Multilayer film and packaging

Abstract

To provide a multilayer film capable of suppressing the occurrence of blocking when it is wound into a roll and stored after being irradiated with an electron beam, and a package made using the multilayer film. [Solution] A multilayer film comprising an outer layer and a sealant layer, which has been irradiated with electron beams at an absorbed dose of 20 to 300 kGy, and in which the tack strength between the sealant layer and the outer layer measured under specified conditions is 9 N.

Description

[Technical Field]

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

[0002] A package in which the contents (packaged items) are placed on a hard tray and then sealed with a film by vacuuming is called a skin pack. In a skin pack, the film, i.e., the skin pack film, is transparent, allowing the contents to be easily seen through it. The skin pack film is also soft, and by vacuuming the storage section inside the skin pack, it can be made to adhere to the contents without causing wrinkles (see, for example, Patent Document 1). Furthermore, since skin packs are equipped with a hard tray (base material), they can be displayed upright without causing the contents to shift position. In view of these characteristics, skin packs are mainly used as packaging for food. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-222259 Summary of the Invention [Problem to be solved by the invention]

[0004] The multilayer film that makes up the skin pack exhibits high shrinkage when irradiated with an electron beam. When the multilayer film is irradiated with an electron beam, the molecular bonds in the resin are broken, generating radicals at the ends of the broken bonds. It is believed that the generated radicals react with other molecular chains to form new bonds, resulting in the formation of a crosslinked structure. This results in high shrinkage and improved conformability to the contents.

[0005] Normally, radicals are deactivated when exposed to oxygen. However, if a multilayer film is wound into a roll after electron beam irradiation and stored in a state where it is less likely to be exposed to oxygen, some of the radicals in the multilayer film remain without being deactivated, forming a crosslinked structure between the multilayer films that are in contact with each other, making blocking more likely to occur. If blocking occurs, a large force is required to unwind the multilayer film, which is undesirable. In some cases, the multilayer film may become impossible to unwind, or the multilayer film may tear if unwinding is attempted forcefully.

[0006] An object of the present invention is to provide a multilayer film that can suppress the occurrence of blocking when the film is rolled up and stored after electron beam irradiation, and a package made using the multilayer film. [Means for solving the problem]

[0007] [1] A multilayer film comprising an outer layer and a sealant layer, the multilayer film having been irradiated with an electron beam at an absorbed dose of 20 to 300 kGy, a circular piece having a planar shape of 10 mm in diameter was cut out from the multilayer film to serve as a first test piece, and the exposed surface of the sealant layer in the first test piece was attached to the circular flat surface of a cylindrical stainless steel probe having a diameter of 10 mm with the centers of the two aligned with each other using double-sided adhesive tape to prepare a test laminate, and a separately prepared multilayer film was used as a second test piece, and the test laminate was subjected to a temperature test at 25°C. a multilayer film in which the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece are arranged parallel to each other, the second test piece is fixed, the probe in the test laminate is moved toward the second test piece at a speed of 0.5 mm / sec, and after the entire exposed surface of the outer layer in the first test piece comes into contact with the exposed surface of the sealant layer in the second test piece, the probe is pressed toward the second test piece at a pressure of 24.517 N for 20 seconds, and then the probe is moved in the opposite direction from the second test piece at a speed of 10 mm / sec, the load measured when this is done is 9 N or less. [2] A multilayer film comprising an outer layer and a sealant layer, wherein the temperature at which the multilayer film exhibits a displacement of 2000 μm during thermomechanical analysis is 120°C or higher, or the gel fraction of the multilayer film is 30% or higher, a circular piece having a planar shape of 10 mm in diameter is cut out from the multilayer film to serve as a first test piece, and the exposed surface of the sealant layer in the first test piece is attached to the circular flat surface of a cylindrical stainless steel probe having a diameter of 10 mm with the centers of the two aligned with each other using double-sided adhesive tape to prepare a test laminate, and a separately prepared multilayer film is used as a second test piece, and the temperature is 2 A multilayer film in which, under a condition of 5°C, the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece of the test laminate are arranged parallel to and facing each other, the second test piece is fixed, and the probe in the test laminate is moved toward the second test piece at a speed of 0.5 mm / sec. After the entire exposed surface of the outer layer in the first test piece comes into contact with the exposed surface of the sealant layer in the second test piece, the probe is pressed toward the second test piece at a pressure of 24.517 N for 20 seconds, and then the probe is moved in the opposite direction from the second test piece at a speed of 10 mm / sec. The load measured when this is done is 9 N or less. [3] The multilayer film according to [1] or [2], wherein the outer layer contains an ethylene-based polymer, and the melting point of the ethylene-based polymer is 115°C or higher. [4] The multilayer film according to [1] or [2], wherein the outer layer has a storage modulus of 80 MPa or more at 30°C when measured by dynamic mechanical analysis (DMA) at a heating rate of 2°C / min and a frequency of 1 Hz. [5] The multilayer film according to [3], wherein the ethylene polymer is polyethylene or an ionomer. [6] The multilayer film according to any one of [1] to [5], wherein the sealant layer contains an ethylene-based polymer. [7] The multilayer film further comprises a functional layer adjacent to the sealant layer; The multilayer film according to any one of [1] to [6], wherein the functional layer contains an ethylene-based polymer. [8] The multilayer film according to any one of [1] to [7], wherein the ratio of the thickness of the sealant layer to the thickness of the multilayer film is 30% or less. [9] The multilayer film according to [2], wherein the displacement at a temperature of 100°C during the thermomechanical analysis is 500 μm or less.

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

[11] The multilayer film according to

[10] , wherein the oxygen barrier layer comprises an ethylene-vinyl alcohol copolymer.

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

[11] .

[13] . The packaging body described in

[12] , wherein the packaging body is a skin pack packaging body. [Effects of the Invention]

[0008] The present invention can provide a multilayer film that can suppress the occurrence of blocking when rolled up and stored after electron beam irradiation, and a package made using the multilayer film. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a multilayer film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the multilayer film of FIG. 1 wound into a roll. [Figure 3] 1 is a cross-sectional view schematically illustrating an example of a packaging body according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] <<Characteristics of multilayer film>> First Embodiment A multilayer film according to one embodiment of the present invention comprises an outer layer and a sealant layer. The multilayer film is not particularly limited as long as it satisfies the conditions of electron beam irradiation and tackiness between the sealant layer and the outer layer, which will be described later.

[0011] The multilayer film is irradiated with an electron beam (EB) at an absorbed dose of 20 to 300 kGy. The multilayer film is preferably irradiated with an EB at an absorbed dose of 20 to 250 kGy, and may be irradiated with an EB at an absorbed dose of 20 to 250 kGy, for example, at an absorbed dose of 20 to 250 kGy, 45 to 250 kGy, or 70 to 250 kGy. When the absorbed dose is within this range, it is easier to obtain a multilayer film in which, during thermomechanical analysis, the temperature at which the multilayer film shows a displacement of 2000 μm and the displacement at a temperature of 100°C are both within the numerical ranges described below. On the other hand, when the absorbed dose is equal to or greater than the lower limit, the crosslinking density of the multilayer film (particularly the outer layer and functional layer in this multilayer film) is further improved, resulting in improved heat resistance and melt tension of the multilayer film as a whole, and improved conformability to the contents. When the absorbed dose is equal to or less than the upper limit, excessive strength of the multilayer film is further prevented.

[0012] The reason why EB irradiation improves the crosslink density of the multilayer film (particularly the outer layer and functional layer in this multilayer film) is unclear, but it is speculated as follows: When the multilayer film is irradiated with EB, molecular bonds in the resin (e.g., polyethylene, ionomer) are broken, and radicals are generated at the ends of the broken bonds. It is speculated that the generated radicals react with other molecular chains to form new bonds, resulting in the formation of a crosslinked structure.

[0013] The acceleration voltage during EB irradiation is preferably 100 to 300 kV, more preferably 120 to 280 kV, and even more preferably 140 to 260 kV. By setting the acceleration voltage during EB irradiation within this range, it is possible to more easily obtain a multilayer film in which, during thermomechanical analysis, the temperature at which the film shows a displacement of 2000 μm and the displacement at a temperature of 100° C. are both within the above-mentioned numerical ranges. On the other hand, by setting the acceleration voltage during EB irradiation at or above the lower limit, the crosslinking density of the multilayer film (particularly the outer layer and functional layer in this multilayer film) is further improved, resulting in improved heat resistance and melt tension for the multilayer film as a whole, and improved conformability to the contents. By setting the acceleration voltage during EB irradiation at or below the upper limit, it is possible to more effectively prevent the multilayer film from becoming excessively strong.

[0014] When a multilayer film is wound into a roll, the sealant layer and the outer layer of the multilayer film come into contact with each other. Therefore, blocking between the multilayer films occurs between the sealant layer and the outer layer. Therefore, blocking between the multilayer films can be suppressed by adjusting the tack strength between the sealant layer and the outer layer.

[0015] In the multilayer film, the tack strength between the sealant layer and the outer layer is 9 N (918 gf) or less. In this specification, tack strength means the strength with which the surface of the sealant layer of the multilayer film sticks to the surface of the outer layer in a short time when they are lightly touched (the stickiness of the surface). When the tack strength between the sealant layer and the outer layer is equal to or less than the upper limit, adhesion between the sealant layer and the outer layer is prevented when the multilayer film is wound into a roll, thereby leaving oxygen between the multilayer film and deactivating residual radicals, thereby suppressing the occurrence of blocking.

[0016] The tack force between the sealant layer and the outer layer is preferably 0.1 N or more and 9.0 N or less (10 gf or more and 918 gf or less), more preferably 0.5 N or more and 4.0 N or less (51 gf or more and 408 gf or less), and even more preferably 1.0 N or more and 3.0 N or less (102 gf or more and 306 gf or less). When the tack strength between the sealant layer and the outer layer is equal to or greater than the lower limit, the occurrence of shear stress when the multilayer film is wound into a roll can be further suppressed. When the tack strength between the sealant layer and the outer layer is equal to or less than the upper limit, the adhesion between the sealant layer and the outer layer when the multilayer film is wound into a roll can be further prevented, thereby leaving more oxygen between the multilayer film, deactivating more residual radicals, and further suppressing the occurrence of blocking.

[0017] The tack strength between the sealant layer and the outer layer can be measured, for example, by the probe tack test described below. That is, a circular piece having a diameter of 10 mm in plan view is cut out from the multilayer film and used as a first test piece. Next, the exposed surface of the sealant layer in the first test piece was attached to the circular flat surface of a cylindrical stainless steel probe with a diameter of 10 mm, with the centers of the two aligned, using double-sided adhesive tape, to prepare a test laminate, i.e., the side of the probe and the side of the first test piece were aligned in the test laminate. Next, the separately prepared multilayer film was used as a second test piece. Next, under the condition of a temperature of 25°C, the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece of the test laminate are placed parallel to each other and face each other. The second test piece is then fixed and the probe in the test stack is moved towards the second test piece at a speed of 0.5 mm / sec. Next, after the entire exposed surface of the outer layer in the first test piece comes into contact with the exposed surface of the sealant layer in the second test piece, the probe is directed toward the second test piece and pressed with a pressure of 24.517 N for 20 seconds. Next, the load when the probe is moved at a speed of 10 mm / sec in the direction opposite to the second test piece side is measured, and the measured value is used as the tack force between the sealant layer and the outer layer.

[0018] The double-sided adhesive tape and the first test piece, and the double-sided adhesive tape and the probe do not peel off during the test, and the structure of the test laminate is stably maintained. The phrase "towards the second test piece" means "in a direction perpendicular to the exposed surface of the sealant layer in the second test piece, in a direction approaching the second test piece." The phrase "on the opposite side to the second test piece" means "in the direction opposite to the approaching direction, away from the second test piece."

[0019] The tackiness between the sealant layer and the outer layer can be adjusted by adjusting the type, amount, or thickness of any of the layers constituting the multilayer film, particularly the sealant layer or the outer layer. For example, by constructing a multilayer film with an outer layer and a sealant layer that contain an antiblocking agent, the tack between the sealant layer and the outer layer can be reduced. By constructing a multilayer film with an outer layer and a sealant layer that contain a slip agent, the tack between the sealant layer and the outer layer can be reduced. By configuring the multilayer film with an outer layer containing an ethylene-based polymer (e.g., high-density polyethylene) having a melting point of 115°C or higher, the tack between the sealant layer and the outer layer can be reduced. By configuring a multilayer film to have an outer layer that has a storage modulus of 80 MPa or more at 30°C when dynamic mechanical analysis (DMA) is performed on the outer layer at a heating rate of 2°C / min and a frequency of 1 Hz, the tackiness between the sealant layer and the outer layer can be reduced. By constructing a multilayer film with a sealant layer that does not contain ethylene-vinyl acetate copolymer (EVA), the tack between the sealant layer and the outer layer can be reduced. By constructing a multilayer film with a sealant layer that includes an antioxidant, the tack between the sealant layer and the outer layer can be reduced. By configuring the multilayer film with a sealant layer containing an anti-smear agent, the tack between the sealant layer and the outer layer can be reduced. By configuring the multilayer film with a sealant layer containing an ethylene-vinyl acetate copolymer with an acid modification degree of 10 mol % or less, the tackiness between the sealant layer and the outer layer can be reduced. By constructing a multilayer film with an outer layer that includes an ionomer, the tack between the sealant layer and the outer layer can be reduced.

[0020] The thickness of the multilayer film is preferably 60 μm or more, more preferably 70 to 400 μm, and even more preferably 80 to 300 μm, and may be, for example, 100 to 200 μm. When the thickness of the multilayer film is equal to or greater than the lower limit, the strength of the multilayer film is further improved. When the thickness of the multilayer film is equal to or less than the upper limit, the multilayer film is further prevented from becoming excessively thick.

[0021] In the multilayer film, it is preferable that all layers have transparency regardless of the type, that is, the multilayer film has transparency, i.e., the multilayer film is a transparent multilayer film. In a package constructed using such a multilayer film, the contents can be easily seen through the multilayer film.

[0022] Second Embodiment A multilayer film according to another embodiment of the present invention comprises an outer layer and a sealant layer. The multilayer film is not particularly limited as long as it satisfies the conditions of the temperature or gel fraction at which it shows a displacement of 2000 μm in the thermomechanical analysis described below, and the tack strength between the sealant layer and the outer layer described above.

[0023] When the multilayer film is subjected to thermomechanical analysis (TMA), the temperature at which the film shows a displacement of 2000 μm is 120° C. or higher, or the multilayer film has a gel fraction of 30% or higher.

[0024] The temperature at which the displacement of 2000 μm is exhibited is more preferably 120 to 300°C, further preferably 123 to 275°C, and may be, for example, 130 to 250°C. When the temperature is equal to or higher than the lower limit, the heat resistance of the multilayer film is further improved, and when the temperature is equal to or lower than the upper limit, the heat resistance of the multilayer film is further prevented from becoming excessive.

[0025] During thermomechanical analysis of the multilayer film, the amount of displacement at a temperature of 100°C is preferably 500 μm or less, more preferably 40 to 500 μm, and even more preferably 45 to 400 μm, and may be, for example, any one of 50 to 350 μm, 55 to 340 μm, and 55 to 250 μm. When the displacement amount is equal to or less than the upper limit, the melt tension of the multilayer film is further improved, and as a result, the conformability of the multilayer film to the contents is further improved.When the displacement amount is equal to or more than the lower limit, the melt tension of the multilayer film is further prevented from becoming excessive.

[0026] The thermomechanical analysis of the multilayer film can be performed in accordance with JIS K 7196 by measuring the amount of thermal expansion of the sample from the difference in the amount of thermal expansion when a standard sample and a sample to be analyzed are heated at a constant rate. Thermomechanical analysis of the multilayer film can be performed, for example, by using a sample 40 mm wide, 150 mm long, and 120 μm thick and measuring the displacement (thermal expansion) of this sample in the film machine direction (MD).

[0027] During thermomechanical analysis of the multilayer film, the temperature at which a displacement of 2000 μm occurs and the displacement at a temperature of 100° C. can be adjusted, for example, by irradiating the multilayer film with EB and adjusting the conditions of EB irradiation. For example, the temperature and displacement can be more easily adjusted by adjusting the conditions of EB irradiation of the outer layer or functional layer in the multilayer film.

[0028] The gel fraction of the multilayer film is more preferably 30 to 90%, and further preferably 32 to 85%, and may be, for example, any one of 40 to 82%, 48 to 82%, and 55 to 82%. When the gel fraction of the multilayer film is equal to or greater than the lower limit, the heat resistance and melt tension of the multilayer film are further improved, resulting in improved conformability to the contents contained therein. When the gel fraction of the multilayer film is equal to or less than the upper limit, the strength of the multilayer film is further prevented from becoming excessive.

[0029] The gel fraction of the multilayer film can be measured in accordance with JIS K 6769, taking advantage of the fact that the crosslinked portions of the film are insoluble in solvents. Specifically, the multilayer film is immersed in an organic solvent such as xylene, and the remaining insoluble film is dried. The mass of the resulting dried product is then measured, and the gel fraction can be calculated from the mass of the multilayer film before dissolution and the mass of the dried insoluble film. More specifically, for example, the multilayer film (mass Xg) is wrapped in a stainless steel mesh (mass Yg) and immersed in a heated solvent. The multilayer film wrapped in the stainless steel mesh (i.e., the insoluble film) is then removed. This is then vacuum-dried, and the mass (Zg) of the dried multilayer film wrapped in the stainless steel mesh (i.e., the insoluble film) is measured. The following formula (1) is then used: Gel fraction of multilayer film (mass%) = (ZY) / X × 100 (1) The gel fraction of the multilayer film is calculated by the following formula.

[0030] The gel fraction of the multilayer film can be adjusted, for example, by irradiating the multilayer film (particularly the outer layer or functional layer in the multilayer film) with EB and adjusting the conditions for EB irradiation. In this case, the conditions for EB irradiation can be the same as those for adjusting the temperature at which a displacement of 2000 μm occurs and the displacement at a temperature of 100° C. during the thermomechanical analysis of the multilayer film described above.

[0031] The multilayer film preferably satisfies either one or both of the conditions of the temperature at which it shows a displacement of 2000 μm during thermomechanical analysis and the gel fraction. That is, examples of the multilayer film include those having a temperature of 120° C. or higher at which it shows a displacement of 2000 μm during thermomechanical analysis and a gel fraction of less than 30%; those having a temperature of less than 120° C. at which it shows a displacement of 2000 μm during thermomechanical analysis and a gel fraction of 30% or higher; and those having a temperature of 120° C. or higher at which it shows a displacement of 2000 μm during thermomechanical analysis and a gel fraction of 30% or higher. However, it is usually more preferable that the multilayer film satisfy both of the above conditions, i.e., that the temperature at which it shows a displacement of 2000 μm during thermomechanical analysis is 120°C or higher and that it has a gel fraction of 30% or higher.

[0032] In the multilayer film, the tack force between the sealant layer and the outer layer is 9 N (918 gf) or less. When the tack strength between the sealant layer and the outer layer is equal to or less than the upper limit, the occurrence of blocking when the film is wound into a roll can be suppressed.

[0033] The tack force between the sealant layer and the outer layer is preferably 0.1 N or more and 9.0 N or less (10 gf or more and 918 gf or less), more preferably 0.5 N or more and 4.0 N or less (51 gf or more and 408 gf or less), and even more preferably 1.0 N or more and 3.0 N or less (102 gf or more and 306 gf or less). When the tack strength between the sealant layer and the outer layer is equal to or greater than the lower limit, the occurrence of shear stress when the multilayer film is wound into a roll can be further suppressed.When the tack strength between the sealant layer and the outer layer is equal to or less than the upper limit, the occurrence of blocking when the multilayer film is wound into a roll can be further suppressed.

[0034] The tack force between the sealant layer and the outer layer can be measured by the probe tack test described above. The tack between the sealant layer and the outer layer can be adjusted by the methods described above.

[0035] The thickness of the multilayer film is the same as that of the multilayer film of the first embodiment described above.

[0036] In the multilayer film, it is preferable that all layers have transparency regardless of the type, that is, the multilayer film has transparency, i.e., the multilayer film is a transparent multilayer film. In a package constructed using such a multilayer film, the contents can be easily seen through the multilayer film.

[0037] The detailed structure of the multilayer film and the method for producing the same will be described in detail later.

[0038] <<Multilayer film composition>> The present invention will be described in more detail below with reference to the drawings. Note that the drawings used in the following description may show essential parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of the components may not necessarily be the same as in reality.

[0039] FIG. 1 is a cross-sectional view schematically illustrating an example of a multilayer film according to one embodiment of the present invention. The multilayer film 1 shown here is constructed by laminating a sealant layer 11, a functional layer 13 (more specifically, a first functional layer 131), and an oxygen barrier layer 14 in this order in the thickness direction.

[0040] Furthermore, the multilayer film 1 includes an outer layer 12 disposed on the surface of the oxygen barrier layer 14 opposite to the sealant layer 11 side. Furthermore, the multilayer film 1 includes a functional layer 13 (more specifically, a second functional layer 132 ) disposed between the oxygen barrier layer 14 and the outer layer 12 . Furthermore, the multilayer film 1 includes an adhesive layer 15 (more specifically, a first adhesive layer 151) arranged between the first functional layer 131 and the oxygen barrier layer 14, and an adhesive layer 15 (more specifically, a second adhesive layer 152) arranged between the oxygen barrier layer 14 and the second functional layer 132. That is, the multilayer film 1 is constructed by laminating a sealant layer 11, a first functional layer 131, a first adhesive layer 151, an oxygen barrier layer 14, a second adhesive layer 152, a second functional layer 132 and an outer layer 12 in this order in the thickness direction. In the multilayer film 1, the outer layer 12 is one outermost layer, and the sealant layer 11 is the other outermost layer.

[0041] FIG. 2 is a schematic diagram showing the multilayer film 1 of FIG. 1 wound into a roll. As shown in Figure 2, when the multilayer film 1 is wound into a roll, the sealant layer 11 and the outer layer 12 in the multilayer film 1 come into contact with each other. Therefore, blocking between the multilayer films 1 occurs between the sealant layer 11 and the outer layer 12. Therefore, the effect of suppressing blocking between the multilayer films 1 can be evaluated by measuring the tack strength between the sealant layer 11 and the outer layer 12 in the multilayer film 1, as described above.

[0042] <Sealant layer> The multilayer film 1 includes a sealant layer 11. By including the sealant layer 11 in the multilayer film 1, the sealing properties of the multilayer film 1 can be improved.

[0043] The sealant layer 11 preferably contains an ethylene-based polymer (sometimes referred to herein as an "ethylene-based polymer in a sealant layer"). When the sealant layer 11 contains an ethylene-based polymer in the sealant layer, the sealing property of the multilayer film 1 can be further improved.

[0044] The ethylene-based polymer refers to a polymer (resin) having at least structural units derived from ethylene, and may be a polyethylene (ethylene homopolymer) having only structural units derived from ethylene, or an ethylene-based copolymer having structural units derived from ethylene and structural units derived from a monomer other than ethylene.

[0045] Examples of the polyethylene contained in the sealant layer 11 include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene-catalyzed linear low-density polyethylene (mLLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), etc. Of these, linear low-density polyethylene (LLDPE) is preferred. Linear low-density polyethylene (LLDPE) and metallocene-catalyzed linear low-density polyethylene (mLLDPE) are both types of low-density polyethylene (LDPE).

[0046] In this specification, the density of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and metallocene-catalyzed linear low density polyethylene (mLLDPE) is 0.910 g / cm 3 More than 0.940g / cm 3 is less than. The density of medium density polyethylene (MDPE) is 0.940 g / cm 3 More than 0.950g / cm 3 is less than. The density of high density polyethylene (HDPE) is 0.950 g / cm 3 That's all.

[0047] Examples of the ethylene copolymer contained in the sealant layer 11 include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ionomer (ION), etc. Among these, ethylene-vinyl acetate copolymer (EVA) is preferred.

[0048] The ionomer may be, for example, a resin in which a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid has an ionic crosslinking structure due to salt formation between the acid moiety in the copolymer and a metal ion. Examples of the metal ion include sodium ions, zinc ions, etc. In this specification, an ionomer in which the metal ion is a sodium ion may be referred to as a sodium-based ionomer, and an ionomer in which the metal ion is a zinc ion may be referred to as a zinc-based ionomer.

[0049] The melting point of the ethylene polymer in the sealant layer is preferably 85°C or higher, more preferably 87°C or higher, and even more preferably 89°C or higher. When the melting point is equal to or higher than the lower limit, the stickiness when touched by hand is reduced, the tackiness is further reduced, and the blocking suppression effect can be further improved. The upper limit of the melting point is not particularly limited. For example, an ethylene polymer in a sealant layer having a melting point of 140°C or less is easily available.

[0050] When the sealant layer 11 contains an ethylene-vinyl acetate copolymer, the ratio of the content of vinyl acetate-derived structural units to the total mass of the ethylene-vinyl acetate copolymer in the sealant layer 11 (degree of acid modification) is preferably 3 mol% or more and 16 mol% or less, more preferably 5 mol% or more and 16 mol% or less, and even more preferably 8 mol% or more and 16 mol% or less. When the ratio is equal to or greater than the lower limit, the sealability of the multilayer film 1 can be further improved. The vinyl acetate-derived structural units in the ethylene-vinyl acetate copolymer can cause sticky feeling when touched and can bond to the outer layer due to residual radicals. Therefore, by making the ratio equal to or less than the upper limit, bonding to the outer layer due to residual radicals can be suppressed when the multilayer film 1 after EB irradiation is wound into a roll, and the occurrence of blocking can be further suppressed.

[0051] The sealant layer 11 may contain only an ethylene-based polymer in the sealant layer (i.e., the sealant layer may consist of an ethylene-based polymer), or may contain an ethylene-based polymer and other components (sometimes referred to as "other components" in this specification) in the sealant layer (i.e., the sealant layer may consist of an ethylene-based polymer and the other components).

[0052] The ethylene polymer contained in the sealant layer 11 may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0053] The other components contained in the sealant layer 11 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component. The other component, which is a resin component, is a resin other than the ethylene polymer in the sealant layer. The other component, which is a resin component, may be a homopolymer, which is a polymer of one type of monomer, or a copolymer, which is a polymer of two or more types of monomers.

[0054] Examples of the other non-resin components include additives known in the art. Examples of the additives include antiblocking agents, slip agents (lubricants), antioxidants, anti-staining agents, antistatic agents, crystal nucleating agents, inorganic particles, viscosity reducers, thickeners, thermal stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, etc. Among these, antiblocking agents, slip agents, antioxidants, and anti-staining agents are preferred. The inclusion of an antiblocking agent or slip agent in the sealant layer 11 can better prevent adhesion, leave more oxygen between the multilayer film 1, deactivate remaining radicals, and suppress the occurrence of blocking when the multilayer film 1 is wound into a roll after EB irradiation. The inclusion of an antioxidant or anti-smear agent in the sealant layer 11 can better deactivate remaining radicals and suppress the occurrence of blocking when the multilayer film 1 is wound into a roll after EB irradiation.

[0055] In this specification, the term "resin" refers to a mass of resin generated during extrusion molding of a multilayer film.

[0056] The other components contained in the sealant layer 11 may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0057] In the sealant layer 11, the content of the ethylene polymer in the sealant layer relative to the total mass of the sealant layer 11 is preferably 65 to 100 mass%, more preferably 70 to 100 mass%, and even more preferably 75 to 100 mass%, and may be, for example, 85 to 100 mass%. When the ratio is equal to or greater than the lower limit, the sealability of the multilayer film 1 can be further improved. The ratio is usually the same as the ratio of the content (parts by mass) of the ethylene polymer in the sealant layer to the total content (parts by mass) of components that do not vaporize at room temperature in the sealant layer-forming composition described below.

[0058] In this specification, "room temperature" means a temperature that is neither particularly cold nor hot, that is, an ordinary temperature, and examples thereof include temperatures of 15 to 25°C.

[0059] The sealant layer 11 may consist of one layer (single layer) or two or more layers. When the sealant layer 11 consists of multiple layers, these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0060] In this specification, not only in the case of the sealant layer 11, "multiple layers may be the same or different" means "all layers may be the same, all layers may be different, or only some layers may be the same," and further, "multiple layers are different" means "at least one of the constituent materials and thicknesses of each layer is different from each other."

[0061] The thickness of the sealant layer 11 is preferably 96 μm or less, more preferably 5 μm or more and 93 μm or less, and even more preferably 10 μm or more and 90 μm or less, and may be, for example, any one of 10 to 20 μm, 15 to 50 μm, and 30 to 70 μm. When the thickness of the sealant layer 11 is equal to or greater than the lower limit, the seal strength of the sealant layer 11 is increased. When the thickness of the sealant layer 11 is equal to or less than the upper limit, the seal strength can be further prevented from becoming too high. Here, "the thickness of the sealant layer 11" means the thickness of the entire sealant layer 11, and for example, the thickness of the sealant layer 11 consisting of multiple layers means the total thickness of all layers that make up the sealant layer 11.

[0062] The ratio of the thickness of the sealant layer 11 to the thickness of the multilayer film 1 is preferably 30% or less. When the ratio is 30% or less, the seal strength can be further prevented from becoming too high. The ratio is more preferably 5% or more and 50% or less, and even more preferably 10% or more and 30% or less. When the ratio is equal to or greater than the lower limit, the seal strength of the sealant layer 11 is increased. When the thickness of the sealant layer 11 is equal to or less than the upper limit, the seal strength can be further prevented from becoming too high.

[0063] In this specification, for any layer constituting the multilayer film, including the above-mentioned sealant layer, the ratio of the thickness of that layer to the thickness of the multilayer film is stated, but the total value of the ratios stated for each layer shall not exceed 100%.

[0064] An exposed surface 11a of the sealant layer 11 opposite to the outer layer 12 side (sometimes referred to as the "first surface" in this specification) is a sealing surface.

[0065] <Outer layer> The multilayer film 1 includes an outer layer 12. By including the outer layer 12, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and conformability to the contents of the multilayer film 1 can be further improved.

[0066] When the outer layer 12 is subjected to dynamic mechanical analysis (DMA) at a temperature rise rate of 2°C / min and a frequency of 1 Hz, the storage modulus at 30°C is preferably 80 MPa or more. When the storage modulus is equal to or more than the lower limit, the sticky feeling when touched by hand is reduced, the tackiness is further reduced, and the blocking suppression effect can be further improved.

[0067] The storage modulus is more preferably 80 MPa or more and 2000 MPa or less, even more preferably 90 MPa or more and 1500 MPa or less, and particularly preferably 100 MPa or more and 1000 MPa or less. When the storage modulus is equal to or greater than the lower limit, the stickiness when touched by hand is reduced, the tackiness is further reduced, and the blocking suppression effect can be further improved. When the storage modulus is equal to or less than the upper limit, the flexibility of the multilayer film and its ability to conform to the contents contained therein can be further improved.

[0068] The storage modulus can be measured, for example, using a dynamic viscoelasticity measuring device ("DMA 7100" manufactured by Hitachi High-Tech Science Corporation) under the following measurement conditions: using a sample with a width of 4 mm, in a tensile mode in a temperature range of 25°C to 160°C, a displacement of 10 μm, a vibration frequency of 1 Hz, and a temperature rise rate of 2°C / min.

[0069] The storage modulus can be adjusted by adjusting the type, amount, or thickness of the components contained in the outer layer. For example, the storage modulus can be easily increased by constructing a multilayer film with outer layers that contain an ionomer and increasing the content of the ionomer in the outer layers.

[0070] The outer layer 12 preferably contains an ethylene-based polymer (sometimes referred to herein as an "ethylene-based polymer in the outer layer"). When the outer layer 12 contains an ethylene-based polymer in the outer layer, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and conformability to the contents of the multilayer film 1 can be further improved.

[0071] The ethylene-based polymer refers to a polymer (resin) having at least structural units derived from ethylene, and may be a polyethylene (ethylene homopolymer) having only structural units derived from ethylene, or an ethylene-based copolymer having structural units derived from ethylene and structural units derived from a monomer other than ethylene.

[0072] Examples of the polyethylene contained in the outer layer 12 include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene-catalyzed linear low-density polyethylene (mLLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). Of these, linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) are preferred, with high-density polyethylene being more preferred. High-density polyethylene has a high melting point and is less sticky to the touch, resulting in low tack and an improved blocking suppression effect.

[0073] Examples of the ethylene copolymer contained in the outer layer 12 include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), and ionomer (ION). Of these, ionomer (ION) is preferred. Ionomers have a low stickiness when touched, so they have low tack and can further improve the blocking suppression effect.

[0074] The ionomer may be, for example, a resin in which a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid has an ionic crosslinking structure due to salt formation between the acid moiety in the copolymer and a metal ion. Examples of the metal ions include sodium ions and zinc ions.

[0075] As described above, the ethylene polymer in the outer layer is preferably polyethylene or an ionomer, and more preferably high-density polyethylene or an ionomer.

[0076] The melting point of the ethylene polymer in the outer layer is preferably 115°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. When the melting point is equal to or higher than the lower limit, the stickiness when touched by hand is reduced, the tackiness is further reduced, and the blocking suppression effect can be further improved. The upper limit of the melting point is not particularly limited. For example, an ethylene polymer for the outer layer having a melting point of 140°C or lower is easily available.

[0077] The outer layer 12 may contain only an ethylene-based polymer in the outer layer (i.e., the outer layer may consist of an ethylene-based polymer), or may contain an ethylene-based polymer and other components (sometimes referred to as "other components" in this specification) in the outer layer (i.e., the outer layer may consist of an ethylene-based polymer and the other components).

[0078] The outer layer may contain only one type of ethylene polymer, or two or more types. When two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0079] The other components contained in the outer layer 12 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component. The other component, which is a resin component, is a resin other than the ethylene polymer in the outer layer. The other component, which is a resin component, may be a homopolymer, which is a polymer of one type of monomer, or a copolymer, which is a polymer of two or more types of monomers.

[0080] Examples of the other non-resin components include additives known in the art. Examples of the additives include antiblocking agents, slip agents (lubricants), antioxidants, anti-staining agents, antistatic agents, crystal nucleating agents, inorganic particles, viscosity reducers, thickeners, thermal stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, etc. Of these, antiblocking agents and slip agents are preferred. By including an antiblocking agent or slip agent in the outer layer 12, adhesion can be better prevented when the multilayer film 1 is wound into a roll after EB irradiation, more oxygen remains between the layers of the multilayer film 1, and residual radicals are more effectively deactivated, thereby better suppressing the occurrence of blocking.

[0081] The outer layer 12 may contain only one type of other component, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0082] The proportion of the ethylene polymer content in the outer layer 12 relative to the total mass of the outer layer 12 is preferably 50% by mass or more, more preferably 55 to 100% by mass, and even more preferably 60 to 100% by mass, and may be, for example, any of 70 to 100% by mass and 85 to 100% by mass. When the ratio is equal to or greater than the lower limit, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with EB, thereby further improving the heat resistance, flexibility, and conformability to the contents of the multilayer film 1. The ratio is usually the same as the ratio of the content (parts by mass) of the ethylene polymer in the outer layer to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming the outer layer, which will be described later.

[0083] The outer layer 12 may consist of one layer (single layer) or two or more layers. When the outer layer 12 consists of multiple layers, these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0084] The thickness of the outer layer 12 is not particularly limited, but is preferably 60 μm or less, more preferably 5 μm or more and 50 μm or less, and even more preferably 8 μm or more and 40 μm or less, and may be, for example, any one of 10 to 20 μm, 15 to 30 μm, and 5 to 20 μm. When the thickness of the outer layer 12 is equal to or greater than the lower limit, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and ability to conform to the contents of the multilayer film 1 can be further improved. When the thickness of the outer layer 12 is equal to or less than the upper limit, the outer layer 12 is prevented from becoming excessively thick. Here, "thickness of outer layer 12" means the thickness of the entire outer layer 12; for example, the thickness of an outer layer 12 consisting of multiple layers means the total thickness of all layers that make up the outer layer 12.

[0085] The ratio of the thickness of the outer layer 12 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 5% or more and 40% or less, more preferably 8% or more and 30% or less, and even more preferably 10% or more and 20% or less. When the ratio is equal to or greater than the lower limit, the crosslink density of the outer layer 12 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and ability to conform to the contents of the multilayer film 1 can be further improved. When the ratio is equal to or less than the upper limit, the thickness of the outer layer 12 is prevented from becoming excessive.

[0086] <Functional layer> The multilayer film 1 may further include a functional layer 13 adjacent to the sealant layer 11. By including the functional layer 13 in the multilayer film 1, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and conformability to the contents of the multilayer film 1 can be further improved.

[0087] The functional layer 13 preferably contains an ethylene-based polymer (sometimes referred to herein as an "ethylene-based polymer in the functional layer"). When the functional layer 13 contains an ethylene-based polymer in the functional layer, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and conformability to the contents of the multilayer film 1 can be further improved.

[0088] The ethylene-based polymer refers to a polymer (resin) having at least structural units derived from ethylene, and may be a polyethylene (ethylene homopolymer) having only structural units derived from ethylene, or an ethylene-based copolymer having structural units derived from ethylene and structural units derived from a monomer other than ethylene.

[0089] Examples of the polyethylene contained in the functional layer 13 include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene-catalyzed linear low-density polyethylene (mLLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0090] Examples of the ethylene copolymer contained in the functional layer 13 include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ionomer (ION), etc. Among these, ethylene-vinyl acetate copolymer (EVA) and ionomer (ION) are preferred. By including an ionomer (ION) in the functional layer 13, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and conformability to the contents of the multilayer film 1 can be further improved.

[0091] The ionomer may be, for example, a resin in which a copolymer of ethylene and a small amount of acrylic acid or methacrylic acid has an ionic crosslinking structure due to salt formation between the acid moiety in the copolymer and a metal ion. Examples of the metal ions include sodium ions and zinc ions.

[0092] The functional layer 13 may be composed of one layer (single layer) or two or more layers. When the functional layer 13 is composed of multiple layers, these multiple layers may be the same or different from each other, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0093] In this embodiment, functional layers 13 are provided at different positions on the multilayer film 1. In this embodiment, in order to distinguish these functional layers 13 from one another, the functional layer 13 disposed between the sealant layer 11 and the first adhesive layer 151 may be referred to as the first functional layer 131, and the functional layer 13 disposed between the second adhesive layer 152 and the outer layer 12 may be referred to as the second functional layer 132, as necessary. These functional layers 13 (first functional layer 131 and second functional layer 132) may be the same as or different from each other.

[0094] The functional layer 13 may contain only an ethylene-based polymer in the functional layer (i.e., it may consist of an ethylene-based polymer in the functional layer), or it may contain an ethylene-based polymer in the functional layer and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of an ethylene-based polymer in the functional layer and the other components).

[0095] The ethylene polymer contained in the functional layer 13 may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0096] The other components contained in the functional layer 13 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component. The other component, which is a resin component, is a resin other than the ethylene-based polymer in the functional layer.

[0097] The functional layer 13 may contain only one type of other component, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0098] The content of the ethylene polymer in the functional layer 13 relative to the total mass of the functional layer 13 is preferably 50% by mass or more, more preferably 55 to 100% by mass, and even more preferably 60 to 100% by mass, and may be, for example, either 70 to 100% by mass or 85 to 100% by mass. When the ratio is equal to or greater than the lower limit, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB, thereby further improving the heat resistance, flexibility, and conformability to the contents of the multilayer film 1. This ratio is usually the same as the ratio of the content (parts by mass) of the ethylene polymer in the functional layer to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming the functional layer described below.

[0099] The thickness of the functional layer 13 (each of the first functional layer 131 and the second functional layer 132) is preferably 4 to 146 μm, more preferably 7 to 143 μm, and even more preferably 10 to 140 μm, and may be, for example, any of 10 to 110 μm, 10 to 80 μm, 10 to 50 μm, and 10 to 30 μm. When the thickness of the functional layer 13 is equal to or greater than the lower limit, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and ability to conform to the contents of the multilayer film 1 can be further improved. When the thickness of the functional layer 13 is equal to or less than the upper limit, the functional layer 13 is prevented from becoming excessively thick. Here, "thickness of functional layer 13" means the overall thickness of functional layer 13 (for example, the overall thickness of functional layer 13 arranged between sealant layer 11 and first adhesive layer 151, or the overall thickness of functional layer 13 arranged between second adhesive layer 152 and outer layer 12), and for example, the thickness of functional layer 13 consisting of multiple layers means the total thickness of all layers that make up functional layer 13.

[0100] The ratio of the thickness of the functional layer 13 to the thickness of the multilayer film 1 is not particularly limited, but is preferably 10% or more, more preferably 11 to 89%, and even more preferably 12 to 88%. When the ratio is equal to or greater than the lower limit, the crosslink density of the functional layer 13 can be further improved when the multilayer film 1 is irradiated with EB. As a result, the heat resistance, flexibility, and ability to conform to the contents of the multilayer film 1 can be further improved. When the ratio is equal to or less than the upper limit, the thickness of the functional layer 13 is prevented from becoming excessive.

[0101] When the functional layer 13 (specifically, the second functional layer 132) is made of an ethylene-based polymer or has an ethylene-based polymer as the main component, the thickness can be increased so that the layer can also function as an outer layer.

[0102] <Oxygen barrier layer> The multilayer film preferably further comprises an oxygen barrier layer 14 . The oxygen barrier layer 14 imparts strong oxygen barrier properties to the multilayer film 1 (in other words, the property of inhibiting the permeation of oxygen gas).

[0103] The oxygen barrier layer 14 preferably contains an ethylene-vinyl alcohol copolymer (EVOH, also known as saponified ethylene-vinyl acetate copolymer). When the oxygen barrier layer 14 contains EVOH, the oxygen barrier properties of the multilayer film 1 can be further improved.

[0104] The oxygen barrier layer 14 may contain polyvinylidene chloride (PVDC) in addition to EVOH (EVOH and PVDC may be referred to as "oxygen barrier property-imparting resins" in this specification). When the oxygen barrier layer 14 contains the oxygen barrier property-imparting resin, the oxygen barrier property of the multilayer film 1 can be further improved.

[0105] In the EVOH, the ratio of the amount of structural units derived from ethylene to the total amount of structural units in the EVOH (sometimes referred to herein as the "copolymerization ratio of ethylene") is preferably 30 to 50 mol%, and may be, for example, 30 to 40 mol% or 40 to 50 mol%. When the copolymerization ratio of ethylene is in this range, the oxygen barrier property and other properties of the multilayer film are improved in a well-balanced manner.

[0106] The oxygen barrier layer 14 may contain only the oxygen barrier property-imparting resin (i.e., it may consist of the oxygen barrier property-imparting resin), or it may contain the oxygen barrier property-imparting resin and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of the oxygen barrier property-imparting resin and the other components).

[0107] The other components contained in the oxygen barrier layer 14 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component. The other component, which is a resin component, is a resin other than the oxygen barrier property-imparting resin. Examples of the other components that are non-resin components include the same additives as those listed above as other components contained in the sealant layer 11.

[0108] The oxygen barrier layer 14 may contain only one other component, or two or more components. When there are two or more components, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0109] The content of the oxygen barrier property-imparting resin in the oxygen barrier layer 14 relative to the total mass of the oxygen barrier layer 14 is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, and even more preferably 70 to 100 mass%, and may be, for example, 85 to 100 mass%. When this proportion is equal to or greater than the lower limit, the oxygen barrier property of the multilayer film 1 is further improved. This ratio is usually the same as the ratio of the content (parts by mass) of the oxygen barrier property-imparting resin to the total content (parts by mass) of components that do not vaporize at room temperature in the composition for forming an oxygen barrier layer, which will be described later.

[0110] The oxygen barrier layer 14 may consist of one layer (single layer) or two or more layers. When the oxygen barrier layer 14 consists of multiple layers, these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0111] The thickness of the oxygen barrier layer 14 is preferably 1 to 100 μm, more preferably 1.5 to 90 μm, and even more preferably 2 to 80 μm, and may be, for example, any one of 4 to 60 μm, 4 to 40 μm, and 4 to 20 μm. When the thickness of the oxygen barrier layer 14 is equal to or greater than the lower limit, the oxygen barrier layer is further prevented from being torn, and the oxygen barrier properties of the multilayer film 1 can be further improved.

[0112] In this specification, "breakage of the oxygen barrier layer" means that the oxygen barrier layer is not formed in part in the multilayer film, which occurs, for example, when the oxygen barrier layer is too thin. When the thickness of the oxygen barrier layer 14 is equal to or less than the upper limit, the shape of the packaged contents can be better maintained. Here, the "thickness of the oxygen barrier layer 14" means the thickness of the entire oxygen barrier layer 14; for example, the thickness of the oxygen barrier layer 14 consisting of multiple layers means the total thickness of all layers that make up the oxygen barrier layer 14.

[0113] The ratio of the thickness of the oxygen barrier layer 14 to the thickness of the multilayer film 1 is 2 to 25%. When the ratio is equal to or greater than the lower limit, it is possible to suppress tearing of the oxygen barrier layer and improve the oxygen barrier properties of the multilayer film 1. When the ratio is equal to or less than the upper limit, it is possible to maintain the shape of the packaged contents.

[0114] The ratio of the thickness of the oxygen barrier layer 14 to the thickness of the multilayer film 1 is more preferably 2.2 to 24.8%, and even more preferably 2.4 to 24.6%. When the ratio is equal to or greater than the lower limit, it is possible to further suppress tearing of the oxygen barrier layer and further improve the oxygen barrier properties of the multilayer film 1. When the ratio is equal to or less than the upper limit, it is possible to further maintain the shape of the packaged contents.

[0115] In the case of food packaging, the multilayer film constituting the packaging is required to have an oxygen barrier layer to prevent oxidative deterioration of the food. However, the presence of an oxygen barrier layer has the problem of reducing the packaging's ability to conform to the food (its ability to adhere to the food without wrinkling). In contrast, a packaging constructed using a multilayer film 1 having an outer layer 12 and a functional layer 13 overcomes this problem. The reason for this is that the presence of the outer layer 12 and the functional layer 13 improves the heat resistance, melt tension, and tensile strength of the multilayer film 1, resulting in the multilayer film 1 having excellent conformability to the contents.

[0116] Recently, there has been a shift from conventional chamber-type skin pack machines (indirect heating method) with a low shot count to continuous skin pack packaging machines (direct heating method) with a high shot count, and a melt strength that can withstand a method in which the film is directly heated at high temperatures by a heated hot plate is required. If the melt strength of the package is low, there is a problem in that the film becomes cloudy when it is in close contact with the hot plate. In contrast, a package constructed using a multilayer film 1 with a functional layer 13 solves this problem. The reason for this is that the multilayer film 1 has excellent melt strength when heated due to the presence of the ionomer contained in the functional layer 13.

[0117] <Adhesive layer> The adhesive layer 15 includes an adhesive. The adhesive layer 15 bonds two adjacent layers together on both sides. In the multilayer film 1, the adhesive layer 15 disposed between the first functional layer 131 and the oxygen barrier layer 14 bonds the first functional layer 131 and the oxygen barrier layer 14, and the adhesive layer 15 disposed between the oxygen barrier layer 14 and the second functional layer 132 bonds the oxygen barrier layer 14 and the second functional layer 132. In this specification, to distinguish between these two adhesive layers 15, the adhesive layer 15 disposed between the first functional layer 131 and the oxygen barrier layer 14 may be referred to as the first adhesive layer 151, and the adhesive layer 15 disposed between the oxygen barrier layer 14 and the second functional layer 132 may be referred to as the second adhesive layer 152, as necessary. These two adhesive layers 15 (first adhesive layer 151 and second adhesive layer 152) may be the same as or different from each other.

[0118] The adhesive contained in adhesive layer 15 is not particularly limited as long as it can bond two layers to be bonded together with sufficient strength. The adhesive may be, for example, an adhesive resin such as an olefin-based resin (that is, a polymer of one or more olefin monomers).

[0119] More specific examples of the olefin-based resin contained in the adhesive layer 15 include ethylene-based copolymers, propylene-based copolymers, and butene-based copolymers. The ethylene copolymer is a copolymer of ethylene and a monomer other than ethylene. The propylene copolymer is a copolymer of propylene and a monomer other than propylene. The butene copolymer is a copolymer of butene and a monomer other than butene.

[0120] The ethylene copolymer contained in the adhesive layer 15 may be, for example, a copolymer of ethylene and a vinyl group-containing monomer. Examples of copolymers of ethylene and vinyl group-containing monomers include maleic anhydride-grafted linear low-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ionomer (ION), and ethylene-based thermoplastic elastomer. Examples of the ionomer include the same ionomers as those listed above as those contained in the functional layer 13.

[0121] The propylene copolymer contained in the adhesive layer 15 may be, for example, a copolymer of propylene and a vinyl group-containing monomer. Examples of copolymers of propylene and vinyl group-containing monomers include maleic anhydride graft-modified linear low-density polypropylene and propylene-based thermoplastic elastomers.

[0122] Examples of the butene copolymer contained in the adhesive layer 15 include a copolymer of 1-butene and a vinyl group-containing monomer, a copolymer of 2-butene and a vinyl group-containing monomer, and modified products of these copolymers (modified copolymers).

[0123] The adhesive layer 15 may contain only an adhesive (i.e., it may consist of an adhesive), or it may contain an adhesive and other components (sometimes referred to as "other components" in this specification) (i.e., it may consist of an adhesive and the other components).

[0124] The adhesive layer 15 may contain only one type of adhesive, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0125] The other components contained in the adhesive layer 15 are not particularly limited and can be selected arbitrarily depending on the purpose, and may be, for example, either a resin component or a non-resin component.

[0126] The other components contained in adhesive layer 15 may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0127] The content of the adhesive in the adhesive layer 15 relative to the total mass of the adhesive layer 15 may be, for example, 50 to 100 mass %. The ratio is usually the same as the ratio of the content (parts by mass) of the adhesive to the total content (parts by mass) of components that do not vaporize at room temperature in the adhesive layer-forming composition described below.

[0128] The adhesive layer 15 may consist of one layer (single layer) or two or more layers. When the adhesive layer 15 consists of multiple layers, these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0129] The thickness of the adhesive layer 15 (the thickness of each of the first adhesive layer 151 and the second adhesive layer 152) is preferably 4 to 96 μm, more preferably 7 to 93 μm, and may be, for example, any one of 7 to 80 μm, 7 to 60 μm, 7 to 40 μm, and 7 to 20 μm. When the thickness of the adhesive layer 15 is equal to or greater than the lower limit, the adhesive strength between the two layers to be bonded is increased. When the thickness of the adhesive layer 15 is equal to or less than the upper limit, the adhesive layer 15 is prevented from becoming excessively thick. Here, "thickness of adhesive layer 15" means the total thickness of adhesive layer 15 (for example, the total thickness of adhesive layer 15 arranged between first functional layer 131 and oxygen barrier layer 14, or the total thickness of adhesive layer 15 arranged between oxygen barrier layer 14 and second functional layer 132), and for example, the thickness of adhesive layer 15 consisting of multiple layers means the total thickness of all layers that make up adhesive layer 15.

[0130] <Other layers> The multilayer film 1 may have other layers that do not fall under any of the sealant layer 11, outer layer 12, functional layer 13, oxygen barrier layer 14, and adhesive layer 15, as long as the effects of the present invention are not impaired.

[0131] The type and arrangement of the other layer are not particularly limited and can be selected arbitrarily depending on the purpose.

[0132] The multilayer film 1 may have only one type of other layer, or two or more types. When there are two or more types, the combination and ratio of the layers can be selected arbitrarily depending on the purpose.

[0133] The other layers may each consist of one layer (single layer) or two or more layers. When the other layers consist of multiple layers, these multiple layers may be the same or different from one another, and the combination of these multiple layers is not particularly limited as long as it does not impair the effects of the present invention.

[0134] The thickness of the other layer can be set arbitrarily depending on the type of the other layer, and is not particularly limited.

[0135] When the multilayer film 1 includes the other layer, it may further include an adhesive layer (for example, adhesive layer 15) for adhering the other layer to other layers.

[0136] The multilayer film of this embodiment is not limited to the one described above, and some of the configuration may be changed, deleted, or added within the scope of the spirit of the present invention. For example, the multilayer film may not include one or two of the functional layer, the oxygen barrier layer, and the adhesive layer. However, it is preferable that the multilayer film comprises a sealant layer, a functional layer, an adhesive layer, an oxygen barrier layer, an adhesive layer, a functional layer, and an outer layer in this order, as shown in FIG.

[0137] <<Multilayer film manufacturing method>> The multilayer film can be produced by a known method depending on the type of film. For example, laminated films such as the multilayer films can be produced by a feed block method in which resins or resin compositions that are materials for forming each layer are melt-extruded using several extruders, a coextrusion T-die method such as a multi-manifold method, or an air-cooled or water-cooled coextrusion inflation method.

[0138] The laminated film can also be produced by coating a resin or resin composition, etc., that will be used to form one of the layers, on the surface of another layer that will form the laminated film, and drying it as needed to form a laminated structure in the laminated film, and then, as needed, further laminating other layers so as to form the desired arrangement.

[0139] The laminated film can also be produced by separately preparing two or more films for constituting any two or more of the layers, laminating these films together using an adhesive by any of dry lamination, extrusion lamination, hot melt lamination, and wet lamination, and then laminating other layers as needed to form the desired arrangement. In this case, the adhesive used may be one capable of forming the adhesive layer.

[0140] The laminated film can also be produced by laminating two or more films that have been prepared separately in advance, as described above, by a thermal lamination method or the like without using an adhesive, and, if necessary, further laminating other layers so as to achieve the desired arrangement.

[0141] When producing the laminated film, two or more of the methods for forming any of the layers (films) in the laminated film mentioned above may be combined.

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

[0143] Examples of resin compositions (sometimes referred to herein as "sealant layer-forming compositions") for forming a sealant layer (sealant layer 11 in the multilayer film 1 shown in Figure 1) include those containing the ethylene polymer in the sealant layer and, if necessary, the other components described above.

[0144] Examples of resin compositions (sometimes referred to herein as "compositions for forming outer layers") for forming outer layers (outer layer 12 in the multilayer film 1 shown in FIG. 1) include those containing the ethylene-based polymer in the outer layer and, if necessary, the other components described above.

[0145] Examples of resin compositions (sometimes referred to in this specification as "compositions for forming functional layers") for forming functional layers (functional layer 13 in the multilayer film 1 shown in Figure 1) include those containing the ethylene-based polymer in the functional layer and, if necessary, the other components described above.

[0146] Examples of resin compositions (sometimes referred to herein as "oxygen barrier layer-forming compositions") for forming an oxygen barrier layer (oxygen barrier layer 14 in the multilayer film 1 shown in FIG. 1) include those containing the oxygen barrier property-imparting resin and, if necessary, the other components described above.

[0147] Examples of resin compositions (sometimes referred to in this specification as "adhesive layer-forming compositions") for forming an adhesive layer (adhesive layer 15 in the multilayer film 1 shown in Figure 1) include those containing the adhesive and, if necessary, the other components described above.

[0148] The multilayer film 1 can be used as a lid material. The package of this embodiment can be produced by heat-sealing this lid material and a base material.

[0149] <<Bottom material>> The base material has an oxygen permeability of 300cc / (m 2 The viscosity is preferably 1000 kJ / day atm or less, and there are no particular limitations as long as it can be used as the base material of a package. The base material may be a known material.

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

[0151] The oxygen permeability of the base material under conditions of a temperature of 23°C and a relative humidity of 60% can be measured in accordance with JIS K 7126-2:2006.

[0152] The oxygen permeability of the sole material can be more easily adjusted by, for example, adjusting the type and amount of components contained in the sole material, the thickness of the sole material, etc.

[0153] The thickness of the base material is preferably 100 μm or more, more preferably 110 μm or more, and even more preferably 120 μm or more. When the thickness of the base material is equal to or greater than the lower limit, the strength of the base material is further improved. The thickness of the base material is preferably 6000 μm or less. By keeping the thickness of the base material at or below the upper limit value, the base material is prevented from becoming excessively thick. The thickness of the base material can be adjusted appropriately within a range set by any combination of any of the above-mentioned lower limit values ​​and upper limit values.

[0154] Regardless of the type of base material, all layers may be transparent and the base material may be transparent, or all or some of the layers may not be transparent and the base material may not be transparent. In a package constructed using a transparent base material, the contents can be easily seen through the base material.

[0155] The base material can be produced by a known method depending on the type.

[0156] <<Packaging>> FIG. 3 is a cross-sectional view schematically illustrating an example of a package according to one embodiment of the present invention. In FIG. 3, the same components as those shown in the drawings that have already been described are given the same reference numerals as those in the drawings that have already been described, and detailed description thereof will be omitted. In FIG. 3, the distinction between the layers in the multilayer film 1 is omitted.

[0157] The packaging body 10 shown here is configured to include the multilayer film 1 (lid material) shown in FIG.

[0158] The package 10 is preferably a skin pack package. In this specification, "skin pack" refers to a package in which the contents are placed on cardboard, corrugated board, a bottom film, a tray, etc., and then a heated film is placed over the contents, and a vacuum is drawn in a chamber so that the film adheres tightly to the contents. The name "skin pack" comes from the feature that the film adheres tightly to the product body, conforming to the shape of the product, just like skin.

[0159] The multilayer film 1 in the package 10 comprises an outer layer 12 and a sealant layer 11 . The multilayer film 1 in the package 10 has been irradiated with EB at an absorbed dose of 20 to 300 kGy. Alternatively, during thermomechanical analysis of the multilayer film 1 in the package, the temperature at which the film shows a displacement of 2000 μm is 120° C. or higher, or the gel fraction of the multilayer film 1 in the package is 30% or higher. A circular piece having a planar shape of 10 mm in diameter was cut out from the multilayer film 1 in the package 10 to form a first test piece, and the exposed surface of the sealant layer 11 in the first test piece was attached to the circular flat surface of a cylindrical stainless steel probe having a diameter of 10 mm with double-sided adhesive tape, with the centers of the two aligned, to form a test laminate. A separately prepared multilayer film 1 was used as a second test piece, and the exposed surface of the outer layer 12 in the first test piece and the sealant layer in the second test piece were attached to each other at a temperature of 25°C. The exposed surface of the outer layer 12 in the first test piece is placed parallel to and facing the exposed surface of the sealant layer 11 in the second test piece, the second test piece is fixed, and the probe in the test laminate is moved toward the second test piece at a speed of 0.5 mm / sec. After the entire exposed surface of the outer layer 12 in the first test piece comes into contact with the exposed surface of the sealant layer 11 in the second test piece, the probe is pressed toward the second test piece at a pressure of 24.517 N for 20 seconds, and then the probe is moved in the opposite direction from the second test piece at a speed of 10 mm / sec. The load measured when this is 9 N (918 gf) or less.

[0160] It is preferable that the outer layer 12 of the multilayer film 1 in the package 10 contains an ethylene-based polymer, and that the melting point of the ethylene-based polymer is 115°C or higher. The outer layer 12 of the multilayer film 1 in the package 10 preferably has a storage modulus of 80 MPa or more at 30°C when measured by dynamic mechanical analysis (DMA) at a temperature rise rate of 2°C / min and a frequency of 1 Hz. In the multilayer film 1 in the package 10, the ethylene polymer is preferably polyethylene or an ionomer. In the multilayer film 1 in the package 10, the sealant layer 11 preferably contains an ethylene-based polymer. The multilayer film 1 in the package 10 further includes a functional layer 13 adjacent to the sealant layer 11, and the functional layer 13 preferably contains an ethylene-based polymer. The ratio of the thickness of the sealant layer 11 to the thickness of the multilayer film 1 in the package 10 is preferably 30% or less. During the thermomechanical analysis of the multilayer film 1 in the package 10, the amount of displacement at a temperature of 100° C. is preferably 500 μm or less. The multilayer film 1 in the package 10 preferably further comprises an oxygen barrier layer. In the multilayer film 1 in the package 10, the oxygen barrier layer preferably contains an ethylene-vinyl alcohol copolymer.

[0161] The packaging body 10 uses the multilayer film 1 as a lid material, and thus maintains the quality of the contents, has excellent conformability to the contents, and can conform softly to the contents. Furthermore, the packaging body 10 uses the multilayer film 1 (lid material) and the base material 8, which provides a high oxygen barrier to the contents 9, and the storage period of the contents 9 is longer than in the case of conventional packaging bodies.

[0162] One surface 8a of the base material 8 (sometimes referred to herein as the "first surface") is a sealing surface, and a portion of the first surface 8a is in close contact with a portion of the first surface 11a of the sealant layer 11 in the multilayer film 1 by sealing. In FIG. 3, the area where the first surface 8a of the base material 8 and the first surface 11a of the sealant layer 11 in the multilayer film 1 are in direct contact is the sealed portion. As a result, a storage section 10a is formed between the first surface 8a of the base material 8 and the first surface 11a of the sealant layer 11. An item 9 is sealed in this storage section 10a.

[0163] In Figure 3, some gaps can be seen between the contents 9 and the multilayer film 1, and between the contents 9 and the base material 8 within the storage section 10a of the package 10, but these gaps may not be present in the package 10 when the contents 9 are stored therein.

[0164] The packaging body of this embodiment is not limited to the one described above, and some of the configuration may be changed, deleted, or added within the scope of the spirit of the present invention.

[0165] <<Packaging manufacturing method>> The package of this embodiment is a package in which contents are vacuum-packaged by the base material and the lid material of the package of this embodiment.

[0166] The packaging body of this embodiment can be manufactured, for example, by placing the contents on the surface of the base material that will be sealed with the lid material, covering the surface of the base material and the contents with the lid material from above, and evacuating the area between the base material and the lid material where the contents are located, thereby tightly fixing the lid material to the contents, while heat-sealing the base material and the lid material in the area where the contents are not located. The test package described below can also be produced in the same manner.

[0167] The sealing temperature during heat sealing is not particularly limited, but is preferably 100 to 170° C. When the sealing temperature is equal to or higher than the lower limit, the seal strength is increased while maintaining easy peelability. When the sealing temperature is equal to or lower than the upper limit, the package is easier to open.

[0168] The heat-sealing time can be adjusted as appropriate depending on the sealing temperature, but is usually preferably 10 to 30 seconds. When the sealing time is equal to or greater than the lower limit, the seal strength is increased while maintaining easy peelability. When the sealing time is equal to or less than the upper limit, the package is easier to open.

[0169] The pressure in the region where the contents are placed, caused by evacuation during heat sealing, is 5000 Pa (50 mbar) or less, preferably 300 Pa to 5000 Pa, more preferably 400 Pa to 4900 Pa, even more preferably 500 Pa to 4800 Pa, and particularly preferably 600 Pa to 4700 Pa. By keeping the pressure at or below the upper limit, the lid material has better conformability (adhesion) to the contents, and a package with better storage suitability can be obtained. [Example]

[0170] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0171] The resins used in each example or comparative example are as follows. HDPE: High-density polyethylene ("Nipolon Hard" manufactured by Tosoh Corporation, density 962 g / cm 3 , melting point 134℃) LDPE: Low-density polyethylene (Sumitomo Chemical Co., Ltd. "Sumikasen", density 924 g / cm 3 , melting point 111℃) LLDPE: Linear low-density polyethylene (Prime Polymer Co., Ltd. "Evolue"; density 920 g / cm 3 , melting point 115℃) ION: Sodium ionomer ("Himilan" manufactured by Mitsui-Dow Polychemicals Co., Ltd., melting point 92°C) Modified PE: Maleic anhydride modified polyethylene (adhesive resin, "Admer" manufactured by Mitsui Chemicals, Inc.) EVOH: Ethylene-vinyl alcohol copolymer ("EVAL" manufactured by Kuraray Co., Ltd., ethylene copolymerization ratio 38 mol%) EVA1: Ethylene-vinyl acetate copolymer ("Evaflex" manufactured by Mitsui Dow Polychemicals Co., Ltd., acid modification degree 16 mol%) EVA2: Ethylene-vinyl acetate copolymer ("Evaflex" manufactured by Mitsui Dow Polychemicals Co., Ltd., acid-modified 10 mol%) AB: Anti-blocking agent (Tokyo Ink Co., Ltd. "PEX AB-0523") SL: Slip agent (erucic acid amide, "PEX SLT-01" manufactured by Tokyo Ink Co., Ltd.) OX: Antioxidant (Sumitomo Chemical Co., Ltd. "Sumikasen") EY: Anti-stain agent (Tokyo Ink Co., Ltd. "PEX PA-0007")

[0172] [ reference Example 1] <<Manufacturing of multilayer films>> The HDPE (72 parts by mass), the LLDPE (25 parts by mass), the AB (2 parts by mass), and the SL (1 part by mass) were mixed at room temperature to prepare outer layer forming composition 1. The EVA1 (97 parts by mass), the AB (2 parts by mass), and the SL (1 part by mass) were mixed at room temperature to prepare a sealant layer-forming composition 1.

[0173] The die temperature was set to 230°C, and the sealant layer-forming composition 1, the EVA 1, the modified PE, the EVOH, the modified PE, the ION, and the outer layer-forming composition 1 were co-extruded in this order (co-extrusion T-die method) to produce a multilayer film (thickness 120 μm) having the configuration shown in Figure 1, in which a sealant layer (thickness 32 μm), a first functional layer (thickness 24 μm), a first adhesive layer (thickness 6 μm), an oxygen barrier layer (thickness 6 μm), a second adhesive layer (thickness 6 μm), a second functional layer (thickness 23 μm), and an outer layer (thickness 23 μm) were laminated in this order in the thickness direction.

[0174] Next, the multilayer film obtained above was irradiated with EB from the outside of the outer layer side under conditions of an absorbed dose of 150 kGy and an acceleration voltage of 150 kV. As a result, the desired EB-irradiated multilayer film (hereinafter sometimes referred to as "EB film") was obtained.

[0175] <<Evaluation of multilayer films>> <Tack between sealant layer and outer layer> For the EB film obtained above, the tack strength between the sealant layer and the outer layer was measured by the following probe tack test. That is, a circular piece with a planar shape of 10 mm diameter was cut out from the EB film to serve as the first test piece, and the exposed surface of the sealant layer in the first test piece was aligned with the circular flat surface of a cylindrical stainless steel probe with a diameter of 10 mm, and the centers of the two were aligned and attached to each other using double-sided adhesive tape (Nicetack, manufactured by Nichiban Co., Ltd.) to prepare a test laminate. The multilayer film prepared separately was used as a second test piece. Under the condition of a temperature of 25°C, the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece of the test laminate were placed parallel to each other and facing each other. The second test piece was fixed, and the probe in the test laminate was moved toward the second test piece at a speed of 0.5 mm / sec. After the entire exposed surface of the outer layer in the first test piece contacted the exposed surface of the sealant layer in the second test piece, the probe was pressed toward the second test piece with a pressure of 24.517 N for 20 seconds, and then the probe was moved toward the opposite side from the second test piece at a speed of 10 mm / sec. The load (the tack force between the sealant layer and the outer layer) was measured. The results are shown in Table 1.

[0176] <Blocking suppression effect> The long EB film (200 m long) obtained above was wound up under a tension of 50 N / m into a roll and stored in a warehouse under conditions of a temperature of 23°C and a relative humidity of 60%. After 30 days, the rolled EB film was removed and the blocking suppression effect was evaluated according to the following criteria. The results are shown in Table 1. [Evaluation criteria] A: It can be cast without getting caught. B: There is some burr, but it can be extended. C: The burr is strong and requires a lot of force to be pulled out. D: Cannot be extended (if you force it out it will tear).

[0177] <Temperature showing a displacement of 2000 μm, Identifying the displacement at a temperature of 100°C> The EB film obtained above was subjected to thermomechanical analysis using a thermal analyzer ("TMA7100" manufactured by Hitachi High-Technologies Corporation) in accordance with JIS K 7196. From the obtained thermomechanical analysis curve, the temperature (°C) showing a displacement of 2000 μm and the displacement (μm) at a temperature of 100°C were determined. The results are shown in Table 1.

[0178] <Gel fraction measurement> The gel fraction of the EB film obtained above was measured in accordance with JIS K 6769. That is, a test piece measuring 3 cm x 3 cm (approximately 0.09 g) was cut out from the EB film, wrapped in a 400 mesh stainless steel wire mesh (100 g), and immersed in xylene (18 mL) at 110°C for 24 hours. The test piece together with the wire mesh was then removed from the xylene and vacuum dried at 110°C for 24 hours under a pressure of 1.7 kPa to obtain a dried product of the test piece after immersion. The mass of the obtained dried product was measured to determine the gel fraction (%) of the EB film. The results are shown in Table 1.

[0179] [ reference Example 2] As the resin constituting the first functional layer, the ION was used instead of the EVA1, except that reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0180] [ reference Example 3] As the resin constituting the second functional layer, the EVA1 was used instead of the ION, except that reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0181] [Example 4] The LLDPE (97 parts by mass), the AB (2 parts by mass), and the SL (1 part by mass) were mixed at room temperature to prepare a sealant layer-forming composition 2. Except for the fact that the sealant layer-forming composition 2 was used instead of the sealant layer-forming composition 1, and that the EVA1 was used instead of the ION as the resin constituting the second functional layer, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0182] [Example 5] Composition 3 for forming a sealant layer was prepared by mixing the EVA1 (93 parts by mass), the AB (2 parts by mass), the SL (1 part by mass), the OX (2 parts by mass), and the EY (2 parts by mass) at room temperature. Except that the sealant layer-forming composition 3 was used instead of the sealant layer-forming composition 1, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0183] [Example 6] Composition 4 for forming a sealant layer was prepared by mixing the EVA2 (93 parts by mass), the AB (2 parts by mass), the SL (1 part by mass), the OX (2 parts by mass), and the EY (2 parts by mass) at room temperature. Except for the fact that the sealant layer-forming composition 4 was used instead of the sealant layer-forming composition 1, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0184] [Example 7] The ION1 (97 parts by mass), the AB (2 parts by mass), and the SL (1 part by mass) were mixed at room temperature to prepare an outer layer forming composition 2. Except for the fact that the sealant layer-forming composition 3 was used instead of the sealant layer-forming composition 1 and the outer layer-forming composition 2 was used instead of the outer layer-forming composition 1, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0185] [Example 8] Except for the fact that the sealant layer-forming composition 4 was used instead of the sealant layer-forming composition 1 and the outer layer-forming composition 2 was used instead of the outer layer-forming composition 1, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0186] [Comparative Example 1] The LDPE (72 parts by mass), the LLDPE (25 parts by mass), the AB (2 parts by mass), and the SL (1 part by mass) were mixed at room temperature to prepare outer layer forming composition 3. Except for the fact that the sealant layer-forming composition 3 was used instead of the sealant layer-forming composition 1, the outer layer-forming composition 3 was used instead of the outer layer-forming composition 1, and the ION1 was used instead of the EVA1 as the resin constituting the first functional layer, reference The EB film was produced and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0187] [Table 1]

[0188] [Table 2]

[0189] [Table 3]

[0190] Reference Examples 1 to 3 and Example 4 The EB films of Comparative Examples 1 to 6 contained HDPE in the outer layer, and therefore had lower tack strength than the EB film of Comparative Example 1, and all of them had a good blocking suppression effect.

[0191] The EB film of Example 4 had a high melting point and was particularly effective in suppressing blocking because the sealant layer did not contain EVA.

[0192] In the EB films of Examples 5 to 8, the sealant layer contained an antioxidant and an anti-smudge agent, so radicals were easily deactivated, and all of them had a good blocking suppression effect.

[0193] The EB film of Example 6 had a lower degree of acid modification of the EVA contained in the sealant layer than the other Examples, and therefore had a high melting point and a particularly good blocking suppression effect.

[0194] The EB films of Examples 7 and 8 contained ION in the outer layer, and therefore had lower tack strength than the EB film of Comparative Example 1, and both had a good blocking suppression effect.

[0195] In contrast, the EB film of Comparative Example 1 contained LDPE in the outer layer, Reference Examples 1 to 3 and Example 4 The tack strength was higher than that of the EB film of 6, and the blocking suppression effect was inferior. [Industrial Applicability]

[0196] The present invention can be used for packaging used for preserving food and the like. [Explanation of symbols]

[0197] 1. Multilayer film 11. Sealant layer 12...outer layer 13. Functional Layer 131...1st functional layer 132...2nd functional layer 14. Oxygen barrier layer 15...adhesive layer 151...1st adhesive layer 152...Second adhesive layer 10...Packaging 8...Bottom material 9. Contents

Claims

1. A multilayer film, The multilayer film comprises an outer layer and a sealant layer; the outer layer contains an ethylene polymer having a melting point of 115°C or higher or an ionomer, The multilayer film has been irradiated with an electron beam at an absorbed dose of 20 to 300 kGy; A circular piece having a planar shape of 10 mm in diameter was cut out from the multilayer film to serve as a first test piece, and the exposed surface of the sealant layer in the first test piece was attached to a circular flat surface of a cylindrical stainless steel probe having a diameter of 10 mm with double-sided adhesive tape, with their centers aligned, to prepare a test laminate; The multilayer film prepared separately was used as a second test piece, Under a temperature condition of 25°C, the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece of the test laminate were placed parallel to each other and opposed to each other; A multilayer film in which the second test piece is fixed, the probe in the test laminate is moved toward the second test piece at a speed of 0.5 mm / sec, and after the entire exposed surface of the outer layer in the first test piece comes into contact with the exposed surface of the sealant layer in the second test piece, the probe is pressed toward the second test piece at a pressure of 24.517 N for 20 seconds, and then the probe is moved in the opposite direction from the second test piece at a speed of 10 mm / sec, and the load measured when this is 4.0 N or less.

2. A multilayer film, The multilayer film comprises an outer layer and a sealant layer; the outer layer contains an ethylene polymer having a melting point of 115°C or higher or an ionomer, When the multilayer film is subjected to thermomechanical analysis, the temperature at which the multilayer film shows a displacement of 2000 μm is 120° C. or higher, or the multilayer film has a gel fraction of 30% or higher; A circular piece having a planar shape of 10 mm in diameter was cut out from the multilayer film to serve as a first test piece, and the exposed surface of the sealant layer in the first test piece was attached to a circular flat surface of a cylindrical stainless steel probe having a diameter of 10 mm with double-sided adhesive tape, with their centers aligned, to prepare a test laminate; The multilayer film prepared separately was used as a second test piece, Under a temperature condition of 25°C, the exposed surface of the outer layer in the first test piece and the exposed surface of the sealant layer in the second test piece of the test laminate were placed parallel to each other and opposed to each other; A multilayer film in which the second test piece is fixed, the probe in the test laminate is moved toward the second test piece at a speed of 0.5 mm / sec, and after the entire exposed surface of the outer layer in the first test piece comes into contact with the exposed surface of the sealant layer in the second test piece, the probe is pressed toward the second test piece at a pressure of 24.517 N for 20 seconds, and then the probe is moved in the opposite direction from the second test piece at a speed of 10 mm / sec, and the load measured when this is 4.0 N or less.

3. 3. The multilayer film according to claim 1, wherein the outer layer has a storage modulus of 80 MPa or more at 30°C when measured by dynamic mechanical analysis (DMA) at a heating rate of 2°C / min and a frequency of 1 Hz.

4. The multilayer film of claim 1 or 2, wherein the sealant layer comprises an ethylene-based polymer.

5. the multilayer film further comprises a functional layer adjacent to the sealant layer; The multilayer film according to claim 1 or 2, wherein the functional layer comprises an ethylene-based polymer.

6. 3. The multilayer film according to claim 1, wherein the ratio of the thickness of the sealant layer to the thickness of the multilayer film is 30% or less.

7. The multilayer film according to claim 2, wherein the amount of displacement at a temperature of 100°C during the thermomechanical analysis is 500 µm or less.

8. The multilayer film according to claim 1 or 2, further comprising an oxygen barrier layer.

9. The multilayer film of claim 8, wherein the oxygen barrier layer comprises an ethylene-vinyl alcohol copolymer.

10. A packaging product comprising the multilayer film according to claim 1 or 2.

11. The package of claim 10, wherein the package is a skin pack package.

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