package

Abstract

To provide a package having excellent heating efficiency and less uneven heating of packaged items.SOLUTION: In a package in which a packaged item is sandwiched between a lid material and a bottom material and heat-sealed, at 100°C, an increase in internal pressure of the package causes a pressure of 30 kPa or more to form through-holes in the heat-sealed portion, and one of the lid material and the bottom material is a packaging material (1) having a tensile elongation at 100°C of 150% or more as measured in accordance with JIS K 7127:1999, and the other is a packaging material (2) having a tensile elongation at 100°C of 100% or less as measured in accordance with JIS K 7127:1999.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a package. [Background technology]

[0002] Skin pack packaging and deep-draw packaging, which are known as packaging for food, are packaging in which the packaged item (contents) is sealed between a lid material (top material) and a base material (bottom material). For example, in skin pack packaging, a film is used as the lid material, and a film or tray that can be fused to the lid material softened by heat is used as the base material, while in deep-draw packaging, a film is used as the base material, and a film or nonwoven fabric that can be heat-pressed to the base material is used as the lid material.

[0003] When forming a skin pack package, first, the packaged item is placed on a base material, and then a lid material is placed on top of the packaged item to cover it. Next, the lid material is heated and softened while the air between the lid material and the base material is sucked out, causing the lid material to deform (conform) to the shape of the packaged item and adhere to it. At this time, the part of the lid material that is not in contact with the packaged item adheres to the base material. When the temperature and pressure are then returned to normal, the lid material hardens, retaining the shape it had when the air was sucked out, but the part that was in contact with the base material hardens in a fused (heat-sealed) state with the base material, resulting in a package in which the lid material adheres to the packaged item and base material (i.e., a skin pack package).

[0004] Deep-draw packaging is obtained by heat-molding a base material to form one or more containers (recesses), placing the packaged item into the container, placing a lid material to cover the opening, degassing the container, and heat-sealing the contact area between the lid material and the base material.

[0005] Because of this manufacturing method, skin pack packages and deep-draw packages are less likely to trap air between the packaged item and the base or lid material. Skin pack packages and deep-draw packages can package a variety of items, but they are often used to package food because they can package items in a way that prevents air from getting in.

[0006] In food packaging (packaged products) including skin pack packaging and deep-draw packaging, the food may be heated in a microwave oven or the like while still packaged in order to warm it up. In such cases, in order to prevent the packaging material from bursting due to an increase in internal pressure caused by steam generated inside the packaging, it has been proposed to provide the packaging material with a steam exhaust section that can exhaust steam when a predetermined internal pressure is reached (for example, Patent Documents 1 and 2), or, in the case of skin pack packaging, to adjust the heat seal strength between the base material and the lid material (for example, Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-59433 [Patent Document 2] International Publication No. 2001 / 081201 [Patent Document 3] Patent Publication No. 2021-17262 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the packages (packaged products) described in Patent Documents 1 to 3, steam is released from inside the package without causing the packaging material to burst, so there is room for improvement in that insufficient heating may result in the need for further heating or uneven heating of the food.

[0009] The present invention has been made in view of the above, and has as its object to provide a package that has excellent heating efficiency and that heats the packaged items with minimal unevenness. [Means for solving the problem]

[0010] As a result of further research, the present inventors have found that the above-mentioned problems can be solved by the following configuration example. In this specification, the numerical range "A to B" indicates A or more and B or less.

[0011] [1] A package in which the packaged item is sandwiched between a lid material and a base material and heat-sealed, At 100°C, the pressure at which a through hole is formed in the heat-sealed portion due to an increase in internal pressure of the package is 30 kPa or more, The package, wherein one of the lid material and the base material is a packaging material (1) having a tensile elongation at 100°C of 150% or more as measured in accordance with JIS K 7127:1999, and the other is a packaging material (2) having a tensile elongation at 100°C of 100% or less as measured in accordance with JIS K 7127:1999.

[0012] [2] The package according to [1], wherein the packaging material (1) is a multilayer film (F) having a surface layer (I) made of a resin material (X) mainly composed of an ionomer resin (A) and a sealant layer (II), and the tensile elongation of the packaging material (1) at 100°C measured in accordance with JIS K 7127 is 500 to 950%.

[0013] [3] The package according to [1] or [2], wherein the packaging material (2) has a tensile elongation of 0 to 50% at 100°C measured in accordance with JIS K 7127:1999.

[0014] [4] The package according to any one of [1] to [3], wherein the seal strength between the lid material and the base material, measured in accordance with JIS Z 0238:1998, is 4 to 20 N / 15 mm.

[0015] [5] The package according to any one of [1] to [4], which is for heating in a microwave oven.

[0016] [6] The package according to any one of [1] to [5], which is a skin pack package. [Effects of the Invention]

[0017] The packaging of the present invention has a higher internal pressure when steam is released than conventional packaging for microwave heating, and can heat the packaged item (e.g., food) in an environment where higher pressure than usual is applied during heating (e.g., microwave heating).This means that the packaged item can be heated at a higher temperature, has excellent heating efficiency, and can reduce uneven heating of the packaged item. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 shows a schematic cross-sectional view of a skin pack package. [Figure 2] Figure 2 shows the layout (plan view) of the packaged items (six food samples or vegetables) used in the evaluation of [pressure for forming through-holes at 100°C] and [heating efficiency, heating unevenness]. [Figure 3] Figure 3 shows the layout (side view from the longitudinal direction) of the packaged items (six food samples or vegetables) in the evaluation of [pressure for forming through-holes at 100°C] and [heating efficiency, heating unevenness]. DETAILED DESCRIPTION OF THE INVENTION

[0019] ≪Packaging body≫ The package of the present invention (hereinafter also referred to as "the package") comprises a lid material and a base material, and the packaged item is sandwiched between the lid material and the base material and heat-sealed. In the package, one of the lid material and the base material is a packaging material (1) having a tensile elongation at 100°C of 150% or more as measured in accordance with JIS K 7127:1999, and the other is a packaging material (2) having a tensile elongation at 100°C of 100% or less as measured in accordance with JIS K 7127:1999. Furthermore, at 100°C, the pressure at which a through-hole is formed in the heat-sealed portion due to an increase in internal pressure of the package is 30 kPa or more.

[0020] The present package is a package in which the packaged item is sandwiched between a lid material and a base material, and examples thereof include skin pack packages and deep-draw packages, with skin pack packages being preferred. The present package will be described with reference to the drawings, taking a skin pack package as an example. As shown in FIG. 1, the skin pack package includes a lid material and a base material. In the skin pack package, the lid material and the base material are heat-sealed in a tightly contacted state with the packaged item sandwiched between them. The skin pack package can store the packaged item in a sealed state for a certain period of time, after which the packaged item can be removed by peeling off the lid material and the base material. Note that the configuration of the skin pack package described above is an example and is not limited thereto. Specifically, for example, the present package may be a deep-draw package in which a base material having a container portion formed by deep-draw molding is heat-sealed to a lid material arranged to cover the opening of the container portion. In the deep-draw package, the packaged item is accommodated in the container portion.

[0021] In the present package, the pressure at which through-holes are formed in the heat-sealed portion due to an increase in internal pressure of the package at 100° C. is 30 kPa or more, preferably 32 kPa or more, and more preferably 35 kPa or more. The upper limit of the pressure at which through-holes are formed is not particularly limited as long as the effects of the present invention are not impaired, but is usually 100 kPa.

[0022] The formation of the through-holes in the present package is not particularly limited as long as it allows steam to be expelled from inside the package, but it is preferable that they be formed by peeling off the heat-sealed portion between the lid and base materials. The pressure at which the through-holes are formed indicates the magnitude of the internal pressure that the package can withstand at 100°C. Packages with a pressure equal to or greater than the lower limit can be heated while applying a pressure equal to or greater than the pressure (approximately 10 kPa) that can be applied to the packaged items in packages for microwave heating, and have superior heating efficiency and less heating unevenness than conventional packages for microwave heating. A specific method for determining the pressure at which the through-holes are formed is the method described in the Examples below.

[0023] The adhesive strength (hereinafter also referred to as "seal strength") between the lid material and the base material of this package, measured in accordance with JIS Z 0238:1998, is preferably 4 to 20 N / 15 mm, more preferably 5 to 10 N / 15 mm. If the seal strength is below the lower limit, the adhesive strength between the base material and the lid material is insufficient, and steam may pass through the heat-sealed portion during heating, resulting in uneven heating and reduced heating efficiency. On the other hand, if the seal strength exceeds the upper limit, the adhesive strength between the base material and the lid material is too strong, and this may result in excessive internal pressure during heating or difficulty in removing the packaged item.

[0024] As described above, the present packaging has superior heating efficiency to conventional packaging for microwave heating and can reduce uneven heating of the packaged items, and therefore can be suitably used as a packaging for microwave heating.

[0025] In this packaging body, one of the lid material and the base material constituting the packaging body is a packaging material (1) having a tensile elongation at 100°C of 150% or more as measured in accordance with JIS K 7127:1999, and the other is a packaging material (2) having a tensile elongation at 100°C of 100% or less as measured in accordance with JIS K 7127:1999.

[0026] <Packaging material (1)> The packaging material (1) has a tensile elongation at 100°C, measured in accordance with JIS K 7127:1999, of 150% or more. The upper limit of the tensile elongation is not particularly limited as long as it does not impair the effects of the present invention, but is typically 1000%. From the viewpoint of being able to apply a predetermined internal pressure to the packaged items when heated to 100°C in this package, the tensile elongation is preferably 500 to 950%, more preferably 700 to 900%. By using packaging material (1) having a tensile elongation at 100°C within the above range, a package that is less likely to burst even when the internal pressure inside the package increases can be easily obtained. When the tensile elongation differs between the longitudinal and lateral directions of the packaging material (1), the smaller tensile elongation is used as the tensile elongation of the packaging material (1) in the present invention, but it is preferable that the tensile elongation in both directions is within the above range.

[0027] The thickness of the packaging material (1) is preferably 50 to 200 μm, more preferably 60 to 150 μm, and even more preferably 70 to 140 μm. When the thickness of the packaging material (1) is within the above range, it has excellent conformability to the packaged items.

[0028] Packaging material (1) has a higher tensile elongation at 100°C than packaging material (2) described below, and therefore has excellent film extensibility and formability. Therefore, when the packaging body is, for example, a skin pack packaging body, packaging material (1) is preferably used as a lid material. On the other hand, when the packaging body is a deep-draw packaging body, packaging material (1) is preferably used as a base material.

[0029] The packaging material (1) is preferably a multilayer film (F) having a surface layer (I) and a sealant layer (II). A package using the multilayer film (F) having a barrier layer (described later) is suitable for packaging food.

[0030] [Surface layer (I)] The surface layer (I) forms one of the surfaces of the multilayer film (F). When the multilayer film (F) is used as a lid material or a base material, the surface layer (I) becomes the surface of the package. The surface layer (I) is preferably made of a resin material (X) containing an ionomer resin (A) as a main component.

[0031] [Resin material (X)] The resin material (X) contains the ionomer resin (A) as a main component, and may further contain one or more selected from the group consisting of resins other than the ionomer resin (A) and additives.

[0032] <Ionomer resin (A)> The ionomer resin (A) is a resin formed from an olefin polymer having a functional group such as a carboxy group and a metal ion. The ionomer resin (A) may be an olefin polymer having no crosslinked structure in the main chain, an olefin polymer having a crosslinked structure in the main chain, or a mixture of a polymer having a crosslinked structure in the main chain and a polymer having no crosslinked structure in the main chain. In other words, the ionomer resin (A) includes an olefin polymer that has become a gel due to a crosslinked structure formed in the main chain.

[0033] The type of monomer constituting the olefin polymer, which is the main chain portion of the ionomer resin (A), is not particularly limited. Examples of ionomer resins (A) include resins in which the molecules of an ethylene-unsaturated carboxylic acid copolymer, such as an ethylene-methacrylic acid copolymer, are crosslinked with metal ions. Examples of unsaturated carboxylic acids used in the polymerization of an ethylene-unsaturated carboxylic acid copolymer include methacrylic acid and acrylic acid. Furthermore, the metal ions contained in the ionomer resin (A) are not particularly limited. Examples of metal ions contained in the ionomer resin (A) include sodium ions, zinc ions, magnesium ions, and lithium ions.

[0034] The ionomer resin (A) may be a polymer obtained by polymerizing monomers that serve as structural units of the ionomer resin (A) by a known method, or may be a commercially available product. For example, "Himilan" manufactured by Mitsui Dow Polychemicals Co., Ltd. can be used as the ionomer resin (A).

[0035] The content of the ionomer resin (A) in the resin material (X) is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, based on 100% by mass of the resin material (X). When the content of the ionomer resin (A) in the resin material (X) is within this range, when a film having a surface layer (I) made of the resin material (X) is used as a lid material or a base material for a package, the lid material or the base material is less likely to be scratched, and even if the surface layer (I) is scratched, the changes in gloss and haze before and after the scratch are relatively small, so deterioration of the appearance due to the scratch is easily prevented.

[0036] The ionomer resin (A) contained in the resin material (X) may be one type or two or more types. The gelled product contained in the ionomer resin (A) contained in the resin material (X) may be one in which a crosslinked structure is formed between the same ionomer resin or one in which a crosslinked structure is formed between different ionomer resins.

[0037] <Other resins and additives> The resin material (X) may further contain other resins besides the ionomer resin (A). Examples of other resins besides the ionomer resin (A) include polyethylene. The content of other resins besides the ionomer resin (A) can be any amount that does not impair the object of the present invention. When other resins besides the ionomer resin (A) are contained, the total content of the other resins is usually about 1 to 50% by mass, preferably about 1 to 20% by mass, based on 100% by mass of the resin material (X). When the resin material (X) further contains a resin other than the ionomer resin (A), the gelled substance contained in the resin material (X) may have a crosslinked structure between the ionomer resin (A) and the other resin, or may have a crosslinked structure in the other resin.

[0038] The resin material (X) may further contain additives, such as antiblocking agents, slip agents, colorants, fillers, antioxidants, heat stabilizers, antistatic agents, antifogging agents, lubricants, and dyes. The content of other additives can be any amount that does not impair the object of the present invention. When other additives are contained, the total content of other additives is usually 0.005 to 10 mass %, preferably 0.01 to 8 mass %, relative to 100 mass % of the resin material (X).

[0039] <Method for producing resin material (X)> The resin material (X) is obtained by mixing the ionomer resin (A) and, optionally, other resins, additives, and other components in the above-mentioned amounts. The mixing method is not particularly limited, and the resin material (X) can be prepared by various known methods, such as dry blending the components using a Henschel mixer, tumbler blender, V-blender, or the like, dry blending the components and then melt-kneading them using a single-screw extruder, twin-screw extruder, Banbury mixer, or the like, or stirring and mixing them in the presence of a solvent.

[0040] [Thickness of surface layer (I)] The thickness of the surface layer (I) is preferably 20 to 80 μm, more preferably 30 to 70 μm. When the thickness of the surface layer (I) is within the above range, the multilayer film (F) can be stretched to such an extent that the internal pressure of the package can be maintained within the above range when the package is heated.

[0041] [Sealant layer (II)] The sealant layer (II) is a layer containing, as a main component, at least one selected from the group consisting of polyethylene-based resins and polypropylene-based resins. Examples of polyethylene-based resins include polyethylene and ethylene-based copolymers. Examples of polyethylene used in the sealant layer (II) include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). Examples of ethylene-based copolymers used in the sealant layer (II) include copolymers of ethylene and other α-olefins, copolymers of ethylene and vinyl acetate (EVA), and copolymers of ethylene and methacrylic acid (EMMA).

[0042] Examples of polypropylene-based resins that can be used for the sealant layer (II) include polypropylene and propylene-based copolymers. Examples of polypropylenes that can be used for the sealant layer (II) include homopolypropylene, block polypropylene, and random polypropylene. Both block polypropylene and random polypropylene have structural units derived from a comonomer. Examples of the comonomer include α-olefins, preferably ethylene.

[0043] The sealant layer (II) is preferably a layer mainly composed of polyethylene or polypropylene. When the sealant layer (II) is a layer mainly composed of polyethylene, the film including the sealant layer (II) is easy to process and has excellent heat-sealability. The sealant layer (II) is not particularly limited as long as it is heat-sealable.

[0044] The sealant layer (II) may contain, in addition to the resin used to form the sealant layer (II), one or more other additives that can be contained in the resin material (X).

[0045] The thickness of the sealant layer (II) is preferably 10 to 70 μm, more preferably 20 to 50 μm. When the thickness of the sealant layer (II) is within the above range, the multilayer film (F) can be easily cut with a heating wire without impairing the ability of the multilayer film (F) to conform to the packaged article.

[0046] [Example of multilayer film (F)] The multilayer film (F) may consist of two layers, a surface layer (I) and a sealant layer (II), or may consist of three or more layers. For example, the multilayer film (F) may be a film having a surface layer (I), a sealant layer (II), and other layers. The other layers may be, for example, a barrier layer having gas barrier properties or an adhesive layer for improving adhesion between multiple layers. Note that, like the surface layer (I), the multilayer film (F) may contain one or more layers made of a resin material (X) in addition to the surface layer (I). Similarly, when the sealant layer (II) and the other layers are contained in the multilayer film (F), they may be contained in one layer or in multiple layers.

[0047] [Other layers] <Barrier layer> The multilayer film (F) may further include a barrier layer having gas barrier properties between the surface layer (I) and the sealant layer (II). Resins used for the barrier layer include ethylene-vinyl alcohol copolymer (EVOH) and polyamide. Examples of polyamide include nylon 6, nylon 66, nylon 610, nylon 6 / 66 copolymer, and polymetaxylylene adipamide.

[0048] The thickness of the barrier layer is preferably 2 to 15 μm, more preferably 4 to 10 μm. When the thickness of the barrier layer is within the above range, the multilayer film (F) can maintain its barrier properties while having high conformability to the packaged items.

[0049] <Adhesive layer> The adhesive layer is not particularly limited as long as it is a resin that can bond the two layers contained in the multilayer film (F), but a polyolefin resin modified with an acid such as maleic anhydride is preferred. Among acid-modified polyolefin resins, maleic anhydride-modified polyethylene is preferred, and maleic anhydride-modified low-density linear polyethylene is particularly preferred because of its excellent adhesive properties.

[0050] [Thickness of multilayer film (F)] The thickness of the multilayer film (F) is preferably 50 to 200 μm, more preferably 60 to 150 μm, and even more preferably 70 to 140 μm. When the thickness of the multilayer film (F) is within the above range, it has good conformability to the packaged items.

[0051] [Method for manufacturing multilayer film (F)] The multilayer film (F) may be produced by laminating the layers constituting the multilayer film (F) in order, or may be produced by co-extruding the raw materials constituting the layers constituting the multilayer film (F). When produced by co-extrusion, the multilayer film (F) may be produced by a co-extrusion inflation method, for example, a water-cooled co-extrusion inflation method.

[0052] Furthermore, in producing the multilayer film (F), a multilayer film (Fa) having a surface layer made of a resin material (Xa) containing an ionomer resin (A) as a main component and having a gel fraction of less than 60 mass % and provided with a sealant layer (II) may be produced first, and then the multilayer film (Fa) may be irradiated with an electron beam to form a crosslinked structure in the resin material (Xa) of the surface layer, thereby converting the resin material (Xa) into the resin material (X). In this case, the method for producing the multilayer film (Fa) is the same as the method for producing the multilayer film (F).

[0053] Furthermore, even when a resin material (X) with a gel fraction of 60% by mass or more is used as the resin material used in the surface layer (I) of a multilayer film, the manufactured multilayer film (F) may be irradiated with an electron beam to increase the crosslinked structure in the resin material (X) so that the gel fraction of the resin material (X) forming the surface layer (I) is 85% by mass or less. Note that, since the amount of crosslinked structure formed increases as the absorbed dose of the electron beam increases for the same irradiation time, when irradiating the multilayer film (F) with an electron beam, the absorbed dose of the irradiated electron beam may be reduced compared to when irradiating the multilayer film (Fa) using the resin material (Xa) in the surface layer, while maintaining the same irradiation time, thereby adjusting the gel fraction of the resin material (X).

[0054] Furthermore, for the same absorbed dose of electron beams, the longer the electron beam irradiation time, the greater the amount of crosslinked structure formed. Therefore, when irradiating the multilayer film (F) with electron beams, the gel fraction of the resin material (X) may be adjusted by shortening the electron beam irradiation time while maintaining the same absorbed dose of electron beams compared to when irradiating the multilayer film (Fa) using the resin material (Xa) in the surface layer.

[0055] <Packaging material (2)> The packaging material (2) has a tensile elongation of 100% or less at 100°C, measured in accordance with JIS K 7127:1999. From the viewpoint of applying a predetermined internal pressure to the packaged items when heated to 100°C, the tensile elongation is preferably 0 to 100%, more preferably 0 to 50%, and even more preferably 0 to 30%. By using a packaging material (2) having a tensile elongation at 100°C within the above range, even if the internal pressure inside the package increases, the packaging material (2) can maintain the internal pressure without deforming. When the tensile elongation differs between the longitudinal and lateral directions of the packaging material (2), the larger tensile elongation is considered to be the tensile elongation of the packaging material (2) in the present invention, but it is preferable that the tensile elongation in both directions is within the above range.

[0056] The thickness of the packaging material (2) is not particularly limited, but is usually 0.2 to 2 mm, preferably 0.3 to 5 mm.

[0057] Packaging material (2) has a smaller tensile elongation at 100°C than packaging material (1), and is therefore less likely to deform when heated. For this reason, when the packaging body is, for example, a skin pack packaging body, packaging material (2) is preferably used as a base material. On the other hand, when the packaging body is, for example, a deep-draw packaging body, packaging material (2) is preferably used as a lid material.

[0058] The packaging material (2) is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include general-purpose flat base films (e.g., flat base sheets such as paperboard, plastic sheets, and polypropylene (PP) sheets) used in conventional skin pack packaging, and general-purpose lid films and nonwoven fabrics used in conventional deep-draw packaging. Furthermore, a molded product formed into a desired shape (e.g., a tray shape) may be used as the packaging material (2).

[0059] <Packaged items> The packaged item of the present package is not particularly limited, but may be, for example, food. The present package can be suitably heated in a heating appliance such as a microwave oven as is, and is therefore particularly suitable for packaging food that is expected to be used in such a manner.

[0060] <<Packaging manufacturing method>> The present package is not particularly limited as long as it is manufactured by a known manufacturing method for packages. For example, when the present package is a skin pack package, the packaged item is placed on the surface of the base material that will be sealed with the lid material, the lid material is placed over the surface of the base material and the packaged item, and the area between the base material and the lid material where the packaged item is located is vacuumed to tightly fix the lid material to the packaged item, while heat-sealing the base material and the lid material in the area where the packaged item is not located. Note that the above-mentioned manufacturing method for a skin pack package is one example and is not limited thereto. When the present package is a deep-draw package, a known manufacturing method for a deep-draw package can be used.

[0061] The sealing temperature when heat-sealing the base material and the lid material is not particularly limited, but is usually 100 to 170°C, and preferably 120 to 150°C. When the sealing temperature is equal to or higher than the lower limit, the seal strength is increased while maintaining easy peelability when removing the packaged items. When the sealing temperature is equal to or lower than the upper limit, the package is easier to open.

[0062] Furthermore, the sealing time when heat-sealing the base material and the lid material is not particularly limited, but is usually 10 to 30 seconds, preferably 15 to 25 seconds. When the sealing time is equal to or greater than the lower limit, the seal strength is increased while maintaining easy peelability when removing the packaged items. When the sealing time is equal to or less than the upper limit, the package is easier to open.

[0063] The pressure in the area where the packaged items are placed, which is generated by vacuuming during heat sealing, is preferably 5 kPa or less. By keeping the pressure at or below the upper limit, the lid material or base material can better conform to (adhere tightly to) the packaged items, and a package with better storage suitability can be easily obtained. [Example]

[0064] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0065] <Measurement method> [Film Thickness] Using a method conforming to JIS C 2151, five points on one piece of multilayer film obtained in the manufacturing example were measured using a dial gauge (PEACOCK UPRIGHT DIAL GUAGE, Ozaki Seisakusho Co., Ltd.), and the average of the measurement results was taken as the thickness of the multilayer film.

[0066] [Tensile elongation] The tensile elongation (%) at 100°C of the multilayer films obtained in the production examples, the base materials used in the examples, and the films used in the comparative examples was measured according to a method in accordance with JIS K 7127:1999.

[0067] [Seal strength] The seal strength (N) of the skin pack packages obtained in the examples was measured by a method in accordance with JIS Z 0238:1998.

[0068] [Through-hole formation pressure at 100°C] Six food samples (cylindrical, 32 mm diameter x 18 mm thick) were used as packaged items in the Examples and Comparative Examples. Air was pumped into the package for one minute in a thermostatic chamber at 100°C using a seal strength tester (seal strength / burst strength tester, manufactured by Sun Scientific Co., Ltd.), and the pressure (kPa) required until a through-hole was formed in the package (the heat-sealed portion of the package peeled off or the packaging material burst) was measured. If no through-hole was formed after one minute of air pumping, the pressure (kPa) at the end of the test was measured. The results are shown in Table 1. In Comparative Examples 2 and 3, no through-hole was formed even after one minute of air pumping. The six food samples were arranged evenly spaced apart within the package without overlapping, as shown in Figures 2 and 3.

[0069] [Heating efficiency, heating unevenness] In the Examples and Comparative Examples, six vegetables (carrots sliced ​​into rings 32 mm in diameter and 18 mm thick) were used as packaged items, and the resulting packages were heated at 600 W for one minute in a microwave oven (ARF-205, manufactured by Yoshii Electric Co., Ltd.). The heated vegetables were removed from the packages, the temperature at the center of the vegetables was measured, and the average center temperature (°C) of the six vegetables was calculated. The results are shown in Table 1. The six vegetables were arranged evenly spaced apart without overlapping within the packages, as shown in Figures 2 and 3. The higher the center temperature of the vegetables, the higher the pressure and temperature at which the vegetables were heated. Therefore, vegetables with a higher average center temperature can be said to have excellent heating efficiency.

[0070] Next, after allowing the vegetables to reach room temperature, an autograph (AGS-X, Shimadzu Corporation) was used to measure the peak strength when the carrot slices were cut perpendicular to the cross section using a 4 cm wide, 1 mm thick board (Sanmodur (urethane synthetic wood), Sanyo Chemical Industries, Ltd.). The average cutting strength (N) and standard deviation of the cutting strength for the six vegetables were calculated. The smaller the average cutting strength, the softer the vegetables were after heating. This indicates that the vegetables were heated under a higher pressure and temperature environment, so vegetables with a higher average cutting strength indicate excellent heating efficiency. The smaller the standard deviation of the cutting strength, the more uniformly the six vegetables were softened after heating. This indicates that vegetables with a smaller standard deviation of the cutting strength were less unevenly heated.

[0071] <Ingredients> "IO1": Ionomer resin (Himilan (registered trademark), manufactured by Mitsui Dow Polychemicals Co., Ltd.) "AD1": Modified polyolefin (Modic (registered trademark), manufactured by Mitsubishi Chemical Corporation) "EVOH1": Ethylene-vinyl alcohol copolymer (EVAL (registered trademark), manufactured by Kuraray Co., Ltd.) "PE1": Polyethylene (Evolue (registered trademark), manufactured by Prime Polymer Co., Ltd.) "PE2 pellets": pellets consisting of 98% by mass of polyethylene (PE2) and 2% by mass of a phosphophenol-based antioxidant (Sumikathen (registered trademark), manufactured by Sumitomo Chemical Co., Ltd.) "Anti-blocking agent": synthetic zeolite (Shilton (registered trademark), manufactured by Mizusawa Industrial Chemicals, Ltd.) "Slip agent": fatty acid amide (Diamid (registered trademark), manufactured by Mitsubishi Chemical Corporation)

[0072] <Production Example 1> [Preparation of resin material] 94 parts by mass of ionomer resin (IO1 listed as raw materials) was mixed (dry blended) with 2 parts by mass of PE2 pellets, 2 parts by mass of antiblocking agent, and 2 parts by mass of slip agent to prepare a resin material. The resulting resin material therefore contained 94% by mass of IO1, 1.96% by mass of PE2, 0.04% by mass of antioxidant, 2% by mass of antiblocking agent, and 2% by mass of slip agent.

[0073] [Production of multilayer film (F1)] The resin material obtained in the preparation of the resin material described above, along with the raw materials AD1, EVOH1, and PE1, was processed by coextrusion water-cooling inflation to produce a 70 μm-thick film (multilayer film (F1)) consisting of the following five layers laminated in the order of Layer 1, Layer 2, Layer 3, Layer 4, and Layer 5. The multilayer film (F1) was then irradiated with an electron beam from the first layer side. Here, the first layer is the layer of the resin material obtained in Preparation Example 1, but since the resin material contains 94% by mass of IO1, in the following description, for convenience, the first layer will be referred to as "IO1." Note that the thickness ratio of each layer is based on the film thickness being 100%. The tensile elongation of the resulting multilayer film (F1) at 100°C was 850%. 1st layer: IO1 (thickness ratio = 49%) Second layer: AD1 (thickness ratio = 7%) 3rd layer: EVOH1 (thickness ratio = 7%) 4th layer: AD1 (thickness ratio = 7%) 5th layer: PE1 (thickness ratio = 30%)

[0074] <Production Example 2> [Production of multilayer film (F2)] The resin material obtained in Preparation Example 1, along with the raw materials AD1, EVOH1, and PE1, was processed by coextrusion water-cooling inflation to produce a 140 μm-thick film (multilayer film (F2)) consisting of the following five layers laminated in the order of Layer 1, Layer 2, Layer 3, Layer 4, and Layer 5. The multilayer film (F2) was then irradiated with an electron beam from the first layer side. Here, the first layer is the layer of the resin material obtained in Preparation Example 1. However, since the resin material contains 94% by mass of IO1, in the following description, for convenience, the first layer will be referred to as "IO1." The thickness ratio of each layer is calculated based on the film thickness being 100%. The resulting multilayer film (F2) had a tensile elongation of 900% at 100°C. 1st layer: IO1 (thickness ratio = 49%) Second layer: AD1 (thickness ratio = 7%) 3rd layer: EVOH1 (thickness ratio = 7%) 4th layer: AD1 (thickness ratio = 7%) 5th layer: PE1 (thickness ratio = 30%)

[0075] <Examples 1 and 2> [Skin pack packaging manufacturing] The packaged item was placed on the base material (a polypropylene (PP) sheet measuring 197 mm long x 155 mm wide x 0.55 mm thick, with a tensile elongation of 15% at 100°C) and set in a skin pack packaging machine (QX-300FLEX, manufactured by Ishida Co., Ltd.). In this state, the multilayer film (F1) or (F2) was heated to 130°C, and the pressure inside the chamber of the packaging machine was reduced to 0.3 kPa. The chamber was then returned to room temperature and pressure, yielding a skin pack package in which the packaged item and the multilayer film (F1) or (F2) were tightly attached to each other for each of the packaged items described in the evaluation methods above. In each skin pack package, the multilayer film (F1) or (F2) was used with the first layer oriented to form the surface facing the lid material.

[0076] <Comparative Example 1> [Packaging manufacturing] The food was packed into a microwave cooking bag with a steam vent (product name "Lead Petit Pressure Cooking Bag", manufactured by Lion Corporation) and the bag was closed with a zipper to obtain a package. Note that this cooking bag is a three-sided bag with a zipper, and since the lid and base materials are made of the same sheet, the tensile elongation of the lid and base materials is the same.

[0077] <Comparative Example 2> [Packaging manufacturing] A three-sided bag made of multilayer film (F1) (the first layer forms the surface of the three-sided bag) was filled with the packaged item, and the opening was heat-sealed at 140°C to obtain a package. Note that, since the lid material and the base material of the three-sided bag are made of the same sheet, the tensile elongation of the lid material and the base material is the same.

[0078] <Comparative Example 3> [Packaging manufacturing] The contents were filled into a five-layer nylon poly three-sided bag (trade name "Kyoubijin", manufactured by Kurilon Chemical Co., Ltd.), and the opening was heat-sealed at 140°C to obtain a package. Note that, since the lid and base materials of this three-sided bag are made of the same sheet, the tensile elongation of the lid and base materials is the same.

[0079] [Table 1]

[0080] As shown in Table 1, the present packages (Examples 1 and 2) had a through-hole formation pressure of 30 kPa or more at 100°C, and compared to the packages of Comparative Examples 1 to 3, the average center temperature of the vegetables after heating was higher and the average strength at cut was smaller, resulting in excellent heating efficiency and less uneven heating due to a smaller standard deviation in the strength of the vegetables at cut after heating.On the other hand, microwave cooking bags with steam vents and three-sided bags made of film with high tensile elongation at 100°C had a through-hole formation pressure of less than 30 kPa at 100°C, which resulted in insufficient heating efficiency and frequent uneven heating. [Explanation of symbols]

[0081] 1. Skin pack packaging 2.Lid material 3. Sole material 4. Packaged goods

Claims

1. A package in which the packaged item is sandwiched between a lid material and a base material and heat-sealed, At 100°C, the pressure at which a through hole is formed in the heat-sealed portion due to an increase in internal pressure of the package is 30 kPa or more, The package, wherein one of the lid material and the base material is a packaging material (1) having a tensile elongation at 100°C of 150% or more as measured in accordance with JIS K 7127:1999, and the other is a packaging material (2) having a tensile elongation at 100°C of 100% or less as measured in accordance with JIS K 7127:1999.

2. 2. The package according to claim 1, wherein the packaging material (1) is a multilayer film (F) including a surface layer (I) made of a resin material (X) containing an ionomer resin (A) as a main component, and a sealant layer (II), and the tensile elongation of the packaging material (1) at 100°C measured in accordance with JIS K 7127 is 500 to 950%.

3. 2. The package according to claim 1, wherein the packaging material (2) has a tensile elongation of 0 to 50% at 100°C measured in accordance with JIS K 7127:1999.

4. 2. The package according to claim 1, wherein the seal strength between the lid material and the base material, measured in accordance with JIS Z 0238:1998, is 4 to 20 N / 15 mm.

5. 10. The package of claim 1, which is for microwave heating.

6. The packaging according to any one of claims 1 to 5, which is a skin pack packaging.

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