Multi-layer film and package

Abstract

To provide a multilayer film for a package that has high followability to the contents and has reduced odors resulting from electron-beam irradiation.SOLUTION: A multilayer film 1 has an outer layer 12 containing polyethylene, and a sealant layer 11 containing a first ionomer. When the multilayer film is subjected to thermomechanical analysis, the temperature indicating the displacement of 2000 μm is 120°C or higher, or the gel fraction of the multilayer film is 30% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer film and a package.

Background Art

[0002] A package in which an article is placed on a rigid tray and the article is sealed with a film is called a skin pack. In a skin pack, the film, that is, the film for the skin pack, is transparent, and the article can be easily visually recognized through the film. Further, the film for the skin pack is soft, and by evacuating the storage portion in the skin pack, it is possible to closely adhere to the article without causing wrinkles (see, for example, Patent Document 1). And, since the skin pack includes a rigid tray, it can be displayed upright without causing displacement of the article. In view of such characteristics, the skin pack is mainly used as a package 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, an oxygen barrier layer needs to be provided in the multilayer film constituting the skin pack. However, there has been a problem that the followability of the skin pack to the food (the ability to closely adhere without causing wrinkles) is reduced due to the presence of the oxygen barrier layer.

[0005] In addition, when an electron beam irradiates a multilayer film that constitutes a skin pack, there is also a problem that components such as ethylene vinyl acetate copolymer contained in the multilayer film (especially the sealant layer) cause a deacetic acid reaction, resulting in the generation of odor. This becomes particularly problematic when the contained product is a food (e.g., cooked rice, etc.) that is sensitive to taste with respect to the odor. Ethylene vinyl acetate copolymer may be preferably contained in the sealant layer.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a multilayer film that is excellent in followability to the contained product and has reduced odor generation due to electron beam irradiation, and a package (e.g., a skin pack package) using the same.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention adopts the following configuration. [1]. A multilayer film, The multilayer film includes an outer layer containing polyethylene, and a sealant layer containing a first ionomer, and when performing thermomechanical analysis on the multilayer film, a multilayer film in which the temperature at which a displacement of 2000 μm is shown is 120°C or higher, or the gel fraction of the multilayer film is 30% or higher. [2]. The multilayer film according to [1], wherein the first ionomer is a zinc-based ionomer. [3]. The multilayer film according to [1] or [2], wherein the multilayer film further includes a second ionomer and has a functional layer adjacent to the outer layer. [4]. The multilayer film according to [3], wherein the second ionomer is a zinc-based ionomer or a sodium-based ionomer. [5]. The multilayer film according to [3] or [4], wherein the ratio of the thickness of the functional layer to the thickness of the multilayer film is 10% or more. [6]. The multilayer film according to any one of [1] to [5], wherein the multilayer film is irradiated with an electron beam under conditions of an absorption dose of 20 to 300 kGy. [7]. The multilayer film according to any one of [1] to [6], wherein during the thermomechanical analysis, the displacement at a temperature of 100 °C is 500 μm or less.

[0008] [8]. The multilayer film according to any one of [1] to [7], wherein the ratio of the thickness of the outer layer to the thickness of the multilayer film is 10% or more. [9]. The multilayer film according to any one of [1] to [8], wherein the thickness of the multilayer film is 60 μm or more.

[10] . The multilayer film according to any one of [1] to [9], wherein the polyethylene is low-density polyethylene having a density of 0.945 g / cm 3 or less.

[11] . The multilayer film according to any one of [1] to

[10] , further comprising an oxygen barrier layer.

[12] . The multilayer film according to

[11] , wherein the oxygen barrier layer contains an ethylene-vinyl alcohol copolymer.

[13] . The multilayer film according to

[12] , wherein in the oxygen barrier layer, the ratio of the content of the ethylene-vinyl alcohol copolymer to the total mass of the oxygen barrier layer is 3 to 25% by mass.

[14] . A package comprising the multilayer film according to any one of [1] to

[13] .

[15] . The package according to

[14] , wherein the package is a skin pack package. [Advantages of the Invention]

[0009] The multilayer film of the present invention includes an outer layer containing polyethylene and a sealant layer containing a first ionomer. During the thermomechanical analysis of the multilayer film, the temperature at which a displacement of 2000 μm is exhibited is 120 °C or higher, or the gel fraction of the multilayer film is 30% or higher. Therefore, it has excellent followability to the contents and the generation of odor by electron beam irradiation is reduced. Further, the package of the present invention (for example, a skin pack package) includes the multilayer film of the present invention. Therefore, it has excellent followability to the contents and the generation of odor by electron beam irradiation is reduced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] <<Multilayer Film>> The multilayer film according to an embodiment of the present invention includes an outer layer containing polyethylene and a sealant layer containing a first ionomer, and when performing thermomechanical analysis on the multilayer film, the temperature at which a displacement of 2000 μm is shown is 120°C or higher, or the gel fraction of the multilayer film is 30% or higher.

[0012] The multilayer film of this embodiment can form a package (for example, a skin pack package) together with a rigid tray. In this specification, "skin pack" means a package in which the contents are placed on cardboard, corrugated board, bottom film, tray, etc., a heated film is placed thereon, and vacuum pumping is performed in a chamber so that the film adheres and fixes to the contents. The name comes from the characteristic that the film adheres closely to the product body like the skin along the shape of the product.

[0013] Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show the main parts enlarged 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.

[0014] FIG. 1 is a cross-sectional view schematically showing a multilayer film according to an embodiment of the present invention. The multilayer film 1 shown here includes an outer layer 12 and a sealant layer 11. In the multilayer film 1, the outer layer 12 is one outermost layer, and the sealant layer 11 is the other outermost layer. Furthermore, the multilayer film 1 includes, from the side of the sealant layer 11 toward the outer layer 12 side, a pinhole-resistant layer 16, an adhesive layer 15 disposed on the pinhole-resistant layer 16, an oxygen barrier layer 14 disposed on the adhesive layer 15, an adhesive layer 15 disposed on the oxygen barrier layer 14, and a functional layer 13 disposed on the adhesive layer 15, and is composed of a plurality of layers.

[0015] <Sealant layer> The multilayer film 1 includes a sealant layer 11 containing a first ionomer. By the sealant layer 11 containing the first ionomer, the adhesion to the adherend can be improved. Further, when the multilayer film 1 is irradiated with electron beams from the outer layer 12 side, the electron beams can reach the sealant layer 11, and the crosslinking density of the sealant layer 11 can be improved. As a result, the followability during skin packaging can be further enhanced.

[0016] More specifically, examples of the first ionomer include a zinc-based ionomer, a sodium-based ionomer, and the like. Among these, a zinc-based ionomer is preferable. By the first ionomer being the above-mentioned ionomer, the adhesion to the adherend can be further improved, and the followability during skin packaging can be further enhanced.

[0017] In the present specification, "ionomer" means a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid having an ion-bridged structure formed by salt formation between an acid moiety and a metal ion. Further, "sodium-based ionomer" means an ionomer when the metal ion is a sodium ion, and "zinc-based ionomer" means an ionomer when the metal ion is a zinc ion.

[0018] The sealant layer 11 may contain only the first ionomer (i.e., it may consist of the first ionomer), or may contain the first ionomer and other components (which may be referred to as "other components" in this specification) (i.e., it may consist of the first ionomer and the other components).

[0019] Conventionally, when an electron beam is irradiated onto a multilayer film constituting a skin pack, there has been a problem that components such as ethylene vinyl acetate copolymer contained in the multilayer film (especially the sealant layer) cause a deacetylation reaction and generate an odor. This is particularly problematic when the contained material is a food (e.g., cooked rice, etc.) that is sensitive to taste with respect to the odor. In this specification, "odor" means an odor derived from vinyl acetate.

Chemical formula

[0020] Therefore, the other components contained in the sealant layer 11 may be either a resin component or a non-resin component, but are preferably components that do not generate an odor even when irradiated with an electron beam. Thereby, the generation of odor due to electron beam irradiation of the multilayer film 1 can be reduced.

[0021] The other component that is a resin component may be a homopolymer that is a polymer of one kind of monomer, or may be a copolymer that is a polymer of two or more kinds of monomers. More specifically, examples of the other component that is a resin component include polyolefins such as polyethylene, and olefin copolymers such as ethylene-propylene copolymer. The sealant layer 11 containing these other components (resin components) can further improve the adhesion to the adherend.

[0022] Examples of the other component that is a non-resin component include additives known in the art. Examples of the additive include an antioxidant, an antistatic agent, a crystal nucleating agent, inorganic particles, a viscosity reducer, a thickener, a heat stabilizer, a lubricant, an infrared absorber, an ultraviolet absorber, and the like.

[0023] The other components contained in the sealant layer 11 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.

[0024] The proportion of the content of the first ionomer in the sealant layer 11 with respect to the total mass of the sealant layer 11 is preferably 50% by mass or more, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 70% by mass or more and 100% by mass or less. By the proportion being not less than the lower limit value, the adhesion to the adherend can be further improved.

[0025] The proportion of the content of the component that generates odor when irradiated with an electron beam in the sealant layer 11 with respect to the total mass of the sealant layer 11 is preferably 5% by mass or less, and may be, for example, either 3% by mass or less or 1% by mass or less. Here, examples of the component that generates odor when irradiated with an electron beam include ethylene vinyl acetate copolymer and the like.

[0026] 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.

[0027] In addition, in this specification, not limited to the case of the sealant layer 11, "the plurality of layers may be the same as or different from each other" means that "all the layers may be the same, all the layers may be different, or only some of the layers may be the same", and further, "the 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".

[0028] The thickness of the sealant layer 11 is preferably 4 μm or more and 96 μm or less, more preferably 7 μm or more and 93 μm or less, and even more preferably 10 μm or more and 90 μm or less. 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 possible to suppress the sealant layer 11 from having an excessive thickness, and when the multilayer film 1 is heat-sealed, the seal strength becomes higher.

[0029] 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 multiple layers means the total thickness of all the layers constituting the sealant layer 11.

[0030] 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 7% or more and 50% or less, and even more preferably 10% or more and 30% or less. When the ratio is equal to or greater than the lower limit value, the adhesion to the adherend can be further improved. When the ratio is equal to or less than the upper limit value, it is possible to suppress the sealant layer 17 from having an excessive thickness.

[0031] The exposed surface 11a of the sealant layer 11 on the side opposite to the pinhole-resistant layer 16 side (which may be referred to as the "first surface" in this specification) is a seal surface.

[0032] <Outer layer> The multilayer film 1 includes an outer layer 12 containing polyethylene. When the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the electron beam reaches the outer layer 12, and the crosslink density of the outer layer 12 can be improved. As a result, the followability during skin packaging can be further enhanced.

[0033] The outer layer 12 may contain only polyethylene (i.e., it may be made of polyethylene), or may contain polyethylene and other components (which may be referred to as "other components" in this specification).

[0034] The polyethylene contained in the outer layer 12 has a density of 0.945 g / cm 3 It is preferably the following low-density polyethylene, and more preferably has a density of 0.943 g / cm 3 It is more preferably the following low-density polyethylene, and even more preferably has a density of 0.941 g / cm 3 It is even more preferably the following low-density polyethylene. By including such low-density polyethylene, when the multilayer film 1 is irradiated with electron beams from the outer layer 12 side, the electron beams can reach the outer layer 12 and further improve the crosslinking density of the outer layer 12.

[0035] The polyethylene contained in the outer layer 12 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.

[0036] The other components contained in the outer layer 12 can be arbitrarily selected according to the purpose. For example, they can be either resin components or non-resin components, but are preferably components that do not generate odors even when irradiated with electron beams. Thereby, the generation of odors due to electron beam irradiation of the multilayer film 1 can be reduced.

[0037] Examples of the other components that are resin components include polyolefin resins other than polyethylene.

[0038] Examples of the other components that are non-resin components include additives known in the art. Examples of the additives include antioxidants, antistatic agents, nucleating agents, inorganic particles, viscosity reducers, thickeners, heat stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, etc.

[0039] The other component(s) included in the outer layer 12 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.

[0040] In the outer layer 12, the proportion of the content of polyethylene relative to the total mass of the outer layer 12 is preferably 50% by mass or more, more preferably 55% by mass or more and 100% by mass or less, and even more preferably 60% by mass or more and 100% by mass or less. When the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the crosslinking density of the outer layer 12 can be further improved by the proportion being not less than the lower limit value.

[0041] 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 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.

[0042] The thickness of the outer layer 12 is preferably 4 μm or more and 146 μm or less, more preferably 7 μm or more and 143 μm or less, and even more preferably 10 μm or more and 140 μm or less. When the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the crosslinking density of the outer layer 12 can be further improved by the thickness of the outer layer 12 being not less than the lower limit value. By the thickness of the outer layer 12 being not more than the upper limit value, it is possible to suppress the outer layer 12 from having an excessive thickness. 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.

[0043] The ratio of the thickness of the outer layer 12 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 10% or more, more preferably 12% or more and 88% or less, and even more preferably 14% or more and 86% or less. When the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the crosslinking density of the outer layer 12 can be further improved by the ratio being equal to or higher than the lower limit value. On the other hand, by the ratio being equal to or lower than the upper limit value, it is possible to suppress the outer layer 12 from having an excessive thickness.

[0044] <Functional layer> The multilayer film 1 may further include a second ionomer and may include a functional layer 13 adjacent to the outer layer 12. By the functional layer 13 including the second ionomer, when the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the electron beam can reach the functional layer 13 and the crosslinking density of the functional layer 13 can be improved. As a result, the followability during skin packing can be further enhanced.

[0045] More specifically, examples of the second ionomer include zinc-based ionomers and sodium-based ionomers. Among these, a zinc-based ionomer or a sodium-based ionomer is preferable, and a sodium-based ionomer is more preferable. By the second ionomer being the above-mentioned ionomer, the crosslinking density of the functional layer 13 can be further improved.

[0046] The functional layer 13 may contain only the second ionomer (that is, it may be composed of the second ionomer), or may contain the second ionomer and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the second ionomer and the other components).

[0047] The second ionomer contained in the functional layer 13 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.

[0048] The second ionomer included in the functional layer 13 and the first ionomer included in the sealant layer 11 may be the same as or different from each other.

[0049] The other components included in the functional layer 13 can be arbitrarily selected according to the purpose. For example, they can be either resin components or non-resin components, but it is preferable that they do not generate odor even when irradiated with electron beams. Thereby, the generation of odor due to electron beam irradiation of the multilayer film 1 can be reduced.

[0050] The other component that is a resin component may be a homopolymer that is a polymer of one type of monomer or a copolymer that is a polymer of two or more types of monomers. The other component that is a resin component is a resin other than the second ionomer.

[0051] Examples of the other component that 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, etc.

[0052] The other components included in the functional layer 13 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.

[0053] In the functional layer 13, the proportion of the content of the second ionomer with respect to the total mass of the functional layer 13 is preferably 50% by mass or more, more preferably 55% by mass or more and 100% by mass or less, and even more preferably 60% by mass or more and 100% by mass or less. When the multilayer film 1 is irradiated with electron beams from the outer layer 12 side, the electron beams can reach the functional layer 13 and the crosslinking density of the functional layer 13 can be further improved when the proportion is at least the lower limit value.

[0054] The functional layer 13 may consist of one layer (single layer) or may consist of two or more layers. When the functional layer 13 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.

[0055] The thickness of the functional layer 13 is preferably 4 μm or more and 146 μm or less, more preferably 7 μm or more and 143 μm or less, and even more preferably 10 μm or more and 140 μm or less. When the thickness of the functional layer 13 is equal to or greater than the lower limit value, when the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the electron beam can reach the functional layer 13, and the crosslinking density of the functional layer 13 can be further improved. When the thickness of the functional layer 13 is equal to or less than the upper limit value, it is possible to suppress the functional layer 13 from having an excessive thickness.

[0056] Here, the "thickness of the functional layer 13" means the total thickness of the functional layer 13. For example, the thickness of the functional layer 13 composed of a plurality of layers means the total thickness of all the layers constituting the functional layer 13.

[0057] 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% or more and 89% or less, and even more preferably 12% or more and 88% or less. When the ratio is equal to or greater than the lower limit value, when the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the crosslinking density of the functional layer 13 can be further improved. On the other hand, when the ratio is equal to or less than the upper limit value, it is possible to suppress the functional layer 13 from having an excessive thickness.

[0058] In the case of a skin pack for food, in order to prevent oxidative deterioration of the food, an oxygen barrier layer is required to be provided in the multilayer film constituting the skin pack. However, there has been a problem that the followability of the skin pack to the food (the ability to adhere without causing wrinkles) is reduced due to the presence of the oxygen barrier layer. On the other hand, the multilayer film 1 of the present embodiment solves this problem by including the outer layer 12 and the functional layer 13. That is, due to the presence of the outer layer 12 and the functional layer 13, the heat resistance and melt tension of the multilayer film 1 are improved, and as a result, a multilayer film 1 excellent in followability to the contents can be obtained.

[0059] <Oxygen barrier layer> The multilayer film 1 may further include an oxygen barrier layer 14. By providing the oxygen barrier layer 14 in the multilayer film 1, a strong oxygen barrier property (in other words, the property of suppressing the permeation of oxygen gas) can be imparted to the multilayer film 1.

[0060] The oxygen barrier layer 14 preferably contains an ethylene-vinyl alcohol copolymer (also known as saponified ethylene-vinyl acetate copolymer, which may be abbreviated as "EVOH" in this specification).

[0061] The oxygen barrier layer 14 may contain only EVOH (that is, it may be composed of EVOH), or may contain EVOH and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of EVOH and the other components).

[0062] The other components contained in the oxygen barrier layer 14 can be arbitrarily selected according to the purpose. For example, they may be either a resin component or a non-resin component, but are preferably components that do not generate odor even when irradiated with electron beams. Thereby, the generation of odor due to electron beam irradiation of the multilayer film 1 can be reduced.

[0063] The other component that is a resin component may be a homopolymer that is a polymer of one type of monomer, or may be a copolymer that is a polymer of two or more types of monomers. The other component that is a resin component is a resin other than EVOH.

[0064] Examples of the other components that are non-resin components 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.

[0065] The other components included in the oxygen barrier layer 14 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.

[0066] The proportion of the content of EVOH in the oxygen barrier layer 14 with respect to the total mass of the oxygen barrier layer 14 is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 70% by mass or more and 100% by mass or less. By the proportion being not less than the lower limit value, a strong oxygen barrier property can be imparted to the multilayer film 1. By the proportion being not more than the upper limit value, a decrease in followability during skin packaging can be suppressed.

[0067] The oxygen barrier layer 14 may be composed of one layer (single layer), or may be composed of two or more layers. When the oxygen 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.

[0068] The thickness of the oxygen barrier layer 14 is preferably 2 μm or more and 100 μm or less, more preferably 3 μm or more and 90 μm or less, and even more preferably 4 μm or more and 80 μm or less. When the thickness of the oxygen barrier layer 14 is equal to or greater than the lower limit value, the multilayer film 1 can impart strong oxygen barrier properties. When the thickness of the oxygen barrier layer 14 is equal to or less than the upper limit value, it is possible to prevent the oxygen barrier layer 14 from having an excessive thickness.

[0069] Here, the "thickness of the oxygen barrier layer 14" means the total thickness of the entire oxygen barrier layer 14. For example, in the case of an oxygen barrier layer 14 composed of multiple layers, the thickness of the oxygen barrier layer 14 means the total thickness of all the layers constituting the oxygen barrier layer 14.

[0070] The ratio of the thickness of the oxygen barrier layer 14 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 1% or more, more preferably 2% or more and 30% or less, and even more preferably 3% or more and 25% or less. When the ratio is equal to or greater than the lower limit value, the multilayer film 1 can impart strong oxygen barrier properties. When the ratio is equal to or less than the upper limit value, it is possible to prevent the oxygen barrier layer 14 from having an excessive thickness.

[0071] <Adhesive layer> The multilayer film 1 may include an adhesive layer 15 containing an adhesive. The adhesive layer 15 adheres the two adjacent layers on both sides thereof. In the multilayer film 1, the adhesive layer 15 disposed between the pinhole-resistant layer 16 and the oxygen barrier layer 14 adheres the pinhole-resistant layer 16 and the oxygen barrier layer 14, and the adhesive layer 15 disposed between the oxygen barrier layer 14 and the functional layer 13 adheres the oxygen barrier layer 14 and the functional layer 13. In this specification, in order to distinguish these two adhesive layers 15 from each other, if necessary, the adhesive layer 15 disposed between the pinhole-resistant layer 16 and the oxygen barrier layer 14 may be referred to as the first adhesive layer 151, and the adhesive layer 15 disposed between the oxygen barrier layer 14 and the functional layer 13 may be referred to as the second adhesive layer 152. These two 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.

[0072] 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 that are one or more monomers).

[0073] More specifically, examples of the olefin resin 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.

[0074] Examples of the ethylene copolymer 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-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ionomer, ethylene-based thermoplastic elastomer, and the like.

[0075] The adhesive layer 15 may contain only the adhesive (that is, it may be composed of the adhesive), or may contain the adhesive and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the adhesive and the other components).

[0076] 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.

[0077] The other components contained 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.

[0078] The other components 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.

[0079] The proportion of the adhesive content in the total mass of the adhesive layer 15 in the adhesive layer 15 may be, for example, 50% by mass or more and 100% by mass or less.

[0080] The proportion of the content of the component that generates odor when irradiated with electron beams in the total mass of the adhesive layer 15 in the adhesive layer 15 is preferably 5% by mass or less, and may be, for example, either 3% by mass or less or 1% by mass or less. Here, examples of the component that generates odor when irradiated with electron beams include ethylene vinyl acetate copolymer.

[0081] The adhesive layer 15 may consist of one layer (single layer) or may consist of two or more layers. When the adhesive layer 15 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.

[0082] The thickness of the adhesive layer 15 is preferably 4 μm or more and 96 μm or less, more preferably 7 μm or more and 93 μm or less, and even more preferably 10 μm or more and 90 μm or less. 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 adhesive layer 15 from having an excessive thickness.

[0083] 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 pinhole-resistant layer 16 and the oxygen barrier layer 14, the thickness of the entire adhesive layer 15 disposed between the oxygen barrier layer 14 and the functional layer 13), and for example, the thickness of the adhesive layer 15 composed of multiple layers means the total thickness of all the layers constituting the adhesive layer 15.

[0084] <Pinhole-resistant layer> The multilayer film 1 may further include a pinhole-resistant layer 16 containing a second ionomer. By the pinhole-resistant layer 16 containing the second ionomer, the pinhole resistance of the multilayer film 1 can be further improved. Also, when the multilayer film 1 is irradiated with an electron beam from the outer layer 12 side, the electron beam can reach the pinhole-resistant layer 16, and the crosslink density of the pinhole-resistant layer 16 can be improved. As a result, the followability during skin packaging can be further enhanced.

[0085] More specifically, examples of the second ionomer include, for example, zinc-based ionomers, sodium-based ionomers, etc. Among these, it is preferably a zinc-based ionomer or a sodium-based ionomer, and more preferably a sodium-based ionomer. By the second ionomer being the above ionomer, the pinhole resistance of the pinhole-resistant layer 16 can be further improved, and the followability during skin packaging can be further enhanced.

[0086] The pinhole-resistant layer 16 may contain only the second ionomer (that is, it may be composed of an ionomer), or may contain the second ionomer and other components (which may be referred to as "other components" in this specification) (that is, it may be composed of the second ionomer and the other components).

[0087] The second ionomer 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.

[0088] The second ionomer included in the pinhole-resistant layer 16 and the first ionomer included in the sealant layer 11 may be the same as each other or different from each other.

[0089] The other components included in the pinhole-resistant layer 16 can be arbitrarily selected according to the purpose. For example, they can be either resin components or non-resin components, but preferably they are components that do not generate odor even when irradiated with electron beams. Thereby, the generation of odor due to electron beam irradiation of the multilayer film 1 can be reduced.

[0090] The other components that are resin components may be homopolymers that are polymers of one type of monomer or copolymers that are polymers of two or more types of monomers. The other components that are resin components are resins other than the second ionomer.

[0091] Examples of the other components that are non-resin components 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, etc.

[0092] 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.

[0093] In the pinhole-resistant layer 16, the ratio of the content of the second ionomer to the total mass of the pinhole-resistant layer 16 is preferably 50% by mass or more, more preferably 55% by mass or more and 100% by mass or less, and even more preferably 60% by mass or more and 100% by mass or less. By the ratio being not less than the lower limit value, the pinhole resistance of the multilayer film 1 can be improved.

[0094] 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 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.

[0095] The thickness of the pinhole-resistant layer 16 is preferably 4 μm or more and 146 μm or less, more preferably 7 μm or more and 143 μm or less, and even more preferably 10 μm or more and 140 μm or less. By the thickness of the pinhole-resistant layer 16 being not less than the lower limit value, the pinhole resistance of the multilayer film 1 can be improved. By the thickness of the pinhole-resistant layer 16 being not more than the upper limit value, it is possible to suppress the pinhole-resistant layer 16 from having an excessive thickness.

[0096] Here, the "thickness of the pinhole-resistant layer 16" means the thickness of the entire pinhole-resistant layer 16. For example, the thickness of the pinhole-resistant layer 16 composed of a plurality of layers means the total thickness of all the layers constituting the pinhole-resistant layer 16.

[0097] 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% or more and 89% or less, and even more preferably 12% or more and 88% or less. By the ratio being not less than the lower limit value, the pinhole resistance of the multilayer film 1 can be improved. On the other hand, by the ratio being not more than the upper limit value, it is possible to suppress the pinhole-resistant layer 16 from having an excessive thickness.

[0098] <Properties of the multilayer film> The multilayer film 1 has a gel fraction of 30% or more. The gel fraction of the multilayer film 1 is preferably 30% or more and 90% or less, more preferably 32% or more and 78% or less, and even more preferably 34% or more and 76% or less. When the gel fraction of the multilayer film 1 is at least the lower limit value, the heat resistance and melt tension of the multilayer film 1 are improved, and as a result, the followability to the contents is improved. When the gel fraction of the multilayer film 1 is at most the upper limit value, it is suppressed that the multilayer film 1 has excessive strength.

[0099] The gel fraction of the multilayer film 1 can be measured by a method conforming to JIS K6769. That is, by utilizing the fact that the crosslinked portion does not dissolve in the solvent, the multilayer film 1 is immersed in an organic solvent such as xylene, and after drying the insoluble film remaining without dissolving, the mass is measured, and the gel fraction can be calculated from the masses of the multilayer film before dissolution and the insoluble film after drying. Specifically, first, X g of the multilayer film is wrapped with Y g of a stainless steel wire mesh, heated and immersed in the solvent, and the multilayer film wrapped with the stainless steel wire mesh is taken out. Next, this is vacuum-dried, and the mass (Z g) of the multilayer film wrapped with the stainless steel wire mesh after drying is measured. Then, the gel fraction can be measured from the following formula (1). Gel fraction (mass %) = (Z - Y) / X × 100 (1)

[0100] The gel fraction of the multilayer film 1 can be adjusted, for example, under the conditions of electron beam irradiation to the outer layer 12, the functional layer 13, the pinhole-resistant layer 16, and the sealant layer 11.

[0101] In thermomechanical analysis, the temperature at which the multilayer film 1 exhibits a displacement of 2000 μm is 120°C or higher. In thermomechanical analysis, it is preferable that the temperature at which the multilayer film 1 exhibits a displacement of 2000 μm is 125°C or higher and 200°C or lower, and more preferably 130°C or higher and 195°C or lower. By the temperature at which the multilayer film 1 exhibits a displacement of 2000 μm being at least the lower limit value in thermomechanical analysis, the heat resistance of the multilayer film 1 is improved, and as a result, the followability to the contents is improved. By the temperature at which the multilayer film 1 exhibits a displacement of 2000 μm being at most the upper limit value in thermomechanical analysis, it is suppressed that the heat resistance of the multilayer film 1 becomes excessive.

[0102] In thermomechanical analysis, it is preferable that the displacement of the multilayer film 1 at a temperature of 100°C is 500 μm or less. In thermomechanical analysis, it is preferable that the displacement of the multilayer film 1 at a temperature of 100°C is 50 μm or more and 490 μm or less, and more preferably 100 μm or more and 480 μm or less. By the displacement of the multilayer film 1 at a temperature of 100°C being at least the lower limit value in thermomechanical analysis, it is suppressed that the melt tension of the multilayer film 1 becomes excessive. By the displacement of the multilayer film 1 at a temperature of 100°C being at most the upper limit value in thermomechanical analysis, the melt tension of the multilayer film 1 is improved, and as a result, the followability to the contents is improved.

[0103] The thermomechanical analysis of the multilayer film 1 can be carried out by the following method. That is, based on JIS K7196, the measurement is carried out by a method of measuring the thermal expansion amount of the sample from the difference in the thermal expansion amounts of the standard sample and the measurement sample when heated at a constant rate.

[0104] The displacement in the thermomechanical analysis of the multilayer film 1 can be adjusted, for example, under the conditions of electron beam irradiation to the outer layer 12, the functional layer 13, the pinhole-resistant layer 16, and the sealant layer 11.

[0105] The multilayer film 1 is preferably irradiated with an electron beam under the condition that the absorbed dose is 20 kGy or more and 300 kGy or less. By irradiating the multilayer film 1 with an electron beam at 20 kGy or more and 300 kGy or less, the crosslinking density of the multilayer film 1 (particularly, the outer layer 12 and the functional layer 13) can be improved. As a result, the heat resistance and the melt tension of the entire multilayer film 1 can be improved.

[0106] The reason why the crosslinking density of the multilayer film 1 is improved by electron beam irradiation is not clear, but it is considered as follows. That is, when the multilayer film 1 is irradiated with an electron beam, the carbon-hydrogen bonds in the polyethylene of the outer layer 12 of the multilayer film 1 are broken, and radicals are generated at the broken bond ends. The generated radicals come into contact with other polyethylene molecular chains by the molecular motion of the molecular chains, pull out hydrogen atoms, and bond to the carbon atoms in the polyethylene molecular chains. As a result, it is considered that a crosslinked structure is formed. It is presumed that the same phenomenon occurs also in the functional layer 13, the pinhole-resistant layer 16, and the sealant layer 11. That is, the outer layer 12 may contain a crosslinked product of polyethylene, and the functional layer 13, the pinhole-resistant layer 16, and the sealant layer 11 may contain a crosslinked product of an ionomer.

[0107] The absorbed dose of electron beam irradiation is more preferably 20 kGy or more and 300 kGy or less, and even more preferably 25 kGy or more and 250 kGy or less. When the absorbed dose of electron beam irradiation is at least the lower limit value, the crosslinking density of the multilayer film 1 can be further improved. When the absorbed dose of electron beam irradiation is at most the upper limit value, it is suppressed that the multilayer film 1 has an excessive strength.

[0108] The acceleration voltage of the electron beam irradiation is preferably 100 kV or more and 300 kV or less, more preferably 120 kV or more and 280 kV or less, and even more preferably 140 kV or more and 260 kV or less. When the acceleration voltage of the electron beam irradiation is at least the lower limit value, the crosslinking density of the multilayer film 1 can be further improved. When the acceleration voltage of the electron beam irradiation is at most the upper limit value, it is possible to suppress the multilayer film 1 from having excessive strength.

[0109] The thickness of the multilayer film 1 is preferably 60 μm or more, more preferably 70 μm or more and 400 μm or less, and even more preferably 80 μm or more and 300 μm or less. When the thickness of the multilayer film 1 is at least the lower limit value, the strength of the multilayer film 1 can be improved. When the thickness of the multilayer film 1 is at most the upper limit value, it is possible to suppress the multilayer film 1 from having excessive thickness.

[0110] <Other layer> The multilayer film 1 may include other layers that do not fall into any of the outer layer 12, the functional layer 13, the adhesive layer 15, the oxygen barrier layer 14, the adhesive layer 15, the pinhole resistant layer 16, and the sealant layer 11 within a range that does not impair the effects of the present invention. The other layer is not particularly limited and can be arbitrarily selected according to the purpose. Further, when the multilayer film 1 includes the other layer, it may further include an adhesive layer (for example, the adhesive layer 15) for adhering the other layer to other layers.

[0111] The multilayer film of the present embodiment is not limited to the above-described one, and some configurations may be changed, deleted, or added within a range not departing from the gist of the present invention.

[0112] <<Method for manufacturing a multilayer film>> The multilayer film of the present embodiment can be manufactured, for example, by a feed block method of melt-extruding a resin, a resin composition, or the like that is a forming material for each layer using several extruders, a coextrusion T-die method such as a multi-manifold method, an air-cooled or water-cooled coextrusion inflation method, or the like.

[0113] Further, the multilayer film of the present embodiment can be manufactured by coating a resin, a resin composition, or the like that is a forming material for any one of the layers on the surface of another layer for constituting the multilayer film, drying it as necessary, forming a laminated structure in the multilayer film, and further laminating these other layers so as to have a target arrangement form as necessary.

[0114] Further, the multilayer film of the present embodiment can be manufactured by separately preparing two or more films for constituting any two or more of the layers in advance, and laminating these films by bonding them together 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 further laminating these other layers so as to have a target arrangement form as necessary. At this time, an adhesive capable of forming the adhesive layer may be used as the adhesive.

[0115] Further, the multilayer film of the present embodiment can be manufactured by laminating two or more films separately prepared in advance by a thermal (heat) lamination method or the like without using an adhesive, and further laminating these other layers so as to have a target arrangement form as necessary.

[0116] When manufacturing the multilayer film of the present embodiment, two or more of the forming methods of any one of the layers (films) in the multilayer film listed so far may be combined.

[0117] <<Package>> The package according to an embodiment of the present invention includes the multilayer film according to the above-described embodiment of the present invention. Such a package is excellent in followability to the contents and has reduced odor. The package of this embodiment is suitable as a skin pack package. Further, the skin pack package of this embodiment is suitable as, for example, a packaging bag or a packaging container for packaging foods and the like.

[0118] FIG. 2 is a cross-sectional view schematically showing the package according to an embodiment of the present invention. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals as in the case of FIG. 1, and the detailed description thereof is omitted.

[0119] The package 10 shown here includes the multilayer film 1 shown in FIG. 1 and the rigid tray 2. By using the multilayer film 1, the package 10 is excellent in followability to the contents 3. In FIG. 2, the distinction between the layers in the multilayer film 1 is omitted.

[0120] The rigid tray 2 is obtained by molding a film and is usually made of an opaque multilayer resin film. As shown in FIG. 2, a part of one surface (which may be referred to as the "first surface" in this specification) 2a of the rigid tray 2 and a part of the first surface 11a of the multilayer film 1 are adhered by sealing. As a result, a storage portion 10a is formed between the first surface 2a of the rigid tray 2 and the first surface 11a of the multilayer film 1. And the content 3 is sealed in this storage part 10a. In FIG. 2, in the storage portion 10a of the package 10, some gaps are seen between the content 3 and the multilayer film 1 and between the content 3 and the rigid tray 2, but the existence of these gaps is not essential in the package 10 in a state where the content 3 is stored.

[0121] The thickness of the rigid tray 2 is preferably 100 μm or more, more preferably 200 μm or more, and even more preferably 300 μm or more. By having the thickness of the rigid tray 2 be at least the lower limit value, the strength of the rigid tray 2 can be increased. On the other hand, the upper limit value of the thickness of the rigid tray 2 is not particularly limited.

[0122] The contained material 3 can be arbitrarily selected according to the purpose and is not particularly limited, but is preferably a food.

[0123] The package of the present 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.

[0124] <<Method for manufacturing a package>> The package of the present embodiment can be manufactured by overlapping and heat-sealing the multilayer film and the rigid tray so as to form the storage portion. When manufacturing the package, before heat-sealing the multilayer film and the rigid tray, the contained material is stored in the storage portion.

Examples

[0125] Hereinafter, the present invention will be described in more detail with specific examples. However, the present invention is not limited to the examples shown below.

[0126] <<Manufacture of multilayer film and package>> [Example 1] The multilayer film having the structure shown in FIG. 1 and the package having the structure shown in FIG. 2 were manufactured according to the procedure shown below.

[0127] <Manufacture of multilayer film> As the substance constituting the sealant layer, a Zn-based ionomer (manufactured by Mitsui DuPont Polychemical Co., Ltd., Himilan 1855) was prepared. As a material constituting the functional layer and the pinhole-resistant layer, a Na-based ionomer (manufactured by Mitsui DuPont Polychemical Co., Ltd., 1601) was prepared. As a resin constituting the adhesive layer, a modified polyolefin resin (manufactured by Mitsui Chemicals, Inc., NF536) was prepared. As a resin constituting the oxygen barrier layer, EVOH (manufactured by Nippon Gohsei Co., Ltd., GH3804B) was prepared. As a resin constituting the outer layer, low-density polyethylene (density 0.922 g / cm 3 , manufactured by Ube Maruzen Polyethylene Co., Ltd., F222NH) was prepared. Next, a multilayer film was produced by coextrusion molding the sealant layer, pinhole-resistant layer, adhesive layer, oxygen barrier layer, adhesive layer, functional layer, and outer layer in this order. The obtained multilayer film had a sealant layer (thickness = 24 μm), pinhole-resistant layer (thickness = 29 μm), adhesive layer (thickness = 8 μm), oxygen barrier layer (thickness = 10 μm), adhesive layer (thickness = 8 μm), functional layer (thickness = 17 μm), and outer layer (thickness = 24 μm) laminated in this order in the thickness direction, and had a thickness of 120 μm.

[0128] Next, electron beam irradiation was performed from the outer layer side of the multilayer film (absorbed dose 175 kGy, acceleration voltage 160 kV).

[0129] Next, based on JIS K7196, thermomechanical analysis of the multilayer film was carried out using EXSTAR6000 manufactured by SII. 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 measurement results are shown in Table 3 below.

[0130] Next, the gel fraction of the multilayer film was measured by a method conforming to JIS K6769. That is, the multilayer film obtained above was cut into a size of 3 cm × 3 cm (about 0.09 g) to prepare a sample piece, wrapped with a 100 g 400-mesh stainless steel wire mesh, and immersed in 18 ml of xylene at 110°C for 24 hours. Then, the sample piece wrapped with the stainless steel wire mesh was vacuum dried at 110°C for 24 hours under a pressure of 1.7 kPa, and then the mass was measured to obtain the gel fraction. The measurement results are shown in Table 3 below.

[0131] <Manufacture of Rigid Tray> As the resin constituting the outer layer, polypropylene (manufactured by Sumitomo Chemical Co., Ltd., FH1016) was prepared. As the resin constituting the oxygen barrier layer, EVOH (manufactured by Nippon Gohsei Co., Ltd., BF3203B) was prepared. As the resin constituting the adhesive layer, a polyolefin-based adhesive resin (manufactured by Mitsubishi Chemical Corporation, ER313-E1) was prepared. Next, a rigid tray was manufactured by coextrusion molding the outer layer, adhesive layer, oxygen barrier layer, adhesive layer, and outer layer in this order. The obtained multilayer film was 800 μm thick, with an outer layer (thickness = 364 μm), an adhesive layer (thickness = 20 μm), an oxygen barrier layer (thickness = 32 μm), an adhesive layer (thickness = 20 μm), and an outer layer (thickness = 364 μm) laminated in this order in the thickness direction.

[0132] <Manufacture of Package> On the rigid tray obtained above, cooked rice (200 g) was placed. From above the cooked rice, the multilayer film obtained above (heated to 130°C) was covered, and the storage portion of the cooked rice was evacuated in a chamber to closely fix the multilayer film to the cooked rice while heat-sealing the multilayer film and the rigid tray. Thus, a package with the cooked rice stored in the storage portion was manufactured.

[0133] [Example 2] <Manufacture of Multilayer Film> Except for changing the absorbed dose of electron beam irradiation from 175 kGy to 125 kGy, a multilayer film was produced in the same manner as in Example 1, and the "temperature (°C) at which displacement of 2000 μm occurs", "displacement (μm) at 100 °C", and gel fraction were measured.

[0134] <Manufacture of Package> Except for using the multilayer film obtained above, a package was manufactured in the same manner as in Example 1.

[0135] [Comparative Example 1] <Manufacture of Multilayer Film> Except for not performing electron beam irradiation, a multilayer film was produced in the same manner as in Example 1, and the "temperature (°C) at which displacement of 2000 μm occurs", "displacement (μm) at 100 °C", and gel fraction were measured.

[0136] <Manufacture of Package> Except for using the multilayer film obtained above, a package was manufactured in the same manner as in Example 1.

[0137] [Comparative Example 2] <Manufacture of Multilayer Film> As the substance constituting the sealant layer, polyethylene (sometimes abbreviated as "PE". Density 0.922 g / cm 3 , manufactured by Ube Maruzen Polyethylene Co., Ltd., F222NH) was used. Except for this, a multilayer film was produced in the same manner as in Example 1, and the "temperature (°C) at which displacement of 2000 μm occurs", "displacement (μm) at 100 °C", and gel fraction were measured.

[0138] <Manufacture of Package> Except for using the multilayer film obtained above, a package was manufactured in the same manner as in Example 1.

[0139] [Comparative Example 3] <Manufacture of Multilayer Film> As the material constituting the sealant layer, a multilayer film was produced in the same manner as in Example 1 except that ethylene-methyl acrylate copolymer (sometimes abbreviated as "EMA", manufactured by Mitsui Dow Chemical Co., Ltd., Elvaloy 1609) was used, and the "temperature (°C) at which a displacement of 2000 μm is shown", "displacement (μm) at a temperature of 100 °C", and gel fraction were measured.

[0140] <Manufacture of Package> A package was manufactured in the same manner as in Example 1 except that the multilayer film obtained above was used.

[0141] [Comparative Example 4] <Manufacture of Multilayer Film> As the material constituting the sealant layer, a multilayer film was produced in the same manner as in Example 1 except that ethylene-methyl methacrylate copolymer (sometimes abbreviated as "EMMA", manufactured by Sumitomo Chemical Co., Ltd., Acrifort WD106) was used, and the "temperature (°C) at which a displacement of 2000 μm is shown", "displacement (μm) at a temperature of 100 °C", and gel fraction were measured.

[0142] <Manufacture of Package> A package was manufactured in the same manner as in Example 1 except that the multilayer film obtained above was used.

[0143] [Comparative Example 5] <Manufacture of Multilayer Film> As the material constituting the sealant layer, a multilayer film was produced in the same manner as in Example 1 except that ethylene-vinyl acetate copolymer (sometimes abbreviated as "EVA", manufactured by Mitsui Dow Chemical Co., Ltd., V5714C) was used, and the "temperature (°C) at which a displacement of 2000 μm is shown", "displacement (μm) at a temperature of 100 °C", and gel fraction were measured.

[0144] <Manufacture of Package> A package was manufactured in the same manner as in Example 1 except that the multilayer film obtained above was used.

[0145] <<Evaluation of Followability>> Visually, the followability of the package to the contents (cooked rice) was evaluated. The evaluation criteria are as shown in Table 1 below. Note that the "lifting" below means the gap between the package and the contents.

Table 1

[0146] <<Evaluation of Odor>> After leaving the package with cooked rice stored in the storage part for 24 hours, the odor of the cooked rice was evaluated by sensory evaluation. The evaluation criteria are as shown in Table 2 below.

Table 2

[0147] The results of evaluating the followability and odor levels of the packages of Examples 1 to 2 and Comparative Examples 1 to 5 are shown in Table 3 below.

[0148]

Table 3

[0149] As is clear from the above results, in Examples 1 to 2 where the temperature showing a displacement of 2000 μm is 120°C or higher, or the gel fraction is 30% or higher, excellent followability to the contents was obtained.

[0150] Also, in Examples 1 to 2 where the component of the sealant layer is ionomer, the cooked rice as the contents was odorless.

[0151] On the other hand, in Comparative Example 1 where the temperature showing a displacement of 2000 μm is less than 120°C, or the gel fraction is less than 30%, the followability was inferior to that of Examples 1 to 2.

[0152] Also, in Comparative Examples 2 to 5 where the components of the sealant layer are PE, EMA, EMMA, and EVA, odors were confirmed from the cooked rice.

Industrial Applicability

[0153] The present invention can be used for a skin pack package used during storage of food.

Explanation of Signs

[0154] 1 ··· Multilayer film 2 ··· Rigid tray 2a ··· One surface (first surface) of the rigid tray 3 ··· Contents 10 ··· Package 10a ··· Storage part 11 ··· Sealant layer 12 ··· Outer layer 13 ··· Functional layer 14 ··· Oxygen barrier layer 15 ··· Adhesive layer 151 ··· First adhesive layer 152 ··· Second adhesive layer 16 ··· Pinhole resistant layer

Claims

1. A multilayer film, wherein the multilayer film comprises an outer layer consisting only of polyethylene and a sealant layer containing a first ionomer, and when performing thermomechanical analysis on the multilayer film, the temperature at which a displacement of 2000 μm is exhibited is 130°C or higher and 195°C or lower, and the gel fraction of the multilayer film is 34% or higher and 76% or lower, in the sealant layer, the ratio of the content of the ethylene vinyl acetate copolymer to the total mass of the sealant layer is 1% by mass or less, the multilayer film further contains a second ionomer and comprises a functional layer adjacent to the outer layer.

2. The multilayer film according to claim 1, wherein the first ionomer is a zinc-based ionomer.

3. The multilayer film according to claim 1, wherein the second ionomer is a zinc-based ionomer or a sodium-based ionomer.

4. The multilayer film according to claim 1 or 3, wherein the ratio of the thickness of the functional layer to the thickness of the multilayer film is 10% or higher.

5. The multilayer film according to any one of claims 1 to 4, which has been irradiated with an electron beam under the condition of an absorbed dose of 20 to 300 kGy.

6. The multilayer film according to any one of claims 1 to 5, wherein the displacement at a temperature of 100°C during the thermomechanical analysis is 500 μm or less.

7. The multilayer film according to any one of claims 1 to 6, wherein the ratio of the thickness of the outer layer to the thickness of the multilayer film is 10% or higher.

8. The multilayer film according to any one of claims 1 to 7, wherein the thickness of the multilayer film is 60 μm or more.

9. wherein the polyethylene has a density of 0.945 g / cm ３ The multilayer film according to any one of claims 1 to 8, wherein the polyethylene is the following low-density polyethylene.

10. The multilayer film according to any one of claims 1 to 9, further comprising an oxygen barrier layer.

11. The multilayer film according to claim 10, wherein the oxygen barrier layer contains an ethylene-vinyl alcohol copolymer.

12. The multilayer film according to claim 11, wherein in the oxygen barrier layer, the ratio of the content of the ethylene-vinyl alcohol copolymer to the total mass of the oxygen barrier layer is 3 to 25% by mass.

13. A package comprising the multilayer film according to any one of claims 1 to 12.

14. The package according to claim 13, wherein the package is a skin pack package.

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