Adhesive film and airtight container

Abstract

The present invention provides an adhesive film that is positioned to cover the steam vent of a sealed container, thereby facilitating the formation of a steam passage when the sealed container is heated. [Solution] The adhesive film is an adhesive film that covers a steam vent for releasing steam from inside a sealed container, and comprises a base film having a first surface, an adhesive layer disposed on at least a part of the first surface, a first shrink layer disposed on a part of the adhesive surface of the adhesive layer, and a second shrink layer disposed on a part of the adhesive surface at a distance from the first shrink layer. The first shrink layer and the second shrink layer each include a first layer disposed closer to the adhesive layer and a second layer disposed further from the adhesive layer than the first layer. The thermal shrinkage rate of the second layer is greater than that of the first layer.

Description

Technical Field

[0001] The present invention relates to an adhesive film that covers a vapor vent portion for venting vapor in a sealed container, and a sealed container.

Background Art

[0002] Patent Document 1 discloses a package that houses frozen foods or chilled foods heated by a microwave oven. The package is, for example, a sealed container including a storage container that houses the contents and a packaging film that seals the opening of the storage container. The packaging film is adhered, for example, to the flange portion of the storage container formed in a flange shape. A vapor vent portion for venting vapor generated from the contents by heating is formed in the packaging film. The vapor vent portion is, for example, a cut. This vapor vent portion is blocked by a sealing film attached to the packaging film. The "adhesive film" in this specification corresponds to the sealing film described in Patent Document 1. Hereinafter, the sealing film described in Patent Document 1 is referred to as an adhesive film.

[0003] The adhesive film is configured by laminating a base film that does not shrink by heating and a shrink film that shrinks and变形 by heating one above the other. In such an adhesive film, when the shrink film shrinks and变形 by heating, the shrink film peels off from the base film and the packaging film. As a result, a gap is formed at the position of the adhesive film to vent the vapor from the vapor vent portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, conventional adhesive films are designed to form a steam passage when a sealed container is heated. However, depending on the type of contents, for example, it may be difficult to form a steam passage for release. In this case, the internal pressure of the sealed container may increase, and a portion of the adhesive between the container and the packaging film may peel off. If this happens, an unintended communication hole will be formed at the point where the adhesive has peeled off, connecting the inside and outside of the sealed container. As a result, excessive steam may be released from this communication hole, potentially preventing the contents from being properly heated.

[0006] One of the objects of the present invention is to provide an adhesive film that is positioned to cover the steam vent of a sealed container and facilitates the formation of a steam passage when the sealed container is heated, and a sealed container equipped with such an adhesive film. [Means for solving the problem]

[0007] (1) An adhesive film according to one embodiment of the present invention is an adhesive film that covers a steam vent for releasing steam in a sealed container, and comprises a base film having a first surface, an adhesive layer disposed on at least a part of the first surface, a first shrink layer disposed on a part of the adhesive surface of the adhesive layer, and a second shrink layer disposed on a part of the adhesive surface at a distance from the first shrink layer. The first shrink layer and the second shrink layer each include a first layer disposed closer to the adhesive layer and a second layer disposed further from the adhesive layer than the first layer. The thermal shrinkage rate of the second layer is greater than that of the first layer.

[0008] The adhesive film with the configuration described in (1) above is attached to the packaging film so as to seal the steam vent of the sealed container. When the sealed container is heated in a microwave oven or the like, high-temperature steam is generated inside the container. Here, because the first shrink layer and the second shrink layer of the adhesive film are spaced apart, the heat of the steam causes the first and second shrink layers to shrink and deform independently. The shrunk and deformed first and second shrink layers pull the portion sandwiched between them away from the packaging film. As a result, a passage for steam is easily formed in the first shrink layer, the second shrink layer, and the portion sandwiched between the first and second shrink layers. When such a passage is formed, the steam inside the sealed container is easily released to the outside. As a result, the internal pressure of the sealed container does not become too high, and the adhesive between the container and the packaging film is less likely to peel off. In other words, no holes other than the steam vent are formed in the packaging film. Therefore, according to the configuration in (1) above, the contents can be properly heated while allowing steam to escape from the sealed container.

[0009] (2) In the adhesive film of (1) above, in a plan view, the first shrink layer may be formed in a strip shape having a first major axis and a first minor axis, and the second shrink layer may be formed in a strip shape having a second major axis and a second minor axis. In this case, the first shrink layer and the second shrink layer may be aligned in a direction along the first minor axis.

[0010] According to the configuration described in (2) above, the strip-shaped first shrink layer and the second shrink layer tend to roll up into a cylindrical shape along their short axes. When the first and second shrink layers roll up into a cylindrical shape, the adhesive film peels away from the packaging film near these shrink layers, forming a passage for steam. Steam from a sealed container can easily be released to the outside through this passage. In addition, a passage for steam is also easily formed in the area sandwiched between the rolled-up first and second shrink layers, and steam from inside the sealed container can easily be released to the outside through this passage.

[0011] (3) In the adhesive film of (2) above, the base film may have a first edge and a second edge facing the first edge when viewed in plan. In this case, the two ends of the first major axis of the first shrink layer may reach the first edge and the second edge, respectively, and the two ends of the second major axis of the second shrink layer may reach the first edge and the second edge, respectively.

[0012] According to the configuration described in (3) above, the steam passage formed by the curling of the first shrink layer and the second shrink layer easily reaches the outer edge of the base film. Therefore, the steam passage is more reliably connected to the outer edge of the base film, and the steam inside the sealed container is more easily discharged to the outside of the sealed container.

[0013] (4) In the adhesive film of (2) or (3) above, the width along the first short axis of the first shrink layer and the width along the second short axis of the second shrink layer may each be 4 mm or more and 15 mm or less.

[0014] According to the configuration described in (4) above, the first shrink layer and the second shrink layer are easily rolled into a cylindrical shape by heat.

[0015] (5) In any of the adhesive films described in (1) to (4) above, the length of the gap between the first shrink layer and the second shrink layer may be 4 mm or more and 10 mm or less.

[0016] According to the configuration described in (5) above, a steam passage is easily formed in the area sandwiched between the first shrink layer and the second shrink layer, which have been rolled into a cylindrical shape by heat.

[0017] (6) In any of the adhesive films described in (1) to (5) above, the first layer may contain at least one of polyethylene terephthalate (PET) resin and biaxially oriented polypropylene (OPP) resin.

[0018] The resin defined in the above (6) has a low heat shrinkage rate. Therefore, when the second layer of the first shrink layer and the second shrink layer shrinks due to heat, the first layer is deformed in the same manner as the second layer due to the shrinkage of the second layer. That is, with the second layer on the inside, the first shrink layer and the second shrink layer are rolled into a cylindrical shape.

[0019] (7) In any of the adhesive films of the above (1) to (6), the second layer may contain at least one resin selected from the group consisting of polystyrene resin, polyethylene terephthalate resin, polyethylene resin, polypropylene resin, and polyvinyl chloride resin.

[0020] The resin defined in the above (7) has a high heat shrinkage rate. Therefore, when the second layer of the first shrink layer and the second shrink layer shrinks due to heat, the second layer shrinks more than the first layer. As a result, with the second layer on the inside, the first shrink layer and the second shrink layer are easily rolled into a cylindrical shape.

[0021] (8) In any of the adhesive films of the above (1) to (7), the average thickness of the second layer may be greater than the average thickness of the first layer.

[0022] If the second layer is thicker than the first layer, when the second layer of the first shrink layer and the second shrink layer shrinks due to heat, the first shrink layer and the second shrink layer are likely to form a cylindrical shape.

[0023] (9) In any of the adhesive films of the above (1) to (8), the average thickness of the first layer may be 9 μm or more and 16 μm or less, and the average thickness of the second layer may be 12 μm or more and 50 μm or less.

[0024] According to the configuration of the above (9), when the second layer of the first shrink layer and the second shrink layer shrinks due to heat, with the second layer on the inside, the first shrink layer and the second shrink layer are easily rolled into a cylindrical shape.

[0025] (10) In any of the adhesive films of (1) to (9) above, a release paper covering the adhesive surface may be provided.

[0026] Since the adhesive film has a release paper, it is possible to prevent the adhesive layer from adhering to other members during storage of the adhesive film and when attaching it to the packaging film.

[0027] (11) Any of the adhesive films of (1) to (10) above may include a third layer having adhesiveness on the second layer.

[0028] Since the first shrink layer and the second shrink layer have an adhesive third layer formed on the second layer, when the adhesive film is attached to the packaging film, the adhesive film adheres tightly to the packaging film over the entire surface. Therefore, it is difficult to form a gap between the adhesive film and the packaging film, and it is possible to prevent foreign substances from entering from the outside to the inside of the sealed container.

[0029] (12) A sealed container according to one embodiment of the present invention includes a storage container in which contents are stored, a packaging film that covers an opening of the storage container and seals the contents in the storage container, and a cover film attached to the packaging film. The packaging film includes a vent portion that penetrates the packaging film in the thickness direction. The cover film is any of the adhesive films of (1) to (11) above that covers the vent portion. The adhesive film has an interlayer region sandwiched between the first shrink layer and the second shrink layer in a plan view. In a plan view, any of the first shrink layer, the second shrink layer, and the interlayer region overlaps the vent portion.

[0030] In the above-mentioned sealed container, heating the contents inside the container in a microwave oven generates high-temperature steam inside the container. If, in a plan view, the first shrink layer, the second shrink layer, and the interlayer region all overlap the steam vent, the high-temperature steam inside the container can easily reach the first and second shrink layers through the steam vent, causing both layers to shrink similarly. As a result, a passage for steam is easily formed in the adhesive film, and the steam inside the container is easily released to the outside. Because the steam inside the container is released, the pressure inside the container does not rise excessively, making it less likely for the adhesive between the container and the packaging film to peel off.

[0031] (13) In the sealed container of (12) above, the steam vent portion may be a straight or corrugated notch, and in a plan view, the steam vent portion may be arranged to extend from the first shrink layer through the interlayer region to the second shrink layer.

[0032] The wave shape can be, for example, a shape in which arcs of different directions are connected alternately, or a shape in which short straight lines are connected in a zigzag pattern. Straight or wave-shaped cuts can be easily formed. Also, if the shape is simple, such as a straight or wave shape, less stress is placed on the packaging film when the cut is formed.

[0033] (14) A sealed container according to one embodiment of the present invention comprises a storage container in which contents are stored, a packaging film that covers the opening of the storage container and seals the contents inside the storage container, and a cover film attached to the packaging film. The packaging film has a vapor vent portion that penetrates the packaging film in the thickness direction. The cover film is the adhesive film of (11) above that covers the vapor vent portion. The adhesive film has an interlayer region sandwiched between the first shrink layer and the second shrink layer in a plan view. The vapor vent portion is a cut having at least one spiral portion formed in a spiral shape in a plan view. In a plan view, at least one of the at least one spiral portion overlaps with the first shrink layer, the second shrink layer, and the interlayer region.

[0034] When an adhesive film has an adhesive third layer, the third layer adheres tightly to the packaging film, making it difficult for a steam passage to form at the location of the adhesive film. As shown in Embodiment 2 and Test Example 2 described later, having a spiral section in the steam vent makes it easier for a steam passage to form at the location of the adhesive film, even if the third layer of the adhesive film adheres tightly to the packaging film. [Effects of the Invention]

[0035] The adhesive film of the present invention is positioned to cover the steam vent of a sealed container, making it easier for a steam passage to form when the sealed container is heated. [Brief explanation of the drawing]

[0036] [Figure 1] Figure 1 is a schematic perspective view of a sealed container according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II of the sealed container shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view of the adhesive film used in the sealed container shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram illustrating the mechanism by which vapor pathways are formed in adhesive films. [Figure 5] Figure 5 is a schematic plan view of the adhesive film shown in Figure 3. [Figure 6] Figure 6 is a schematic cross-sectional view of the adhesive film provided in the sealed container according to Embodiment 2. [Figure 7] Figure 7 is a schematic diagram showing the shape pattern of the steam vent in a sealed container according to Embodiment 2. [Figure 8] Figure 8 is the first matrix diagram showing the test results for Test Example 1. [Figure 9] Figure 9 is a second matrix diagram showing the test results for Test Example 1. [Figure 10] Figure 10 is a third matrix diagram showing the test results for Test Example 2. [Modes for carrying out the invention]

[0037] Specific examples of the adhesive film and airtight container of the present invention will be described below with reference to the drawings. Identical reference numerals in the drawings indicate the same or corresponding parts. The dimensions of the components shown in each drawing are represented for illustrative purposes only and do not necessarily represent actual dimensions. The present invention is not limited to these examples and is as defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended.

[0038] [Embodiment 1] <Airtight container> The sealed container 1 shown in Figures 1 and 2 comprises a box-shaped storage container 9, a resin packaging film 2 that seals the storage container 9, and a cover film 25 that covers a steam vent 20 formed in the packaging film 2. The cover film 25 is made of an adhesive film 3, as will be described later. As shown in Figure 2, the storage container 9 stores contents 8 inside. The contents 8 are, for example, frozen food or chilled food. The contents 8 are heated in a microwave oven along with the sealed container 1. The heating conditions of the microwave oven are, for example, 1500W for a commercial microwave oven in a convenience store, and for example, 500W or 600W for a household microwave oven.

[0039] <Storage containers> The storage container 9 is made of a heat-resistant material that is less likely to deform when heated in a microwave oven. The material of the storage container 9 is, for example, PP (polypropylene) resin. The storage container 9 may be transparent or opaque. If the storage container 9 is transparent, the contents 8 can be seen from the outside of the storage container 9. If the storage container 9 is opaque, the contents 8 are shielded from light, making it easier to suppress the deterioration of the contents 8.

[0040] 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 top. In this embodiment, the external shape of the storage container 9 is generally an inverted truncated square pyramid. Unlike this embodiment, the external shape of the storage container 9 may be, for example, an inverted truncated cone, a cylinder, or a prism.

[0041] An annular flange portion 9F is formed on the edge of the opening 90 of the storage container 9. As will be described later, the packaging film 2 is adhered to this flange portion 9F. The annular shape of the flange portion 9F is similar to the contour shape of the opening 90. In this embodiment, the flange portion 9F is rectangular annular in shape. If the contour shape of the opening 90 is circular, the flange portion 9F will be annular in shape.

[0042] <Packaging film> In this embodiment, the packaging film 2 is large enough to cover the entire opening 90 of the storage container 9. The outer edge of the packaging film 2 is bonded to the flange portion 9F of the storage container 9. In this embodiment, the packaging film 2 is heat-sealed to the flange portion 9F. By bonding the outer edge and the flange portion 9F, the airtightness of the sealed container 1 is maintained, and deterioration of the contents 8 is suppressed.

[0043] The material of the packaging film 2 is not particularly limited as long as it has a predetermined tensile strength and can maintain the airtightness of the sealed container 1. Examples of materials for the packaging film 2 include PP resin, PE (polyethylene) resin, PA (polyamide) resin, or PET (polyethylene terephthalate) resin. The packaging film 2 may have a multilayer structure, in which case the material of each layer may be different.

[0044] The average thickness of the packaging film 2, that is, the average length between the inner surface 21 and the outer surface 22 of the packaging film 2, is, for example, 10 μm or more and 100 μm or less. A packaging film 2 with an average thickness of 10 μm or more has a predetermined strength and is therefore less likely to tear during storage or transport of the sealed container 1. A packaging film 2 with an average thickness of 100 μm or less is not too thick. The average thickness of the packaging film 2 may also be 12 μm or more and 60 μm or less.

[0045] The average thickness of the packaging film 2 can be determined, for example, by a commercially available thickness gauge, such as a non-contact film thickness gauge that measures the thickness of a thin film by irradiating it with light in a broad wavelength range. In this embodiment, the thickness of the areas of the packaging film 2 where the adhesive film 3 is not attached is measured with a thickness gauge, and the average thickness of the packaging film 2 is determined by averaging these measurements. The number of measurement points is, for example, five or more.

[0046] The packaging film 2 is provided with a steam vent 20 that penetrates the packaging film 2. That is, the steam vent 20 is open on both the inner surface 21 and the outer surface 22. In this embodiment, the steam vent 20 is a straight-shaped cut formed in the center of the packaging film 2 when viewed from above. The steam vent 20, consisting of a straight-shaped cut, is easy to form and makes it easy to prevent foreign matter from entering the storage container 9 before the adhesive film 3 is attached to the packaging film 2. As shown in Test Example 1 described later, the number of steam vents 20 may be one or more. Also, the steam vent 20 may be a wavy cut in which arcs of different directions are connected alternately, or a wavy cut in which short straight lines are connected in a zigzag pattern.

[0047] The length of the straight steam vent section 20 is, for example, 10 mm to 50 mm. If the length of the steam vent section 20 is 10 mm or more, the steam generated by heating the contents 8 in the microwave oven can easily come into sufficient contact with the adhesive film 3, which will be described later. If the length of the steam vent section 20 is 50 mm or less, the strength of the packaging film 2 can be easily maintained. The length of the steam vent section 20 may also be, for example, 15 mm to 40 mm, or 20 mm to 30 mm.

[0048] <Adhesive film> The adhesive film 3, which is a cover film 25 covering the steam vent portion 20 of the packaging film 2, is attached to the outer surface 22 of the packaging film 2. In this embodiment, the adhesive film 3 covers a portion of the outer surface 22. As shown in Figure 3, the adhesive film 3 comprises a base film 4, an adhesive layer 5, a first shrink layer 6, and a second shrink layer 7 in that order. The adhesive film 3 in Figure 3 is in its state before being attached to the packaging film 2 and includes a release paper 30 to protect the adhesive layer 5. As shown in Figure 3, the release paper 30 is provided on the side of the first shrink layer 6 and the second shrink layer 7 opposite to the adhesive layer 5 side. As will be described later, the first shrink layer 6 and the second shrink layer 7 are provided not on the entire adhesive surface 51 of the adhesive layer 5, but on a portion of it. That is, the adhesive surface 51 of the adhesive layer 5 is partially exposed. The release paper 30 is provided using this exposed adhesive surface 51. The release paper 30 is peeled off when the adhesive film 3 is used. Known release paper 30 can be used.

[0049] ≪Base film≫ The base film 4 has a first surface 41 on the side facing the adhesive layer 5 and a second surface 42 on the opposite side of the first surface 41. The first surface 41 is the surface facing the packaging film 2 in the sealed container 1 shown in Figure 1. The average thickness of the base film 4, that is, the average length between the first surface 41 and the second surface 42, is, for example, 12 μm or more and 100 μm or less. If the average thickness of the base film 4 is 12 μm or more, the adhesive film 3 is easy to handle and easy to apply to the packaging film 2. If the average thickness of the base film 4 is 100 μm or less, the adhesive film 3 will not become too thick. The average thickness of the base film 4 may also be, for example, 12 μm or more and 75 μm or less, or 25 μm or more and 50 μm or less.

[0050] The planar shape of the base film 4 is not limited to anything that can cover the entire steam vent section 20. In this embodiment, the planar shape of the base film 4 is a long rectangle in the direction along the length of the steam vent section 20. Unlike this embodiment, the planar shape of the base film 4 may be, for example, an ellipse.

[0051] The material of the base film 4 is, for example, PET resin. Alternatively, the material of the base film 4 may be OPP resin or PE resin. The base film 4 may also be a combination of these resins.

[0052] ≪Adhesive layer≫ The adhesive layer 5 is formed on the first surface 41 of the base film 4. In this embodiment, the adhesive layer 5 is formed over the entire surface of the first surface 41. Unlike this embodiment, the adhesive layer 5 may be formed on only a part of the first surface 41.

[0053] The material of the adhesive layer 5 is, for example, an acrylic adhesive, a rubber adhesive, or a hot-melt adhesive. The adhesive layer 5 is formed by applying the material of the adhesive layer 5 to the first surface 41. The side of the adhesive layer 5 opposite to the side that is in contact with the first surface 41 is the adhesive surface 51. At least a first shrink layer 6 and a second shrink layer 7 are formed on this adhesive surface 51. In Figure 3, which is simplified, the release paper 30 is in contact with the parts of the adhesive surface 51 where both shrink layers 6 and 7 are not formed, as indicated by the upward and downward arrows.

[0054] ≪First shrink layer and second shrink layer≫ The first shrink layer 6 and the second shrink layer 7 are independent components and are separated from each other on the adhesive surface 51. In other words, in a plan view, there is a gap between the first shrink layer 6 and the second shrink layer 7. In a plan view, the adhesive surface 51 is exposed in the interlayer region 70 sandwiched between the first shrink layer 6 and the second shrink layer 7. The structure of the first shrink layer 6 and the second shrink layer 7 is the same. Therefore, the following explanation will mainly refer to the structure of the first shrink layer 6. Also, the first shrink layer 6 and the second shrink layer 7 may not be distinguished and may simply be referred to as shrink layers 6 and 7.

[0055] The first shrink layer 6 comprises a first layer 61, a second layer 62, and an adhesive layer 64. The first layer 61 is a layer positioned close to the adhesive layer 5. The second layer 62 is a layer positioned further from the adhesive layer 5 than the first layer 61. In an adhesive film 3 having a release liner 30, the second layer 62 is a layer that is in direct contact with the release liner 30. The adhesive layer 64 is a layer that adheres the first layer 61 and the second layer 62. The adhesive layer 64 can be a known material. For example, the adhesive layer 64 is a layer made of a dry laminating adhesive. When forming the second layer 62 on the first layer 61, the adhesive layer 64 may be omitted if the first layer 61 and the second layer 62 are sufficiently adhered to each other.

[0056] The thermal shrinkage rate of the second layer 62 is greater than that of the first layer 61. In other words, when the first layer 61 and the second layer 62 are exposed to the same temperature, the second layer 62 shrinks more than the first layer 61. The thermal shrinkage rate can be measured, for example, by a measurement method compliant with JIS C 2151:2019.

[0057] Considering the relationship between the thermal shrinkage rate of the first layer 61 and the thermal shrinkage rate of the second layer 62, the materials of the first layer 61 and the second layer 62 can be appropriately selected. The material of the first layer 61 is, for example, PET resin. Alternatively, the material of the first layer 61 may be OPP resin or PE resin. On the other hand, the material of the second layer 62 is, for example, uniaxially oriented polystyrene resin. Alternatively, the material of the second layer 62 may be PET resin, PE resin, PP resin, or polyvinyl chloride resin.

[0058] <Arrangement of adhesive film in packaging film> As shown in Figure 1, the adhesive film 3 attached to the packaging film 2 covers the entire steam vent portion 20 formed in the packaging film 2. More specifically, when the adhesive film 3 is viewed from above, the adhesive film 3 is attached to the packaging film 2 such that the first shrink layer 6, the second shrink layer 7, and the interlayer region 70 all overlap the steam vent portion 20. In this example, the steam vent portion 20 is a straight cut. If we consider the positional relationship between the adhesive film 3 and the steam vent portion 20 with respect to this cut, the cut is positioned to extend from the first shrink layer 6 through the interlayer region 70 to the second shrink layer 7.

[0059] <Mechanism by which steam pathways are formed> The deformation of the adhesive film 3, which has the aforementioned shrink layers 6 and 7, due to steam generated inside the storage container 9 will be explained with reference to Figure 4. In Figure 4, the adhesive layer 5 is shown with a thick line, and the adhesive layer 64 is omitted from the illustration. The following explanation assumes that the storage container 9 and contents 8 shown in Figure 2 are located beneath the packaging film 2.

[0060] As shown in the upper part of Figure 4, the adhesive layer 5 of the adhesive film 3 is in close contact with the outer surface 22 of the packaging film 2. Here, a step is formed between the adhesive layer 5 and the shrink layers 6 and 7, so a tiny gap 31 is formed near the edges of the shrink layers 6 and 7 where the adhesive layer 5 and the packaging film 2 are not in close contact. When the sealed container 1 is heated in a microwave oven from this state, the contents 8 are heated by the microwaves of the microwave oven, and steam 80 is generated. The steam 80 passes through the steam vent 20 and directly hits the shrink layers 6 and 7, heating them. At this time, as shown in the middle part of Figure 4, of the shrink layers 6 and 7, the second layer 62, which is more susceptible to thermal shrinkage, is directly exposed to the steam 80 and shrinks significantly. The first layer 61, which has a smaller thermal shrinkage rate than the second layer 62, is less directly exposed to the steam 80 and therefore hardly shrinks. When the shrink layers 6 and 7 are further exposed to the steam 80, the steam 80 reduces the adhesion between the first layer 61 and the adhesive layer 5 at the edges of the shrink layers 6 and 7 in the width direction, and the first layer 61 may peel off from the adhesive layer 5. As a result, as shown in the lower part of Figure 4, both ends of the shrink layers 6 and 7 in the width direction curl up with the second layer 62 on the inside, resulting in a state where two cylinders are placed side by side. The tubular shrink layers 6 and 7 are in almost line contact with the packaging film 2.

[0061] As the shrink layers 6 and 7 deform and curl as shown in Figure 4, the portion of the adhesive film 3 facing the steam vent 20 lifts away from the outer surface 22 of the packaging film 2. As a result, steam passages 32 are formed at the position of the first shrink layer 6, the position of the second shrink layer 7, and the position sandwiched between the first shrink layer 6 and the second shrink layer 7. In this example, the passages 32 extend in a direction perpendicular to the length direction of the steam vent 20, that is, in the thickness direction of the paper in Figure 4.

[0062] <Preferred configuration of the first shrink layer and the second shrink layer> The shapes of the shrink layers 6 and 7 will be explained based on Figure 5. Figure 5 is a plan view of the adhesive film 3 from the side where the adhesive layer 5 is placed. In this figure, the adhesive layer 5 is cross-hatched. In this embodiment, one of the two long sides of the rectangular base film 4 in a plan view is called the first edge 45, and the long side opposite the first edge 45 is called the second edge 46. Unlike this embodiment, in the case of an elliptical base film 4, the edges of the outer periphery of the base film 4 that face each other and have small curvature are considered to be the first edge 45 and the second edge 46.

[0063] The planar shape of the first shrink layer 6 is formed in a strip shape having a first major axis 6L and a first minor axis 6S. When the strip-shaped first shrink layer 6 shrinks due to heat, the first shrink layer 6 tends to roll up into a cylindrical shape having an axis extending in the direction along the first major axis 6L. In other words, in this example, the passage 32 described in Figure 4 is formed to extend in the direction along the first major axis 6L. In this embodiment, the two ends 65 and 66 of the first major axis 6L in the first shrink layer 6 reach the first edge 45 and the second edge 46, respectively. Therefore, the passage 32 at the position of the first shrink layer 6, formed by the rolling up of the first shrink layer 6, opens to the first edge 45 and the second edge 46 of the base film 4.

[0064] The planar shape of the second shrink layer 7 is formed in a strip shape having a second major axis 7L and a second minor axis 7S. When the strip-shaped second shrink layer 7 shrinks due to heat, the second shrink layer 7 tends to roll up into a cylindrical shape having an axis extending in the direction along the second major axis 7L. In other words, in this example, the passage 32 described in Figure 4 is formed to extend in the direction along the second major axis 7L. In this embodiment, the two ends 75 and 76 of the second major axis 7L in the second shrink layer 7 reach the first edge 45 and the second edge 46, respectively. Therefore, the passage 32 at the position of the second shrink layer 7, formed by the rolling up of the second shrink layer 7, opens to the first edge 45 and the second edge 46 of the base film 4.

[0065] The strip-shaped first shrink layer 6 and the second shrink layer 7 are aligned in the direction along the first minor axis 6S. In other words, the first shrink layer 6 and the second shrink layer 7 are aligned in the direction along the second minor axis 7S. In this embodiment, the first major axis 6L and the second major axis 7L are parallel. In this embodiment, since the first shrink layer 6 and the second shrink layer 7 reach the first edge 45 and the second edge 46, the passage 32 in the interlayer region 70 between the first shrink layer 6 and the second shrink layer 7 also opens to the first edge 45 and the second edge 46 of the base film 4. Because the passage 32 opens to the first edge 45 and the second edge 46, the steam 80 inside the sealed container 1 is efficiently discharged to the outside of the sealed container 1.

[0066] The planar shape of the shrink layers 6 and 7 is not limited to a strip shape. For example, the planar shape of the shrink layers 6 and 7 may be elliptical.

[0067] In this embodiment, the length L of the first shrink layer 6 and the length L of the second shrink layer 7 are the same. The length L of the first shrink layer 6 is the length along the first major axis 6L, and the length L of the second shrink layer 7 is the length along the second major axis 7L. The length L is the same as the length LS of the short side of the base film 4. Unlike this embodiment, the length L of the first shrink layer 6 and the length L of the second shrink layer 7 may be different. The specific value of the length L may be, for example, 5 mm or more and 30 mm or less, 5 mm or more and 20 mm or less, or 5 mm or more and 10 mm or less.

[0068] In this embodiment, the width W of the first shrink layer 6 and the width W of the second shrink layer 7 are the same. Unlike this embodiment, the width W of the first shrink layer 6 and the width W of the second shrink layer 7 may be different. For example, the specific value of the width W is 4 mm or more and 15 mm or less. If the width W is 4 mm or more and 15 mm or less, the shrink layers 6 and 7 will easily roll into a cylindrical shape. If the width W is too large, only the edges in the width direction will deform into a round shape, and the entire shrink layer 6 and 7 will not easily roll into a cylindrical shape. For example, the width W may be 4 mm or more and 10 mm or less, or 4 mm or more and 8 mm or less.

[0069] The width of the interlayer region 70, that is, the length G of the gap between the first shrink layer 6 and the second shrink layer 7, is, for example, 4 mm to 10 mm. If the gap length G is 4 mm to 10 mm, when the first shrink layer 6 and the second shrink layer 7 curl up due to heat, a pipe-like steam passage 32 is easily formed at the location of the interlayer region 70. If the length G is too large, the adhesive layer 5 will not easily peel off at the location of the interlayer region 70 shown in the upper part of Figure 4, and the cross-sectional area of ​​the passage 32 shown in the lower part will tend to be small. The length G may be, for example, 4 mm to 8 mm, or 5 mm to 8 mm.

[0070] The sum of the width W of the first shrink layer 6, the length G of the gap between them, and the width W of the second shrink layer 7 is shorter than the length LL of the long side of the base film 4. That is, in Figure 5, from left to right, the adhesive layer 5, the first shrink layer 6, the adhesive layer 5, the second shrink layer 7, and the adhesive layer 5 are arranged in that order. In this case, the left and right edges of the adhesive film 3 in Figure 4 adhere firmly to the packaging film 2, making it difficult for the adhesive film 3 to peel off during storage or transport of the sealed container 1.

[0071] The length from the left edge of the first shrink layer 6 to the right edge of the second shrink layer 7 is shorter than the length of the steam vent 20, as shown in Figure 4. Because the left edge of the first shrink layer 6 is positioned closer to the center than one end of the steam vent 20, steam 80 can easily enter the gap 31 formed near the left edge of the first shrink layer 6. Similarly, because the right edge of the second shrink layer 7 is positioned closer to the center than the other end of the steam vent 20, steam 80 can easily enter the gap 31 formed near the right edge of the second shrink layer 7. As steam 80 enters the gap 31, the shrink layers 6 and 7 tend to curl up.

[0072] The average thickness of the second layer 62 of the shrink layers 6 and 7 is, for example, greater than the average thickness of the first layer 61. When the average thickness of the second layer 62 is thicker, the curvature of the cylindrical shape tends to increase when the shrink layers 6 and 7 are rolled into a cylindrical shape by heat. As a result, a passage 32 for steam 80 with a large flow path cross-sectional area is more easily formed. For example, the average thickness of the first layer 61 is between 9 μm and 16 μm. For example, the average thickness of the second layer 62 is between 12 μm and 50 μm.

[0073] <Other> The adhesive film 3 may include a third shrink layer independent of the first shrink layer 6 and the second shrink layer 7. For example, the third shrink layer may be located in the interlayer region 70. The number of third shrink layers may be one or more.

[0074] [Embodiment 2] Embodiment 2 describes an adhesive film 3 having shrink layers 6 and 7 different from those in Embodiment 1, based on Figure 6. The interpretation of Figure 6 is the same as in Figure 3.

[0075] The shrink layers 6 and 7 of the adhesive film 3 in Embodiment 2 further include an adhesive third layer 63. The inclusion of the third layer 63 in the shrink layers 6 and 7 ensures that when the adhesive film 3 is attached to the packaging film 2 (Figures 1 and 2), the adhesive film 3 adheres tightly to the packaging film 2 across its entire surface. As a result, gaps between the adhesive film 3 and the packaging film 2 are less likely to form, effectively preventing foreign matter from entering the sealed container 1 (Figures 1 and 2) from the outside.

[0076] The material of the third layer 63 is, for example, an acrylic adhesive, a rubber adhesive, or a hot-melt adhesive. The third layer 63 is formed by applying the material of the third layer 63 onto the second layer 62.

[0077] If the adhesive film 3 is tightly adhered to the packaging film 2 over its entire surface, it is difficult for a steam passage to form at the location of the adhesive film 3. Even in such cases, the shape of the steam vent 20 formed in the packaging film 2 can make it easier for a steam passage to form at the location of the adhesive film 3. In other words, by designing the shape of the steam vent 20, it is easier for a steam passage to form at the location of the adhesive film 3, and as a result, the adhesive between the storage container 9 and the packaging film 2 shown in Figures 1 and 2 is less likely to peel off.

[0078] Figure 7 shows an example of a shape pattern for the steam vent section 20 that facilitates the formation of steam passages at the location of the adhesive film 3, even when the shrink layers 6 and 7 are equipped with a third layer 63. In Figure 7, the vertical relationship between the steam vent section 20 and the shrink layers 6 and 7 is ignored, and only the positional relationship between the steam vent section 20 and the shrink layers 6 and 7 is shown when the adhesive film 3 is viewed from above. The areas with cross-hatching indicate the adhesive layer 5 (Figure 6).

[0079] Each of the steam vents 20 shown in Figure 7 has at least one spiral section 20A formed in a spiral shape in plan view. Furthermore, in plan view, at least one of the spiral sections 20A overlaps with the first shrink layer 6, the second shrink layer 7, and the interlayer region 70.

[0080] Pattern A in Figure 7 shows a shape pattern in which there are three steam vents 20, and each steam vent 20 consists of one spiral section 20A. The spiral section 20A has a shape that rotates counterclockwise from the center to the outer circumference. Unlike this example, the spiral section 20A may have a shape that rotates clockwise from the center to the outer circumference.

[0081] In pattern A, each of the three spiral sections 20A is arranged so as to overlap the first shrink layer 6, the second shrink layer 7, and the interlayer region 70 in a plan view.

[0082] Pattern B shows a shape pattern in which one steam vent section 20 has three spiral sections 20A. Two adjacent spiral sections 20A, 20A are connected by a connecting section 20C. The connecting section 20C may be a straight line shape as shown in the figure, or a curved shape. In Pattern B, each of the three spiral sections 20A is arranged so as to overlap the first shrink layer 6, the second shrink layer 7, and the interlayer region 70 in a plan view.

[0083] Pattern C shows a single steam vent section 20 consisting of a single spiral section 20A. The spiral section 20A in Pattern C has a shape that extends in the direction in which the first shrink layer 6 and the second shrink layer 7 are arranged in parallel. In Pattern C, the single spiral section 20A is arranged so as to span the first shrink layer 6, the interlayer region 70, and the second shrink layer 7 in a plan view.

[0084] Pattern D shows a pattern in which one steam vent section 20 has two vortex sections 20A and 20B. In Pattern D, each of the two vortex sections 20A and 20B is connected to the other at the center of the vortex and is arranged alternately outward from the center of the vortex. Thus, a turn in the other vortex section 20B is placed between adjacent turns in one vortex section 20A. In Pattern D, both vortex sections 20A are arranged so as to span the first shrink layer 6, the interlayer region 70, and the second shrink layer 7 in a plan view.

[0085] [Test Example 1] In Test Example 1, samples were prepared consisting of multiple adhesive films 3,300 with different shrink layer morphologies 6 and 7. Adhesive film 3 is the adhesive film 3 according to Embodiment 1. Adhesive film 300 is the adhesive film 300 according to the Comparative Example. The influence of the morphologies of the shrink layers 6 and 7 present in each sample on the formation of the steam 80 passage 32 was investigated. The arrangement of the shrink layers 6 and 7 in each adhesive film 3,300 and the layer configuration of the shrink layers 6 and 7 are shown in the matrix diagrams of Figures 8 and 9. In the "Arrangement" section of the shrink layers 6 and 7, only the positional relationship between the steam vent 20 and the shrink layers 6 and 7 when the adhesive film 3,300 is viewed from above is shown, ignoring the vertical relationship between the steam vent 20 and the shrink layers 6 and 7. In the "Layer Configuration" section, the cross-sectional structure of the base film 4 and the shrink layer 6 is shown, while the other shrink layers 7 and adhesive layer 5 are omitted.

[0086] <Sample No. 1> The adhesive film 3 of sample No. 1 comprises a first shrink layer 6 and a second shrink layer 7. The base film 4 of the adhesive film 3 was a rectangular sheet formed of PET resin. The average thickness of the base film 4 was 50 μm, the length of the long side LL was 45 mm, and the length of the short side LS was 10 mm. The length L of the shrink layers 6 and 7 was 10 mm, and the width W was 8 mm. The distance G between the first shrink layer 6 and the second shrink layer 7 was 4 mm. The first layer 61 of the shrink layers 6 and 7 was formed of PET resin, and the second layer 62 was formed of shrinkable PET resin. The average thickness of the first layer 61 was 12 μm, and the average thickness of the second layer 62 was 30 μm.

[0087] Next, a sealed container 1 was prepared by sealing the opening 90 of the storage container 9 containing the contents 8 with a packaging film 2, and an adhesive film 3 was attached to the packaging film 2 so as to block the steam vent 20 of the packaging film 2. The contents 8 stored in the storage container 9 were white rice. The steam vent 20 was a straight cut, and the length of the steam vent 20 was 25 mm. As shown in the "Arrangement" section of Figure 8, the shrink layers 6 and 7 are arranged so that their long axes are perpendicular to the steam vent 20. The shrink layers 6 and 7 are arranged so as not to protrude from the steam vent 20 in the direction along the length of the steam vent 20.

[0088] <Sample No. 2> The adhesive film 3 of sample No. 2, shown in Figure 8, has the same configuration as sample No. 1, except that the length G of the gap between the first shrink layer 6 and the second shrink layer 7 is 8 mm.

[0089] <Sample No. 3> The adhesive film 3 of sample No. 3 shown in Figure 8 has the same configuration as sample No. 2. On the other hand, the steam vents 20 formed in the packaging film 2 are four parallel, straight-shaped cuts. Both ends of each steam vent 20 are positioned to overlap with the first shrink layer 6 and the second shrink layer 7 in a plan view.

[0090] <Sample No. 4> The adhesive film 3 of sample No. 4 shown in Figure 8 has the same configuration as sample No. 2. On the other hand, the steam vents 20 formed in the packaging film 2 are three parallel zigzag-shaped cuts. Both ends of each steam vent 20 are positioned to overlap with the first shrink layer 6 and the second shrink layer 7 in a plan view.

[0091] <Sample No. 101> Sample No. 101, shown in Figure 9, has the same configuration as Sample No. 1, except that it is equipped only with the first shrink layer 6. The first shrink layer 6 is located in the center of the steam vent section 20.

[0092] <Sample No. 102> Sample No. 102, shown in Figure 9, has the same configuration as sample No. 101, except that the width W of the first shrink layer 6 is 24 mm.

[0093] <Sample No. 103> Sample No. 103, shown in Figure 9, has the same configuration as sample No. 2, except that the first shrink layer 6 and the second shrink layer 7 are adjacent to each other. The length G between the adjacent first shrink layer 6 and second shrink layer 7 is 0 mm.

[0094] <Sample No. 104> Sample No. 104, shown in Figure 9, has the same configuration as Sample No. 2, except that the second layer 62 is formed closer to the base film 4 and the first layer 61 is formed further away from the base film 4, as shown in the "Layer Structure" section of Figure 9.

[0095] <Heating Test> The sealed containers 1 of each sample described above were heated in a microwave oven. The microwave heating conditions were 1500W for 40 seconds. After heating in the microwave oven, it was visually checked whether a steam passage 32 was formed along the long axis of the shrink layers 6 and 7, and whether there were any areas where the packaging film 2 had peeled away from the storage container 9 at the flange portion 9F (see Figures 1 and 2). The test results for each sample are shown in Figure 8 or Figure 9. Regarding the steam passage 32, if a passage 32 was formed that was continuously connected from one end to the other along the length of the shrink layers 6 and 7, it was judged as "present," and otherwise as "absent." Regarding the peeling of the packaging film 2, if there was even one area where the packaging film 2 had peeled away, it was judged as "present," and if there were no areas of peeling at all, it was judged as "absent."

[0096] As shown in the test results for samples No. 1 to No. 4, it was found that by providing a first shrink layer 6 and a second shrink layer 7 with the adhesive film 3 spaced apart, the packaging film 2 can form a passage 32 for steam 80 without peeling off the storage container 9.

[0097] In the case of sample No. 101, where only the first shrink layer 6 was formed on the adhesive film 3, although a passage 32 for the steam 80 was formed, delamination of the packaging film 2 occurred. In the case of sample No. 102, where only the first shrink layer 6 was formed on the adhesive film 3, even if the width W of the first shrink layer 6 was wide, delamination of the packaging film 2 could not be prevented. Moreover, the first shrink layer 6 of sample No. 102 was not rolled into a cylindrical shape, and a passage 32 for the steam 80 opening at the edge of the base film 4 was not formed.

[0098] As in sample No. 103, when the first shrink layer 6 and the second shrink layer 7 are adjacent to each other in the adhesive film 3, a passage 32 for the steam 80 is formed, but the packaging film 2 peels off. This is presumed to be because the steam 80 has difficulty getting between the adjacent first shrink layer 6 and second shrink layer 7, and the packaging film 2 peels off before the passage 32 can be formed.

[0099] As in sample No. 104, when the first layer 61, which is prone to heat shrinkage, is positioned in contact with the base film 4, the shrink layers 6 and 7 do not curl easily, and the steam passage 32 is not formed. As a result, the packaging film 2 peels off.

[0100] Based on the test results described above, it was found that arranging the first shrink layer 6 and the second shrink layer 7 in the adhesive film 3 with a gap between them, and positioning the second layer 62, which is more susceptible to heat shrinkage in the shrink layers 6 and 7, to face the steam vent 20, is effective in forming the steam passage 32 for the steam 80 and preventing the packaging film 2 from peeling off.

[0101] [Test Example 2] In Test Example 2, sample No. 14 was prepared from sample No. 11 using the adhesive film 3 shown in Embodiment 2. This adhesive film 3 has an adhesive third layer 63. In Test Example 2, the effect of the shape of the steam vent section 20 in each sample on the formation of the steam passage 32 80 was investigated. Figure 10 shows information such as the arrangement and layer configuration of the shrink layers 6 and 7 in each sample. The interpretation of Figure 10 is the same as in Figures 8 and 9.

[0102] The adhesive film 3 of samples No. 11 to No. 14 is the same as the adhesive film 3 of Embodiment 2 shown in Figure 6, i.e., the shrink layers 6 and 7 are adhesive film 3 with a third layer 63. The third layer 63 is made of the same material as the adhesive layer 5. That is, the adhesive strength of the third layer 63 is approximately the same as the adhesive strength of the adhesive layer 5.

[0103] <Sample No. 11> The shape and arrangement of the steam vent section 20 in sample No. 11 corresponded to pattern A in Figure 7. That is, in sample No. 11, each of the three independent spiral sections 20A (see Figure 7) is arranged to overlap the first shrink layer 6, the interlayer region 70, and the second shrink layer 7.

[0104] <Sample No. 12> The steam vent section 20 of sample No. 12 corresponds to pattern B in Figure 7. That is, in sample No. 12, each of the three spiral sections 20A connected by the connecting section 20C is arranged to overlap the first shrink layer 6, the interlayer region 70, and the second shrink layer 7.

[0105] <Sample No. 13> The steam vent section 20 of sample No. 13 corresponds to pattern C in Figure 7. That is, in sample No. 13, one large spiral section 20A is arranged across the first shrink layer 6, the interlayer region 70, and the second shrink layer 7.

[0106] <Sample No. 14> The steam vent section 20 of sample No. 14 corresponds to pattern D in Figure 7. That is, in sample No. 14, both large spiral sections 20A and 20B are arranged across the first shrink layer 6, the interlayer region 70, and the second shrink layer 7.

[0107] <Heating Test> The sealed containers 1 of each sample were heated in a microwave oven under the same conditions as in Test Example 1, and the presence or absence of steam passages 32 and the presence or absence of peeling of the packaging film 2 were evaluated in the same manner as in Test Example 1. The evaluation results are shown in Figure 10.

[0108] As shown in the test results for samples No. 11 to No. 14, it was found that if the steam vent section 20 has a spiral section 20A, even if the steam vent section 20 is covered with an adhesive film 3 having an adhesive third layer 63, the packaging film 2 does not peel off from the storage container 9, and a passage 32 for the steam 80 can be formed.

[0109] When the adhesive film 3 of each sample was lifted from the packaging film 2 after the heating test, the portion of the packaging film 2 along the notch of the spiral portion 20A lifted together with the adhesive film 3, similar to when the central part of a spiral spring is lifted. As a result, a large hole was formed in the packaging film 2, along the outer contour of the spiral portion 20A. It is presumed that the formation of this large hole made it easier for the steam 80 to come into contact with the shrink layers 6,7 and the interlayer region 70, thus weakening the adhesion between the shrink layers 6,7 and the interlayer region 70, and as a result, a passage 32 for the steam 80 was formed.

[0110] [Test Example 3] For the steam vents 20 with the shapes shown in Samples No. 11 to No. 14 of Test Example 2, the adhesive film 3 of Sample No. 2 of Test Example 1 was attached, and the same heating tests as in Test Examples 1 and 2 were carried out. This adhesive film 3 does not have an adhesive third layer 63. As a result, in all samples, the steam 80 passage 32 was formed without the packaging film 2 peeling off from the storage container 9. [Explanation of symbols]

[0111] 1. Airtight container 2 Packaging film 3,300 Adhesive Film 4. Base film 5 Adhesive layer 6. First shrink layer 7. Second shrink layer 8 Contents 9 Storage containers 20 Steam vent section, 20A, 20B Spiral section, 20C Connecting section 21 Inner surface, 22 Outer surface, 25 Cover film 30 Release paper, 31 Gap, 32 Pathway 41 First surface, 42 Second surface, 45 First edge, 46 Second edge 51 Adhesive surface 6L first major axis, 6S first minor axis 61 first layer, 62 second layer, 63 third layer, 64 adhesive layer, 65,66 end 7L second major axis, 7S second minor axis 70 interlayer area, 75,76 edge 80 Steam 9F flange section, 90 opening G, L, LL, LS: Length, W: Width

Claims

1. An adhesive film that covers a steam vent that releases steam from inside a sealed container, A base film having a first surface, An adhesive layer disposed on at least a portion of the first surface, A first shrink layer is placed on a portion of the adhesive surface of the aforementioned adhesive layer, The adhesive surface comprises a second shrink layer, which is positioned on a portion of the adhesive surface at a distance from the first shrink layer, The first shrink layer and the second shrink layer each include a first layer positioned closer to the adhesive layer and a second layer positioned further from the adhesive layer than the first layer. The thermal shrinkage rate of the second layer is greater than that of the first layer. Adhesive film.

2. In a plan view, the first shrink layer is formed in a strip shape having a first major axis and a first minor axis, and the second shrink layer is formed in a strip shape having a second major axis and a second minor axis. The adhesive film according to claim 1, wherein the first shrink layer and the second shrink layer are aligned in a direction along the first short axis.

3. The base film, in plan view, has a first edge and a second edge facing the first edge. The two ends of the first major axis in the first shrink layer reach the first edge and the second edge, respectively. The adhesive film according to claim 2, wherein the two ends of the second long axis in the second shrink layer each reach the first edge and the second edge, respectively.

4. The adhesive film according to claim 2 or claim 3, wherein the width along the first short axis of the first shrink layer and the width along the second short axis of the second shrink layer are each 4 mm or more and 15 mm or less.

5. The adhesive film according to any one of claims 1 to 3, wherein the length of the gap between the first shrink layer and the second shrink layer is 4 mm or more and 10 mm or less.

6. The adhesive film according to any one of claims 1 to 3, wherein the layer comprises at least one of polyethylene terephthalate resin and biaxially oriented polypropylene resin.

7. The adhesive film according to claim 6, wherein the second layer comprises at least one resin selected from the group consisting of polystyrene resin, polyethylene terephthalate resin, polyethylene resin, polypropylene resin, and polyvinyl chloride resin.

8. The adhesive film according to any one of claims 1 to 3, wherein the average thickness of the second layer is greater than the average thickness of the first layer.

9. The average thickness of the aforementioned single layer is 9 μm or more and 16 μm or less. The adhesive film according to any one of claims 1 to 3, wherein the average thickness of the second layer is 12 μm or more and 50 μm or less.

10. The adhesive film according to any one of claims 1 to 3, comprising a release liner covering the adhesive surface.

11. The adhesive film according to any one of claims 1 to 3, further comprising an adhesive third layer on the second layer.

12. A storage container containing the contents, A packaging film that covers the opening of the storage container and seals the contents inside the storage container, The packaging film comprises a cover film attached to the aforementioned packaging film, The packaging film is provided with a steam vent that penetrates the packaging film in the thickness direction, The cover film is an adhesive film according to any one of claims 1 to 3 that covers the steam vent portion. The adhesive film has an interlayer region sandwiched between the first shrink layer and the second shrink layer in a plan view. In a plan view, the first shrink layer, the second shrink layer, and the interlayer region all overlap the steam vent portion. A sealed container.

13. The steam vent section is a straight or corrugated notch. The sealed container according to claim 12, wherein, in a plan view, the steam vent portion is arranged to extend from the first shrink layer through the interlayer region to the second shrink layer.

14. A storage container containing the contents, A packaging film that covers the opening of the storage container and seals the contents inside the storage container, The packaging film comprises a cover film attached to the aforementioned packaging film, The packaging film is provided with a steam vent that penetrates the packaging film in the thickness direction, The cover film is the adhesive film according to claim 11 that covers the steam vent portion. The adhesive film has an interlayer region sandwiched between the first shrink layer and the second shrink layer in a plan view. The steam vent portion is a notch having at least one spiral portion formed in a spiral shape in a plan view, In a plan view, at least one of the spiral portions overlaps with the first shrink layer, the second shrink layer, and the interlayer region. A sealed container.

Images