Packaging film and sealed container

Abstract

To provide a packaging film which enables formation of a steam hole at a desired position in the packaging film.SOLUTION: A packaging film includes a first resin film, a second resin film, and a heat generation part. The first film has a first slit, a second slit, and a butted area. The second film does not have a slit and the heat generation part includes a heat-generating ink which absorbs microwaves to generate heat. When the first film is viewed in a plan view, the butted area, at least a part of the first slit, and at least a part of the second slit are disposed at positions which overlap the heat generation part. The first film, the second film, and the heat generation part in the butted area are configured to be broken as the heat generation part generates heat.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a packaging film and a sealed container.

Background Art

[0002] Patent Document 1 and Patent Document 2 disclose a package for storing frozen foods or chilled foods heated by a microwave oven. The package is a sealed container including a tray and a lid for sealing an opening of the tray. The tray has a storage space capable of storing contents such as frozen foods. The lid includes a sheet containing a heat generating layer that generates heat by microwaves, and a steam vent provided in the sheet. The steam vent is a portion where the strength is locally reduced, specifically, a cut.

[0003] The heat generating layer of the sheet generates heat by the microwaves of the microwave oven. Further, the moisture of the contents becomes water vapor by the microwaves, and the internal pressure of the storage space increases. As a result, steam holes for discharging water vapor are formed at the position of the cut, and the water vapor in the sealed container escapes from the steam holes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technologies of Patent Document 1 and Patent Document 2, it is difficult to control at which position in the cut and what size of steam holes are formed, and it is difficult to appropriately control the discharge amount of water vapor. If the steam holes are too large, more water vapor than necessary is discharged from the sealed container, the quality of the contents deteriorates, or the inside of the microwave oven gets wet with water vapor.

[0006] One object of the present invention is to provide a packaging film capable of forming pores at a desired position in the packaging film, and a sealed container including such a packaging film.

Means for Solving the Problems

[0007] (1) The packaging film according to one embodiment of the present invention includes a first resin film having a first surface and a second surface opposite to the first surface, a second resin film adhered to the first surface, and a heat generating portion disposed on at least one of the first surface and the second surface. The first film has a first cut, a second cut, and a butting region formed on the second surface. The first cut and the second cut are arranged non-parallel with a space therebetween, and the butting region is located between the endpoints of the first cut and the endpoints of the second cut that are close to each other. The second film has no cut, and the heat generating portion includes a heat generating ink that absorbs microwaves and generates heat. When the first film is viewed in a plan view, the butting region, at least a part of the first cut, and at least a part of the second cut are arranged at positions overlapping the heat generating portion, and the first film, the second film, and the heat generating portion in the butting region are configured to break along with the heat generation of the heat generating portion.

[0008] In the sealed container sealed by the packaging film described in (1) above, when the heating part is heated by the microwave of the microwave oven, the resin-made first film and second film shrink. The first cut formed in the first film guides the tensile stress accompanying the shrinkage of the first film onto the extension line of the first cut. Similarly, the second cut formed in the first film guides the tensile stress accompanying the shrinkage of the first film onto the extension line of the second cut. Since the first cut and the second cut are arranged non-parallelly, the direction of the tensile stress guided by the first cut and the direction of the tensile stress guided by the second cut are different. "The first cut and the second cut are arranged non-parallelly" means anything other than "the first cut and the second cut are arranged parallelly". For example, when the first cut and the second cut are arranged in a straight line, it is included in the case where the first cut and the second cut are arranged non-parallelly. The extension lines of the first cut and the second cut arranged parallelly do not intersect or overlap, but the extension lines of the first cut and the second cut arranged non-parallelly intersect or overlap. Therefore, the butting region including the portion where the extension line of the first cut and the extension line of the second cut intersect or overlap is pulled by tensile stresses in different directions. As a result, the first film, the second film, and the heating part break at the position of the butting region, and steam holes penetrating the packaging film are formed.

[0009] In the packaging film described in (1) above, steam holes are formed in the butting region as the heating part generates heat, and water vapor is discharged from the steam holes. By forming steam holes in the butting region, it is difficult for steam holes to be formed in parts other than the butting region. Therefore, small pieces of the melted packaging film are less likely to fall off into the storage container.

[0010] The packaging film having no cut in the second film is excellent in strength. Therefore, even when a mechanical load acts on the packaging film, the packaging film is not easily torn. For example, even when a plurality of sealed containers sealed with this packaging film are stacked and stored, it is difficult for holes to be formed in the packaging film of each sealed container, and the airtightness of the sealed container is easily maintained.

[0011] (2) In the packaging film described in (1) above, the extension line of the first cut and the extension line of the second cut may be arranged on the same straight line.

[0012] When the first cut and the second cut are arranged on the same straight line, the direction of the tensile stress guided by the first cut and the direction of the tensile stress guided by the second cut are opposite to each other. As a result, a very strong tensile stress acts on the butting region, so pores are likely to be formed in the butting region.

[0013] (3) In the packaging film described in (1) above, among the angles between the extension line of the first cut and the extension line of the second cut in the butting region, the smaller angle may be 120° or more and less than 180°.

[0014] Even in the configuration of (3) above, similar to the configuration of (2), the tensile stress guided by the first cut and the tensile stress guided by the second cut are likely to concentrate in the butting region, and pores are likely to be formed in the butting region.

[0015] (4) In the packaging film described in any one of (1) to (3) above, in a plan view of the first film, the length L1 where the first cut and the heat generating part overlap, and the length L2 where the second cut and the heat generating part overlap may be larger than the distance S1 between the first cut and the second cut.

[0016] In the packaging film described in (4) above, the tensile stress guided by the first cut and the tensile stress guided by the second cut are likely to concentrate in the narrow butting region, and pores are likely to be formed in the butting region.

[0017] (5) In the packaging film described in (4) above, each of the length L1 and the length L2 may be 3 mm or more.

[0018] If the overlapping length L1 between the first cut and the heat generating part is 3 mm or more, the tensile stress accompanying the shrinkage of the first film is likely to be guided in the direction along the first cut. Similarly, if the overlapping length L2 between the second cut and the heat generating part is 3 mm or more, the tensile stress accompanying the shrinkage of the first film is likely to be guided in the direction along the second cut. Therefore, the tensile stress acting on the butting region is likely to increase, and steam holes are likely to be formed in the butting region.

[0019] (6) In the packaging film according to the above (4) or (5), the interval S1 may be 1 mm or more and 4 mm or less.

[0020] If the interval S1 is 1 mm or more, the first cut and the second cut are sufficiently separated, so that it is possible to suppress the first cut and the second cut from functioning like one large cut. With one large cut, there is a risk that the cut itself will tear during heating by a microwave oven. If the interval S1 is 4 mm or less, the tensile stress in the butting region is difficult to disperse, and steam holes of a predetermined size are likely to be formed in the butting region.

[0021] (7) In the packaging film according to any one of the above (1) to (6), the area of the heat generating part is 50 mm 2 or more and 450 mm 2 or less.

[0022] If the area of the heat generating part is 50 mm 2 or more, the shrinkage amount of the first film formed with the heat generating part is sufficiently large, and sufficient tensile stress can be applied to the butting region. If the area of the heat generating part is 450 mm 2 or less, it is difficult for steam holes to be formed at positions other than the butting region in the heat generating part, and the dropout of small pieces accompanying the formation of steam holes at that position is suppressed.

[0023] (8) In the packaging film according to any one of the above (1) to (7), the heat generating part may be arranged only on the first surface.

[0024] In the above configuration, the heat generating part is disposed between the first film and the second film. Therefore, the heat of the heat generating part is easily transmitted to the first film and the second film, and the first film and the second film are easily and effectively shrunk.

[0025] (9) In the packaging film according to any one of (1) to (7) above, the heat generating part may be disposed only on the second surface.

[0026] In the above configuration, an existing packaging film including the first film and the second film can be used. For example, by printing a heat generating part on an existing packaging film held in stock and forming a cut, a packaging film having the above configuration can be obtained.

[0027] (10) In the packaging film according to any one of (1) to (9) above, a plurality of pairs each including the first cut and the second cut may be provided, and the butting regions of different pairs may overlap.

[0028] In the packaging film described in (10) above, since the tensile stresses of a plurality of different pairs concentrate on one butting region, pores are easily formed in the butting region.

[0029] (11) In the packaging film according to any one of (1) to (10) above, a plurality of pairs each including the first cut and the second cut may be provided, and the plurality of pairs may include pairs having different butting regions.

[0030] The packaging film described in (11) above has a plurality of butting regions, and thus a plurality of pores are formed when heated by a microwave oven. As a result, the water vapor in the sealed container is more reliably discharged to the outside of the sealed container.

[0031] (12) In the packaging film according to any one of (1) to (11) above, the material of the second film may be a polypropylene resin, a polyethylene resin, or a polyethylene terephthalate resin.

[0032] A packaging film comprising a second film made of polypropylene resin (PP resin), polyethylene resin (PE resin), or polyethylene terephthalate resin (PET resin) is likely to ensure airtightness within a sealed container when sealed to a storage container.

[0033] (13) In the packaging film according to any one of (1) to (12) above, the average thickness of the second film may be 10 μm or more and 60 μm or less.

[0034] The second film with an average thickness of 10 μm or more has a predetermined strength and is thus less likely to tear during storage of the sealed container. The second film with an average thickness of 60 μm or less has a strength that is not too high, so steam holes are likely to be formed when heating the sealed container in a microwave oven.

[0035] (14) The sealed container according to the embodiment includes a storage container containing contents to be heated by microwave and a packaging film that seals the contents within the storage container, and the packaging film is the packaging film according to any one of (1) to (13) above.

[0036] In the above sealed container, when heated in a microwave oven, steam holes are formed at a predetermined position of the packaging film, and it is less likely that steam holes are formed at an unintended position. Therefore, the contents are likely to be heated appropriately.

[0037] In the above sealed container, even when a mechanical load acts on the packaging film, the packaging film is less likely to tear. This is because there are no cuts in the second film provided on the packaging film. Therefore, even when the sealed containers are stacked and stored, it is less likely that holes are formed in the packaging film of each sealed container, and the airtightness of the sealed container is likely to be maintained.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0039] Hereinafter, specific examples of the packaging film and the sealed container of the present invention will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. The sizes of the members shown in each drawing are represented for the purpose of clarifying the description and do not necessarily represent actual dimensions. It should be noted that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0040] <Embodiment 1> ≪Overall Configuration≫ The sealed container 1 shown in FIGS. 1 and 2 includes a box-shaped storage container 9 and a resin-made packaging film 2 that seals the storage container 9. As shown in FIG. 2, the storage container 9 stores the contents 8 therein. The contents 8 are, for example, frozen foods or chilled foods. The contents 8 are heated together with the sealed container 1 by a microwave oven. The heating conditions of the microwave oven are, for example, 1500 W for a commercial microwave oven in a convenience store or the like, and 500 W for a household microwave oven.

[0041] ≪Storage Container≫ The storage container 9 is made of a heat-resistant material that is difficult to deform by heating with a microwave oven. The material of the storage container 9 is, for example, PP resin. The storage container 9 may be transparent or opaque. If the storage container 9 is transparent, the contents 8 can be confirmed from the outside of the storage container 9. If the storage container 9 is opaque, the contents 8 are shielded from light, and it is easy to suppress the deterioration of the contents 8.

[0042] The external shape of the storage container 9 is not particularly limited as long as it is box-shaped with an opening 90 at the upper end. The external shape of the storage container 9 in this example is generally an inverted quadrangular frustum shape. Different from this example, the external shape of the storage container 9 may be, for example, an inverted conical frustum shape, a cylindrical shape, or a prismatic shape.

[0043] A flange portion 9F is formed at the edge of the opening 90 of the storage container 9. A second film 5 provided on the packaging film 2 described later is heat-sealed to the flange portion 9F.

[0044] [Packaging Film] As shown in FIGS. 2 and 3, the packaging film 2 in this example includes a resin-made first film 3, a resin-made second film 5, and a heat-generating portion 4. Hereinafter, each component of the packaging film 2 will be sequentially described.

[0045] [First Film] The first film 3 includes a first surface 3f and a second surface 3b opposite to the first surface 3f. A heat-generating portion 4 described later is printed on a part of the first surface 3f. In order to improve the adhesion of the heat-generating portion 4, the first surface 3f may be pretreated. The pretreatment is, for example, corona treatment, plasma treatment, or ozone treatment. Further, the second film 5 described later is adhered to the heat-generating portion 4 and the portion of the first surface 3f other than the portion where the heat-generating portion 4 is printed. In this example, the first surface 3f faces the storage container 9, and the second surface 3b faces the outside of the storage container 9.

[0046] The first film 3 has a size that covers the entire opening 90 of the storage container 9. This first film 3 is made of resin. The material of the first film 3 is not particularly limited as long as it has a predetermined tensile strength and can maintain the airtightness of the sealed container 1. The material of the first film 3 is, for example, PP resin, PE resin, or PET resin.

[0047] The average thickness of the first film 3 is, for example, 10 μm or more and 50 μm or less. Since the first film 3 with an average thickness of 10 μm or more has a predetermined strength, it is not easily torn during the storage of the sealed container 1. Since the first film 3 with an average thickness of 50 μm or less does not have too high strength, steam holes 39 (Fig. 4) are easily formed when the sealed container 1 is heated by a microwave oven. The steam holes 39 and their formation positions will be described later.

[0048] The average thickness of the first film 3 can be obtained, for example, by a non-contact thickness gauge that measures the thickness of the thin film by irradiating light with a wide wavelength. In this example, the average thickness of the first film 3 is obtained by measuring the thicknesses at a plurality of different locations on the first film 3 and averaging these measured values. The number of measurement locations is, for example, 5 or more.

[0049] As shown in Fig. 1, the first film 3 has a first cut 3A, a second cut 3B, and a butting region 3C formed on the second surface 3b. The butting region 3C is a region located between the end points of the first cut 3A and the end points of the second cut 3B that are close to each other. These configurations will be described in a later section with dedicated items.

[0050] [Second Film] The second film 5 is adhered to the first surface 3f of the first film 3 and the heat generating part 4. The adhesion between the second film 5 and the first film 3 is borne by the adhesive layer 50. The adhesive layer 50 is formed on one side surface of the second film.

[0051] The second film 5 in this example has the same size as the first film 3. The outer peripheral edge of the second film 5 is heat-sealed to the flange portion 9F of the storage container 9. The seal portion 10 where the outer peripheral edge and the flange portion 9F are heat-sealed maintains the airtightness of the sealed container 1 and suppresses the deterioration of the content 8.

[0052] The second film 5 in this example is made of a material that is more excellent in heat-sealing property than the first film 3. Therefore, the packaging film 2 in this example is easily heat-sealed to the flange portion 9F of the storage container 9, and the seal portion 10 between the packaging film 2 and the flange portion 9F is difficult to peel off. The material of the second film is, for example, PP resin, PE resin, or PET resin. A general food-use dry laminate adhesive or non-solvent laminate adhesive may be used for the adhesive layer 50.

[0053] The average thickness of the second film 5 is, for example, 10 μm or more and 60 μm or less. Since the second film 5 with an average thickness of 10 μm or more has a predetermined strength, it is difficult to break during storage of the sealed container 1. Since the second film 5 with an average thickness of 60 μm or less does not have too high strength, steam holes 39 (FIG. 4) are easily formed when the sealed container 1 is heated by a microwave oven. The steam holes 39 and their formation positions will be described later. The measuring method of the average thickness of the second film 5 is the same as that of the first film 3.

[0054] The second film 5 does not have a cut. The packaging film 2 without a cut in the second film 5 is excellent in strength. Therefore, even if a mechanical load acts on the packaging film 2, the packaging film 2 is difficult to break. For example, even if a plurality of sealed containers 1 sealed with this packaging film 2 are stacked and stored, holes are hardly formed in the packaging film 2 of each sealed container 1, and the airtightness of the sealed container 1 is easily maintained.

[0055] [Heat generating part] The heat generating part 4 is disposed on at least one of the first surface 3f and the second surface 3b of the first film 3. In this example, the heat generating part 4 is disposed only on the first surface 3f. That is, this heat generating part 4 is disposed between the first film 3 and the second film 5. As shown by the two-dot chain line in FIG. 2, the heat generating part 4 may be disposed on both the first surface 3f and the second surface 3b, or may be disposed only on the second surface 3b. If the heat generating part 4 is disposed only on the first surface 3f or the second surface 3b, the labor for forming the heat generating part 4 can be reduced as compared with the configuration in which the heat generating part 4 is disposed on both the first surface 3f and the second surface 3b.

[0056] The heat generating part 4 contains heat generating ink that absorbs microwaves and generates heat. The heat generating ink contains a conductive material. The frequency of microwaves is generally from 300 megahertz to 300 gigahertz. The frequency of a household, commercial, or industrial microwave oven is 2450 megahertz. The conductive material is, for example, carbon black, silver, aluminum, indium tin oxide, or a conductive organic compound. The conductive organic compound is, for example, at least one selected from the group consisting of polyanilines, polypyrroles, and polythiophenes. The heat generating ink may contain a resin. The resin is, for example, a polyvinyl alcohol resin.

[0057] The printing method of the heat generating part 4 is not particularly limited. If it is intaglio printing or letterpress printing, the heat generating ink can be efficiently printed on the first film 3 wound around the drum. For example, the heat generating part 4 may be printed by a gravure printing machine.

[0058] The thickness of the heat generating part 4 is, for example, 0.3 μm or more and 3.0 μm or less. If the thickness is 0.3 μm or more, a sufficient amount of heat generating ink contained in the heat generating part 4 is ensured. If the thickness is 3.0 μm or less, the heat generating part 4 does not become too thick.

[0059] The size of the heat generating part 4, that is, the area of the heat generating part 4 when viewed in plan, is smaller than that of the first film 3. The area of the heat generating part 4 is, for example, 50 mm 2 or more and 450 mm 2The following applies. When there are a plurality of heat generating portions 4, the size of each heat generating portion 4 is 50 mm 2 or more and 450 mm 2 or less. If the area of the heat generating portion 4 is 50 mm 2 or more, the shrinkage amount of the first film 3 on which the heat generating portion 4 is formed is sufficiently large, and a sufficient tensile stress can be applied to the butting region 3C described later. If the area of the heat generating portion 4 is 450 mm 2 or less, it is difficult to form the steam holes 39 at positions other than the butting region 3C in the heat generating portion 4, and the dropping of small pieces accompanying the formation of the steam holes 39 at that position is suppressed. The area of the heat generating portion 4 may be 64 mm 2 or more and 450 mm 2 or less, or may be 100 mm 2 or more and 400 mm 2 or less.

[0060] [First cut · Second cut · Butting region] As shown in FIG. 4, the first cut 3A and the second cut 3B are arranged non-parallel with a space therebetween. The non-parallel arrangement means a state in which the extension line of the first cut 3A and the extension line of the second cut 3B intersect or overlap. The first cut 3A and the second cut 3B in this example are formed on the second surface 3b. Further, the butting region 3C is located between the end point 3Ae of the first cut 3A and the end point 3Be of the second cut 3B. In the following description, the first cut 3A and the second cut 3B may not be distinguished and may be simply expressed as cuts 3A, 3B.

[0061] The cuts 3A, 3B are formed in the packaging film 2 by, for example, a cutter such as a slitter or a die roll, or a laser. As shown in FIG. 3, the cuts 3A, 3B in this example penetrate the first film 3 and the heat generating portion 4 and reach the adhesive layer 50, but do not reach the second film 5. Different from the example shown in FIG. 3, the cuts 3A, 3B may not penetrate the adhesive layer 50. In addition, the cuts 3A, 3B may penetrate the first film 3 but may not penetrate the heat generating portion 4. When the heat generating layer 4 is formed on the second surface 3b, the cuts 3A, 3B are formed after the heat generating portion 4 is formed.

[0062] The first cut 3A and the second cut 3B in this example shown in FIG. 4 are arranged on the same straight line. That is, the first cut 3A and the second cut 3B are arranged such that the extension line of the first cut 3A and the extension line of the second cut 3B overlap. The region including the overlapping portion of the two extension lines is the butting region 3C.

[0063] When the first film 3 is viewed in plan view, at least a part of the first cut 3A and at least a part of the second cut 3B overlap the heat generating portion 4. With such a configuration, when the heat generating portion 4 is heated by the microwave of the microwave oven, the resin-made first film 3 and the second film 5 contract. In particular, if the heat generating portion 4 is arranged between the first film 3 and the second film 5, the heat of the heat generating portion 4 is easily transmitted to both the first film 3 and the second film 5, and the first film 3 and the second film 5 are likely to contract in the same manner. The first cut 3A formed in the first film 3 guides the tensile stress accompanying the contraction of the first film 3 onto the extension line of the first cut 3A. Similarly, the second cut 3B formed in the first film 3 guides the tensile stress accompanying the contraction of the first film 3 onto the extension line of the second cut 3B. Since the first cut 3A and the second cut 3B are arranged non-parallel, the direction of the tensile stress guided by the first cut 3A is different from the direction of the tensile stress guided by the second cut 3B. Therefore, the butting region 3C including the location where the extension line of the first cut 3A and the extension line of the second cut 3B intersect is pulled by tensile stresses in different directions. As a result, the first film 3, the second film 5, and the heat generating portion 4 break at the position of the butting region 3C, and a steam hole 39 (see the dotted circle) penetrating the packaging film 2 is formed. The heating condition of the microwave oven for forming the steam hole 39 is, for example, 500 W × 2 minutes. This heating condition can be realized by a household microwave oven. Depending on the type and amount of the contents 8, the heating time can be shortened or extended.

[0064] The length L1 where the first cut 3A overlaps with the heat generating part 4 and the length L2 where the second cut 3B overlaps with the heat generating part 4 affect the formation of the steam holes 39. In this example, since the first cut 3A overlaps with the heat generating part 4 over the entire length, the length L1 is equal to the length of the first cut 3A. Similarly, since the second cut 3B overlaps with the heat generating part 4 over the entire length, the length L2 is equal to the length of the second cut 3B. The measurement of the lengths L1 and L2 can be performed manually, for example, using calipers.

[0065] For example, the length L1 and the length L2 are each 3 mm or more. If the length L1 is 3 mm or more, the tensile stress associated with the shrinkage of the first film 3 is easily guided in the direction along the first cut 3A. Similarly, if the length L2 is 3 mm or more, the tensile stress associated with the shrinkage of the first film 3 is easily guided in the direction along the second cut 3B. Therefore, the tensile stress acting on the butting region 3C tends to increase, and the steam holes 39 are easily formed in the butting region 3C. The lengths L1 and L2 may also be 5 mm or more. There is no upper limit for the lengths L1 and L2, but in order to increase the lengths L1 and L2, the area of the heat generating part 4 must be increased. The upper limits of the lengths L1 and L2 are defined within the preferred area range of the heat generating part 4.

[0066] The distance S1 between the first cut 3A and the second cut 3B also affects the formation of the steam holes 39. The distance S1 is the length of the straight line connecting the end point 3Ae and the end point 3Be. The measurement of the distance S1 can be performed manually, for example, using calipers.

[0067] The distance S1 is, for example, 1 mm or more and 4 mm or less. If the distance S1 is 1 mm or more, the first cut 3A and the second cut 3B are sufficiently separated, so it is possible to suppress the first cut 3A and the second cut 3B from functioning like one large cut. With one large cut, there is a risk that the cut itself will tear during heating by a microwave oven. If the distance S1 is 4 mm or less, the tensile stress is easily concentrated in the butting region 3C, and steam holes 39 of a predetermined size are easily formed in the butting region 3C. The distance S1 may also be 1 mm or more and 2 mm or less.

[0068] The interval S1 is preferably smaller than the lengths L1 and L2. In other words, it is desirable that the lengths L1 and L2 are larger than the interval S1. When the interval S1 is smaller than the lengths L1 and L2, the tensile stress of the first cut 3A and the tensile stress of the second cut 3B tend to concentrate in the narrow butting region 3C. As a result, pores 39 are likely to be formed in the butting region 3C.

[0069] According to the above configuration, by forming pores 39 in the butting region 3C sandwiched between the first cut 3A and the second cut 3B, water vapor is discharged from the pores 39. By forming pores 39 in the butting region 3C, locations other than the butting region 3C are not broken, and pores 39 are not formed in locations other than the butting region 3C. Therefore, it is easy to suppress the detachment of small pieces of the first film 3 due to the formation of pores 39.

[0070] The butting region 3C is preferably disposed at the central portion of the first film 3, that is, at the central portion of the opening 90 of the storage container 9. When the internal pressure in the storage container 9 increases, the central portion of the packaging film 2 bulges. If pores 39 are formed at the bulging location, the water vapor in the sealed container 1 can be efficiently discharged.

[0071] In the configuration of this example, pores 39 are likely to be formed before the internal pressure of the sealed container 1 rises excessively. If water vapor is generated from the content 8 with heating in a microwave oven and pores 39 are formed earlier than the internal pressure in the sealed container 1 rises enough to peel off the adhesion of the seal portion 10, the possibility that the seal portion between the storage container 9 and the packaging film 2 peels off is very low. Therefore, in the packaging film 2 of the sealed container 1 of this example, the position where pores 39 are formed can be limited to approximately the butting region 3C, and it is easy to control the amount of water vapor discharged from the pores 39.

[0072] The formation pattern of the first cut 3A and the second cut 3B is not limited to the example shown in FIG. 4. The formation pattern may be, for example, patterns A to E shown in FIG. 5.

[0073] In pattern A of FIG. 5, a part of the cuts 3A and 3B overlaps with the heat generating part 4. In this case, the length L1 is shorter than the length of the first cut 3A, and the length L2 is shorter than the length of the second cut 3B.

[0074] In pattern B, among the angles between the extension line of the first cut 3A and the extension line of the second cut 3B, the smaller angle θ is 120° or more and less than 180°. Also in this configuration, since stress concentration occurs in the butting region 3C, the steam holes 39 can be formed in the butting region 3C.

[0075] Patterns C to E show examples having a plurality of pairs 3P each consisting of a first cut 3A and a second cut 3B. In pattern C, pairs 3P of cuts 3A and 3B arranged vertically on the drawing and pairs 3P of cuts 3A and 3B arranged horizontally are arranged. That is, four cuts are arranged in a cross shape. In this example, the butting regions 3C of two different pairs 3P overlap.

[0076] In pattern D, two pairs 3P each consisting of a first cut 3A and a second cut 3B arranged at an angle of 120° are arranged. The second cut 3B of one pair 3P also serves as the first cut 3A of the other pair 3P. In patterns C and D, since the tensile stresses of a plurality of different pairs 3P concentrate on one butting region 3C, the steam holes 39 are likely to be formed in the butting region 3C.

[0077] In pattern E, a plurality of different pairs 3P are arranged in the butting region 3C. In this case, a plurality of steam holes 39 are formed when heating with a microwave oven. The water vapor in the sealed container 1 is efficiently discharged to the outside of the sealed container 1 through the plurality of steam holes 39. Since it is easy to control the discharge amount of the water vapor according to the number of the steam holes 39, it is easy to appropriately heat the content 8.

[0078] [Others] The packaging film 2 may be provided with a printing layer on the second surface 3b. The printing layer is, for example, a layer on which a product name, product photo, etc. are drawn. When the sealed container 1 is sold in a state of being enclosed in a product package or the like, the printing layer may not be formed on the second surface 3b. That is, the packaging film 2 may be plain.

[0079] Furthermore, the packaging film 2 may be provided with a heat-sensitive layer. The heat-sensitive layer is a layer containing ink that develops color by heat. The manufacturing date, etc. are printed on the heat-sensitive layer. The heat-sensitive layer may not overlap with the printing layer within the plane of the second surface 3b, or may be formed on the printing layer.

[0080] <Test Example> In the test example, packaging films 2 of sample No. 1 to sample No. 9 and sample No. 100 to sample No. 102 were produced, and the influence of the cuts 3A, 3B on the formation of the steam holes 39 was examined.

[0081] ≪Sample No. 1 to Sample No. 9≫ A plurality of packaging films 2 including the first film 3, the heat-generating part 4, and the second film 5 were produced. The material of the first film 3 was PET resin (FE2002 manufactured by Futamura Chemical Co., Ltd.), and the material of the second film 5 was PP resin (9501K2 manufactured by Toray Film Processing Co., Ltd.) or PET resin (E7800TT manufactured by DIC Corporation). The average thickness of the first film 3 was 12 μm, and the average thickness of the second film 5 was 30 μm.

[0082] The heat-generating ink contained in the heat-generating part 4 was LG-MW heat agent manufactured by Tokyo Ink Co., Ltd. The size of the heat-generating part 4 was 15 mm × 15 mm in plan view, and the area of the heat-generating part 4 was 225 mm 2 was.

[0083] Next, using a cutter, first cut lines 3A and second cut lines 3B were formed in each packaging film 2. The formation patterns of the cut lines 3A and 3B are shown in the matrix diagrams of FIGS. 6 and 7. The squares in the 'formation pattern' of the matrix diagram are the heat generating portions 4, and the dashed lines are the cut lines 3A and 3B. The dashed lines are shown thick to make the arrangement of the cut lines 3A and 3B easier to understand, but the actual widths of the cut lines 3A and 3B are very small. The depth of the cut lines 3A and 3B reached the adhesive layer 50 but did not reach the second film 5, as illustrated in FIG. 3. The lengths L1 and L2 of the cut lines 3A and 3B, and the interval S1 are also shown in accordance with FIGS. 6 and 7. As already explained, the lengths L1 and L2 are the lengths where the cut lines 3A and 3B overlap with the heat generating portion 4.

[0084] Next, a cubic container made of PP was prepared, and 180 g of rice for a range cooker was placed in the container. The volume of the container was 900 cm 3 It was. The packaging film 2 was placed over the opening of the container containing the rice for a range cooker. The outer peripheral edge of the second film 5 was heat-sealed to the flange portion 9F of the storage container 9 to form a seal portion 10, and a test container simulating the sealed container 1 was produced. The test container was heated by a microwave oven to examine whether steam holes 39 were formed in the packaging film 2. The heating conditions of the microwave oven were 500 W × 2 minutes. The presence or absence of the steam holes 39 was confirmed visually. The results are shown in the 'presence or absence of steam holes' item in FIGS. 6 and 7. The'sealing material' in FIGS. 6 and 7 refers to the material of the second film 5.

[0085] ≪Sample No. 100 to Sample No. 102≫ As shown in the matrix diagram of FIG. 8, Sample No. 100 is a packaging film that has a heat generating portion 4 but does not have cut lines 3A and 3B in any of the first film 3, the second film 5, and the heat generating portion 4. The size of the heat generating portion 4 of Sample No. 100 was the same 15 mm × 15 mm as that of Samples No. 1 to No. 9.

[0086] Samples No. 101 to No. 102 are packaging films that have cuts 3A and 3B in the first film 3 but do not have a heating part 4. The second film 5 does not have a cut. In sample No. 101, the two cuts 3A and 3B are arranged on the same straight line. In sample No. 102, the four cuts are arranged in a cross shape.

[0087] The arrangement patterns, lengths L1 and L2, interval S1, and the presence or absence of the steam holes 39 from sample No. 101 to sample No. 102 are shown in FIG. 8.

[0088] ≪Summary of Test Results≫ As shown in FIGS. 6 and 7, in samples No. 1 to No. 9, the steam holes 39 were formed at the position of the butting region 3C. Also, the steam holes 39 were not formed at locations other than the butting region 3C. From these facts, it was found that even in a household microwave oven with low output, by arranging the first cut 3A and the second cut 3B to butt at a position overlapping the heating part 4, the steam holes 39 can be formed in the butting region 3C. Also, the seal part 10 of these samples was maintained, and no gap serving as a passage for water vapor was formed at the position of the flange part 9F.

[0089] As shown in FIG. 8, in samples No. 100 to No. 102, the steam holes 39 were not formed in the packaging film 2. That is, in a configuration where either the heating part 4 or the cuts 3A and 3B are missing, the steam holes 39 could not be formed. If the heating conditions of the microwave oven change, there may be a possibility that the steam holes 39 are formed even in samples No. 100 to No. 102, but it is considered difficult to control the formation position of the steam holes 39. Also, in the seal part 10 of these samples, there were scattered places where the packaging film 2 peeled off from the flange part 9F.

Explanation of Signs

[0090] 1 Sealed container 10 Seal part 2 Packaging film 3 First film 3b Second side, 3f First side 3A First cut, 3B Second cut, 3C Alignment area, 3P Pair 3Ae, 3Be End points 39 Steam holes 4 Heating part 5 Second film 50 Adhesive layer 8 Contents 9 Storage container 9F Flange part, 90 Opening L1, L2 Lengths S1 Distance θ Angle

Claims

1. A first resin film having a first surface and a second surface opposite to the first surface, A second resin film adhered to the first surface, A heat generating portion disposed on at least one of the first surface and the second surface, comprising: The first film has a first cut, a second cut, and a butting region formed on the second surface, The first cut and the second cut are arranged non-parallel with a space therebetween, The butting region is located between the endpoints of the first cut and the endpoints of the second cut that are close to each other, The second film has no cut, The heat generating portion contains heat generating ink that absorbs microwaves and generates heat, When the first film is viewed in a plan view, the butting region, at least a part of the first cut, and at least a part of the second cut are arranged at positions overlapping the heat generating portion, The first film, the second film, and the heat generating portion in the butting region are configured to break with the heat generation of the heat generating portion, Packaging film.

2. The packaging film according to claim 1, wherein an extension line of the first cut and an extension line of the second cut are arranged on the same straight line.

3. The packaging film according to claim 1, wherein the smaller of the angles between the extension line of the first cut and the extension line of the second cut in the butting region is 120° or more and less than 180°.

4. In a state where the first film is viewed in a plan view, The length L1 where the first cut overlaps the heat generating portion and the length L2 where the second cut overlaps the heat generating portion are larger than the distance S1 between the first cut and the second cut. The packaging film according to any one of claims 1 to 3.

5. The packaging film according to claim 4, wherein each of the length L1 and the length L2 is 3 mm or more.

6. The packaging film according to claim 4, wherein the distance S1 is 1 mm or more and 4 mm or less.

7. The area of the heat generating part is 50 mm ２ or more and 450 mm ２ or less. The packaging film according to any one of claims 1 to 3.

8. The packaging film according to any one of claims 1 to 3, wherein the heat generating portion is disposed only on the first surface.

9. The packaging film according to any one of claims 1 to 3, wherein the heat generating portion is disposed only on the second surface.

10. A plurality of pairs consisting of the first cut and the second cut are provided, The packaging film according to any one of claims 1 to 3, wherein the alignment regions of different pairs overlap. **Claim 11** Comprising a plurality of pairs consisting of the first cut and the second cut, The packaging film according to any one of claims 1 to 3, wherein the plurality of pairs include pairs having different alignment regions. **Claim 12** The packaging film according to any one of claims 1 to 3, wherein the material of the second film is a polypropylene resin, a polyethylene resin, or a polyethylene terephthalate resin. **Claim 13** The packaging film according to claim 12, wherein the average thickness of the second film is 10 μm or more and 60 μm or less. **Claim 14** A storage container containing contents heated by microwave, A packaging film for sealing the contents in the storage container, The packaging film is the packaging film according to any one of claims 1 to 3, Sealed container.

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