Multilayer film, and container

Abstract

To provide a multilayer film which easily suppresses curvature to a first layer side of a multilayer film when being heated.SOLUTION: A multilayer film includes a first layer 12 which is an outer layer bondable to a polyethylene-based resin, and a second layer 17 which is an inner layer thermally welded to a paper base material that has been previously three-dimensionally formed, wherein the first layer 12 is a linear low density polyethylene blended layer, a ratio of the whole polyethylene-based resin is 60 wt.% or more, and the first layer 12 is irradiated with an electron beam under the condition of an absorption dose of 100 kGy or more and 300 kGy or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multilayer film and a container that can be heat-sealed to a paper substrate that has been previously formed into a three-dimensional shape. [Background technology]

[0002] There is known a multilayer film that is adhered to a paper substrate that has been previously formed into a three-dimensional shape. For example, Patent Document 1 discloses a multilayer film (laminate film for paper containers) in which an inner layer is heat-welded to a paper substrate (paper container) that has been previously formed into a three-dimensional shape. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-146996 A Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the inner layer of the multilayer film is heat-sealed to a paper substrate, and after filling the container with contents such as foodstuffs, a lid material is adhered to the outer layer side of the multilayer film. Here, when heat-sealing the multilayer film to the paper substrate, it is considered to heat-seal the multilayer film in a state where the end of the multilayer film protrudes outward from the end of the paper substrate in order to reliably heat-seal the multilayer film to the heat-sealed portion of the paper substrate. However, when the contents such as foodstuffs are filled and then heated before adhering the lid material, there is a problem that the end of the multilayer film heated together with the contents curves toward the outer layer side, which becomes an obstacle when adhering the lid material, for example.

[0005] It is therefore desirable to develop a multilayer film that is easily prevented from curving toward the outer layer side when heated. [Means for solving the problem]

[0006] The multilayer film according to the present disclosure is a multilayer film comprising a first layer which is an outer layer capable of bonding to a polyethylene-based resin, and a second layer which is an inner layer capable of being heat-sealed to a paper substrate previously formed into a three-dimensional shape, the first layer being a linear low-density polyethylene (LLDPE) blended layer in which the overall ratio of polyethylene-based resin is 60% by weight or more, and which has been irradiated with an electron beam at an absorbed dose of 100 kGy or more and 300 kGy or less.

[0007] The container according to the present disclosure comprises the substrate made of paper that has been three-dimensionally formed in advance, and the multilayer film described above, and the multilayer film is heat-sealed to the substrate.

[0008] According to this configuration, since the first layer, which is the outer layer, is a layer containing linear low-density polyethylene irradiated with an electron beam, the first layer is less likely to bend, and therefore, when the multilayer film is heated, it is easy to prevent the multilayer film from curving toward the outer layer side, i.e., the first layer side.

[0009] Preferred embodiments of the present invention will be described below. However, the scope of the present invention is not limited to the preferred embodiments described below.

[0010] In one embodiment, the proportion of linear low-density polyethylene in the first layer is preferably 60% by weight or more.

[0011] In one embodiment, it is preferable that in dynamic viscoelasticity measurement in a tensile mode in the MD direction, the storage modulus at a measurement temperature of 175° C. is 0.3 MPa or more and 3 MPa or less.

[0012] As one embodiment, it is preferable that in dynamic viscoelasticity measurement in a tensile mode in the MD direction, the storage modulus at a measurement temperature of 210° C. is 0.3 MPa or more and 3 MPa or less.

[0013] In one embodiment, the second layer is preferably an ethylene-vinyl acetate copolymer (EVA) blend layer.

[0014] In one embodiment, it is preferable that an intermediate layer, which is an ethylene-vinyl alcohol copolymer (EVOH) blend layer, is provided between the first layer and the second layer.

[0015] In one embodiment, a first functional layer is provided between the first layer and the second layer, and the first functional layer is preferably a low density polyethylene (LDPE) blend layer.

[0016] In one embodiment, a first functional layer is provided between the first layer and the second layer, and the first functional layer is preferably an ionomer (ION) blend layer.

[0017] In one embodiment, a first functional layer is provided between the first layer and the second layer, and the first functional layer is preferably an ethylene-vinyl acetate copolymer (EVA) blend layer.

[0018] In one embodiment, the overall thickness is preferably 80 μm or more and 180 μm or less.

[0019] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments, which are given with reference to the drawings. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view showing a layer structure of a multilayer film according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a schematic cross-sectional view showing a configuration of a container according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of a method for manufacturing the container of FIG. 2. [Figure 4] FIG. 3 is a diagram showing an example of how to use the container of FIG. 2. [Diagram 5] FIG. 10 explains the heat bending evaluation test [Figure 6] FIG. 13 is a diagram showing an example in which the heating bending angle is 0 degrees or more and less than 90 degrees. [Figure 7] A diagram showing an example in which the heating bending angle is 90 degrees or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, a multilayer film 10 according to an embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the layer structure of the multilayer film 10. FIG. 2 is a schematic cross-sectional view showing the structure of a container 20. The multilayer film 10 includes a first layer 12, which is an outer layer that can be adhered to a polyethylene-based resin, and a second layer 17, which is an inner layer that can be heat-sealed to a paper substrate 21. In this embodiment, the multilayer film 10 includes the first layer 12 provided on the first surface side, an intermediate layer 14, and the second layer 17 provided on the second surface side, in the order described above. The second layer 17 of the multilayer film 10 is heat-sealed to a paper substrate 21 that has been previously formed three-dimensionally to form the container 20.

[0022] Here, the term "polyethylene resin" refers to a polymer containing at least ethylene as a monomer unit. Examples of the "polyethylene resin" include high-density polyethylene resin, medium-density polyethylene resin, low-density polyethylene resin, linear low-density polyethylene resin, modified polyethylene resin, ethylene-vinyl acetate resin (e.g., ethylene-vinyl acetate copolymer, etc.), ethylene-vinyl alcohol resin (e.g., ethylene-vinyl alcohol copolymer, etc.), ethylene-methyl acrylate resin (e.g., ethylene-methyl acrylate copolymer, etc.), ethylene-methacrylic acid resin (e.g., ethylene-methacrylic acid copolymer, etc.), ethylene-aliphatic unsaturated carboxylic acid resin, ethylene-aliphatic unsaturated carboxylic acid ester resin, ionomer resin, etc.

[0023] Examples of the "modified polyethylene resin" include ethylene-unsaturated carboxylic acid copolymers, ethylene-methyl methacrylate copolymers, and the like.

[0024] Moreover, the term "polypropylene-based resin" refers to a polymer that contains at least propylene as a monomer unit. Examples of the "polypropylene-based resin" include homopolypropylene, block polypropylene, and random polypropylene.

[0025] Examples of "modified polypropylene resins" include modified polymers obtained by graft-copolymerizing unsaturated carboxylic acids, such as maleic acid and fumaric acid, or their acid anhydrides onto polypropylene resins, such as propylene-α-olefin copolymers and terpolymers of propylene, ethylene, and α-olefin.

[0026] Moreover, the term "polyolefin resin" refers to a polymer containing units derived from olefin. Examples of the "polyolefin resin" include, in addition to the above-mentioned polyethylene and polypropylene, homopolymers of olefins such as polybutene and poly-4-methylpentene, copolymers of two or more olefins, or copolymers of one or more olefins with different components other than olefins.

[0027] The abbreviations for resin names in this embodiment are shown below. PE: Polyethylene HDPE: High density polyethylene MDPE: Medium Density Polyethylene LDPE: Low density polyethylene LLDPE: Linear low density polyethylene ION: Ionomer EVA: Ethylene-vinyl acetate copolymer EVOH: Ethylene-vinyl alcohol copolymer EMA: Ethylene-methyl acrylate copolymer EMAA: Ethylene-methacrylic acid copolymer MAA: Methyl methacrylate PET: Polyethylene terephthalate PO: Polyolefin PP: Polypropylene NY: Nylon

[0028] In this embodiment, the multilayer film 10 includes an intermediate layer 14 between the first layer 12 and the second layer 17. The multilayer film 10 also includes a first functional layer 16 between the first layer 12 and the second layer 17. In the illustrated example, the multilayer film 10 includes, in order from the first layer 12 side, which is the outermost layer, the intermediate layer 14, the first functional layer 16, and the second layer 17.

[0029] The first layer 12 is an outer layer that can be bonded to a polyethylene-based resin. In this embodiment, the first layer 12 is a layer that is in direct contact with the contents of the container 20 and is preferably made of various thermoplastic resins. The first layer 12 is made of, for example, a polyethylene-based resin, a polypropylene-based resin, other polyolefin-based resins, a polyamide-based resin, a polyester-based resin, a polycarbonate-based resin, a polystyrene-based resin, a thermoplastic elastomer, or the like.

[0030] In this embodiment, the first layer 12 is a linear low-density polyethylene blended layer. Here, the linear low-density polyethylene blended layer is a layer blended with linear low-density polyethylene (LLDPE). The linear low-density polyethylene blended layer in the first layer 12 is preferably a layer blended with 60% by weight or more, more preferably 70% by mass or more, and even more preferably 95% by mass or more of linear low-density polyethylene.

[0031] The second layer 17 is a layer that can be thermally welded to the paper substrate 21 that has been three-dimensionally formed in advance. The second layer 17 can be made of a known resin layer that exhibits a certain degree of thermal weldability. The second layer 17 is not particularly limited, but can be made of, for example, a polyethylene resin, an ionomer resin, an ethylene copolymer (such as an ethylene-vinyl acetate copolymer), or a mixture of a polyethylene resin and a polypropylene resin.

[0032] In this embodiment, the second layer 17 is an ethylene-vinyl acetate copolymer blended layer. Here, the ethylene-vinyl acetate copolymer blended layer is a layer blended with ethylene-vinyl acetate copolymer (EVA). The ethylene-vinyl acetate copolymer blended layer in the second layer 17 is preferably a layer blended with 50% by weight or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of ethylene-vinyl acetate copolymer.

[0033] The second layer 17 may contain a modified polyolefin resin having a polar group. When the second layer 17 contains the modified polyolefin resin, it has excellent adhesion to the paper substrate 21. The modified polyolefin resin preferably has a structural unit derived from a monomer having a carboxy group or a group in which two carboxy groups have been anhydridized.

[0034] The modified polyolefin resin is preferably a modified polypropylene resin or a modified polyethylene resin. The second layer 17 may contain only one type of modified polyolefin resin, or may contain two or more types of modified polyolefin resin. The second layer 17 may be composed of a modified polyolefin resin alone, or may be composed of a mixture of the modified polyolefin resin and another material. The other material is not particularly limited and may be selected arbitrarily depending on the purpose.

[0035] In this embodiment, the multilayer film 10 includes an intermediate layer 14 between the first layer 12 and the second layer 17. The function of the intermediate layer 14 is not particularly limited, but preferably provides the multilayer film 10 with gas barrier properties. "Gas barrier properties" refers to the resistance to gas permeation. The intermediate layer 14 provides the multilayer film 10 with gas barrier properties against, for example, carbon dioxide gas (CO2), nitrogen gas (N2), and oxygen gas (O2).

[0036] In this embodiment, the intermediate layer 14 is an ethylene-vinyl alcohol copolymer blended layer. Here, the ethylene-vinyl alcohol copolymer blended layer is a layer blended with an ethylene-vinyl alcohol copolymer (EVOH). The ethylene-vinyl alcohol copolymer blended layer in the intermediate layer 14 is an oxygen barrier layer blended with an ethylene-vinyl alcohol copolymer in an amount of preferably 50% by weight or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0037] Here, it is preferable to use an ethylene-vinyl alcohol copolymer with an ethylene content of 38 mol% or less in the intermediate layer 14, since this has particularly high gas barrier properties. In addition to the ethylene-vinyl alcohol copolymer, the material contained in the intermediate layer 14 is preferably polyamide MXD6, polyvinylidene chloride, or the like. The intermediate layer 14 may also contain an additive having gas barrier properties (mica, clay, or the like). The intermediate layer 14 preferably contains 70% by mass or more of a polyethylene-based resin. More preferably, it contains 80% by mass or more of a polyethylene-based resin. Even more preferably, it contains 90% by mass or more of a polyethylene-based resin.

[0038] The material and thickness of the intermediate layer 14 have a large effect on the gas barrier properties of the multilayer film 10, and therefore the material and thickness of the intermediate layer 14 must be selected within a range that provides the required gas barrier properties. The material and thickness of the intermediate layer 14 must be selected so that the oxygen transmission rate of a film made of the material and having a thickness of 5.0 ml / m2 or less, as measured according to JIS K 7126-2:2006 (constant pressure method). 2 For example, if the intermediate layer 14 is made of an ethylene-vinyl alcohol copolymer with an ethylene content of 38 mol % or less and has a thickness of 6 μm or more, the oxygen permeability is determined to be 5.0 ml / m 2 The material and thickness of the intermediate layer 14 are such that the oxygen permeability of a film made of the material and having the specified thickness is 3.0 ml / m 2 More preferably, the concentration is determined to be equal to or less than 1.0 ml / m 2It is further preferred that the temperature is determined to be equal to or less than 1·day·atm.

[0039] In this embodiment, the multilayer film 10 includes a first adhesive layer 13 between the intermediate layer 14 and the first layer 12. The multilayer film 10 also includes a second adhesive layer 15 between the intermediate layer 14 and the second layer 17. The first adhesive layer 13 and the second adhesive layer 15 have the function of adhering adjacent layers on both sides of each other. The first adhesive layer 13 is preferably adjacent to the intermediate layer 14. The second adhesive layer 15 is preferably adjacent to the intermediate layer 14. The materials constituting the first adhesive layer 13 and the second adhesive layer 15 are selected according to the combination of the two layers to be adhered to each other, and for example, known adhesive polymers are used.

[0040] In this embodiment, a first functional layer 16 is provided between the first layer 12 and the second layer 17. In the illustrated example, the first functional layer 16 is provided between the intermediate layer 14 and the second layer 17, but may be provided between the first layer 12 and the intermediate layer 14. In the example shown in Fig. 1, the first functional layer 16 is disposed between the second adhesive layer 15 and the second layer 17. The function of the first functional layer 16 is not particularly limited, but for example, it imparts heat resistance, freezing resistance, etc. to the multilayer film 10.

[0041] An example of the first functional layer 16 is a low-density polyethylene blended layer. Here, the low-density polyethylene blended layer is a layer blended with low-density polyethylene (LDPE). The low-density polyethylene blended layer in the first functional layer 16 is preferably a layer blended with 50% by weight or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of low-density polyethylene. Since low-density polyethylene is easily curved by heating, the first layer 12 is a linear low-density polyethylene blended layer and the first functional layer 16 is a low-density polyethylene blended layer, so that the multilayer film 10 can be easily curved toward the second layer 17 when heated. Preferably, the first functional layer 16, which is a low-density polyethylene blended layer, is provided between the intermediate layer 14 and the second layer 17.

[0042] An example of the first functional layer 16 is an ionomer-containing layer. Here, the ionomer-containing layer is a layer containing an ionomer (ION). The ionomer-containing layer in the first functional layer 16 is preferably a layer containing 50% by weight or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of an ionomer. Ionomer has a high tension when melted, and can suppress the formation of holes during molding.

[0043] An example of the first functional layer 16 is an ethylene-vinyl acetate copolymer blended layer. Here, the ethylene-vinyl acetate copolymer blended layer is a layer blended with ethylene-vinyl acetate copolymer (EVA). The ethylene-vinyl acetate copolymer blended layer in the first functional layer 16 is preferably a layer blended with 50% by weight or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of ethylene-vinyl acetate copolymer. Since the ethylene-vinyl acetate copolymer is a resin that is easily softened, it can improve moldability.

[0044] Known additives may be added to the polymeric materials used in each layer constituting the multilayer film 10 of this embodiment. Examples of such additives include plasticizers, antioxidants, flame retardants, stabilizers, UV absorbers, antistatic agents, lubricants, water repellents, and oil repellents.

[0045] In this embodiment, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 100 kGy or more. Preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 125 kGy or more. More preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 150 kGy or more. Even more preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 175 kGy or more. When the absorbed dose of the electron beam irradiation is within this range, it is possible to impart high heat resistance to the multilayer film 10, and the rigidity when heated can be maintained.

[0046] In this embodiment, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 300 kGy or less. Preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 275 kGy or less. More preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 250 kGy or less. Even more preferably, the multilayer film 10 is irradiated with an electron beam at an absorbed dose of 225 kGy or less. By irradiating the multilayer film 10 with an absorbed dose within this range, discoloration of the multilayer film 10 due to an excessive absorbed dose can be prevented.

[0047] The reason why the crosslink density of the multilayer film 10 is improved by electron beam irradiation is not clear, but it is believed to be as follows. That is, when the multilayer film 10 is irradiated with an electron beam, the carbon-hydrogen bonds in the polyethylene of the first layer 12 of the multilayer film 10 are broken, and radicals are generated at the ends of the broken bonds. It is believed that the generated radicals come into contact with other polyethylene molecular chains due to the molecular motion of the molecular chains, extract hydrogen atoms, and bond with carbon atoms in the polyethylene molecular chains, resulting in the formation of a crosslinked structure. It is believed that a similar phenomenon occurs in the first functional layer 16 and the intermediate layer 14. However, the above-mentioned mechanism is merely a conjecture, and the scope of the present invention is not affected by its truth or falsity.

[0048] In this embodiment, the electron beam is irradiated from the side of the first layer 12. In this manner, it is possible to effectively improve the heat resistance of the first layer 12, which is the surface that comes into contact with the contents such as food. In addition, it is possible to suppress a decrease in the adhesive strength of the second layer 17 that is thermally fused to the paper substrate 21.

[0049] In this embodiment, the overall thickness of the multilayer film 10 is 80 μm or more. The overall thickness of the multilayer film 10 is preferably 90 μm or more, and more preferably 100 μm or more. If the thickness of the multilayer film 10 is less than 80 μm, the intermediate layer 14 becomes thin and the gas barrier property may not meet the required level. In addition, if the thickness of the multilayer film 10 is less than 80 μm, the yield when manufacturing the multilayer film 10 may be low.

[0050] In this embodiment, the overall thickness of the multilayer film 10 is 180 μm or less. The overall thickness of the multilayer film 10 is preferably 160 μm or less, and more preferably 140 μm or less. If the thickness of the multilayer film 10 exceeds 180 μm, heat is less likely to be transferred to the bonding surface when the second layer 17 is thermoformed (thermal welded) to the substrate 21, and thermoforming (thermal welding) defects may be more likely to occur.

[0051] In this embodiment, the ratio of polyethylene-based resin in the multilayer film 10 is 60% by weight or more. Preferably, the ratio of polyethylene-based resin in the multilayer film 10 is 70% by weight or more. More preferably, the ratio of polyethylene-based resin in the multilayer film 10 is 80% by weight or more. The ratio of polyethylene-based resin in the multilayer film 10 is a value calculated by dividing the total weight of the polyethylene-based resin in each layer by the total weight of the multilayer film 10.

[0052] In this embodiment, in dynamic viscoelasticity measurement in a tensile mode in the MD (machine direction), the storage modulus of the multilayer film 10 at a measurement temperature of 175°C is 0.3 MPa or more. Preferably, the storage modulus is 0.4 MPa or more. More preferably, the storage modulus is 0.5 MPa or more. Even more preferably, the storage modulus is 0.6 MPa or more.

[0053] In this embodiment, in dynamic viscoelasticity measurement in the tensile mode in the MD direction, the storage modulus of the multilayer film 10 at a measurement temperature of 210°C is 0.3 MPa or more. Preferably, the storage modulus is 0.4 MPa or more. More preferably, the storage modulus is 0.5 MPa or more. Even more preferably, the storage modulus is 0.6 MPa or more.

[0054] In this embodiment, in dynamic viscoelasticity measurement in the tensile mode in the MD direction, the storage modulus of the multilayer film 10 at a measurement temperature of 175°C is 3 MPa or less. Preferably, the storage modulus is 2.7 MPa or less. More preferably, the storage modulus is 2.3 MPa or less. Even more preferably, the storage modulus is 2.0 MPa or less. In this way, good thermoformability (conformability) to a three-dimensional paper substrate 21 (paper container) described below can be obtained.

[0055] In this embodiment, in dynamic viscoelasticity measurement in the tensile mode in the MD direction, the storage modulus of the multilayer film 10 at a measurement temperature of 210°C is 3 MPa or less. Preferably, the storage modulus is 2.7 MPa or less. More preferably, the storage modulus is 2.3 MPa or less. Even more preferably, the storage modulus is 2.0 MPa or less. In this way, good thermoformability (conformability) can be obtained to a three-dimensional paper substrate 21 (paper container) described below.

[0056] Preferably, in dynamic viscoelasticity measurement in a tensile mode in the MD direction, the storage modulus of the multilayer film 10 at a measurement temperature of 175° C. or more and 210° C. or less is in the above range.

[0057] As shown in FIG. 2, the container 20 includes a paper substrate 21 that has been formed three-dimensionally in advance, and a multilayer film 10, and the multilayer film 10 is heat-sealed to the substrate 21. In this embodiment, the container 20 further includes a lid 22. The container 20 contains, for example, food or medicine as contents. As the lid 22, for example, a top film for top-seal packaging made of a polyethylene resin or a skin film for skin-pack packaging made of an ethylene-vinyl acetate copolymer resin is used. "Top-seal packaging" is packaging in which the contents are filled in a container, and the top film is heat-sealed to the container to preferably seal it. "Skin-pack packaging" is a packaging method in which a product is placed in a container such as a tray, a mount, an air cap, or a film, and a heated skin film is placed on top of the container, and air is removed from below at the same time, and the skin film is brought into close contact with the surface of the food and the container to preferably seal it. In the illustrated example, the substrate 21 that has been formed three-dimensionally in advance is a paper container for top-seal packaging, and the lid 22 is a top film.

[0058] When the first layer 12 contains a polyethylene resin, the first layer 12 has oil resistance, so that damage to the substrate 21 caused by oil contained in food or the like can be avoided. In addition, since the first layer 12 is given heat resistance by electron beam crosslinking, it has sufficient heat resistance for food heated in a microwave oven, for example. Preferably, the multilayer film 10 is a multilayer film for microwave-heated food that can be used for microwave-heated food. Here, microwave-heated food means food that is cooked in a microwave oven. Also, preferably, the container 20 has microwave-heating resistance. Having microwave-heating resistance means that food can be cooked in a microwave oven. Preferably, having microwave-heating resistance means that it complies with the "Microwave High Frequency Suitability Test" and "Microwave Durability Test" specified in JIS S2029:2002. Since the container 20 has microwave-heating resistance, the container 20 can be suitably used for microwave-heated food.

[0059] The first layer 12 is heat-sealed to the lid 22. This makes it possible to seal food or the like in the space defined by the multilayer film 10 and the lid 22. For example, the multilayer film 10 has high gas barrier properties (particularly oxygen barrier properties, with an oxygen permeability of 5.0 ml / m 2 ) derived from the intermediate layer 14. 2 1·day·atm or less. Since the lid material 22 also has high gas barrier properties, food and the like can be sealed with a member having high gas barrier properties, so deterioration of the food and the like can be suppressed.

[0060] 3 is a diagram showing a method for manufacturing the container 20. The method for manufacturing the container 20 includes a substrate forming step S11, a multilayer film forming step S12, a heat softening step S13, and a lamination step S14.

[0061] The substrate forming step S11 is a step of forming a substrate 21 having a three-dimensional shape from a planar paper material. A known forming method can be used for the substrate forming step S11. Examples of such forming methods include vacuum forming, pressure forming, vacuum pressure forming, match forming forming, and press forming. As the paper material, recycled paper pulp, virgin pulp, and pulp obtained by appropriately mixing these may be used. The container 20 may be formed into a three-dimensional shape by assembling paperboard by cutting it into a desired shape, or may be formed using a mold.

[0062] The multilayer film forming step S12 is a step of forming a multilayer film 10 having a first layer 12, an intermediate layer 14, and a second layer 17 in the order described above. For example, co-extrusion molding is used as the multilayer film forming step S12. That is, the materials constituting the first layer 12, the intermediate layer 14, the first functional layer 16, and the second layer 17 are extruded from an extruder and discharged from a T-die to form the multilayer film 10 having the above configuration. As another forming method, the multilayer film 10 may be formed by a method in which the first layer 12, the intermediate layer 14, the first functional layer 16, and the second layer 17, which are formed into a film shape for each layer, are heat-welded to each other. The multilayer film 10 may also be formed by bonding the layers together using an adhesive by any of a dry lamination method, a hot melt lamination method, and a wet lamination method. In the illustrated example, the multilayer film forming step S12 is performed after the substrate forming step S11, but the order may be reversed or the layers may be performed in parallel.

[0063] The heat-softening step S13 is a step of heating and softening the multilayer film 10. In this embodiment, the substrate 21 is placed in the lower mold of a mold, and the multilayer film 10 is placed on a hot plate, which is the upper mold of the mold, so that the second layer 17 side faces the substrate 21, and is heated and softened at 120°C to 150°C.

[0064] The laminating step S14 is a step of thermally welding the multilayer film 10 softened in the heat-softening step S13 by bringing the second layer 17 into contact with the substrate 21. In this embodiment, the upper mold on which the multilayer film 10 is arranged is lowered to bring the second layer 17 of the multilayer film 10 into contact with the substrate 21 arranged in the lower mold, and a pressure of 1.0 kgf to 2.5 kgf, preferably 1.5 kgf to 2.0 kgf is applied, and this state is maintained for 1 to 5 seconds, thereby thermally welding the multilayer film 10 and the substrate 21.

[0065] FIG. 4 is a diagram showing an example of a method of using the container 20. The first heating step S21 is a heating step performed while the contents are accommodated in the container 20. The first heating step S21 is, for example, a step of heating the contents in an oven. The lid material bonding step S22 is a step of bonding the lid material 22 to the first layer 12 of the multilayer film 10 in the container 20. The lid material bonding step S22 is, for example, a step of sealing the contents between the container 20 and the lid material 22. The second heating step S23 is a heating step performed before the contents are removed from the container 20. The second heating step S23 is, for example, a step of heating the contents in a microwave oven.

[0066] In this embodiment, the storage modulus at the measurement temperature of 175°C and the measurement temperature of 210°C in the dynamic viscoelasticity measurement is the heat resistance corresponding to the first heating step S21. Examples of the contents of the container 20 used in the step of FIG. 4 include foods such as gratin and doria. According to the above-mentioned multilayer film 10 and container 20, since the first layer 12 is a linear low-density polyethylene blend layer irradiated with an electron beam, the first layer 12 is less likely to bend. Therefore, when the multilayer film 10 is heated, it is easy to suppress the curvature of the multilayer film 10 toward the first layer 12 side. For example, it is possible to suppress the curvature of the multilayer film 10 toward the first layer 12 side in the first heating step S21. Therefore, it is easy to adhere the lid material 22 to the first layer 12 of the multilayer film 10 in the lid material adhering step S22.

[0067] Other embodiments Next, other embodiments of the multilayer film 10 will be described.

[0068] (1) In the above embodiment, the multilayer film 10 includes the first layer 12, the first adhesive layer 13, the intermediate layer 14, the second adhesive layer 15, the first functional layer 16, and the second layer 17. However, the present invention is not limited to such an example. For example, a second functional layer having a different function from the first functional layer 16 and the intermediate layer 14 may be provided between the first layer 12 and the intermediate layer 14. For example, the first functional layer 16 and the second functional layer may be provided on both sides of the intermediate layer 14 in the stacking direction, symmetrically with respect to the intermediate layer 14. For example, the first functional layer 16 and the second functional layer may be layers having the same function. For example, the multilayer film 10 may not include the first adhesive layer 13, the intermediate layer 14, the second adhesive layer 15, or the first functional layer 16.

[0069] (2) In the above embodiment, a container manufacturing method including a base material forming step S11, a multilayer film forming step S12, a heat softening step S13, and a lamination step S14 has been described as an example. However, the method is not limited to such an example, and may include other steps. For example, a lid material forming step, a gravure printing step, etc. may be further provided.

[0070] (3) In the above embodiment, the method of using the container 20 including the lid material 22 includes the first heating step S21, the lid material bonding step S22, and the second heating step S23. However, the present invention is not limited to such an example, and for example, the first heating step S21 or the second heating step S23 may not be performed. In addition, the container 20 may not include the lid material 22, in which case the lid material bonding step S22 may not be performed.

[0071] (4) In the above embodiment, the storage modulus is 0.3 MPa or more and 3 MPa or less at both the measurement temperature of 175° C. and the measurement temperature of 210° C. However, the present invention is not limited to such an example, and the storage modulus may be 0.3 MPa or more and 3 MPa or less at only one of the measurement temperature of 175° C. and the constant temperature of 210° C. For example, the storage modulus may be lower than 0.3 MPa or higher than 3 MPa regardless of the measurement temperature range.

[0072] (5) In the above embodiment, the multilayer film 10 has a total thickness of 80 μm or more and 180 μm or less. However, the present invention is not limited to such an example, and the multilayer film 10 may have a total thickness less than 80 μm. Also, the multilayer film 10 may have a total thickness greater than 180 μm.

[0073] (6) The configurations disclosed in the above-described embodiments can be combined with configurations disclosed in other embodiments as long as no contradiction occurs. As for other configurations, the embodiments disclosed in this specification are merely examples in all respects. Therefore, various modifications can be made as appropriate within the scope of the present disclosure.

[0074] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the following examples.

[0075] After the multilayer films 10 of Samples 1 to 10 described below were produced, a "dynamic viscoelasticity measurement" and a "heat bending property evaluation test" were carried out.

[0076] In each of the samples 1 to 10, the first layer 12, the first adhesive layer 13, the intermediate layer 14, the second adhesive layer 15, the first functional layer 16, and the second layer 17 are arranged in the order described above, and the thickness ratio thereof is 25:10:15:10:25:15. The total thickness of the multilayer film of each of the samples 1 to 10 is 100 μm. The polyethylene resin ratio of each of the samples 1 to 10 is 85%. The first adhesive layer 13 and the second adhesive layer 15 of each of the samples 1 to 10 are adhesive polyolefin (product number: Admer NF536 (manufactured by Mitsui Chemicals)), the intermediate layer 14 is EVOH (product number: EVAL XEP-1393B (manufactured by Kuraray Co., Ltd.)), and the second layer 17 is EVA (product number: Evaflex V5714C (manufactured by Mitsui-Dow Polychemicals Co., Ltd.)).

[0077] The resins of the first layer 12 and the first functional layer 16 constituting the samples 1 to 10 are as follows.

[0078] Sample 1 First layer: “LLDPE” (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "LDPE" (Product number: UBE Polyethylene F222NH (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) Sample 2 First layer: “LLDPE” (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "ION" (Product number: Ionomer 1601 (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) Sample 3 First layer: “LLDPE” (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "EVA" (Product number: Evaflex V5714C (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) Sample 4 First layer: “LLDPE” (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "LLDPE" (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) Sample 5 First layer: "LLDPE" (60% blend ratio) (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) : "LDPE" (40% blend) (Product number: UBE Polyethylene F222NH (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "ION" (Product number: Ionomer 1601 (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) Sample 6 First layer: "LLDPE" (40% blend ratio) (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) : "LDPE" (60% blended) (Product number: UBE Polyethylene F222NH (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "ION" (Product number: Ionomer 1601 (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) Sample 7 First layer: "LDPE" (Product number: UBE Polyethylene F222NH (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "LLDPE" (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) Sample 8 First layer: "ION" (Product number: Ionomer 1601 (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) First functional layer: "LLDPE" (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) Sample 9 First layer: "EVA" (Product number: Evaflex V5714C (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) First functional layer: "LLDPE" (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) Sample 10 First layer: "LLDPE" (40% blend ratio) (Product number: Yumerit 4040FC (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) : "LDPE" (60% blended) (Product number: UBE Polyethylene F222NH (manufactured by Ube Maruzen Polyethylene Co., Ltd.)) First functional layer: "ION" (Product number: Ionomer 1601 (manufactured by Dow Mitsui Polychemicals Co., Ltd.))

[0079] "Dynamic Mechanical Analysis (DMA)" The storage modulus was measured by dynamic mechanical analysis (DMA) under the following conditions.

[0080] (Measurement conditions) - Multilayer film shape: length 20mm, width 4mm, thickness 100μm Test equipment model: DMA7100 (Hitachi High-Tech Fielding Corporation) ·Measurement temperature: 210℃ Measurement mode: Tensile Frequency: 10Hz ·Minimum tension: 50mN Tension Gain: 1.2 Initial force amplitude: 50mN

[0081] "Heat bending evaluation test" The heat curvature was measured by a heat curvature evaluation test, as described below.

[0082] (Measurement method) Fig. 5 is a diagram for explaining the heat curvature evaluation test. As shown in Fig. 5, the multilayer film 10 (26 cm x 26 cm x 100 μm thick) of each of the samples 1 to 10 was sandwiched between iron plates 41 and 42 (20 cm x 20 cm x 1 cm thick) from both sides in the thickness direction with the end of the multilayer film 10 sticking outward, and heated for 6 seconds by a 600°C hot plate 45 placed at an interval on the first layer 12 side. The dimension t1 of the part where the end of the multilayer film 10 sticks outward was 3 cm, and the interval t2 between the iron plate 41 and the hot plate 45 was 8 cm.

[0083] After the above heating, the angle between the tangent to the tip of the multilayer film 10 outside the iron plate 42 and the tangent to the surface of the iron plate 42 (i.e., the tangent to the tip of the multilayer film 10 before bending) was taken as the heat bending angle θ and was measured with a protractor, as shown in Figures 6 and 7. Figure 6 shows an example where the heat bending angle θ is equal to or greater than 0 degrees and less than 90 degrees, and Figure 7 shows an example where the heat bending angle θ is 90 degrees or greater. The heat bending angle θ was measured at multiple points and evaluated as the maximum value.

[0084] The outline of the configuration of Samples 1 to 10, the results of the dynamic viscoelasticity measurement (storage modulus), and the results of the heat bending property evaluation test (heat bending angle θ) are shown in Table 1 below. In Table 1, the bending toward the second layer 17 side, i.e., the case where the heat bending angle θ is less than 0 degrees, is shown as - (minus). In Table 1, among the bending toward the first layer 12 side, the case where the heat bending angle θ is 0 degrees or more and less than 45 degrees is shown as small, the case where the heat bending angle θ is 45 degrees or more and less than 90 degrees is shown as medium, and the case where the heat bending angle θ is 90 degrees or more is shown as large.

[0085] [Table 1]

[0086] As shown in Table 1, samples 1 to 4 showed good results because the direction of curvature due to heat was not toward the first layer 12. Samples 5 and 6 showed good results because the direction of curvature due to heat was toward the first layer 12, but was less than 90 degrees, which did not hinder the bonding of the lid material. Sample 1, in which the first functional layer 16 was LDPE, was able to bend significantly toward the second layer 17. [Explanation of symbols]

[0087] 10: Multilayer film 12:First layer 14: Middle class 16:First functional layer 17:Second layer 20: Container 21: Base material

Claims

1. A multilayer film comprising a first layer which is an outer layer capable of adhering to a polyethylene-based resin, and a second layer which is an inner layer capable of being heat-sealed to a paper substrate previously formed into a three-dimensional shape, The first layer is a linear low density polyethylene blend layer, A multilayer film having an overall polyethylene resin ratio of 60% by weight or more, which has been irradiated with electron beams at an absorbed dose of 100 kGy to 300 kGy.

2. 2. The multilayer film according to claim 1, wherein the proportion of linear low density polyethylene in said first layer is 60% by weight or more.

3. 2. The multilayer film according to claim 1, which has a storage modulus of 0.3 MPa or more and 3 MPa or less at a measurement temperature of 175°C in dynamic viscoelasticity measurement in a tensile mode in the MD direction.

4. 2. The multilayer film according to claim 1, which has a storage modulus of 0.3 MPa or more and 3 MPa or less at a measurement temperature of 210°C in dynamic viscoelasticity measurement in a tensile mode in the MD direction.

5. 2. The multilayer film of claim 1, wherein said second layer is an ethylene-vinyl acetate copolymer blend layer.

6. 2. The multilayer film of claim 1, further comprising an intermediate layer between said first layer and said second layer, said intermediate layer being an ethylene-vinyl alcohol copolymer blend layer.

7. 2. The multilayer film of claim 1, further comprising a first functional layer between said first layer and said second layer, said first functional layer being a low density polyethylene blend layer.

8. The multilayer film according to claim 1 , further comprising a first functional layer between the first layer and the second layer, the first functional layer being an ionomer blend layer.

9. 2. The multilayer film according to claim 1, further comprising a first functional layer between said first layer and said second layer, said first functional layer being an ethylene-vinyl acetate copolymer blend layer.

10. 2. The multilayer film of claim 1, having a total thickness of 80 μm or more and 180 μm or less.

11. A container comprising: a substrate made of paper that has been three-dimensionally formed in advance; and the multilayer film according to any one of claims 1 to 10, wherein the multilayer film is heat-sealed to the substrate.

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