there has been a growing demand for convenient, easy-to-open packaging. Various types of easy-to-open packaging have been proposed, and one example is called "Easy Peel," which uses a sealant film that provides opening capabilities. It is widely used as a lid for cup containers for desserts such as jelly, yogurt, and pudding, as well as for rice and prepared foods, and for packs of processed meat products such as ham and bacon.

[0004] To improve the ease of opening of sealant films, a co-extruded multilayer film consisting of a heat-seal layer made by mixing polypropylene resin and polyethylene resin in a specific ratio has been proposed. (See, for example, Patent Documents 1 and 2.) However, even when the co-extruded multilayer films proposed in the aforementioned Patent Documents 1 and 2 were used as sealant films, there were problems such as the opening strength becoming stronger when the sealing conditions changed, making it impossible to open with moderate force, or the lid tearing during opening. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-95162 [Patent Document 2] Japanese Patent Publication No. 2019-209541 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a laminated film that, when used as a lid material for containers, offers excellent punchability, prevents tearing during opening, and allows for easy opening. [Means for solving the problem]

[0007] To solve the above problems, the present invention is as follows.

[0008] A laminated film having a heat-seal layer and at least one support layer, wherein the elongation at break A1 and tensile strength B1 before heat sealing, and the elongation at break A2 and tensile strength B2 after heat sealing with a polyethylene terephthalate film at a sealing temperature of 200°C, a sealing pressure of 0.2 MPa, and a sealing time of 1 second, and after peeling off the polyethylene terephthalate film, the elongation at break A2 and tensile strength B2 are such that A1 / A2 is 2.5 or less and B1 / B2 is 3.0 or less in both the longitudinal and width directions. [Effects of the Invention]

[0009] The laminated film of the present invention can be used as a lid material to open normally without the lid tearing or other damage occurring during opening, and can be easily opened with moderate force. Furthermore, by laminating at least one layer selected from biaxially oriented polyamide film, biaxially oriented polyester film, printed paper, metal foil, etc., on the support layer side of the laminated film, a packaging body can be obtained that can be used as a lid material to open normally without the lid tearing occurring during opening. [Modes for carrying out the invention]

[0010] The laminated film of the present invention will be described in detail.

[0011] The laminated film of the present invention is a laminated film having a heat-sealable heat-seal layer and one or more support layers. The heat-seal layer is easily openable, and by laminating at least one or more support layers, it can be opened normally without the lid tearing during opening. The laminated film of the present invention has good film-forming properties even with only one support layer, and the lid can be opened normally without tearing during opening. However, by using two support layers, support layer 1 can improve film-forming properties such as increasing the film-forming speed, and support layer 2 can suppress lid tearing when opened when used as a lid material.

[0012] The laminated film of the present invention is a laminated film having a heat-seal layer and at least one support layer, wherein the elongation at break A1 and tensile strength B1 of the laminated film before heat sealing and the elongation at break A2 and tensile strength B2 after heat sealing at 200°C for 1 second are such that A1 / A2 is 2.5 or less and B1 / B2 is 3.0 or less in both the longitudinal and width directions of the laminated film, preferably A1 / A2 is 2.3 or less and B1 / B2 is 2.8 or less, with a lower limit of 1.0 for both.

[0013] In the laminated film of the present invention, by setting the A1 / A2 ratio to 2.5 or less in both the longitudinal and width directions of the film, the film becomes more flexible and the lid does not tear when opened. By setting the B1 / B2 ratio to 3.0 or less in both the longitudinal and width directions of the film, wrinkles do not occur when winding the film during film formation, resulting in good film formation properties.

[0014] The laminated film of the present invention preferably has a heat seal strength of 10 N / 15 mm or more, and more preferably 12 N / 15 mm or more, when the heat seal layer of the laminated film is heat-sealed with a polypropylene sheet at 140°C for 1 second. Having a heat seal strength of 10 N / 15 mm or more when heat-sealed with a polypropylene sheet at 140°C for 1 second results in better heat sealability over a wide temperature range starting from a low heat seal temperature of 140°C, which is preferable because it improves workability during the manufacture of packaging materials and when filling the packaging materials with contents.

[0015] When the heat-sealing layer of the laminated film of the present invention is heat-sealed with a polypropylene sheet at 180°C for 4 seconds and at 1 second, the heat-sealing strength in both cases is preferably in the range of 20 N / 15 mm or more and 28 N / 15 mm or less, and the difference between them is 3.5 N / 15 mm or less.

[0016] By setting the heat-sealing strength at 140°C for 1 second to be 10 N / 15 mm or more, and the heat-sealing strengths at 180°C for 4 seconds and 1 second to be both in the range of 20 N / 15 mm or more and 28 N / 15 mm or less, with the difference being 3.5 N / 15 mm or less, the seal temperature dependency is small, the heat-sealing property is better in a wide temperature range, and the workability during the production of the packaging material and the filling of the contents into the packaging material becomes higher.

[0017] The heat-sealing layer of the laminated film of the present invention preferably consists of a resin composition in which a polyethylene-based resin and a polypropylene-based resin are mixed. Furthermore, a resin composition in which 51% to 80% by mass of the polyethylene-based resin and 20% to 49% by mass of the polypropylene-based resin are mixed is preferable because the seal temperature dependency is small and the heat-sealing property is good in a wide temperature range.

[0018] Examples of the above polyethylene-based resin include at least one or more of high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene·α-olefin random copolymer elastomer, etc. Among them, a mixed resin composition of linear low-density polyethylene and ethylene·α-olefin random copolymer elastomer is preferable.

[0019] The above linear low-density polyethylene has a density of 0.910 to 0.940 g / cm 3 , 3 , and the melt flow rate (hereinafter sometimes abbreviated as MFR) is preferably in the range of 1.0 to 40.0 g / 10 minutes at 190°C. The ethylene·α-olefin random copolymer elastomer has a density of 0.865 to 0.895 g / cm 3 and an MFR in the range of 0.5 to 10.0 g / 10 minutes at 190°C, which is preferable because the miscibility of each is good.

[0020] The polypropylene resin used in the heat-seal layer is preferably an ethylene-propylene random copolymer of propylene and a comonomer. The comonomer can be preferably selected from ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc., and it is preferable that the comonomer content be less than 5% by mass.

[0021] The above-mentioned polypropylene resin preferably includes a polypropylene resin polymerized using a single-site catalyst (metallocene catalyst), as this results in good miscibility with the polyethylene resin, low dependence on sealing temperature, the ability to seal from low temperatures, and good heat sealability over a wide temperature range.

[0022] Polypropylene resins polymerized using single-site catalysts may have a narrower molecular weight distribution, a narrower compositional distribution, and fewer low-regularity components compared to those polymerized using multi-site catalysts (Ziegler-Natta catalysts). As a result, they may exhibit superior low-temperature sealing properties, high rigidity, and high tensile strength and impact resistance.

[0023] The type of single-site catalyst is not particularly limited, but a typical example is a metallocene catalyst. In the production of metallocene polypropylene, it is generally exemplified that (i) a transition metal compound of Group 4 of the periodic table (a so-called metallocene compound) containing a ligand having a cyclopentadienyl skeleton and (ii) a co-catalyst that can be activated into a stable ionic state by reversing with the metallocene compound. This co-catalyst may be reacted with an organoaluminum compound or the like as necessary. The metallocene compound is preferably a crosslinked metallocene compound that enables polymerization with stereoregularity of propylene, and more preferably a crosslinked metallocene compound that enables polymerization with isotactic regularity of propylene.

[0024] There are no particular limitations on the method for producing polypropylene resins using a single-site catalyst; known methods such as slurry polymerization, bulk polymerization, and gas-phase polymerization can be used. It is also possible to produce them using a multi-stage polymerization method.

[0025] The melting point of polypropylene resins produced using a single-site catalyst is preferably 120 to 160°C, more preferably 140°C or lower, and the Vicat softening temperature is preferably 100 to 135°C. Within this temperature range, heat sealing can be performed from low temperatures, and a better film can be obtained.

[0026] The density of the above polypropylene resin is 0.87 to 0.93 g / cm³. 3 The MFR is preferably in the range of 1 to 30 g / min at 230°C, in which case the film-forming properties are good and the heat seal strength is also appropriate, which is preferable.

[0027] The resin composition of the heat-seal layer is preferably a resin composition in which 51 to 80% by mass of polyethylene resin and 20 to 49% by mass of polypropylene resin are mixed, as described above. When used as a container lid material, the heat-seal layer undergoes cohesive failure, resulting in a heat-seal strength of 10 to 28 N / 15 mm at a heat-seal temperature of 140 to 180°C, and a film with better opening properties that does not string when opened.

[0028] In the laminated film of the present invention, the support layer preferably contains 50% by mass or more of linear low-density polyethylene. If the amount of linear low-density polyethylene is less than 50% by mass, the flexibility of the laminated film may decrease, causing the film to tear when opened, and preventing it from being opened properly when used as a lid for a container. If there are two or more support layers, it is preferable that each support layer contains 50% by mass or more of linear low-density polyethylene.

[0029] The linear low-density polyethylene described above may be obtained using single-site or multi-site catalytic methods, and the comonomer can be selected from 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Linear low-density polyethylene may have a higher melting point (Tm) than high-pressure low-density polyethylene, improving the heat resistance of the film and providing excellent cold resistance, which may result in stronger resistance to tearing of the lid. The density is 0.905~0.95 g / cm³ 3 A range of 0.910 to 0.940 g / cm³ is preferred. 3 A range of 0.5 to 100 g / 10 min at 190°C is preferred, and a range of 1 to 20 g / 10 min is more preferred.

[0030] The resin other than the linear low-density polyethylene in the support layer described above is preferably at least one selected from high-pressure low-density polyethylene, high-density polyethylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, and ethylene-α-olefin random copolymer elastomer, as this provides good dispersibility in linear low-density polyethylene.

[0031] In the support layer and heat seal layer of the present invention, to the extent that the objectives of the present invention are not impaired, specific additives may be selected and used to ensure slipperiness and lamination suitability suitable for film processing. Specifically, these may include organic lubricants such as erucic acid amide, antioxidants with a molecular weight of 500 or more, inorganic particles such as silica, zeolite, and calcium carbonate, or organic particles such as polymethyl methacrylate crosslinked particles. Antioxidants, heat stabilizers, and antistatic agents that improve film formation properties may also be included. The support layer may, if necessary, be mixed with selvages and slitting waste generated during the production of the laminated film of the present invention, as long as it does not impair the effects of the present invention.

[0032] In the present invention, the support layer and heat seal layer may be made of plant-derived polyethylene resin or plant-derived polypropylene resin (hereinafter sometimes referred to as biomass resin) to reduce environmental impact. In this case, the index representing the ratio (mass %) of plant-derived raw materials in the total composition is called the biomass degree, and it is the radioactive carbon (C) that is present in a certain concentration in plant-derived raw materials and is hardly present in petroleum-derived raw materials. 14 The biomass content (%) can be calculated by measuring the concentration of ) using accelerator mass spectrometry. However, in recent years, even without performing accelerator mass spectrometry on the actual product, raw material manufacturers provide the minimum biomass content values ​​for each plant-derived raw material. Therefore, based on the minimum biomass content of each plant-derived raw material provided by these raw material manufacturers and the amount of each plant-derived raw material used, the biomass content, which is the ratio (%) of plant-derived raw materials in the total composition, can be calculated with approximate accuracy.

[0033] Examples of plant-derived resins include polyterpene resins. Examples of polyterpene resins include α-pinene, β-pinene, dipentene, styrene-modified terpenes, and their hydrogenated products.

[0034] When a plant-derived resin is added to the laminated film of the present invention, the biomass content is preferably 1% by mass or more and 45% by mass or less, and more preferably 3% by mass or more and 40% by mass or less. If the biomass content is less than 1% by mass, the contribution to reducing environmental impact is low, and the contribution to reducing environmental impact increases as the biomass content increases, but if it exceeds 45% by mass, the film-forming properties may deteriorate, and the film may become brittle and its processability may deteriorate.

[0035] The thickness of the laminated film of the present invention is preferably 15 to 100 μm. The thickness of the support layer is preferably 10 to 70 μm, and more preferably in the range of 13 to 60 μm, as this provides good punchability and handling when used as a container lid material.

[0036] The thickness of the heat seal layer is preferably in the range of 1 to 30 μm, more preferably 1.5 to 20 μm. If the thickness of the heat seal layer exceeds 30 μm, peeling defects such as stringing, feathering, and film residue may occur during peeling, and if the thickness of the heat seal layer is less than 1 μm, stable heat seal strength may not be obtained.

[0037] Here, "stringing" refers to the state in which the film stretches like a thread and peels off when opened, while "feathering" and "film residue" refer to the state in which the film remains attached to the container and peels off when opened.

[0038] The laminated film of the present invention is preferably used by laminating at least one other substrate layer selected from polyamide film, polyester film, printing paper, and metal foil on the support layer side, either alone or in combination as needed.

[0039] Examples of polyamide films include nylon 6, nylon 11, and nylon 66, with biaxially oriented nylon 66 film being the most preferable in terms of heat resistance and moisture resistance.

[0040] Examples of polyester films include biaxially oriented polyethylene terephthalate film (hereinafter sometimes abbreviated as PET), biaxially oriented polyethylene naphthalate film, and biaxially oriented polybutylene terephthalate film. Among these, biaxially oriented polyethylene terephthalate film is the most preferable overall in terms of heat resistance and film price.

[0041] The thickness of the polyamide film or polyester film is preferably in the range of 5 to 100 μm, and in particular, a thickness of 12 to 50 μm is preferable because it has good printability and, when used as a lid material, is preferable in terms of lid tear resistance and die-cutting properties.

[0042] Examples of metal foils include aluminum foil and copper foil, with aluminum foil being more preferable. A thickness of 5 to 30 μm is preferable for use as a lid material, considering factors such as punchability, handling, and cost-effectiveness.

[0043] Examples of the printing paper include synthetic paper, high-quality paper, medium-quality paper, art paper, coated paper, and blotting paper. Among them, art paper is preferred in terms of printing quality.

[0044] The method for laminating these other substrate layers on the support layer side is not particularly limited, and examples thereof include lamination via an adhesive, a hot melt agent, or a low melting point extrusion laminate resin.

[0045] Next, an example of the manufacturing method of the laminated film of the present invention will be described.

[0046] Using three extruders, from one extruder, as the support layer 1, a polyethylene resin having a density of 0.90 to 0.97 g / cm 3 and an MFR (190 °C) in the range of 1.0 to 40.0 g / 10 minutes is extruded at 180 to 250 °C, from another extruder, as the support layer 2, a polyethylene resin having a density of 0.90 to 0.97 g / cm 3 and an MFR (190 °C) in the range of 1.0 to 40.0 g / 10 minutes is extruded at 180 to 250 °C, from another extruder, as the heat seal layer, a resin composition in which a linear low-density polyethylene having a density of 0.90 to 0.94 g / cm 3 and an MFR (190 °C) in the range of 1.0 to 40.0 g / 10 minutes and an ethylene-propylene random copolymer having a density of 0.87 to 0.93 g / cm 3 and an MFR (230 °C) in the range of 1 to 40 g / min are mixed is extruded at 200 to 250 °C and laminated with a co-extrusion multilayer T-die. Here, the thicknesses of the support layer 1 / support layer 2 / heat seal layer are extruded into a film shape so as to be, for example, 5 μm / 45 μm / 5 μm, and cast and cooled and solidified with a cooling roll at 25 to 50 °C to obtain a laminated film. Subsequently, corona discharge treatment is performed on the surface of the support layer 1 as necessary.

Example

[0047] The present invention will be described based on examples, but the present invention is not limited to these examples. The method for measuring the characteristics and the method for evaluating the effects in the present invention are as follows.

[0048] (1) Density of the resin The density was measured according to the density gradient pipe method specified in JIS K 7112 (1980).

[0049] (2) Film thickness A dial gauge type thickness gauge (JIS B 7509 (1992), 5mmΦ flat probe) was used to measure the thickness at 10cm intervals in the longitudinal and widthwise directions of the film, and the average value was taken.

[0050] (3) Thickness of each layer The cross-section of the film was cut using a microtome, and the cross-section was observed at 1000x magnification using a digital microscope VHX-5000 (manufactured by Keyence Corporation). The distance in the thickness direction of each layer was measured using the resulting cross-sectional photographs, and the thickness of each layer was calculated by working backward from the magnification. In determining the thickness of each layer, five cross-sectional photographs were used, each taken from five arbitrarily selected locations within different measurement fields, and the average value of these photographs was used for the calculation.

[0051] (4) Melt Flow Rate (MFR) In accordance with JIS K 7210 (1999), polyethylene resins were measured at 190°C and polypropylene resins at 230°C.

[0052] (5) Composite film for sealing A polyurethane adhesive is applied to the support layer side of the laminated film at a rate of 2 g / m². 2 A 12 μm thick PET sheet was dry-laminated and aged at 40°C for 72 hours to create a composite film for sealing.

[0053] (6) Polypropylene sheet for evaluation (substrate) Homopolypropylene (PP-3, described later) resin was melted from an extruder at a temperature of 220-230°C, extruded into a film shape through a die, and cast and cooled to solidify on a cooling roll at 25-50°C to create an evaluation polypropylene sheet with a thickness of 300 μm.

[0054] (7) Film elongation and breaking strength before heat sealing and after 200°C sealing The elongation at break and breaking strength of the laminated film before heat sealing were measured at 23°C room temperature using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd., at a tensile speed of 1000 mm / min. Other measurements were taken in accordance with JIS K 7127.

[0055] The film's elongation and breaking strength after sealing at 200°C were measured by layering 12μm thick PET (Toray Industries, Inc.'s "Lumirror®" P60) on both sides of the laminated film. A flat plate heat seal tester (TP-701B) manufactured by Tester Sangyo Co., Ltd. was used to heat-treat the film by heating one side from the support layer side under the conditions of a sealing temperature of 200°C, a sealing pressure of 0.2MPa, and a sealing time of 1 second. After that, the layered 12μm thick PET was peeled off at room temperature of 23°C, and the heat-treated area was measured at a tensile speed of 1000 mm / min using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd. at room temperature of 23°C. Other measurements were taken in accordance with JIS K 7127.

[0056] (8) Method for creating a composite film for sealing Apply 12 μm thick PET to the support layer side of the laminated film using polyurethane adhesive at a rate of 2 g / m². 2 The sample was dry-laminated and aged at 40°C for 72 hours to create a composite film for sealing.

[0057] (9) Heat seal strength The composite film for sealing prepared in (8) was cut to 100 mm x 15 mm, and the heat-seal layer and the 300 μm evaluation polypropylene sheet prepared in (6) were placed on top of each other. Using a flat plate seal tester (TP-701B) manufactured by Tester Industries Co., Ltd., the sample was heat-sealed by heating one side from the PET side at a sealing temperature of 140 °C, a sealing pressure of 0.2 MPa, and a sealing time of 1 second. The heat seal strength was measured at room temperature of 23 °C when peeled 180° using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd. at a tensile speed of 300 mm / min. At that time, the average value of n=10 measurements was taken for one sample, and those with a value of 10 N / 15 mm or more were marked with ○ for good low-temperature sealing, sealing, and peelability, while those with a value of less than 10 N / 15 mm were marked with ×.

[0058] (10) Time dependence of heat seal strength The composite film for sealing prepared in (8) was cut to 100 mm x 15 mm and placed on top of the heat seal layer and the 300 μm evaluation polypropylene sheet prepared in (6). Using a flat plate seal tester (TP-701B) manufactured by Tester Industries Co., Ltd., samples were heat-sealed by heating one side from the PET side at a sealing temperature of 180°C, a sealing pressure of 0.2 MPa, and sealing times of 1 second and 4 seconds. The heat seal strength was measured at room temperature of 23°C using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd. at a tensile speed of 300 mm / min when peeled at 180°. At that time, the average value of n=10 measurements was taken for one sample, and samples with a difference of 3.5 N / 15 mm or less between sealing times of 1 second and 4 seconds in the range of 20~28 N / 15 mm were judged to have good sealing and peelability, and high workability during the manufacture of packaging materials and filling of contents into packaging materials, and were judged as ○.

[0059] (11) Peeled appearance When the heat seal strength measurement samples prepared in (9) were peeled off by hand, the peeled appearance was visually evaluated, and stringing and film residue were determined as follows. ○: No stringing or film residue observed. ×: Long stringing or film residue of 1.5 mm or more is observed.

[0060] (12) Lid splitting Samples were prepared by cutting out a 100mm x 100mm sample of the composite film for sealing created in (8), placing it on top of a heat-seal layer and a polypropylene container (95Φ x 61.9H, manufactured by Tokan Kogyo Co., Ltd.), and heat-sealing them using a hand sealer manufactured by Aishin Pack Kogyo Co., Ltd. under the conditions of a heat-seal temperature of 200℃, a seal pressure of 0.3MPa, and a seal time of 1 second. Samples were marked with a ○ if the composite film did not tear when peeled off by hand, and a × if the composite film tore.

[0061] The raw materials used in this embodiment are as follows: (1) 1-Butene copolymer linear low-density polyethylene (LL-1) MFR=7.0g / 10min, density=0.920g / cm 3 Tm=123℃ (2) 1-Octene copolymer linear low-density polyethylene (LL-2) MFR=2.2g / 10min, density=0.921g / cm 3 Tm=120℃ (3) High-pressure low-density polyethylene (LD-1) MFR=7.0g / 10min, density=0.919g / cm 3 Tm=106℃ (4) High-density polyethylene (HD-1) MFR=8.0g / 10min, density=0.961g / cm 3 Tm=130℃ (5) Ethylene-propylene random copolymer (PP-1) produced by single-site catalyst method MFR=7.0g / 10min, density=0.900g / cm 3 Tm=120℃ (6) Ethylene-propylene random copolymer (PP-2) produced by multi-site catalytic method MFR=6.0g / 10min, density=0.900g / cm 3 Tm=145℃ (7) Ethylene-α-olefin random copolymer elastomer (E-1) MFR=3.6g / 10min, density 0.885g / cm3 (8) Plant-derived polyterpene resin (PT-1) Softening point = 115°C, Biomass content = 90% (9) Homopolypropylene (PP-3) MFR=8.0g / 10min, density=0.900g / cm 3 .

[0062] Example 1 For support layers 1 and 2, 100% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) was used, and for the heat seal layer, a resin composition was used which was a mixture of 30% by mass of single-site catalytic ethylene-propylene random copolymer (PP-1) and 70% by mass of 1-butene copolymer linear low-density polyethylene (LL-1). These were fed into three extruders of a three-layer, three-type unstretched film molding machine, respectively. Support layers 1 and 2 and the heat seal layer were melt-kneaded at an extrusion temperature of 230°C, extruded from a three-layer, three-type T-die at 230°C, rapidly cooled on a casting roll at 40°C to form a laminated film, and the surface of support layer 1 was subjected to corona discharge treatment. The total thickness of the obtained laminated film was 50 μm, with support layer 1 having a thickness of 5 μm, support layer 2 having a thickness of 40 μm, and the heat seal layer having a thickness of 5 μm. The laminated film of the present invention satisfied all the required characteristics.

[0063] Example 2 A laminated film was obtained in the same manner as in Example 1, except that the 1-butene copolymer linear low-density polyethylene (LL-1) in the heat-seal layer of Example 1 was replaced with 1-octene copolymer linear low-density polyethylene (LL-2). The laminated film of the present invention satisfied all the required characteristics.

[0064] Example 3 A laminated film was obtained in the same manner as in Example 1, except that the heat-seal layer of Example 1 used a resin composition which was a mixture of 35% by mass of ethylene-propylene random copolymer (PP-1) produced by a single-site catalyst, 60% by mass of 1-octene copolymer linear low-density polyethylene (LL-2), and 5% by mass of ethylene-α-olefin random copolymer elastomer (E-1). The laminated film of the present invention satisfied all the required properties.

[0065] Example 4 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used which was a mixture of 25% by mass of single-site catalytic ethylene-propylene random copolymer (PP-1), 5% by mass of single-site catalytic ethylene-propylene random copolymer (PP-2), and 70% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) for the heat-seal layer of Example 1. The laminated film of the present invention satisfied all the required properties.

[0066] Example 5 A laminated film was obtained in the same manner as in Example 1, except that 100% by mass of 1-octene copolymer linear low-density polyethylene (LL-2) was used as support layer 1, and 100% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) was used as support layer 2. The laminated film of the present invention satisfied all the required characteristics.

[0067] Example 6 A laminated film was obtained in the same manner as in Example 1, except that the same resin composition as in Example 5 was used and the thickness of the heat-seal layer was 3 μm. The laminated film of the present invention satisfied all the required characteristics.

[0068] Example 7 Using the same resin composition as in Example 5, a laminated film was obtained in the same manner as in Example 1, except that the support layer was a single layer with a thickness of 35 μm and the heat seal layer was a single layer with a thickness of 15 μm, using a two-layer T-die at 230°C. The laminated film of the present invention satisfied all the required characteristics.

[0069] Example 8 A laminated film was obtained in the same manner as in Example 5, except that a resin composition was used as the support layer 1, which consisted of a mixture of 70% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 30% by mass of high-density polyethylene (HD-1). The laminated film of the present invention satisfied the required characteristics.

[0070] Example 9 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used as support layers 1 and 2, which consisted of a mixture of 70% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 30% by mass of high-density polyethylene (HD-1). The laminated film of the present invention satisfied the required characteristics.

[0071] Example 10 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used as support layers 1 and 2, which consisted of a mixture of 90% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 10% by mass of plant-derived polyterpene resin (PT-1). The laminated film of the present invention satisfied the required properties.

[0072] Example 11 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used as support layers 1 and 2, which consisted of a mixture of 90% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 10% by mass of ethylene-α-olefin random copolymer elastomer (E-1). The laminated film of the present invention satisfied the required properties.

[0073] Example 12 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used as support layers 1 and 2, which consisted of a mixture of 70% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 30% by mass of high-pressure low-density polyethylene (LD-1). The laminated film of the present invention satisfied the required characteristics.

[0074] Comparative Example 1 A laminated film was obtained in the same manner as in Example 1, except that a resin composition was used as support layers 1 and 2, which consisted of a mixture of 30% by mass of 1-butene copolymer linear low-density polyethylene (LL-1) and 70% by mass of high-density polyethylene (HD-1). The obtained film was evaluated in the same manner as in Example 1. Due to the high amount of high-density polyethylene added to support layer 1, which increased its crystallinity, both the elongation at break and the tensile strength after sealing decreased significantly, and the film did not satisfy the required properties of the present invention.

[0075] Comparative Example 2 A laminated film was obtained in the same manner as in Comparative Example 1, except that the support layers 1 and 2 had the same composition as in Comparative Example 1, and the heat seal layer used a resin composition obtained by mixing 70% by mass of ethylene-propylene random copolymer (PP-1) produced by a single-site catalyst method with 30% by mass of 1-butene copolymer linear low-density polyethylene (LL-1). The obtained film was evaluated in the same manner as in Example 1. This film had high elongation at break and tensile strength before and after sealing, and the amount of ethylene-propylene random copolymer added to the heat seal layer was large, resulting in a large difference in strength in the time-dependent heat seal strength at a heat seal temperature of 180°C, and thus it did not satisfy the required characteristics of the present invention.

[0076] Comparative Example 3 A laminated film was obtained in the same manner as in Comparative Example 1, except that the support layers 1 and 2 had the same composition as in Comparative Example 1, and the heat seal layer was made of 70% by mass of ethylene-propylene random copolymer (PP-2) produced by a single-site catalyst method. The obtained film was evaluated in the same manner as in Example 1. This film had high elongation and tensile strength before and after sealing, and the low-temperature sealing properties were impaired due to the high melting point of the ethylene-propylene random copolymer (PP-2) in the heat seal layer. The heat seal strength at 140°C for 1 second was weak, and the strength difference in the time-dependent heat seal strength at a heat seal temperature of 180°C was large, so it did not satisfy the required characteristics of the present invention.

[0077] Comparative Example 4 Support layers 1 and 2 had the same composition as in Comparative Example 1, and a laminated film was obtained in the same manner as in Comparative Example 3, except that the thickness of the heat seal layer was 25 μm and the thickness of support layer 2 was 20 μm. The obtained film was evaluated in the same manner as in Example 1. This film had high elongation and tensile strength before and after sealing, and the peel appearance was poor due to the thickness of the heat seal layer. Furthermore, the low-temperature sealability was impaired due to the high melting point of ethylene-propylene random copolymer (PP-2), resulting in weak heat seal strength at 140°C for 1 second, and there was a large difference in strength in the time-dependent heat seal strength at a heat seal temperature of 180°C, thus failing to satisfy the required characteristics of the present invention.

[0078] Table 1-1

[0079] Table 1-2

[0080] Table 2

Claims

1. A laminated film having a heat-seal layer and at least one support layer, The heat-seal layer is made of a resin composition obtained by mixing polyethylene resin and polypropylene resin, wherein the polyethylene resin is 51% to 80% by mass and the polypropylene resin is 20% to 49% by mass. The support layer contains 50% by mass or more of linear low-density polyethylene, The polyethylene-based resin has a mixed resin composition of linear low-density polyethylene and ethylene-α-olefin random copolymer elastomer. A laminated film having a breaking elongation A1 and breaking strength B1 before heat sealing, and after heat sealing with a polyethylene terephthalate film at a sealing temperature of 200°C, a sealing pressure of 0.2 MPa, and a sealing time of 1 second, and after peeling off the polyethylene terephthalate film, the breaking elongation A2 and breaking strength B2 are such that in both the longitudinal and width directions, A1 / A2 is 2.5 or less and B1 / B2 is 3.0 or less.

2. The laminated film according to claim 1, wherein the heat seal strength when the heat seal layer is heat-sealed with a polypropylene sheet at 140°C for 1 second is 10 N / 15 mm or more.

3. The laminated film according to claim 1, wherein the heat seal strength when the heat seal layer is heat-sealed with a polypropylene sheet at 180°C for 4 seconds and the peel strength when heat-sealed at the same temperature for 1 second are both in the range of 20 N / 15 mm or more and 28 N / 15 mm or less, and the difference between them is 3.5 N / 15 mm or less.

4. The laminated film according to claim 1, wherein the polyethylene resin of the heat-seal layer contains 50% by mass or more of linear low-density polyethylene, and the polypropylene resin contains 20% by mass or more of polypropylene resin produced by a single-site catalyst method.

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