JP7659366B2 - bag - Google Patents

Description

The present invention relates to a bag made of a laminate including a stretched plastic film.

Conventionally, many bags made of plastic laminates are available on the market that are filled and sealed with cooked or semi-cooked liquid, viscous material, or a mixture of liquid and solid. In the bag, the non-sealed parts where the laminates are not joined together form the storage section in which the contents are stored. Also, the sealed parts where the laminates are joined together seal the storage section. The contents are, for example, cooked foods such as curry, stew, soup, etc. The contents are heated in a microwave oven or the like while contained in the bag.

However, when the contents stored in a sealed bag are heated in a microwave oven, the moisture contained in the contents evaporates as the bag is heated, and the pressure in the storage section increases. If the pressure in the storage section of the bag increases, the bag may burst, scattering the contents and soiling the inside of the microwave oven. In consideration of this problem, for example, Patent Document 1 proposes providing a mechanism for automatically connecting the storage section to the outside when the pressure in the storage section increases, and releasing the steam in the storage section to the outside. Patent Document 1 also proposes using, as the laminate constituting the bag, stretched polyethylene terephthalate film, silica-deposited stretched polyethylene terephthalate film, alumina-deposited stretched polyethylene terephthalate film, stretched nylon film, stretched polypropylene film, or polypropylene/ethylene-vinyl alcohol copolymer co-extruded co-stretched film, or a composite film made by laminating two or more of these films, in order to make the bag resistant to heat.

JP 2015-120550 A

When removing the contents from the storage section, the consumer tears the bag to open it. For consumer convenience, it is preferable that the laminated body of the bag is configured so that the bag can be opened by tearing it with the hands or the like.

The present invention was made with these points in mind, and aims to provide a bag that has a steam venting mechanism and is tearable.

The present invention is a bag having a steam venting mechanism, and the laminate constituting the bag comprises, in order from the outer surface side to the inner surface side, at least a first stretched plastic film, a second stretched plastic film, and a sealant layer, the first stretched plastic film contains polyester or polyamide as a main component, and when the first stretched plastic film contains polyester as a main component, the second stretched plastic film contains polyester or polyamide as a main component, and when the first stretched plastic film contains polyamide as a main component, the second stretched plastic film contains polyester as a main component, and when the width direction of the bag is defined as a first direction and a direction perpendicular to the first direction is defined as a second direction, the tensile strength of the second stretched plastic film in the first direction is greater than the tensile strength of the second stretched plastic film in the second direction.

In the bag according to the present invention, the tensile strength of the second stretched plastic film in the first direction may be 1.05 times or more the tensile strength of the second stretched plastic film in the second direction.

In the bag according to the present invention, both the first stretched plastic film and the second stretched plastic film may contain polyester as a main component.

In the bag according to the present invention, the first stretched plastic film may contain polyamide as a main component, and the second stretched plastic film may contain polyester as a main component.

In the bag according to the present invention, the first stretched plastic film may contain polyester as a main component, and the second stretched plastic film may contain polyamide as a main component.

The present invention provides a bag that is equipped with a steam vent mechanism and has tearability.

FIG. 2 is a front view showing a bag according to the embodiment of the present invention. 2 is a cross-sectional view showing the bag shown in FIG. 1 as viewed along line II-II. FIG. 2 is a cross-sectional view showing an example of a layer structure of a laminate constituting a bag. FIG. 2 is a cross-sectional view showing an example of a layer structure of a first stretched plastic film. 4 is a cross-sectional view showing an example of heat transfer from the inner surface side to the outer surface side of the laminate. FIG. FIG. 1 is a diagram showing an example of a method for measuring piercing strength. FIG. 2 is a plan view showing a test piece for evaluating impact strength. FIG. 8 is a cross-sectional view of the test piece shown in FIG. 7. FIG. 2 is a diagram showing an example of a method for measuring impact strength. FIG. 2 is a plan view showing a test piece for evaluating tearability. FIG. 1 is a diagram showing the evaluation results of Examples 1 to 4 and Comparative Example 1.

One embodiment of the present invention will be described with reference to Figures 1 to 5. Note that in the drawings attached to this specification, the scale and aspect ratios have been appropriately altered and exaggerated from those of the actual objects for the sake of ease of illustration and understanding.

In addition, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "same," as well as values of length and angle, are not to be bound by strict meanings, but are to be interpreted to include the range within which similar functions can be expected.

Figure 1 is a front view of a bag 10 according to this embodiment. Bag 10 has a storage section 17 for storing contents. Note that Figure 1 shows bag 10 in a state before contents are stored in it. Bag 10 according to this embodiment is configured so that it can be suitably used as a microwave pouch in which the contents are heated in a microwave oven.

As shown in FIG. 1, the bag 10 according to this embodiment includes a steam vent mechanism 20 for releasing steam generated when the contents contained in the bag 10 are heated to the outside. The steam vent mechanism 20 is configured to communicate between the inside and outside of the bag 10 to release steam when the steam pressure reaches or exceeds a predetermined value, and to prevent steam from escaping from any location other than the steam vent mechanism 20. The configuration of the bag 10 will be described below.

In this embodiment of the bag , the bag 10 is a gusset-type bag configured to be self-supporting. The bag 10 includes an upper portion 11, a lower portion 12, and a pair of side portions 13, and has a generally rectangular outline in a front view. The names "upper portion", "lower portion", and "side portion", as well as the terms "upper" and "lower portion", merely indicate the relative positions and directions of the bag 10 and its components based on a state in which the bag 10 stands on its own with the gusset portion facing down. The position of the bag 10 during transportation or use is not limited by the names and terms used in this specification.

In this embodiment, the width direction of the bag 10 is also referred to as the first direction D1. The pair of side portions 13 described above face each other in the first direction D1. The direction perpendicular to the first direction D1 is also referred to as the second direction D2. The bag 10 of this embodiment is intended to be used in such a way that the consumer opens the bag 10 by tearing the bag 10 along the first direction D1 after the contents of the bag 10 are heated in a microwave oven.

As shown in FIG. 1, the bag 10 includes a surface film 14 that forms the surface, a back film 15 that forms the back, and a lower film 16 that forms the lower portion 12. The lower film 16 is folded back at the fold back portion 16f and is disposed between the surface film 14 and the back film 15.

The terms "surface film", "back film" and "lower film" mentioned above merely divide each film according to its positional relationship, and the method of providing the films when manufacturing the bag 10 is not limited by the terms mentioned above. For example, the bag 10 may be manufactured using one film in which the surface film 14, the back film 15 and the lower film 16 are connected together, or may be manufactured using two films in total, one film in which the surface film 14 and the lower film 16 are connected together and one back film 15, or may be manufactured using three films in total, one surface film 14, one back film 15 and one lower film 16.

The inner surfaces of the front film 14, back film 15, and bottom film 16 are joined together by a seal. In a plan view of the bag 10 such as Figure 1, the seal is hatched.

As shown in FIG. 1, the seal portion has an outer edge seal portion that extends along the outer edge of the bag 10, and a steam release seal portion 20a that constitutes the steam release mechanism 20. The outer edge seal portion includes a lower seal portion 12a that extends to the lower portion 12, and a pair of side seal portions 13a that extend along a pair of side portions 13. Note that, in the bag 10 before the contents are placed inside it, as shown in FIG. 1, the upper portion 11 of the bag 10 forms an opening 11b. After the contents are placed inside the bag 10, the inner surface of the front film 14 and the inner surface of the back film 15 are joined at the upper portion 11 to form the upper seal portion and seal the bag 10.

The side seal portion 13a, the steam release seal portion 20a, and the upper seal portion are seal portions formed by joining the inner surface of the front film 14 and the inner surface of the back film 15. On the other hand, the lower seal portion 12a includes a seal portion formed by joining the inner surface of the front film 14 and the inner surface of the lower film 16, and a seal portion formed by joining the inner surface of the back film 15 and the inner surface of the lower film 16.

As long as the bag 10 can be sealed by joining opposing films together, there is no particular limitation on the method for forming the seal portion. For example, the seal portion may be formed by melting the inner surfaces of the films by heating or the like and fusing the inner surfaces together, i.e., by heat sealing. Alternatively, the seal portion may be formed by bonding the inner surfaces of the opposing films together using an adhesive or the like.

Steam Release Mechanism Below, we will explain the configuration of the steam release mechanism 20. Figure 2 is a cross-sectional view showing the steam release mechanism 20 of the bag 10 shown in Figure 1 as viewed along line II-II.

The steam release seal portion 20a of the steam release mechanism 20 has a shape that is easily peeled off as the pressure in the storage section 17 increases. For example, the steam release seal portion 20a has a shape that protrudes from the side seal portion 13a toward the inside of the bag 10. This allows the force applied to the steam release seal portion 20a when the pressure in the storage section 17 increases to be greater than the force applied to the side seal portion 13a. In addition, the width of the steam release seal portion 20a is smaller than the width of the side seal portion 13a. In addition, as shown in Figures 1 and 2, a non-sealed portion 20b is formed between the steam release seal portion 20a and the outer edge of the side portion 13. This makes it easier for the steam release seal portion 20a to communicate with the storage section 17 and the outside due to peeling of the seal portion compared to the side seal portion 13a. As long as the storage section 17 can communicate with the outside of the bag 10 when the pressure in the storage section 17 increases, the configuration and arrangement of the steam release mechanism 20 are not limited to the examples shown in Figures 1 and 2.

Easy-opening means The front film 14 and the back film 15 may be provided with easy-opening means 25 for tearing the front film 14 and the back film 15 along the first direction D1 to open the bag 10. For example, as shown in Fig. 1, the easy-opening means 25 may include a notch 26 that serves as a starting point for tearing, formed in the side seal portion 13a of the bag 10. In addition, a half-cut line formed by laser processing, a cutter, or the like may be provided as the easy-opening means 25 in a portion that serves as a path for tearing the bag 10.

Although not shown, the easy-opening means 25 may include a cut or a group of scars formed in the area of the front film 14 and the back film 15 where the seal portion is formed. The group of scars may include, for example, a plurality of through holes formed so as to penetrate the front film 14 and/or the back film 15. Alternatively, the group of scars may include a plurality of holes formed on the outer surface of the front film 14 and/or the back film 15 so as not to penetrate the front film 14 and/or the back film 15.

In the example shown in FIG. 1, the easy-to-open means 25 is located closer to the upper portion 11 than the steam release mechanism 20. However, this is not limited to this, and although not shown, the easy-to-open means 25 may be located closer to the lower portion 12 than the steam release mechanism 20.

Layer Structure of the Front Film and the Back Film Next, a description will be given of the layer structure of the front film 14 and the back film 15. Fig. 3 is a cross-sectional view showing an example of the layer structure of a laminate 30 constituting the front film 14 and the back film 15.

As shown in FIG. 3, the laminate 30 comprises at least a first stretched plastic film 40, a first adhesive layer 45, a second stretched plastic film 50, a second adhesive layer 55, and a sealant layer 70, in this order. The first stretched plastic film 40 is located on the outer surface 30y side, and the sealant layer 70 is located on the inner surface 30x side opposite the outer surface 30y. The inner surface 30x is the surface located on the storage section 17 side.

Each layer of the laminate 30 is described in detail below.

(First Stretched Plastic Film)
The first stretched plastic film 40 is a plastic film stretched in a predetermined direction. The first stretched plastic film 40 functions as a base layer for imparting a predetermined strength to the laminate 30. The first stretched plastic film 40 may be a uniaxially stretched film stretched in one predetermined direction, or a biaxially stretched film stretched in two predetermined directions. The stretching direction of the first stretched plastic film 40 is not particularly limited. For example, the first stretched plastic film 40 may be stretched in the direction in which the side portion 13 extends, or may be stretched in a direction perpendicular to the direction in which the side portion 13 extends. The stretching ratio of the first stretched plastic film 40 is, for example, 1.05 times or more.

The first stretched plastic film 40 contains, for example, polyester as a main component. For example, the first stretched plastic film 40 contains 51% by mass or more of polyester. Examples of polyester include polyethylene terephthalate (hereinafter also referred to as PET) and polybutylene terephthalate (hereinafter also referred to as PBT). Note that the 51% by mass or more of polyester in the first stretched plastic film 40 may be composed of one type of polyester, or may be composed of two or more types of polyester.

When the first stretched plastic film 40 contains polyester as a main component, the thickness of the first stretched plastic film 40 is preferably 9 μm or more, more preferably 12 μm or more. When the first stretched plastic film 40 contains polyester as a main component, the thickness of the first stretched plastic film 40 is preferably 25 μm or less, more preferably 20 μm or less. By making the thickness of the first stretched plastic film 40 9 μm or more, the first stretched plastic film 40 has sufficient strength. By making the thickness of the first stretched plastic film 40 25 μm or less, the first stretched plastic film 40 exhibits excellent formability. Therefore, the process of processing the laminate 30 to manufacture the bag 10 can be carried out efficiently.

When the first stretched plastic film 40 contains polyester as a main component, the thermal conductivity of the material constituting the first stretched plastic film 40 is preferably 0.05 W/m·K or more, and more preferably 0.1 W/m·K or more. The thermal conductivity of PET is, for example, 0.14 W/m·K. The thermal conductivity of PBT is higher than that of PET, for example, 0.25 W/m·K. By having the thermal conductivity of the material constituting the first stretched plastic film 40 be equal to or greater than a predetermined value, the heat resistance of the laminate 30 can be improved.

In addition, when the first stretched plastic film 40 contains polyester as a main component, the melting point of the first stretched plastic film 40 is preferably 200°C or higher, and more preferably 220°C or higher. By making the melting point of the first stretched plastic film 40 220°C or higher, it is possible to prevent holes from being formed in the first stretched plastic film 40 and to prevent wrinkles from being formed in the first stretched plastic film 40 when the contents contained in the bag 10 manufactured using the laminate 30 are heated.

The first stretched plastic film 40 may contain polyamide as a main component. For example, the first stretched plastic film 40 contains 51% or more by mass of polyamide. Examples of polyamide-based films include aliphatic polyamides and aromatic polyamides. Examples of aliphatic polyamides include nylons such as nylon-6, nylon-6,6, and copolymers of nylon 6 and nylon 6,6, and examples of aromatic polyamides include polymetaxylene adipamide (MXD6). By including polyamide as a main component in the first stretched plastic film 40, the puncture strength of the laminate 30 including the first stretched plastic film 40 can be increased.

When the first stretched plastic film 40 contains polyamide as a main component, the thickness of the first stretched plastic film 40 is preferably 12 μm or more, more preferably 15 μm or more. When the first stretched plastic film 40 contains polyamide as a main component, the thickness of the first stretched plastic film 40 is preferably 25 μm or less, more preferably 20 μm or less. When the first stretched plastic film 40 contains polyamide as a main component, the thermal conductivity of the first stretched plastic film 40 is preferably 0.25 W/m·K or more, more preferably 0.3 W/m·K or more. The thermal conductivity of nylon is, for example, 0.35 W/m·K. When the first stretched plastic film 40 contains polyamide as a main component, the stretch ratio of the first stretched plastic film 40 is, for example, 1.05 times or more.

The first stretched plastic film 40 may be composed of a single layer or multiple layers. When the first stretched plastic film 40 includes multiple layers, the first stretched plastic film 40 is, for example, a co-extrusion film produced by co-extrusion. The first stretched plastic film 40 produced by co-extrusion includes, for example, a first layer 41 made of a polyester such as PET, a second layer 42 made of a polyamide such as nylon, and a third layer 43 made of a polyester such as PET, which are laminated in this order, as shown in FIG. 4. In addition, when the mass of the second layer 42 made of a polyamide such as nylon is 51% or more of the mass of the entire first stretched plastic film 40, it can be said that the main component of the first stretched plastic film 40 produced by co-extrusion is polyamide.

(First Adhesive Layer)
The first adhesive layer 45 contains an adhesive for bonding the first stretched plastic film 40 and the second stretched plastic film 50 by a dry lamination method. The adhesive constituting the first adhesive layer 45 is produced from an adhesive composition produced by mixing a first composition containing a base agent and a solvent with a second composition containing a curing agent and a solvent. Specifically, the adhesive contains a cured product produced by reaction of the base agent and the solvent in the adhesive composition.

An example of an adhesive is polyurethane. Polyurethane is a cured product produced by reacting a polyol as a base agent with an isocyanate compound as a curing agent. Examples of polyurethane are polyether polyurethane and polyester polyurethane. Polyether polyurethane is a cured product produced by reacting a polyether polyol as a base agent with an isocyanate compound as a curing agent. Polyester polyurethane is a cured product produced by reacting a polyester polyol as a base agent with an isocyanate compound as a curing agent.

As the isocyanate compound, aromatic isocyanate compounds such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), etc., aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), etc., or adducts or oligomers of the above various isocyanate compounds can be used.

The material constituting the first adhesive layer 45 preferably has a higher thermal conductivity than the materials constituting the first stretched plastic film 40, the second stretched plastic film 50, and the sealant layer 70. For example, the thermal conductivity of the material constituting the first adhesive layer 45 is preferably 1.0 W/m·K or more, more preferably 3.0 W/m·K or more. The thermal conductivity of polyurethane is in the range of 3.0 W/m·K to 5.0 W/m·K, for example 5.0 W/m·K. Due to the high thermal conductivity of the material constituting the first adhesive layer 45, when the bag 10 made using the laminate 30 is heated, the heat generated in the storage section 17 is easily diffused in the surface direction of the laminate 30 while being transferred from the inner surface 30x side to the outer surface 30y side of the laminate 30. This can increase the heat dissipation of the laminate 30, thereby suppressing the temperature rise of the laminate 30. This can suppress damage to the laminate 30 caused by heat when the bag 10 is heated. In other words, the heat resistance of the laminate 30 can be improved.

The thickness of the first adhesive layer 45 is preferably 2 μm or more, and more preferably 3 μm or more. The thickness of the first adhesive layer 45 is preferably 6 μm or less, and more preferably 5 μm or less. By making the thickness of the first adhesive layer 45 3 μm or more, heat diffusion in the surface direction of the laminate 30 becomes easier to occur.

(Second Stretched Plastic Film)
The second stretched plastic film 50 is a plastic film stretched in a predetermined direction, similar to the first stretched plastic film 40. Similar to the first stretched plastic film 40, the second stretched plastic film 50 also functions as a base layer for imparting a predetermined strength to the laminate 30. Similarly to the first stretched plastic film 40, the stretching direction of the second stretched plastic film 50 is not particularly limited.

The second stretched plastic film 50 also functions as a base layer to impart tearability to the laminate 30, as described below.

As shown in FIG. 3, the second stretched plastic film 50 is adjacent to the sealant layer 70 via the second adhesive layer 55. The sealant layer 70 has a smaller tensile modulus than the stretched plastic films such as the first stretched plastic film 40 and the second stretched plastic film 50, and is therefore more likely to stretch. For this reason, when a consumer tears open the bag 10, if the sealant layer 70 peels off from the second stretched plastic film 50, the force applied to the bag 10 by the consumer mainly acts as a force to stretch the sealant layer 70 peeled off from the second stretched plastic film 50, making it difficult to tear the bag 10.

In consideration of these issues, in this embodiment, the second stretched plastic film 50 is configured to have tearability in the first direction D1. This makes it easier for the force applied to the bag 10 by the consumer to act as a force that tears the laminate 30 including the second stretched plastic film 50. This makes it possible to prevent the sealant layer 70 from stretching when the consumer tears the bag 10 to open it.

The mechanical properties of the second stretched plastic film 50 for imparting tearability in the first direction D1 to the laminate 30 will be described. In this embodiment, the tensile strength of the second stretched plastic film 50 in the first direction D1 is greater than the tensile strength of the second stretched plastic film 50 in the second direction D2. The tensile strength can be measured in accordance with JIS K 7127. As a measuring instrument, a thermostatic bath-equipped tensile tester RTC-1310A manufactured by Orientec Co., Ltd. can be used. Unless otherwise specified, the tensile strength is measured at 25°C. In the bag 10 shown in Figure 1, the first direction D1 corresponds to the machine direction (MD) of the second stretched plastic film 50. The second direction D2 corresponds to the perpendicular direction (TD) of the second stretched plastic film 50.

In the second stretched plastic film 50, the tensile strength of the second stretched plastic film 50 in the first direction D1 is preferably 1.05 times or more, more preferably 1.10 times or more, and even more preferably 1.2 times or more, of the tensile strength of the second stretched plastic film 50 in the second direction D2. In addition, the tensile strength of the second stretched plastic film 50 in the first direction D1 is, for example, 200 MPa or more and 300 MPa or less.

Next, the material constituting the second stretched plastic film 50 described above will be described. The second stretched plastic film 50 contains polyester or polyamide as a main component. In order to provide heat resistance to the laminate 30, it is preferable that at least one of the first stretched plastic film 40 and the second stretched plastic film 50 contains polyester as a main component. Therefore, when the first stretched plastic film 40 contains polyamide as a main component, the second stretched plastic film 50 contains polyester as a main component. When the first stretched plastic film 40 contains polyester as a main component, the second stretched plastic film 50 may contain polyester as a main component or may contain polyamide as a main component.

When the second stretched plastic film 50 contains polyester as a main component, for example, when it contains 51% by mass or more of polyester, examples of polyester include PET, PBT, etc., as in the case of the first stretched plastic film 40. The thickness of the second stretched plastic film 50 is preferably 9 μm or more, more preferably 12 μm or more. Furthermore, when the second stretched plastic film 50 contains polyester as a main component, the thickness of the second stretched plastic film 50 is preferably 25 μm or less, more preferably 20 μm or less. When the second stretched plastic film 50 contains polyester as a main component, the thermal conductivity, melting point, etc. of the second stretched plastic film 50 are the same as those of the first stretched plastic film 40 containing polyester as a main component.

When the second stretched plastic film 50 contains polyamide as a main component, for example, when it contains 51 mass% or more of polyamide, examples of polyamide include aliphatic polyamide or aromatic polyamide, as in the case of the first stretched plastic film 40. The thickness of the second stretched plastic film 50 is preferably 12 μm or more, more preferably 15 μm or more. In addition, when the second stretched plastic film 50 contains polyamide as a main component, the thickness of the second stretched plastic film 50 is preferably 25 μm or less, more preferably 20 μm or less. When the second stretched plastic film 50 contains polyamide as a main component, the thermal conductivity, melting point, etc. of the second stretched plastic film 50 are the same as those of the first stretched plastic film 40 containing polyamide as a main component.

(Second Adhesive Layer)
The second adhesive layer 55 contains an adhesive for bonding the second stretched plastic film 50 and the sealant layer 70 by a dry lamination method. An example of the adhesive for the second adhesive layer 55 is polyurethane, as in the case of the first adhesive layer 45. In addition to the configurations, materials, and characteristics described below, the second adhesive layer 55 can adopt the same configurations, materials, and characteristics as the first adhesive layer 45.

The material constituting the second adhesive layer 55, like the first adhesive layer 45, preferably has a higher thermal conductivity than the materials constituting the first stretched plastic film 40, the second stretched plastic film 50, and the sealant layer 70. For example, the thermal conductivity of the material constituting the second adhesive layer 55 is preferably 1 W/m·K or more, and more preferably 3 W/m·K or more.

The thickness of the second adhesive layer 55 is preferably 2 μm or more, and more preferably 3 μm or more. The thickness of the second adhesive layer 55 is preferably 6 μm or less, and more preferably 5 μm or less.

As described above, the isocyanate compounds constituting the curing agent of the adhesive include aromatic isocyanate compounds and aliphatic isocyanate compounds. Among these, aromatic isocyanate compounds leach out components that cannot be used for food applications in high-temperature environments such as heat sterilization. The second adhesive layer 55 is in contact with the sealant layer 70. Therefore, when the second adhesive layer 55 contains an aromatic isocyanate compound, components leach out from the aromatic isocyanate compound may adhere to the contents contained in the storage section 17 that is in contact with the sealant layer 70.

Considering these issues, it is preferable to use a cured product produced by reacting a polyol as the base agent with an aliphatic isocyanate compound as the curing agent as the adhesive that constitutes the second adhesive layer 55. This makes it possible to prevent components that cannot be used for food applications, which are caused by the second adhesive layer 55, from adhering to the contents.

(Relationship)
Next, a description will be given of the relationship that holds between the stretched plastic films 40, 50 and the adhesive layers 45, 55. In the laminate 30, the following relationship preferably holds.
A1+A2<B1+B2
A1 is the product of the thickness and thermal conductivity of the first stretched plastic film 40.
A2 is the product of the thickness and thermal conductivity of the second stretched plastic film 50.
B1 is the product of the thickness and thermal conductivity of the first adhesive layer 45.
B2 is the product of the thickness and thermal conductivity of the second adhesive layer 55.

The above relational expression means that the adhesive layers 45, 55 have higher thermal conductivity in the plane direction of the laminate 30 than the stretched plastic films 40, 50. This makes it possible to prevent the laminate 30 from being damaged by heat when the contents contained in the bag 10 are heated. Examples of damage caused to the laminate 30 by heat include holes being made in the laminate 30 and wrinkles being formed in the laminate 30.

We will now consider why satisfying the above-mentioned relational equations makes it possible to suppress damage caused by heat. Note that the reasons for this effect are not limited to the following considerations, and other considerations may also be adopted.

Figure 5 is a diagram showing the state in which contents 18 are attached to the inner surface 30x of the laminate 30 constituting the bag 10. The attachment of contents 18 to the inner surface 30x can occur, for example, when the contents 18 contained in the bag 10 are heated using a microwave oven, and part of the contents 18 splashes and reaches the inner surface 30x. If the contents 18 attached to the inner surface 30x are further heated, the temperature of the laminate 30 in contact with the contents 18 also rises, and it is conceivable that holes will appear in the laminate 30 or wrinkles will form in the laminate 30.

Here, in this embodiment, the laminate 30 is configured so that the above-mentioned relational expression is established. In addition, the laminate 30 includes two or more stretched plastic films 40, 50 and adhesive layers 45, 55. Therefore, as shown in FIG. 5, while the heat generated in the contents 18 is transferred from the inner surface 30x side to the outer surface 30y side of the laminate 30, the heat is easily diffused in the surface direction of the laminate 30, particularly in the adhesive layers 45, 55. This makes it easier to release heat to the outside of the bag 10, so that the temperature rise in the part of the laminate 30 to which the contents 18 are attached can be suppressed. This makes it possible to suppress damage to the laminate 30 due to heat. In other words, the heat resistance of the laminate 30 can be improved.

B1+B2 is preferably 3.5 times or more, more preferably 4.0 times or more, and even more preferably 4.5 times or more, of A1+A2.

(Sealant Layer)
Next, the sealant layer 70 will be described. As a material constituting the sealant layer 70, one or more resins selected from polyethylene such as low density polyethylene and linear low density polyethylene, and polypropylene can be used. The sealant layer 70 may be a single layer or may be a multilayer. In addition, the sealant layer 70 is preferably made of an unstretched film. Note that the concept of "unstretched" includes not only a film that is not stretched at all, but also a film that is slightly stretched due to the tension applied during film formation.

The bag 10 made of the laminate 30 is subjected to sterilization treatment such as boiling or retorting at high temperatures. Therefore, the sealant layer 70 used is one that has heat resistance that can withstand these high-temperature treatments.

The melting point of the material constituting the sealant layer 70 is preferably 150°C or higher, and more preferably 160°C or higher. By increasing the melting point of the sealant layer 70, it becomes possible to carry out the retort treatment of the bag 10 at a high temperature, and therefore the time required for the retort treatment can be shortened. The melting point of the material constituting the sealant layer 70 is lower than the melting point of the resin constituting the stretched plastic films 40, 50, and 60.

From the viewpoint of retort processing, a material mainly composed of propylene can be used as the material constituting the sealant layer 70. Here, a material "mainly composed" of propylene means a material having a propylene content of 90% by mass or more. Specific examples of materials mainly composed of propylene include propylene-ethylene block copolymers, propylene-ethylene random copolymers, polypropylene such as homopolypropylene, and mixtures of polypropylene and polyethylene. Here, "propylene-ethylene block copolymers" means a material having the structural formula shown in the following formula (I). Also, "propylene-ethylene random copolymers" means a material having the structural formula shown in the following formula (II). Also, "homopolypropylene" means a material having the structural formula shown in the following formula (III).

When a mixture of polypropylene and polyethylene is used as a material mainly composed of propylene, the material may have an island-in-a-sea structure. Here, "island-in-a-sea structure" refers to a structure in which polyethylene is discontinuously dispersed within a region in which polypropylene is continuous.

Considering the boiling treatment, examples of the material constituting the sealant layer 70 include polyethylene, polypropylene, or a combination thereof. Examples of polyethylene include medium density polyethylene, linear low density polyethylene, or a combination thereof. For example, it is also possible to use the materials listed as the material constituting the sealant layer 70 from the viewpoint of the above-mentioned retort treatment. The material constituting the sealant layer 70 has a melting point of, for example, 100°C or more, more preferably 105°C or more, and even more preferably 110°C or more. When polyethylene is used as the material constituting the sealant layer 70, a melting point of 100°C or more can be achieved, for example, when the density of the polyethylene is 0.920 g/ ^cm3 or more. Specific examples of sealant films for constituting the sealant layer 70 having a melting point of 100°C or more include TUX-HC manufactured by Mitsui Chemicals Tohcello, L6101 manufactured by Toyobo, and LS700C manufactured by Idemitsu Unitech. Specific examples of sealant films for constituting the sealant layer 70 having a melting point of 105° C. or higher include NB-1 manufactured by Tamapoly Co., Ltd. Specific examples of sealant films for constituting the sealant layer 70 having a melting point of 110° C. or higher include LS760C manufactured by Idemitsu Unitech Co., Ltd. and TUX-HZ manufactured by Mitsui Chemicals Tohcello Co., Ltd.

Preferably, the sealant layer 70 is a single-layer film containing a propylene-ethylene block copolymer. For example, the sealant film containing the sealant layer 70 is a single-layer unstretched film whose main component is a propylene-ethylene block copolymer. By using a propylene-ethylene block copolymer, the impact resistance of the sealant film can be increased, which can prevent the bag 10 from breaking due to an impact when dropped. In addition, the puncture resistance of the laminate 30 can be increased.

In addition, by using a propylene-ethylene block copolymer, the strength of the seal portion (hereinafter also referred to as hot seal strength) formed by the sealant layer 70 at high temperatures, for example at 100°C or higher, is extremely small compared to the seal strength at low temperatures, for example at room temperature. For example, the hot seal strength at 100°C is one third or less, preferably one quarter or less, of the seal strength at 25°C (hereinafter also referred to as room temperature seal strength). For example, the hot seal strength at 15 mm width at 100°C is 30 N or less, preferably 25 N or less, more preferably 20 N or less, and even more preferably 15 N or less. In addition, the room temperature seal strength at 15 mm width at 25°C is 23 N or more, preferably 40 N or more, more preferably 50 N or more, and even more preferably 60 N or more. Due to the low hot seal strength, when the bag 10 is heated using a microwave oven, the steam release seal portion 20a is easily peeled off, and the steam in the storage portion 17 is easily released to the outside of the bag 10. This prevents the internal pressure of the storage section 17 from becoming excessive, thereby preventing damage to the laminate 30 when heated. The seal strength can be measured in accordance with JIS Z1707 7.5. For example, a thermostatic chamber equipped tensile tester RTC-1310A manufactured by Orientec Co., Ltd. can be used as a measuring device.

The propylene-ethylene block copolymer contains, for example, a sea component made of polypropylene and an island component made of an ethylene-propylene copolymer rubber component. The sea component can contribute to improving the blocking resistance, heat resistance, rigidity, seal strength, etc. of the propylene-ethylene block copolymer. The island component can also contribute to improving the impact resistance of the propylene-ethylene block copolymer. Therefore, by adjusting the ratio of the sea component to the island component, the mechanical properties of the sealant film containing the propylene-ethylene block copolymer can be adjusted.

In the propylene-ethylene block copolymer, the mass ratio of the sea component made of polypropylene is higher than the mass ratio of the island component made of the ethylene-propylene copolymer rubber component. For example, in the propylene-ethylene block copolymer, the mass ratio of the sea component made of polypropylene is at least 51 mass% or more, preferably 60 mass% or more, and more preferably 70 mass% or more.

The single-layer sealant film may further contain a second thermoplastic resin in addition to the first thermoplastic resin consisting of a propylene-ethylene block copolymer. Examples of the second thermoplastic resin include an α-olefin copolymer and polyethylene. An example of the α-olefin copolymer is linear low-density polyethylene. Examples of polyethylene include low-density polyethylene, medium-density polyethylene, and high-density polyethylene. The second thermoplastic resin may contribute to increasing the impact resistance of the sealant film.

Low density polyethylene is polyethylene having a density of 0.910 g/cm ³ or more and 0.925 g/cm ³ or less. Medium density polyethylene is polyethylene having a density of 0.926 g/cm ³ or more and 0.940 g/cm ³ or less. High density polyethylene is polyethylene having a density of 0.941 g/cm ³ or more and 0.965 g/cm ³ or less. Low density polyethylene is obtained, for example, by polymerizing ethylene at a high pressure of 1000 atmospheres or more and less than 2000 atmospheres. Medium density polyethylene and high density polyethylene are obtained, for example, by polymerizing ethylene at a medium or low pressure of 1 atmosphere or more and less than 1000 atmospheres.

The medium-density polyethylene and the high-density polyethylene may partially contain a copolymer of ethylene and an α-olefin. Even when ethylene is polymerized at a medium or low pressure, if a copolymer of ethylene and an α-olefin is contained, a medium-density or low-density polyethylene can be produced. Such a polyethylene is called the above-mentioned linear low-density polyethylene. The linear low-density polyethylene is obtained by copolymerizing an α-olefin with a linear polymer obtained by polymerizing ethylene at a medium or low pressure to introduce short-chain branches. Examples of the α-olefin include 1-butene (C ₄ ), 1-hexene (C ₆ ), 4-methylpentene (C ₆ ), and 1-octene (C ₈ ). The density of the linear low-density polyethylene is, for example, 0.915 g/cm ³ or more and 0.945 g/cm ³ or less.

The α-olefin copolymer constituting the second thermoplastic resin of the propylene-ethylene block copolymer is not limited to the linear low-density polyethylene described above. The α-olefin copolymer refers to a material having the structural formula shown in formula (IV) below.

Ｒ_１、Ｒ_２はいずれも、Ｈ（水素原子）、又はＣＨ_３、Ｃ_２Ｈ_５などのアルキル基である。また、ｊ及びｋはいずれも、１以上の整数である。また、ｊはｋよりも大きい。すなわち、式（IV）に示すα－オレフィン共重合体においては、Ｒ_１を含む左側の構造がベースとなる。Ｒ_１は例えばＨであり、Ｒ_２は例えばＣ_２Ｈ_５である。

Both R ₁ and R ₂ are H (hydrogen atom) or an alkyl group such as CH ₃ or C ₂ H _5. Both j and k are integers of 1 or more. Furthermore, j is greater than k. That is, in the α-olefin copolymer shown in formula (IV), the structure on the left side including R ₁ is the base. _{R 1} is, for example, H, and R ₂ is, for example, C ₂ H ₅ .

In the sealant film, the mass ratio of the first thermoplastic resin consisting of a propylene-ethylene block copolymer is higher than the mass ratio of the second thermoplastic resin containing at least an α-olefin copolymer or polyethylene. For example, in a single-layer sealant film, the mass ratio of the first thermoplastic resin consisting of a propylene-ethylene block copolymer is at least 51% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more.

As described above, the second thermoplastic resin can contribute to increasing the impact resistance of the sealant film. Therefore, by adjusting the mass ratio of the second thermoplastic resin containing at least an α-olefin copolymer or polyethylene in the single-layer sealant film, the mechanical properties of the sealant film can be adjusted.

The sealant layer 70 may further include a thermoplastic elastomer. By using a thermoplastic elastomer, the impact resistance and puncture resistance of the sealant layer 70 can be further improved.

The thermoplastic elastomer is, for example, a hydrogenated styrene-based thermoplastic elastomer. The hydrogenated styrene-based thermoplastic elastomer has a structure consisting of a polymer block A mainly made of at least one vinyl aromatic compound and a polymer block B mainly made of at least one hydrogenated conjugated diene compound. The thermoplastic elastomer may also be an ethylene-α-olefin elastomer. The ethylene-α-olefin elastomer is a low-crystalline or amorphous copolymer elastomer, and is a random copolymer of 50 to 90% by mass of ethylene as the main component and an α-olefin as a copolymerization monomer.

The content of propylene-ethylene block copolymer in the sealant layer 70 is, for example, 80% by mass or more, and preferably 90% by mass or more.

One method for producing propylene-ethylene block copolymers is to polymerize the raw materials propylene and ethylene using a catalyst. Ziegler-Natta type or metallocene catalysts can be used as the catalyst.

The thickness of the sealant layer 70 is preferably 30 μm or more, and more preferably 40 μm or more. The thickness of the sealant layer 70 is preferably 100 μm or less, and more preferably 80 μm or less.

Preferred mechanical properties of the single-layer sealant film containing a propylene-ethylene block copolymer will now be described.
The tensile elongation of the sealant film in the machine direction (MD) at 25°C is preferably 600% or more and 1300% or less. The product of the tensile elongation (%) of the sealant film in the machine direction (MD) and the thickness (μm) of the sealant film is preferably 35000 or more and 80000 or less. The tensile elongation of the sealant film in the transverse direction (TD) at 25°C is preferably 700% or more and 1400% or less. The product of the tensile elongation (%) of the sealant film in the transverse direction (TD) and the thickness (μm) of the sealant film is preferably 40000 or more and 85000 or less.
The tensile modulus of the sealant film in the machine direction (MD) at 25°C is preferably 400 MPa or more and 1100 MPa or less. The product of the tensile modulus of the sealant film in the machine direction (MD) (MPa) and the thickness (μm) of the sealant film is preferably 30000 or more and 55000 or less. The tensile modulus of the sealant film in the perpendicular direction (TD) at 25°C is preferably 250 MPa or more and 900 MPa or less. The product of the tensile modulus of the sealant film in the perpendicular direction (TD) (MPa) and the thickness (μm) of the sealant film is preferably 20000 or more and 45000 or more.

The tensile modulus and tensile elongation can be measured in accordance with JIS K7127. An Orientec RTC-1310A tensile tester with thermostatic chamber can be used as a measuring device. In the bag 10 shown in FIG. 1, the direction in which the upper portion 11 and the lower portion 12 extend is the flow direction of the film constituting the bag 10, such as a sealant film, and the direction in which the side portion 13 extends is the vertical direction of the film constituting the bag 10, such as a sealant film. Although not shown, the bag 10 may be configured so that the direction in which the upper portion 11 and the lower portion 12 extend is the vertical direction of the film, and the direction in which the side portion 13 extends is the flow direction of the film.

There are mainly two types of single-layer sealant films containing a propylene-ethylene block copolymer.
The first type is a type having high tensile elongation and impact resistance, such as ZK500 described later. The first type of sealant film preferably further has a property of low hot seal strength. This makes it possible to prevent the internal pressure of the storage section 17 from becoming excessive when the bag 10 is heated, and to prevent damage to the laminate 30.
The second type is a type having a high tensile modulus, such as ZK207 described later. By using the second type of sealant film, it is possible to improve the tearability when a consumer opens the bag 10 by tearing the bag 10 along the first direction D1.

The product of the tensile elongation (%) of the first type sealant film in the machine direction (MD) and the thickness (μm) of the sealant film is preferably 45,000 or more, more preferably 50,000 or more, or may be 55,000 or more, or 60,000 or more. The product of the tensile elongation (%) of the first type sealant film in the vertical direction (TD) and the thickness (μm) of the sealant film is preferably 53,000 or more, more preferably 60,000 or more. When the sealant film has a high tensile elongation, it is possible to prevent the bag 10 from being broken due to an impact when dropped, etc.
Moreover, the product of the tensile modulus (MPa) of the first type sealant film in the machine direction (MD) and the thickness (μm) of the sealant film is preferably not more than 38000, more preferably not more than 35000. Moreover, the product of the tensile modulus (MPa) of the first type sealant film in the transverse direction (TD) and the thickness (μm) of the sealant film is preferably not more than 30000, more preferably not more than 25000.

The product of the tensile modulus (MPa) of the second type sealant film in the machine direction (MD) and the thickness (μm) of the sealant film is preferably 35000 or more, more preferably 38000 or more, and even more preferably 45000 or more. The product of the tensile modulus (MPa) of the second type sealant film in the vertical direction (TD) and the thickness (μm) of the sealant film is preferably 25000 or more, more preferably 30000 or more, even more preferably 35000 or more, and may be 38000 or more. The sealant film has a high tensile modulus, which can improve the tearability when opening the bag 10.
Moreover, the product of the tensile elongation (%) of the second type sealant film in the machine direction (MD) and the thickness (μm) of the sealant film is preferably not more than 55000, more preferably not more than 50000. Moreover, the product of the tensile elongation (%) of the second type sealant film in the transverse direction (TD) and the thickness (μm) of the sealant film is preferably not more than 60000, more preferably not more than 55000.

(Other layers)
The laminate 30 may include additional layers not shown in Figure 3. Examples of additional layers are described below.

The laminate 30 may further include a printed layer. The printed layer is a layer provided on the laminate 30 to provide product information and aesthetic appeal to the bag 10, and is printed, for example, on the first stretched plastic film 40. The printed layer expresses letters, numbers, symbols, figures, pictures, etc. Ink for gravure printing or ink for flexographic printing can be used as a material for the printed layer. A specific example of an ink for gravure printing is Finart manufactured by DIC Graphics Corporation.

The laminate 30 may further include a transparent gas barrier layer. The transparent gas barrier layer is formed on the surface of the stretched plastic film 40, 50, 60, etc., and includes at least a transparent vapor deposition layer made of a transparent inorganic material. The transparent gas barrier layer may further include a transparent gas barrier coating film formed on the surface of the transparent vapor deposition layer, and includes a transparent gas barrier coating film.

The transparent deposition layer functions as a layer having a gas barrier function that prevents the permeation of oxygen gas and water vapor. Two or more transparent deposition layers may be provided. When two or more transparent deposition layers are provided, each may have the same composition or different compositions. Examples of methods for forming the transparent deposition layer include physical vapor deposition methods (Physical Vapor Deposition method, PVD method) such as vacuum deposition method, sputtering method, and ion plating method, or chemical vapor deposition methods (Chemical Vapor Deposition method, CVD method) such as plasma chemical vapor deposition method, thermal chemical vapor deposition method, and photochemical vapor deposition method. Specifically, the deposition layer can be formed on a film-forming roller using a roller-type deposition film forming device. Examples of inorganic materials constituting the transparent deposition layer include aluminum oxide (aluminum oxide) and silicon oxide. The thickness of the transparent deposition layer is preferably 40 Å or more and 130 Å or less, more preferably 50 Å or more and 120 Å or less.

The transparent gas barrier coating film functions as a layer that suppresses the transmission of oxygen gas, water vapor, etc. The transparent gas barrier coating film 37 is obtained from a transparent gas barrier composition that contains at least one alkoxide represented by the general formula R ¹ _n M(OR ² ) _m (wherein R ¹ and R ² represent an organic group having 1 to 8 carbon atoms, M represents a metal atom, n represents an integer of 0 or more, m represents an integer of 1 or more, and n+m represents the atomic valence of M) and the above-mentioned polyvinyl alcohol resin and/or ethylene-vinyl alcohol copolymer, and is further polycondensed by a sol-gel method in the presence of a sol-gel catalyst, an acid, water, and an organic solvent.

Layer Structure of the Lower Film Next, the layer structure of the lower film 16 will be described.

The layer structure of the lower film 16 is arbitrary, so long as it has an inner surface that can be joined to the inner surface of the front film 14 and the inner surface of the back film 15. For example, the above-mentioned laminate 30 may be used as the lower film 16, similar to the front film 14 and the back film 15. Alternatively, a film whose inner surface is formed of a sealant layer and has a different structure from the laminate 30 may be used as the lower film 16.

Manufacturing Method of the Laminate Next, an example of a manufacturing method of the laminate 30 will be described.

First, the first stretched plastic film 40 and the second stretched plastic film 50 are prepared. Next, the first stretched plastic film 40 and the second stretched plastic film 50 are laminated together via the first adhesive layer 45 by a dry lamination method. After that, the laminate including the first stretched plastic film 40 and the second stretched plastic film 50 and the sealant film for constituting the sealant layer 70 are laminated together via the second adhesive layer 55 by a dry lamination method. This makes it possible to obtain the laminate 30 including the first stretched plastic film 40, the second stretched plastic film 50, and the sealant layer 70.

Alternatively, the second stretched plastic film 50 and the sealant film may first be laminated together via the second adhesive layer 55 by dry lamination, and then the first stretched plastic film 40 and the laminate including the second stretched plastic film 50 and the sealant film may be laminated together via the first adhesive layer 45 by dry lamination to produce the laminate 30.

In the dry lamination method, an adhesive composition is first applied to one of the two films to be laminated. The applied adhesive composition is then dried to volatilize the solvent. The two films are then laminated via the dried adhesive composition. The two laminated films are then rolled up and aged, for example, for 24 hours or more in an environment of 20°C or higher.

Manufacturing method of the bag Next, a method of manufacturing the bag 10 using the laminate 30 described above will be described. First, the surface film 14 and the back film 15 made of the laminate 30 are prepared. In addition, the lower film 16 in a folded state is inserted between the surface film 14 and the back film 15. Next, the inner surfaces of each film are heat-sealed to form seal parts such as the lower seal part 12a and the side seal part 13a. In addition, the films joined to each other by heat sealing are cut into an appropriate shape to obtain the bag 10 shown in FIG. 1. Next, the contents 18 are filled into the bag 10 through the opening 11b of the upper part 11. The contents 18 are, for example, cooked foods containing moisture such as curry, stew, soup, etc. In addition, the contents 18 may have materials containing a lot of oil, such as meat, fish, and seasonings for them. In addition to food, things that can be heated by hot water or the like can be contained in the bag 10 as contents. After that, the upper part 11 is heat-sealed to form the upper seal part. In this way, the bag 10 containing the contents 18 and sealed can be obtained.

Method for Heating Contents Next, an example of a method for heating the contents 18 contained in the bag 10 will be described.

First, the bag 10 is placed inside a microwave oven with the bottom 12 facing down and the bag 10 standing upright. Next, the microwave oven is used to heat the contents. This increases the temperature of the contents 18, which in turn evaporates the water contained in the contents 18, increasing the pressure in the storage section 17.

When the pressure in the storage section 17 increases, the surface film 14 and the back film 15 bulge outward due to the force received from the storage section 17. In this embodiment, the laminate 30 constituting the surface film 14 and the back film 15 includes two stretched plastic films 40, 50. This increases the rigidity of the laminate 30, and as a result, the surface film 14 and the back film 15 can be prevented from stretching when they are subjected to force. This allows the force generated by the pressure generated in the storage section 17 to be mainly used as a force for peeling off the steam release seal section 20a, rather than a force for stretching the surface film 14 and the back film 15. This allows the force applied to the steam release seal section 20a to be increased. This makes it easier for the steam release seal section 20a to peel off when heated, and allows the steam in the storage section 17 to escape to the outside via the steam release mechanism 20.

In addition, according to this embodiment, as described above, the laminate 30 has heat resistance. This makes it possible to prevent holes from being formed in the laminate 30 or wrinkles from being formed in the laminate 30 when heated.

In addition, according to this embodiment, when the above-mentioned first type sealant film having high tensile elongation and impact resistance is used, the impact strength of the laminate 30 can be increased. This can increase the impact resistance of the bag 10 formed from the laminate 30. For example, it is possible to prevent the bag 10 from breaking due to the impact when dropped. The impact strength of the laminate 30 is preferably 500 kJ/m or more, and more preferably 600 kJ/m or more.

In addition, according to this embodiment, as described above, the laminate 30 includes at least two stretched plastic films 40, 50. This makes it possible to impart puncture resistance to the laminate 30 and the bag 10 formed by the laminate 30. The puncture strength of the laminate 30 is preferably 14 N or more, more preferably 16 N or more, even more preferably 17 N or more, and particularly preferably 18 N or more.

Method of opening the bag After heating the contents, the consumer opens the bag 10 by tearing the bag 10 along the first direction D1. In this embodiment, as described above, the second stretched plastic film 50 adjacent to the sealant layer 70 has tearability in the first direction D1. This makes it possible to prevent the sealant layer 70 from stretching when the consumer tears the bag 10 to open it. Therefore, the consumer can easily tear the bag 10. Note that, in order to improve the tearability of the bag 10, it is preferable to use the above-mentioned second type of sealant film having a high tensile modulus.

Note that various modifications can be made to the above-described embodiment. Below, modified examples will be described with reference to the drawings as necessary. In the following description and the drawings used in the following description, parts that can be configured similarly to the above-described embodiment will be given the same reference numerals as those used for the corresponding parts in the above-described embodiment, and duplicated descriptions will be omitted. Also, if it is clear that the effects obtained in the above-described embodiment can also be obtained in the modified example, the description may be omitted.

(Variations of the bag)
In the above-described embodiment, an example has been shown in which the bag 10 is a gusset-type bag, but there is no particular limitation on the specific configuration of the bag 10. For example, the bag 10 may be a so-called four-sided sealed bag formed by joining the inner surfaces of the front film 14 and the back film 15 made of the laminate 30 at the upper portion 11, the lower portion 12, and the side portions 13.

In addition, in the above-described embodiment, an example is shown in which the contents 18 contained in the bag 10 are heated using a microwave oven, but this is not limited to this. For example, the contents 18 contained in the bag 10 may be heated by a hot water bath. In this case, the bag 10 does not need to be equipped with the steam release mechanism 20 described above.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

The puncture strength, impact strength, and tear resistance of the laminate 30 of the present invention were evaluated using Examples 1 to 4 and Comparative Example 1.

Example 1
As the first stretched plastic film 40, a stretched PET film having a thickness of 16 μm was prepared. As the second stretched plastic film 50, a stretched PET film having a thickness of 12 μm and tearability in the machine direction (MD) was prepared. In the following description, the stretched PET film having tearability in the machine direction (MD) is also referred to as straight cut PET. As the straight cut PET, Emblet (registered trademark) PC manufactured by Unitika Co., Ltd. was used. As a film for constituting the sealant layer 70, an unstretched polypropylene film ZK500 manufactured by Toray Film Processing Co., Ltd. was prepared. ZK500 contains the above-mentioned propylene-ethylene block copolymer and elastomer. The thickness of the sealant layer 70 was 60 μm.

Emblett® PC has higher tear resistance in the machine direction (MD) than general stretched PET films. The tensile strength of Emblett® PC in the machine direction (MD) is 200 MPa, and the tensile strength of Emblett® PC in the transverse direction (TD) is 180 MPa.

ZK500 has a higher tensile elongation than general unstretched polypropylene films. Specifically, the tensile elongation of ZK500 in the machine direction (MD) is 1180% when the thickness is 50 μm, and 1100% when the thickness is 60 μm. The tensile elongation of ZK500 in the perpendicular direction (TD) is 1240% when the thickness is 50 μm, and 1150% when the thickness is 60 μm. Therefore, the product of the tensile elongation (%) and thickness (μm) of ZK500 in the machine direction is 59,000 when the thickness is 50 μm, and 66,000 when the thickness is 60 μm. The product of the tensile elongation (%) and thickness (μm) of ZK500 in the perpendicular direction is 62,000 when the thickness is 50 μm, and 69,000 when the thickness is 60 μm.

ZK500 also has a lower tensile modulus than a typical unstretched polypropylene film. Specifically, the tensile modulus of ZK500 in the machine direction (MD) is 640 MPa when the thickness is 50 μm, and 550 MPa when the thickness is 60 μm. The tensile modulus of ZK500 in the perpendicular direction (TD) is 480 MPa when the thickness is 50 μm, and 400 MPa when the thickness is 60 μm. Therefore, the product of the tensile modulus (MPa) and thickness (μm) of ZK500 in the machine direction is 32,000 when the thickness is 50 μm, and 33,000 when the thickness is 60 μm. The product of the tensile modulus (MPa) and thickness (μm) of ZK500 in the perpendicular direction is 24,000 when the thickness is 50 μm, and 35,000 when the thickness is 60 μm.

Then, the first stretched plastic film 40, the second stretched plastic film 50, and the sealant layer 70 were laminated by dry lamination to produce the laminate 30. A two-component polyurethane adhesive (base: RU-40, hardener: H-4) manufactured by Rock Paint Co., Ltd. was used for the first adhesive layer 45 and the second adhesive layer 55. The base RU-40 is a polyester polyol. The thickness of the first adhesive layer 45 and the second adhesive layer 55 was 3.5 μm.

[Evaluation of puncture resistance]
Next, the piercing strength of the laminate 30 was measured in accordance with JIS Z1707 7.4. A Tensilon universal material testing machine RTC-1310 manufactured by A&D was used as the measuring device. Specifically, as shown in FIG. 6, a semicircular needle 90 having a diameter of 1.0 mm and a tip shape radius of 0.5 mm was pierced from the outer surface 30y side of the test piece of the laminate 30 in a fixed state at a speed of 50 mm/min (50 mm per minute), and the maximum value of the stress until the needle 90 penetrated the laminate 30 was measured. The maximum value of the stress was measured for five or more test pieces, and the average value was taken as the piercing strength of the laminate 30. The environment during the measurement was a temperature of 23° C. and a relative humidity of 50%. As a result, the piercing strength was 16.7 N.

[Evaluation of impact resistance]
Next, two sheets of the laminate 30 were stacked and heated at 190° C. for one second to heat-seal the inner surfaces 30x of the laminate 30. Next, the two heat-sealed sheets of the laminate 30 were cut out to a width of 15 mm to prepare a test piece 100. FIG. 7 is a plan view showing the test piece 100, and FIG. 8 is a cross-sectional view of the test piece 100 in FIG. 7. The test piece 100 has a width W3 of 15 mm and a length W4 of 50 mm, and a sealed portion 101 is formed over a length W5 of 10 mm from one end, and no sealed portion is formed over a length of 40 mm from the other end. Next, as shown in FIG. 9, the unsealed portion of one laminate 30 and the unsealed portion of the other laminate 30 were arranged so as to be inverse to each other in a direction perpendicular to the surface direction of the seal portion 101, i.e., to be T-shaped, and then the end of the unsealed portion of one laminate 30 and the end of the unsealed portion of the other laminate 30 were fixed to jigs 102 and 103, respectively. At this time, the distance T between the jigs 102 and 103 in a direction perpendicular to the surface direction of the seal portion 101 was set to 40 mm. Next, the one jig 102 was struck with a hammer 104 from the surface of the one laminate 30 on the first stretched plastic film 40 side, to measure the impact strength when the one laminate 30 and the other laminate 30 were separated. The evaluation was performed using a digital impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. as a measuring instrument. A hammer of 2J was used as a hammer for applying an impact to the test piece 100. As a result, the impact strength was 675 kJ/m.

[Evaluation of tearability]
Next, the two laminates 30 joined via the sealant layer 70 were cut out to have a width W1 of 15 mm and a length W2 of 100 mm as shown in FIG. 10 to prepare a test piece 110. The width W1 direction of the test piece 110 is parallel to the second direction D2 shown in FIG. 1. The length W2 direction of the test piece 110 is parallel to the machine direction (MD) when the second stretched plastic film 50 is formed, and is also parallel to the first direction D1 shown in FIG. 1. Next, as shown in FIG. 10, a slit 28 was formed in the center of the width W1 direction of the test piece 110. Next, the test piece 110 was torn by hand in the direction of the length W2 starting from the slit 28. As a result, the sealant layer 70 of the laminate 30 was not stretched in the middle, and the test piece 110 could be torn in the direction of the length W2.

Example 2
The laminate 30 was produced in the same manner as in Example 1, except that a stretched plastic film containing polyamide as a main component and having a thickness of 15 μm was used as the first stretched plastic film 40. Specifically, the first stretched plastic film 40 used was a co-extruded film produced by co-extrusion, including a first layer 41 made of PET having a thickness of 2 μm, a second layer 42 made of nylon-6 having a thickness of 11 μm, and a third layer 43 made of PET having a thickness of 2 μm.

Then, the puncture strength and impact strength of the laminate 30 were measured in the same manner as in Example 1. As a result, the puncture strength was 15 N and the impact strength was 642 kJ/m.

Then, the tearability of the laminate 30 was evaluated in the same manner as in Example 1. As a result, the test piece 110 could be torn in the direction of length W2 without the sealant layer 70 of the laminate 30 stretching during the process.

Example 3
The laminate 30 was produced in the same manner as in Example 1, except that a stretched PET film having a thickness of 12 μm was used as the first stretched plastic film 40, and a stretched plastic film containing polyamide, specifically nylon, as a main component, having a thickness of 15 μm, and having tearability in the machine direction (MD) was used as the second stretched plastic film 50. In the following description, the stretched nylon film having tearability in the machine direction (MD) is also referred to as straight cut nylon. Bonyl CL manufactured by Kohjin Film & Chemicals Co., Ltd. was used as the straight cut nylon.

Bonyl CL has higher tear resistance in the machine direction (MD) than typical oriented nylon films. The tensile strength of Bonyl CL in the machine direction (MD) is 269 MPa, and the tensile strength of Bonyl CL in the transverse direction (TD) is 255 MPa.

Next, the puncture strength and impact strength of the laminate 30 were measured in the same manner as in Example 1. As a result, the puncture strength was 17 N and the impact strength was 1531 kJ/m.

Then, the tearability of the laminate 30 was evaluated in the same manner as in Example 1. As a result, the test piece 110 could be torn in the direction of length W2 without the sealant layer 70 of the laminate 30 stretching during the process.

Example 4
The laminate 30 was produced in the same manner as in Example 1, except that an unstretched polypropylene film ZK207 manufactured by Toray Advanced Film Co., Ltd. was used as the sealant film for constituting the sealant layer 70. The thickness of the unstretched polypropylene film ZK207 was 70 μm.

ZK207 has a higher tensile modulus than ZK500. Specifically, the tensile modulus of ZK207 in the machine direction (MD) is 780 MPa when the thickness is 50 μm, and 680 MPa when the thickness is 60 μm. The tensile modulus of ZK207 in the perpendicular direction (TD) is 630 MPa when the thickness is 50 μm, and 560 MPa when the thickness is 60 μm. Therefore, the product of the tensile modulus of ZK207 (MPa) and the thickness (μm) in the machine direction is 39000 when the thickness is 50 μm, and 40800 when the thickness is 60 μm. The product of the tensile modulus of ZK207 (MPa) and the thickness (μm) in the perpendicular direction is 31500 when the thickness is 50 μm, and 33600 when the thickness is 60 μm. By using ZK207, the tearability of the laminate 30 and the bag 10 including the laminate 30 can be improved.

ZK207 also has a lower tensile elongation than ZK500. Specifically, the tensile elongation of ZK207 in the machine direction (MD) is 790% when the thickness is 50 μm, and 730% when the thickness is 60 μm. The tensile elongation of ZK207 in the perpendicular direction (TD) is 1020% when the thickness is 50 μm, and 870% when the thickness is 60 μm. Therefore, the product of the tensile elongation (%) and thickness (μm) of ZK207 in the machine direction is 39500 when the thickness is 50 μm, and 43800 when the thickness is 60 μm. The product of the tensile elongation (%) and thickness (μm) of ZK207 in the perpendicular direction is 51000 when the thickness is 50 μm, and 52200 when the thickness is 60 μm.

Next, the puncture strength and impact strength of the laminate 30 were measured in the same manner as in Example 1. As a result, the puncture strength was 16.5 N and the impact strength was 463 kJ/m.

Then, the tearability of the laminate 30 was evaluated in the same manner as in Example 1. As a result, the test piece 110 could be torn in the direction of length W2 without the sealant layer 70 of the laminate 30 stretching during the tear. In addition, the positional deviation in the direction of width W1 of the two laminates 30 at the torn portion was 5 mm or less.

(Comparative Example 1)
The laminate 30 was produced in the same manner as in Example 1, except that a stretched PET film having a thickness of 12 μm was used as the first stretched plastic film 40, and a stretched PET film having no tearability in the machine direction (MD) was used as the second stretched plastic film 50. Specifically, a stretched PET film having the same tensile strength in the machine direction (MD) and the same tensile strength in the perpendicular direction (TD) and having a thickness of 12 μm was used as the second stretched plastic film 50.

Next, the puncture strength and impact strength of the laminate 30 were measured in the same manner as in Example 1. As a result, the puncture strength was 13.7 N and the impact strength was 1109 kJ/m.

Then, the tearability of the laminate 30 was evaluated in the same manner as in Example 1. As a result, the sealant layer 70 of the laminate 30 stretched during the process, and the test piece 110 could not be torn in the direction of length W2.

The layer structures and evaluation results of the laminates of Examples 1 to 4 and Comparative Example 1 are shown together in Figure 11. In Figure 11, in the "Layer Structure" column, the components of the laminate are listed in order from the outer layer to the top.

As can be seen from the comparison between Examples 1 to 4 and Comparative Example 1, by using a stretched plastic film having tearability in the machine direction (MD) as the second stretched plastic film 50 adjacent to the sealant layer 70, it was possible to suppress the sealant layer 70 from stretching when the laminate 30 was torn. Regarding the tearability, in Examples 1 to 3, the test piece 110 could be torn smoothly over the entire area in the direction of length W2, so the evaluation result was "good". In Example 4, the test piece 110 could be torn smoothly over the entire area in the direction of length W2, and the positional deviation in the direction of width W1 of the two laminates 30 constituting the test piece 110 was 5 mm or less, so the evaluation result was "great". On the other hand, in Comparative Example 1, the sealant layer 70 of the laminate 30 stretched midway, and therefore the test piece 110 could not be torn smoothly over the entire area in the direction of length W2, so the evaluation result was "bad".

10 Bag 11 Upper portion 12 Lower portion 12a Lower seal portion 13 Side portion 13a Side seal portion 14 Surface film 15 Back film 16 Lower film 17 Storage portion 18 Contents 20 Steam release mechanism 20a Steam release seal portion 25 Easy-opening means 26 Notch 30 Laminate 40 First stretched plastic film 45 First adhesive layer 50 Second stretched plastic film 55 Second adhesive layer 70 Sealant layer

Claims (2)

A bag having a steam venting mechanism,
A laminate;
A seal portion in which inner surfaces of the laminate are joined together,
The laminate comprises, from the outer surface side to the inner surface side, at least a first stretched plastic film, a second stretched plastic film, and a sealant layer (excluding the sealant layer made of a polypropylene-based film containing a hydrogenated styrene-based thermoplastic elastomer), in this order;
The first stretched plastic film contains polyester as a main component,
The second stretched plastic film contains polyamide as a main component,
When the machine direction of the second stretched plastic film is defined as a first direction and a direction perpendicular to the first direction is defined as a second direction, the tensile strength of the second stretched plastic film in the first direction is 1.05 times or more of the tensile strength of the second stretched plastic film in the second direction,
The tensile strength of the second stretched plastic film in the first direction is 200 MPa or more and 300 MPa or less,
the sealant layer is an unstretched film containing a first thermoplastic resin and a second thermoplastic resin,
the first thermoplastic resin is a propylene-ethylene block copolymer;
The second thermoplastic resin contains at least an α-olefin copolymer or polyethylene,
The mass ratio of the first thermoplastic resin is higher than the mass ratio of the second thermoplastic resin,
The room temperature seal strength of the seal portion at 25°C in a width of 15 mm is 40 N or more,
The bag has a hot seal strength of 15 N or less at 100° C. over a width of 15 mm. The bag of claim 1 , wherein the width direction of the bag is the first direction.