Laminated Film

Abstract

To provide a laminate film which, when used as a lid material for a container or the like, has a small change in an opening strength even when a sealing condition changes, and can be easily opened with an appropriate force.SOLUTION: There is provided a laminate film having a heat seal layer and one or more support layers, in which when the heat seal layer and a polypropylene sheet are heat sealed at 200°C for 1 second and at 200°C for 4 seconds, heat seal strengths are both 15 to 27 N / 15 mm, and a difference is 7 N / 15 mm or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] The primary purpose of packaging is to protect the contents, and it is important that it does not easily open when subjected to external forces during transportation or display. At the same time, it is also required to be easy to open, so that the lid can be opened normally and easily without cracking during use.

[0003] In particular, in recent years, with the increase in the elderly population and the trend toward individual meals, there has been an increasing demand for convenient, easily openable packaging. Various types of easy-to-open packaging have been proposed, and packaging called easy-peel uses a sealant film that is made easy to open, and is widely used as a lid material for cup containers for desserts such as jelly, yogurt, and pudding, as well as for cooked rice and prepared foods, and as packs for processed meat products such as ham and bacon.

[0004] To improve the ease of opening of sealant films, a coextruded multilayer film has been proposed, which has a heat seal layer made of a specific mixture of polypropylene resin and polyethylene resin (see, for example, Patent Documents 1 and 2). However, even when the co-extruded multilayer films proposed in Patent Documents 1 and 2 are used as sealant films, if the sealing conditions change, the opening strength increases, and there are problems such as the package being unable to be opened with a moderate force or the lid tearing during opening. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-144015 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-055433 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a laminated film that, when used as a lid for a container, exhibits little change in opening strength even when sealing conditions change, and can be easily opened with a moderate force. [Means for solving the problem]

[0007] That is, the present invention is This laminated film has a heat seal layer and one or more support layers, and when the heat seal layer and a polypropylene sheet are heat sealed at 200°C for 1 second and at 200°C for 4 seconds, the heat seal strength is 15 to 27 N / 15 mm, with the difference being 7 N / 15 mm or less. [Effects of the Invention]

[0008] The laminated film of the present invention, when used as a lid material, exhibits little change in opening strength even when the sealing conditions are changed, and can be easily opened with an appropriate force.

[0009] The present invention provides a laminated film that, when used as a lid for a container, exhibits little change in opening strength even when sealing conditions change, and can be easily opened with a moderate force. Furthermore, by laminating at least one layer selected from a biaxially oriented polyamide film, a biaxially oriented polyester film, a printed paper, a metal foil, etc., on the support layer side of the laminated film, a package that can be used as a lid and can be easily opened with a moderate force can be obtained. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] The laminated film of the present invention must have a heat-sealable heat-sealable layer and one or more support layers, and the heat-sealable layer is important because it provides the film with easy-open properties. The support layer is important because laminating one or more layers allows the film to be opened normally without tearing the lid when opened.

[0012] The laminated film of the present invention is a heat seal film formed by sealing a heat seal layer and a polypropylene sheet at a sealing pressure of 2 kg / cm 2 The heat seal strength (pulling speed 300 mm / min, peel angle 180°) when heat sealed at a sealing temperature of 200°C for 1 second and 4 seconds must be in the range of 15 to 27 N / 15 mm in both cases, and a range of 16 to 25 N / 15 mm in both cases is more preferable.

[0013] The difference in heat seal strength between the heat seal layer and the polypropylene sheet when heat sealed for 1 second and 4 seconds at 200°C must be 7N / 15mm or less, and preferably 6N / 15mm or less. When the difference in heat seal strength between when heat sealed for 1 second at 200°C and when heat sealed for 4 seconds at 200°C is 7N / 15mm or less, the openability is stable regardless of the sealing conditions, making it a good easy-peel packaging material.

[0014] Sealing pressure 2kg / cm 2 Under the condition of a sealing time of 1 second, the heat seal strength at a temperature of 150°C is preferably in the range of 10 to 20 N / 15 mm, and the difference in heat seal strength compared to when heat sealed at a temperature of 200°C is preferably 10 N / 15 mm or less. This is preferable because it reduces the dependency on sealing temperature, provides good heat sealability over a wide temperature range, and improves workability when producing the packaging material and filling the packaging material with contents.

[0015] The heat seal layer in the present invention is made of a resin composition in which a polyethylene resin and a polypropylene resin are mixed, and it is preferable that the amount of the polyethylene resin is greater than that of the polypropylene resin, since this results in less dependency on sealing temperature and good heat sealability over a wide temperature range. It is preferable that the heat seal layer is made of a resin composition in which 51% to 95% by mass of the polyethylene resin and 5% to 49% by mass of the polypropylene resin are mixed.

[0016] The polyethylene resin may include at least one of high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene-α-olefin random copolymer elastomer, etc. Among these, a mixed resin composition of linear low-density polyethylene, high-pressure low-density polyethylene, and ethylene-α-olefin random copolymer elastomer is particularly preferred.

[0017] The polyethylene resin of the heat seal layer in the present invention preferably contains linear low-density polyethylene as the main component, where the main component means that the content is 50% by mass or more of the mixed resin composition.

[0018] The linear low-density polyethylene has a density of 0.910 to 0.940 g / cm 3 , MFR (190°C) is in the range of 1.0 to 40.0 g / 10 min, and high-pressure low-density polyethylene has a density of 0.880 to 0.930 g / cm 3 The MFR (190°C) is in the range of 1.0 to 20.0 g / 10 min. The ethylene-α-olefin random copolymer elastomer has a density of 0.865 to 0.895 g / cm. 3 It is preferable that the MFR (190°C) is in the range of 0.5 to 10.0 g / 10 min, as this provides good compatibility with each other and adequate dispersibility in the ethylene-propylene random copolymer.

[0019] The polypropylene-based resin of the heat seal layer in the present invention is preferably an ethylene-propylene random copolymer of propylene and a comonomer, and the comonomer can be preferably selected from ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc., and the comonomer content is preferably less than 5% by mass.

[0020] The polypropylene resin may be mixed with a polypropylene resin polymerized using a multi-site catalyst (Ziegler-Natta catalyst) or a metallocene catalyst (Kaminsky catalyst).

[0021] The density of the ethylene-propylene random copolymer is 0.90 to 0.96 g / cm 3 It is preferable that the MFR (230°C) is in the range of 1 to 30 g / min, since this provides good film-forming properties and appropriate heat seal strength.

[0022] As described above, the resin mixing ratio of the heat seal layer is preferably a resin composition comprising 51 to 95% by mass of polyethylene-based resin and 5 to 49% by mass of polypropylene-based resin. In this case, when used as a lid material, the heat seal layer undergoes cohesive failure, resulting in a heat seal strength in the range of 15 to 27 N / 15 mm, and a film with good openability and no stringiness when opened can be obtained.

[0023] The support layer in the present invention is preferably made of a resin composition in which an ethylene-propylene block copolymer and a polyethylene resin are mixed.

[0024] The resin constituting the support layer in the present invention is preferably a resin composition comprising 70 to 97% by mass of an ethylene-propylene block copolymer (a) and 3 to 30% by mass of a polyethylene resin (b). If the amount of polyethylene resin (b) is less than 2% by mass, the film may lose flexibility, causing it to tear when opened and making it impossible to open properly when used as a container lid. If the amount of polyethylene resin (b) is more than 30% by mass, the film may wrinkle easily when wound up during film formation, resulting in poor film formability and poor punchability as a lid.

[0025] The propylene-ethylene block copolymer (a) is a copolymer consisting of a propylene polymer (a1) and an ethylene polymer (a2), and has a density of 0.90 to 0.96 g / cm 3 It is preferable that the density is 0.90 g / cm 3 If the density is less than 0.96 g / cm, the mechanical strength of the film may be low, and the film may stretch during the slitting process after film formation or during lamination, resulting in poor processability. 3 If the temperature exceeds this range, the film may have high crystallinity, which may result in poor resistance to lid tearing. The polyethylene resin is preferably a resin composition of at least one of an ethylene-α-olefin random copolymer elastomer and a linear low-density polyethylene.

[0026] The ethylene-α-olefin random copolymer elastomer has a density of 0.860 to 0.900 g / cm 3 is preferable, and 0.865 to 0.895 g / cm 3 The MFR (190°C) is preferably 0.2 to 20.0 g / 10 min, more preferably 0.5 to 10.0 g / 10 min. The α-olefin can be preferably selected from propylene, 1-butene, and 1-octene, and specifically, an ethylene-propylene copolymer, an ethylene-1-butene copolymer, or an ethylene-1-hexene copolymer is preferred.

[0027] The linear low-density polyethylene may be obtained using either a single-site or multi-site catalyst, and the comonomer may be 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene. Linear low-density polyethylene has a higher melting point (Tm) than high-pressure low-density polyethylene, improving the heat resistance of the film and also providing excellent cold resistance, resulting in strong resistance to lid tearing. The density is usually 0.905 to 0.95 g / cm. 3 is preferable, and 0.910 to 0.940 g / cm 3 The MFR (190°C) is preferably from 0.5 to 100 g / 10 min, more preferably from 1 to 20 g / 10 min.

[0028] In the support layer and heat seal layer of the present invention, specific additives may be selected and used to ensure the slip properties and lamination suitability suitable for film processing, specifically 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, and organic particles such as polymethyl methacrylate crosslinked particles, as long as the purpose of the present invention is not impaired. Antioxidants, heat stabilizers, antistatic agents, etc., which improve film formability, may also be included. If necessary, scraps and slit scraps generated during the production of the laminated film of the present invention may be mixed into the support layer, as long as the effects of the present invention are not impaired.

[0029] In addition, plant-derived resins (hereinafter sometimes referred to as biomass resins) may be selected and used for the purpose of reducing the environmental load. In this case, the index that indicates the ratio (mass%) of plant-derived raw materials in the total composition is called the biomass ratio, which is a constant concentration of radioactive carbon (C) that is hardly present in petroleum-derived raw materials. 14The biomass degree (%) can be calculated by measuring the concentration of plant-derived raw materials by accelerator mass spectrometry. However, in recent years, raw material manufacturers have been providing values ​​for the minimum biomass degree of each plant-derived raw material, even without subjecting the actual product to accelerator mass spectrometry. Therefore, the biomass degree, which is the ratio (%) of plant-derived raw materials to the total composition, can be calculated with a high degree of accuracy based on the minimum biomass degree of each plant-derived raw material provided by these raw material manufacturers and the blending amount of each plant-derived raw material.

[0030] The plant-derived resin is preferably a polyterpene resin, such as α-pinene, β-pinene, dipentene, styrene-modified terpene, or a hydrogenated product thereof.

[0031] The content of the plant-derived polyterpene resin is preferably 1 to 50% by mass of the entire film. If the content is less than 1% by mass, the effect of the addition may be ineffective, while if it exceeds 50% by mass, the heat seal strength may decrease.

[0032] The biomass ratio of the laminated film of the present invention is preferably 1% or more and 45% or less, more preferably 3% or more and 40% or less. A biomass ratio of less than 1% contributes little to reducing the environmental load, and the higher the biomass ratio, the greater the contribution to reducing the environmental load. However, if the biomass ratio exceeds 45%, film formability may deteriorate, and the film may become brittle and processability may deteriorate. 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, which is suitable for good punching ability.

[0033] The thickness of the heat seal layer is preferably in the range of 1 to 30 μm, and more preferably 1.5 to 20 μm. If the thickness of the heat seal layer exceeds 30 μm, poor appearance during peeling, such as stringiness, feathering, or residual film, may occur. If the thickness of the heat seal layer is less than 1 μm, stable heat seal strength may not be obtained.

[0034] Here, stringiness refers to a state in which the film stretches like a string and peels off when the package is opened, and feathering or film residue refers to a state in which the film remains on the container as the adherend and peels off when the package is opened.

[0035] The laminated film of the present invention preferably includes at least one other substrate layer selected from polyamide film, polyester film, printing paper, and metal foil, laminated to the support layer side, either alone or in combination as necessary. Examples of polyamide films include nylon 6, nylon 11, and nylon 66. Of these, biaxially oriented nylon 66 film is more preferred in terms of heat resistance and moisture resistance. 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. Of these, biaxially oriented polyethylene terephthalate film is more preferred overall in terms of heat resistance, film price, and other factors. Examples of metal foils include aluminum foil and copper foil, with aluminum foil being more preferred. Examples of printing paper include synthetic paper, fine paper, medium-quality paper, art paper, coated paper, and wood-burning paper. However, art paper is preferred for its printing quality.

[0036] The thickness of the polyamide film or polyester film is preferably in the range of 10 to 100 μm, and particularly in the range of 12 to 50 μm, which is preferable in terms of printability, resistance to lid tearing, and punchability when used as a lid material.

[0037] The thickness of the metal foil is preferably in the range of 5 to 30 μm from the viewpoints of punching properties, handling properties and economy when used as a lid material.

[0038] The method for laminating these other substrate layers on the support layer side is not particularly limited, but examples include lamination via an adhesive, a hot melt agent, or a low-melting extrusion laminating resin.

[0039] Next, an example of a method for producing the laminated film of the present invention will be described.

[0040] Using two extruders, one extruder extruded a support layer with a density of 0.90 to 0.96 g / cm3. 3 ethylene-propylene block copolymers with MFR (230°C) in the range of 1 to 10 g / min, and polyethylene resins with densities of 0.865 to 0.895 g / cm 3 A resin composition containing an ethylene-α-olefin random copolymer elastomer having a MFR (190°C) in the range of 0.5 to 10.0 g / 10 min was extruded at 200 to 280°C, and a resin composition containing an ethylene-α-olefin random copolymer elastomer having a density of 0.910 to 0.940 g / cm was extruded from another extruder as a heat seal layer. 3 , linear low-density polyethylene with a MFR (190°C) in the range of 1.0 to 40.0 g / 10 min, and a density of 0.880 to 0.930 g / cm 3 , high-pressure low-density polyethylene with a MFR (190°C) in the range of 1.0 to 20.0 g / 10 min, and a density of 0.865 to 0.895 g / cm 3 , an ethylene-α-olefin random copolymer elastomer with a MFR (190°C) in the range of 0.5 to 10.0 g / 10 min, and a density of 0.90 to 0.96 g / cm 3 A resin composition containing a mixture of ethylene and propylene random copolymers with an MFR (230°C) of 1 to 30 g / min is extruded at 200 to 250°C and laminated using a coextrusion multilayer die. The resulting film is then extruded so that the thickness of the support layer / heat seal layer is, for example, 45 μm / 5 μm, and cast onto a cooling roll at 25 to 50°C, where it is cooled and solidified to form a laminated film. If necessary, the surface of the support layer is then corona discharge treated. [Example]

[0041] The present invention will be described based on examples, but the present invention is not limited to these examples. The methods for measuring the properties and evaluating the effects in the present invention are as follows.

[0042] (1) Density of resin The density was measured according to the density gradient tube method specified in JIS K 7112 (1980).

[0043] (2) Film Thickness Using a dial gauge type thickness meter (JIS B 7509 (1992), flat type probe with a diameter of 5 mm), measurements were taken at 10 points at 10 cm intervals in the longitudinal and transverse directions of the film, and the average value was calculated.

[0044] (3) Thickness of each layer The cross section of the film was cut out with a microtome, and the cross section was observed at 1000x magnification using a VHX-5000 digital microscope (Keyence Corporation) to take a cross-sectional photograph. The distance in the thickness direction of each layer was measured using the cross-sectional photograph, and the thickness of each layer was calculated by back-calculating from the magnification. Note that, to determine the thickness of each layer, five cross-sectional photographs were used, each taken at five locations randomly selected from different measurement fields, and the thickness was calculated as the average value.

[0045] (4) Melt flow rate (MFR) The measurements were made in accordance with JIS K 7210 (1999) at 190°C for polyethylene resins and 230°C for polypropylene resins.

[0046] (5) Method for producing composite film for sealing Apply polyurethane adhesive to the support layer side of the laminated film at a rate of 2 g / m 2 The film was dry-laminated with 12 μm thick PET at 40° C. for 72 hours to prepare a sample composite film for sealing.

[0047] (6) Polypropylene sheet for evaluation (adherend) Homopolypropylene (PP-2, described below) resin was melted from the extruder at a temperature of 220-230°C, extruded into a film form through a die, and cast onto a cooling roll at 25-50°C, where it was cooled and solidified to produce a 300 μm thick polypropylene sheet for evaluation.

[0048] (7) Dependence of heat seal strength on the number of seconds The composite film for sealing prepared in (5) was cut into a piece of 100 mm x 15 mm, and the heat seal layer was placed on the 300 μm polypropylene sheet for evaluation prepared in (6). Using a flat plate heat seal tester (TP-701B) manufactured by Tester Sangyo Co., Ltd., the sealing temperature was 200°C and the sealing pressure was 2 kg / cm. 2 The heat seal strength was measured under conditions of 1 second and 4 second sealing times. Samples heat-sealed by heating one side from the PET side were measured at a room temperature of 23°C using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd. at a tensile speed of 300 mm / min and a 180° peel angle. The average of 10 measurements was taken for each sample. Those with a heat seal strength in the range of 15 to 27 N / 15 mm were evaluated as having good sealability and peelability, with those outside this range being evaluated as "good." Furthermore, those with a difference in heat seal strength of 7 N / 15 mm or less under conditions of 200°C for 1 second and 4 seconds were evaluated as having good opening stability, with those outside this range being evaluated as "good."

[0049] (8) Temperature dependence of heat seal strength The composite film for sealing prepared in (5) was cut into a piece of 100 mm x 15 mm, and the heat seal layer was placed on the 300 μm polypropylene sheet for evaluation prepared in (6). Using a flat plate heat seal tester (TP-701B) manufactured by Tester Sangyo Co., Ltd., the sealing temperatures were 150°C and 200°C, and the sealing pressure was 2 kg / cm. 2 The heat seal strength was measured under the following conditions: heat seal strength, tensile speed, and sealing time of 1 second. Samples heat-sealed by heating one side from the PET side were measured at a room temperature of 23°C using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd., at a tensile speed of 300 mm / min and a 180° peel angle. The average of 10 measurements was taken for each sample. Those with a heat seal strength of 10 to 20 N / 15 mm at a heat seal temperature of 150°C and 15 to 27 N / 15 mm at a heat seal temperature of 200°C were evaluated as having good sealability and peelability, with a rating of ○. Those outside these ranges were evaluated as ×. Those with a difference in heat seal strength between 1 second at 150°C and 1 second at 200°C of 10 N / 15 mm or less were evaluated as having good sealing temperature stability, with a rating of ○. Those outside these ranges were evaluated as ×.

[0050] (9) Punchability The sealing composite film prepared in (5) was sampled to a size of 50 mm x 50 mm and set in a sample holder with a 20 mm diameter hole. Using a Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd., a needle (1.0 mm diameter, 0.5 mm tip shape) was pierced at a rate of 50 ± 5 mm per minute, and the elongation of the film during piercing was measured. Films with an elongation of less than 3 mm were marked with a circle, and films with an elongation of 3 mm or more were marked with an x.

[0051] (10) Peeling appearance When the heat seal strength measurement sample prepared in (7) was peeled off by hand, the peeling appearance was visually evaluated, and stringiness and film residue were evaluated as follows.

[0052] ○: No stringiness or film residue is observed. ×: Long stringiness or film residue of 1.5 mm or more remains.

[0053] (11) Lid cracking The sealing composite film prepared in (5) was cut into a sample of 100 mm x 100 mm, and the heat seal layer was placed on a polypropylene container (95φ x 61.9H, manufactured by Tokan Kogyo Co., Ltd.). A sample was then heat-sealed using a hand sealer manufactured by Eishin Pack Kogyo Co., Ltd. under the conditions of a heat seal temperature of 200°C, a sealing pressure of 0.3 MPa, and a sealing time of 2 seconds. When the composite film was peeled off by hand, samples that did not tear were evaluated as ◯, and samples that tore were evaluated as ×.

[0054] (12) Film forming properties When the laminated film was produced and wound up, the film was not torn, the winding tension was easily adjusted, and no wrinkles were formed, and it was marked as "O." The film was marked as "X" when it was difficult to adjust the winding tension and severe wrinkles occurred, or when the film had low breaking elongation or breaking strength, causing the film to break during production.

[0055] The raw materials used in this example are as follows: (1) Ethylene-propylene block polymer (BPP-1) MFR=2.5g / 10min, density=0.900g / cm 3、 Tm=163℃ (2) Ethylene-α-olefin random copolymer elastomer (E-1) MFR=3.6g / 10min, density=0.885g / cm 3 (3) 1-butene copolymer linear low-density polyethylene (LL-1) MFR=8.0g / 10min, density=0.920g / cm 3 , Tm=123℃ (4) 1-octene copolymer linear low-density polyethylene (LL-2) MFR=2.2g / 10min, density=0.921g / cm 3 , Tm=120°C (5) High-pressure low-density polyethylene (LD-1) MFR=7.0g / 10min, density 0.919g / cm 3 , Tm=106℃ (6) Ethylene-propylene random copolymer (PP-1) MFR=6.0g / 10min, density=0.900g / cm 3 , Tm=145°C (7) Homopolypropylene (PP-2) MFR=8.0g / 10min, density=0.900g / cm 3 , Tm=163℃ (8) Plant-derived polyterpene resin (PT-1) Softening point = 115°C, biomass content = 90%.

[0056] Example 1 The support layer consisted of a resin composition containing 95% ethylene-propylene copolymer (BPP-1) and 5% ethylene-α-olefin random copolymer elastomer (E-1) by mass. The heat-seal layer consisted of a resin composition containing 30% ethylene-propylene random copolymer (PP-1), 60% linear low-density polyethylene (LL-1), 5% high-pressure low-density polyethylene (PE-1), and 5% ethylene-α-olefin random copolymer elastomer (E-1) by mass. The resins were melt-mixed at 260°C for the support layer and 200°C for the heat-seal layer. The extruded films were then extruded through a T-die at 230°C and quenched on a casting roll at 40°C to form a laminated film. The support layer was corona-treated. The resulting laminated film had a total thickness of 50 μm, with the heat-seal layer being 5 μm thick. The film-forming properties were good, there was no curling of the edges during casting, and no wrinkles occurred during winding, allowing for stable winding. All of the required properties of the laminated film of the present invention were satisfied.

[0057] Example 2 A laminate film was obtained in the same manner as in Example 1, except that the total thickness of the laminate film was 25 μm and the thickness of the heat seal layer was 5 μm. All of the required properties of the laminate film of the present invention were satisfied.

[0058] Example 3 A laminated film was obtained in the same manner as in Example 1, except that the linear low-density polyethylene (LL-1) in the heat-sealable layer of Example 1 was replaced with linear low-density polyethylene (LL-2). All of the required properties of the laminated film of the present invention were satisfied.

[0059] Example 4 A laminated film was obtained in the same manner as in Example 1, except that the heat seal layer was made of a resin composition consisting of 40% by mass of ethylene-propylene random copolymer (PP-1), 55% by mass of linear low-density polyethylene (LL-1), and 5% by mass of ethylene-α-olefin random copolymer elastomer (E-1). All of the required properties of the laminated film of the present invention were satisfied.

[0060] Example 5 A laminated film was obtained in the same manner as in Example 1, except that the support layer was a resin composition comprising a mixture of 80% by mass of ethylene-propylene polymer (BPP-1) and 20% by mass of ethylene-α-olefin random copolymer elastomer (E-1). All of the required properties of the laminated film of the present invention were satisfied.

[0061] Example 6 A laminated film was obtained in the same manner as in Example 1, except that the support layer was a resin composition consisting of a mixture of 80% by mass of ethylene-propylene polymer (BPP-1) and 20% by mass of linear low-density polyethylene (LL-2). All of the required properties of the laminated film of the present invention were satisfied.

[0062] Example 7 A laminated film was obtained in the same manner as in Example 1, except that the support layer was a resin composition consisting of 85 mass% ethylene-propylene polymer (BPP-1), 5 mass% ethylene-α-olefin random copolymer elastomer (E-1), and 10 mass% plant-derived polyterpene resin (PT-1). All of the required properties of the laminated film of the present invention were satisfied.

[0063] Comparative Example 1 A laminated film was obtained in the same manner as in Example 1, except that the heat-sealable layer contained 60% by mass of ethylene-propylene random copolymer (PP-1) and 40% by mass of linear low-density polyethylene (LL-1). The obtained film was evaluated in the same manner as in Example 1. Because the heat-sealable layer contained a large amount of ethylene-propylene random copolymer, the heat-sealing strength dependent on the number of seconds showed high strength when heat-sealed for 4 seconds at a sealing temperature of 200°C, with a large difference in strength from when heat-sealed for 1 second. Furthermore, the difference in strength when heat-sealed for 1 second at sealing temperatures of 150°C and 200°C was large, so the film did not satisfy the required properties of the present invention.

[0064] Comparative Example 2 A laminate film was obtained in the same manner as in Example 1, except that the heat seal layer was made of 60% by mass of homopropylene (PP-2) and 40% by mass of linear low-density polyethylene (LL-1), the total thickness of the laminate film was 50 μm, and the thickness of the heat seal layer was 30 μm. The obtained film was evaluated in the same manner as in Example 1. Because the melting point of the homopolypropylene was high, the strength after 1 second of heat sealing at 150°C was weak, and the heat seal strength dependent on the number of seconds was also high after 4 seconds of heat sealing at a sealing temperature of 200°C, resulting in a large difference in strength from the 1-second heat seal. In addition, because the heat seal layer was thick, severe stringiness occurred when peeled from the adherend, resulting in a poor peel appearance and not satisfying the required properties of the present invention.

[0065] Comparative Example 3 A laminated film was obtained in the same manner as in Example 1, except that the heat seal layer was made of 1% by mass of ethylene-propylene random copolymer (PP-1) and 99% by mass of linear low-density polyethylene (LL-1). The obtained film was evaluated in the same manner as in Example 1. The amount of ethylene-propylene random copolymer added to the heat seal layer was small, and the heat seal strength was too weak to satisfy the required properties of the present invention.

[0066] Comparative Example 4 A laminate film was obtained in the same manner as in Example 1, except that the support layer was a resin composition consisting of 50% by mass of ethylene-propylene polymer (BPP-1) and 50% by mass of ethylene-α-olefin random copolymer elastomer (E-1), and the heat-seal layer was a composition consisting of 60% by mass of ethylene-propylene random copolymer (PP-1) and 40% by mass of linear low-density polyethylene (LL-1). The high content of ethylene-propylene random copolymer in the heat-seal layer resulted in a large difference in heat-seal strength depending on the number of seconds, failing to meet the required properties of the present invention. Furthermore, the high proportion of ethylene-α-olefin random copolymer (E-1) in the support layer resulted in wrinkles during winding and poor rigidity, resulting in poor punchability, and the laminate film did not meet the required properties.

[0067] Comparative Example 5 A laminated film was obtained in the same manner as in Example 1, except that the support layer consisted of 95% by mass of homopolypropylene (PP-2) and 5% by mass of ethylene-α-olefin random copolymer elastomer (E-1), and the heat-seal layer consisted of 60% by mass of ethylene-propylene random copolymer (PP-1) and 40% by mass of linear low-density polyethylene (LL-1). Because the homopolypropylene (PP-2) in the support layer was highly crystalline, film tearing occurred during film formation, resulting in poor film formability and causing the lid to tear upon opening, failing to satisfy the required properties of the present invention. Furthermore, the heat-seal layer contained a large amount of ethylene-propylene random copolymer, resulting in a large difference in strength with respect to the heat-seal strength, which is dependent on the number of seconds, failing to satisfy the required properties of the present invention.

[0068] [Table 1]

[0069] [Table 2]

Claims

1. A laminated film having a heat seal layer and one or more support layers, the heat seal layer is made of a resin composition obtained by mixing a polyethylene-based resin and a polypropylene-based resin, and the polyethylene-based resin is 51% by mass to 95% by mass and the polypropylene-based resin is 5% by mass to 49% by mass, the support layer is made of a resin composition obtained by mixing 70 to 97% by mass of an ethylene-propylene block copolymer and 3 to 30% by mass of a polyethylene-based resin, The laminated film has a heat seal strength of 15 to 27 N / 15 mm when the heat seal layer and the polypropylene sheet are heat sealed at 200°C for 1 second and at 200°C for 4 seconds, and the difference between the heat seal strengths is 7 N / 15 mm or less.

2. 2. The laminated film according to claim 1, wherein the heat seal strength when the heat seal layer and the polypropylene sheet are heat sealed at 150°C for 1 second is 10 to 20 N / 15 mm, and the difference from when the heat seal layer and the polypropylene sheet are heat sealed at 200°C for 1 second is 10 N / 15 mm or less.

3. 2. The laminated film according to claim 1, wherein the polyethylene resin of the heat seal layer is mainly composed of linear low-density polyethylene.

4. The laminated film according to any one of claims 1 to 3, which has a thickness of 15 to 100 µm.

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