Method for manufacturing packaging body

Abstract

To provide a packaging body using a multilayer film as a lid material that does not deform the bottom container and has excellent melting strength when heated.SOLUTION: A method for manufacturing a package in which a food product is packaged by a lid material and a bottom material, comprises the steps of: placing the food on the bottom material; placing the lid material in the area on the bottom material that covers the food and its surroundings; and bringing the lid material into contact with the food while heating it to 90-250°C, forming it along the food, and bonding the portion of the lid material in contact with the bottom material with the bottom material, thereby packaging the food by the lid material and bottom material, wherein the lid material is composed of a multilayer film, the multilayer film is composed of a sealant layer, a functional layer, and a gas barrier layer, which are laminated in this order in these thickness directions, the functional layer contains ionomer, the melting strength of the ionomer at a temperature of 180°C is 60-540 mN, and the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2-25%.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a package.

Background Art

[0002] A package in which food (the object to be packaged) is placed on a rigid tray and the food is sealed with a film by evacuation is called a skin pack. In a skin pack, the film, that is, the film for the skin pack, is transparent, and the food can be easily visually recognized through it. Further, the film for the skin pack is soft, and by evacuating the storage part in the skin pack, it is possible to closely adhere to the food without causing wrinkles (see, for example, Patent Document 1). And, since the skin pack includes a rigid tray (base material), it can be displayed upright without causing displacement of the position of the food. In view of such characteristics, skin packs are mainly used as packages for food.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of a skin pack for food, in order to prevent oxidative deterioration of the food, a gas barrier layer is required to be provided in the multilayer film constituting the skin pack. However, generally, since the resin contained in the gas barrier layer has a high dynamic elastic modulus, for example, when the ratio of the gas barrier layer is high, there is a problem that the bottom material container is deformed when the multilayer film is adhered to the food. In recent years, the trend is shifting from conventional chamber-type skin pack machines (indirect heating method) with a low number of shots to continuous skin pack packaging machines (direct heating method) with a high number of shots, and a melt strength that can withstand the method of directly heating the film at a high temperature on a heated hot plate is required.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a package (for example, a skin pack package) using, as a lid material, a multilayer film that does not deform the bottom material container and has excellent melt strength during heating.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention adopts the following configuration. [1]. A method for manufacturing a package in which food is packaged by a lid material and a bottom material, the method including: a step of disposing the food on the bottom material; a step of disposing the lid material in a region that covers the food and its periphery among the regions on the bottom material; a step of bringing the lid material into contact with the food while heating the lid material to 90 to 250°C and shaping it along the food, and bonding a portion of the lid material that is in contact with the bottom material to the bottom material, thereby packaging the food with the lid material and the bottom material, wherein the lid material is composed of a multilayer film, the multilayer film is configured by laminating a sealant layer, a functional layer, and a gas barrier layer in this order in their thickness directions, the functional layer contains an ionomer, the melt strength of the ionomer at a temperature of 180°C is 60 to 540 mN, and the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2 to 25%. A method for manufacturing a package. [2]. The method for manufacturing a package according to [1], wherein the temperature at which a displacement of 2000 μm is exhibited during thermomechanical analysis of the multilayer film is 120°C or higher. [3]. The method for manufacturing the package according to [1] or [2], wherein the gel fraction of the multilayer film is 30% or more. [4]. The method for manufacturing the package according to [2], wherein the displacement at a temperature of 100 °C during the thermomechanical analysis of the multilayer film is 500 μm or less. [5]. The dynamic elastic modulus E' of the multilayer film at a temperature of 140 °C is 1×10 4 Pa or more and 1×10 7 Pa or less. The method for manufacturing the package according to any one of [1] to [4]. [6]. The method for manufacturing the package according to any one of [1] to [5], wherein the multilayer film is irradiated with an electron beam under the condition of an absorbed dose of 13 to 300 kGy. [7]. The method for manufacturing the package according to any one of [1] to [6], wherein the ratio of the thickness of the sealant layer to the thickness of the multilayer film is 5% or more. [8]. The method for manufacturing the package according to any one of [1] to [7], wherein the ratio of the thickness of the functional layer to the thickness of the multilayer film is 10% or more. [9]. The method for manufacturing the package according to any one of [1] to [8], wherein the gas barrier layer contains an ethylene-vinyl alcohol copolymer.

[10] . The method for manufacturing the package according to any one of [1] to [9], wherein the package is a skin pack package. [Effect of the Invention]

[0007] The manufacturing method of the package of the present invention is a method for manufacturing a package in which food is packaged with a lid material and a bottom material, including a step of disposing the food on the bottom material, and a step of disposing the lid material in a region that covers the food and its periphery among the regions on the bottom material. While heating the lid material to 90 to 250 °C, it is brought into contact with the food and formed along the food, and the portion of the lid material in contact with the bottom material is adhered to the bottom material, thereby packaging the food with the lid material and the bottom material. The lid material is composed of a multilayer film, and the multilayer film is composed of a sealant layer, a functional layer, and a gas barrier layer laminated in this order in the thickness direction thereof. The functional layer contains an ionomer, the melt strength of the ionomer at a temperature of 180 °C is 60 to 540 mN, and the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2 to 25%. Therefore, it is possible to provide a package (for example, a skin pack package) that does not deform the bottom material container and uses a multilayer film with excellent melt strength during heating as the lid material.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] <<Multilayer Film (Lid Material)>> The lid material (multilayer film) of the package manufactured by the method according to an embodiment of the present invention is composed of a sealant layer, a functional layer, and a gas barrier layer laminated in this order in their thickness directions, and the functional layer contains an ionomer. The multilayer film (lid material) is not particularly limited as long as it satisfies the conditions of the melt strength of the ionomer and the ratio of the thickness of the gas barrier layer, which will be described later.

[0010] The oxygen transmission rate of the multilayer film (lid material) under the conditions of a temperature of 23°C and a relative humidity of 60% is preferably 100 cc / (m 2 ·day·atm) or less. By the oxygen transmission rate being 100 cc / (m 2 ·day·atm) or less, deterioration of the packaged food can be suppressed and long-term storage can be achieved.

[0011] The oxygen transmission rate of the multilayer film (lid material) under the conditions of a temperature of 23°C and a relative humidity of 60% is more preferably 95 cc / (m 2 ·day·atm) or less, even more preferably 90 cc / (m 2 ·day·atm) or less, particularly preferably 85 cc / (m 2 ·day·atm) or less, and for example, it may be 80 cc / (m 2 ·day·atm) or less. By the oxygen transmission rate being below the upper limit value, the effect of suppressing deterioration of the packaged food and achieving long-term storage can be further improved.

[0012] On the other hand, the oxygen transmission rate is 0 cc / (m 2 ·day·atm) or more, preferably 0.1 cc / (m 2 ·day·atm) or more, more preferably 0.2 cc / (m 2 ·day·atm) or more, even more preferably 0.3 cc / (m 2 ·day·atm) or more, particularly preferably 0.4 cc / (m 2 ·day·atm) or more, and for example, it may be 0.5 cc / (m 2·day·atm) or more. By having the oxygen transmission rate be at least the lower limit value, the thickness of the gas barrier layer falls within an appropriate range, and an adverse effect on followability can be suppressed.

[0013] The oxygen transmission rate of the multilayer film (lid material) under the conditions of a temperature of 23°C and a relative humidity of 60% can be measured in accordance with JIS K 7126-2:2006.

[0014] The oxygen transmission rate of the multilayer film (lid material) can be adjusted more easily, for example, by adjusting the type and content of the components contained in the gas barrier layer described later, the thickness of the gas barrier layer, its ratio, and the like.

[0015] The temperature indicating a displacement of 2000 μm during the thermomechanical analysis (TMA) of the multilayer film (lid material) is preferably 120°C or higher, more preferably 120 to 200°C, even more preferably 123 to 190°C, and may be, for example, 130 to 190°C. By having the temperature be at least the lower limit value, the heat resistance of the multilayer film is further improved. By having the temperature be at most the upper limit value, it is further suppressed that the heat resistance of the multilayer film becomes excessive.

[0016] During the thermomechanical analysis of the multilayer film, the displacement at a temperature of 100°C is preferably 500 μm or less, more preferably 40 to 500 μm, even more preferably 45 to 400 μm, and may be any of, for example, 50 to 350 μm, 55 to 340 μm, and 55 to 250 μm. By having the displacement be at most the upper limit value, the melt tension of the multilayer film is further improved. By having the displacement be at least the lower limit value, it is further suppressed that the melt tension of the multilayer film becomes excessive.

[0017] The thermomechanical analysis of the multilayer film can be performed by measuring the thermal expansion amount of the sample from the difference in the thermal expansion amounts of a standard sample and the sample to be analyzed when the temperature is raised at a constant rate in accordance with JIS K 7196. The thermomechanical analysis of the multilayer film can be performed, for example, by using a sample with a width of 40 mm, a length of 150 mm, and a thickness of 120 μm and measuring the displacement (thermal expansion amount) in the film flow direction (MD) of this sample.

[0018] During the thermomechanical analysis of the multilayer film, the temperature indicating a displacement of 2000 μm and the displacement at a temperature of 100 °C can be adjusted, for example, by using the multilayer film irradiated with an electron beam and adjusting the conditions of the electron beam irradiation at this time. For example, by adjusting the conditions of the electron beam irradiation to the outer layer or the functional layer in this multilayer film, the temperature and the displacement can be adjusted more easily.

[0019] The multilayer film is preferably irradiated with an electron beam under the condition of an absorbed dose of 13 to 300 kGy, more preferably irradiated with an electron beam under the condition of an absorbed dose of 15 to 250 kGy, and may be irradiated with an electron beam under any of the conditions of an absorbed dose of 20 to 250 kGy, 45 to 250 kGy, and 70 to 250 kGy, for example. When the absorbed dose is within such a range, a multilayer film in which both the temperature indicating a displacement of 2000 μm and the displacement at a temperature of 100 °C are within the above numerical ranges during the thermomechanical analysis of the multilayer film can be obtained more easily. On the other hand, when the absorbed dose is not less than the lower limit value, the crosslinking density of the multilayer film (particularly, the outer layer and the functional layer in this multilayer film) is further improved, and as a result, the heat resistance and the melt tension of the entire multilayer film are further improved. When the absorbed dose is not more than the upper limit value, it is more suppressed that the strength of the multilayer film becomes excessive.

[0020] Although the reason why the crosslinking density of the multilayer film (especially the outer layer and the functional layer in this multilayer film) is improved by electron beam irradiation is not clear, it is presumed as follows. That is, when the multilayer film is irradiated with an electron beam, the carbon-hydrogen bonds in the resin (for example, polyethylene, ionomer) are broken, and radicals are generated at the broken bond ends. The generated radicals come into contact with the molecular chains of other resins (for example, other polyethylene molecular chains, other ionomer molecular chains) due to the molecular motion of the molecular chains, extract hydrogen atoms, and bond with the carbon atoms in the molecular chains of other resins (for example, other polyethylene molecular chains, other ionomer molecular chains). As a result, it is presumed that a crosslinked structure is formed.

[0021] The acceleration voltage during electron beam irradiation is preferably 100 to 300 kV, more preferably 120 to 280 kV, and even more preferably 140 to 260 kV. When the acceleration voltage during electron beam irradiation is within such a range, the multilayer film in which both the temperature showing a displacement of 2000 μm and the displacement at a temperature of 100 °C are within the above numerical ranges during the thermomechanical analysis of the multilayer film can be obtained more easily. On the other hand, when the acceleration voltage during electron beam irradiation is equal to or higher than the lower limit value, the crosslinking density of the multilayer film (especially the outer layer and the functional layer in this multilayer film) is further improved. As a result, the heat resistance and melt tension of the entire multilayer film are further improved. When the acceleration voltage during electron beam irradiation is equal to or lower than the upper limit value, it is more suppressed that the strength of the multilayer film becomes excessive.

[0022] The gel fraction of the multilayer film is preferably 30% or more, more preferably 30 to 90%, even more preferably 32 to 85%, and may be any of, for example, 40 to 82%, 48 to 82%, and 55 to 82%. When the gel fraction of the multilayer film is equal to or higher than the lower limit value, the heat resistance and melt tension of the multilayer film are further improved. When the gel fraction of the multilayer film is equal to or lower than the upper limit value, it is more suppressed that the strength of the multilayer film becomes excessive.

[0023] The gel fraction of the multilayer film can be measured in accordance with JIS K 6769 by utilizing the fact that the crosslinked portion of the film does not dissolve in the solvent. That is, the multilayer film is immersed in an organic solvent such as xylene, the insoluble film that remains undissolved is dried, and then the mass of the obtained dried product is measured, and the gel fraction can be calculated from the mass of the multilayer film before dissolution and the mass of the dried product of the insoluble film. More specifically, for example, a multilayer film (mass X g) is wrapped with a stainless steel wire mesh (mass Y g) and immersed in a heated solvent, and then the multilayer film wrapped with the stainless steel wire mesh (in other words, the insoluble film) is taken out. Next, this is dried in vacuo, and the mass (Z g) of the multilayer film wrapped with the stainless steel wire mesh after drying (in other words, the insoluble film) is measured. And the following formula (1): Gel fraction of multilayer film (mass %) = (Z - Y) / X × 100 (1) is used to calculate the gel fraction of the multilayer film.

[0024] The gel fraction of the multilayer film can be adjusted, for example, by subjecting the multilayer film (particularly, the outer layer or the functional layer in this multilayer film) to electron beam irradiation and adjusting the conditions of the electron beam irradiation at this time. As the conditions during the electron beam irradiation in this case, the absorbed dose and the acceleration voltage of the electron beam irradiation, which are the same as those when adjusting the temperature showing a displacement of 2000 μm and the displacement at a temperature of 100°C during the thermomechanical analysis of the multilayer film described above, can be adopted.

[0025] It is preferable that the multilayer film satisfies either one or both of the conditions of the temperature showing a displacement of 2000 μm and the gel fraction during the above-described thermomechanical analysis. That is, as the multilayer film, for example, those in which the temperature showing a displacement of 2000 μm during the thermomechanical analysis is 120°C or higher and the gel fraction is less than 30%; those in which the temperature showing a displacement of 2000 μm during the thermomechanical analysis is less than 120°C and the gel fraction is 30% or higher; and those in which the temperature showing a displacement of 2000 μm during the thermomechanical analysis is 120°C or higher and the gel fraction is 30% or higher can be mentioned. However, usually, the multilayer film preferably satisfies both of the above conditions, that is, the temperature at which the displacement of 2000 μm is shown during its thermomechanical analysis is 120°C or higher, and the gel fraction is 30% or higher.

[0026] The dynamic elastic modulus E' of the multilayer film (lid material) at a temperature of 140°C is 1×10 4 Pa or more and 1×10 7 Pa or less, which is preferable. When the dynamic elastic modulus E' is equal to or higher than the lower limit value, the followability of the lid material to the food can be improved. As a result, drips generated during storage can be suppressed, outflow of umami components can be prevented, and long-term storage is possible without degrading the taste. When the dynamic elastic modulus E' is equal to or lower than the upper limit value, the food can be packaged without compressing its shape as much, and deformation of the bottom material container can be further suppressed when it adheres to the food.

[0027] The dynamic elastic modulus E' of the multilayer film (lid material) at a temperature of 140°C is preferably 1.1×10 4 Pa or more and 9.9×10 6 Pa or less, more preferably 1.2×10 4 Pa or more and 9.8×10 6 Pa or less, still more preferably 1.3×10 4 Pa or more and 9.7×10 6 Pa or less, and for example, it may be 1.4×10 4 Pa or more and 9.6×10 6 Pa or less. When the dynamic elastic modulus E' is equal to or higher than the lower limit value, the followability of the lid material to the food can be further improved. When the dynamic elastic modulus E' is equal to or lower than the upper limit value, the food can be packaged without compressing its shape as much, and deformation of the bottom material container can be further suppressed when it adheres to the food.

[0028] The dynamic elastic modulus E' of the multilayer film (lid material) at a temperature of 140 °C can be measured in accordance with JIS K7244-4. Specifically, for example, it can be measured using a dynamic viscoelasticity measuring device ("DMA 7100" manufactured by Hitachi High-Technologies Corporation). The measurement conditions can be, for example, using a sample with a width of 4 mm, in a tensile mode, in a temperature range from 25 °C to 160 °C, with a displacement of 10 μm, a vibration frequency of 1 Hz, and a heating rate of 3 °C / min.

[0029] When the crosslink density of the multilayer film (lid material) improves, the heat resistance and melt tension of the multilayer film (lid material) improve, and the dynamic elastic modulus E' also improves. Therefore, the dynamic elastic modulus E' of the multilayer film (lid material) can be more easily adjusted, for example, by adjusting the absorbed dose of electron beam irradiation or the like.

[0030] Generally, the resin contained in the gas barrier layer (for example, the gas barrier property-imparting resin described later, etc.) has a higher dynamic elastic modulus E' than ordinary resins. Therefore, the dynamic elastic modulus E' of the multilayer film (lid material) can also be more easily adjusted by adjusting the type and content of the resin contained in the gas barrier layer, the thickness and ratio of the gas barrier layer, and the like.

[0031] The thickness of the multilayer film (lid material) is preferably 60 μm or more, more preferably 70 to 400 μm, even more preferably 80 to 300 μm, and may be, for example, 100 to 200 μm. When the thickness of the multilayer film is at least the lower limit value, the strength of the multilayer film is further improved. When the thickness of the multilayer film is at most the upper limit value, it is more suppressed that the thickness of the multilayer film becomes excessive.

[0032] The multilayer film (lid material) is composed of a sealant layer, a functional layer, and a gas barrier layer laminated in this order in the thickness direction thereof.

[0033] In the multilayer film (lid material), regardless of its type, all layers have transparency, and it is preferable that the multilayer film has transparency, that is, the multilayer film is a transparent multilayer film. In a package configured using such a multilayer film, the food can be easily visually recognized through the multilayer film (lid material).

[0034] The more detailed configuration of the multilayer film (lid material) and its manufacturing method will be described in detail separately.

[0035] Hereinafter, the present invention will be described in more detail with reference to the drawings. Note that the drawings used in the following description may show an enlarged view of the main part for the sake of easy understanding of the features of the present invention, and the dimensional ratios of each component are not necessarily the same as the actual ones.

[0036] <<Lid Material (Multilayer Film) of the First Embodiment>> FIG. 1 is a cross-sectional view schematically showing an example of a lid material (multilayer film) of the first embodiment of a package manufactured by the method according to an embodiment of the present invention.

[0037] The multilayer film 1 shown here is composed of a sealant layer 11, a functional layer 13, and a gas barrier layer 14 laminated in this order in the thickness direction thereof.

[0038] Furthermore, the multilayer film 1 includes an outer layer 12 disposed on the surface of the gas barrier layer 14 opposite to the sealant layer 11 side. Furthermore, the multilayer film 1 includes a pinhole-resistant layer 16 disposed between the functional layer 13 and the gas barrier layer 14. Furthermore, the multilayer film 1 includes an adhesive layer 15 (more specifically, a first adhesive layer 151) disposed between the functional layer 13 and the pinhole-resistant layer 16, and an adhesive layer 15 (more specifically, a second adhesive layer 152) disposed between the gas barrier layer 14 and the outer layer 12. That is, the multilayer film 1 is composed of a sealant layer 11, a functional layer 13, a first adhesive layer 151, a pinhole resistant layer 16, a gas barrier layer 14, a second adhesive layer 152, and an outer layer 12 laminated in this order in their thickness directions. In the multilayer film 1, the outer layer 12 is one outermost layer, and the sealant layer 11 is the other outermost layer.

[0039] <Sealant layer> The sealant layer 11 may contain a polyethylene-based resin such as ethylene-vinyl acetate copolymer (EVA), polyethylene, ionomer, polyethylene-based copolymer (which may be referred to as "polyethylene-based resin in the sealant layer" in this specification). When the sealant layer 11 contains the polyethylene-based resin in the sealant layer, the easy peelability due to the pseudo-adhesion property of the multilayer film 1 to the adherend is improved.

[0040] In this specification, the "polyethylene-based resin" is a resin having at least a structural unit derived from ethylene, which may have only a structural unit derived from ethylene, or may have a structural unit derived from ethylene and other structural units.

[0041] The sealant layer 11 may contain only the polyethylene-based resin in the sealant layer (that is, it may be composed of only the polyethylene-based resin in the sealant layer), or may contain the polyethylene-based resin in the sealant layer and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the polyethylene-based resin in the sealant layer and the said other components).

[0042] The other components contained in the sealant layer 11 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either a resin component or a non-resin component. The other components that are resin components are resins that do not correspond to the polyethylene-based resin in the sealant layer. The other component which is a resin component may be a homopolymer which is a polymer of one kind of monomer, or may be a copolymer which is a polymer of two or more kinds of monomers.

[0043] Examples of the other component which is a non-resin component include additives known in the art. Examples of the additives include antioxidants, antistatic agents, crystal nucleating agents, inorganic particles, viscosity reducers, thickeners, heat stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, and the like.

[0044] The other component contained in the sealant layer 11 may be only one kind, or may be two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0045] In the sealant layer 11, the ratio of the content of the polyethylene-based resin in the sealant layer to the total mass of the sealant layer 11 is preferably 65 to 100% by mass, more preferably 70 to 100% by mass, still more preferably 75 to 100% by mass, and may be, for example, 85 to 100% by mass. When the ratio is at least the lower limit value, the easy peelability due to the pseudo-adhesion with the adherend is further improved. The ratio is usually the same as the ratio of the content (parts by mass) of the polyethylene-based resin in the sealant layer to the total content (parts by mass) of the components that do not vaporize at normal temperature in the composition for forming the sealant layer described later.

[0046] In this specification, "normal temperature" means a temperature that is not particularly cooled or heated, that is, an ordinary temperature, and examples thereof include a temperature of 15 to 25°C.

[0047] The sealant layer 11 may be composed of one layer (single layer), or may be composed of two or more layers. When the sealant layer 11 is composed of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0048] In this specification, not limited to the case of the sealant layer 11, "a plurality of layers may be the same as or different from each other" means that "all layers may be the same, all layers may be different, or only some layers may be the same", and further, "a plurality of layers are different from each other" means that "at least one of the constituent materials and thicknesses of each layer is different from each other".

[0049] The thickness of the sealant layer 11 is not particularly limited, but is preferably 4 to 96 μm, more preferably 7 to 93 μm, still more preferably 10 to 90 μm, and may be any of, for example, 10 to 70 μm, 10 to 50 μm, and 10 to 30 μm. When the thickness of the sealant layer 11 is equal to or greater than the lower limit value, the strength of the sealant layer 11 becomes higher. When the thickness of the sealant layer 11 is equal to or less than the upper limit value, it is more suppressed that the thickness of the sealant layer 11 becomes excessive, and when the multilayer film 1 is sealed by heating, the seal strength becomes higher. Here, the "thickness of the sealant layer 11" means the thickness of the entire sealant layer 11. For example, the thickness of the sealant layer 11 composed of a plurality of layers means the total thickness of all the layers constituting the sealant layer 11.

[0050] The ratio of the thickness of the sealant layer 11 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 5% or more, more preferably 6 to 80%, and still more preferably 7 to 75%. When the ratio is equal to or greater than the lower limit value, the strength of the sealant layer 11 becomes higher. When the ratio is equal to or less than the upper limit value, it is more suppressed that the thickness of the sealant layer 11 becomes excessive, and when the multilayer film 1 is sealed by heating, the seal strength becomes higher.

[0051] The exposed surface 11a of the sealant layer 11 on the side opposite to the outer layer 12 side (which may be referred to as the "first surface" in this specification) is a sealing surface.

[0052] <Outer layer> The outer layer 12 may contain a polyolefin resin such as polyethylene (PE) or a polyester resin such as polyethylene terephthalate resin (PET, PETG) (in this specification, the polyolefin resin and the polyester resin may be referred to as "resins in the outer layer"). When the outer layer 12 contains the resins in the outer layer, the crosslinking density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with electron beams. As a result, the followability of the multilayer film 1 to food is further improved.

[0053] The outer layer 12 may contain only the resins in the outer layer (that is, it may be composed of the resins in the outer layer), or may contain the resins in the outer layer and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the resins in the outer layer and the other components).

[0054] The resins in the outer layer contained in the outer layer 12 preferably have a density of 0.945 g / cm 3 or less of the following low-density polyethylene, and more preferably have a density of 0.943 g / cm 3 or less of the following low-density polyethylene, and even more preferably have a density of 0.941 g / cm 3 or less of the following low-density polyethylene. By including such low-density polyethylene (LDPE), the crosslinking density of the outer layer 12 can be further improved by irradiating the multilayer film 1 with electron beams from the outside on the outer layer 12 side.

[0055] The resins in the outer layer contained in the outer layer 12 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0056] The other components contained in the outer layer 12 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either resin components or non-resin components. The other components that are resin components are resins other than the resins in the outer layer.

[0057] The other component(s) included in the outer layer 12 may be only one kind, or may be two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0058] In the outer layer 12, the ratio of the resin content in the outer layer to the total mass of the outer layer 12 is preferably 50% by mass or more, more preferably 55 - 100% by mass, still more preferably 60 - 100% by mass. For example, it may be either 70 - 100% by mass or 85 - 100% by mass. When the ratio is at least the lower limit value, the crosslink density of the outer layer 12 can be further improved by irradiating the outer layer 12 with electron beams from the outside of the multi-layer film 1 on the outer layer 12 side. The ratio is usually the same as the ratio of the resin content (parts by mass) in the outer layer to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the outer layer, which will be described later.

[0059] The outer layer 12 may be composed of one layer (single layer) or may be composed of two or more layers. When the outer layer 12 is composed of a plurality of layers, these layers may be the same as or different from each other, and the combination of these layers is not particularly limited as long as the effects of the present invention are not impaired.

[0060] The thickness of the outer layer 12 is not particularly limited, but is preferably 4 - 146 μm, more preferably 7 - 143 μm, still more preferably 10 - 140 μm. For example, it may be any one of 10 - 110 μm, 10 - 100 μm, 10 - 90 μm, 10 - 80 μm, and 10 - 70 μm. When the thickness of the outer layer 12 is at least the lower limit value, the crosslink density of the outer layer 12 can be further improved by irradiating the outer layer 12 with electron beams from the outside of the multi-layer film 1 on the outer layer 12 side. When the thickness of the outer layer 12 is at most the upper limit value, it is more suppressed that the thickness of the outer layer 12 becomes excessive. Here, the "thickness of the outer layer 12" means the thickness of the entire outer layer 12. For example, the thickness of the outer layer 12 composed of a plurality of layers means the total thickness of all the layers constituting the outer layer 12.

[0061] Although the ratio of the thickness of the outer layer 12 to the thickness of the multilayer film 1 is not particularly limited, it is preferably 10% or more, more preferably 12 to 88%, and even more preferably 14 to 86%. When the ratio is at least the lower limit value, the effect obtained by irradiating the multilayer film 1 with electron beams from the outside on the outer layer 12 side becomes higher. When the ratio is at most the upper limit value, it is more suppressed that the thickness of the outer layer 12 becomes excessive.

[0062] <Functional layer> The functional layer 13 contains an ionomer. The ionomer means a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid having an ion crosslinked structure formed by forming a salt between an acid moiety and a metal ion.

[0063] Examples of the metal ion include sodium ion, zinc ion, etc. In this specification, an ionomer in the case where the metal ion is a sodium ion may be referred to as a sodium-based ionomer, and an ionomer in the case where the metal ion is a zinc ion may be referred to as a zinc-based ionomer.

[0064] The melt strength of the ionomer at a temperature of 180°C is 60 to 540 mN. When the melt strength is at least the lower limit value, generation of holes in the multilayer film can be suppressed when the multilayer film 1 adheres to a hot plate. When the melt strength is at most the upper limit value, the functional layer can be easily spread during film formation of the multilayer film 1. Also, deformation of the bottom substrate container can be suppressed when the multilayer film 1 adheres to food.

[0065] The melt strength of the ionomer at a temperature of 180°C is preferably 60 to 540 mN, more preferably 62 to 538 mN, even more preferably 64 to 536 mN, and particularly preferably 66 to 534 mN. When the melt strength is equal to or higher than the lower limit value, generation of holes in the multilayer film 1 can be more suppressed when the multilayer film 1 adheres to the hot plate. When the melt strength is equal to or lower than the upper limit value, the functional layer can more easily spread when the multilayer film 1 is formed. Further, deformation of the bottom material container can be more suppressed when the multilayer film 1 adheres to food.

[0066] The melt strength of the ionomer at a temperature of 180°C can be measured in accordance with JIS K7199.

[0067] The melt strength of the ionomer at a temperature of 180°C can be more easily adjusted, for example, by adjusting the type of ionomer.

[0068] In addition to the ionomer, the functional layer 13 may contain a polyethylene-based resin such as ethylene-vinyl acetate copolymer (EVA), polyethylene, or a polyethylene-based copolymer (in this specification, the ionomer and the polyethylene-based resin may be referred to as "polyethylene-based resin in the functional layer"). When the functional layer 13 contains a polyethylene-based resin in the functional layer, the crosslinking density of the functional layer 13 can be improved when the multilayer film 1 is irradiated with an electron beam.

[0069] The functional layer 13 may consist of one layer (single layer) or may consist of two or more layers.

[0070] Examples of the case where the functional layer 13 consists of one layer (single layer) include those in which the functional layer 13 is disposed between the sealant layer 11 and the first adhesive layer 151.

[0071] The functional layer 13 may contain only an ionomer (i.e., it may consist of an ionomer), or it may contain an ionomer and other components (which may be referred to as "other components" in this specification).

[0072] The ionomer contained in the functional layer 13 may be only one kind, or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0073] The other components contained in the functional layer 13 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either resin components or non-resin components. The other components that are resin components are resins other than the ionomer.

[0074] The other components contained in the functional layer 13 may be only one kind, or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0075] The proportion of the content of the ionomer in the functional layer 13 with respect to the total mass of the functional layer 13 is preferably 50% by mass or more, more preferably 55 - 100% by mass, and even more preferably 60 - 100% by mass. For example, it may be either 70 - 100% by mass or 85 - 100% by mass. When the proportion is at or above the lower limit value, the crosslinking density of the functional layer 13 can be further improved by irradiating the multilayer film 1 with electron beams from the outside on the outer layer 12 side. The proportion is usually the same as the proportion of the content (parts by mass) of the ionomer to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the functional layer described later.

[0076] The thickness of the functional layer 13 is preferably 4 to 146 μm, more preferably 7 to 143 μm, even more preferably 10 to 140 μm, and may be any of, for example, 10 to 110 μm, 10 to 80 μm, 10 to 50 μm, and 10 to 30 μm. When the thickness of the functional layer 13 is equal to or greater than the lower limit value, the crosslinking density of the functional layer 13 can be further improved by irradiating the multilayer film 1 with an electron beam from the outside on the outer layer 12 side. When the thickness of the functional layer 13 is equal to or less than the upper limit value, it is more possible to suppress the thickness of the functional layer 13 from becoming excessive. Here, the "thickness of the functional layer 13" means the total thickness of the entire functional layer 13. For example, the thickness of the functional layer 13 composed of multiple layers means the total thickness of all the layers constituting the functional layer 13.

[0077] The ratio of the thickness of the functional layer 13 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 10% or more, more preferably 11 to 89%, and even more preferably 12 to 88%. When the ratio is equal to or greater than the lower limit value, the effect obtained by irradiating the multilayer film 1 with an electron beam becomes higher. When the ratio is equal to or less than the upper limit value, it is more possible to suppress the thickness of the functional layer 13 from becoming excessive.

[0078] <Gas barrier layer> The gas barrier layer 14 imparts strong gas barrier properties (in other words, the property of suppressing the permeation of oxygen gas) to the multilayer film 1.

[0079] The gas barrier layer 14 preferably contains an ethylene-vinyl alcohol copolymer (EVOH, also known as saponified ethylene-vinyl acetate copolymer). By including EVOH in the gas barrier layer 14, the gas barrier properties of the multilayer film 1 can be further improved.

[0080] In addition to EVOH, the gas barrier layer 14 may contain polyvinylidene chloride (PVDC) (in this specification, EVOH and PVDC may be referred to as "gas barrier-imparting resins"). By the gas barrier layer 14 containing a gas barrier-imparting resin, the gas barrier property of the multilayer film 1 can be further improved.

[0081] The gas barrier layer 14 may contain only the gas barrier-imparting resin (that is, it may be composed of the gas barrier-imparting resin), or may contain the gas barrier-imparting resin and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the gas barrier-imparting resin and the other components).

[0082] The other components contained in the gas barrier layer 14 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either resin components or non-resin components. The other components that are resin components are resins other than the gas barrier-imparting resin. Examples of the other components that are non-resin components include the same additives as those listed above for the other components contained in the sealant layer 11.

[0083] The other components contained in the gas barrier layer 14 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0084] The ratio of the content of the gas barrier-imparting resin to the total mass of the gas barrier layer 14 in the gas barrier layer 14 is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, still more preferably 70 to 100% by mass. For example, it may be 85 to 100% by mass. When the ratio is at least the lower limit value, the gas barrier property of the multilayer film 1 becomes higher. The ratio is usually the same as the ratio of the content (parts by mass) of the gas barrier property-imparting resin to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the gas barrier layer described later.

[0085] The gas barrier layer 14 may be composed of one layer (single layer) or may be composed of two or more layers. When the gas barrier layer 14 is composed of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0086] The thickness of the gas barrier layer 14 is preferably 1 to 100 μm, more preferably 1.5 to 90 μm, still more preferably 2 to 80 μm, and may be, for example, any one of 4 to 60 μm, 4 to 40 μm, and 4 to 20 μm. When the thickness of the gas barrier layer 14 is equal to or greater than the lower limit value, the gas barrier property of the multilayer film 1 becomes higher. When the thickness of the gas barrier layer 14 is equal to or less than the upper limit value, it is more suppressed that the thickness of the gas barrier layer 14 becomes excessive. Here, the "thickness of the gas barrier layer 14" means the total thickness of the entire gas barrier layer 14. For example, the thickness of the gas barrier layer 14 composed of a plurality of layers means the total thickness of all the layers constituting the gas barrier layer 14.

[0087] The ratio of the thickness of the gas barrier layer 14 to the thickness of the multilayer film 1 is 2 to 25%. When the ratio is equal to or greater than the lower limit value, it is possible to suppress the breakage of the gas barrier layer and improve the gas barrier property of the multilayer film 1. In this specification, the "breakage of the gas barrier layer" means that the gas barrier layer is not partially formed in the multilayer film, which is caused, for example, by the thickness of the gas barrier layer being too thin. When the ratio is equal to or less than the upper limit value, it is suppressed that the dynamic elastic modulus E' of the multilayer film 1 at a temperature of 140°C becomes excessive, and it is possible to suppress the deformation of the bottom material container when it adheres to food.

[0088] The ratio of the thickness of the gas barrier layer 14 to the thickness of the multilayer film 1 is more preferably 2.2 to 24.8%, and even more preferably 2.4 to 24.6%. When the ratio is at least the lower limit value, breakage of the gas barrier layer can be suppressed, and the gas barrier property of the multilayer film 1 can be further improved. When the ratio is at most the upper limit value, it is more suppressed that the dynamic elastic modulus E' of the multilayer film 1 at 140°C becomes excessive, and when adhering to food, deformation of the bottom substrate container can be more suppressed.

[0089] In the case of a skin pack for food, in order to prevent oxidative deterioration of the food, it is necessary for the multilayer film constituting the skin pack to be provided with a gas barrier layer. However, generally, since the resin contained in the gas barrier layer has a high dynamic elastic modulus, for example, when the ratio of the gas barrier layer is high, there is a problem that the bottom substrate container is deformed when the multilayer film is adhered to food. On the other hand, in the package constituted by using the multilayer film 1 provided with the gas barrier layer 14, such problems are improved. The reason is that when the ratio of the thickness of the gas barrier layer 14 is 25% or less, it is suppressed that the dynamic elastic modulus E' of the multilayer film 1 at 140°C becomes excessive, and when adhering to food, deformation of the bottom substrate container can be suppressed.

[0090] Recently, the shift from a conventional chamber type skin pack machine (indirect heating method) with a low number of shots to a continuous skin pack packaging machine (direct heating method) with a high number of shots is becoming mainstream, and a melt strength that can withstand the method of directly heating the film to a high temperature on a heated hot plate is required. When the melt strength of the package is low, there is a problem that the film becomes cloudy when adhering to the hot plate. On the other hand, in the package constituted by using the multilayer film 1 provided with the functional layer 13, such problems are improved. The reason is that due to the presence of the ionomer contained in the functional layer 13, the multilayer film 1 is excellent in melt strength during heating.

[0091] <Adhesive layer> The adhesive layer 15 contains an adhesive. The subsequent layer 15 bonds the two layers adjacent to both of its sides. In the multilayer film 1, the adhesive layer 15 disposed between the pinhole-resistant layer 16 and the gas barrier layer 14 bonds the pinhole-resistant layer 16 and the gas barrier layer 14, and the adhesive layer 15 disposed between the gas barrier layer 14 and the functional layer 13 bonds the gas barrier layer 14 and the functional layer 13. In this specification, in order to distinguish these two-layer adhesive layers 15 from each other, if necessary, the adhesive layer 15 disposed between the pinhole-resistant layer 16 and the gas barrier layer 14 may be referred to as the first adhesive layer 151, and the adhesive layer 15 disposed between the gas barrier layer 14 and the functional layer 13 may be referred to as the second adhesive layer 152. These two-layer adhesive layers 15 (the first adhesive layer 151 and the second adhesive layer 152) may be the same as each other or different from each other.

[0092] The adhesive included in the adhesive layer 15 is not particularly limited as long as it can bond the two layers to be bonded with sufficient strength. Examples of the adhesive include adhesive resins such as olefin resins (that is, polymers of olefins which are one or more kinds of monomers).

[0093] More specifically, examples of the olefin resin included in the adhesive layer 15 include ethylene copolymers, propylene copolymers, butene copolymers, and the like. The ethylene copolymer is a copolymer of ethylene and a monomer other than ethylene. The propylene copolymer is a copolymer of propylene and a monomer other than propylene. The butene copolymer is a copolymer of butene and a monomer other than butene.

[0094] Examples of the ethylene copolymer included in the adhesive layer 15 include copolymers of ethylene and vinyl group-containing monomers. Examples of the copolymer of ethylene and a vinyl group-containing monomer include maleic anhydride graft-modified linear low density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ionomer (ION), ethylene-based thermoplastic elastomer, and the like. Examples of the ionomer include the same ionomers as those listed above that are included in the functional layer 13.

[0095] Examples of the propylene-based copolymer included in the adhesive layer 15 include a copolymer of propylene and a vinyl group-containing monomer. Examples of the copolymer of propylene and a vinyl group-containing monomer include maleic anhydride graft-modified linear low density polypropylene, propylene-based thermoplastic elastomer, and the like.

[0096] Examples of the butene-based copolymer included in the adhesive layer 15 include a copolymer of 1-butene and a vinyl group-containing monomer, a copolymer of 2-butene and a vinyl group-containing monomer, and modified products (modified copolymers) of these copolymers.

[0097] The adhesive layer 15 may contain only an adhesive (i.e., it may be composed of an adhesive), or it may contain an adhesive and other components (which may be referred to as "other components" in this specification) (i.e., it may be composed of an adhesive and the other components).

[0098] The adhesive contained in the adhesive layer 15 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0099] The other components included in the adhesive layer 15 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they can be either resin components or non-resin components.

[0100] The other components included in the adhesive layer 15 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0101] The proportion of the content of the adhesive in the total mass of the adhesive layer 15 in the adhesive layer 15 may be, for example, 50 to 100% by mass. The said proportion is usually the same as the proportion of the content (parts by mass) of the adhesive to the total content (parts by mass) of the components that do not vaporize at normal temperature in the composition for forming the adhesive layer described later.

[0102] The adhesive layer 15 may be composed of one layer (single layer) or may be composed of two or more layers. When the adhesive layer 15 is composed of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0103] The thickness of the adhesive layer 15 (the thickness of each of the first adhesive layer 151 and the second adhesive layer 152) is preferably 4 to 96 μm, more preferably 7 to 93 μm, and may be, for example, any one of 7 to 80 μm, 7 to 60 μm, 7 to 40 μm, and 7 to 20 μm. When the thickness of the adhesive layer 15 is equal to or greater than the lower limit value, the adhesive strength between the two layers to be adhered becomes higher. When the thickness of the adhesive layer 15 is equal to or less than the upper limit value, it is possible to suppress the thickness of the adhesive layer 15 from becoming excessive. Here, the "thickness of the adhesive layer 15" means the thickness of the entire adhesive layer 15 (for example, the thickness of the entire adhesive layer 15 disposed between the functional layer 13 and the pinhole-resistant layer 16, the thickness of the entire adhesive layer 15 disposed between the gas barrier layer 14 and the outer layer 12). For example, the thickness of the adhesive layer 15 composed of a plurality of layers means the total thickness of all the layers constituting the adhesive layer 15.

[0104] <Pinhole-resistant layer> The multilayer film 1 may not include the pinhole-resistant layer 16, but by including the pinhole-resistant layer 16, its pinhole resistance becomes higher. And in the package formed using this multilayer film 1, a decrease in strength during heat treatment can be suppressed.

[0105] The resin contained in the pinhole-resistant layer 16 is not particularly limited, and examples include polyamide resins. By the pinhole-resistant layer 16 containing a polyamide resin, the pinhole resistance of the multilayer film 1 can be improved.

[0106] Specific examples of the polyamide resin contained in the pinhole-resistant layer 16 include polyamide resins obtained by polymerizing or copolymerizing nylon salts composed of lactams having 3 or more members, amino acids, or diamines and dicarboxylic acids.

[0107] Specific examples of lactams having 3 or more members include ε-caprolactam, ω-enanthlactam, ω-laurolactam, α-pyrrolidone, and α-piperidone.

[0108] Specific examples of amino acids include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

[0109] Specific examples of the diamine constituting the nylon salt include, for example, aliphatic amines, alicyclic diamines, and aromatic diamines. Examples of the aliphatic amine include tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine. Examples of the alicyclic diamine include 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, isophoronediamine, piperazine, bis(4-aminocyclohexyl)methane, and 2,2-bis-(4-aminocyclohexyl)propane. Examples of the aromatic diamine include metaxylylenediamine and paraxylylenediamine.

[0110] Specific examples of the dicarboxylic acid constituting the nylon salt include, for example, aliphatic dicarboxylic acids, alicyclic carboxylic acids, and aromatic dicarboxylic acids. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. Examples of the alicyclic carboxylic acid include hexahydroterephthalic acid and hexahydroisophthalic acid. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid (1,2-isomer, 1,3-isomer, 1,4-isomer, 1,5-isomer, 1,6-isomer, 1,7-isomer, 1,8-isomer, 2,3-isomer, 2,6-isomer, or 2,7-isomer).

[0111] Examples of polyamide resins include, specifically, 4-nylon, 6-nylon, 7-nylon, 11-nylon, 12-nylon, 46-nylon, 66-nylon, 69-nylon, 610-nylon, 611-nylon, 612-nylon, 6T-nylon, 6I-nylon, copolymers of 6-nylon and 66-nylon (nylon 6 / 66), copolymers of 6-nylon and 610-nylon, copolymers of 6-nylon and 611-nylon, copolymers of 6-nylon and 12-nylon (nylon 6 / 12), copolymers of 6-nylon and 612-nylon, copolymers of 6-nylon and 6T-nylon, copolymers of 6-nylon and 6I-nylon, copolymers of 6-nylon, 66-nylon and 610-nylon, copolymers of 6-nylon, 66-nylon and 12-nylon (nylon 6 / 66 / 12), copolymers of 6-nylon, 66-nylon and 612-nylon, copolymers of 66-nylon and 6T-nylon, copolymers of 66-nylon and 6I-nylon, copolymers of 6T-nylon and 6I-nylon, and copolymers of 66-nylon, 6T-nylon and 6I-nylon. Among these, 6-nylon, 12-nylon, 66-nylon, nylon 6 / 66, nylon 6 / 12, and nylon 6 / 66 / 12 are preferred in terms of heat resistance, mechanical strength, and ease of availability.

[0112] The pinhole-resistant layer 16 may contain only a polyamide resin (i.e., it may be composed of a polyamide resin), or it may contain a polyamide resin and other components (which may be referred to as "other components" in this specification).

[0113] The polyamide resin contained in the pinhole-resistant layer 16 may be only one type, or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0114] The other components included in the pinhole-resistant layer 16 are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either a resin component or a non-resin component. The other component that is a resin component is a resin other than the polyamide resin.

[0115] The other components included in the pinhole-resistant layer 16 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0116] In the pinhole-resistant layer 16, the proportion of the polyamide resin content to the total mass of the pinhole-resistant layer 16 is preferably 50% by mass or more, more preferably 55 - 100% by mass, and even more preferably 60 - 100% by mass. For example, it may be either 70 - 100% by mass or 85 - 100% by mass. When the proportion is at least the lower limit value, the effect obtained by the multi-layer film 1 containing the polyamide resin becomes higher. Usually, the proportion is the same as the proportion of the polyamide resin content (parts by mass) to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the pinhole-resistant layer described later.

[0117] The pinhole-resistant layer 16 may be composed of one layer (single layer) or may be composed of two or more layers. When the pinhole-resistant layer 16 is composed of multiple layers, these multiple layers may be the same as or different from each other, and the combination of these multiple layers is not particularly limited as long as the effects of the present invention are not impaired.

[0118] The thickness of the pinhole-resistant layer 16 is preferably 4 to 146 μm, more preferably 7 to 143 μm, still more preferably 10 to 140 μm, and may be, for example, any of 10 to 110 μm, 10 to 80 μm, and 10 to 50 μm. When the thickness of the pinhole-resistant layer 16 is equal to or greater than the lower limit value, the pinhole resistance of the multilayer film 1 becomes higher. When the thickness of the pinhole-resistant layer 16 is equal to or less than the upper limit value, it is possible to suppress the thickness of the pinhole-resistant layer 16 from becoming excessive. Here, the "thickness of the pinhole-resistant layer 16" means the total thickness of the entire pinhole-resistant layer 16. For example, in the case of a pinhole-resistant layer 16 composed of multiple layers, the thickness of the pinhole-resistant layer 16 means the total thickness of all the layers constituting the pinhole-resistant layer 16.

[0119] The ratio of the thickness of the pinhole-resistant layer 16 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 10% or more, more preferably 11 to 89%, and still more preferably 12 to 88%. When the ratio is equal to or greater than the lower limit value, the pinhole resistance of the multilayer film 1 becomes higher. When the ratio is equal to or less than the upper limit value, it is possible to suppress the thickness of the pinhole-resistant layer 16 from becoming excessive.

[0120] <<Cover material (multilayer film) of the second embodiment>> FIG. 2 is a cross-sectional view schematically showing an example of a cover material (multilayer film) of the second embodiment of a package manufactured by the method according to an embodiment of the present invention.

[0121] Hereinafter, the cover material (multilayer film) of the second embodiment will be described mainly focusing on the differences from the first embodiment, and the description of the same matters will be omitted. In FIG. 2, the same components as those in the first embodiment are denoted by the same reference numerals.

[0122] The multilayer film 2 shown here is configured by laminating a sealant layer 11, a functional layer 13 (more specifically, a first functional layer 131), and a gas barrier layer 14 in this order in the thickness direction thereof.

[0123] Furthermore, the multilayer film 2 includes an outer layer 12 disposed on a surface opposite to the sealant layer 11 side of the gas barrier layer 14. Furthermore, the multilayer film 2 includes a functional layer 13 (more specifically, a second functional layer 132) disposed between the gas barrier layer 14 and the outer layer 12. Furthermore, the multilayer film 2 includes an adhesive layer 15 (more specifically, a first adhesive layer 151) disposed between the first functional layer 131 and the gas barrier layer 14, and an adhesive layer 15 (more specifically, a second adhesive layer 152) disposed between the gas barrier layer 14 and the second functional layer 132. That is, the multilayer film 2 is configured by laminating the sealant layer 11, the first functional layer 131, the first adhesive layer 151, the gas barrier layer 14, the second adhesive layer 152, the second functional layer 132, and the outer layer 12 in this order in their thickness directions. In the multilayer film 2, the outer layer 12 is one outermost layer, and the sealant layer 11 is the other outermost layer.

[0124] <Functional layer> The functional layer 13 may be composed of one layer (single layer) or may be composed of two or more layers. When the functional layer 13 is composed of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0125] In the present embodiment, the functional layer 13 is provided at different positions in the multilayer film 2. In the present embodiment, in order to distinguish these functional layers 13 from each other, if necessary, the functional layer 13 disposed between the sealant layer 11 and the first adhesive layer 151 may be referred to as the first functional layer 131, and the functional layer 13 disposed between the second adhesive layer 152 and the outer layer 12 may be referred to as the second functional layer 132. These functional layers 13 (the first functional layer 131 and the second functional layer 132) may be the same as or different from each other.

[0126] A first functional layer 131 is disposed between the sealant layer 11 and the first adhesive layer 151, and a second functional layer 132 is disposed between the second adhesive layer 152 and the outer layer 12. As a result, the gas barrier layer 14 is sandwiched between the first functional layer 131 and the second functional layer 132, and the elongation of the multilayer film 2 can be stabilized.

[0127] The thickness of the functional layer 13 (the thicknesses of the first functional layer 131 and the second functional layer 132 respectively) is preferably 4 to 146 μm, more preferably 7 to 143 μm, still more preferably 10 to 140 μm, and may be any of, for example, 10 to 110 μm, 10 to 80 μm, 10 to 50 μm, and 10 to 30 μm. When the thickness of the functional layer 13 is equal to or greater than the lower limit value, the crosslinking density of the functional layer 13 can be further improved by irradiating the multilayer film 2 with electron beams from the outside on the outer layer 12 side. When the thickness of the functional layer 13 is equal to or less than the upper limit value, it is more suppressed that the thickness of the functional layer 13 becomes excessive. Here, the "thickness of the functional layer 13" means the total thickness of the entire functional layer 13 (for example, the total thickness of the functional layer 13 disposed between the sealant layer 11 and the first adhesive layer 151, the total thickness of the functional layer 13 disposed between the second adhesive layer 152 and the outer layer 12). For example, the thickness of the functional layer 13 composed of multiple layers means the total thickness of all the layers constituting the functional layer 13.

[0128] The ratio of the thickness of the functional layer 13 to the thickness of the multilayer film 2 is not particularly limited, but is preferably 10% or more, more preferably 11 to 89%, and still more preferably 12 to 88%. When the ratio is equal to or greater than the lower limit value, the effect obtained by irradiating the multilayer film 2 with electron beams becomes higher. When the ratio is equal to or less than the upper limit value, it is more suppressed that the thickness of the functional layer 13 becomes excessive.

[0129] <Other layers> The multilayer films 1 and 2 may include other layers that do not correspond to any of the sealant layer 11, the outer layer 12, the functional layer 13, the gas barrier layer 14, the adhesive layer 15, and the pinhole resistant layer 16, as long as the effects of the present invention are not impaired.

[0130] The type and arrangement position of the other layers are not particularly limited and can be arbitrarily selected according to the purpose.

[0131] The other layers included in the multilayer films 1 and 2 may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0132] Each of the other layers may consist of one layer (single layer) or may consist of two or more layers. When the other layers consist of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0133] The thickness of the other layers can be arbitrarily set according to their types and is not particularly limited.

[0134] When the multilayer films 1 and 2 include the other layers, they may further include an adhesive layer (for example, the adhesive layer 15, etc.) for adhering the other layers to the other layers.

[0135] The thickness of the multilayer films 1 and 2 is the same as the thickness of the multilayer film (lid material) described above.

[0136] The multilayer films 1 and 2 are not limited to the above, and some configurations may be changed, deleted, or added within the scope not departing from the gist of the present invention. For example, the multilayer film may not include any one or more of an outer layer, an adhesive layer, and a pinhole-resistant layer. However, as shown in FIG. 1, the multilayer film preferably includes a sealant layer, a functional layer, a first adhesive layer, a pinhole-resistant layer, a gas barrier layer, a second adhesive layer, and an outer layer in this order, or as shown in FIG. 2, preferably includes a sealant layer, a first functional layer, a first adhesive layer, a gas barrier layer, a second adhesive layer, a second functional layer, and an outer layer in this order.

[0137] <<Manufacturing Method of Multilayer Film (Lid Material)>> The multilayer film (lid material) can be manufactured by a known method according to its type. For example, laminated films such as the multilayer film can be manufactured by a feed block method in which resins, resin compositions, etc. that are forming materials for each layer are melt-extruded using several extruders, a co-extrusion T-die method such as a multi-manifold method, an air-cooled or water-cooled co-extrusion inflation method, etc.

[0138] In addition, the laminated film can be manufactured by coating a resin, a resin composition, etc. that is a forming material for any one of the layers in the laminated film on the surface of another layer for constituting the laminated film, drying it as necessary to form a laminated structure in the laminated film, and further laminating other layers as necessary so as to have a target arrangement form.

[0139] In addition, for the laminated film, two or more films for constituting any two or more of the layers are separately prepared in advance, and these films are bonded and laminated by any one of a dry lamination method, an extrusion lamination method, a hot melt lamination method, and a wet lamination method using an adhesive, and other layers are further laminated as necessary so as to have a target arrangement form. At this time, an adhesive capable of forming the adhesive layer may be used as the adhesive.

[0140] Further, as described above, the laminated film can be manufactured by laminating two or more films prepared separately in advance without using an adhesive by a thermal (heat) lamination method or the like, and further laminating other layers as required so as to have a desired arrangement form.

[0141] When manufacturing the laminated film, two or more of the formation methods of any layer (film) in the laminated film listed so far may be combined.

[0142] Regardless of the manufacturing method, the resin composition that is the formation material of any layer in the laminated film may be manufactured by adjusting the types and contents of the contained components so that the layer to be formed contains the target components (constituent materials) in the target contents. For example, the ratio of the contents of the components that do not vaporize at room temperature in the resin composition is usually the same as the ratio of the contents of the components in the layer formed from this resin composition.

[0143] Examples of the resin composition for forming the sealant layer (sealant layer 11 in the multilayer film 1 shown in FIG. 1 and the multilayer film 2 shown in FIG. 2) (which may be referred to as "sealant layer forming composition" in this specification) include those containing a polyethylene-based resin in the sealant layer and, if necessary, the other components.

[0144] Examples of the resin composition for forming the outer layer (outer layer 12 in the multilayer film 1 shown in FIG. 1 and the multilayer film 2 shown in FIG. 2) (which may be referred to as "outer layer forming composition" in this specification) include those containing a resin in the outer layer and, if necessary, the other components.

[0145] Examples of the resin composition for forming the functional layer (functional layer 13 in the multilayer film 1 shown in FIG. 1 and the multilayer film 2 shown in FIG. 2) (which may be referred to as "functional layer forming composition" in this specification) include those containing a polyethylene-based resin in the functional layer and, if necessary, the other components.

[0146] As a resin composition for forming a gas barrier layer (in the multilayer film 1 shown in FIG. 1 and the multilayer film 2 shown in FIG. 2, the gas barrier layer 14; may be referred to as "composition for forming gas barrier layer" in this specification), for example, those containing the gas barrier property-imparting resin and, if necessary, the other components are mentioned.

[0147] As a resin composition for forming an adhesive layer (in the multilayer film 1 shown in FIG. 1 and the multilayer film 2 shown in FIG. 2, the adhesive layer 15; may be referred to as "composition for forming adhesive layer" in this specification), for example, those containing the adhesive and, if necessary, the other components are mentioned.

[0148] The multilayer films 1 and 2 can be used as a lid material. By heat-sealing this lid material and a bottom material, a package can be manufactured.

[0149] <<Bottom material>> The bottom material is not particularly limited as long as it can be used as the bottom material of the package. The bottom material may be a known one.

[0150] The oxygen transmission rate of the bottom material under the conditions of a temperature of 23°C and a relative humidity of 60% is preferably 300 cc / (m 2 ·day·atm) or less, more preferably 260 cc / (m 2 ·day·atm) or less, and for example, it may be any of 200 cc / (m 2 ·day·atm) or less, 150 cc / (m 2 ·day·atm) or less, 100 cc / (m 2 ·day·atm) or less, and 50 cc / (m 2 ·day·atm) or less. On the other hand, the oxygen transmission rate is 0 cc / (m 2 ·day·atm) or more.

[0151] Under the conditions of a temperature of 23°C and a relative humidity of 60%, the oxygen transmission rate of the substrate can be measured in accordance with JIS K 7126-2:2006.

[0152] The oxygen transmission rate of the substrate can be more easily adjusted, for example, by adjusting the type and content of the components contained in the substrate, the thickness of the substrate, and the like.

[0153] The thickness of the substrate is preferably 100 μm or more, more preferably 110 μm or more, and even more preferably 120 μm or more. When the thickness of the substrate is at least the above lower limit value, the strength of the substrate is further improved. The thickness of the substrate is preferably 6000 μm or less. When the thickness of the substrate is at most the above upper limit value, it is possible to suppress the thickness of the substrate from becoming excessive. The thickness of the substrate can be appropriately adjusted within a range set by arbitrarily combining any of the above lower limit values and the upper limit value.

[0154] In the substrate, regardless of its type, all layers may have transparency, and the substrate may have transparency, or all layers or some layers may not have transparency, and the substrate may not have transparency. In a package formed using a transparent substrate, the food can be easily visually recognized through the substrate.

[0155] The more detailed configuration of the substrate and its manufacturing method will be described separately in detail.

[0156] <<An Embodiment of the Substrate>> The substrate is preferably a laminate formed by laminating a plurality of layers. Preferred examples of the substrate that is a laminate include, for example, a resin laminate including a foamed resin layer and a non-foamed resin layer provided on the foamed resin layer.

[0157] The foamed resin layer may be a known one. Examples of the foamed resin layer include a resin layer containing a foam of a polystyrene-based resin (PSP).

[0158] The density of the foamed resin layer is not particularly limited, but is preferably 0.05 to 0.5 g / cm 3 . The foaming ratio of the foamed resin layer is not particularly limited, but is preferably 2 to 20 times. The thickness of the foamed resin layer is not particularly limited, but is preferably 500 to 6000 μm.

[0159] Examples of the non-foamed resin layer include a multi-layer film for a substrate in which an easy peel layer, a gas barrier layer, a pinhole resistant layer, and an adhesive layer are laminated in this order in the thickness direction thereof. In the multi-layer film for a substrate, the easy peel layer is one outermost layer, and the adhesive layer is the other outermost layer.

[0160] The multi-layer film for a substrate may include, for example, an intermediate adhesive layer for bonding these two layers between the easy peel layer and the gas barrier layer. Further, the multi-layer film for a substrate may include, for example, an intermediate adhesive layer for bonding these two layers between the gas barrier layer and the pinhole resistant layer. That is, the multi-layer film for a substrate may be configured by laminating an easy peel layer, an intermediate adhesive layer, a gas barrier layer, an intermediate adhesive layer, a pinhole resistant layer, and an adhesive layer in this order in the thickness direction thereof.

[0161] In this specification, in order to distinguish between these two intermediate adhesive layers, if necessary, the intermediate adhesive layer disposed between the easy peel layer and the gas barrier layer may be referred to as a first intermediate adhesive layer, and the intermediate adhesive layer disposed between the gas barrier layer and the pinhole resistant layer may be referred to as a second intermediate adhesive layer. These two intermediate adhesive layers (the first intermediate adhesive layer and the second intermediate adhesive layer) may be the same as each other or different from each other.

[0162] <Easy peel layer> As the easy peel layer in the multilayer film for a substrate, those showing peelability due to cohesive failure can be mentioned. Examples of the easy peel layer showing peelability due to cohesive failure include those containing two incompatible polyolefins.

[0163] Examples of the two incompatible polyolefins contained in the easy peel layer in the multilayer film for a substrate include an ethylene-based polymer having at least a structural unit derived from ethylene and a propylene-based polymer having at least a structural unit derived from propylene. That is, examples of the easy peel layer include those containing an ethylene-based polymer having at least a structural unit derived from ethylene and a propylene-based polymer having at least a structural unit derived from propylene.

[0164] Examples of the ethylene-based polymer contained in the easy peel layer in the multilayer film for a substrate include a homopolymer of ethylene and an ethylene-based copolymer.

[0165] Examples of the homopolymer of ethylene include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene-catalyzed linear low density polyethylene (mLLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), etc.

[0166] The ethylene-based copolymer has a structural unit derived from ethylene and a structural unit derived from a monomer other than ethylene. Examples of the ethylene-based copolymer include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ionomer (ION), etc. Examples of the ionomer include the same ionomers as those mentioned above as being included in the functional layer 13 in the multilayer film 1 described above.

[0167] The easy peel layer in the multilayer film for the substrate preferably contains low density polyethylene as the ethylene-based polymer. The easy peel property of such an easy peel layer is better.

[0168] Examples of the propylene-based polymer included in the easy peel layer in the multilayer film for the substrate include a homopolymer of propylene (i.e., polypropylene or homopolypropylene, hPP) and a propylene-based copolymer.

[0169] The propylene-based copolymer has a structural unit derived from propylene and a structural unit derived from a monomer other than propylene. Examples of the propylene-based copolymer include a propylene-ethylene random copolymer (also known as polypropylene random copolymer, rPP), a propylene-ethylene block copolymer (also known as polypropylene block copolymer, bPP), and the like.

[0170] The easy peel layer in the multilayer film for the substrate preferably contains polypropylene as the propylene-based polymer. The easy peel property of such an easy peel layer is better.

[0171] The component that exhibits the easy peel property included in the easy peel layer in the multilayer film for the substrate may be only one kind or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose. For example, when the component that exhibits the easy peel property is the above-mentioned two incompatible polyolefins, each of these polyolefins included in the easy peel layer may be only one kind or two or more kinds.

[0172] In the easy peel layer of the multilayer film for a substrate, the ratio of the content (parts by mass) of the ethylene-based polymer to the total content (parts by mass) of the ethylene-based polymer and the propylene-based polymer is preferably 10 to 90% by mass, and may be, for example, any one of 30 to 90% by mass, 45 to 90% by mass, and 60 to 90% by mass. When the ratio is at least the lower limit value, the easy peel property of the easy peel layer becomes better. When the ratio is at most the upper limit value, the peel strength becomes more stable. The ratio is usually the same as the ratio of the content (parts by mass) of the ethylene-based polymer to the total content (parts by mass) of the ethylene-based polymer and the propylene-based polymer in the easy peel layer forming composition for a substrate described below.

[0173] The easy peel layer in the multilayer film for a substrate may contain other components in addition to the components that exhibit the easy peel property (for example, the above-described two incompatible polyolefins) as long as the easy peel property is not impaired. The other components contained in the easy peel layer may be only one kind or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0174] In the easy peel layer of the multilayer film for a substrate, the ratio of the content of the component that exhibits the easy peel property (for example, the total content ratio of the above-described two incompatible polyolefins) to the total mass of the easy peel layer is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and may be, for example, any one of 80 to 100% by mass, 90 to 100% by mass, 95 to 100% by mass, 97 to 100% by mass, and 99 to 100% by mass. When the ratio is at least the lower limit value, the easy peel property of the easy peel layer becomes better. The ratio is usually the same as the ratio of the content (parts by mass) of the component that exhibits the easy peel property to the total content (parts by mass) of the components that do not vaporize at room temperature in the easy peel layer forming composition for a substrate described below.

[0175] Examples of the other components included in the easy peel layer in the multilayer film for a substrate include an anti-fogging agent, an anti-blocking agent, and the like.

[0176] The easy peel layer in the multilayer film for a substrate may be composed of one layer (single layer) or may be composed of two or more layers. When the easy peel layer is composed of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0177] The thickness of the easy peel layer in the multilayer film for a substrate is preferably 2 to 50 μm. When the thickness of the easy peel layer is equal to or greater than the lower limit value, the seal strength of the easy peel layer becomes moderately high. When the thickness of the easy peel layer is equal to or less than the upper limit value, the easy peel property becomes higher. Here, the "thickness of the easy peel layer" means the thickness of the entire easy peel layer. For example, the thickness of the easy peel layer composed of a plurality of layers means the total thickness of all the layers constituting the easy peel layer.

[0178] The ratio of the thickness of the easy peel layer to the thickness of the multilayer film for a substrate is not particularly limited, but is preferably 5 to 40%. When the ratio is equal to or greater than the lower limit value, the seal strength of the easy peel layer becomes moderately high. When the ratio is equal to or less than the upper limit value, the easy peel property becomes higher.

[0179] <Gas barrier layer> The gas barrier layer imparts gas barrier properties (in other words, the property of suppressing the permeation of oxygen gas) to the multilayer film for a substrate.

[0180] The gas barrier layer in the multilayer film for a substrate preferably contains an ethylene-vinyl alcohol copolymer (EVOH, also known as saponified ethylene-vinyl acetate copolymer) or polyamide.

[0181] Examples of the polyamide include 4-nylon, 6-nylon, 7-nylon, 11-nylon, 12-nylon, 46-nylon, 66-nylon, 69-nylon, 610-nylon, 611-nylon, 612-nylon, 6T-nylon, 6I-nylon, a copolymer of 6-nylon and 66-nylon (nylon 6 / 66), a copolymer of 6-nylon and 610-nylon, a copolymer of 6-nylon and 611-nylon, a copolymer of 6-nylon and 12-nylon (nylon 6 / 12), a copolymer of 6-nylon and 612-nylon, a copolymer of 6-nylon and 6T-nylon, a copolymer of 6-nylon and 6I-nylon, a copolymer of 6-nylon, 66-nylon and 610-nylon, a copolymer of 6-nylon, 66-nylon and 12-nylon (nylon 6 / 66 / 12), a copolymer of 6-nylon, 66-nylon and 612-nylon, a copolymer of 66-nylon and 6T-nylon, a copolymer of 66-nylon and 6I-nylon, a copolymer of 6T-nylon and 6I-nylon, a copolymer of 66-nylon, 6T-nylon and 6I-nylon, and the like.

[0182] In terms of heat resistance, mechanical strength, ease of availability, etc., the polyamide is preferably 6-nylon (which may be abbreviated as "Ny6" in this specification), 12-nylon, 66-nylon, nylon 6 / 66, nylon 6 / 12 or nylon 6 / 66 / 12.

[0183] The polyamide contained in the gas barrier layer in the multilayer film for the base material may be only one kind or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0184] The gas barrier layer in the multilayer film for a substrate may contain only one or both of an ethylene-vinyl alcohol copolymer and a polyamide (i.e., it may be composed of only one or both of an ethylene-vinyl alcohol copolymer and a polyamide), or may contain one or both of an ethylene-vinyl alcohol copolymer and a polyamide and other components (which may be referred to as "other components" in this specification).

[0185] The other components contained in the gas barrier layer in the multilayer film for a substrate are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either a resin component or a non-resin component. The other component that is a resin component is a resin that does not correspond to either an ethylene-vinyl alcohol copolymer or a polyamide. Examples of the other component that is a non-resin component include the same additives as those listed above as the other components contained in the sealant layer 11 in the multilayer film 1 described above.

[0186] The other components contained in the gas barrier layer in the multilayer film for a substrate may be only one kind or two or more kinds. When there are two or more kinds, their combinations and ratios can be arbitrarily selected according to the purpose.

[0187] The ratio of the total content of the ethylene-vinyl alcohol copolymer and the polyamide to the total mass of the gas barrier layer in the gas barrier layer in the multilayer film for a substrate is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and may be, for example, either 70 to 100% by mass or 85 to 100% by mass. Usually, the above ratio is the same as the ratio of the total content (parts by mass) of the ethylene-vinyl alcohol copolymer and the polyamide to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming a gas barrier layer for a substrate, which will be described later.

[0188] The gas barrier layer in the multilayer film for a substrate may consist of one layer (single layer) or may consist of two or more layers. When the gas barrier layer consists of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0189] The thickness of the gas barrier layer in the multilayer film for a substrate is preferably 2 to 20 μm. When the thickness of the gas barrier layer is equal to or greater than the lower limit value, the gas barrier property of the gas barrier layer becomes higher. When the thickness of the gas barrier layer is equal to or less than the upper limit value, it is possible to suppress the thickness of the gas barrier layer from becoming excessive. Here, the "thickness of the gas barrier layer" means the total thickness of the entire gas barrier layer. For example, the thickness of a gas barrier layer composed of a plurality of layers means the total thickness of all the layers constituting the gas barrier layer.

[0190] The ratio of the thickness of the gas barrier layer to the thickness of the multilayer film for a substrate is not particularly limited, but is preferably 5 to 15%. When the ratio is equal to or greater than the lower limit value, the gas barrier property of the multilayer film for a substrate becomes higher. When the ratio is equal to or less than the upper limit value, it is possible to suppress the thickness of the gas barrier layer from becoming excessive.

[0191] <Pinhole-resistant layer> The pinhole-resistant layer is a layer for protecting the structure of the multilayer film for a substrate, such as suppressing the generation of pinholes in the multilayer film for a substrate.

[0192] The pinhole-resistant layer in the multilayer film for a substrate preferably contains a polyolefin. Examples of the polyolefin include polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene-catalyzed linear low-density polyethylene (mLLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE); and polypropylene.

[0193] The pinhole-resistant layer in the multilayer film for a substrate may contain only polyolefin (i.e., it may be composed of polyolefin), or may contain polyolefin and other components (which may be referred to as "other components" in this specification) (i.e., it may be composed of polyolefin and the other components).

[0194] The other components contained in the pinhole-resistant layer in the multilayer film for a substrate are not particularly limited and can be arbitrarily selected according to the purpose. For example, they may be either resin components or non-resin components. The other components that are resin components are resins other than polyolefin. Examples of the other components that are non-resin components include the same additives as those listed above as the other components contained in the sealant layer 11 in the multilayer film 1 described above.

[0195] The other components contained in the pinhole-resistant layer in the multilayer film for a substrate may be only one type, or may be two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0196] The ratio of the content of polyolefin to the total mass of the pinhole-resistant layer in the pinhole-resistant layer in the multilayer film for a substrate is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and may be, for example, either 70 to 100% by mass or 85 to 100% by mass. This ratio is usually the same as the ratio of the content (parts by mass) of polyolefin to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the pinhole-resistant layer for a substrate, which will be described later.

[0197] The pinhole-resistant layer in the multilayer film for a substrate may consist of one layer (single layer) or may consist of two or more layers. When the pinhole-resistant layer consists of multiple layers, these multiple layers may be the same as or different from each other, and the combination of these multiple layers is not particularly limited as long as the effects of the present invention are not impaired.

[0198] The thickness of the pinhole-resistant layer in the multilayer film for a substrate is preferably 2 to 50 μm. When the thickness of the pinhole-resistant layer is equal to or greater than the lower limit value, the protective ability of the pinhole-resistant layer becomes higher. When the thickness of the pinhole-resistant layer is equal to or less than the upper limit value, it is possible to suppress the thickness of the pinhole-resistant layer from becoming excessive. Here, the "thickness of the pinhole-resistant layer" means the total thickness of the entire pinhole-resistant layer. For example, the thickness of a pinhole-resistant layer composed of multiple layers means the total thickness of all the layers constituting the pinhole-resistant layer.

[0199] The ratio of the thickness of the pinhole-resistant layer to the thickness of the multilayer film for a substrate is not particularly limited, but is preferably 5 to 40%. When the ratio is equal to or greater than the lower limit value, the pinhole resistance of the multilayer film for a substrate becomes higher. When the ratio is equal to or less than the upper limit value, it is possible to suppress the thickness of the pinhole-resistant layer from becoming excessive.

[0200] <Adhesive layer> The adhesive layer is a layer for adhering the multilayer film for a substrate to the foamed resin layer and contains an adhesive.

[0201] The adhesive is preferably an adhesive resin, more preferably an ethylene-vinyl acetate copolymer resin. The ethylene-vinyl acetate copolymer resin has a structural unit derived from ethylene and a structural unit derived from vinyl acetate, and may or may not have other structural units other than these. Preferred examples of the ethylene-vinyl acetate copolymer resin include partially saponified ethylene-vinyl acetate copolymers.

[0202] The adhesive layer in the multilayer film for a substrate may contain only an adhesive (i.e., it may consist of only an adhesive), or may contain an adhesive and other components (which may be referred to as "other components" in this specification) (i.e., it may consist of an adhesive and the other components).

[0203] The adhesive contained in the adhesive layer in the multilayer film for a substrate may be only one type, or may be two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0204] The other components contained in the adhesive layer in the multilayer film for a substrate are not particularly limited and can be arbitrarily selected according to the purpose. For example, they can be either resin components or non-resin components.

[0205] The other components contained in the adhesive layer in the multilayer film for a substrate may be only one type, or may be two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0206] The ratio of the content of the adhesive to the total mass of the adhesive layer in the adhesive layer in the multilayer film for a substrate may be, for example, 50 to 100% by mass. Usually, the ratio is the same as the ratio of the content (parts by mass) of the adhesive to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the adhesive layer for a substrate described below.

[0207] The adhesive layer in the multilayer film for a substrate may consist of one layer (single layer), or may consist of two or more layers. When the adhesive layer consists of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0208] The thickness of the adhesive layer in the multilayer film for the substrate is preferably 2 to 40 μm. When the thickness of the adhesive layer is equal to or greater than the lower limit value, the adhesive strength between the two layers to be adhered becomes higher. When the thickness of the adhesive layer is equal to or less than the upper limit value, it is possible to suppress the thickness of the adhesive layer from becoming excessive. Here, the "thickness of the adhesive layer" means the thickness of the entire adhesive layer. For example, the thickness of an adhesive layer composed of multiple layers means the total thickness of all the layers constituting the adhesive layer.

[0209] The ratio of the thickness of the adhesive layer to the thickness of the multilayer film for the substrate is not particularly limited, but is preferably 5 to 40%. When the ratio is equal to or greater than the lower limit value, the adhesive strength between the two layers to be adhered becomes higher. When the ratio is equal to or less than the upper limit value, it is possible to suppress the thickness of the adhesive layer from becoming excessive.

[0210] <First intermediate adhesive layer, second intermediate adhesive layer> The first intermediate adhesive layer and the second intermediate adhesive layer contain an adhesive. The adhesive is preferably an adhesive resin. Examples of the adhesive resin include polyolefin resins and the like. The polyolefin resin is a resin having a structural unit derived from an olefin, and may be a modified polyolefin such as an acid-modified polyolefin having an acidic group (for example, acid-modified polyethylene, acid-modified polypropylene). Examples of the polyolefin resin include ethylene copolymers, propylene copolymers, butene copolymers, and modified products of these copolymers (in other words, modified copolymers). The polyolefin resin is preferably a random copolymer, a graft copolymer, or a block copolymer in terms of further improving the adhesiveness.

[0211] Examples of the ethylene copolymer include the ethylene copolymer described above as included in the easy peel layer and modified products thereof (modified copolymers). Examples of the propylene-based copolymer include a copolymer of propylene and a vinyl group-containing monomer, a modified product thereof (modified copolymer), and the like. More specific examples of such a propylene-based copolymer include maleic anhydride graft-modified linear low-density polypropylene, propylene-based thermoplastic elastomer, and the like. Examples of the butene-based copolymer include a copolymer of 1-butene and a vinyl group-containing monomer, a copolymer of 2-butene and a vinyl group-containing monomer, a modified product of these copolymers (modified copolymer), and the like.

[0212] The first intermediate adhesive layer and the second intermediate adhesive layer may contain only an adhesive (i.e., may be composed of an adhesive), or may contain an adhesive and other components (which may be referred to as "other components" in this specification) (i.e., may be composed of an adhesive and the other components).

[0213] The adhesive contained in the first intermediate adhesive layer and the second intermediate adhesive layer may be only one type or two or more types. In the case of two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0214] The other components contained in the first intermediate adhesive layer and the second intermediate adhesive layer are not particularly limited and can be arbitrarily selected according to the purpose. For example, they can be either a resin component or a non-resin component.

[0215] The other components contained in the first intermediate adhesive layer and the second intermediate adhesive layer may be only one type or two or more types. In the case of two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0216] The ratio of the content of the adhesive to the total mass of the first intermediate adhesive layer in the first intermediate adhesive layer of the multilayer film for a substrate may be, for example, 50 to 100% by mass. The ratio is usually the same as the ratio of the content (parts by mass) of the adhesive to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the first intermediate adhesive layer for the base material, which will be described later. The ratio of the content of the adhesive to the total mass of the second intermediate adhesive layer in the multilayer film for the base material may be, for example, 50 to 100% by mass. The ratio is usually the same as the ratio of the content (parts by mass) of the adhesive to the total content (parts by mass) of the components that do not vaporize at room temperature in the composition for forming the second intermediate adhesive layer for the base material, which will be described later.

[0217] Both the first intermediate adhesive layer and the second intermediate adhesive layer in the multilayer film for the base material may each consist of one layer (single layer), or may consist of two or more layers. When the first intermediate adhesive layer or the second intermediate adhesive layer consists of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combination of these plurality of layers is not particularly limited as long as the effects of the present invention are not impaired.

[0218] The thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer in the multilayer film for the base material are preferably each independently 2 to 15 μm. When the thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer are equal to or greater than the lower limit value, the adhesive strength between the two layers to be adhered is higher. When the thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer are equal to or less than the upper limit value, it is possible to suppress the thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer from becoming excessive. Here, the "thickness of the first intermediate adhesive layer" means the thickness of the entire first intermediate adhesive layer. For example, the thickness of the first intermediate adhesive layer composed of a plurality of layers means the total thickness of all the layers constituting the first intermediate adhesive layer. The same applies to the second intermediate adhesive layer.

[0219] The ratios of the thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer to the thickness of the multilayer film for a substrate are not particularly limited, but are preferably 3 to 20% respectively. When the ratios are at least the lower limit values, the adhesive strength between the two layers to be adhered becomes higher. When the ratios are at most the upper limit values, it is suppressed that the thicknesses of the first intermediate adhesive layer and the second intermediate adhesive layer become excessive.

[0220] <Other layer> The multilayer film for a substrate may include other layers that do not fall into any of the easy peel layer, the first intermediate adhesive layer, the gas barrier layer, the second intermediate adhesive layer, the pinhole resistant layer, and the adhesive layer, as long as the effects of the present invention are not impaired.

[0221] The types and arrangement positions of the other layers in the multilayer film for a substrate are not particularly limited and can be arbitrarily selected according to the purpose.

[0222] The other layers included in the multilayer film for a substrate may be only one type or two or more types. When there are two or more types, their combinations and ratios can be arbitrarily selected according to the purpose.

[0223] The other layers in the multilayer film for a substrate may each consist of one layer (single layer) or two or more layers. When the other layers consist of a plurality of layers, these plurality of layers may be the same as or different from each other, and the combinations of these plurality of layers are not particularly limited as long as the effects of the present invention are not impaired.

[0224] The thicknesses of the other layers in the multilayer film for a substrate can be arbitrarily set according to their types and are not particularly limited.

[0225] When the multilayer film for a substrate includes the other layers, it may further include an intermediate adhesive layer for adhering the other layers to the other layers. Examples of the intermediate adhesive layer in that case include the same ones as the above-mentioned first intermediate adhesive layer or second intermediate adhesive layer.

[0226] The thickness of the non-foamed resin layer such as the multilayer film for the substrate is not particularly limited, but is preferably 40 to 120 μm.

[0227] <<Manufacturing method of the substrate>> The substrate can be manufactured by a known method according to its type. For example, when the substrate is a resin laminate provided with the above-described foamed resin layer and non-foamed resin layer, one surface of the foamed resin layer and one surface of the non-foamed resin layer (when the non-foamed resin layer is the multilayer film for the substrate, the adhesive layer therein) are bonded together by heat lamination to manufacture the substrate. The heat lamination at this time may be performed, for example, by the melt pressure bonding lamination method or the extrusion lamination method as described later in the examples. Among the non-foamed resin layers, the multilayer film for the substrate can be manufactured in the same manner as in the case of the above-described multilayer film (lid material) except that the types of the resins or resin compositions serving as the forming materials for the respective layers are different.

[0228] Regardless of the manufacturing method, the resin composition serving as the forming material for any layer in the multilayer film for the substrate may be manufactured by adjusting the types and contents of the contained components so that the layer to be formed contains the target components (constituent materials) in the target contents. For example, the ratio of the contents of the components that do not vaporize at room temperature in the resin composition is usually the same as the ratio of the contents of the components in the layer formed from this resin composition.

[0229] Examples of the resin composition for forming the easy peel layer in the multilayer film for the substrate (which may be referred to as the "composition for forming the easy peel layer for the substrate" in this specification) include those containing the polyolefin and, if necessary, the other components.

[0230] As a resin composition for forming a gas barrier layer in a multilayer film for a substrate (which may be referred to as "composition for forming a gas barrier layer for a substrate" in this specification), for example, those containing either one or both of an ethylene-vinyl alcohol copolymer and a polyamide, and optionally the other components, may be mentioned.

[0231] As a resin composition for forming a pinhole-resistant layer in a multilayer film for a substrate (which may be referred to as "composition for forming a pinhole-resistant layer for a substrate" in this specification), for example, those containing the polyolefin and optionally the other components, may be mentioned.

[0232] As a resin composition for forming an adhesive layer in a multilayer film for a substrate (which may be referred to as "composition for forming an adhesive layer for a substrate" in this specification), a resin composition for forming a first intermediate adhesive layer (which may be referred to as "composition for forming a first intermediate adhesive layer for a substrate" in this specification), and a resin composition for forming a second intermediate adhesive layer (which may be referred to as "composition for forming a second intermediate adhesive layer for a substrate" in this specification), all of them, for example, those containing the adhesive and optionally the other components, may be mentioned.

[0233] <<Package>> FIG. 3 is a cross-sectional view schematically showing an example of a package manufactured by the method according to an embodiment of the present invention. In the figures after FIG. 3, the same components as those shown in the already described figures are given the same reference numerals as in the case of the already described figures, and the detailed description thereof is omitted. In FIG. 3, the distinction between the layers in the multilayer film 1 is omitted.

[0234] The package 10 shown here is configured to include the multilayer film (lid material) 1 shown in FIG. 1 and the substrate 8.

[0235] The package 10 is preferably a skin pack. As used herein, "skin pack" means a package in which food is placed on cardboard, corrugated cardboard, a bottom film, a tray, etc., a heated film is placed thereon, and the film is adhered and fixed to the food by evacuating in a chamber. The feature that the film adheres closely to the product body like skin along the shape of the product is the origin of the name "skin pack".

[0236] In the package 10, a multilayer film (lid material) 1 is composed of a sealant layer 11, a functional layer 13, and a gas barrier layer 14 laminated in this order in the thickness direction thereof, the functional layer 13 contains an ionomer, and the melt strength of the ionomer at 180°C is 60 to 540 mN. In the package 10, the ratio of the thickness of the gas barrier layer 14 to the thickness of the multilayer film (lid material) 1 is 2 to 25%. In the package 10, the dynamic elastic modulus E' of the multilayer film (lid material) 1 at 140°C is preferably 1×10 4 Pa or more and 1×10 7 Pa or less. In the package 10, the oxygen permeability of the multilayer film (lid material) 1 under the conditions of a temperature of 23°C and a relative humidity of 60% is preferably 100 cc / (m 2 ·day·atm) or less. In the package 10, when performing thermomechanical analysis on the multilayer film (lid material) 1, the temperature at which a displacement of 2000 μm is shown is preferably 120°C or higher. In the package 10, the gel fraction of the multilayer film (lid material) 1 is preferably 30% or more. In the package 10, when performing the thermomechanical analysis on the multilayer film (lid material) 1, the displacement at a temperature of 100°C is preferably 500 μm or less. In the package 10, the multilayer film (lid material) 1 is preferably irradiated with an electron beam under the condition of an absorbed dose of 13 to 300 kGy. In the package 10, the gas barrier layer 14 preferably contains an ethylene-vinyl alcohol copolymer. In the package 10, it is preferable that the ratio of the thickness of the functional layer 13 to the thickness of the multilayer film (lid material) 1 is 10% or more. In the package 10, it is preferable that the ratio of the thickness of the sealant layer 11 to the thickness of the multilayer film (lid material) 1 is 5% or more.

[0237] In the package 10, the oxygen transmission rate of the bottom material 8 under the conditions of a temperature of 23 °C and a relative humidity of 60% is preferably 300 cc / (m 2 ·day·atm) or less.

[0238] By using the multilayer film 1 as the lid material, the package 10 prevents the bottom material container from deforming and has excellent melt strength during heating. Further, by using the multilayer film (lid material) 1 and the bottom material 8, the package 10 has high oxygen barrier properties against the food 9, and the storage period of the food 9 is longer than that of conventional packages.

[0239] One surface of the bottom material 8 (which may be referred to as the "first surface" in this specification) 8a is a sealing surface, and a part of the first surface 8a and a part of the first surface 11a of the sealant layer 11 in the multilayer film 1 are adhered by sealing. In FIG. 3, the part where the first surface 8a of the bottom material 8 and the first surface 11a of the sealant layer 11 in the multilayer film 1 are in direct contact is the seal part. As a result, a storage part 10a is formed between the first surface 8a of the bottom material 8 and the first surface 11a of the sealant layer 11. And the food 9 is sealed in this storage part 10a.

[0240] When the bottom material 8 is the multilayer film for the bottom material, the first surface 8a of the bottom material 8 is the surface on the side opposite to the gas barrier layer side of the easy peel layer.

[0241] In FIG. 3, in the storage part 10a of the package 10, there are some gaps between the food 9 and the multilayer film 1 and between the food 9 and the bottom material 8, but these gaps may not exist in the package 10 in the state where the food 9 is stored.

[0242] The package of this embodiment is not limited to the above, and within the scope not departing from the gist of the present invention, some configurations may be changed, deleted, or added. In FIG. 3, a package 10 configured using the multilayer film 1 shown in FIG. 1 is shown as the lid material. However, the package of this embodiment may be configured using other multilayer films (lid materials) including, for example, the multilayer film 2 shown in FIG. 2.

[0243] <<Method for manufacturing a package>> The method of this embodiment is a method for manufacturing a package in which food is packaged with a lid material and a bottom material. The method of this embodiment may also be a method for manufacturing a package in which food is vacuum packaged with a lid material and a bottom material.

[0244] The method for manufacturing the package of this embodiment includes a step of disposing the food on the bottom material, a step of disposing the lid material in a region that covers the food and its periphery among the regions on the bottom material, and a step of heating the lid material to 90 to 250°C and bringing it into contact with the food, shaping it along the food, and adhering (sealing) the portion of the lid material that is in contact with the bottom material to the bottom material, thereby packaging the food with the lid material and the bottom material. The test package described later can also be manufactured by the method for manufacturing the package of this embodiment.

[0245] In the step of disposing the food on the bottom material, for example, when using a resin laminate provided with the multilayer film for the bottom material described above as the bottom material, the food is disposed on the easy peel layer in the multilayer film for the bottom material.

[0246] In the step of disposing the lid material, the multilayer film described above is disposed with its sealant layer facing the bottom material and the food side.

[0247] While heating the lid material to 90 to 250°C, bring it into contact with the food, shape it along the food, and adhere the portion of the lid material that is in contact with the base material to the base material, thereby packaging the food with the lid material and the base material. In this process, the region where the food is disposed between the base material and the lid material may be evacuated.

[0248] The heating temperature for heating the lid material is preferably 100 to 170°C, more preferably 105 to 170°C, and even more preferably 110 to 170°C. When the heating temperature is at or above the lower limit value, the seal strength becomes higher while having easy peelability. When the heating temperature is at or below the upper limit value, the opening of the package becomes easier.

[0249] The heating time for heating the lid material to 90 to 250°C can be appropriately adjusted according to the heating temperature, but usually it is preferably 10 to 30 seconds. When the heating time is at or above the lower limit value, the seal strength becomes higher while having easy peelability. When the heating time is at or below the upper limit value, the opening of the package becomes easier.

[0250] When evacuating the region where the food is disposed, the pressure in this region is preferably 0 to 10,000 Pa (100 mbar), more preferably 0 to 9,000 Pa (90 mbar), and even more preferably 0 to 8,000 Pa (80 mbar). When the pressure is at or below the upper limit value, a package with higher followability (adhesion) of the lid material to the contents and better storage suitability can be obtained.

[0251] The pressure when adhering (sealing) the portion of the lid material that is in contact with the base material to the base material is preferably 0 to 1,000 Pa (100 mbar), more preferably 0 to 9,000 Pa (90 mbar), and even more preferably 0 to 8,000 Pa (80 mbar). When the pressure is at or below the upper limit value, a package with a good peeling feeling can be obtained.

Example

[0252] Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples shown below.

[0253] [Example 1] [Manufacture of Multilayer Film (Lid Material A)] A multilayer film having the configuration shown in FIG. 1 was manufactured according to the procedure shown below. That is, as the resin constituting the sealant layer, low-density polyethylene (LDPE, "F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.) was prepared. As the resin constituting the outer layer, amorphous PET (PETG, "S2008" manufactured by SK Chemicals Co., Ltd.) was prepared. As the resin constituting the pinhole-resistant layer, 6-nylon (Ny, "1030B2" manufactured by Ube Industries, Ltd.) was prepared. As the resin constituting the gas barrier layer, ethylene-vinyl alcohol copolymer (EVOH, "J171B" manufactured by Kuraray Co., Ltd.) was prepared. As the resin constituting the functional layer, ionomer (ION, "1601" manufactured by Mitsui Dow Polychemical Co., Ltd.) was prepared. As the adhesive (adhesive resin) constituting the first adhesive layer, maleic anhydride-modified polyethylene (modified PE, "NF536" manufactured by Mitsui Chemicals, Inc.) was prepared. As the adhesive (adhesive resin) constituting the second adhesive layer, maleic anhydride-modified polyethylene (modified PE, "F515A" manufactured by Mitsubishi Chemical Corporation) was prepared.

[0254] The temperature of the die was set at 250°C, and the LDPE, ION, modified PE, NY, EVOH, modified PE, and PETG were co-extruded in this order (co-extrusion T-die method) to form a sealant layer (thickness 12 μm), a functional layer (thickness 17 μm), a first adhesive layer (thickness 6 μm), a pinhole-resistant layer (thickness 20 μm), a gas barrier layer (thickness 12 μm), a second adhesive layer (thickness 8 μm), and an outer layer (thickness 45 μm) in this order and stacked in the thickness direction thereof to manufacture a multilayer film (thickness 120 μm). Thus, the target multilayer film (hereinafter sometimes referred to as "lid material A-I") was obtained.

[0255] <<Evaluation of Multilayer Film (Lid Material A)>> <Measurement of Dynamic Elastic Modulus at 140°C> Regarding the multilayer film (lid material A-I) obtained above, using a dynamic viscoelasticity measuring device ("DMA 7100" manufactured by Hitachi High-Tech Science Corporation), in accordance with JIS K7244-4, using a sample with a width of 4 mm, in a tensile mode, in the temperature range from 25°C to 160°C, with a displacement of 10 μm, a vibration frequency of 1 Hz, and a heating rate of 3°C / min., the dynamic elastic modulus (E') was measured. The results are shown in Table 1.

[0256] <Ionomer Melt Strength at 180°C> Regarding the multilayer film (lid material A-I) obtained above, using a melt strength device ("Capillograph" manufactured by Toyo Seiki Seisakusho), in accordance with JIS K7199, under the condition of a winding speed of 15 m / min., the melt strength of the ionomer contained in the functional layer was measured. The results are shown in Table 1.

[0257] <Ease of Spreading of the Functional Layer during Film Formation> Regarding the multilayer film (lid material A-I) obtained above, the functional layer was visually observed, and in accordance with the following criteria, the spreading of the functional layer during film formation was evaluated. The results are shown in Table 1. [Evaluation Criteria] A: The functional layer spreads easily during film formation. B: The functional layer spreads slightly less easily during film formation. C: The functional layer spreads hardly during film formation.

[0258] <<Manufacture of the Substrate>> <Manufacture of the Multilayer Film for Substrate> The multilayer film for substrate was manufactured according to the procedure shown below. That is, as the resins constituting the easy peel layer, low-density polyethylene (LDPE, "L211" manufactured by Sumitomo Chemical Co., Ltd.) and polypropylene (PP, "FS2011DG2" manufactured by Sumitomo Chemical Co., Ltd.) were prepared. As the resin constituting the pinhole-resistant layer, metallocene-catalyzed linear low-density polyethylene (mLLDPE) (manufactured by Ube Maruzen Polyethylene Co., Ltd., "Yumelite (registered trademark) 1520F", density 0.913 g / cm 3 ) was prepared. As the resin constituting the gas barrier layer, ethylene-vinyl alcohol copolymer (EVOH, manufactured by Kuraray Co., Ltd., "J171B", density: 1180 kg / m 3 , MFR: 4.2 g / 10 min) was prepared. As the resin constituting the first intermediate adhesive layer, acid-modified polypropylene (acid-modified PP, adhesive resin, manufactured by Mitsui Chemicals, Inc., "Admer QF551") was prepared. As the resin constituting the second intermediate adhesive layer, acid-modified polyethylene (acid-modified PE, adhesive resin, manufactured by Mitsui Chemicals, Inc., "Admer NF536") was prepared. As the resin constituting the adhesive layer, ethylene-vinyl acetate copolymer resin (EVA-based resin, adhesive resin, manufactured by Tosoh Corporation, "Melsen (registered trademark) MX02D") was prepared.

[0259] By mixing the above LDPE (70 parts by mass) and PP (30 parts by mass) at room temperature, a composition for forming an easy-peel layer for a substrate was manufactured.

[0260] The temperature of the die was set at 250 °C, and the composition for forming an easy-peel layer for a substrate, the acid-modified PP, the EVOH, the acid-modified PE, the mLLDPE, and the EVA-based resin were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film for a substrate (thickness 70 μm) in which an easy-peel layer (thickness 25.9 μm), a first intermediate adhesive layer (thickness 5.6 μm), a gas barrier layer (thickness 8.4 μm), a second intermediate adhesive layer (thickness 5.6 μm), a pinhole-resistant layer (thickness 10.5 μm), and an adhesive layer (thickness 14 μm) were laminated in this order in the thickness direction thereof.

[0261] <Manufacture of Substrate> Using a foamed resin sheet (manufactured by Chuo Chemical Co., Ltd., thickness 3000 μm) containing a foam of polystyrene-based resin (PSP), the exposed surface of the adhesive layer of the multilayer film for the base material obtained above was heat-laminated and bonded to one surface thereof to obtain a base material (hereinafter sometimes referred to as "base material (α)"). The heat lamination of the foamed resin sheet and the multilayer film for the base material was performed by melt-pressure bonding lamination using a roll device equipped with a melt-pressure bonding roll. The melt-pressure bonding roll is composed of a heating roll and a counter roll provided opposite to the heating roll, and the foamed resin sheet and the multilayer film for the base material were melt-pressure bonded at 180° C. between the heating roll and the counter roll to bond them together.

[0262] <<Evaluation of the base material>> <Measurement of oxygen transmission rate> Regarding the base material (base material (α)) obtained above, under the conditions of a temperature of 23° C. and a relative humidity of 60%, the oxygen transmission rate (cc / (m 2 ·day·atm)) was measured in accordance with JIS K 7126-2:2006. The results are shown in Table 5.

[0263] <<Manufacture of the package (test package)>> Frozen tempura with a mass of 100 g was used as the test meat. Then, with a continuous skin pack packaging machine ("T300" manufactured by Multivac), the sealant layer in the lid material A-I obtained above and the easy peel layer in the base material (α) were opposed to each other, the test meat was placed between these lid material A-I and the base material (α), and while evacuating the area where the test meat was placed, the peripheral portions of the lid material A-I and the base material (α) were heat-sealed under the conditions of a hot plate temperature (seal temperature) of 140° C. and a seal time of 10 seconds to produce a test package which is a skin pack package. At the time of evacuation, the pressure in the area where the test meat was placed was set to 1000 Pa (10 mbar). The pressure when bonding (sealing) the portion of the lid material A-I in contact with the base material (α) to the base material (α) was set to 9000 Pa (9 mbar). As the base material (α), one with a size of 20 cm × 20 cm was used. A plurality of the test packages were produced by the same procedure. These test packages were frozen and stored at -30°C in an air atmosphere.

[0264] <<Evaluation 1 of the Package (Test Package)>> <Food Discoloration> Ninety days after the start of storage, the test packages were thawed from the -30°C frozen state to 4°C over 16 hours. Immediately after thawing, the unopened test packages were visually observed from the lid side, and the presence or absence of discoloration (surface oxidation discoloration) of the test meat was evaluated according to the following criteria. The results are shown in Table 6. [Evaluation Criteria] A: No discoloration of the test meat occurred. B: Slight discoloration of the test meat occurred. C: Discoloration of the test meat occurred.

[0265] <Perforation> During the production of the test package, visual observation was made, and the presence or absence of perforation was evaluated according to the following criteria. The results are shown in Table 6. [Evaluation Criteria] A: No perforation occurred in the test package. B: Slight perforation occurred in the test package. C: Perforation occurred in the test package.

[0266] <Bottom Substrate Container Deformation> During the adhesion of the test package to the test meat, visual observation was made, and the presence or absence of deformation of the bottom substrate container was evaluated according to the following criteria. The results are shown in Table 6. [Evaluation Criteria] A: The bottom substrate container is not deformed. B: The bottom substrate container is slightly deformed. C: The bottom substrate container is deformed.

[0267] <<Evaluation 2 of the Package (Test Package)>> Using a continuous skin pack packaging machine (model "T300" manufactured by Tokyo Food Machinery Co., Ltd.), test packages were formed by varying the temperature to 100°C, 140°C, 180°C, and 220°C under the condition of a final vacuum degree of 9000 Pa (9 mbar). The presence or absence of film clouding was evaluated according to the following criteria. The results are shown in Table 7. [Evaluation Criteria] A: The film is not clouded. B: The film is slightly clouded. C: The film is clouded.

[0268] [Example 2] A multilayer film (hereinafter sometimes referred to as "lid material A-II") was manufactured and evaluated in the same manner as in Example 1, except that the thickness of the gas barrier layer was changed from 12 μm to 17 μm and the thickness of the outer layer was changed from 45 μm to 40 μm. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that this multilayer film (lid material A-II) was used. The results are shown in Tables 1, 5, and 6.

[0269] [Example 3] A multilayer film (hereinafter sometimes referred to as "lid material A-III") was manufactured and evaluated in the same manner as in Example 1, except that the thickness of the gas barrier layer was changed from 12 μm to 24 μm and the thickness of the outer layer was changed from 45 μm to 33 μm. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that this multilayer film (lid material A-III) was used. The results are shown in Tables 1, 5, and 6.

[0270] [Example 4] A multilayer film (hereinafter sometimes referred to as "lid material A-IV") was manufactured and evaluated in the same manner as in Example 1, except that an ionomer (ION, "1855" manufactured by Mitsui Dow Chemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Chemical Co., Ltd.) as the resin constituting the functional layer. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that this multilayer film (lid material A-IV) was used. The results are shown in Tables 1, 5, and 6.

[0271] [Comparative Example 1] A multilayer film (hereinafter sometimes referred to as "lid material A-V") was manufactured and evaluated in the same manner as in Example 1, except that an ionomer (ION, "1652" manufactured by Mitsui Dow Polychemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Polychemical Co., Ltd.) as the resin constituting the functional layer. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that this multilayer film (lid material A-V) was used. The results are shown in Tables 1, 5, and 8.

[0272] [Comparative Example 2] A multilayer film (hereinafter sometimes referred to as "lid material A-VI") was manufactured and evaluated in the same manner as in Example 1, except that an ionomer (ION, "1554W" manufactured by Mitsui Dow Polychemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Polychemical Co., Ltd.) as the resin constituting the functional layer. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that this multilayer film (lid material A-VI) was used. The results are shown in Tables 1, 5, and 8.

[0273] [Example 5] [Manufacture of Multilayer Film (Lid Material B)] A multilayer film having the configuration shown in FIG. 2 was manufactured according to the procedure shown below. That is, an ethylene-vinyl acetate copolymer (EVA, "V5714C" manufactured by Mitsui Dow Polychemical Co., Ltd.) was prepared as the resin constituting the sealant layer. As the resin constituting the outer layer, low-density polyethylene (LDPE, density 0.922 g / cm 3 , "F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.) was prepared. As the resin constituting the functional layers (the first functional layer and the second functional layer), an ionomer (ION, "1601" manufactured by Mitsui Dow Polychemical Co., Ltd.) was prepared. As the resin constituting the gas barrier layer, an ethylene-vinyl alcohol copolymer (EVOH, "GH3804B" manufactured by Nippon Gosei Co., Ltd.) was prepared. As the adhesive (adhesive resin) constituting the adhesive layers (the first adhesive layer and the second adhesive layer), maleic anhydride-modified polyethylene (modified PE, "NF536" manufactured by Mitsui Chemicals, Inc.) was prepared.

[0274] The temperature of the die was set at 250 °C, and the EVA, the ION, the modified PE, the EVOH, the modified PE, the ION, and the LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (thickness 120 μm) in which a sealant layer (thickness 24 μm), a functional layer (the first functional layer, thickness 29 μm), an adhesive layer (the first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 10 μm), an adhesive layer (the second adhesive layer, thickness 8 μm), a functional layer (the second functional layer, thickness 17 μm), and an outer layer (thickness 24 μm) were laminated in this order in the thickness direction thereof.

[0275] Next, the multilayer film obtained above was irradiated with an electron beam from the outside on the outer layer side under the conditions of an absorbed dose of 175 kGy and an accelerating voltage of 160 kV. Thus, the target multilayer film irradiated with an electron beam (hereinafter sometimes referred to as "lid material B-I") was obtained.

[0276] <<Evaluation of Multilayer Film (Lid Material B)>> <Measurement of Dynamic Elastic Modulus at 140 °C> For the multilayer film irradiated with an electron beam (lid material B-I) obtained above, the dynamic elastic modulus (E') was measured in the same manner as in Example 1. The results are shown in Table 2.

[0277] <Ionomer Melt Strength at 180 °C> For the electron beam irradiated multilayer film (lid material B-I) obtained above, the melt strength of the ionomer contained in the first functional layer was measured in the same manner as in Example 1. The results are shown in Table 2.

[0278] <Temperature indicating a displacement of 2000 μm, identification of displacement at a temperature of 100°C> For the electron beam irradiated multilayer film (lid material B-I) obtained above, thermomechanical analysis was performed in accordance with JIS K 7196 using a thermal analyzer ("EXSTAR6000" manufactured by SII). Then, from the obtained thermomechanical analysis curve, the temperature (°C) indicating a displacement of 2000 μm and the displacement (μm) at a temperature of 100°C were determined. The results are shown in Table 2.

[0279] <Measurement of gel fraction> For the electron beam irradiated multilayer film (lid material B-I) obtained above, the gel fraction was measured in accordance with JIS K 6769. That is, a test piece having a size of 3 cm × 3 cm (about 0.09 g) was cut out from the multilayer film, and this test piece was wrapped with a 400-mesh stainless steel wire mesh (100 g) and immersed in xylene (18 mL) at 110°C for 24 hours. Next, the test piece was taken out of the xylene together with the wire mesh and vacuum dried at 110°C for 24 hours under a pressure of 1.7 kPa to obtain a dried product of the test piece after immersion. The mass of the obtained dried product was measured, and the gel fraction (%) of the electron beam irradiated multilayer film was determined. The results are shown in Table 2.

[0280] <Evaluation of delamination of gas barrier layer> For the electron beam irradiated multilayer film (lid material B-I) obtained above, the gas barrier layer was visually observed, and the presence or absence of delamination of the gas barrier layer was evaluated according to the following criteria. The results are shown in Table 2. [Evaluation criteria] A: No delamination of the gas barrier layer has occurred. B: Slight delamination of the gas barrier layer has occurred. C: Delamination of the gas barrier layer has occurred.

[0281] <<Manufacture and Evaluation of Package (Test Package)>> A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-I) was used. The results are shown in Tables 2, 5 and 6.

[0282] [Example 6] An electron beam irradiated multilayer film (hereinafter sometimes referred to as "lid material B-II") was manufactured and evaluated in the same manner as in Example 5, except that the absorbed dose was changed to 120 kGy instead of 175 kGy during the electron beam irradiation of the multilayer film. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-II) was used. The results are shown in Tables 2, 5 and 6.

[0283] [Example 7] An electron beam irradiated multilayer film (hereinafter sometimes referred to as "lid material B-III") was manufactured and evaluated in the same manner as in Example 5, except that the absorbed dose was changed to 90 kGy instead of 175 kGy during the electron beam irradiation of the multilayer film. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-III) was used. The results are shown in Tables 2, 5 and 6.

[0284] [Example 8] An electron beam irradiated multilayer film (hereinafter sometimes referred to as "lid material B-IV") was manufactured and evaluated in the same manner as in Example 5, except that the absorbed dose was changed to 15 kGy instead of 175 kGy during the electron beam irradiation of the multilayer film. A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-IV) was used. The results are shown in Tables 2, 5 and 6.

[0285] [Example 9] A lid material (a multilayer film not irradiated with electron beams, hereinafter sometimes referred to as "lid material B-V") was produced and evaluated in the same manner as in Example 5, except that the multilayer film was not irradiated with electron beams. A package (test package) was produced and evaluated in the same manner as in Example 1, except that this multilayer film not irradiated with electron beams (lid material B-V) was used. The results are shown in Tables 2, 5 and 6.

[0286] [Example 10] A multilayer film (120 μm thick) in which a sealant layer (20 μm thick), a functional layer (first functional layer, 29 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (18 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 17 μm thick), and an outer layer (20 μm thick) were laminated in this order in the thickness direction thereof was produced by co-extruding the EVA, the ION, the modified PE, the EVOH, the modified PE, the ION, and the LDPE in this order at a die temperature of 250°C (co-extrusion T-die method). A lid material (a multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-VI") was produced and evaluated in the same manner as in Example 5, except for this point. A package (test package) was produced and evaluated in the same manner as in Example 1, except that this multilayer film irradiated with electron beams (lid material B-VI) was used. The results are shown in Tables 3, 5 and 7.

[0287] [Example 11] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (120 μm thick) in which a sealant layer (16 μm thick), a functional layer (first functional layer, 29 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (26 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 17 μm thick), and an outer layer (16 μm thick) were laminated in this order in the thickness direction thereof. Except for this point, a lid material (a multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-VII") was produced and evaluated in the same manner as in Example 5. Except for using this multilayer film irradiated with electron beams (lid material B-VII), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 3, 5, and 7.

[0288] [Comparative Example 3] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (120 μm thick) in which a sealant layer (12 μm thick), a functional layer (first functional layer, 29 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (34 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 17 μm thick), and an outer layer (12 μm thick) were laminated in this order in the thickness direction thereof. Except for this point, a lid material (a multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-VIII") was produced and evaluated in the same manner as in Example 5. Except for using this multilayer film irradiated with electron beams (lid material B-VIII), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 3, 5, and 8.

[0289] [Example 12] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (120 μm thick) in which a sealant layer (27 μm thick), a functional layer (first functional layer, 29 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (4 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 17 μm thick), and an outer layer (27 μm thick) were laminated in this order in the thickness direction thereof. Except for this, a lid material (a multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-IX") was produced and evaluated in the same manner as in Example 5. Except for using this electron beam-irradiated multilayer film (lid material B-IX), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 3, 5, and 7.

[0290] [Comparative Example 4] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (120 μm thick) in which a sealant layer (28 μm thick), a functional layer (first functional layer, 29 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (1 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 17 μm thick), and an outer layer (29 μm thick) were laminated in this order in the thickness direction thereof. Except for this, a lid material (a multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-X") was produced and evaluated in the same manner as in Example 5. Except for using this electron beam-irradiated multilayer film (lid material B-X), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 3, 5, and 8.

[0291] [Example 13] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multi-layer film (with a thickness of 120 μm) in which a sealant layer (thickness 32 μm), a functional layer (first functional layer, thickness 21 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 10 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a functional layer (second functional layer, thickness 9 μm), and an outer layer (thickness 32 μm) were laminated in this order in their thickness directions. Except for this point, a lid material (a multi-layer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-XI") was produced and evaluated in the same manner as in Example 5. Except for using this multi-layer film irradiated with electron beams (lid material B-XI), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 3, 5, and 7.

[0292] [Example 14] The temperature of the die was set at 250°C, and the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE were co-extruded in this order (co-extrusion T-die method) to produce a multi-layer film (with a thickness of 120 μm) in which a sealant layer (thickness 40 μm), a functional layer (first functional layer, thickness 7 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 10 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a functional layer (second functional layer, thickness 7 μm), and an outer layer (thickness 40 μm) were laminated in this order in their thickness directions. Except for this point, a lid material (a multi-layer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-XII") was produced and evaluated in the same manner as in Example 5. Except for using this multi-layer film irradiated with electron beams (lid material B-XII), a package (test package) was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 4, 5, and 7.

[0293] [Example 15] The temperature of the die was set at 250°C, and a multilayer film (120 μm thick) was produced by co-extruding the EVA, ION, modified PE, EVOH, modified PE, ION, and LDPE in this order (co-extrusion T-die method), in which a sealant layer (41 μm thick), a functional layer (first functional layer, 6 μm thick), an adhesive layer (first adhesive layer, 8 μm thick), a gas barrier layer (10 μm thick), an adhesive layer (second adhesive layer, 8 μm thick), a functional layer (second functional layer, 5 μm thick), and an outer layer (42 μm thick) were laminated in this order in the thickness direction thereof. A lid material (multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-XIII") was produced and evaluated in the same manner as in Example 5, except for the above. A package (test package) was produced and evaluated in the same manner as in Example 1, except that the multilayer film irradiated with electron beams (lid material B-XIII) was used. The results are shown in Tables 4, 5, and 7.

[0294] [Example 16] A lid material (multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-XIV") was produced and evaluated in the same manner as in Example 5, except that 6-nylon (Ny, "1030B2" manufactured by Ube Industries, Ltd.) was used instead of the EVOH ("GH3804B" manufactured by Nippon Gohsei Co., Ltd.) as the resin constituting the gas barrier layer. A package (test package) was produced and evaluated in the same manner as in Example 1, except that the multilayer film irradiated with electron beams (lid material B-XIV) was used. The results are shown in Tables 4, 5, and 7.

[0295] [Example 17] A lid material (multilayer film irradiated with electron beams, hereinafter sometimes referred to as "lid material B-XV") was produced and evaluated in the same manner as in Example 5, except that an ionomer (ION, "1855" manufactured by Mitsui Dow Chemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Chemical Co., Ltd.) as the resin constituting the functional layers (first functional layer and second functional layer). A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-XV) was used. The results are shown in Tables 4, 5, and 7.

[0296] [Comparative Example 5] A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material B-XVI") was manufactured and evaluated in the same manner as in Example 5, except that an ionomer (ION, "1652" manufactured by Mitsui Dow Chemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Chemical Co., Ltd.) as the resin constituting the functional layers (first functional layer and second functional layer). A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-XVI) was used. The results are shown in Tables 4, 5, and 8.

[0297] [Comparative Example 6] A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material B-XVII") was manufactured and evaluated in the same manner as in Example 5, except that an ionomer (ION, "1554W" manufactured by Mitsui Dow Chemical Co., Ltd.) was used instead of the ION ("1601" manufactured by Mitsui Dow Chemical Co., Ltd.) as the resin constituting the functional layers (first functional layer and second functional layer). A package (test package) was manufactured and evaluated in the same manner as in Example 1, except that the electron beam irradiated multilayer film (lid material B-XVII) was used. The results are shown in Tables 4, 5, and 8.

[0298]

Table 1

[0299]

Table 2

[0300]

Table 3

[0301]

Table 4

[0302]

Table 5

[0303]

Table 6

[0304]

Table 7

[0305]

Table 8

[0306] For the lid material A of the test packages of Examples 1 to 4, since the ionomer melt strength at 180°C was 540 mN or less in all cases, the functional layer was likely to spread during film formation. Also, for the lid material B of the test packages of Examples 5 to 17, since the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was 2% or more in all cases, no delamination of the gas barrier layer occurred. Since the ratio of the thickness of the gas barrier layer in the test packages of Examples 1 to 17 was 2% or more, although slight discoloration of the test meat occurred in the test package of Example 16, no discoloration of the test meat occurred in the test packages of Examples 1 to 15 and 17. Further, since the ionomer melt strength at 180°C in the test packages of Examples 1 to 17 was 60 mN or more, although slight perforation occurred during skin packaging in the test package of Example 15, no perforation occurred during skin packaging in the test packages of Examples 1 to 14, 16, and 17. Furthermore, since the ionomer melt strength at 180°C in the test packages of Examples 1 to 17 was 540 mN or less and the ratio of the thickness of the gas barrier layer was 25% or less, the bottom substrate container did not deform when adhering to the test meat. Thus, in the test packages of Examples 1 to 17, the bottom substrate container did not deform and they had excellent melt strength during heating. Regarding moldability, in the test package of Example 8, although the film was slightly cloudy at a molding temperature of 220°C, in the test packages of Examples 5 to 7 and 10 to 17, the film did not become cloudy over the molding temperature range of 100°C to 220°C and they had excellent heat resistance.

[0307] On the other hand, in the test package of Comparative Example 1, since the melt strength of the ionomer contained in the functional layer was less than 60 mN, perforation occurred during skin packaging. In the test package of Comparative Example 2, since the melt strength of the ionomer contained in the functional layer exceeded 540 mN, the functional layer was difficult to spread during film formation of the lid material, and the bottom substrate container deformed when the lid material was adhered to the test meat. In the test package of Comparative Example 3, since the ratio of the thickness of the gas barrier layer exceeded 25%, the dynamic elastic modulus E’ at 140°C became more than 1×10 7 Pa, so the bottom substrate container deformed when the lid material was adhered to the test meat. In the test package of Comparative Example 4, since the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was less than 2%, layer breakage of the gas barrier layer occurred in the lid material, and thus discoloration occurred in the packaged test meat. In the test package of Comparative Example 5, since the melt strength of the ionomer contained in the functional layer was less than 60 mN, perforations occurred during skin packaging. In the test package of Comparative Example 6, since the melt strength of the ionomer contained in the functional layer exceeded 540 mN, the bottom substrate container was deformed when the lid material was adhered to the test meat. Regarding the moldability, in the test packages of Comparative Examples 1 to 4, the film was slightly turbid at a molding temperature of 140°C and became turbid at 180°C or higher.

Industrial Applicability

[0308] The present invention can provide a package (for example, a skin pack package) using, as a lid material, a multilayer film that does not deform the bottom substrate container and has excellent melt strength during heating.

Explanation of Symbols

[0309] 1 ··· Multilayer film (lid material) 2 ··· Multilayer film (lid material) 11 ··· Sealant layer 12 ··· Outer layer 13 ··· Functional layer 131 ··· First functional layer 132 ··· Second functional layer 14 ··· Gas barrier layer 15 ··· Adhesive layer 16 ··· Pinhole-resistant layer 151 ··· First adhesive layer 152 ··· Second adhesive layer 10 ··· Package (test package) 8 ··· Bottom substrate 9 ··· Food (test meat)

Claims

1. A method for manufacturing a package in which food is packaged with a lid material and a base material, comprising the steps of: placing the food on the base; A step of placing the lid material in an area on the base material that covers the food and its surroundings; and heating the lid material to 90 to 250°C while contacting the lid material with the food, forming the lid material to conform to the food, and adhering the portion of the lid material in contact with the base material to the base material, thereby packaging the food with the lid material and the base material. The lid material is made of a multilayer film, The multilayer film is configured by laminating a sealant layer, a functional layer, and a gas barrier layer in this order in a thickness direction, the functional layer comprises an ionomer, The melt strength of the ionomer at a temperature of 180° C. is 60 to 540 mN; A method for producing a packaging body, wherein the ratio of a thickness of the gas barrier layer to a thickness of the multilayer film is 2 to 25%.

2. The method for producing a packaging body according to claim 1 , wherein the temperature at which the multilayer film shows a displacement of 2000 μm during thermomechanical analysis is 120° C. or higher.

3. The method for producing a packaging body according to claim 1 or 2, wherein the multilayer film has a gel fraction of 30% or more.

4. The method for producing a packaging body according to claim 2 , wherein the multilayer film has a displacement of 500 μm or less at a temperature of 100° C. during the thermomechanical analysis.

5. The dynamic elastic modulus E' of the multilayer film at a temperature of 140° C. is 1×10 ４ Pa or more 1×10 ７ The method for producing the package according to any one of claims 1 to 4, wherein the viscosity is 0.01 Pa or less.

6. The method for producing a package according to any one of claims 1 to 5, wherein the multilayer film is irradiated with an electron beam at an absorbed dose of 13 to 300 kGy.

7. The method for producing a package according to any one of claims 1 to 6, wherein a ratio of a thickness of the sealant layer to a thickness of the multilayer film is 5% or more.

8. The method for producing a packaging body according to any one of claims 1 to 7, wherein a ratio of a thickness of the functional layer to a thickness of the multilayer film is 10% or more.

9. The method for producing a package according to any one of claims 1 to 8, wherein the gas barrier layer comprises an ethylene-vinyl alcohol copolymer.

10. The method for producing a packaging body according to any one of claims 1 to 9, wherein the packaging body is a skin pack packaging body.

Images