JP7740061B2 - Food skin pack packaging - Google Patents

Description

The present invention relates to a multilayer film and a packaging body.

A package in which the contents (packaged items) are placed on a hard tray and then sealed with a film by drawing a vacuum is called a skin pack. In a skin pack, the film, i.e., the skin pack film, is transparent, allowing the contents to be easily seen through it. Furthermore, the skin pack film is soft, and by drawing a vacuum in the storage area inside the skin pack, it can be tightly attached to the contents without creating wrinkles (see, for example, Patent Document 1). Furthermore, because skin packs have a hard tray (base), they can be displayed upright without the contents shifting out of place. In light of these characteristics, skin packs are primarily used as packaging for food.

Japanese Patent Application Laid-Open No. 2016-222259

Skin packs for food, pharmaceuticals, and cosmetics must be equipped with a gas barrier layer on the multilayer film that makes up the skin pack to prevent oxidative deterioration of the food, pharmaceuticals, and cosmetics. However, the presence of a gas barrier layer can reduce the skin pack's ability to conform to the food, pharmaceuticals, and cosmetics (its ability to adhere without wrinkling). Furthermore, to enhance marketability, it is also required that the skin pack be able to adhere to soft contents without crushing them.

The present invention was made in consideration of the above circumstances, and aims to provide a multilayer film that maintains the quality of the contents, has excellent conformability to the contents, and can softly conform to the contents, as well as a package (e.g., a skin pack package) using the same.

In order to solve the above problems, the present invention employs the following configuration.
[1] A multilayer film comprising a sealant layer, a follower layer, and a gas barrier layer laminated in this order in the thickness direction, wherein the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2 to 25%, the tensile strength of the multilayer film at a temperature of 140°C measured in accordance with JIS K 7127:1999 is 0.3 N/mm2 or ^more and 4 N/ ^mm2 or less, and the oxygen transmission rate of the multilayer film at a temperature of 23°C and a relative humidity of 60% measured in accordance with JIS K 7126-2:2006 is 100 cc/( ^m2 ·day·atm) or less.
[2] The compliance layer contains an ionomer,
The multilayer film according to [1], wherein the ionomer has a melt strength of 60 to 540 mN at a temperature of 180°C.
[3] The multilayer film according to [1] or [2], wherein the multilayer film has a dynamic modulus of elasticity E' of 1 x 10 ⁴ Pa or more and 1 x 10 ⁷ Pa or less at a temperature of 140°C.
[4] The multilayer film according to any one of [1] to [3], wherein the temperature at which the multilayer film shows a displacement of 2000 μm during thermomechanical analysis is 120° C. or higher.
[5] The multilayer film according to any one of [1] to [4], wherein the multilayer film has a gel fraction of 30% or more.
[6] The multilayer film according to [4], wherein the displacement at a temperature of 100°C during the thermomechanical analysis of the multilayer film is 500 μm or less.
[7] The multilayer film according to any one of [1] to [6], wherein the multilayer film is irradiated with an electron beam at an absorbed dose of 13 to 300 kGy.
[8] The multilayer film according to any one of [1] to [7], wherein the gas barrier layer contains an ethylene-vinyl alcohol copolymer.
[9] The multilayer film according to any one of [1] to [8], wherein the ratio of the thickness of the follow-up layer to the thickness of the multilayer film is 10% or more.
[10] The multilayer film according to any one of [1] to [9], wherein the ratio of the thickness of the sealant layer to the thickness of the multilayer film is 5% or more.
[11] The multilayer film according to ^{any one} of [1] to [10], wherein the tensile strength of the multilayer film at a temperature of 140°C, measured in accordance with JIS K 7127:1999, is 0.3 N/mm2 or more and 3.5 N/ ^mm2 or less.
[12] A package comprising the multilayer film according to any one of [1] to [11].
[13] The package according to [12], wherein the package is a skin pack package.

The multilayer film of the present invention is constructed by laminating a sealant layer, a conforming layer, and a gas barrier layer in this order in the thickness direction, wherein the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2 to 25%; the multilayer film has a tensile strength of 0.3 N/mm2 or ^more and 4 N/mm2 or ^less at 140°C as measured in accordance with JIS K 7127:1999; and the multilayer film has an oxygen permeation rate of 100 cc/( ^m2 ·day·atm) or less at 23°C and a relative humidity of 60% as measured in accordance with JIS K 7126-2:2006. Therefore, the film maintains the quality of the contents contained therein, has excellent conformability to the contents, and is capable of softly conforming to the contents.

Furthermore, because the packaging of the present invention includes the above-mentioned multilayer film, it not only maintains the quality of the contents, but also has excellent conformability to the contents and can gently conform to the contents.

1 is a cross-sectional view schematically illustrating an example of a multilayer film according to one embodiment of the present invention. 1 is a cross-sectional view schematically illustrating an example of a packaging body according to an embodiment of the present invention.

<<Multi-layer film (lid material)>>
A multilayer film (lid material) according to one embodiment of the present invention is configured by laminating a sealant layer, a conforming layer, and a gas barrier layer in this order in the thickness direction. The multilayer film (lid material) is not particularly limited as long as it satisfies the conditions of the thickness ratio of the gas barrier layer, tensile strength, and oxygen permeability, which will be described later.

The oxygen transmission rate of the multilayer film (lid material) under conditions of a temperature of 23°C and a relative humidity of 60% is 100 cc/( ^m2 ·day·atm) or less. By having the oxygen transmission rate of 100 cc/( ^m2 ·day·atm) or less, deterioration of the packaged contents can be suppressed and the contents can be stored for a long period of time.

The oxygen transmission rate of the multilayer film (lid material) under conditions of a temperature of 23°C and a relative humidity of 60% is preferably 95 cc/( ^m2 day atm) or less, more preferably 90 cc/( ^m2 day atm) or less, even more preferably 85 cc/( ^m2 day atm) or less, particularly preferably 80 cc/( ^m2 day atm) or less, and may be, for example, 75 cc/( ^m2 day atm) or less. By having the oxygen transmission rate be equal to or less than the upper limit, deterioration of the packaged contents can be suppressed, and the effect of long-term storage can be further improved.

On the other hand, the oxygen transmission rate is 0 cc/( ^m2 day atm) or more, preferably 0.1 cc/( ^m2 day atm) or more, more preferably 0.2 cc/( ^m2 day atm) or more, even more preferably 0.3 cc/( ^m2 day atm) or more, particularly preferably 0.4 cc/( ^m2 day atm) or more, and may be, for example, 0.5 cc/( ^m2 day atm) or more. When the oxygen transmission rate is equal to or more than the lower limit, the thickness of the gas barrier layer falls within an appropriate range, and adverse effects on conformability can be suppressed.

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

The oxygen permeability of the multilayer film (lid material) can be more easily adjusted by, for example, adjusting the type and content of the components contained in the gas barrier layer (described below), the thickness and proportions of the gas barrier layer, etc.

The temperature at which the multilayer film (lid material) shows a displacement of 2000 μm during thermomechanical analysis (TMA) is preferably 120°C or higher, more preferably 120 to 200°C, and even more preferably 123 to 190°C, and may be, for example, 130 to 190°C. When the temperature is equal to or higher than the lower limit, the heat resistance of the multilayer film is further improved. When the temperature is equal to or lower than the upper limit, the heat resistance of the multilayer film is further prevented from becoming excessive.

When the multilayer film is subjected to thermomechanical analysis, the displacement at a temperature of 100°C is preferably 500 μm or less, more preferably 40 to 500 μm, and even more preferably 45 to 400 μm, and may be, for example, any of 50 to 350 μm, 55 to 340 μm, and 55 to 250 μm. When the displacement is equal to or less than the upper limit, the melt tension of the multilayer film is further improved, and as a result, the ability of the multilayer film to conform to the contents is further improved. When the displacement is equal to or greater than the lower limit, the melt tension of the multilayer film is further prevented from becoming excessive.

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

During thermomechanical analysis of the multilayer film, the temperature at which a displacement of 2000 μm occurs and the displacement at a temperature of 100°C can be adjusted, for example, by irradiating the multilayer film with an electron beam and adjusting the conditions of the electron beam irradiation. For example, the temperature and displacement can be more easily adjusted by adjusting the conditions of electron beam irradiation on the outer layer or the follow-up layer in the multilayer film.

The multilayer film is preferably irradiated with an electron beam at an absorbed dose of 13 to 300 kGy, more preferably 15 to 250 kGy. For example, the multilayer film may be irradiated with an electron beam at an absorbed dose of 20 to 250 kGy, 45 to 250 kGy, or 70 to 250 kGy. By setting the absorbed dose within this range, it is easier to obtain a multilayer film in which, during thermomechanical analysis, the temperature at which the film exhibits a displacement of 2000 μm and the displacement at a temperature of 100°C are both within the above-mentioned numerical ranges. On the other hand, by setting the absorbed dose at or above the lower limit, the crosslink density of the multilayer film (particularly the outer layer and the follower layer within the multilayer film) is further improved, resulting in improved heat resistance and melt tension for the multilayer film as a whole, and improved conformability to the contents. By setting the absorbed dose at or below the upper limit, excessive strength of the multilayer film is further suppressed.

While the reason why electron beam irradiation improves the crosslink density of the multilayer film (particularly the outer and follower layers within this multilayer film) is unclear, it is speculated as follows: When the multilayer film is irradiated with an electron beam, carbon-hydrogen bonds in the resin (e.g., polyethylene, ionomer) are broken, generating radicals at the ends of the broken bonds. The generated radicals, due to molecular chain movement, come into contact with molecular chains of other resins (e.g., other polyethylene molecular chains, other ionomer molecular chains), abstract hydrogen atoms, and bond with carbon atoms in the molecular chains of other resins (e.g., other polyethylene molecular chains, other ionomer molecular chains), resulting in the formation of a crosslinked structure.

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. By using an acceleration voltage during electron beam irradiation within this range, it is possible to more easily obtain a multilayer film in which, during thermomechanical analysis, the temperature at which the film shows a displacement of 2000 μm and the displacement at a temperature of 100°C are both within the above-mentioned numerical ranges. On the other hand, by using an acceleration voltage during electron beam irradiation that is equal to or greater than the lower limit, the crosslink density of the multilayer film (particularly the outer layer and the follower layer within the multilayer film) is further improved, resulting in improved heat resistance and melt tension for the multilayer film as a whole, and improved conformability to the contents. By using an acceleration voltage during electron beam irradiation that is equal to or less than the upper limit, excessive strength of the multilayer film is further prevented.

The gel fraction of the multilayer film is preferably 30% or more, more preferably 30 to 90%, and even more preferably 32 to 85%, and may be, for example, any of 40 to 82%, 48 to 82%, and 55 to 82%. When the gel fraction of the multilayer film is equal to or greater than the lower limit, the heat resistance and melt tension of the multilayer film are further improved, resulting in improved conformability to the contents contained therein. When the gel fraction of the multilayer film is equal to or less than the upper limit, excessive strength of the multilayer film is further prevented.

The gel fraction of the multilayer film can be measured in accordance with JIS K 6769, taking advantage of the fact that the crosslinked portions of the film are insoluble in the solvent. Specifically, the multilayer film is immersed in an organic solvent such as xylene, and the remaining insoluble film is dried. The mass of the resulting dried product is then measured, and the gel fraction can be calculated from the mass of the multilayer film before dissolution and the mass of the dried insoluble film. More specifically, for example, the multilayer film (mass Xg) is wrapped in a stainless steel mesh (mass Yg) and immersed in a heated solvent. The multilayer film wrapped in the stainless steel mesh (in other words, the insoluble film) is then removed. This is then vacuum-dried, and the mass (Zg) of the dried multilayer film wrapped in the stainless steel mesh (in other words, the insoluble film) is measured. The following formula (1):
Gel fraction of multilayer film (mass%) = (Z - Y) / X × 100 (1)
The gel fraction of the multilayer film is calculated by the following formula.

The gel fraction of the multilayer film can be adjusted, for example, by irradiating the multilayer film (particularly the outer layer or follower layer within the multilayer film) with an electron beam and adjusting the conditions for the electron beam irradiation. In this case, the conditions for electron beam irradiation can be the same as those used to adjust the temperature at which a displacement of 2000 μm occurs and the displacement at a temperature of 100°C during the thermomechanical analysis of the multilayer film described above.

The multilayer film preferably satisfies either one or both of the conditions of the temperature at which a displacement of 2000 μm is exhibited during thermomechanical analysis and the gel fraction. That is, examples of the multilayer film include those having a temperature of 120° C. or higher at which a displacement of 2000 μm is exhibited during thermomechanical analysis and a gel fraction of less than 30%; those having a temperature of less than 120° C. at which a displacement of 2000 μm is exhibited during thermomechanical analysis and a gel fraction of 30% or higher; and those having a temperature of 120° C. or higher at which a displacement of 2000 μm is exhibited during thermomechanical analysis and a gel fraction of 30% or higher.
However, it is usually more preferable that the multilayer film satisfies both of the above conditions, i.e., that the temperature at which it shows a displacement of 2000 μm during thermomechanical analysis is 120° C. or higher and that it has a gel fraction of 30% or higher.

The tensile strength of the multilayer film (lid material) at a temperature of 140°C is 0.3 N/ ^mm2 or more and 4 N/ ^mm2 or less. When the tensile strength is 0.3 N/ ^mm2 or more, the conformability of the lid material to the contents can be improved. As a result, dripping that occurs during storage is suppressed, preventing the outflow of umami components, and enabling long-term storage without deteriorating the taste. When the tensile strength is 4 N/mm2 or ^less , the contents can be packaged without compressing their shape.

The tensile strength of the multilayer film (lid material) at a temperature of 140°C is preferably 0.3 N/mm2 or ^more and 3.5 N/ ^mm2 or less, more preferably 0.3 N/ ^mm2 or more and 3.4 N/ ^mm2 or less, and even more preferably 0.3 N/ ^mm2 or more and 3.3 N/mm2 or ^less , and may be, for example, 0.3 N/ ^mm2 or more and 3.2 N/ ^mm2 or less. When the tensile strength is equal to or more than the lower limit, the ability of the lid material to conform to the contents can be further improved. When the tensile strength is equal to or less than the upper limit, the shape of the contents can be packaged without compressing it as much.

The tensile strength of the multilayer film (lid material) at a temperature of 140°C can be measured in accordance with JIS K 7127:1999. Specifically, it can be measured using a tensile strength measuring device (Shimadzu Corporation's "AGS-X Thermostatic Tensile Tester"). Measurement conditions include, for example, a tensile speed of 500 mm/min.

Increasing the crosslink density of the multilayer film (lid material) improves the heat resistance and melt tension of the multilayer film (lid material), as well as the tensile strength. Therefore, the tensile strength of the multilayer film (lid material) can be more easily adjusted, for example, by adjusting the absorbed dose of electron beam irradiation.

The tensile strength of the multilayer film (lid material) can be more easily adjusted by adjusting the thickness and proportion of the gas barrier layer.

The dynamic modulus of elasticity E' of the multilayer film (lid material) at a temperature of 140°C is preferably 1 x 10 ⁴ Pa or more and 1 x 10 ⁷ Pa or less. When the dynamic modulus of elasticity E' is equal to or more than the lower limit, the ability of the lid material to conform to the contents can be further improved. When the dynamic modulus of elasticity E' is equal to or less than the upper limit, the contents can be packaged without compressing their shape.

The dynamic modulus E' of the multilayer film (lid material) at a temperature of 140°C is more preferably 1.1 x 10 ⁴ Pa or more and 9.9 x 10 ⁶ Pa or less, even more preferably 1.2 x 10 ⁴ Pa or more and 9.8 x 10 ⁶ Pa or less, and particularly preferably 1.3 x 10 ⁴ Pa or more and 9.7 x 10 ⁶ Pa or less, and may be, for example, 1.4 x 10 ⁴ Pa or more and 9.6 x 10 ⁶ Pa or less. When the dynamic modulus E' is equal to or more than the lower limit, the conformability of the lid material to the contents can be further improved. When the dynamic modulus E' is equal to or less than the upper limit, the contents can be packaged without compressing their shape.

The dynamic modulus of elasticity E' of the multilayer film (lid material) at a temperature of 140°C can be measured in accordance with JIS K7244-4. Specifically, it can be measured, for example, using a dynamic viscoelasticity measuring device ("DMA 7100" manufactured by Hitachi High-Tech Science Corporation). Measurement conditions, for example, can be measured using a 4 mm wide sample in tensile mode in the temperature range of 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.

Increasing the crosslink density of the multilayer film (lid material) improves the heat resistance and melt tension of the multilayer film (lid material), as well as the dynamic modulus of elasticity E'. Therefore, the dynamic modulus of elasticity E' of the multilayer film (lid material) can be more easily adjusted, for example, by adjusting the absorbed dose of electron beam irradiation.

Generally, the resin contained in the gas barrier layer (for example, the gas barrier resin described below) has a higher dynamic modulus of elasticity E' than ordinary resins. Therefore, the dynamic modulus of elasticity E' of the multilayer film (lid material) can be more easily adjusted by adjusting the type and content of the resin contained in the gas barrier layer, the thickness and proportion of the gas barrier layer, etc.

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 equal to or greater than the lower limit, the strength of the multilayer film is further improved. When the thickness of the multilayer film is equal to or less than the upper limit, the multilayer film is further prevented from becoming excessively thick.

The multilayer film (lid material) is composed of, for example, a sealant layer, a conforming layer, and a gas barrier layer laminated in this order in the thickness direction.

Regardless of the type, it is preferable that all layers of the multilayer film (lid material) be transparent, i.e., that the multilayer film is transparent. In a package constructed using such a multilayer film, the contents can be easily seen through the multilayer film (lid material).

The detailed structure of the multilayer film (lid material) and its manufacturing method will be described in detail separately.

The present invention will now be described in more detail with reference to the drawings. Note that the drawings used in the following description may show enlarged essential parts for the sake of convenience, in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as in reality.

FIG. 1 is a cross-sectional view schematically showing an example of the multilayer film (laminate film) among the multilayer films (covering materials) in this embodiment.
The multilayer film 1 shown here is constructed by laminating a sealant layer 11, a conformal layer 13 (more specifically, a first conformal layer 131), and a gas barrier layer 14 in this order in the thickness direction.

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 compliant layer 13 (more specifically, a second compliant layer 132 ) disposed between the gas barrier layer 14 and the outer layer 12 .
Furthermore, the multilayer film 1 includes an adhesive layer 15 (more specifically, a first adhesive layer 151) disposed between the first compliance 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 compliance layer 132.
That is, the multilayer film 1 is constructed by laminating a sealant layer 11, a first conforming layer 131, a first adhesive layer 151, a gas barrier layer 14, a second adhesive layer 152, a second conforming layer 132 and an outer layer 12 in this order in the thickness direction.
In the multilayer film 1, the outer layer 12 is one outermost layer, and the sealant layer 11 is the other outermost layer.

<Sealant layer>
The sealant layer 11 may contain a polyethylene-based resin such as ethylene-vinyl acetate copolymer (EVA), polyethylene, ionomer, or polyethylene-based copolymer (sometimes referred to herein as a "polyethylene-based resin in the sealant layer"). When the sealant layer 11 contains a polyethylene-based resin in the sealant layer, the multilayer film 1 exhibits pseudo-adhesion to the adherend, improving the easy-peelability.

In this specification, a "polyethylene resin" refers to a resin having at least structural units derived from ethylene, and may have only structural units derived from ethylene, or may have structural units derived from ethylene and other structural units.

The sealant layer 11 may contain only polyethylene-based resin (i.e., the sealant layer may consist of polyethylene-based resin), or it may contain polyethylene-based resin and other components (sometimes referred to as "other components" in this specification) (i.e., the sealant layer may consist of polyethylene-based resin and the other components).

The other components contained in the sealant layer 11 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.
The other resin component is a resin that does not fall under the category of polyethylene resin in the sealant layer.
The other component, which is a resin component, may be a homopolymer, which is a polymer of one type of monomer, or a copolymer, which is a polymer of two or more types of monomers.

Examples of the other 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, and ultraviolet absorbers.

The other components contained in the sealant layer 11 may be one type only, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The content of the polyethylene resin in the sealant layer 11 relative to the total mass of the sealant layer 11 is preferably 65 to 100 mass%, more preferably 70 to 100 mass%, and even more preferably 75 to 100 mass%, and may be, for example, 85 to 100 mass%. When the content is equal to or greater than the lower limit, the easy peel property is further improved due to the development of pseudo-adhesion to the adherend.
This ratio is usually the same as the ratio of the content (parts by mass) of the polyethylene resin in the sealant layer to the total content (parts by mass) of components that do not vaporize at room temperature in the sealant layer-forming composition described below.

In this specification, "room temperature" means a temperature that is neither particularly cold nor hot, i.e., a normal temperature, such as a temperature between 15 and 25°C.

The sealant layer 11 may consist of one layer (single layer), or two or more layers. When the sealant layer 11 consists of multiple layers, these layers may be the same or different, and there are no particular restrictions on the combination of these layers as long as it does not impair the effects of the present invention.

In this specification, not only in the case of the sealant layer 11, "multiple layers may be the same or different" means "all layers may be the same, all layers may be different, or only some layers may be the same," and further, "multiple layers are different" means "at least one of the constituent materials and thicknesses of each layer is different from each other."

The thickness of the sealant layer 11 is not particularly limited, but is preferably 4 to 96 μm, more preferably 7 to 93 μm, and even more preferably 10 to 90 μm, and may be, for example, any of 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, the strength of the sealant layer 11 is increased. When the thickness of the sealant layer 11 is equal to or less than the upper limit, the sealant layer 11 is prevented from becoming excessively thick, and the seal strength is increased when the multilayer film 1 is sealed by heating.
Here, the "thickness of the sealant layer 11" means the thickness of the entire sealant layer 11, and for example, the thickness of the sealant layer 11 consisting of multiple layers means the total thickness of all layers that make up the sealant layer 11.

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 even more preferably 7 to 75%. When this ratio is equal to or greater than the lower limit, the effect obtained by externally irradiating the multilayer film 1 with an electron beam from the outer layer 12 side is enhanced. When this ratio is equal to or less than the upper limit, excessive thickness of the sealant layer 11 is further suppressed, and the seal strength is increased when the multilayer film 1 is sealed by heating.

The exposed surface 11a of the sealant layer 11 opposite the outer layer 12 (sometimes referred to herein as the "first surface") is the sealing surface.

<Outer layer>
The outer layer 12 may contain a polyolefin resin such as polyethylene (PE) or ethylene-vinyl acetate copolymer (EVA), or a polyester resin such as polyethylene terephthalate resin (PET, PETG) (the polyolefin resin and the polyester resin may be referred to as the "resin in the outer layer" in this specification). When the outer layer 12 contains a resin in the outer layer, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with an electron beam. As a result, the conformability of the multilayer film 1 to the contents contained therein is further improved.

The outer layer 12 may contain only the outer layer resin (i.e., it may consist of the outer layer resin), or it may contain the outer layer resin and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of the outer layer resin and the other components).

Examples of the resin contained in the outer layer 12 include 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). Of these, low-density polyethylene (LDPE) is preferred.
The low-density polyethylene is, for example, preferably a low-density polyethylene having a density of 0.945 g/cm ^or less, more preferably a low-density polyethylene having a density of 0.943 g/cm ^or less, and even more preferably a low-density polyethylene having a density of ^0.941 g/cm or less. By including such a low-density polyethylene (LDPE), the crosslink density of the outer layer 12 can be further improved by irradiating the multilayer film 1 with an electron beam from the outside on the outer layer 12 side. As a result, the conformability of the multilayer film 1 to the contents contained therein is further improved.

The outer layer 12 may contain only one type of resin, or two or more types. If two or more types are contained, the combination and ratio of these resins can be selected as desired depending on the purpose.

The other components contained in the outer layer 12 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.
The other resin component is a resin other than the resin in the outer layer.

The outer layer 12 may contain only one type of other component, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The proportion of the resin content in the outer layer 12 relative to the total mass of the outer layer 12 is preferably 50% by mass or more, more preferably 55 to 100% by mass, and even more preferably 60 to 100% by mass, and may be, for example, 70 to 100% by mass or 85 to 100% by mass. When the proportion is equal to or greater than the lower limit, the crosslink density of the outer layer 12 can be further improved by irradiating the multilayer film 1 with an electron beam from the outside on the outer layer 12 side.
The ratio is usually the same as the ratio of the content (parts by mass) of the resin in the outer layer to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming the outer layer, which will be described later.

The outer layer 12 may consist of one layer (single layer), or two or more layers. When the outer layer 12 consists of multiple layers, these layers may be the same or different, and there are no particular limitations on the combination of these layers as long as it does not impair the effects of the present invention.

The thickness of the outer layer 12 is not particularly limited, but is preferably 4 to 146 μm, more preferably 7 to 143 μm, and even more preferably 10 to 140 μm, and may be, for example, any of 10 to 110 μm, 10 to 100 μm, 10 to 90 μm, 10 to 80 μm, and 10 to 70 μm. When the thickness of the outer layer 12 is equal to or greater than the lower limit, the crosslink density of the outer layer 12 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 outer layer 12 is equal to or less than the upper limit, the outer layer 12 is prevented from becoming excessively thick.
Here, the "thickness of the outer layer 12" means the thickness of the entire outer layer 12, and for example, the thickness of the outer layer 12 consisting of multiple layers means the total thickness of all layers that make up the outer layer 12.

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 to 88%, and even more preferably 14 to 86%. When this ratio is equal to or greater than the lower limit, the effect obtained by irradiating the multilayer film 1 with an electron beam from the outside on the outer layer 12 side is enhanced. When this ratio is equal to or less than the upper limit, the outer layer 12 is prevented from becoming excessively thick.

<Followers>
The conforming layer 13 may contain an ionomer. The ionomer means a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid, which has an ionically crosslinked structure formed by forming a salt between the acid moiety and a metal ion.

Examples of the metal ion include sodium ions and zinc ions. In this specification, an ionomer in which the metal ion is sodium ions may be referred to as a sodium-based ionomer, and an ionomer in which the metal ion is zinc ions may be referred to as a zinc-based ionomer.

The melt strength of the ionomer at a temperature of 180°C may be 60 to 540 mN. When the melt strength is equal to or greater than the lower limit, clouding of the multilayer film 1 can be further suppressed when the multilayer film 1 is adhered to a hot plate. When the melt strength is equal to or less than the upper limit, deformation of the base container can be further suppressed when the multilayer film 1 is adhered to the contents.

The melt strength of the ionomer at a temperature of 180°C is preferably 62 to 538 mN, more preferably 64 to 536 mN, and even more preferably 66 to 534 mN. When the melt strength is equal to or greater than the lower limit, clouding of the multilayer film 1 can be further suppressed when the multilayer film 1 is adhered to a hot plate. When the melt strength is equal to or less than the upper limit, deformation of the base container can be further suppressed when the multilayer film 1 is adhered to the contents.

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

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.

In addition to the ionomer, the conforming 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 the "polyethylene-based resin in the conforming layer"). By including a polyethylene-based resin in the conforming layer 13, the crosslink density of the conforming layer 13 can be improved when the multilayer film 1 is irradiated with an electron beam. As a result, the conformability of a package constructed using the multilayer film 1 to the contents is further improved.

The follow-up layer 13 may consist of one layer (single layer), or two or more layers. When the follow-up layer 13 consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

In this embodiment, the following layers 13 are provided at different positions on the multilayer film 1. In this embodiment, in order to distinguish these following layers 13 from one another, the following layer 13 disposed between the sealant layer 11 and the first adhesive layer 151 may be referred to as the first following layer 131, and the following layer 13 disposed between the second adhesive layer 152 and the outer layer 12 may be referred to as the second following layer 132, as necessary.
These compliant layers 13 (first compliant layer 131 and second compliant layer 132) may be the same as or different from each other.

The compliance layer 13 may contain only an ionomer (i.e., it may consist of an ionomer), or it may contain an ionomer and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of an ionomer and the other components).

The ionomer contained in the follow-up layer 13 may be one type only, or two or more types. If two or more types are used, the combination and ratio of these can be selected as desired depending on the purpose.

The other components contained in the follow-up layer 13 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.
The other component, which is a resin component, is a resin other than an ionomer.

The other components contained in the follow-up layer 13 may be one type only, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The proportion of the ionomer content in the following layer 13 relative to the total mass of the following layer 13 is preferably 50% by mass or more, more preferably 55 to 100% by mass, and even more preferably 60 to 100% by mass, and may be, for example, any of 70 to 100% by mass and 85 to 100% by mass. When the proportion is equal to or greater than the lower limit, the crosslink density of the following 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.
The ratio is usually the same as the ratio of the content (parts by mass) of the ionomer to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming the follow-up layer, which will be described later.

The thickness of the following layer 13 (each of the first following layer 131 and the second following layer 132) is preferably 4 to 146 μm, more preferably 7 to 143 μm, and even more preferably 10 to 140 μm, and may be, for example, any of 10 to 110 μm, 10 to 80 μm, 10 to 50 μm, and 10 to 30 μm. When the thickness of the following layer 13 is equal to or greater than the lower limit, the crosslink density of the following layer 13 can be further improved by externally irradiating the multilayer film 1 with an electron beam from the side of the outer layer 12. When the thickness of the following layer 13 is equal to or less than the upper limit, the following layer 13 is prevented from becoming excessively thick.
Here, the "thickness of the follower layer 13" means the overall thickness of the follower layer 13 (for example, the overall thickness of the follower layer 13 arranged between the sealant layer 11 and the first adhesive layer 151, or the overall thickness of the follower layer 13 arranged between the second adhesive layer 152 and the outer layer 12), and for example, the thickness of the follower layer 13 consisting of multiple layers means the total thickness of all the layers that make up the follower layer 13.

The ratio of the thickness of the follower 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 this ratio is equal to or greater than the lower limit, the effect obtained by irradiating the multilayer film 1 with an electron beam is enhanced. When this ratio is equal to or less than the upper limit, excessive thickness of the follower layer 13 is prevented.

If the compliance layer is made of ionomer (ION) or has ionomer (ION) as its main component, making it thicker will allow it to function as an outer layer as well.

<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 .

The gas barrier layer 14 preferably contains 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.

In addition to EVOH, the gas barrier layer 14 may also contain polyvinylidene chloride (PVDC) (EVOH and PVDC may be referred to as "gas barrier resins" in this specification). When the gas barrier layer 14 contains a gas barrier resin, the gas barrier properties of the multilayer film 1 can be further improved.

The gas barrier layer 14 may contain only the gas barrier resin (i.e., it may consist of the gas barrier resin), or it may contain the gas barrier resin and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of the gas barrier resin and the other components).

The other components contained in the gas barrier layer 14 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.
The other component, which is a resin component, is a resin other than the gas barrier property-imparting resin.
Examples of the other components that are non-resin components include the same additives as those listed above as other components contained in the sealant layer 11 .

The other components contained in the gas barrier layer 14 may be one type only, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The content of the gas barrier resin in the gas barrier layer 14 relative to the total mass of the gas barrier layer 14 is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, and even more preferably 70 to 100 mass%, and may be, for example, 85 to 100 mass%. When this proportion is equal to or greater than the lower limit, the gas barrier properties of the multilayer film 1 are further improved.
This 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 components that do not vaporize at room temperature in the composition for forming a gas barrier layer, which will be described later.

The gas barrier layer 14 may consist of one layer (single layer), or two or more layers. When the gas barrier layer 14 consists of multiple layers, these layers may be the same or different, and there are no particular restrictions on the combination of these layers as long as it does not impair the effects of the present invention.

The thickness of the gas barrier layer 14 is preferably 1 to 100 μm, more preferably 1.5 to 90 μm, and even more preferably 2 to 80 μm, and may be, for example, any of 4 to 60 μm, 4 to 40 μm, and 4 to 20 μm. Having a thickness of the gas barrier layer 14 equal to or greater than the above-mentioned lower limit can further suppress layer breakage in the gas barrier layer, thereby further improving the gas barrier properties of the multilayer film 1. In this specification, "layer breakage in the gas barrier layer" means that the gas barrier layer is not partially formed in the multilayer film, which occurs, for example, when the gas barrier layer is too thin. Having a thickness of the gas barrier layer 14 equal to or less than the above-mentioned upper limit can more reliably ensure that the tensile strength of the multilayer film 1 at a temperature of 140°C is 4 N/ ^mm2 or less, thereby better maintaining the shape of the packaged contents.
Here, the "thickness of the gas barrier layer 14" means the thickness of the entire gas barrier layer 14; for example, the thickness of the gas barrier layer 14 made up of multiple layers means the total thickness of all layers that make up the gas barrier layer 14.

The ratio of the thickness of the gas barrier layer 14 to the thickness of the multilayer film 1 is 2 to 25%. When this ratio is equal to or greater than the lower limit, it is possible to suppress delamination of the gas barrier layer and improve the gas barrier properties of the multilayer film 1. When this ratio is equal to or less than the upper limit, it is possible to make the tensile strength of the multilayer film 1 at a temperature of 140°C 4 N/ ^mm2 or less, and it is possible to maintain the shape of the packaged contents.

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 this ratio is equal to or greater than the lower limit, it is possible to further suppress layer tearing of the gas barrier layer and further improve the gas barrier properties of the multilayer film 1. When this ratio is equal to or less than the upper limit, it is possible to more reliably ensure that the tensile strength of the multilayer film 1 at a temperature of 140°C is 4 N/ ^mm2 or less, and the shape of the packaged contents can be more reliably maintained.

In the case of food packaging, the multilayer film that makes up the packaging is required to have a gas barrier layer to prevent oxidative deterioration of the food. However, the presence of a gas barrier layer can reduce the packaging's ability to conform to the food (its ability to adhere to the food without wrinkling). In contrast, this problem is resolved with a packaging constructed using the multilayer film 1 of this embodiment, which has an outer layer 12 and a conforming layer 13. This is because the presence of the outer layer 12 and the conforming layer 13 improves the heat resistance, melt tension, and tensile strength of the multilayer film 1, resulting in the multilayer film 1 having excellent conformability to the contents inside.

In addition, there has recently been a mainstream shift from conventional chamber-type skin pack machines (indirect heating method) with a low shot count to continuous skin pack packaging machines (direct heating method) with a high shot count, and there is a demand for melt strength that can withstand a method in which the film is directly heated at high temperatures by a heated hot plate. If the melt strength of the package is low, there is a problem in that the film becomes cloudy when it is in close contact with the hot plate. In contrast, this problem is resolved with a package constructed using the multilayer film 1 of this embodiment equipped with a follower layer 13. This is because the multilayer film 1 has excellent melt strength when heated due to the presence of the ionomer contained in the follower layer 13.

<Adhesive layer>
The adhesive layer 15 includes an adhesive.
The adhesive layer 15 bonds two adjacent layers together on both 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 together, and the adhesive layer 15 disposed between the gas barrier layer 14 and the following layer 13 bonds the gas barrier layer 14 and the following layer 13 together. In this specification, in order to distinguish between these two adhesive layers 15, the adhesive layer 15 disposed between the pinhole-resistant layer 16 and the gas barrier layer 14 may be referred to as a first adhesive layer 151, and the adhesive layer 15 disposed between the gas barrier layer 14 and the following layer 13 may be referred to as a second adhesive layer 152, as necessary.
These two adhesive layers 15 (first adhesive layer 151 and second adhesive layer 152) may be the same as or different from each other.

The adhesive contained in the adhesive layer 15 is not particularly limited as long as it can bond two layers to be bonded together with sufficient strength.
Examples of the adhesive include adhesive resins such as olefin-based resins (that is, polymers of one or more olefin monomers).

More specifically, examples of the olefin-based resin contained in the adhesive layer 15 include ethylene-based copolymers, propylene-based copolymers, and butene-based copolymers.
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.

The ethylene copolymer contained in the adhesive layer 15 may be, for example, a copolymer of ethylene and a vinyl group-containing monomer.
Examples of copolymers of ethylene and vinyl group-containing monomers 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), and ethylene-based thermoplastic elastomer.
Examples of the ionomer include the same ionomers as those listed above as those contained in the following layer 13 .

The propylene copolymer contained in the adhesive layer 15 may be, for example, 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 and propylene-based thermoplastic elastomers.

Examples of the butene copolymer contained in adhesive layer 15 include copolymers of 1-butene and vinyl group-containing monomers, copolymers of 2-butene and vinyl group-containing monomers, and modified products of these copolymers (modified copolymers).

The adhesive layer 15 may contain only adhesive (i.e., it may consist of adhesive), or it may contain adhesive and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of adhesive and the other components).

The adhesive layer 15 may contain only one type of adhesive, or two or more types. If two or more types are used, the combination and ratio of these adhesives can be selected as desired depending on the purpose.

The other components contained in adhesive layer 15 are not particularly limited and can be selected arbitrarily depending on the purpose. For example, they may be either resin components or non-resin components.

The other components contained in adhesive layer 15 may be one type only, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The content of the adhesive in the adhesive layer 15 relative to the total mass of the adhesive layer 15 may be, for example, 50 to 100 mass %.
This 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 components that do not vaporize at room temperature in the adhesive layer-forming composition described below.

The adhesive layer 15 may consist of one layer (single layer), or two or more layers. When the adhesive layer 15 consists of multiple layers, these layers may be the same or different, and there are no particular restrictions on the combination of these layers as long as it does not impair the effects of the present invention.

The thickness of the adhesive layer 15 (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 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, the adhesive strength between the two layers to be bonded is increased. When the thickness of the adhesive layer 15 is equal to or less than the upper limit, the adhesive layer 15 is prevented from becoming excessively thick.
Here, the "thickness of adhesive layer 15" means the overall thickness of adhesive layer 15 (for example, the overall thickness of adhesive layer 15 arranged between pinhole-resistant layer 16 and gas barrier layer 14, or the overall thickness of adhesive layer 15 arranged between gas barrier layer 14 and conforming layer 13), and for example, the thickness of adhesive layer 15 consisting of multiple layers means the total thickness of all layers constituting adhesive layer 15.

<Other demographics>
The multilayer film 1 may also have other layers that do not fall under any of the sealant layer 11, outer layer 12, conforming layer 13, gas barrier layer 14, and adhesive layer 15, as long as the effects of the present invention are not impaired.

The type and location of the other layers are not particularly limited and can be selected as desired depending on the purpose.

The other layers provided in the multilayer film 1 may be of one type only, or of two or more types. If there are two or more types, the combination and ratio of these layers can be selected as desired depending on the purpose.

The other layers may consist of one layer (single layer) per type, or two or more layers. When the other layers consist of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thickness of the other layers can be set arbitrarily depending on their type and is not particularly limited.

When the multilayer film 1 includes the other layer, it may further include an adhesive layer (e.g., adhesive layer 15) for adhering the other layer to other layers.

The thickness of the multilayer film 1 is the same as the thickness of the multilayer film (lid material) described above.

The multilayer film of this embodiment is not limited to the one described above, and some of the configuration may be changed, deleted, or added within the scope of the spirit of the present invention.
For example, the multilayer film may not include one or both of the outer layer and the adhesive layer, but preferably includes a sealant layer, a conforming layer, an adhesive layer, a gas barrier layer, an adhesive layer, a conforming layer, and an outer layer in this order, as shown in Figure 1.

<<Manufacturing method of multilayer film (lid material)>>
The multilayer film (lid material) can be produced by a known method depending on the type.
For example, laminated films such as the multilayer films can be produced by a feed block method in which resins or resin compositions that are materials for forming each layer are melt-extruded using several extruders, a coextrusion T-die method such as a multi-manifold method, or an air-cooled or water-cooled coextrusion inflation method.

The laminated film can also be produced by coating the resin or resin composition that will form one of the layers on the surface of another layer that will form the laminated film, and drying it as needed to form a layered structure in the laminated film, and then, as needed, laminating other layers in the desired arrangement.

The laminated film can also be produced by first separately preparing two or more films to form any two or more of the layers, then laminating these films together using an adhesive by dry lamination, extrusion lamination, hot melt lamination, or wet lamination, and then, if necessary, laminating other layers in the desired arrangement. In this case, an adhesive capable of forming the adhesive layer may be used.

The laminated film can also be produced by laminating two or more films that have been prepared separately in advance, as described above, using a thermal lamination method or the like without using an adhesive, and then, if necessary, laminating other layers in the desired arrangement.

When producing the laminated film, two or more of the methods for forming any of the layers (films) in the laminated film mentioned above may be combined.

Regardless of the manufacturing method, the resin composition that forms one of the layers in the laminated film can be manufactured by adjusting the types and amounts of the components contained so that the layer to be formed contains the desired components (constituent materials) in the desired amounts. For example, the ratio of the contents of components that do not vaporize at room temperature in the resin composition will usually be the same as the ratio of the contents of those components in a layer formed from this resin composition.

The resin composition (sometimes referred to herein as the "sealant layer-forming composition") used to form the sealant layer (sealant layer 11 in the multilayer film 1 shown in Figure 1) may, for example, contain the polyethylene resin in the sealant layer and, if necessary, the other components described above.

The resin composition (sometimes referred to herein as the "outer layer-forming composition") used to form the outer layer (outer layer 12 in the multilayer film 1 shown in Figure 1) may, for example, contain the resin in the outer layer and, if necessary, the other components described above.

The resin composition (sometimes referred to herein as the "composition for forming a follower layer") used to form the follower layer (follower layer 13 in the multilayer film 1 shown in Figure 1) may, for example, contain the polyethylene resin of the follower layer and, if necessary, the other components described above.

The resin composition (sometimes referred to herein as the "gas barrier layer-forming composition") used to form the gas barrier layer (gas barrier layer 14 in the multilayer film 1 shown in Figure 1) may, for example, contain the gas barrier resin described above and, if necessary, the other components described above.

The resin composition (sometimes referred to herein as the "adhesive layer-forming composition") used to form the adhesive layer (adhesive layer 15 in the multilayer film 1 shown in Figure 1) may, for example, contain the adhesive and, if necessary, the other components described above.

The multilayer film 1 can be used as a lid material. The packaging body of this embodiment can be produced by heat-sealing this lid material and a base material.

<<Bottom material>>
The base material is not particularly limited as long as it has an oxygen permeability of 300 cc/(m ² ·day·atm) or less and can be used as a base material for a package.
The base material may be a known material.

The oxygen permeability of the base material under conditions of a temperature of 23°C and a relative humidity of 60% is 300 cc/( ^m2 ·day·atm) or less, preferably 260 cc/( ^m2 ·day·atm) or less, and may be, for example, 200 cc/( ^m2 ·day·atm) or less, 150 cc/( ^m2 ·day·atm) or less, 100 cc/( ^m2 ·day·atm) or less, or 50 cc/( ^m2 ·day·atm) or less.
On the other hand, the oxygen permeability is 0 cc/(m ² ·day·atm) or more.

The oxygen permeability of the base material can be measured in accordance with JIS K 7126-2:2006 under conditions of a temperature of 23°C and a relative humidity of 60%.

The oxygen permeability of the sole material can be more easily adjusted by, for example, adjusting the type and amount of ingredients contained in the sole material, the thickness of the sole material, etc.

The thickness of the base material 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 base material is equal to or greater than the lower limit, the strength of the base material is further improved.
The thickness of the base material is preferably 6000 μm or less. When the thickness of the base material is equal to or less than the upper limit value, the base material is prevented from becoming excessively thick.
The thickness of the base material can be adjusted appropriately within a range set by any combination of any of the above-mentioned lower limit values and upper limit values.

Regarding the type of base material, all layers may be transparent, meaning that the base material itself is transparent, or all or some of the layers may not be transparent, meaning that the base material itself is not transparent. In a package constructed using a transparent base material, the contents can be easily seen through the base material.

The detailed structure of the base material and its manufacturing method will be explained in detail separately.

<<One embodiment of the base material>>
The base material is preferably a laminated body formed by laminating a plurality of layers.
A preferred example of a base material that is a laminate is a resin laminate that includes a foamed resin layer and a non-foamed resin layer provided on the foamed resin layer.

The foamed resin layer may be a known one.
The foamed resin layer may be, for example, a resin layer containing a foamed polystyrene resin (PSP).

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. The thickness of the foamed resin layer is not particularly limited, but is preferably 500 to 6000 μm.

An example of the non-foamed resin layer is a multi-layer film for base materials, which is constructed by laminating an easy-peel layer, a gas barrier layer, a pinhole-resistant layer, and an adhesive layer in this order in the thickness direction. In the multi-layer film for base materials, the easy-peel layer is one of the outermost layers, and the adhesive layer is the other outermost layer.

The multi-layer film for base materials may include, for example, an intermediate adhesive layer between the easy-peel layer and the gas barrier layer for bonding these two layers together.
The multi-layer film for base materials may also include, for example, an intermediate adhesive layer between the gas barrier layer and the pinhole-resistant layer for bonding these two layers together.
That is, the multilayer film for base materials may be constructed 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.

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

<Easy-peel layer>
The easy peel layer in the multi-layer film for base materials may be one that exhibits peelability by cohesive failure.
An example of an easy-peel layer that exhibits peelability by cohesive failure is one that contains two incompatible polyolefins.

Examples of the two incompatible polyolefins contained in the easy-peel layer of the multilayer film for base materials 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, the easy-peel layer may include, for example, 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.

The ethylene-based polymer contained in the easy-peel layer of the multilayer film for base materials includes ethylene homopolymers and ethylene-based copolymers.

Examples of the ethylene homopolymer include 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).

The ethylene copolymer has structural units derived from ethylene and structural units derived from a monomer other than ethylene.
Examples of the ethylene 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), and ionomer (ION).
Examples of the ionomer include the same ionomers as those listed above as those contained in the conforming layer 13 in the multilayer film 1 described above.

The easy-peel layer in the multilayer film for base materials preferably contains low-density polyethylene as the ethylene polymer. This provides better peelability for the easy-peel layer.

The propylene-based polymer contained in the easy-peel layer of the multilayer film for base materials includes propylene homopolymers (i.e., polypropylene or homopolypropylene, hPP) and propylene-based copolymers.

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

The easy-peel layer in the multilayer film for base materials preferably contains polypropylene as the propylene-based polymer. This provides better peelability for the easy-peel layer.

The easy-peel layer in the multilayer film for base materials may contain only one component that exhibits easy-peel properties, or two or more components. If there are two or more components, the combination and ratio of these components can be selected as desired depending on the purpose. For example, if the components that exhibit easy-peel properties are the two incompatible polyolefins described above, the easy-peel layer may contain only one component or two or more components of each of these polyolefins.

In the easy-peel layer of the multilayer film for base materials, 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, 30 to 90% by mass, 45 to 90% by mass, or 60 to 90% by mass. When this ratio is equal to or greater than the lower limit, the easy-peel property of the easy-peel layer becomes better. When this ratio is equal to or less than the upper limit, 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 composition for forming an easy peel layer for a base material, which will be described later.

The easy-peel layer in the multilayer film for base materials may contain components other than the components that exhibit easy-peel properties (for example, the two incompatible polyolefins described above) as long as the easy-peel properties are not impaired.
The other components contained in the easy-peel layer may be one kind or two or more kinds. When two or more kinds are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

In the easy-peel layer of the multilayer film for base materials, the ratio of the content of the component that exhibits easy-peel properties to the total mass of the easy-peel layer (for example, the ratio of the combined content of the two incompatible polyolefins described above) is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and may be, for example, any 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 this ratio is equal to or greater than the lower limit, the easy-peel property of the easy-peel layer becomes better.
The above ratio is usually the same as the ratio of the content (parts by mass) of components that exhibit easy peel properties to the total content (parts by mass) of components that do not evaporate at room temperature in the composition for forming an easy peel layer for base materials described below.

Examples of other components contained in the easy-peel layer of the multilayer film for base materials include anti-fogging agents, anti-blocking agents, etc.

The easy-peel layer in the multilayer film for base materials may consist of one layer (single layer), or two or more layers. When the easy-peel layer consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thickness of the easy-peel layer in the multilayer film for base materials is preferably 2 to 50 μm. When the thickness of the easy-peel layer is equal to or greater than the lower limit, the seal strength of the easy-peel layer is appropriately increased. When the thickness of the easy-peel layer is equal to or less than the upper limit, the easy-peel property is further increased.
Here, "thickness of the easy peel layer" means the thickness of the entire easy peel layer, for example, the thickness of an easy peel layer consisting of multiple layers means the total thickness of all layers that make up the easy peel layer.

The ratio of the thickness of the easy-peel layer to the thickness of the multilayer film for base materials is not particularly limited, but is preferably 5 to 40%. When this ratio is equal to or greater than the lower limit, the seal strength of the easy-peel layer is appropriately high. When this ratio is equal to or less than the upper limit, the easy-peel properties are further improved.

<Gas barrier layer>
The gas barrier layer imparts gas barrier properties (in other words, the property of inhibiting the permeation of oxygen gas) to the multi-layer film for base material.

The gas barrier layer in the multilayer film for base materials preferably contains ethylene-vinyl alcohol copolymer (EVOH, also known as saponified ethylene-vinyl acetate copolymer) or polyamide.

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, copolymer of 6-nylon and 66-nylon (nylon 6/66), copolymer of 6-nylon and 610-nylon, copolymer of 6-nylon and 611-nylon, copolymer of 6-nylon and 12-nylon (nylon 6/12), copolymer of 6-nylon and 612-nylon, 6- Examples include copolymers of 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.

In terms of heat resistance, mechanical strength, and availability, the polyamide is preferably 6-nylon (sometimes abbreviated as "Ny6" in this specification), 12-nylon, 66-nylon, nylon 6/66, nylon 6/12, or nylon 6/66/12.

The gas barrier layer of the multilayer film for base materials may contain only one type of polyamide, or two or more types. If two or more types are used, the combination and ratio of these can be selected as desired depending on the purpose.

The gas barrier layer in the multilayer film for base materials may contain only one or both of an ethylene-vinyl alcohol copolymer and a polyamide (i.e., it may consist of one or both of an ethylene-vinyl alcohol copolymer and a polyamide), or it may contain one or both of an ethylene-vinyl alcohol copolymer and a polyamide and other components (sometimes referred to herein as "other components") (i.e., it may consist of one or both of an ethylene-vinyl alcohol copolymer and a polyamide and the other components).

The other component contained in the gas barrier layer of the multi-layer film for base material is not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component. The other component that is a resin component is a resin that does not fall into either an ethylene-vinyl alcohol copolymer or a polyamide.
Examples of the other components that are non-resin components include the same additives as those listed above as other components contained in the sealant layer 11 in the multilayer film 1 described above.

The other components contained in the gas barrier layer of the multilayer film for base materials may be one type only, or two or more types. If there are two or more types, the combination and ratio of these can be selected as desired depending on the purpose.

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

The gas barrier layer in the multilayer film for base materials may consist of one layer (single layer), or two or more layers. When the gas barrier layer consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thickness of the gas barrier layer in the multilayer film for base material is preferably 2 to 20 μm. When the thickness of the gas barrier layer is equal to or greater than the lower limit, the gas barrier properties of the gas barrier layer are improved. When the thickness of the gas barrier layer is equal to or less than the upper limit, the gas barrier layer is prevented from becoming excessively thick.
Here, the "thickness of the gas barrier layer" means the thickness of the entire gas barrier layer, and for example, the thickness of a gas barrier layer consisting of multiple layers means the total thickness of all layers that make up the gas barrier layer.

The ratio of the thickness of the gas barrier layer to the thickness of the multi-layer film for base materials is not particularly limited, but is preferably 5 to 15%. When this ratio is equal to or greater than the lower limit, the gas barrier properties of the multi-layer film for base materials are improved. When this ratio is equal to or less than the upper limit, the gas barrier layer is prevented from becoming excessively thick.

<Pinhole-resistant layer>
The pinhole-resistant layer is a layer for protecting the structure of the multi-layer film for base material, for example, by suppressing the occurrence of pinholes in the multi-layer film for base material.

The pinhole-resistant layer in the multi-layer film for base materials preferably contains polyolefin.
Examples of the polyolefin include polyethylenes 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.

The pinhole-resistant layer in the multilayer film for base materials may contain only polyolefin (i.e., it may consist of polyolefin), or it may contain polyolefin and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of polyolefin and the other components).

The other components contained in the pinhole-resistant layer in the multi-layer film for base materials are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.
The other component, which is a resin component, is a resin other than polyolefin.
Examples of the other components that are non-resin components include the same additives as those listed above as other components contained in the sealant layer 11 in the multilayer film 1 described above.

The other components contained in the pinhole-resistant layer in the multilayer film for base materials may be one type only, or two or more types. If there are two or more types, the combination and ratio of these can be selected as desired depending on the purpose.

The proportion of the polyolefin content in the pinhole-resistant layer in the multi-layer film for base materials relative to the total mass of the pinhole-resistant layer is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, and may be, for example, either 70 to 100 mass% or 85 to 100 mass%.
The ratio is usually the same as the ratio of the polyolefin content (parts by mass) to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming a pinhole-resistant layer for base materials described below.

The pinhole-resistant layer in the multilayer film for base materials may consist of one layer (single layer), or two or more layers. When the pinhole-resistant layer consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thickness of the pinhole-resistant layer in the multilayer film for base materials is preferably 2 to 50 μm. When the thickness of the pinhole-resistant layer is equal to or greater than the lower limit, the protective ability of the pinhole-resistant layer is enhanced. When the thickness of the pinhole-resistant layer is equal to or less than the upper limit, the pinhole-resistant layer is prevented from becoming excessively thick.
Here, "thickness of the pinhole-resistant layer" means the thickness of the entire pinhole-resistant layer; for example, the thickness of a pinhole-resistant layer consisting of multiple layers means the total thickness of all layers that make up the pinhole-resistant layer.

The ratio of the thickness of the pinhole-resistant layer to the thickness of the multilayer film for base materials is not particularly limited, but is preferably 5 to 40%. When this ratio is equal to or greater than the lower limit, the pinhole resistance of the multilayer film for base materials is improved. When this ratio is equal to or less than the upper limit, the pinhole-resistant layer is prevented from becoming excessively thick.

<Adhesive layer>
The adhesive layer is a layer for adhering the base multi-layer film to the foamed resin layer, and contains an adhesive.

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 any other structural units.
A preferred example of the ethylene-vinyl acetate copolymer resin is a partially saponified ethylene-vinyl acetate copolymer.

The adhesive layer in the multi-layer film for base materials may contain only adhesive (i.e., it may consist of adhesive), or it may contain adhesive and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of adhesive and said other components).

The adhesive layer in the multi-layer film for base materials may contain only one type of adhesive, or two or more types. If there are two or more types, the combination and ratio of these adhesives can be selected as desired depending on the purpose.

The other components contained in the adhesive layer of the multi-layer film for base materials are not particularly limited and can be selected as desired depending on the purpose. For example, they may be either resin components or non-resin components.

The other components contained in the adhesive layer of the multi-layer film for base materials may be one type only, or two or more types. If there are two or more types, the combination and ratio of these can be selected as desired depending on the purpose.

The content of the adhesive in the adhesive layer in the multi-layer film for base material may be, for example, 50 to 100% by mass relative to the total mass of the adhesive layer.
The ratio is usually the same as the ratio of the adhesive content (parts by mass) to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming an adhesive layer for a base material, which will be described later.

The adhesive layer in the multi-layer film for base materials may consist of one layer (single layer), or two or more layers. When the adhesive layer consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thickness of the adhesive layer in the multi-layer film for base materials is preferably 2 to 40 μm. When the thickness of the adhesive layer is equal to or greater than the lower limit, the adhesive strength between the two layers to be bonded is increased. When the thickness of the adhesive layer is equal to or less than the upper limit, the adhesive layer is prevented from becoming excessively thick.
Here, "thickness of adhesive layer" means the thickness of the entire adhesive layer; for example, the thickness of an adhesive layer consisting of multiple layers means the total thickness of all layers that make up the adhesive layer.

The ratio of the thickness of the adhesive layer to the thickness of the multi-layer film for base materials is not particularly limited, but is preferably 5 to 40%. Having this ratio equal to or greater than the lower limit increases the adhesive strength between the two layers to be bonded. Having this ratio equal to or less than the upper limit prevents the adhesive layer from becoming excessively thick.

<First intermediate adhesive layer, second intermediate adhesive layer>
The first and second intermediate adhesive layers include an adhesive.
The adhesive is preferably an adhesive resin.
Examples of the adhesive resin include polyolefin resins.
The polyolefin resin is a resin having structural units 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 polyolefin resins 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 adhesiveness.

Examples of the ethylene copolymer include the ethylene copolymers described above as being contained in the easy-peel layer, and modified products thereof (modified copolymers).
Examples of the propylene copolymer include a copolymer of propylene and a vinyl group-containing monomer, a modified product thereof (modified copolymer), etc. More specific examples of such a propylene copolymer include a maleic anhydride-grafted linear low-density polypropylene, a propylene-based thermoplastic elastomer, etc.
Examples of the butene copolymer 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 of these copolymers (modified copolymers).

The first and second intermediate adhesive layers may contain only adhesive (i.e., may consist of adhesive), or may contain adhesive and other components (sometimes referred to as "other components" in this specification) (i.e., may consist of adhesive and the other components).

The first intermediate adhesive layer and the second intermediate adhesive layer may contain only one type of adhesive, or two or more types. If two or more types are used, the combination and ratio of these adhesives can be selected as desired depending on the purpose.

The other components contained in the first intermediate adhesive layer and the second intermediate adhesive layer are not particularly limited and can be selected arbitrarily depending on the purpose. For example, they may be either resin components or non-resin components.

The first intermediate adhesive layer and the second intermediate adhesive layer may contain only one type of other component, or two or more types. If there are two or more types, the combination and ratio of these components can be selected as desired depending on the purpose.

The content of the adhesive in the first intermediate adhesive layer in the multi-layer film for base materials may be, for example, 50 to 100% by mass relative to the total mass of the first intermediate adhesive layer.
This ratio is usually the same as the ratio of the adhesive content (parts by mass) to the total content (parts by mass) of components that do not evaporate at room temperature in the composition for forming the first intermediate adhesive layer for the base material described below.
The content of the adhesive in the second intermediate adhesive layer in the multi-layer film for base materials may be, for example, 50 to 100% by mass relative to the total mass of the second intermediate adhesive layer.
This ratio is usually the same as the ratio of the adhesive content (parts by mass) to the total content (parts by mass) of components that do not evaporate at room temperature in the composition for forming the second intermediate adhesive layer for the base material described below.

The first and second intermediate adhesive layers in the multilayer film for base materials may each consist of a single layer (single layer), or may consist of two or more layers. When the first or second intermediate adhesive layer consists of multiple layers, these multiple layers may be the same or different, and there are no particular restrictions on the combination of these multiple layers as long as it does not impair the effects of the present invention.

The thicknesses of the first and second intermediate adhesive layers in the multilayer film for base materials are preferably each independently 2 to 15 μm. When the thicknesses of the first and second intermediate adhesive layers are equal to or greater than the lower limit, the adhesive strength between the two layers to be bonded is increased. When the thicknesses of the first and second intermediate adhesive layers are equal to or less than the upper limit, the first and second intermediate adhesive layers are prevented from becoming excessively thick.
Here, the "thickness of the first intermediate adhesive layer" refers to the overall thickness of the first intermediate adhesive layer, and for example, the thickness of a first intermediate adhesive layer consisting of multiple layers refers to the total thickness of all layers that make up the first intermediate adhesive layer. This also applies to the second intermediate adhesive layer.

The ratio of the thickness of the first intermediate adhesive layer and the second intermediate adhesive layer to the thickness of the base multilayer film is not particularly limited, but is preferably 3 to 20%. Having this ratio equal to or greater than the lower limit increases the adhesive strength between the two layers to be bonded. Having this ratio equal to or less than the upper limit prevents the first intermediate adhesive layer and the second intermediate adhesive layer from becoming excessively thick.

<Other demographics>
The multilayer film for base materials may also have other layers that do not fall under 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.

The types and locations of the other layers in the multilayer film for base materials are not particularly limited and can be selected as desired depending on the purpose.

The multilayer film for base materials may have only one type of other layer, or two or more types. If there are two or more types, the combination and ratio of these layers can be selected as desired depending on the purpose.

The other layers in the multi-layer film for base materials may each consist of one layer (single layer), or two or more layers. When the other layers consist of multiple layers, these layers may be the same or different, and there are no particular restrictions on the combination of these layers as long as it does not impair the effects of the present invention.

The thickness of the other layers in the multilayer film for base materials can be set arbitrarily depending on their type and is not particularly limited.

When the multilayer film for base materials includes the other layer, it may further include an intermediate adhesive layer for adhering the other layer to the other layer. In this case, the intermediate adhesive layer may be, for example, the same as the first intermediate adhesive layer or second intermediate adhesive layer described above.

The thickness of the non-foamed resin layer of a multi-layer film for base materials, etc., is not particularly limited, but is preferably 40 to 120 μm.

<<Sole material manufacturing method>>
The base material can be produced by a known method depending on the type.
For example, when the base material is a resin laminate comprising the above-mentioned foamed resin layer and non-foamed resin layer, the base material can be produced by bonding one side of the foamed resin layer to one side of the non-foamed resin layer (or the adhesive layer therein, when the non-foamed resin layer is the multilayer film for base material) by heat lamination. The heat lamination in this case may be carried out by, for example, a melt-press lamination method as described later in the Examples, or by an extrusion lamination method.
Of the non-foamed resin layers, the multilayer film for base material can be produced in the same manner as the multilayer film (lid material) described above, except that the types of resins or resin compositions used to form each layer are different.

Regardless of the manufacturing method, the resin composition that forms one of the layers in the multi-layer film for base materials can be manufactured by adjusting the types and amounts of the components contained so that the layer to be formed contains the desired components (constituent materials) in the desired amounts. For example, the ratio of the contents of components that do not vaporize at room temperature in the resin composition will usually be the same as the ratio of the contents of those components in a layer formed from this resin composition.

The resin composition for forming the easy-peel layer in the multilayer film for base materials (sometimes referred to herein as the "composition for forming the easy-peel layer for base materials") may, for example, contain the polyolefin and, if necessary, the other components described above.

Examples of resin compositions for forming the gas barrier layer in multilayer films for base materials (sometimes referred to herein as "compositions for forming gas barrier layers for base materials") include those containing either or both of an ethylene-vinyl alcohol copolymer and a polyamide, and, if necessary, the other components described above.

Examples of resin compositions for forming pinhole-resistant layers in multilayer films for base materials (sometimes referred to herein as "compositions for forming pinhole-resistant layers for base materials") include those containing the polyolefins described above and, if necessary, the other components described above.

The resin composition for forming the adhesive layer in the multi-layer film for base material (sometimes referred to herein as the "composition for forming the adhesive layer for base material"), the resin composition for forming the first intermediate adhesive layer (sometimes referred to herein as the "composition for forming the first intermediate adhesive layer for base material"), and the resin composition for forming the second intermediate adhesive layer (sometimes referred to herein as the "composition for forming the second intermediate adhesive layer for base material") all contain, for example, the adhesive and, if necessary, the other components described above.

＜＜Package＞＞
FIG. 2 is a cross-sectional view schematically showing an example of the packaging body of this embodiment.
In FIG. 2, the same components as those shown in the drawings already described are given the same reference numerals as those in the drawings already described, and detailed description thereof will be omitted.
In FIG. 2, the distinction between the layers in the multilayer film 1 is omitted.

The packaging body 10 shown here is composed of a multilayer film (lid material) 1 and a base material 8, as shown in Figure 1.

The package 10 is preferably a skin pack package. In this specification, "skin pack" refers to packaging in which the contents are placed on cardboard, corrugated board, a bottom film, a tray, etc., and then a heated film is placed over it, and a vacuum is drawn in a chamber, so that the film adheres tightly to the contents. The name "skin pack" comes from the feature that the film adheres tightly to the product body, conforming to the shape of the product, just like skin.

In the packaging body 10, the multilayer film (lid material) 1 is constructed by laminating a sealant layer 11, a conforming layer 13, and a gas barrier layer 14 in this order in the thickness direction.
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 packaging body 10, the tensile strength of the multilayer film (lid material) 1 at a temperature of 140°C is 0.3 N/mm ² or more and 4 N/mm ² or less.
In the package 10, the oxygen transmission rate of the multilayer film (lid material) 1 under conditions of a temperature of 23°C and a relative humidity of 60% is 100 cc/(m ² ·day·atm) or less.
In the packaging body 10, the conforming layer 13 preferably contains an ionomer, and the melt strength of the ionomer at a temperature of 180° C. is preferably 60 to 540 mN.
In the packaging body 10, the dynamic elastic modulus E' of the multilayer film (lid material) 1 at a temperature of 140°C is preferably 1 x 10 ⁴ Pa or more and 1 x 10 ⁷ Pa or less.
In the packaging body 10, it is preferable that the temperature at which the multilayer film (lid material) 1 shows a displacement of 2000 μm during thermomechanical analysis is 120° C. or higher.
In the packaging body 10, the gel fraction of the multilayer film (lid material) 1 is preferably 30% or more.
In the packaging body 10, it is preferable that the displacement of the multilayer film (lid material) 1 at a temperature of 100° C. is 500 μm or less during the thermomechanical analysis.
In the packaging body 10, the multilayer film (lid material) 1 is preferably irradiated with electron beams at 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 packaging body 10, the ratio of the thickness of the conforming layer 13 to the thickness of the multilayer film (lid material) 1 is preferably 10% or more.
In the packaging body 10, the ratio of the thickness of the sealant layer 11 to the thickness of the multilayer film (lid material) 1 is preferably 5% or more.
In the packaging body 10, the tensile strength of the multilayer film (lid material) 1 at a temperature of 140°C is preferably 0.3 N/mm ² or more and 3.5 N/mm ² or less.

In the package 10, it is preferable that the oxygen transmission rate of the base material 8 under conditions of a temperature of 23°C and a relative humidity of 60% is 100 cc/(m ² ·day·atm) or less.

The packaging body 10 uses the multilayer film 1 as a lid material, thereby maintaining the quality of the contents, and has excellent conformability to the contents, and can conform softly to the contents.
Furthermore, the packaging body 10 uses a multilayer film (lid material) 1 and a base material 8, which provides high oxygen barrier properties to the contents 9, and the storage period of the contents 9 is longer than in the case of conventional packaging bodies.

One surface 8a of the base material 8 (sometimes referred to herein as the "first surface") is a sealing surface, and a portion of the first surface 8a is in close contact with a portion of the first surface 11a of the sealant layer 11 in the multilayer film 1. In Figure 2, the area where the first surface 8a of the base material 8 and the first surface 11a of the sealant layer 11 in the multilayer film 1 are in direct contact is the sealed portion. As a result, a storage portion 10a is formed between the first surface 8a of the base material 8 and the first surface 11a of the sealant layer 11. The contents 9 are sealed within this storage portion 10a.

When the base material 8 is the multilayer film for a base material, the first surface 8a of the base material 8 is the surface of the easy-peel layer opposite the gas barrier layer.

In Figure 2, some gaps can be seen between the contents 9 and the multilayer film 1, and between the contents 9 and the base material 8 within the storage section 10a of the package 10, but these gaps may not be present in the package 10 when the contents 9 are stored inside.

The packaging body of this embodiment is not limited to the one described above, and some of the configuration may be changed, deleted, or added within the scope of the spirit of the present invention.
Although Figure 2 shows a package 10 constructed using the multilayer film 1 shown in Figure 1 as a lid material, the package of this embodiment may be constructed using another multilayer film (lid material).

<<Manufacturing method of packaging body>>
The package of this embodiment is a package in which contents are vacuum-packaged by the base material and the lid material of the package of this embodiment.

The packaging body of this embodiment can be manufactured, for example, by placing the contents on the surface of the base material that will be sealed with the lid material, covering the surface of the base material and the contents with the lid material from above, and evacuating the area between the base material and the lid material where the contents are located, thereby tightly fixing the lid material to the contents, while heat-sealing the base material and the lid material in the area where the contents are not located.
The test package described below can also be produced in the same manner.

The sealing temperature during heat sealing is not particularly limited, but is preferably 100 to 170°C. By keeping the sealing temperature at or above the lower limit, the seal strength will be higher while maintaining easy-peel properties. By keeping the sealing temperature at or below the upper limit, the package will be easier to open.

The heat-sealing time can be adjusted as needed depending on the sealing temperature, but is typically preferably 10 to 30 seconds. By keeping the sealing time at or above the lower limit, the seal strength will be higher while maintaining easy-peel properties. By keeping the sealing time at or below the upper limit, the package will be easier to open.

The pressure in the area where the contents are placed, due to vacuuming during heat sealing, is 5000 Pa (50 mbar) or less, preferably 300 Pa to 5000 Pa, more preferably 400 Pa to 4900 Pa, even more preferably 500 Pa to 4800 Pa, and particularly preferably 600 Pa to 4700 Pa. By keeping the pressure at or below the upper limit, the lid material has better conformability (adhesion) to the contents, resulting in a package with better storage suitability.

The present invention will be explained in more detail below using specific examples. However, the present invention is not limited to the examples shown below.

[Example 1]
<<Manufacturing of multilayer film (lid material)>>
A multilayer film having the structure shown in FIG. 1 was produced according to the following procedure.
That is, an ethylene-vinyl acetate copolymer (EVA, "V5714C" manufactured by Mitsui Dow Polychemicals) was prepared as the resin constituting the sealant layer.
As a resin for forming the outer layer, low-density polyethylene (LDPE, density 0.922 g/cm ³ , "F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.) was prepared.
As a resin for forming the following layers (first following layer and second following layer), a sodium-based ionomer (ION, "1601" manufactured by Mitsui Dow Polychemicals) was prepared.
As the resin for forming the gas barrier layer, an ethylene-vinyl alcohol copolymer (EVOH, "GH3804B" manufactured by Nippon Synthetic Co., Ltd.) was prepared.
As the adhesive (adhesive resin) constituting the adhesive layers (first adhesive layer and second adhesive layer), maleic anhydride modified polyethylene (modified PE, "NF536" manufactured by Mitsui Chemicals, Inc.) was prepared.

The die temperature was set to 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) composed of a sealant layer (24 μm thick), a follower layer (first follower layer, 29 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 follower layer (second follower layer, 17 μm thick), and an outer layer (24 μm thick), laminated in this order in the thickness direction.

Next, the multilayer film obtained above was irradiated with electron beams from the outside of the outer layer side under conditions of an absorbed dose of 175 kGy and an acceleration voltage of 160 kV.
In this way, the desired electron beam irradiated multilayer film (hereinafter, sometimes referred to as "lid material (I)") was obtained.

<<Evaluation of multilayer film (lid material)>>
<Measurement of tensile strength at 140°C>
The tensile strength of the electron beam irradiated multilayer film (lid material (I)) obtained above was measured using a tensile strength measuring device (Shimadzu Corporation's "AGS-X") in accordance with JIS K 7127: 1999 at a pulling rate of 500 mm/min. The results are shown in Table 1.
<Measurement of dynamic elastic modulus at 140°C>
The electron beam irradiated multilayer film (covering material (I)) obtained above was subjected to measurement of dynamic modulus of elasticity (E') in accordance with JIS K7244-4 using a 4 mm wide sample in a tensile mode at a temperature range of 25°C to 160°C, a displacement of 10 μm, a vibration frequency of 1 Hz, and a heating rate of 3°C/min, using a dynamic viscoelasticity measuring device ("DMA 7100" manufactured by Hitachi High-Tech Science Corporation). The results are shown in Table 1.

<Ionomer Melt Strength at 180°C>
The melt strength of the ionomer contained in the first following layer of the electron beam irradiated multilayer film (lid material (I)) obtained above was measured in accordance with JIS K 7199 using a melt strength measuring device ("Capilograph" manufactured by Toyo Seiki Seisaku-sho, Ltd.) at a winding speed of 15 m/min. The results are shown in Table 1.

<Temperature showing a displacement of 2000 μm, Identification of displacement at a temperature of 100° C.>
The electron beam irradiated multilayer film (lid material (I)) obtained above was subjected to thermomechanical analysis in accordance with JIS K 7196 using a thermal analyzer ("EXSTAR6000" manufactured by SII Corporation). From the obtained thermomechanical analysis curve, the temperature (°C) showing a displacement of 2000 μm and the displacement (μm) at a temperature of 100°C were determined. The results are shown in Table 1.

<Measurement of gel fraction>
The gel fraction of the electron beam irradiated multilayer film (lid material (I)) obtained above was measured in accordance with JIS K 6769.
That is, a test piece measuring 3 cm x 3 cm (approximately 0.09 g) was cut out from the multilayer film, wrapped in a 400-mesh stainless steel wire mesh (100 g), and immersed in xylene (18 mL) at 110°C for 24 hours.
The test piece together with the wire mesh was then removed from the xylene 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 calculated. The results are shown in Table 1.

<Measurement of oxygen permeability>
The oxygen transmission rate (cc/(m2 day atm)) of the electron beam irradiated multilayer film (lid material (I)) obtained above was measured under conditions of a temperature of ²³ °C and a relative humidity of 60% in accordance with JIS K 7126-2: 2006. The results are shown in Table 1.

<Evaluation of gas barrier layer breakage>
The gas barrier layer of the electron beam irradiated multilayer film (lid material (I)) obtained above was visually observed and evaluated for the presence or absence of layer breakage in the gas barrier layer according to the following criteria. The results are shown in Table 1.
[Evaluation criteria]
A: No breakage of the gas barrier layer occurred.
B: The gas barrier layer was slightly torn.
C: The gas barrier layer was cut.

<<Manufacture of sole materials>>
<Production of multilayer film for base material>
A multi-layer film for a base material was produced according to the following procedure.
That is, low-density polyethylene (LDPE, "L211" manufactured by Sumitomo Chemical Co., Ltd.) and polypropylene (PP, "FS2011DG2" manufactured by Sumitomo Chemical Co., Ltd.) were prepared as resins for forming the easy-peel layer.
As the resin for forming the pinhole resistant layer, metallocene-catalyzed linear low-density polyethylene (mLLDPE) (Umerit (registered trademark) 1520F, manufactured by Ube Maruzen Polyethylene Co., Ltd., density 0.913 g/cm ³ ) was prepared.
An ethylene-vinyl alcohol copolymer (EVOH, "J171B" manufactured by Kuraray Co., Ltd., density: 1180 kg/m ³ , MFR: 4.2 g/10 min) was prepared as the resin for forming the gas barrier layer.
As the resin constituting the first intermediate adhesive layer, acid-modified polypropylene (acid-modified PP, adhesive resin, "Admer QF551" manufactured by Mitsui Chemicals, Inc.) was prepared.
As the resin constituting the second intermediate adhesive layer, acid-modified polyethylene (acid-modified PE, adhesive resin, "Admer NF536" manufactured by Mitsui Chemicals, Inc.) was prepared.
As the resin constituting the adhesive layer, an ethylene-vinyl acetate copolymer resin (EVA resin, adhesive resin, "MELTHEN (registered trademark) MX02D" manufactured by Tosoh Corporation was prepared.

The LDPE (70 parts by mass) and the PP (30 parts by mass) were mixed at room temperature to produce a composition for forming an easy-peel layer for base materials.

The die temperature was set to 250°C, and the composition for forming the easy-peel layer for base materials, 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 base materials (70 μm thick) composed of an easy-peel layer (25.9 μm thick), a first intermediate adhesive layer (5.6 μm thick), a gas barrier layer (8.4 μm thick), a second intermediate adhesive layer (5.6 μm thick), a pinhole-resistant layer (10.5 μm thick), and an adhesive layer (14 μm thick), laminated in this order in the thickness direction.

<Manufacture of sole material>
A foamed resin sheet (manufactured by Chuo Chemical Co., Ltd., thickness 3000 μm) containing a foamed polystyrene resin (PSP) was used, and the exposed surface of the adhesive layer of the multi-layer film for base material obtained above was bonded to one side of the foamed resin sheet by heat lamination to obtain a base material (hereinafter sometimes referred to as "base material (α)"). The heat lamination of the foamed resin sheet and the multi-layer film for base material was carried out by melt-press lamination using a roll device equipped with a melt-press roll. The melt-press roll was composed of a heated roll and an opposing roll arranged opposite the heated roll, and the foamed resin sheet and the multi-layer film for base material were bonded by melt-press lamination at 180°C between the heated roll and the opposing roll.

<<Evaluation of base material>>
<Measurement of oxygen permeability>
The oxygen transmission rate (cc/( ^m2 ·day·atm)) of the base material (base material (α)) obtained above was measured in accordance with JIS K 7126-2:2006 under conditions of a temperature of 23°C and a relative humidity of 60%. The results are shown in Table 5.

<<Manufacturing of Package (Test Package)>>
A 400 g piece of beef thigh meat was cut out and used as the test meat. Then, in a continuous skin pack packaging machine (Multivac "T300"), the sealant layer in the lid material (I) and the easy-peel layer in the base material (α) were placed opposite each other, and the test meat was placed between the lid material (I) and the base material (α). While evacuating the area where the test meat was placed, the periphery of the lid material (I) and the base material (α) were heat-sealed at a hot plate temperature (sealing temperature) of 140°C and a sealing time of 10 seconds to produce a test package (skin pack package). During evacuation, the pressure in the area where the test meat was placed was 1000 Pa (10 mbar). The base material (α) measured 20 cm x 20 cm.
A plurality of test packages were prepared using the same procedure, and these test packages were frozen and stored at −30° C. in an air atmosphere.

<<Evaluation of the package (test package)>>
<Film condition>
The test package was visually observed when it was in close contact with the hot plate, and the film was evaluated for cloudiness according to the following criteria. The results are shown in Table 6.
[Evaluation criteria]
A: The film is not cloudy.
B: The film is slightly cloudy.
C: The film is cloudy.

<Bottom container deformation>
The test package was visually observed when it was in close contact with the test meat, and the presence or absence of deformation of the base container was evaluated according to the following criteria. The results are shown in Table 6.
[Evaluation criteria]
A: The base container is not deformed.
B: The base container is slightly deformed.
C: The base container is deformed.

<Shape of contents>
After 14 days of storage, the meat was thawed from a frozen state of -30°C to 4°C over 16 hours. Immediately after thawing, the unopened test packages were visually observed from the lid side, and the shape of the test meat was evaluated according to the following criteria. The results are shown in Table 6.
[Evaluation criteria]
A: The shape of the test meat is maintained.
B: The shape of the test meat is slightly crushed.
C: The shape of the test meat is crushed.

<Discoloration of contents>
After 14 days of storage, the meat was thawed from a frozen state at -30°C 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 oxidative 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: The test meat was slightly discolored.
C: Discoloration of the test meat has occurred.

<Drip>
After 14 days of storage, the meat was thawed from a frozen state at -30°C to 4°C over 16 hours. Immediately after thawing, the test meat was removed from the unopened test package and left for 5 minutes, after which it was visually observed and the amount of dripping was evaluated according to the following criteria. The results are shown in Table 6.
[Evaluation criteria]
A: No dripping occurs.
B: There is some dripping.
C: Dripping occurs.

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

[Example 3]
An electron beam-irradiated multilayer film (hereinafter, sometimes referred to as "lid material (III)") was produced and evaluated in the same manner as in Example 1, except that the absorbed dose when irradiating the multilayer film with electron beams was 90 kGy instead of 175 kGy.
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (III)) was used.
The results are shown in Tables 1, 5 and 6.

[Example 4]
An electron beam-irradiated multilayer film (hereinafter sometimes referred to as "covering material (IV)") was produced and evaluated in the same manner as in Example 1, except that the absorbed dose when irradiating the multilayer film with electron beams was 15 kGy instead of 175 kGy.
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (IV)) was used.
The results are shown in Tables 1, 5 and 6.

[Comparative Example 1]
A lid material (a multilayer film not irradiated with electron beams, hereinafter sometimes referred to as "lid material (V)") was produced and evaluated in the same manner as in Example 1, 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 (lid material (V)) that had not been irradiated with electron beams was used.
The results are shown in Tables 1, 5 and 8.

[Example 5]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (VI)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (20 μm thick), a follower layer (first follower layer, thickness 29 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 18 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a follower layer (second follower layer, thickness 17 μm), and an outer layer (thickness 20 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (VI)) was used.
The results are shown in Tables 1, 5 and 6.

[Example 6]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (VII)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (thickness 16 μm), a following layer (first following layer, thickness 29 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 26 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a following layer (second following layer, thickness 17 μm), and an outer layer (thickness 16 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (VII)) was used.
The results are shown in Tables 2, 5 and 6.

[Comparative Example 2]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (VIII)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (12 μm thick), a follower layer (first follower layer, thickness 29 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 34 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a follower layer (second follower layer, thickness 17 μm), and an outer layer (thickness 12 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (VIII)) was used.
The results are shown in Tables 2, 5 and 8.

[Example 7]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (IX)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (thickness 27 μm), a follower layer (first follower layer, thickness 29 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 4 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a follower layer (second follower layer, thickness 17 μm), and an outer layer (thickness 27 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (IX)) was used.
The results are shown in Tables 2, 5 and 6.

[Comparative Example 3]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (X)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (thickness 28 μm), a follower layer (first follower layer, thickness 29 μm), an adhesive layer (first adhesive layer, thickness 8 μm), a gas barrier layer (thickness 1 μm), an adhesive layer (second adhesive layer, thickness 8 μm), a follower layer (second follower layer, thickness 17 μm), and an outer layer (thickness 29 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (X)) was used.
The results are shown in Tables 2, 5 and 8.

[Example 8]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XI)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (32 μm thick), a follower layer (first follower 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 follower layer (second follower layer, thickness 9 μm), and an outer layer (thickness 32 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XI)) was used.
The results are shown in Tables 2, 5 and 7.

[Example 9]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XII)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (40 μm thick), a follower layer (first follower layer, 7 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 follower layer (second follower layer, 7 μm thick), and an outer layer (40 μm thick) in this order.
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XII)) was used.
The results are shown in Tables 3, 5 and 7.

[Example 10]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XIII)") was produced and evaluated in the same manner as in Example 1, except that the die temperature was set to 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 (120 μm thick) configured by laminating in the thickness direction a sealant layer (41 μm thick), a follower layer (first follower layer, thickness 6 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 follower layer (second follower layer, thickness 5 μm), and an outer layer (thickness 42 μm).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XIII)) was used.
The results are shown in Tables 3, 5 and 7.

[Comparative Example 4]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XIV)") was produced and evaluated in the same manner as in Example 1, except that 6-nylon (Ny, "1030B2" manufactured by Ube Industries, Ltd.) was used instead of the EVOH ("GH3804B" manufactured by Nippon Synthetic 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 this electron beam irradiated multilayer film (lid material (XIV)) was used.
The results are shown in Tables 3, 5 and 8.

[Example 11]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XV)") was produced and evaluated in the same manner as in Example 1, except that linear low-density polyethylene (LLDPE, density 0.938 g/cm ³ , "4040FC" manufactured by Ube Maruzen Polyethylene Co., Ltd.) was used as the resin constituting the outer layer instead of the LDPE ("F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XV)) was used.
The results are shown in Tables 3, 5 and 7.

[Example 12]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XVI)") was produced and evaluated in the same manner as in Example 1, except that high-density polyethylene (HDPE, density 0.949 g/cm ³ , "3300F" manufactured by Prime Polymer Co., Ltd.) was used as the resin constituting the outer layer instead of the LDPE ("F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.).
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XVI)) was used.
The results are shown in Tables 3, 5 and 7.

[Example 13]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XVII)") was produced and evaluated in the same manner as in Example 1, except that an ethylene-vinyl acetate copolymer (EVA, "V5714C" manufactured by Mitsui Dow Polychemicals) was used instead of the LDPE ("F222NH" manufactured by Ube Maruzen Polyethylene Co., Ltd.) as the resin constituting the outer layer.
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XVII)) was used.
The results are shown in Tables 4, 5 and 7.

[Example 14]
A lid material (electron beam irradiated multilayer film, hereinafter sometimes referred to as "lid material (XVIII)") was manufactured and evaluated in the same manner as in Example 1, except that no outer layer was provided and the thickness of the second conformal layer was set to 41 μm.
A package (test package) was produced and evaluated in the same manner as in Example 1, except that this electron beam irradiated multilayer film (lid material (XVIII)) was used.
The results are shown in Tables 4, 5 and 7.

In the lid materials of the test packages of Examples 1 to 14, the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was 2% or more, and therefore no layer breakage occurred in the gas barrier layer in any of them.
The test packages of Examples 1 to 14 had a tensile strength of 4 N/ ^mm2 or less at 140°C, and therefore were able to maintain the shape of the packaged test meat.
In the test packages of Examples 1 to 14, the oxygen transmission rate was 100 cc/(m ² ·day ·atm) or less, and therefore no discoloration of the packaged test meat occurred.
The test packages of Examples 1 to 14 had a tensile strength of 0.3 N/ ^mm2 or more at 140°C. Therefore, although the test package of Example 10 caused some dripping of the test meat when it was removed, the test packages of Examples 1 to 9 and 11 to 14 did not cause any dripping.

As such, the test packages of Examples 1 to 14 maintained the quality of the contents, had excellent conformability to the contents, and were able to conform softly to the contents.

Furthermore, in the test packages of Examples 1 to 14, the melt strength of the ionomer at a temperature of 180° C. was 60 mN or more, and therefore the film did not become cloudy when adhered to the hot plate.
In the test packages of Examples 1 to 14, the melt strength of the ionomer at a temperature of 180° C. was 540 mN or less, and therefore the base container did not deform when it was in close contact with the test meat.

In contrast, in the test package of Comparative Example 1, the multilayer film was not irradiated with electron beams, so the heat resistance was not improved and the film became cloudy when it was in close contact with the hot plate. Furthermore, because the multilayer film was not irradiated with electron beams, the tensile strength at 140°C was less than 0.3 N/ ^mm2 , so the ability of the lid material to conform to the test meat was reduced and drips occurred when the test meat was removed.

In the test package of Comparative Example 2, the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was more than 25%, so the tensile strength at 140°C was more than 4 N/ ^mm2 , and therefore the base container was deformed when it was in close contact with the test meat. Furthermore, because the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was more than 25%, the tensile strength at 140°C was more than 4 N/ ^mm2 , and therefore the shape of the packaged test meat was crushed.

In the test package of Comparative Example 3, the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film was less than 2%, which resulted in the gas barrier layer breaking and discoloration of the packaged test meat.

In the test package of Comparative Example 4, Ny was used as the resin constituting the gas barrier layer, and the oxygen transmission rate exceeded 100 cc/( ^m2 ·day·atm), causing discoloration of the packaged test meat.

The present invention provides a multilayer film that maintains the quality of the contents, has excellent conformability to the contents, and can softly conform to the contents, as well as packaging (e.g., skin pack packaging) using the same.

1... Multilayer film (lid material)
REFERENCE SIGNS LIST 11: Sealant layer 12: Outer layer 13: Compliant layer 131: First compliant layer 132: Second compliant layer 14: Gas barrier layer 15: Adhesive layer 151: First adhesive layer 152: Second adhesive layer 10: Package (test package)
8: Base material 9: Contents (test meat)

Claims (9)

A multilayer film,
The multilayer film is configured by laminating a sealant layer, a conforming layer, a gas barrier layer , and an outer layer in this order in a thickness direction,
the ratio of the thickness of the gas barrier layer to the thickness of the multilayer film is 2 to 25%;
the tensile strength of the multilayer film at a temperature of 140°C, measured in accordance with JIS K 7127:1999, is 0.3 N/mm2 or ^more and 4 N/ ^mm2 or less;
the oxygen transmission rate of the multilayer film measured in accordance with JIS K 7126-2:2006 under conditions of a temperature of 23°C and a relative humidity of 60% is 16 cc/( ^m2 ·day·atm) or less ;
the following layer contains an ionomer, and the melt strength of the ionomer at a temperature of 180°C, measured in accordance with JIS K7199, is 60 to 540 mN;
A skin pack packaging body for food having a multilayer film, the outer layer of which contains a polyolefin-based resin . 2. The skin pack for food according to claim 1 , wherein the multilayer film has a dynamic modulus of elasticity E' at a temperature of 140° C. of 1×10 ⁴ Pa or more and 1×10 ⁷ Pa or less. 3. The skin pack for food 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. The skin pack for food according to any one of claims 1 to 3 , wherein the multilayer film has a gel fraction of 30% or more. The skin pack packaging for food according to claim 3 , wherein the multilayer film has a displacement of 500 μm or less at a temperature of 100° C. during the thermomechanical analysis. The skin pack for food according to any one of claims 1 to 5 , wherein the gas barrier layer comprises an ethylene-vinyl alcohol copolymer. The skin pack for food according to any one of claims 1 to 6 , wherein the ratio of the thickness of the conformal layer to the thickness of the multilayer film is 10% or more. The skin pack for food according to any one of claims 1 to 7 , wherein the ratio of the thickness of the sealant layer to the thickness of the multilayer film is 5% or more. The skin pack packaging for food according to any one of claims 1 to 8 , wherein the tensile strength of the multilayer film measured in accordance with JIS K 7127:1999 at a temperature of 140°C is 0.3 N/ ^mm2 or more and 3.5 N/mm2 or ^less .