Packaging using gas barrier film

Abstract

To provide a package that is excellent at gas barrier and airtightness, and can extend freshness retention period.SOLUTION: A package of the present invention is a package in which content is wrapped with a multilayer film containing a gas barrier layer that contains gas barrier resin, the outermost layer and the innermost layer of the multilayer film contain thermoplastic resin having a melting point of 130°C or less, the multilayer film is folded at least on the bottom side of the content, there is a portion where the innermost layers are welded together and a portion where the outermost layers are welded together on the bottom side of content, and the in-pushing load measured by the following method is 3 to 10 N.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The present invention relates to a package.

Background Art

[0002] As a form of gas replacement packaging that can extend the conventional freshness retention period, there are pillow packaging and top seal packaging used for tray packaging, and bag packaging in packaging that does not use a tray. A film has been used for the conventional package. As the film, for example, films described in Patent Documents 1 and 2 are known. However, in recent years, it has been required to extend the freshness retention period, and the films described in the documents were not sufficient in terms of freshness retention period, gas barrier property, and airtightness.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] That is, the present invention is as follows. [1] A package in which the contents are wrapped with a multilayer film including a gas barrier layer containing a gas barrier resin, where the outermost layer and the innermost layer of the multilayer film contain a thermoplastic resin having a melting point of 130°C or lower, at least on the bottom surface side of the contents, the multilayer film is folded, on the bottom surface side of the contents, there are portions where the innermost layers are welded together and portions where the outermost layers are welded together, the pushing load measured by the following method is 3 to 10 N, The multilayer film comprises, in the thickness direction, a skin layer, an adhesive layer, a gas barrier layer, an adhesive layer, and a skin layer in this order. The aforementioned skin layer is the innermost layer and the outermost layer, The skin layer contains 80% by weight or more of thermoplastic resin based on 100% by mass of the skin layer. The Vicat softening point (SVst) and melting point (STm) of the thermoplastic resin and the glass transition point (GTg) of the resin contained in the gas barrier layer satisfy the following relationship (1): In an adhesive strength measurement using a probe tack tester TAC-II (manufactured by Resca Co., Ltd.) to evaluate the adhesive strength to a 5 mm diameter stainless steel cylindrical probe under the conditions of an entry speed of 120 mm / min, applied pressure of 600 gf, pressurization time of 1 second, release speed of 600 mm / min, and temperature of 100 degrees Celsius, the adhesive strength of the film surface was 90 gf or higher. A packaging body characterized by the following features. GTg(℃) <SVst(℃)≦STm(℃)<130(℃) ···(1) (Method for measuring indentation load) To measure the indentation load, the multilayer film was first peeled off the packaging and stretched and fixed onto a 125 x 125 x 50 mm frame. Then, using a tensile and compression testing machine (Shimadzu Corporation AG-IS), a 15φ matte stainless steel indentation rod was pressed perpendicularly against the film surface of the packaging at a speed of 1000 mm / min and an indentation depth of 15 mm. The load at a depth of 15 mm was measured (unit: N). Three measurements were taken, and the average value was used as the measured value. The measurements were performed in an atmosphere of 23°C and 50% RH. [2] The packaging according to [1], wherein the multilayer film has gas barrier and water vapor barrier properties, and the interior wrapped by the multilayer film is replaced with nitrogen, oxygen, carbon dioxide, or a mixture thereof. [3] The packaging according to [1] or [2], wherein the contents include an oxygen absorber and / or a CO2 generating agent. [4] The packaging according to any one of [1] to [3], wherein the adhesion work of the film surface of the multilayer film, as measured by the following method, is 0.60 mJ or more and less than 2.10 mJ. (Measurement of work done at close contact) Bottom area 25cm 2 Two cylindrical aluminum jigs, 55 mm high and weighing 400 g, were prepared, and a piece of filter paper the same shape as the bottom surface was attached to the bottom surface of each jig. The sample was placed over the jig, ensuring that no wrinkles formed on the bottom surface of the filter paper, and secured with a rubber band. The two jigs, each covered with a sample, were placed on top of each other with the sample-covered sides facing each other, and pressed together with a load of 500 g for 1 minute. Next, the amount of work required to separate the sample surfaces from each other perpendicular to each other (work of adhesion, unit: mJ) was measured at a speed of 5 mm / min using a tensile and compression testing machine (Shimadzu AG-IS 5KN MS type). The measurement was performed in an atmosphere of 23°C and 50% RH. [5] The packaging according to any one of [1] to [4], wherein the tensile elongation at break in the TD direction of the multilayer film, as measured in accordance with ASTM-D882, is 150 to 400%. [6] The oxygen permeability of the aforementioned multilayer film at 23°C and 65%RH, measured in accordance with JIS K7126-1, is 20 cm 3 20 μm / m 2 • Packaging that is 24 hours or less and meets any of the following conditions: [1] to [5]. [7] The packaging according to any one of [1] to [6], wherein the thermal shrinkage rate in the MD direction and the TD direction of the multilayer film after being left standing at 80°C for 30 minutes is 10% or more in both directions. [Means for solving the problem]

[0005] In other words, the present invention is as follows: [1] A package in which the contents are wrapped in a multilayer film containing a gas barrier layer containing a gas barrier resin, The outermost and innermost layers of the multilayer film contain a thermoplastic resin with a melting point of 130°C or lower. At least on the bottom side of the contents, the multilayer film is folded, The bottom surface of the contents has a portion where the innermost layers are welded together and a portion where the outermost layers are welded together. The indentation load measured by the following method is 3 to 10 N. A packaging body characterized by the following features. (Method for measuring indentation load) To measure the indentation load, the multilayer film was first peeled off the packaging and stretched and fixed onto a 125 x 125 x 50 mm frame. Then, using a tensile and compression testing machine (Shimadzu Corporation AG-IS), a 15φ matte stainless steel indentation rod was pressed perpendicularly against the film surface of the packaging at a speed of 1000 mm / min and an indentation depth of 15 mm. The load at a depth of 15 mm was measured (unit: N). Three measurements were taken, and the average value was used as the measured value. The measurements were performed in an atmosphere of 23°C and 50% RH. [2] The packaging according to [1], wherein the multilayer film has gas barrier and water vapor barrier properties, and the interior wrapped by the multilayer film is replaced with nitrogen, oxygen, carbon dioxide, or a mixture thereof. [3] The packaging according to [1] or [2], wherein the contents include an oxygen absorber and / or a CO2 generating agent. [4] The multilayer film comprises, in the thickness direction, a skin layer, an adhesive layer, a gas barrier layer, an adhesive layer, and a skin layer in this order. The aforementioned skin layer is the innermost layer and the outermost layer, The skin layer contains 80% by weight or more of thermoplastic resin based on 100% by mass of the skin layer. The Vicat softening point (SVst) and melting point (STm) of the thermoplastic resin and the glass transition point (GTg) of the resin contained in the gas barrier layer satisfy the following relationship (1): In an adhesive strength measurement using a probe tack tester TAC-II (manufactured by Resca Co., Ltd.) to evaluate the adhesive strength to a 5 mm diameter stainless steel cylindrical probe under the conditions of an entry speed of 120 mm / min, applied pressure of 600 gf, pressurization time of 1 second, release speed of 600 mm / min, and temperature of 100 degrees Celsius, the adhesive strength of the film surface was 90 gf or higher. The packaging described in any of [1] to [3]. GTg(℃) <SVst(℃)≦STm(℃)<130(℃) ···(1) [5] The packaging according to [4], wherein the adhesion work of the film surface of the multilayer film, as measured by the following method, is 0.60 mJ or more and less than 2.10 mJ. (Measurement of work done at close contact) Bottom area 25cm 2 Two cylindrical aluminum jigs, 55 mm high and weighing 400 g, were prepared, and a piece of filter paper the same shape as the bottom surface was attached to the bottom surface of each jig. The sample was placed over the jig, ensuring that no wrinkles formed on the bottom surface of the filter paper, and secured with a rubber band. The two jigs, each covered with a sample, were placed on top of each other with the sample-covered sides facing each other, and pressed together with a load of 500 g for 1 minute. Next, the amount of work required to separate the sample surfaces from each other perpendicular to each other (work of adhesion, unit: mJ) was measured at a speed of 5 mm / min using a tensile and compression testing machine (Shimadzu AG-IS 5KN MS type). The measurement was performed in an atmosphere of 23°C and 50% RH. [6] The packaging according to [4] or [5], wherein the tensile elongation at break in the TD direction of the multilayer film, as measured in accordance with ASTM-D882, is 150-400%. [7] The oxygen permeability of the aforementioned multilayer film at 23°C and 65%RH, measured in accordance with JIS K7126-1, is 20 cm 3 20 μm / m 2 The packaging described in any of [4] to [6] is 24 hours or less at ATM. [8] The packaging according to any one of [4] to [7], wherein the thermal shrinkage rate in the MD direction and the TD direction of the multilayer film after being left standing at 80°C for 30 minutes is 10% or more in both directions. [Effects of the Invention]

[0006] Because the packaging of the present invention has the above configuration, it has excellent gas barrier properties and airtightness, and can extend the freshness preservation period. [Brief explanation of the drawing]

[0007] [Figure 1A] This diagram shows an example of the overlap packaging process. [Figure 1B] This figure shows the bottom side of a package manufactured using the method shown in Figure 1A. [Figure 2A] This diagram shows an example of the overlap packaging process. [Figure 2B] This figure shows the bottom side of the packaging manufactured using the method in Figure 2A. [Figure 3A] This is a cross-sectional view of XX in Figure 1B. [Figure 3B] Figure 1B is a cross-sectional view of the YY direction. [Modes for carrying out the invention]

[0008] The embodiments for carrying out the present invention (hereinafter referred to as "this embodiment") will be described in detail below. The present invention is not limited to the following embodiments, and can be implemented in various modifications within the scope of its gist.

[0009] [Packaging] The packaging of this embodiment is a packaging in which the contents are wrapped in a multilayer film including a gas barrier layer containing a gas barrier resin, wherein the outermost and innermost layers of the multilayer film contain a thermoplastic resin with a melting point of 130°C or lower, the multilayer film is folded at least on the bottom side of the contents, and on the bottom side of the contents, there is a portion where the innermost layers are welded together and a portion where the outermost layers are welded together, and the indentation load measured by the following method is 3 to 10 N. (Method for measuring indentation load) To measure the indentation load, the multilayer film was first peeled off the packaging and stretched and fixed onto a 125 x 125 x 50 mm frame. Then, using a tensile and compression testing machine (Shimadzu Corporation AG-IS), a 15φ matte stainless steel indentation rod was pressed perpendicularly against the film surface of the packaging at a speed of 1000 mm / min and an indentation depth of 15 mm. The load at a depth of 15 mm was measured (unit: N). Three measurements were taken, and the average value was used as the measured value. The measurements were performed in an atmosphere of 23°C and 50% RH.

[0010] The above-mentioned indentation load is preferably 3 to 10 N, more preferably 4 to 9 N, and even more preferably 5 to 8 N, from the viewpoint of providing superior tear resistance and airtightness, and extending the freshness preservation period. When the indentation load is within the above range, the raised packaging can conform to bulky contents, and a packaging with excellent airtightness and appearance can be obtained without causing tearing of the film or deformation of the tray.

[0011] (Contents) The contents described above preferably include a tray, on which ingredients such as beef, pork, chicken, fresh fish, fish fillets, fruits and vegetables may be placed. Furthermore, from the viewpoint of extending the freshness retention period, the above contents preferably contain freshness-preserving agents such as oxygen absorbers, CO2 generators, ethanol vaporizers, ethylene gas absorbers, and desiccants, and more preferably contain oxygen absorbers and / or CO2 generators. The shape of the tray is not particularly limited, and examples include a roughly polygonal shape such as a roughly square or a roughly circular shape in plan view. The tray may be in the shape of a plate, or it may have walls on the sides and bottom and an open top. The material of the tray is not particularly limited, and may be resin, wood, metal, glass, etc.

[0012] The contents described above may be "overflowing items" where the contents of the tray protrude from the top edge of the tray's height. In this specification, a package containing overflowing items wrapped in a multilayer film may be referred to as an "overflowing package." The raised portion described above preferably has an overhang of more than 0% but less than 50% of the tray's height, and more preferably 0.1 to 20%.

[0013] (Multilayer film) The above multilayer film contains, in the thickness direction, a skin layer, an adhesive layer, a gas barrier layer, an adhesive layer, and another skin layer in this order, with the skin layer being the innermost and outermost layer, and the skin layer containing 80% by weight or more of thermoplastic resin relative to 100% by mass of the skin layer, and the Vicat softening point (SVst) and melting point (STm) of the thermoplastic resin and the glass transition point (GTg) of the resin contained in the gas barrier layer satisfy the following relationship (1), and in an adhesive strength measurement evaluating the adhesive strength to a 5 mm diameter stainless steel cylindrical probe using a probe tack tester TAC-II (manufactured by Resca Co., Ltd.) under the conditions of an insertion speed of 120 mm / min, an applied pressure of 600 gf, an applied pressure time of 1 second, a release speed of 600 mm / min, and a temperature of 100 degrees, it is preferable that the adhesive strength of the film surface is 90 gf or more. GTg(℃) <SVst(℃)≦STm(℃)<130(℃) ···(1)

[0014] The above multilayer film may further include other layers. Examples of these other layers include an intermediate layer provided between the skin layer and the adhesive layer. The above multilayer film is preferably a film with 5 to 7 layers, for example, 7 layers of skin layer / intermediate layer / adhesive layer / gas barrier layer / adhesive layer / intermediate layer / skin layer, or 6 layers of skin layer / intermediate layer / adhesive layer / gas barrier layer / adhesive layer / skin layer, or 5 layers of skin layer / adhesive layer / gas barrier layer / adhesive layer / skin layer. Among these, 5 layers are preferred from the viewpoint of stretch moldability.

[0015] In the above multilayer film, it is preferable that both the outermost layer, which includes one surface, and the innermost layer, which includes the other surface, are skin layers. The composition and properties of the two skin layers in the above multilayer film may be the same or different. Similarly, the composition and properties of the two adhesive layers may be the same or different.

[0016] -Characteristics of multilayer films- The characteristics of the above-mentioned multilayer film will be explained below.

[0017] The above multilayer film is preferably made with high adhesive strength from the viewpoint of airtightness and freshness preservation period. The above multilayer film preferably has an adhesive strength of 90 gf or more on the film surface (e.g., the skin layer surface) as measured by the following method, more preferably 90 to 500 gf, and even more preferably 200 to 450 gf. The adhesive strength of the film surface can be adjusted by the composition of the skin layer (for example, mixing polyethylene resin and terpene resin, or mixing ethylene vinyl acetate copolymer as a thermoplastic resin), the thickness of the skin layer, etc. (Method for measuring adhesive strength) The adhesive strength to a 5 mm diameter stainless steel cylindrical probe was evaluated using a probe tack tester TAC-II (manufactured by Resca Co., Ltd.) under the following conditions: insertion speed 120 mm / min, applied pressure 600 gf, applied pressure time 1 second, release speed 600 mm / min, and temperature 100 degrees Celsius. More specifically, the measurement can be performed by the method described in the examples below.

[0018] From the viewpoint of airtightness and freshness retention period, the above multilayer film preferably has an adhesion work of 0.60 mJ or more and less than 2.10 mJ, more preferably 0.65 to 1.50 mJ, and even more preferably 0.70 to 1.40 mJ, at the time of measurement of the film surface (e.g., skin layer surface) as measured by the method described below. The amount of adhesion work on the film surface can be adjusted by the composition and thickness of the skin layer, etc. (Method for measuring the amount of work done by contact) Bottom area 25cm 2Prepare two cylindrical jigs made of aluminum with a height of 55 mm and a weight of 400 g, and attach filter paper of the same shape as the bottom surface to the bottom surface of each jig. Cover the sample on the bottom surface of the jig with the filter paper attached so that no wrinkles are formed, and hold it down with an O-ring to fix it. Overlap the two jigs with the sample covered so that the surfaces on the side with the sample are overlapped, and press-bond them with a load of 500 g for 1 minute. Next, using a tensile-compression testing machine (AG-IS 5KN MS type manufactured by Shimadzu Corporation), measure the amount of work required (adhesion work amount, unit: mJ) when peeling the sample surfaces from each other in a direction perpendicular to the surface at a speed of 5 mm / min. The measurement was performed in an atmosphere of 23°C and 50% RH. More specifically, it can be measured by the method described in the examples below.

[0019] From the viewpoint that the multilayer film becomes less likely to break in one layer during packaging, enables continuous packaging at high speed, and improves productivity, the tensile break elongation in the TD direction measured in accordance with ASTM-D882 is preferably 150 to 400%, more preferably 170 to 400%, and even more preferably 190 to 400%. The above-mentioned tensile break elongation in the TD direction can be adjusted, for example, by the composition of each layer of the film, the thickness ratio of each layer of the film, the draw ratio, heat treatment or annealing after stretching, and the like. The above-mentioned tensile break elongation can be measured by the method described in the examples below.

[0020] The above-mentioned multilayer film preferably has gas barrier properties and water vapor barrier properties. As the above-mentioned gas barrier properties, the oxygen permeability described below is 20.0 cm 3 ·20 μm / m 2 · atm for 24 h or less, the nitrogen gas permeability described below is 1.5 cm 3 ·20 μm / m 2 · atm for 24 h or less, and the carbon dioxide gas permeability described below is 51.0 cm 3 ·20 μm / m 2 It is preferable to satisfy at least one selected from the group consisting of · atm for 24 h or less, and more preferably to satisfy all of them. The oxygen permeability, nitrogen gas permeability, and carbon dioxide gas permeability can be measured by the method described in the examples below. The above-mentioned water vapor barrier properties include a water vapor permeability of 60 g / m², as described later. 2 It is preferable that the water vapor permeability is less than or equal to 1 day. The water vapor permeability can be measured by the method described in the examples below.

[0021] The above multilayer film, from the perspective of extending the freshness retention period, has an oxygen permeability of 20 cm at 23°C and 65% RH, as measured in accordance with JIS K7126-1. 3 20 μm / m 2 The humidity is preferably 24h·atm or less, and more preferably 3-19cm². 3 20 μm / m 2 24 hours atm, more preferably 5-18 cm 3 20 μm / m 2 It is a 24-hour ATM. The nitrogen gas permeability of the multilayer film of this embodiment at 23°C and 65% RH is set to 1.6 cm² from the viewpoint of further extending the freshness preservation period. 3 20 μm / m 2 Preferably, the humidity is 24 hours atm or less, and more preferably 1.5 cm 3 20 μm / m 2 • 24-hour ATM or less. The carbon dioxide permeability of the multilayer film of this embodiment at 23°C and 65% RH is 52.0 cm², from the viewpoint of further extending the freshness preservation period. 3 20 μm / m 2 The humidity is preferably 24h·atm or less, and more preferably 51.0cm². 3 20 μm / m 2 • 24-hour ATM or less. The above-mentioned oxygen permeability, nitrogen permeability, and carbon dioxide permeability can be adjusted, for example, by the composition of the gas barrier layer, the thickness of the gas barrier layer, and the resin of the gas barrier layer.

[0022] From the viewpoint of preventing deterioration, wrinkles, and sagging of the packaged material, the above multilayer film preferably has a thermal shrinkage rate in the MD direction of 10% or more after being left to stand at 80°C for 30 minutes, more preferably 20-40%, and even more preferably 25-40%. Furthermore, the thermal shrinkage rate in the TD direction after standing at 80°C for 30 minutes is preferably 10% or more, more preferably 20-40%, and even more preferably 25-40%. The thermal shrinkage rate in the MD direction and the thermal shrinkage rate in the TD direction may be the same or different. The thermal shrinkage rate in the MD direction can be adjusted, for example, by the composition of each layer of the film, the thickness ratio of each layer of the film, the stretching ratio, heat treatment or annealing after stretching, etc. Similarly, the thermal shrinkage rate in the TD direction can be adjusted, for example, by the composition of each layer of the film, the thickness ratio of each layer of the film, the stretching ratio, heat treatment or annealing after stretching, etc.

[0023] The total thickness of the above multilayer film is preferably 7 to 30 μm, more preferably 8 to 20 μm, and even more preferably 9 to 15 μm, from the viewpoint of stretchability and cost. The thickness ratio of each skin layer in the above multilayer film is preferably 10-25%, more preferably 10-20%, and even more preferably 10-15%, relative to 100% of the total thickness of the skin layer, adhesive layer, gas barrier layer, adhesive layer, and skin layer, from the viewpoint of adhesion, bonding, and stretchability of the film surface. The two skin layers may be of the same thickness or of different thicknesses. The thickness ratio of each adhesive layer in the above multilayer film is preferably 15-45%, more preferably 20-40%, and even more preferably 30-35%, relative to 100% of the total thickness of the skin layer, adhesive layer, gas barrier layer, adhesive layer, and skin layer, from the viewpoint of adhesive strength with adjacent layers. The two adhesive layers may be of the same thickness or different thicknesses. The thickness ratio of the gas barrier layer in the above multilayer film is preferably 5 to 15%, more preferably 6 to 12%, and even more preferably 8 to 10%, relative to 100% of the total thickness of the skin layer, adhesive layer, gas barrier layer, adhesive layer, and skin layer, from the viewpoint of freshness retention period, gas barrier properties, stretchability, cost, etc. From the viewpoint of stretchability, the ratio of the total thickness of the skin layer, adhesive layer, gas barrier layer, adhesive layer, and skin layer to the total thickness of the above multilayer film (100%) is preferably 50% or more, and more preferably 70% or more.

[0024] The following describes each layer of the multilayer film mentioned above.

[0025] -Skin layer- In the above-described multilayer film, it is preferable that each of the two skin layers satisfies one or all of the following requirements.

[0026] The above skin layer preferably contains 80% by mass or more of thermoplastic resin per 100% by mass of the skin layer, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass. Furthermore, the above skin layer preferably contains only the above thermoplastic resin as the resin component, and the above skin layer may be a layer consisting only of thermoplastic resin. The thermoplastic resin contained in the above-mentioned skin layer may be one type or multiple types. If multiple thermoplastic resins are included, it is preferable that their total mass satisfies the above requirements.

[0027] The above-mentioned skin layer may be a layer that imparts heat-sealability to the above-mentioned multilayer film. From the viewpoint of heat-sealability, it is preferable that the above-mentioned skin layer does not contain a thermoplastic resin with a melting point exceeding 130°C.

[0028] The above thermoplastic resin preferably includes a polyethylene-based resin containing structural units derived from ethylene, and more preferably consists solely of a polyethylene-based resin. Examples of the above polyethylene-based resin include ethylene homopolymers, ethylene-α-olefin copolymers, and ethylene-vinyl acetate copolymers. The above thermoplastic resin may be used alone or in combination of two or more types.

[0029] Examples of the polyethylene resins mentioned above include high-density polyethylene, medium-density polyethylene, low-density polyethylene (LDPE) (preferably linear low-density polyethylene (LLDPE)), and ultra-low-density polyethylene. Examples of ultra-low-density polyethylene include linear ultra-low-density polyethylene (referred to as "VLDPE" or "ULDPE"). Here, polyethylene resins can be classified by density according to JIS K6922. Specifically, those with a density of 942 kg / m³ 3 The above material is called high-density polyethylene, and its density is 930 kg / m³. 3 More than 942kg / m 3 Polyethylene with a density of less than 910 kg / m³ is called medium-density polyethylene. 3 More than 930kg / m 3 Polyethylene with a density of less than 910 kg / m³ is called low-density polyethylene. 3 Polyethylene with a density of less than 100% is called ultra-low density polyethylene.

[0030] Ethylene-α-olefin copolymer (polyolefin plastomer) refers to a copolymer of ethylene and α-olefin. Examples of the above α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. As the ethylene-α-olefin copolymer mentioned above, copolymers of ethylene and at least one comonomer selected from propylene comonomer, butene comonomer, hexene comonomer, and octen comonomer are generally readily available and can be suitably used.

[0031] The above-mentioned ethylene-α-olefin copolymer is preferably a soft copolymer in which the proportion of α-olefin in the total monomers constituting the copolymer (based on the starting monomer) is 5% by mass or more and 30% by mass or less.

[0032] As for the ethylene-vinyl acetate copolymer, from the viewpoint of film adhesion, bonding, heat sealability, flexibility, and slipperiness, the mass ratio of constituent units derived from vinyl acetate to 100% by mass of total monomer units is preferably 3 to 25% by mass, and more preferably 5 to 20% by mass.

[0033] Polyethylene resins may be polymerized using known catalysts such as single-site catalysts or multi-site catalysts, and from the viewpoint of obtaining even better transparency, strength, and heat sealability of the film, polymerization using a single-site catalyst is preferable.

[0034] Polyethylene resins have a density of 860 kg / m³, which improves heat sealability at low temperatures. 3 More than 925kg / m 3 Preferably, it is 870 kg / m 3 More than 920kg / m 3 More preferably, it is 875 kg / m 3 More than 910kg / m 3 The following is even more preferable: The lower the density of the polyethylene resin, the better the heat sealability at low temperatures tends to be, and a density of 925 kg / m³ is preferable. 3 The following conditions tend to improve heat sealability:

[0035] As for polyethylene-based resins, polyethylene-based resins in which the crystalline / amorphous structure (morphology) is controlled at the nano-order can also be used.

[0036] The thermoplastic resin is preferably a copolymer of multiple types of ethylene-α-olefins or a copolymer of one type of ethylene-vinyl acetate.

[0037] The melt flow rate (MFR) of the above thermoplastic resin is preferably 1 to 20 g / 10 min, more preferably 1.5 to 10 g / 10 min, and even more preferably 2 to 8 g / 10 min, from the viewpoint of heat sealability and film strength. The melt flow rate described above can be measured by the method described in the examples below. It is preferable that at least one of the thermoplastic resins contained in the skin layer satisfies the MFR, and more preferably that all of them satisfy the MFR.

[0038] The melting point (Tm) of the above thermoplastic resin is preferably 65°C or higher and less than 130°C, more preferably 70 to 125°C, and even more preferably 75 to 120°C, from the viewpoint of heat sealability at low temperatures and stretch moldability. The above melting point can be measured by the method described in the examples below. It is preferable that at least one of the thermoplastic resins contained in the skin layer satisfies the melting point, and it is more preferable that all of them satisfy the melting point.

[0039] The Vicat softening point of the above thermoplastic resin is preferably 40 to 120°C, more preferably 50 to 110°C, and even more preferably 55 to 100°C, from the viewpoint of film adhesion and stretch moldability. The Vicat softening point described above can be measured by the method described in the examples below. Preferably, at least one of the thermoplastic resins contained in the skin layer satisfies the Vicat softening point, and more preferably, all of them satisfy the Vicat softening point.

[0040] The above-mentioned skin layer may contain additives other than the above-mentioned thermoplastic resin. Examples of the above-mentioned additives include various surfactants, tackifying resins, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, UV absorbers, colorants, and inorganic fillers. These additives may be used individually or in combination of two or more types.

[0041] The total mass ratio of the above additives to 100% by mass of the above skin layer is preferably 0.1 to 30% by mass, more preferably 1.0 to 25% by mass, and even more preferably 5.0 to 20% by mass, from the viewpoint of heat sealability, anti-fogging properties and slipperiness of the film.

[0042] As the surfactant mentioned above, a glycerin-based fatty acid ester can be added to impart anti-fogging properties to the shrink film. From the viewpoint of the anti-fogging properties and slipperiness of the film, the mass percentage of the glycerin-based fatty acid ester is preferably 0.1 to 5.0% by mass relative to 100% by mass of the skin layer. Examples of glycerin-based fatty acid esters include monoglycerin fatty acid esters, diglycerin fatty acid esters, triglycerin fatty acid esters, and polyglycerin fatty acid esters of glycerin, and examples of monoglycerin esters, diglycerin esters, triglycerin esters, and tetraglycerin esters of saturated or unsaturated fatty acids having 8 to 18 carbon atoms. Among these, diglycerin oleate, diglycerin laurate, glycerin stearate, glycerin monooleate, or mixtures thereof are preferred from the viewpoint of excellent anti-fogging properties. One of the above surfactants may be used alone, or two or more may be used in combination.

[0043] Examples of the tackifying resins mentioned above include rosins such as gum rosin, tall oil rosin, and wood rosin; modified rosins such as hydrogenated rosin, disproportionated rosin, and polymerized rosin; rosin-based resins such as rosin esters such as glycerin esters and pentaerythritol esters of these rosins and modified rosins; terpene-based resins such as terpene resins mainly composed of α-pinene, β-pinene, and dipentene, aromatically modified terpene resins, hydrogenated terpene resins, and terpene phenol resins; synthetic resins such as (hydrogenated) aliphatic (C5) petroleum resins, (hydrogenated) aromatic (C9) petroleum resins, (hydrogenated) copolymer (C5 / C9) petroleum resins, (hydrogenated) dicyclopentadiene petroleum resins, and alicyclic saturated hydrocarbon resins; and among these, terpene-based resins are preferred from the viewpoint of excellent adhesion, heat sealability at low temperatures, and film transparency. The mass ratio of the tackifying resin to 100% by mass of the skin layer is preferably 0.1 to 10% by mass, and more preferably 0.5 to 7.0% by mass, from the viewpoint of film adhesion, bonding, blocking properties, etc. The above-mentioned tackifying resin is preferably used together with ethylene-α-olefin copolymer or ethylene-vinyl acetate copolymer.

[0044] -Adhesive layer- In the above-described multilayer film, it is preferable that both of the adhesive layers satisfy any or all of the following requirements. The adhesive layer is preferably provided adjacent to the gas barrier layer.

[0045] The above adhesive layer may contain at least a resin and may further contain additives. The above adhesive layer may also consist of a layer made of resin alone. Examples of the above-mentioned resins include thermoplastic resins. Examples of the above-mentioned thermoplastic resins include acid-modified olefin resins, modified olefin resins such as modified LLDPE, etc.

[0046] Examples of the acid-modified olefin resins mentioned above include polyolefins modified with carboxylic acids (including carboxylic anhydrides). The acid-modified olefin resin may be either a homopolymer or a copolymer, and it is preferable that it has repeating units derived from ethylene and / or α-olefin. Examples of the α-olefin include one selected from the group consisting of propylene, 1-butene, and 1-octene. The olefin structures constituting the above acid-modified olefin resins include, for example, homopolymers (homopolymers) such as polyethylene, polypropylene, polybutene, and polyoctene; ethylene-propylene copolymer; ethylene-1-butene copolymer; propylene-1-butene copolymer; propylene-1-hexene copolymer; propylene-4-methyl-1-pentene copolymer; propylene-1-octene copolymer; propylene-1-decene copolymer; propylene-1,4-hexadiene copolymer; propylene-dicyclopentadiene copolymer; propylene-5-ethylidene-2-norbornene copolymer; propylene-2,5-norbornadiene copolymer; propylene-5-ethylidene-2-norbornene copolymer; 1-octene-ethylene copolymer; and 1-butene-propylene copolymer. Two-component copolymers such as propylene copolymer, 1-butene·1-hexene copolymer, 1-butene·4-methyl-1-pentene copolymer, 1-butene·1-octene copolymer, 1-butene·1-decene copolymer, 1-butene·1,4-hexadiene copolymer, 1-butene·dicyclopentadiene copolymer, 1-butene·5-ethylidene-2-norbornene copolymer, 1-butene·2,5-norbornadiene copolymer, 1-butene·5-ethylidene-2-norbornene copolymer, ethylene·propylene·1-butene copolymer, ethylene·propylene·1-hexene copolymer, ethylene·propylene·1-octene copolymer, ethylene·propylene·1,4-hexadiene copolymer, ethylene·propylene·1,4-Hexadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-5-ethlylidene-2-norbornene copolymer, ethylene-propylene-5-ethlylidene-2-norbornene copolymer, ethylene-propylene-2,5-norbornadiene copolymer, ethylene-propylene-2,5-norbornadiene copolymer, ethylene-propylene-5-ethlylidene-2-norbornene copolymer, ethylene-propylene-5-ethlylidene-2-norbornene copolymer, 1-butene-ethylene-propylene copolymer, 1-butene-ethylene-1-hexene copolymer, 1-butene-ethylene-1-octene copolymer, 1-butene-propylene Examples include multi-component copolymers such as 1-octene copolymer, 1-butene-ethylene-1,4-hexadiene copolymer, 1-butene-propylene-1,4-hexadiene copolymer, 1-butene-ethylene-dicyclopentadiene copolymer, 1-butene-propylene-dicyclopentadiene copolymer, 1-butene-ethylene-5-ethylidene-2-norbornene copolymer, 1-butene-propylene-5-ethylidene-2-norbornene copolymer, 1-butene-ethylene-2,5-norbornadiene copolymer, 1-butene-propylene-2,5-norbornadiene copolymer, 1-butene-ethylene-5-ethylidene-2-norbornene copolymer, and 1-butene-propylene-5-ethylidene-2-norbornene copolymer. Of these, it is preferable to use ethylene-α-olefin copolymers such as polypropylene and ethylene-propylene copolymer.

[0047] In acid-modified olefin resins, the content of the acid-modifying component is preferably 1% to 10% by mass, preferably 1% to 8% by mass, and more preferably 2% to 7% by mass, from the viewpoint of adhesion between the adhesive layer and the adjacent layer. Examples of acid-modifying components include unsaturated carboxylic acids. Specifically, examples include maleic acid, fumaric acid, acrylic acid, crotonic acid, methacrylic acid, itaconic acid, or acid anhydrides of these acids. Of these, maleic anhydride, maleic acid, and acrylic acid are preferred. Acid-modified olefin resins are preferably polyolefins modified with maleic anhydride, and particularly preferably maleic anhydride-modified polyethylene.

[0048] Acid-modified olefin resins may be produced by conventional methods, for example, by graft polymerization of an unsaturated carboxylic acid onto the above-mentioned polyolefin under conventional conditions, such as stirring under heating, or commercially available products may be used. Examples include polymers obtained by grafting maleic anhydride onto LDPE, HDPE, LLDPE, PS, or PP.

[0049] The adhesive layer may contain an olefin resin (for example, an unmodified olefin resin) in addition to the modified olefin resin. The olefin resin is a homopolymer of olefins and / or a copolymer using olefins as monomers.

[0050] Examples of olefins (olefin monomers) that constitute olefin resins include ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Examples of ethylene-based polymers include ethylene homopolymers (polyethylene) and copolymers of ethylene with other monomers (ethylene copolymers). Examples of ethylene copolymers include ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-1-pentene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, and ethylene-4-methyl-1-pentene copolymer.

[0051] The melt flow rate (MFR) of the resin contained in the adhesive layer is preferably 1 to 20 g / 10 min, more preferably 1.5 to 10 g / 10 min, and even more preferably 2 to 8 g / 10 min, from the viewpoint of adhesive strength with adjacent layers and stretch moldability. The melt flow rate described above can be measured by the method described in the examples below. It is preferable that at least one of the resins contained in the adhesive layer satisfies the MFR, and more preferably that all of them satisfy the MFR.

[0052] The melting point (Tm) of the resin contained in the adhesive layer is preferably 70 to 190°C, more preferably 75 to 180°C, and even more preferably 80 to 170°C, from the viewpoint of adhesive strength with adjacent layers and extrusion moldability. The above melting point can be measured by the method described in the examples below. It is preferable that at least one of the resins contained in the adhesive layer satisfies the melting point, and it is more preferable that all of them satisfy the melting point.

[0053] The Vicat softening point of the resin contained in the adhesive layer is preferably 40 to 120°C, more preferably 50 to 110°C, and even more preferably 55 to 100°C, from the viewpoint of adhesive strength with adjacent layers and stretch moldability. The Vicat softening point described above can be measured by the method described in the examples below. Preferably, at least one of the resins contained in the adhesive layer satisfies the Vicat softening point, and more preferably, all of them satisfy the Vicat softening point.

[0054] The above adhesive layer preferably contains few components other than resin. Other components in the adhesive layer include additives such as various surfactants, tackifying resins, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, UV absorbers, colorants, and inorganic fillers. The mass ratio of components other than resin to 100% by mass of the above adhesive layer is preferably 5.0% by mass or less, and more preferably 1.0% by mass or less, from the viewpoint of adhesion to adjacent layers.

[0055] -Gas barrier layer- The above-mentioned gas barrier layer is a layer containing at least a resin, and may be a layer consisting solely of the above-mentioned resin. The layer containing the gas barrier resin in the above-mentioned multilayer film may be the above-mentioned gas barrier layer. Examples of the above-mentioned resins include ethylene-vinyl alcohol copolymer saponified (EVOH), polyamide resins, polyester resins, and polyvinylidene chloride resins. Among these, ethylene-vinyl alcohol copolymer saponified (EVOH) and polyamide resins are preferred, and ethylene-vinyl alcohol copolymer saponified (EVOH) is more preferred, from the viewpoint of having particularly excellent gas barrier properties and stretch moldability. The above resin may be of one type or a combination of multiple types.

[0056] The melting point of the above ethylene-vinyl alcohol copolymer saponified product is preferably 180°C or lower, more preferably 140 to 175°C, and even more preferably 150 to 170°C. If the melting point is 180°C or lower (preferably 170°C or lower), it exhibits excellent stretchability.

[0057] The above-mentioned ethylene-vinyl alcohol copolymer saponified material tends to have better stretchability as its crystallinity and melting point decrease as the content of structural units derived from ethylene (sometimes referred to as ethylene content in this specification) increases. Generally, the melting point is 183°C when the ethylene content is 32 mol%, 173°C when it is 38 mol%, and 163°C when it is 44 mol%. A preferred ethylene content is 30 mol% to 60 mol%, more preferably 31 mol% to 50 mol%, and even more preferably 32 mol% to 45 mol%. When the ethylene content is within the above range, a film with excellent stretchability and gas barrier properties can be obtained.

[0058] Generally, gas barrier performance tends to be better the greater the interaction between molecular chains, and ethylene-vinyl alcohol copolymer saponifies in particular have high gas barrier performance due to their large intermolecular interactions. On the other hand, because of the large intermolecular interactions, the thermal shrinkage stress is high, and when used as a shrinkable film, it is prone to deformation of the packaging container.

[0059] The above-mentioned ethylene-vinyl alcohol copolymer saponified material can achieve both a melting point of 180°C or lower (preferably 170°C or lower) and an ethylene content of 45 mol% or lower by controlling its crystal structure. Furthermore, by using an ethylene-vinyl alcohol copolymer saponified material with a larger supercooling temperature difference (the difference between the melting point and the cooling crystallization temperature) compared to general ethylene-vinyl alcohol copolymer saponified materials, the lamellar thickness becomes smaller and the crystals become more uniform. In the case of a gas barrier layer containing such an ethylene-vinyl alcohol copolymer saponified material, stress concentration is reduced, and container deformation during gas pack packaging can be suppressed. The above-mentioned supercooling temperature difference is preferably 25°C or higher, more preferably 26°C or higher, and even more preferably 27°C or higher.

[0060] The reason for the above effects is not entirely clear, but it is thought to be as follows: The thermal shrinkage characteristics of a multilayer film occur when the amorphous region, which was stretched due to the molecular orientation of the constituent resins, relaxes and tries to return to an unoriented state, while the crystalline region plays a role in preventing the shrinkage of the amorphous region up to near the melting temperature. Generally, ethylene-vinyl alcohol copolymer saponifies have strong intermolecular interactions and high thermal shrinkage stress, so they tend to dominate the thermal shrinkage stress of the entire multilayer film. However, by controlling the crystal structure, it is thought that stress concentration due to the relaxation of orientation in the amorphous and crystalline regions can be suppressed, and a multilayer film with excellent barrier properties can be provided.

[0061] Examples of the above-mentioned polyamide resins include polyamide 6, polyamide 66, polyamide 610, polyamide 11, polyamide 12, polyamide 6 / 66, polyamide 6 / 12, polyamide 6 / 610, polyamide 6 / 66 / 12, polyamide 6 / 66 / 610, and polyamide 6 / 66 / 612.

[0062] The glass transition temperature of the resin contained in the gas barrier layer is preferably 40 to 80°C, more preferably 45 to 70°C, and even more preferably 50 to 60°C, from the viewpoint of stretch moldability. The above glass transition temperature can be measured by the method described in the examples below.

[0063] In the above multilayer film, it is preferable that the thermoplastic resin contained in the skin layer and the resin contained in the gas barrier layer satisfy the following relationship (1). By satisfying the following relationship (1), the freshness retention period is extended, it becomes less prone to tearing during packaging, and it has excellent airtightness. GTg(℃) <SVst(℃)≦STm(℃)<130(℃) ···(1) Here, if the skin layer contains multiple thermoplastic resins, the Vicat softening point (SVst) of the thermoplastic resin contained in the skin layer in equation (1) may be the lowest Vicat softening point among the thermoplastic resins contained in the skin layer. The same applies to the melting point of the thermoplastic resin contained in the skin layer and the glass transition point of the resin contained in the gas barrier layer. The above multilayer film is more preferably such that the thermoplastic resin contained in the skin layer and the resin contained in the gas barrier layer satisfy the following relation (2), and even more preferably such that they satisfy relation (3). GTg+5 <SVst≦STm<125 ···(2) GTg+10 <SVst≦STm<120 ···(3) It is preferable that both skin layers of the above multilayer film satisfy the above relation.

[0064] -Middle class- The intermediate layer is preferably provided between the skin layer and the adhesive layer. The intermediate layer contains at least a resin and may further contain additives. The intermediate layer may consist only of a resin. Examples of the resin include thermoplastic resins. Examples of thermoplastic resins include layers containing ethylene-α-olefin copolymers. The thermoplastic resin contained in the intermediate layer may be one type or more types.

[0065] -Manufacturing method- The method for manufacturing the above multilayer film is not particularly limited, but a preferred method includes a step of laminating a laminate (hereinafter sometimes referred to as "unstretched raw material") having at least a skin layer, an adhesive layer, a gas barrier layer, an adhesive layer, and a skin layer in this order in the thickness direction by co-extrusion and then heat-stretching it. The co-extrusion method will be described below.

[0066] In the co-extrusion method, unstretched raw material can be obtained by melt-extruding each material from a separate extruder, laminating them in a multi-layer die, and then rapidly cooling them after melt-co-extrusion. The method of melt-co-extrusion is not particularly limited, and examples include methods using multi-layer T-dies or multi-layer circular dies. Among these, the method using multi-layer circular dies is preferred. Using multi-layer circular dies is advantageous in terms of the required space and investment cost for equipment, is suitable for high-mix low-volume production, and makes it easier to obtain the desired thermal shrinkage rate.

[0067] For rapid cooling, water at a temperature of 60°C or lower is typically preferred as the refrigerant. This refrigerant can be used either in direct contact with the molten resin or indirectly as an internal refrigerant for the metal roll. When used as an internal refrigerant, other known substances such as oil can be used in addition to water, and in some cases, it can be used in combination with blowing cold air.

[0068] In the stretching process, it is preferable to heat the obtained unstretched raw material to a temperature above the softening temperature of the resin constituting the unstretched raw material, for example, and stretch it by 2.5 times or more in the MD (Machine Direction: longitudinal direction) and 2.5 times or more in the TD (Transverse Direction: transverse direction (width direction)).

[0069] The stretching ratio is appropriately selected according to the purpose, and if necessary, heat treatment (thermal relaxation treatment) can be performed after stretching. Thermal relaxation treatment relaxes the molecular orientation of the multilayer film, further suppressing dimensional changes during transportation and / or storage.

[0070] The stretching process can also be carried out by a direct inflation method, in which air or nitrogen is blown into the tube immediately after melt extrusion to perform stretching. A multilayer film with a predetermined thermal shrinkage rate can also be easily obtained by this method. However, in order to more reliably achieve an appropriate thermal shrinkage rate, a biaxial stretching method is preferred, and the tubular method (also called the double bubble method), in which the unstretched raw material obtained with the above-mentioned circular die is heated and biaxially stretched, is even more preferred. In other words, the above multilayer film is preferably a biaxially oriented multilayer film produced by the biaxial stretching tubular method.

[0071] The above manufacturing method may include a crosslinking step in which the resin is crosslinked before or after stretching.

[0072] When performing crosslinking treatment, it is preferable to perform the crosslinking treatment by energy ray irradiation before heating and stretching the resin. This increases the melt tension of the laminate during heat stretching, allowing for greater stability during stretching. Alternatively, the resin may be crosslinked by irradiating the stretched laminate with energy rays. Examples of energy rays that can be used include ionizing radiation such as ultraviolet rays, electron beams, X-rays, and gamma rays. Among these, electron beams are preferred.

[0073] The above multilayer film can be used, for example, as a packaging film for overlap packaging in which the skin layers are bonded together and then the bonded areas are sealed to the bottom surface with a heat-sealing plate. Examples of contents that can be packaged include fresh meat such as beef, pork, and chicken; fresh fish; fish fillets; Chinese side dishes such as dumplings and shumai; processed fish products such as kamaboko and oden; and fried foods such as karaage and tempura.

[0074] (Packaging form) In this embodiment, the packaging is such that the multilayer film is folded at least on the bottom side of the contents, and it is preferable that a fold exists in the multilayer film at least on the bottom side (Figures 1B, 2B, 3A, 3B). The packaging can be formed, for example, by a linear overlap packaging (Figure 1A) or a push-up overlap packaging (Figure 2A), with the linear overlap packaging being preferred. The folds described above may also be present on surfaces other than the bottom (for example, the sides). Preferably, the total length of the folds is longest on the bottom side of the packaging. Preferably, the folds are not present on the top surface of the contents. Here, "bottom surface" refers to the bottom surface of the contents. If a tray is used, it may refer to the bottom surface of the tray. If food or other items are packaged directly without a tray, it may refer to the vertically downward surface of the contents.

[0075] The packaging of this embodiment has a portion on the bottom side of the contents where the innermost layers are welded together and a portion where the outermost layers are welded together (Figures 3A, 3B). That is, a single multilayer film has a portion where the surfaces of the innermost layers are welded together and a portion where the surfaces of the outermost layers are welded together.

[0076] The areas where the innermost layers are welded together can be formed, for example, when the bottom of the contents is folded over and the bottom is sealed after being bonded together with the lower center roller during packaging (Figure 1A), or when the bottom of the contents is covered and heat-sealed after being pushed onto the multilayer film (Figure 2A). The portions where the innermost layers are welded together preferably exist continuously in one direction on the bottom side of the contents (Figures 1B, 3A, 3B), and more preferably exist continuously in two orthogonal directions (Figure 1B).

[0077] The areas where the outermost layers are welded together can be formed, for example, when folding the end face of the primary packaging towards the bottom of the contents to create a bottom seal (Figure 1A), or when heat-sealing the bottom of the contents after pushing them onto the multilayer film (Figure 2A). The areas where the innermost layers are welded together and the areas where the outermost layers are welded together may be formed simultaneously (Figure 2A) or at different times (Figure 1A). The portions where the outermost layers are welded together preferably exist continuously in one direction on the bottom side of the contents (Figures 1B, 3A, 3B), and more preferably exist continuously in two orthogonal directions (Figure 1B).

[0078] The above fold may be formed at the end of the portion where the innermost layers are welded together (Figures 1B, 3A, 3B).

[0079] It is preferable that the portion where the innermost layers are welded together and the portion where the outermost layers are welded together are adjacent to each other in the height direction of the contents (adjacent welded portion) exist on the bottom side of the contents (Figures 1B, 3A, 3B). It is preferable that the adjacent welded portion exists continuously in at least two directions on the bottom side of the contents, and preferably in two orthogonal directions (Figures 1B, 3A, 3B). For example, in Figure 1B, there is an adjacent portion where the innermost layers are welded together and the portion where the outermost layers are welded together in two orthogonal directions in the horizontal and vertical directions of the bottom of the packaging (Figures 1B, 3A, 3B).

[0080] At the bottom of the contents described above, there are areas where the multilayer film is folded or welded, resulting in overlapping layers of film. The area ratio of the overlapping portion of the multilayer film (i.e., the portion where two or more layers of multilayer film overlap in the height direction of the contents) to 100% of the bottom surface area of ​​the contents is preferably 30% or more, more preferably 50% or more and less than 100%, and even more preferably 70-95%, from the viewpoint of achieving superior airtightness.

[0081] (Packaging method) The packaging of this embodiment can be obtained, for example, by packaging the contents with a multilayer film. The above packaging includes overlap packaging, and overlap packaging using an overlap packaging machine is preferred. The above packaging may be carried out while gas replacement is performed, or after gas replacement has been performed.

[0082] The above overlap packaging is not particularly limited, but the following methods can be used. The innermost layers at both ends of a multilayer film (for example, the ends perpendicular to the flow direction of the multilayer film) are joined together to form a tube, and the contents are placed inside, with a center seal on the bottom side of the contents. Next, the front and back of the contents are cut perpendicular to the center seal, the cut front and back are folded towards the bottom side of the contents, the bottom side of the contents is heat-sealed, and the contents are heat-shrunk in a heat shrink tunnel (Figure 1A).

[0083] The temperature during bottom sealing may be 110-170°C. The temperature of the heat shrink tunnel may be 80-130°C. The packaging speed may be 40-80 pieces / minute.

[0084] Another example of the overlap packaging described above is the following method: The contents are pushed up from the bottom in the thickness direction of the multilayer film, the front and back of the contents are cut, and the multilayer film is folded into the bottom side of the film. At this time, folds are formed randomly, and there are places where the innermost layers face each other and the outermost layers face each other. Then, the bottom side of the contents is heat-sealed and heat-shrinked in a heat shrink tunnel (Figure 2A).

[0085] The temperature during bottom sealing may be 110-170°C. The temperature of the heat shrink tunnel may be 80-130°C. The packaging speed may be 20-40 pieces / minute.

[0086] Because the above multilayer film contains a thermoplastic resin with a melting point of 130°C or less in its outermost and innermost layers, even when the multilayer film is folded or welded together, the outermost and / or innermost layers are firmly welded together by heat sealing, improving airtightness. Improved airtightness reduces the leakage of odors and liquids from the contents. Furthermore, it reduces the leakage of gases within the packaging, allowing freshness to be preserved for a longer period.

[0087] From the viewpoint of maintaining freshness over a long period, it is preferable that the inside of the above-mentioned packaging, which is wrapped in a multilayer film, is replaced with nitrogen, oxygen, carbon dioxide, or a mixture thereof.

[0088] The above-mentioned packaging may be kept at any temperature, including frozen, refrigerated, or at room temperature. [Examples]

[0089] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0090] [evaluation] The melt flow rate, melting point, Vicat softening point of the constituent resins, as well as the adhesive strength, adhesion work, tensile elongation at break, oxygen permeability, thermal shrinkage rate, interlaminar peel strength, gas permeability, airtightness, tear resistance in packaging machines, and shelf life of the multilayer film were measured and evaluated using the following methods.

[0091] (Melt flow rate) This refers to the value measured under conditions of 230°C and 2.16 kg load, in accordance with JIS K7210 or ASTM D1238.

[0092] (Melting point / glass transition point) The melting point and glass transition temperature were measured using differential scanning calorimetry (DSC). 5 mg of resin was weighed, and to cancel the resin's thermal history, it was first heated at a rate of 10°C / min, followed by cooling at a rate of 10°C / min. Then, it was heated again at a rate of 10°C / min, and the resulting curve was used as the DSC curve. This DSC curve was analyzed according to the method compliant with JIS K7122 to obtain the melting point and glass transition temperature.

[0093] (Vicat softening point) Measurements were taken under a load of 50N in accordance with JIS K7206.

[0094] (Indentation load) To measure the indentation load, the multilayer film was first peeled from the packaging and stretched onto a 125 x 125 x 50 mm square frame with just enough force to avoid stretching and wrinkles, securing all four sides with tape. Then, using a tensile and compression testing machine (Shimadzu AG-IS), a 15φ matte stainless steel indentation rod was pressed perpendicularly against the film surface of the packaging at a speed of 1000 mm / min and an indentation depth of 15 mm. The load at a depth of 15 mm was measured (unit: N). Three measurements were taken, and the average value was used as the measured value. The measurements were performed in an atmosphere of 23°C and 50% RH.

[0095] (Tensile elongation at fracture) The tensile elongation at break was measured in accordance with ASTM-D882. Using a tensile testing machine, the sample was pulled in the TD direction at a speed of 200 mm / min, and the elongation (stretch) at which the sample broke (fractured) was determined. The tensile elongation was calculated using the following formula. Tensile elongation (%) = 100 × (L - L0) / L0 L0: Sample length before testing L: Sample length at fracture

[0096] (Adhesion strength of the film surface) The measuring device used was a probe tack tester TAC-II (manufactured by Resca Co., Ltd.). The sample was placed on a plate heated to 100°C and held there for 10 seconds. A 5mm diameter cylindrical SUS probe was also heated to 100°C, inserted into the sample at a speed of 120mm / min, and pressed with a pressure of 600gf for 1 second. The force when the probe was pulled away from the sample at a speed of 600mm / min was measured under conditions of 100°C, and the peak value was defined as the adhesive strength (gf) of the film surface. Measurements were performed 5 times on each film surface, and the average value of the total 10 points was used as the measured value.

[0097] (Workload) To measure the amount of work done in contact with the surface, first, the base area is 25 cm². 2Two cylindrical aluminum jigs, 55 mm high and weighing 400 g, were prepared, and filter paper of the same shape as the bottom surface was attached to the bottom surface of both jigs. The sample was placed over the bottom surfaces of the two jigs, ensuring that no wrinkles formed on the bottom surfaces, and secured with rubber bands. The two jigs with the sample on them were then placed together so that the surfaces with the sample on them were tightly overlapping, and pressed together with a load of 500 g for 1 minute. Next, the amount of work required to separate the two sample surfaces perpendicular to each other (work of adhesion) was measured at a speed of 5 mm / min using a tensile and compression testing machine (Shimadzu AG-IS 5KN MS type) (unit: mJ). This measurement was performed in an atmosphere of 23°C and 50% RH. The measurement was performed three times on each film surface, and the average value of the total of six points was used as the measurement value.

[0098] (transparency) Nitrogen gas permeability, carbon dioxide permeability, oxygen gas permeability, and water vapor permeability were evaluated using the following methods.

[0099] - Nitrogen gas permeability - Nitrogen gas permeability was measured in accordance with JIS K7126-1 (differential pressure method) under conditions of 23°C and 65% RH. The measuring equipment used was a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T-F], [GTR-30XAD, G6800T-F(S)] (manufactured by GTR Tech Co., Ltd. and Yanako Technical Science Co., Ltd.). The detector used was a gas chromatograph [thermal conductivity detector (TCD)]. The test conditions were set to a temperature of 23°C and a humidity of 65% RH, with partial pressures of 74.6 cmHg for gas and 1.4 cmHg for water vapor. The permeation area was 15.2 × 10⁻⁶. -4 m 2 (Transmission part diameter φ4.4×10 -2 Let m) be the number of tests, and n=1. <Evaluation Criteria for Nitrogen Gas Permeability> 〇(Good): 1.5cm 3 20 μm / m 2 ·24h · atm or less × (Inferior): 1.5cm 3 20 μm / m 2 ·24h·atm super

[0100] -Carbon dioxide permeability- Carbon dioxide permeability was measured under conditions of 23°C and 65%RH in accordance with JIS K7126-1 (differential pressure method). The measuring equipment used was a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T-F], [GTR-30XAD, G6800T-F(S)] (manufactured by GTR Tech Co., Ltd. and Yanako Technical Science Co., Ltd.). The detector used was a gas chromatograph [thermal conductivity detector (TCD)]. The test conditions were set to a temperature of 23°C and a humidity of 65% RH, with partial pressures of 74.6 cmHg for gas and 1.4 cmHg for water vapor. The permeation area was 15.2 × 10⁻⁶. -4 m 2 (Transmission part diameter φ4.4×10 -2 Let m) be the number of tests, and n=1. <Evaluation Criteria for Carbon Dioxide Permeability> 〇(Good): 51.0cm 3 20 μm / m 2 ·24h · atm or less × (Inferior): 51.0cm 3 20 μm / m 2 ·24h·atm super

[0101] -Oxygen gas permeability- Oxygen gas permeability was measured under conditions of 23°C and 65% RH in accordance with JIS K7126-1 (differential pressure method). The measuring equipment used was a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T-F], [GTR-30XAD, G6800T-F(S)] (manufactured by GTR Tech Co., Ltd. and Yanako Technical Science Co., Ltd.). The detector used was a gas chromatograph [thermal conductivity detector (TCD)]. The test conditions were set to a temperature of 23°C and a humidity of 65% RH, with partial pressures of 74.6 cmHg for gas and 1.4 cmHg for water vapor. The permeation area was 15.2 × 10⁻⁶. -4 m 2 (Transmission part diameter φ4.4×10 -2 Let m) be the number of tests, and n=1. <Evaluation Criteria for Oxygen Gas Permeability> 〇(Good): 20.0cm 320 μm / m 2 ·24h · atm or less × (Inferior): 20.0cm 3 20 μm / m 2 ·24h·atm super

[0102] -Water vapor permeability- Water vapor permeability was measured under conditions of 38°C and 90% RH, in accordance with ASTM F1249. The measuring device used was a PERMATRAN W-398 water vapor transmission rate analyzer [manufactured by MOCON]. The number of tests was set to n=1. <Evaluation Criteria for Water Vapor Permeability> 〇(Good): 60g / m 2 ·day or less × (Inferior): 60g / m 2 ·day super

[0103] (Heat shrinkage rate at 80°C) Multilayer film cut into 100mm x 100mm squares was left to stand in a constant temperature bath set to an ambient temperature of 80°C for 30 minutes, and the following formula was used to calculate the result. Thermal shrinkage rate (%) = 100 × (100 - W) / 100 W: Dimension of the film in the MD or TD direction after removal from the constant temperature bath.

[0104] (airtightness) Packaging was prepared using the STC-N2 overlap packaging machine manufactured by Omori Machinery Industry Co., Ltd. A 100g rubber sheet and the Everfresh CO-500 oxygen absorber / carbon dioxide generator were placed on a CN20-13F tray manufactured by Chuo Chemical Co., Ltd., using film slit to a width of 400mm. The packaging was then carried out at a speed of 50 packs / minute, with a bottom seal temperature of 150°C and a tunnel temperature of 100°C. After storing the packaging at room temperature for 2 hours, the oxygen and carbon dioxide concentrations inside the packaging were measured and evaluated according to the following criteria. The number of measurements was n=2. ○ (Good): Oxygen concentration 10% or less and carbon dioxide concentration 5% or more. × (Inferior): Oxygen concentration greater than 10% or carbon dioxide concentration less than 5%

[0105] (Storability) Packaging was prepared using the "STC-N2" overlap packaging machine manufactured by Omori Machinery Industry Co., Ltd. A 100g rubber sheet and the oxygen absorber / carbon dioxide generator "Everfresh CO-500" were placed on a "CN20-13F" tray manufactured by Chuo Chemical Co., Ltd., using film slit to a width of 400mm. The packaging was then carried out at a speed of 50 packs / minute, with a bottom seal temperature of 150°C and a tunnel temperature of 100°C. The oxygen and carbon dioxide concentrations inside the packaging were measured after 72 hours of storage at room temperature. The number of measurements was n=2. ○ (Good): Oxygen concentration 5% or less and carbon dioxide concentration 10% or more. × (Inferior): Oxygen concentration greater than 5% or carbon dioxide concentration less than 10%

[0106] (Welding of the innermost layers) The welding of the innermost layers was evaluated according to the following criteria based on the state when attempting to peel off one end of the multilayer film perpendicular to the center seal (either the ends in Figure 1B or Figure 2B) with a fingertip. ○ (Good): The innermost layers do not easily separate from each other, and attempting to forcibly separate them may leave white peeling marks on part of the film or cause the film to tear. × (Inferior): The innermost layers easily separate from each other.

[0107] (Welding of the outermost layers) The welding of the outermost layers was evaluated according to the following criteria based on the state when attempting to peel off the ends of the multilayer film perpendicular to the center seal (either the ends in Figure 1B or Figure 2B) with a fingertip. ○ (Good): The outermost layers do not easily separate from each other, and attempting to forcibly separate them may leave white peeling marks on part of the film or cause the film to tear. × (Inferior): The outermost layers easily separate from each other.

[0108] [Resin used] The resins used in the examples and comparative examples are as follows: • Ethylene-α-olefin copolymer LLDPE1: Ethylene-α-olefin copolymer (product name "Yumerit 0520F", manufactured by Ube Industries, Ltd., density 904 kg / m³)3 (MFR 2.0g / 10 min, melting point 118℃, Vicat softening point 82℃) LLDPE2: Ethylene-α-olefin copolymer (product name "SLH218", manufactured by Braskem, density 916 kg / m³) 3 (MFR 2.3g / 10 min, melting point 125℃, Vicat softening point 98℃) ·Adhesive resin PPGL1: Modified polypropylene polymer (product name "Admer QF500", manufactured by Mitsui Chemicals, Inc., density 901 kg / m³) 3 (MFR 3.0g / 10 min, melting point 165℃) PPGL2: Modified polypropylene polymer (product name "Admer QF580", manufactured by Mitsui Chemicals, Inc., density 896 kg / m³) 3 (MFR 7.7g / 10 min, melting point 140℃) PEGL1: Modified ethylene-α-olefin copolymer (product name "Admer NF587", manufactured by Mitsui Chemicals, Inc., density 907 kg / m³) 3 (MFR 2.3g / 10 min, melting point 120℃) PEGL2: Modified ethylene-α-olefin copolymer (product name "Admer NF307", manufactured by Mitsui Chemicals, Inc., density 922 kg / m³) 3 (MFR 1.3g / 10 min, melting point 120℃) • Ethylene-vinyl alcohol copolymer EVOH1: Ethylene-vinyl alcohol copolymer saponified (product name "G Soanol GH3804B", manufactured by Mitsubishi Chemical Corporation, MFR 4.0g / 10min, ethylene content 38mol%, melting point 160℃, glass transition point 55℃) EVOH2: Ethylene-vinyl alcohol copolymer saponified (product name "Soanol AT4403B", manufactured by Mitsubishi Chemical Corporation, MFR 3.5g / 10min, ethylene content 44mol%, melting point 164℃, glass transition point 55℃) ·polyamide NY1: Polyamide 6 / 66 copolymer (product name "UBE NYLON 5034B", manufactured by Ube Industries, Ltd., density 1140 kg / m³) 3 (Melting point 192°C, glass transition temperature 46°C) • Polyolefin plastomer POP1: Ethylene-1-octene copolymer (product name "Affinity PT1450G1", manufactured by Dow Chemical Japan Ltd., density 902 kg / m³) 3 (MFR 7.5g / 10 min, melting point 97℃, Vicat softening point 77℃) POP2: Ethylene-propylene copolymer (product name "Versify3200", manufactured by Dow Chemical Japan Ltd., density 876 kg / m³) 3 (MFR 8.0g / 10 min, melting point 81℃, Vicat softening point 59℃) • Ethylene-vinyl acetate copolymer EVA1: Ethylene-vinyl acetate copolymer (product name "UBE Polyethylene VF215C", manufactured by Ube Maruzen Polyethylene Co., Ltd., MFR 2.3g / 10min, melting point 90℃, vinyl acetate content = 15% by mass, Vicat softening point 68℃) EVA2: Ethylene-vinyl acetate copolymer (product name "UBE Polyethylene VF218G", manufactured by Ube Maruzen Polyethylene Co., Ltd., MFR 2.5g / 10min, melting point 86℃, vinyl acetate content = 18% by mass, Vicat softening point 63℃) ·polystyrene PS1: Polystyrene (Product name "PSJ Polystyrene HF77", manufactured by PS Japan Co., Ltd., density 1050 kg / m³) 3 (MFR 7.5g / 10min, glass transition temperature 100℃) ·polypropylene PP1: Ethylene-propylene copolymer (product name "Sun Allomer PC540R", manufactured by Sun Allomer Co., Ltd., density 900 kg / m³) 3 (MFR 5.3g / 10 min, melting point 132℃, Vicat softening point 120℃) • Adhesion-imparting resin TF1: Polyterpene resin (product name "YS Resin PX1000", manufactured by Yasuhara Chemical Co., Ltd., softening point 100℃) • Anti-fogging agent AF1: A mixture of diglycerin laurate and glycerin monooleate in a ratio of 1 / 2.

[0109] [Examples 1-8, Comparative Examples 1-4] Using the resins shown in Tables 1 and 2, a five-layer film was formed by the double-bubble inflation method. Subsequently, biaxial stretching was performed in the MD and TD directions at the stretching ratios shown in Tables 1 and 2 to obtain a stretched laminated film. The thickness of each layer is as shown in Tables 1 and 2. The stretch ratio in the MD direction was adjusted by the speed ratio of the pinch rolls between the bubbles, and the stretch ratio in the TD direction was adjusted by the volume of air sealed in the bubbles. Here, the MD direction refers to the longitudinal direction (flow direction) when the laminated film is extruded. On the other hand, the TD direction refers to the width direction (lateral direction) when the laminated film is extruded.

[0110] [Table 1]

[0111] [Table 2] [Explanation of Symbols]

[0112] 1 Multilayer film 2 Contents

Claims

1. A package in which the contents are wrapped in a multilayer film containing a gas barrier layer containing a gas barrier resin, The outermost and innermost layers of the multilayer film contain a thermoplastic resin with a melting point of 130°C or lower. At least on the bottom side of the contents, the multilayer film is folded, The bottom surface of the contents has a portion where the innermost layers are welded together and a portion where the outermost layers are welded together. The indentation load measured by the following method is between 3 and 10 N. The multilayer film comprises, in the thickness direction, a skin layer, an adhesive layer, a gas barrier layer, an adhesive layer, and a skin layer in this order. The aforementioned skin layer is the innermost layer and the outermost layer, The skin layer contains 80% by weight or more of thermoplastic resin based on 100% by mass of the skin layer. The Vicat softening point (SVst) and melting point (STm) of the thermoplastic resin and the glass transition point (GTg) of the resin contained in the gas barrier layer satisfy the following relationship (1): In an adhesive strength measurement using a probe tack tester TAC-II (manufactured by Resca Co., Ltd.) to evaluate the adhesive strength to a 5 mm diameter stainless steel cylindrical probe under the conditions of an entry speed of 120 mm / min, applied pressure of 600 gf, pressurization time of 1 second, release speed of 600 mm / min, and temperature of 100 degrees Celsius, the adhesive strength of the film surface was 90 gf or higher. A packaging body characterized by the following features. GTg (℃) < SVst (℃) ≦ STm (℃) < 130 (℃) ... (1) (Method for measuring indentation load) To measure the indentation load, the multilayer film was first peeled off the packaging and stretched and fixed onto a 125 x 125 x 50 mm frame. Then, using a tensile and compression testing machine (Shimadzu Corporation AG-IS), a 15φ matte stainless steel indentation rod was pressed perpendicularly against the film surface of the packaging at a speed of 1000 mm / min and an indentation depth of 15 mm. The load at a depth of 15 mm was measured (unit: N). Three measurements were taken, and the average value was used as the measured value. The measurements were performed in an atmosphere of 23°C and 50% RH.

2. The packaging according to claim 1, wherein the multilayer film has gas barrier and water vapor barrier properties, and the interior wrapped by the multilayer film is replaced with nitrogen, oxygen, carbon dioxide, or a mixture thereof.

3. The contents are an oxygen absorber and / or CO ２ A packaging body according to claim 1 or 2, comprising a generating agent.

4. The packaging according to any one of claims 1 to 3, wherein the adhesion work of the film surface of the multilayer film, as measured by the following method, is 0.60 mJ or more and less than 2.10 mJ. (Measurement of work done in close contact) Bottom area 25cm ２ Two cylindrical aluminum jigs, 55 mm high and weighing 400 g, were prepared, and a piece of filter paper the same shape as the bottom surface was attached to the bottom surface of each jig. The sample was placed over the bottom surface of the jig, ensuring that no wrinkles formed, and secured with a rubber band. The two jigs, each covered with a sample, were placed on top of each other with the sample-covered sides facing each other, and pressed together with a load of 500 g for 1 minute. Next, the amount of work required to separate the sample surfaces from each other perpendicular to each other (work of adhesion, unit: mJ) was measured at a speed of 5 mm / min using a tensile and compression testing machine (Shimadzu Corporation AG-IS 5KN MS type). The measurement was performed in an atmosphere of 23°C and 50% RH.

5. The packaging according to any one of claims 1 to 4, wherein the tensile elongation at break in the TD direction of the multilayer film, as measured in accordance with ASTM-D882, is 150 to 400%.

6. The oxygen permeability of the aforementioned multilayer film at 23°C and 65% RH, measured in accordance with JIS K7126-1, is 20 cm². ３ 20 μm / m ２ A packaging body according to any one of claims 1 to 5, wherein the humidity is 24 h·atm or less.

7. The packaging according to any one of claims 1 to 6, wherein the thermal shrinkage rate in the MD direction and the TD direction of the multilayer film after being left standing at 80°C for 30 minutes is 10% or more in both directions.

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