JP2024107327A - Packaging material and pouch comprising packaging material - Google Patents

Abstract

[Problem] To provide a packaging material with excellent drop strength and puncture strength. [Solution] The packaging material comprises, in order from the outer surface side to the inner surface side, at least a first biaxially oriented plastic film, a second biaxially oriented plastic film, and a sealant layer. The first biaxially oriented plastic film and the second biaxially oriented plastic film contain polyester as a main component. One of the first biaxially oriented plastic film and the second biaxially oriented plastic film is a high-stiffness polyester film having a loop stiffness of 0.0017 N or more in at least one direction. The puncture strength of the packaging material is 14.0 N or more. [Selected Figure] Figure 2

Description

The present invention relates to a packaging material and a pouch comprising the packaging material.

Conventionally, various packaging materials have been developed and proposed as packaging materials for constructing packaged products in which various items such as food and beverages, pharmaceuticals, chemicals, cosmetics, sanitary products, daily necessities, and the like are filled and packaged. The packaging materials include a plastic film as a substrate. For example, Patent Document 1 discloses an example in which the packaging material includes two substrates containing polyethylene terephthalate.

Utility Model Application Publication No. 2-8784

Packaging materials are sometimes required to have drop strength and puncture strength. Drop strength is necessary to prevent damage such as tearing of the packaging material when a packaging container containing the packaging material is dropped. Puncture strength is necessary to prevent the packaging container from tearing when a sharp member with a pointed tip comes into contact with the packaging container. In packaging materials containing two base materials including polyethylene terephthalate, such as those described in Patent Document 1, the puncture strength was sometimes insufficient.

The present invention was made in consideration of these points, and aims to provide a packaging material that has excellent drop strength and puncture resistance.

The present invention is a packaging material comprising, in order from the outer surface side to the inner surface side, at least a first biaxially oriented plastic film, a second biaxially oriented plastic film, and a sealant layer, the first biaxially oriented plastic film and the second biaxially oriented plastic film contain polyester as a main component, and the puncture strength of the packaging material is 14.0 N or more. One of the first biaxially oriented plastic film and the second biaxially oriented plastic film may be a high-stiffness polyester film having a loop stiffness of 0.0017 N or more in at least one direction. The loop stiffness of the packaging material in one direction may be less than 0.150 N.

In the packaging material according to the present invention, both the first biaxially oriented plastic film and the second biaxially oriented plastic film may contain polyethylene terephthalate as a main component.

The packaging material according to the present invention may have a printed layer.

The packaging material according to the present invention may include a deposition layer located on the surface of the first biaxially oriented plastic film or the surface of the second biaxially oriented plastic film, and a gas barrier coating film located on the deposition layer.

In the packaging material according to the present invention, the puncture strength of the packaging material may be 16.0 N or more.

In the packaging material according to the present invention, the sealant layer may contain polypropylene as a main component. The sealant layer may be made of a single layer sealant film containing a propylene-ethylene block copolymer.

In the packaging material according to the present invention, the sealant layer may contain polyethylene having a melting point of 100°C or higher.

In the packaging material according to the present invention, the sealant layer may have a first layer mainly composed of polyethylene or polypropylene, and a second layer located on the inner side of the first layer and containing a mixed resin of polyethylene and polypropylene.

The packaging material according to the present invention is a retort pouch comprising the packaging material described above.

The packaging material according to the present invention is a microwave pouch having a storage section, and is provided with the packaging material described above and a seal section that joins the inner surfaces of the packaging material together and includes a steam release seal section that is configured to be peeled off by an increase in pressure in the storage section.

The present invention provides packaging materials with excellent drop strength and puncture resistance.

FIG. 2 is a front view showing a bag according to the embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of a layer structure of a packaging material that constitutes a bag. FIG. 11 is a cross-sectional view showing a modified example of the layer structure of the packaging material that constitutes the bag. FIG. 11 is a cross-sectional view showing a modified example of the layer structure of the packaging material that constitutes the bag. FIG. 2 is a plan view showing an example of a loop stiffness measuring device. FIG. 6 is a cross-sectional view of the loop stiffness measuring device of FIG. 5 taken along line VI-VI. FIG. 1 is a diagram showing an example of a method for preparing a test piece used in a loop stiffness measuring device. FIG. 1 is a diagram for explaining a process of attaching a test piece to a loop stiffness measuring device. FIG. 13 is a diagram for explaining a step of forming a loop portion in a test piece. FIG. 13 is a diagram for explaining a process of applying a load to a loop portion of a test piece. FIG. 13 is a diagram for explaining a process of applying a load to a loop portion of a test piece. FIG. 2 is a diagram showing an example of a layer structure of a sealant layer. FIG. 1 shows an example of the results of analyzing a transparent vapor-deposited layer formed on a surface of a biaxially stretched plastic film using a time-of-flight secondary ion mass spectrometer. FIG. 1 is a diagram showing an example of a method for filling a bag with contents. FIG. 13 is a front view showing a modified example of the bag. FIG. 13 is a front view showing a modified example of the bag. FIG. 13 is a front view showing a modified example of the bag. FIG. 1 is a longitudinal cross-sectional view showing an example of a container containing packaging material. FIG. 1 is a plan view illustrating an example of a container containing packaging material. FIG. 1 is a diagram showing an example of a method for measuring piercing strength. FIG. 1 is a diagram showing the evaluation results of Examples A1 to A3. FIG. 1 is a diagram showing evaluation results of Comparative Examples 1 to 3. FIG. 1 is a diagram showing the evaluation results of Examples B1 to B3. FIG. 1 is a diagram showing the evaluation results of Examples C1 to C3.

One embodiment of the present invention will be described with reference to Figures 1 to 14. 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 in which similar functions can be expected.

Figure 1 is a front view showing a bag 10 according to this embodiment. The bag 10 has a storage section 17 for storing contents. Note that Figure 1 shows the bag 10 in a state before the contents are stored in it. The configuration of the bag 10 will be described below.

Bag In this embodiment, the bag 10 is a so-called flat pouch that is produced by joining a film on the front side of the bag 10 with a film on the back side of the bag 10. The bag 10 includes an upper portion 11, a lower portion 12, and a pair of side portions 13, and has a substantially rectangular outline in a front view. The names "upper portion", "lower portion", and "side portion", as well as the terms "upper" and "lower" merely indicate the relative positions and directions of the bag 10 and its components with respect to a state in which an opening for filling the contents is located at the upper portion. 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. It is assumed that the bag 10 of this embodiment will be used in such a way that the consumer tears the bag 10 along the first direction D1 to open the bag 10.

As shown in FIG. 1, the bag 10 has a surface film 14 that forms the surface, and a back film 15 that forms the back.

The terms "surface film" and "back film" mentioned above merely divide each film according to its positional relationship, and the method of providing the film 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 and the back film 15 are connected together, or may be manufactured using a total of two films, one surface film 14 and one back film 15.

The inner surfaces of the front film 14 and the back film 15 are joined together by a seal. In the front 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. The outer edge seal portion includes a lower seal portion 12a that extends along 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, the upper portion 11 of the bag 10 forms an opening 11b, as shown in FIG. 1. 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 lower seal portion 12a, the side seal portion 13a, 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.

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.

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. Also, 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.

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. 2 is a cross-sectional view showing an example of the layer structure of the packaging material 30 constituting the front film 14 and the back film 15.

As shown in FIG. 2, the packaging material 30 comprises at least a first biaxially oriented plastic film 40, a first adhesive layer 45, a second biaxially oriented plastic film 50, a second adhesive layer 55, and a sealant layer 70, in this order. The first biaxially oriented 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 film constituting the packaging material 30, such as the first biaxially oriented plastic film 40 and the second biaxially oriented plastic film 50, and the packaging material 30 have a flow direction and a vertical direction. When the sealant layer 70 is composed of a sealant film, the sealant layer 70 also has a flow direction and a vertical direction. The flow direction is the direction in which the film flows when it is formed, and is the so-called MD (Machine Direction). The vertical direction is the direction perpendicular to the flow direction, and is the so-called TD (Transverse Direction). 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, and the direction in which the side portion 13 extends is the vertical direction.

The packaging material 30 of this embodiment is configured to have excellent puncture strength. This can prevent the bag 10 from being torn when a sharp member with a pointed tip comes into contact with the bag 10. That is, a packaged product such as the bag 10 made of the packaging material 30 can have puncture resistance. Furthermore, the packaging material 30 of this embodiment is configured to have excellent drop strength. This can prevent the packaging material from being torn or damaged when a packaging container containing the packaging material is dropped. That is, a packaged product such as the bag 10 made of the packaging material 30 can have impact resistance.

Each layer of the packaging material 30 is described in detail below.

(Biaxially oriented plastic film)
The first biaxially stretched plastic film 40 and the second biaxially stretched plastic film 50 are both biaxially stretched films stretched in two predetermined directions. A biaxially stretched plastic film is a plastic film that is intentionally stretched to improve the mechanical strength of the plastic film. The stretching direction of each biaxially stretched plastic film 40, 50 is not particularly limited. For example, the biaxially stretched plastic film 40, 50 may be stretched in the direction in which the side portion 13 extends and in a direction perpendicular to the direction in which the side portion 13 extends. In addition, the stretching directions of each biaxially stretched plastic film 40, 50 may be the same as or different from each other. The stretching ratio of each biaxially stretched plastic film 40, 50 is, for example, 1.05 times or more.

In this embodiment, it is proposed to use a biaxially stretched plastic film having a loop stiffness of 0.0017 N or more in at least one direction and containing polyester as a main component as one of the first biaxially stretched plastic film 40 and the second biaxially stretched plastic film 50. In the following description, a biaxially stretched plastic film having a loop stiffness of 0.0017 N or more in at least one direction and containing polyester as a main component is also referred to as a high-stiffness polyester film. The high-stiffness polyester film has a loop stiffness of 0.0017 N or more in at least one of the machine direction (MD) and the transverse direction (TD), for example. The high-stiffness polyester film may have a loop stiffness of 0.0017 N or more in both the machine direction (MD) and the transverse direction (TD), for example. The packaging material 30 contains a high-stiffness polyester film, so that the packaging material 30 can have excellent puncture strength. In this application, the term "main component" refers to a component that accounts for 51% by mass. The high stiffness polyester film does not contain polyamide.
The polyester is preferably a polyester mainly composed of an aromatic polyester consisting of at least one aromatic dicarboxylic acid selected from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and at least one aliphatic alcohol selected from ethylene glycol, 1,3-propanediol, and 1,4-butanediol. For example, the polyester is polyethylene terephthalate (hereinafter also referred to as PET), polybutylene terephthalate (hereinafter also referred to as PBT), etc. Examples of high-stiffness polyester films include high-stiffness PET films containing 51% by mass or more of PET as a main component, and high-stiffness PBT films containing 51% by mass or more of PBT as a main component. The thickness of the high-stiffness polyester film is preferably 5 μm or more, more preferably 7 μm or more. The thickness of the high-stiffness polyester film is preferably 25 μm or less, more preferably 20 μm or less.

Loop stiffness is a parameter that indicates the stiffness of a film such as a biaxially stretched plastic film. Below, a method for measuring loop stiffness will be described with reference to Figures 5 to 11. The measurement method described below can be used not only for single-layer films such as biaxially stretched plastic film, but also for films with multiple layers such as vapor-deposited films and laminated films. A vapor-deposited film is a film that includes a single-layer film such as a biaxially stretched plastic film and a vapor-deposited layer formed on the single-layer film. A laminated film is a film that includes multiple laminated films, such as packaging material 30.

Figure 5 is a plan view showing the test piece 80 and the loop stiffness measuring instrument 85, and Figure 6 is a cross-sectional view of the test piece 80 and the loop stiffness measuring instrument 85 of Figure 5 taken along line VI-VI. The test piece 80 is a rectangular film having long and short sides. In this application, the length L1 of the long side of the test piece 80 is set to 150 mm, and the length L2 of the short side is set to 15 mm. As the loop stiffness measuring instrument 85, for example, No. 581 Loop Stiffness Tester (registered trademark) LOOP STIFFNESS TESTER DA type manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used. The length L1 of the long side of the test piece 80 can be adjusted as long as the test piece 80 can be gripped by a pair of chuck parts 86 described later.

The loop stiffness measuring device 85 has a pair of chucks 86 for gripping a pair of ends in the long side direction of the test piece 80, and a support member 87 for supporting the chucks 86. The chucks 86 include a first chuck 861 and a second chuck 862. In the state shown in Figs. 5 and 6, the test piece 80 is placed on the pair of first chucks 861, and the second chuck 862 does not yet grip the test piece 80 between the first chuck 861 and the second chuck 862. As described later, during measurement, the test piece 80 is gripped between the first chuck 861 and the second chuck 862 of the chucks 86. The second chuck 862 may be connected to the first chuck 861 via a hinge mechanism.

When the film to be measured, such as a biaxially oriented plastic film, a vapor deposition film, or a laminated film, is available in a state before the film is processed into a packaging product, the test piece 80 may be prepared by cutting the film to be measured. The test piece 80 may also be prepared by cutting a packaging product made from the packaging material 30, such as a bag. FIG. 7 is a diagram showing an example of a method for preparing the test piece 80 by cutting the surface film 14 or the back film 15 of the bag 10. When measuring the loop stiffness of the packaging material 30 in the flow direction, the test piece is prepared by cutting the surface film 14 or the back film 15 of the bag 10 so that the long side direction of the test piece coincides with the flow direction, as shown by reference numeral 80A in FIG. 7. When measuring the loop stiffness of the packaging material 30 in the vertical direction, the test piece is prepared by cutting the surface film 14 or the back film 15 of the bag 10 so that the long side direction of the test piece coincides with the vertical direction, as shown by reference numeral 80B in FIG. 7.

A method for measuring the loop stiffness of the test piece 80 using the loop stiffness measuring device 85 will be described. First, as shown in FIG. 5 and FIG. 6, the test piece 80 is placed on the first chuck 861 of a pair of chuck parts 86 arranged with a gap L3 between them. In this application, the gap L3 is set so that the length of the loop part 81 (hereinafter also referred to as the loop length) described later is 60 mm. The test piece 80 includes an inner surface 80x located on the first chuck 861 side and an outer surface 80y located on the opposite side of the inner surface 80x. When the test piece 80 is made of the packaging material 30, the inner surface 80x and the outer surface 80y of the test piece 80 coincide with the inner surface 30x and the outer surface 30y of the packaging material 30. When the loop part 81 described later is formed in the test piece 80, the inner surface 80x is located inside the loop part 81, and the outer surface 80y is located outside the loop part 81. Next, as shown in FIG. 8, the second chuck 862 is placed on the test piece 80 so as to grip the end of the long side of the test piece 80 between the first chuck 861 and the second chuck 862.

Next, as shown in FIG. 9, at least one of the pair of chucks 86 is slid on the support member 87 in a direction in which the distance between the pair of chucks 86 is reduced. This allows a loop portion 81 to be formed on the test piece 80. The test piece 80 shown in FIG. 9 has a loop portion 81, a pair of intermediate portions 82, and a pair of fixing portions 83. The pair of fixing portions 83 are portions of the test piece 80 that are gripped by the pair of chucks 86. The pair of intermediate portions 82 are portions of the test piece 80 that are located between the loop portion 81 and the pair of intermediate portions 82. As shown in FIG. 9, the chuck portion 86 is slid on the support member 87 until the inner surfaces 80x of the pair of intermediate portions 82 come into contact with each other. This allows a loop portion 81 having a loop length of 60 mm to be formed. The loop length of the loop portion 81 is the length of the test piece 80 between position P1 where the surface of one second chuck 862 on the loop portion 81 side intersects with the test piece 80, and position P2 where the surface of the other second chuck 862 on the loop portion 81 side intersects with the test piece 80. If the thickness of the test piece 80 is ignored, the above-mentioned interval L3 is the value obtained by adding 2×t to the length of the loop portion 81. t is the thickness of the second chuck 862 of the chuck portion 86.

After that, as shown in FIG. 10, the posture of the chuck portion 86 is adjusted so that the protruding direction Y of the loop portion 81 relative to the chuck portion 86 is horizontal. For example, the posture of the chuck portion 86 supported by the support member 87 is adjusted by moving the support member 87 so that the normal direction of the support member 87 is horizontal. In the example shown in FIG. 10, the protruding direction Y of the loop portion 81 coincides with the thickness direction of the chuck portion. In addition, a load cell 88 is prepared at a position distance Z1 away from the second chuck 862 in the protruding direction Y of the loop portion 81. In this application, the distance Z1 is set to 50 mm. Next, the load cell 88 is moved at a speed V by the distance Z2 shown in FIG. 10 toward the loop portion 81 of the test piece 80. The distance Z2 is set so that the load cell 88 contacts the loop portion 81 and then pushes the loop portion 81 toward the chuck portion 86 side, as shown in FIG. 10 and FIG. 11. In this application, the distance Z2 is set to 40 mm. In this case, the distance Z3 between the load cell 88 and the second chuck 862 of the chuck portion 86 when the load cell 88 is pressing the loop portion 81 toward the chuck portion 86 is 10 mm. The speed V at which the load cell 88 is moved is set to 3.3 mm/sec.

Next, as shown in FIG. 11, the load cell 88 is moved a distance Z2 toward the chuck portion 86, and in the state where the load cell 88 is pressing into the loop portion 81 of the test piece 80, the value of the load applied to the load cell 88 from the loop portion 81 is stabilized, and then the value of the load is recorded. The value of the load thus obtained is used as the loop stiffness of the film constituting the test piece 80. In this application, unless otherwise specified, the environment during the measurement of the loop stiffness is a temperature of 23°C and a relative humidity of 50%.

The preferred mechanical properties of the high stiffness polyester film will now be described further.
The puncture strength of the high stiffness polyester film is preferably 10 N or more, and more preferably 11 N or more.

The tensile strength of the high stiffness polyester film in at least one direction is preferably 250 MPa or more, more preferably 280 MPa or more. For example, the tensile strength of the high stiffness polyester film in the machine direction is preferably 250 MPa or more, more preferably 280 MPa or more. The tensile strength of the high stiffness polyester film in the perpendicular direction is preferably 250 MPa or more, more preferably 280 MPa or more.
The tensile elongation of the high stiffness polyester film in at least one direction is preferably 130% or less, more preferably 120% or less. For example, the tensile elongation of the high stiffness polyester film in the machine direction is preferably 130% or less, more preferably 120% or less. Also, the tensile elongation of the high stiffness polyester film in the perpendicular direction is preferably 120% or less, more preferably 110% or less.
Preferably, the tensile strength of the high stiffness polyester film divided by the tensile elongation in at least one direction is 2.0 [MPa/%] or more. For example, the tensile strength of the high stiffness polyester film divided by the tensile elongation in the transverse direction (TD) is preferably 2.0 [MPa/%] or more, more preferably 2.2 [MPa/%] or more. The tensile strength of the high stiffness polyester film divided by the tensile elongation in the machine direction (MD) is preferably 1.8 [MPa/%] or more, more preferably 2.0 [MPa/%] or more.

The tensile strength and tensile elongation can be measured in accordance with JIS K7127. As a measuring instrument, a tensile tester STA-1150 manufactured by Orientec Co., Ltd. can be used. As a test piece, a high stiffness polyester film cut into a rectangular film having a width of 15 mm and a length of 150 mm can be used. The distance between a pair of chucks holding the test piece at the start of the measurement is 100 mm, and the tensile speed is 300 mm/min. The length of the test piece can be adjusted as long as the test piece can be held by the pair of chucks. In this application, unless otherwise specified, the environment during the measurement of the tensile strength and tensile elongation is a temperature of 23° C. and a relative humidity of 50%.
The tensile strength and tensile elongation of the packaging material 30 are measured in the same manner as for the high stiffness polyester film, except that a tensile tester RTC-1310A manufactured by Orientec Co., Ltd. is used as the measuring instrument, and the distance between the pair of chucks holding the test piece at the start of the measurement is 50 mm. When measuring the tensile strength and tensile elongation of the packaging material 30, a test piece can be prepared by cutting the front film 14 or the back film 15 of the bag 10 so that the long side direction of the test piece coincides with the flow direction or the perpendicular direction, as in the case of measuring the loop stiffness shown in Figure 7.

The heat shrinkage of the high stiffness polyester film in at least one direction is preferably 0.7% or less, more preferably 0.5% or less. For example, the heat shrinkage of the high stiffness polyester film in the machine direction is preferably 0.7% or less, more preferably 0.5% or less. The heat shrinkage of the high stiffness polyester film in the perpendicular direction is preferably 0.7% or less, more preferably 0.5% or less. The heating temperature for measuring the heat shrinkage is 100° C., and the heating time is 40 minutes.
The Young's modulus of the high stiffness polyester film in at least one direction is preferably 4.0 GPa or more, more preferably 4.5 MPa or more. For example, the Young's modulus of the high stiffness polyester film in the machine direction is preferably 4.0 GPa or more, more preferably 4.5 MPa or more. The Young's modulus of the high stiffness polyester film in the perpendicular direction is preferably 4.0 GPa or more, more preferably 4.5 GPa or more.

Young's modulus can be measured in accordance with JIS K7127, as with tensile strength and tensile elongation. As a measuring instrument, a tensile tester STA-1150 manufactured by Orientec Co., Ltd. can be used. As a test piece, a high stiffness polyester film cut into a rectangular film having a width of 15 mm and a length of 150 mm can be used. The distance between a pair of chucks holding the test piece at the start of measurement is 100 mm, and the tensile speed is 300 mm/min. The length of the test piece can be adjusted as long as the test piece can be held by the pair of chucks. In this application, unless otherwise specified, the environment during measurement of Young's modulus is a temperature of 23° C. and a relative humidity of 50%.
The Young's modulus of the packaging material 30 is measured in the same manner as for the high stiffness polyester film, except that a tensile tester RTC-1310A manufactured by Orientec Co., Ltd. is used as the measuring instrument, and the distance between the pair of chucks holding the test piece at the start of the measurement is 50 mm. When measuring the Young's modulus of the packaging material 30, a test piece can be prepared by cutting the front film 14 or the back film 15 of the bag 10 so that the long side direction of the test piece coincides with the flow direction or the vertical direction, as in the case of measuring the loop stiffness shown in Figure 7.

In the packaging material 30 comprising a high stiffness polyester film, the high stiffness polyester film may be provided with a deposition layer 34, which will be described later. In this case, the high stiffness polyester film provided with the deposition layer 34 may have mechanical properties equivalent to those of a single high stiffness polyester film. For example, the high stiffness polyester film provided with the deposition layer 34 may have a loop stiffness of 0.0017 N or more in at least one direction.

As described below, a gas barrier coating film 36 may be provided on the deposition layer 34. In this case, the high stiffness polyester film provided with the deposition layer 34 and the gas barrier coating film 36 may have mechanical properties equivalent to those of a single high stiffness polyester film. For example, the high stiffness polyester film provided with the deposition layer 34 and the gas barrier coating film 36 may have a loop stiffness of 0.0017 N or more in at least one direction.

In the manufacturing process of high stiffness polyester film, for example, first, a first stretching process is carried out in which a plastic film obtained by melting and molding polyester is stretched 3 to 4.5 times in the machine direction and perpendicular direction at 90°C to 145°C. Then, a second stretching process is carried out in which the plastic film is stretched 1.1 to 3.0 times in the machine direction and perpendicular direction at 100°C to 145°C. Then, heat setting is carried out at a temperature of 190°C to 220°C. Next, relaxation treatment (treatment to reduce the film width) of about 0.2% to 2.5% is carried out at a temperature of 100°C to 190°C in the machine direction and perpendicular direction. In these processes, by adjusting the stretch ratio, stretching temperature, heat setting temperature, and relaxation treatment rate, a high stiffness polyester film with the above-mentioned mechanical properties can be obtained.

According to this embodiment, the packaging material 30 contains a high-stiffness polyester film, and thus excellent puncture strength can be imparted to the packaging material 30 and to the packaged product such as the bag 10 made from the packaging material 30. This can prevent the bag 10 from being torn when a sharp member with a pointed tip comes into contact with the bag 10, for example. The puncture strength of the packaging material 30 is preferably 14.0 N or more, more preferably 15.0 N or more, more preferably 16.0 N or more, more preferably 17.0 N or more, more preferably 18.0 N or more, and even more preferably 19.0 N or more. The method for measuring the puncture strength will be described in the examples described later.

In addition, according to this embodiment, the packaging material 30 contains a high stiffness polyester film, so that the Young's modulus of the packaging material 30 can be increased. The Young's modulus of the packaging material 30 in one direction is, for example, 3200 MPa or more, may be 3300 MPa or more, may be 3400 MPa or more, may be 3500 MPa or more, may be 3600 MPa or more, or may be 3700 MPa or more. The Young's modulus of the packaging material 30 in a direction perpendicular to the above-mentioned one direction is, for example, 2700 MPa or more, may be 2800 MPa or more, may be 2900 MPa or more, may be 3000 MPa or more, may be 3100 MPa or more, or may be 3200 MPa or more. For example, the Young's modulus of the packaging material 30 in the machine direction (MD) is, for example, 3200 MPa or more, may be 3300 MPa or more, 3400 MPa or more, 3500 MPa or more, 3600 MPa or more, or 3700 MPa or more. The Young's modulus of the packaging material 30 in the perpendicular direction (TD) perpendicular to the machine direction (MD) is, for example, 2700 MPa or more, 2800 MPa or more, 2900 MPa or more, 3000 MPa or more, 3100 MPa or more, or 3200 MPa or more. The high Young's modulus of the packaging material 30 makes the packaging material 30 less likely to stretch. For this reason, the processing accuracy when processing the packaging material 30 in the manufacturing process of a packaged product such as a bag 10 is increased. In addition, when the packaging material 30 is used to manufacture a gusset-type bag 10 configured to be self-supporting, as described below, the self-supporting property of the bag 10 is increased.

In this embodiment, the loop stiffness of the packaging material 30 in at least one direction is, for example, 0.100 N or more, may be 0.110 N or more, or may be 0.120 N or more. For example, the loop stiffness of the packaging material 30 in the machine direction (MD) is, for example, 0.100 N or more, may be 0.110 N or more, or may be 0.120 N or more. Also, the loop stiffness of the packaging material 30 in the vertical direction (TD) is, for example, 0.100 N or more, may be 0.110 N or more, or may be 0.120 N or more.

On the other hand, if the loop stiffness of the packaging material 30 is too large, the packaging material 30 may be easily damaged, such as torn, when a packaged product made of the packaging material 30 is dropped. Taking this into consideration, the loop stiffness of the packaging material 30 in at least one direction may be less than 0.150 N, less than 0.140 N, or less than 0.130 N. For example, the loop stiffness of the packaging material 30 in the machine direction (MD) may be less than 0.150 N, less than 0.140 N, or less than 0.130 N. Also, the loop stiffness of the packaging material 30 in the vertical direction (TD) may be less than 0.150 N, less than 0.140 N, or less than 0.130 N.

When the high stiffness polyester film is a high stiffness PET film containing PET as a main component, the PET constituting the high stiffness PET film may contain biomass-derived PET. In this case, the high stiffness PET film may be composed only of biomass-derived PET. Alternatively, the high stiffness PET film may be composed of biomass-derived PET and fossil fuel-derived PET. By containing biomass-derived PET in the high stiffness PET film, the amount of fossil fuel-derived PET can be reduced compared to the conventional method, so that carbon dioxide emissions can be reduced and the environmental load can be reduced. Note that the biomass-derived PET has ethylene glycol derived from biomass as the diol unit and terephthalic acid derived from fossil fuel as the dicarboxylic acid unit. The fossil fuel-derived PET has ethylene glycol derived from fossil fuel as the diol unit and terephthalic acid derived from fossil fuel as the dicarboxylic acid unit.

Since atmospheric carbon dioxide contains a certain percentage of C14 (105.5 pMC), it is known that the C14 content in plants that grow by absorbing atmospheric carbon dioxide, such as corn, is also about 105.5 pMC. It is also known that fossil fuels contain almost no C14. Therefore, by measuring the percentage of C14 in the total carbon atoms in PET, the percentage of carbon derived from biomass can be calculated. In this invention, the "biomass degree" indicates the weight ratio of biomass-derived components. Taking PET as an example, PET is a polymer of ethylene glycol containing 2 carbon atoms and terephthalic acid containing 8 carbon atoms in a molar ratio of 1:1. If only biomass-derived ethylene glycol is used for PET, the weight ratio of biomass-derived components in PET is 31.25%, so the theoretical value of the biomass degree of PET is 31.25%. Specifically, the mass of PET is 192, of which the mass derived from biomass-derived ethylene glycol is 60, so 60÷192×100=31.25. The weight ratio of biomass-derived components in PET derived from fossil fuels is 0%, and the biomass degree of PET derived from fossil fuels is 0%. In the present invention, the biomass degree of the high stiffness PET film is preferably 5.0% or more, and more preferably 10.0% or more. The biomass degree of the high stiffness PET film is preferably 30.0% or less.

Biomass-derived ethylene glycol is made from ethanol (biomass ethanol) produced from biomass. For example, biomass-derived ethylene glycol can be obtained by a method of producing ethylene glycol from biomass ethanol via ethylene oxide using a conventionally known method. Examples of raw materials for biomass ethanol include corn, sugar cane, beet, and manioc. Commercially available biomass ethylene glycol may also be used, and for example, biomass ethylene glycol commercially available from India Glycoal Limited can be suitably used. Note that India Glycoal Limited's biomass ethylene glycol is made from sugar cane molasses.

When one of the first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 is a high-stiffness polyester film, the other of the first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 contains polyester as a main component. For example, when the first biaxially stretched plastic film 40 is a high-stiffness polyester film, the second biaxially stretched plastic film 50 may be a biaxially stretched plastic film containing polyester as a main component. Also, when the second biaxially stretched plastic film 50 is a high-stiffness polyester film, the first biaxially stretched plastic film 40 may be a biaxially stretched plastic film containing polyester as a main component. Also, both the first biaxially stretched plastic film 40 and the second biaxially stretched plastic film 50 may be high-stiffness polyester films. By having the other of the first biaxially oriented plastic film 40 or the second biaxially oriented plastic film 50 contain polyester as a main component, the bag 10 can be made heat resistant to high-temperature sterilization treatments such as boiling and retort treatments.

A biaxially stretched plastic film containing polyester as a main component (hereinafter also referred to as biaxially stretched polyester film) contains, for example, 51% by mass or more of polyester. As with the high stiffness polyester film, the polyester is preferably a polyester mainly composed of an aromatic polyester consisting of at least one aromatic dicarboxylic acid selected from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and at least one aliphatic alcohol selected from ethylene glycol, 1,3-propanediol, and 1,4-butanediol. Examples of polyester include PET and PBT. For example, a biaxially stretched polyester film may contain 51% by mass or more of PET as a main component, or 51% by mass or more of PBT as a main component. In the biaxially stretched polyester film, the 51% by mass or more of polyester may be composed of one type of polyester, or may be composed of two or more types of polyester. The biaxially stretched polyester film does not contain polyamide.

The preferred mechanical properties of the biaxially oriented polyester film will now be described in further detail.
The Young's modulus of the biaxially oriented polyester film in at least one direction is preferably 3000 MPa or more, for example, the Young's modulus of the biaxially oriented polyester film in the machine direction and perpendicular direction is preferably 3000 MPa or more.
The tensile elongation of the biaxially oriented polyester film in at least one direction is preferably 200% or less, for example, the tensile elongation of the biaxially oriented polyester film in both the machine direction and the perpendicular direction is preferably 200% or less.

The Young's modulus and tensile elongation of a biaxially stretched film containing polyester as the main component can be measured in accordance with JIS K7127, as in the case of a high stiffness polyester film. The measuring device can be an Orientec tensile tester STA-1150. The test piece can be a rectangular film cut from the film with a width of 15 mm and a length of 150 mm. The distance between the pair of chucks holding the test piece at the start of the measurement is 100 mm, and the tensile speed is 300 mm/min.

The thickness of the biaxially oriented polyester film is preferably 9 μm or more, more preferably 12 μm or more. The thickness of the biaxially oriented polyester film is preferably 25 μm or less, more preferably 20 μm or less. By making the thickness of the biaxially oriented polyester film 9 μm or more, the biaxially oriented polyester film has sufficient strength. By making the thickness of the biaxially oriented polyester film 25 μm or less, the biaxially oriented polyester film exhibits excellent formability. Therefore, the process of processing the packaging material 30 to manufacture the bag 10 can be carried out efficiently.

Preferably, the material constituting the biaxially oriented polyester film has a thermal conductivity equal to or greater than a predetermined value. For example, the thermal conductivity of the material constituting the biaxially oriented polyester film is preferably equal to or greater than 0.05 W/m·K, and more preferably equal to or greater than 0.1 W/m·K. 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 using a material with a thermal conductivity equal to or greater than a predetermined value, the heat resistance of the packaging material 30 can be increased.

The melting point of the biaxially oriented polyester film is preferably 200°C or higher, and more preferably 220°C or higher. By making the melting point of the biaxially oriented polyester film 220°C or higher, it is possible to prevent holes from being formed in the biaxially oriented polyester film and prevent wrinkles from being formed in the biaxially oriented polyester film when the contents contained in the bag 10 manufactured using the packaging material 30 are heated.

The biaxially stretched polyester film constituting the other of the first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 may be configured to have tearability in the machine direction (MD). In the following description, a biaxially stretched polyester film having tearability in the machine direction (MD) is also referred to as a biaxially stretched straight cut film. By using a biaxially stretched straight cut film, the packaging material 30 can be made to have tearability in the machine direction (MD). In the bag 10 shown in FIG. 1, the first direction D1 corresponds to the machine direction (MD) of the film such as the biaxially stretched plastic film 40, 50. Also, the second direction D2 corresponds to the perpendicular direction (TD) of the film such as the biaxially stretched plastic film 40, 50.

The biaxially stretched straight-cut film is described below. The tensile strength of the biaxially stretched straight-cut film in the machine direction (MD) is greater than the tensile strength of the biaxially stretched straight-cut film in the perpendicular direction (TD). The tensile strength of the biaxially stretched straight-cut film in the machine direction (MD) 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 biaxially stretched straight-cut film in the perpendicular direction (TD). The tensile strength of the biaxially stretched straight-cut film in the machine direction (MD) is, for example, 200 MPa or more and 300 MPa or less.

When the biaxially stretched polyester film constituting the other of the first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 contains PET, the PET may contain biomass-derived PET, as in the case of the high stiffness polyester film described above. In this case, the biaxially stretched polyester film may be composed only of biomass-derived PET. Alternatively, the biaxially stretched polyester film may be composed of biomass-derived PET and fossil fuel-derived PET. The biomass-derived PET contained in the biaxially stretched polyester film and the biomass degree of the biaxially stretched polyester film are the same as those in the case of the high stiffness polyester film described above, so explanations are omitted.

In this embodiment, examples of combinations of the first biaxially oriented plastic film 40 and the second biaxially oriented plastic film 50 are as follows.

(First Adhesive Layer)
The first adhesive layer 45 includes an adhesive for bonding the first biaxially oriented plastic film 40 and the second biaxially oriented 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 including a base agent and a solvent with a second composition including a curing agent and a solvent. Specifically, the adhesive includes 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 biaxially oriented plastic film 40, the second biaxially oriented 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 packaging material 30 is heated, the heat generated in the storage section 17 is easily diffused in the surface direction of the packaging material 30 while being transferred from the inner surface 30x side to the outer surface 30y side of the packaging material 30. This makes it possible to enhance the heat dissipation of the packaging material 30, thereby suppressing the temperature rise of the packaging material 30. This makes it possible to prevent the packaging material 30 from being damaged by heat when the bag 10 is heated. In other words, the heat resistance of the packaging material 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 packaging material 30 becomes easier to occur.

(Second Adhesive Layer)
When the sealant layer 70 is made of a sealant film, the second adhesive layer 55 contains an adhesive for bonding the second biaxially oriented plastic film 50 and the sealant film 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 have 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 biaxially oriented plastic film 40, the second biaxially oriented plastic film 50, and the sealant film. 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 adhesive curing agent 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 film. 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 film.

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.

(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 a multilayer. The sealant layer 70 may be composed of an unstretched sealant film. The term "unstretched" is a concept that 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 sealant film constituting the sealant layer 70 is, for example, a plastic film that has been stretched to an extent necessary for transport but has not been intentionally stretched. Preferred mechanical properties of the sealant film will be further described.
The Young's modulus of the sealant film in at least one direction is preferably 1000 MPa or less, for example, the Young's modulus of the sealant film in the machine direction and perpendicular direction is preferably 1000 MPa or less.
The tensile elongation of the sealant film in at least one direction is preferably 300% or more. For example, the tensile elongation of the sealant film in the machine direction and the perpendicular direction is preferably 300% or more.

The Young's modulus and tensile elongation of the sealant film can be measured in accordance with JIS K7127, as in the case of high stiffness polyester films. The measuring device can be an Orientec tensile tester STA-1150. The test piece can be a rectangular film cut from the film with a width of 15 mm and a length of 150 mm. The distance between the pair of chucks holding the test piece at the start of the measurement is 100 mm, and the tensile speed is 300 mm/min.

The bag 10 made of the packaging material 30 may be subjected to a sterilization treatment such as boiling or retort treatment at high temperatures. The sealant layer 70 preferably has heat resistance that can withstand these high-temperature treatments. The retort treatment is a process in which the bag 10 is filled with the contents, sealed, and then heated under pressure using steam or heated water. The temperature of the retort treatment is, for example, 120°C or higher. The boiling treatment is a process in which the bag 10 is filled with the contents, sealed, and then heated in a water bath under atmospheric pressure. The temperature of the boiling treatment is, for example, 90°C or higher and 100°C or lower.

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 biaxially oriented plastic films 40, 50.

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 of continuous polypropylene.

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, more preferably 110°C or more, and even more preferably 115°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 the sealant layer 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. A specific example of a sealant layer for constituting the sealant layer 70 having a melting point of 105° C. or more is NB-1 manufactured by Tamapoly Co., Ltd. A specific example of a sealant layer for constituting the sealant layer 70 having a melting point of 110° C. or more is LS760C manufactured by Idemitsu Unitech Co., Ltd., 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 layer 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 layer can be increased, thereby preventing the bag 10 from breaking due to an impact when dropped. In addition, the puncture resistance of the packaging material 30 can be increased.

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 layer 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 sealant layer 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 α-olefin copolymer and polyethylene. The α-olefin copolymer is, for example, 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 layer.

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.

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 layer, 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 sealant layer, 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 layer. Therefore, by adjusting the mass ratio of the second thermoplastic resin containing at least an α-olefin copolymer or polyethylene in the single sealant layer, the mechanical properties of the sealant layer can be adjusted.

The sealant layer 70 may further contain 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.

In the following, preferred mechanical properties of the sealant film when the sealant layer 70 is made of a single-layer sealant film containing a propylene-ethylene block copolymer will 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.
In the bag 10 shown in Fig. 1, the first direction D1 corresponds to the machine direction (MD) of the sealant film, and the second direction D2 corresponds to the vertical direction (TD) of the sealant film.

The tensile modulus and tensile elongation can be measured in accordance with JIS K7127. A tensile tester STA-1150 manufactured by Orientec Co., Ltd. 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 perpendicular 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 perpendicular 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 unstretched polypropylene film ZK500 manufactured by Toray Advanced Film Co., Ltd. The first type of sealant film preferably also has the 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 packaging material 30.
The second type is a type having a high tensile modulus, such as unstretched polypropylene film ZK207 manufactured by Toray Advanced Film Co., Ltd. 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. The sealant film has a high tensile elongation, which can prevent the bag 10 from breaking 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.

As shown in the examples described below, when the first type of sealant film is used, the drop strength of a packaging container such as a bag 10 made of the packaging material 30 can be increased. Therefore, when the packaging material 30 is used in an application requiring drop strength, it is preferable that the packaging material 30 is provided with the first type of sealant film.

The sealant layer 70 may have easy peel properties. Easy peel properties are properties that, for example, when a packaging material 30 having a sealant layer 70 is used to form a lid for a container, the lid can be easily peeled off from the flange of the container at its underside, i.e., at the sealant layer 70. Easy peel properties can be achieved, for example, by forming the sealant layer 70 from two or more types of resin, with one resin being incompatible with the other resin. Examples of resins that can achieve easy peel properties include mixed resins of polyethylene and polypropylene, such as high-density polyethylene.

When the sealant layer 70 has easy peel properties, as shown in FIG. 12, the sealant layer 70 may include a first layer 71 located on the second biaxially oriented plastic film 50 side, and a second layer 72 located inside the first layer 71 and constituting the inner surface 30x of the packaging material 30. There are mainly two types of the first layer 71 and second layer 72 of the sealant layer 70 having easy peel properties, such as Type A and Type B described below.

In the A-type sealant layer 70, the first layer 71 is a layer whose main component is polyethylene, and the second layer 72 is a layer containing a mixed resin of polyethylene and polypropylene. In the second layer 72, the blend ratio of polypropylene is greater than the blend ratio of polyethylene. The mass ratio of polypropylene to polyethylene in the second layer 72 is 6:4 to 8:2.

When the packaging material 30 having the A-type sealant layer 70 is used in a packaging product for heat sterilization, it is preferable that the density of the polyethylene in the sealant layer 70 is 0.940 g/cm ³ or more.

The polypropylene in the second layer 72 of the A-type sealant layer 70 can be, for example, an ethylene-propylene random copolymer.

In type A sealant layer 70, the ratio of the thickness of first layer 71 to the thickness of second layer 72 can be 5:1 to 10:1.

In the B-type sealant layer 70, the first layer 71 is a layer whose main component is polypropylene, and the second layer 72 is a layer containing a mixed resin of polyethylene and polypropylene. In the second layer 72, the blend ratio of polypropylene is greater than the blend ratio of polyethylene. The mass ratio of polypropylene to polyethylene in the second layer 72 is 6:4 to 8:2.

When the packaging material 30 having the B-type sealant layer 70 is used in a packaging product for heat sterilization, it is preferable that the density of the polyethylene in the sealant layer 70 is 0.940 g/cm ³ or more.

The polypropylene in the first layer 71 of the B-type sealant layer 70 can be, for example, an ethylene-propylene block copolymer. The polypropylene in the second layer 72 of the B-type sealant layer 70 can be, for example, an ethylene-propylene random copolymer.

In type B sealant layer 70, the ratio of the thickness of first layer 71 to the thickness of second layer 72 can be 3:1 to 8:1.

The sealant layer 70 may be a resin layer provided on the inner surface side of the second biaxially oriented plastic film 50 by an extrusion method or the like. In this case, the above-mentioned second adhesive layer 55 does not need to be present between the second biaxially oriented plastic film 50 and the sealant layer 70.

(Other layers)
The packaging material 30 may further include a printed layer 32. In the example shown in Figure 2, the printed layer 32 is located between the first biaxially oriented plastic film 40 and the first adhesive layer 45.

The printing layer 32 is a layer for indicating information about the contents or packaged product, and for imparting an aesthetic feel to packaged products such as bags 10. The printing layer expresses letters, numbers, symbols, figures, pictures, etc. The printing layer contains a binder resin and a coloring material such as a dye or pigment dispersed in the binder resin. Inks for gravure printing or flexographic printing can be used as materials for forming the printing layer. A specific example of an ink for gravure printing is Finart manufactured by DIC Graphics Corporation.

Figure 3 is a cross-sectional view showing one modified example of the layer structure of the packaging material 30. As shown in Figure 3, the packaging material 30 may have a deposition layer 34 located on the surface of the inner surface 30x side of the first biaxially stretched plastic film 40. In addition, the packaging material 30 may further have a transparent gas barrier coating film 36 located on the surface of the deposition layer 34.

Figure 4 is a cross-sectional view showing a modified example of the layer structure of the packaging material 30. As shown in Figure 4, the deposition layer 34 may be located on the surface of the second biaxially stretched plastic film 50 on the outer surface 30y side. In addition, a gas barrier coating film 36 may be provided on the surface of the deposition layer 34.

The deposition layer 34 and the gas barrier coating film 36 are described below.

The vapor deposition layer 34 is a layer provided on the packaging material 30 to enhance the gas barrier properties of the packaging material 30. Materials constituting the vapor deposition layer 34 include metals such as aluminum, metal oxides such as aluminum oxide, and inorganic oxides such as silicon oxide.

The deposition layer 34 functions as a layer having a gas barrier function that prevents the permeation of oxygen gas and water vapor. The deposition layer 34 may be provided in two or more layers. When the deposition layer 34 has two or more layers, each layer may have the same composition or different compositions. Examples of the method for forming the deposition layer 34 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.

The deposition layer 34 may be a transparent deposition layer formed of an inorganic material having transparency, such as aluminum oxide (aluminum oxide) or silicon oxide. In particular, when the printing layer 32 is provided on the inner surface 30x side of the deposition layer 34, the deposition layer 34 is configured as a transparent deposition layer. It is preferable to use an amorphous thin film of aluminum oxide as the transparent deposition layer. Specifically, the transparent deposition layer is an amorphous thin film of aluminum oxide represented by the formula AlO _x (wherein X represents a number in the range of 0.5 to 1.5). The transparent deposition layer can be an amorphous thin film of aluminum oxide in which the value of X decreases in the depth direction from the film surface toward the inner surface. It is preferable that the amorphous thin film of aluminum oxide is represented by the formula AlO _x (wherein X represents a number in the range of 0.5 to 1.5), and the value of X increases in the depth direction from the film surface toward the inner surface. In addition, as the value of X in the above formula, basically, X=0.5 or more can be used, but if X is less than 1.0, coloring is severe and transparency is poor, so it is preferable to use X=1.0 or more. Furthermore, since X=1.5 is a state in which Al and oxygen are completely oxidized, X=1.5 is the upper limit that can be used. In addition, when the value of X in the above formula is 0, it is a completely inorganic element (pure substance) and is not transparent.

The rate of decrease in the value of X can be confirmed by performing elemental analysis of the transparent deposition layer using a surface analysis device such as an X-ray photoelectron spectroscopy (XPS) or a secondary ion mass spectroscopy (SIMS) and analyzing the layer by ion etching in the depth direction.

<First Preferred Form of Transparent Vapor Deposition Layer>
A first preferred embodiment of the transparent vapor deposition layer will be described below. The transparent vapor deposition layer may be a layer made of a mixture of inorganic compounds containing a covalent bond between an aluminum atom and a carbon atom. In this case, the transparent vapor deposition layer may show the presence of a covalent bond between an aluminum atom and a carbon atom in a peak measured by ion etching in the depth direction using an X-ray photoelectron spectroscopy device (measurement conditions: X-ray source AlKα, X-ray output 120 W), and may have transparency and gas barrier properties that prevent the transmission of oxygen, water vapor, etc.

At the interface between the transparent vapor deposition layer and the biaxially stretched plastic film, a covalent bond between a metal atom and a carbon atom may be formed. For example, when the transparent vapor deposition layer contains aluminum oxide, a covalent bond between an aluminum atom and a carbon atom may be formed at the interface between the biaxially stretched plastic film and the transparent vapor deposition layer. The covalent bond can be detected by measurement using X-ray photoelectron spectroscopy (hereinafter, abbreviated as "XPS measurement").

In addition, in the transparent vapor deposition layer, the ratio of covalent bonds between aluminum atoms and carbon atoms is preferably within the range of 0.3% to 30% of all bonds including carbon atoms observed when the interface between the transparent vapor deposition layer and the biaxially stretched plastic film is measured by XPS measurement. This strengthens the adhesion between the transparent vapor deposition layer and the biaxially stretched plastic film, and provides a vapor deposition film with excellent transparency and well-balanced gas barrier properties.

If the proportion of covalent bonds between aluminum atoms and carbon atoms is less than 0.3%, the adhesion of the transparent vapor deposition layer is not sufficiently improved, making it difficult to stably maintain the barrier properties.

Furthermore, it is preferable that the AL (aluminum)/O (oxygen) ratio of the transparent vapor deposition layer, which is mainly composed of aluminum oxide, is 1.0 or less within a range of 3 nm from the interface between the biaxially stretched plastic film and the transparent vapor deposition layer toward the surface of the transparent vapor deposition layer on the side opposite the biaxially stretched plastic film.
If the AL/O ratio exceeds 1.0 in the range from the interface between the transparent vapor deposition layer and the biaxially oriented plastic film toward the surface of the transparent vapor deposition layer opposite the biaxially oriented plastic film, the adhesion between the biaxially oriented plastic film and the transparent vapor deposition layer becomes insufficient, and the proportion of aluminum increases, reducing the transparency of the transparent vapor deposition layer.

The thickness of the transparent deposition layer is, for example, 20 Å or more and 200 Å, preferably 30 Å or more and 150 Å. If it is less than 30 Å, the gas barrier property may be insufficient. On the other hand, if it exceeds 150 Å, the gas barrier performance of the packaging material 30 may not be maintained. The reason for this is unclear, but it is thought that if the thickness of the transparent deposition layer exceeds 150 Å, the flexibility of the packaging material 30 decreases, and when the packaging material 30 is used in a bag 10, cracks or pinholes occur in part of the transparent deposition layer, resulting in a decrease in the gas barrier property. 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 thickness of the transparent deposition layer can be measured by the fundamental parameter method using, for example, a fluorescent X-ray analyzer (product name: RIX2000 type, manufactured by Rigaku Co., Ltd.). In addition, the thickness of the transparent deposition layer can be changed by changing the deposition rate of the transparent deposition layer, changing the deposition rate, etc.

The surface of the biaxially stretched plastic film may be subjected to a pretreatment such as corona discharge treatment, frame treatment, plasma treatment, etc. If the pretreatment is plasma treatment, plasma is supplied to the surface of the biaxially stretched plastic film in a reduced pressure environment of 0.1 Pa to 100 Pa using a pretreatment device. Plasma can be generated by using an inert gas such as argon alone or a mixture of oxygen, nitrogen, carbon dioxide, or one or more of these gases as a plasma raw material gas, and exciting the plasma raw material gas by a potential difference caused by a high-frequency voltage, etc.

By pretreatment, it is possible to confine plasma near the surface of the biaxially stretched plastic film. This changes the surface shape, chemical bonding state, and functional groups of the biaxially stretched plastic film, and changes the chemical properties of the surface of the biaxially stretched plastic film. This makes it possible to improve the adhesion between the biaxially stretched plastic film and the transparent vapor deposition layer.

<Second Preferred Form of Transparent Vapor Deposition Layer>
Next, a second preferred embodiment of the transparent deposition layer will be described. In the present application, the transparent deposition layer may satisfy both the first preferred embodiment described above and the second preferred embodiment described below, or may satisfy only one of the two. In addition, the transparent deposition layer of the present application may not satisfy either the first preferred embodiment described above or the second preferred embodiment described below.

In the transparent vapor deposition layer, a transition region that defines the adhesive strength between a substrate such as a biaxially stretched plastic film and a transparent vapor deposition layer such as an aluminum oxide vapor deposition film may be formed in the transparent vapor deposition layer. When the transparent vapor deposition layer is an aluminum oxide vapor deposition film, the transition region contains a bond structure (Al2O4H) that is transformed into aluminum hydroxide, which is detected by etching the aluminum oxide vapor deposition film using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The transformation rate of the transition region, defined by the ratio of the transformed transition region defined by TOF-SIMS to the aluminum oxide vapor deposition film defined by etching using TOF-SIMS, is preferably 45% or less. This form is based on the finding that by defining the transformation rate of the transition region, a packaging material 30 having barrier properties and improved adhesive strength between a biaxially stretched plastic film and an aluminum oxide vapor deposition film can be specified.

The transformation rate in the transition region will be explained in detail. First, the outermost surface of the aluminum oxide vapor-deposited film is etched with Cs using a time-of-flight secondary ion mass spectrometer, and the elemental bonds at the interface between the aluminum oxide vapor-deposited film and the biaxially stretched plastic film and the elemental bonds in the vapor-deposited film are measured. Next, actual measurement graphs of the measured elements and elemental bonds are obtained, as shown in Figure 13.

In order to narrow the transition region of the interface between the biaxially stretched plastic film and the vapor deposition film formed by aluminum hydroxide in the aluminum oxide vapor deposition film as much as possible, attention is paid to AL2O4H, and 1) the position where the intensity _H0 of the graph of element C6 becomes half (the position where the intensity becomes _H1 in FIG. 13) is specified as the interface between the biaxially stretched plastic film and the aluminum oxide vapor deposition film (the position of the horizontal axis (Cycle) _T1 in FIG. 13). Also, the area from the interface to the surface of the aluminum oxide vapor deposition film (the position of the horizontal axis (Cycle) _T0 in FIG. 13) is specified as the aluminum oxide vapor deposition film. Next, 2) the peak in the graph representing the element bond AL2O4H (the position of the horizontal axis (Cycle) _T2 in FIG. 13) is obtained, and the area from the position of the peak to the position of the interface is specified as the transition region. Next, 3) the conversion rate of the transition region to aluminum hydroxide is calculated as (the transition region from the peak of the element bond AL2O4H to the interface/aluminum oxide vapor deposition film)×100(%). In the example shown in FIG. 13, the transformation rate is (W2/W1)×100(%).

In forming the aluminum oxide vapor deposition film, it is preferable to perform plasma pretreatment on the surface of the biaxially stretched plastic film before the aluminum oxide vapor deposition process in order to set the conversion rate of the transition region of the aluminum oxide vapor deposition film to a preferred value. In the plasma pretreatment, the mixture ratio of oxygen gas and argon or helium supplied as plasma gas is 5:1, preferably 2:1. By setting the mixture ratio to 5:1, the film formation energy of vapor-deposited aluminum on the surface of the biaxially stretched plastic film increases, and by further setting it to 2:1, aluminum hydroxide is formed near the interface of the substrate, i.e., the conversion rate of the transition region decreases.

As a vapor deposition method for forming the vapor deposition film, various vapor deposition methods can be applied from among physical vapor deposition and chemical vapor deposition. As a physical vapor deposition method, a method can be selected from the group consisting of vapor deposition, sputtering, ion plating, ion beam assisted deposition, and cluster ion beam deposition, and as a chemical vapor deposition method, a method can be selected from the group consisting of plasma CVD, plasma polymerization, thermal CVD, and catalytic reaction CVD. In this embodiment, the vapor deposition method of physical vapor deposition is preferred.

The thickness of the aluminum oxide vapor deposition film formed as described above is preferably 3 nm or more and 50 nm or less, and more preferably 8 nm or more and 30 nm or less. Within this range, it is easy to maintain the barrier properties.

[Gas barrier coating film]
The gas barrier coating film 36 is obtained from a transparent gas barrier composition which 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 which is further polycondensed by a sol-gel process in the presence of a sol-gel catalyst, an acid, water, and an organic solvent. It is preferable that the gas barrier coating film 36 is transparent.

As the alkoxide represented by the above general formula R ¹ _n M(OR ² ) _m , at least one of a partial hydrolyzate of an alkoxide and a condensate of hydrolysis of an alkoxide can be used. In addition, as the partial hydrolyzate of an alkoxide, it is not necessary that all of the alkoxy groups are hydrolyzed, and one or more alkoxy groups may be hydrolyzed, or a mixture thereof. As the condensate of hydrolysis of an alkoxide, a dimer or more of a partially hydrolyzed alkoxide, specifically a dimer to hexamer, is used.

In the alkoxide represented by the above general formula R ¹ _n M(OR ² ) _m , silicon, zirconium, titanium, aluminum, and the like can be used as the metal atom represented by M. Examples of preferred metals include silicon and titanium. In the present embodiment, the alkoxide can be used alone or in the form of a mixture of two or more different metal atoms in the same solution.

In the alkoxides represented by the above general formula R ¹ _n M(OR ² ) _m , specific examples of the organic group represented by R ¹ include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, t-butyl, n-hexyl, n-octyl, etc. In the alkoxides represented by the above general formula R ¹ _n M(OR ² ) _m , specific examples of the organic group represented by R ² include methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, etc. These alkyl groups may be the same or different in the same molecule.

When preparing the transparent gas barrier composition, for example, a silane coupling agent may be added. As the silane coupling agent, a known organoalkoxysilane containing an organic reactive group may be used. In particular, an organoalkoxysilane having an epoxy group is preferably used, and specifically, for example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane may be used. The above-mentioned silane coupling agents may be used alone or in combination of two or more.

The oxygen permeability and water vapor permeability of the packaging material 30 having the deposition layer 34 are preferably 2 or less (cc/ ^m2 -day-atm) and 2 or less (g/ ^m2 -day), respectively. The oxygen permeability is measured in accordance with JIS K7126 (isobaric method) using an oxygen barrier measuring device OXTRAN manufactured by Mocon, Inc., USA, under conditions of 23°C and 90% RH. The water vapor permeability is measured in accordance with JIS K7129 (Method B) using a water vapor barrier measuring device PERMATRAN manufactured by Mocon, Inc., USA, under conditions of 40°C and 90% RH.

Manufacturing Method of Packaging Material Next, an example of a manufacturing method of the packaging material 30 will be described.

First, the first biaxially stretched plastic film 40 and the second biaxially stretched plastic film 50 are prepared. The first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 is provided with a printing layer 32, a deposition layer 34, a gas barrier coating film 36, etc., as necessary.

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

Alternatively, the packaging material 30 may be produced by first laminating the second biaxially oriented plastic film 50 and the sealant layer 70 via the second adhesive layer 55 by a dry lamination method, and then laminating the first biaxially oriented plastic film 40 and a laminate including the second biaxially oriented plastic film 50 and the sealant layer 70 via the first adhesive layer 45 by a dry lamination method.

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 at 20°C or higher.

Manufacturing Method of Bag Next, a method of manufacturing the bag 10 using the above-mentioned packaging material 30 will be described. First, the front film 14 and the back film 15 made of the packaging material 30 are prepared. Next, the inner surfaces of the films are heat-sealed to form seals such as the bottom seal 12a and the side seal 13a. The films joined together by heat sealing are then cut into an appropriate shape to obtain the bag 10 shown in FIG.

Next, the contents 18 are filled into the bag 10 through the opening 11b of the upper portion 11. Specifically, as shown in FIG. 14, the pair of side seal portions 13a of the bag 10 that are close to the upper portion 11 are gripped by a pair of chuck portions 105. Also, as shown by the arrow P in FIG. 14, the chuck portions 105 are moved in a direction in which the gap between the pair of chuck portions 105 narrows in the width direction of the bag 10. This causes the surface film 14 and the back film 15 to deform so as to form the opening 11b in the upper portion 11. At this time, as shown in FIG. 14, the suction portion 106 may be attached to the outer surfaces of the surface film 14 and the back film 15, and the suction portion 106 may be moved in the direction of the arrow Q. This makes it easier to form the opening 11b. Next, the contents 18 are filled into the bag 10 through the opening 11b. After that, the upper portion 11 is heat-sealed to form the upper seal portion 11a. In this manner, the bag 10 in which the contents 18 are contained and sealed can be obtained.

The contents 18 are, for example, cooked foods that contain moisture, such as curry, stew, soup, etc. The contents 18 may also contain ingredients that contain a lot of oil, such as meat, fish, and seasonings for those. In addition to food, the bag 10 may also contain items that can be heated by boiling in hot water, etc. Contents that do not require heating may also be contained in the bag 10.

In this embodiment, a high-stiffness polyester film is used as the first biaxially oriented plastic film 40 or the second biaxially oriented plastic film 50 of the packaging material 30 constituting the bag 10. This allows the packaging material 30 and the bag 10 to have excellent puncture strength. This prevents the bag 10 from being torn when a sharp member with a pointed tip comes into contact with the bag 10. The puncture strength of the packaging material 30 is preferably 14.0 N or more, more preferably 15.0 N or more, more preferably 16.0 N or more, more preferably 17.0 N or more, more preferably 18.0 N or more, and even more preferably 19.0 N or more. The method for measuring the puncture strength will be described in the examples described below.

In addition, in this embodiment, the second biaxially oriented plastic film 50 contains polyester as a main component. Therefore, compared to when the second biaxially oriented plastic film 50 is a nylon film, it is possible to suppress the occurrence of coloring of the packaging material 30 due to the contents. This makes it possible to favorably maintain the appearance of the packaged product made of the packaging material 30.

In addition, in this embodiment, by using a high-stiffness polyester film as the first biaxially oriented plastic film 40 or the second biaxially oriented plastic film 50, the rigidity of the packaging material 30 can be easily increased. For example, the packaging material 30 has a loop stiffness of 0.100 N or more in at least one direction. For example, the loop stiffness of the packaging material 30 in the machine direction (MD) is 0.100 N or more. When the packaging material 30 has rigidity, it becomes easier to form the opening 11b in the upper portion 11 when the chuck portion 105 is moved as shown in FIG. 14. For example, the front surface film 14 and the back surface film 15 are each easily deformed to have a curved shape that is convex on the outer surface side. This makes it easier to ensure the opening width K of the opening 11b. In addition, when the packaging material 30 constituting the front surface film 14 and the back surface film 15 has rigidity, wrinkles are less likely to occur in the front surface film 14 and the back surface film 15. For this reason, the suction portion 106 is easily suctioned to the outer surfaces of the front surface film 14 and the back surface film 15. This can also contribute to ensuring the opening width K of the opening 11b.

On the other hand, if the loop stiffness of the packaging material 30 is too large, the packaging material 30 may be more susceptible to breakage, such as tearing, when a packaged product made of the packaging material 30 is dropped. In this embodiment, the packaging material 30 is configured so that the loop stiffness of the packaging material 30 in at least one direction is less than 0.150 N. In other words, the packaging material 30 is configured to have a moderate degree of flexibility. This makes it possible to prevent breakage, such as tearing, of the packaging material 30 when a packaged product made of the packaging material 30 is dropped.

As shown in the examples below, one method for making the loop stiffness of the packaging material 30 in at least one direction less than 0.150 N is to use a first type of sealant film, such as the unstretched polypropylene film ZK500 described above, which has high tensile elongation and impact resistance.

Method of opening the bag Next, a method of opening the bag 10 will be described. Here, a case where a consumer opens the bag 10 by tearing the bag 10 along the first direction D1 will be described. In this embodiment, as described above, a biaxially stretched straight cut film may be used as the first biaxially stretched plastic film 40 or the second biaxially stretched plastic film 50 of the packaging material 30. In this case, it is possible to prevent the tear direction from deviating from the first direction D1 when the consumer tears the bag 10 to open it. Therefore, the consumer can easily tear the bag 10. 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 labeled with 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)
Figure 15 is a diagram showing another example of bag 10 including packaging material 30. Bag 10 shown in Figure 15 differs only in that it further includes a lower film 16, and other configurations are substantially the same as bag 10 shown in Figure 1. In bag 10 shown in Figure 15, the same parts as bag 10 shown in Figure 1 are given the same reference numerals and detailed description will be omitted.

The bag 10 shown in FIG. 15 is a gusset-type bag that is configured to be self-supporting. In addition to the components of the bag 10 shown in FIG. 1, the bag 10 includes a lower film 16 that configures the lower portion 12. The lower film 16 is folded back at the fold-back portion 16f and disposed between the front film 14 and the back film 15. In this case, the sealed portion includes a lower sealed portion 12a that extends to the lower portion 12. The lower sealed portion 12a includes a sealed portion configured by joining the inner surface of the front film 14 and the inner surface of the lower film 16, and a sealed portion configured by joining the inner surface of the back film 15 and the inner surface of the lower film 16.

Manufacturing method of the bag A method of manufacturing the bag 10 shown in Fig. 15 will be described. First, a front film 14 and a back film 15 made of a packaging material 30 are prepared. A folded-over lower film 16 is inserted between the front film 14 and the back film 15. Next, the inner faces of the films are heat-sealed to form seals such as a lower seal 12a and a side seal 13a. The films joined together by heat sealing are then cut into an appropriate shape to obtain the bag 10 shown in Fig. 15.

(Variations of the bag)
Figure 16 is a diagram showing another example of bag 10 including packaging material 30. Bag 10 shown in Figure 16 differs only in that it further includes a steam venting mechanism 20, and other configurations are substantially the same as bag 10 shown in Figure 15. In bag 10 shown in Figure 16, the same parts as bag 10 shown in Figure 15 are given the same reference numerals and detailed description will be omitted.

As shown in FIG. 16, the bag 10 is provided with a steam vent mechanism 20 for releasing steam generated when the contents stored in the storage section 17 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 place other than the steam vent mechanism 20.

When a bag 10 equipped with a steam vent mechanism 20 is heated using a microwave oven or the like, the pressure inside the bag 10 may not rise to a level that allows steam to escape from the steam vent mechanism 20 to the outside. In other words, depending on how the bag 10 is used, the steam vent mechanism 20 may have a low probability of performing its function of releasing steam to the outside. Even in this case, providing the bag 10 with the steam vent mechanism 20 can further reduce the probability that steam will escape from a location other than the steam vent mechanism 20 or that the bag 10 will burst.

In the example shown in FIG. 16, the steam release mechanism 20 has a steam release seal portion 20a that protrudes from the side seal portion 13a toward the inside of the bag 10, and a non-seal portion 20b that is isolated from the storage portion 17 by the steam release seal portion 20a. The non-seal portion 20b is connected to the outside of the bag 10. When the pressure in the storage portion 17 increases due to heating in a microwave oven or the like, the steam release seal portion 20a peels off. Steam in the storage portion 17 can escape to the outside of the bag 10 through the peeled portion of the steam release seal portion 20a and the non-seal portion 20b. At this time, since the packaging material 30 has heat resistance, it is possible to suppress the formation of holes or wrinkles in the packaging material 30 when heated.

The configuration of the steam release mechanism 20 is not limited to the configuration shown in FIG. 16. The configuration of the steam release mechanism 20 is arbitrary as long as it can communicate between the storage section 17 and the outside of the bag 10 when the steam pressure reaches or exceeds a predetermined value.

For example, as shown in FIG. 17, the surface film 14 may include a palm portion 14a in which the inner surfaces of the surface films 14 are partially overlapped. The palm portion 14a may be formed, for example, by folding back a single surface film 14 at a fold back portion 14f to form a fold. The palm portion 14a may also be formed by overlapping portions of two surface films 14.

The joint portion 14a is formed with a joint seal portion 14b that extends from one side seal portion 13a to the other side seal portion 13a. In this case, the steam release mechanism 20 has, for example, a steam release seal portion 20a that protrudes from the joint seal portion 14b toward the storage portion 17, a non-seal portion 20b surrounded by the steam release seal portion 20a and the joint seal portion 14b, and a cut 20c formed in the surface film 14 in the non-seal portion 20b. As shown in FIG. 17, among the multiple non-seal portions 14c located in the joint portion 14a between the side portion 13 and the steam release mechanism 20, a cut 14d may also be formed in the surface film 14 in the non-seal portion 14c of the steam release mechanism 20 that is the most prominent.

In this modified example, when the pressure in the storage section 17 increases, the steam release seal section 20a peels off, connecting the storage section 17 to the non-sealed section 20b. Steam that flows from the storage section 17 to the non-sealed section 20b through the peeled portion of the steam release seal section 20a escapes to the outside of the bag 10 through the slit 20c.

The bag 10 shown in FIG. 17 is placed in a microwave oven so that the back film 15 is in contact with the turntable or the bottom surface (flat table) of the microwave oven over a wide area. Therefore, the contents are more easily heated uniformly than in the freestanding bag 10 shown in FIG. 16. In addition, since the area of the part of the bag 10 in contact with the microwave oven is large, the position of the liquid level of the contents is less likely to change even if the bag 10 is softened by heating. Therefore, in the heating process using a microwave oven, the contents are less likely to adhere to the inner surface of the front film 14 or back film 15 above the liquid level of the contents. This makes it possible to suppress the phenomenon in which the contents adhering to the inner surface of the front film 14 or back film 15 are excessively overheated and holes are formed in the front film 14 or back film 15.

18A and 18B are a longitudinal section and a plan view showing a container with a lid 110, which is an example of an application of the packaging material 30. The container with a lid 110 includes a container body 112 manufactured by sheet molding such as drawing or injection molding, and a lid material 114 joined to the container body 112. The container body 112 has a bottom surface 112a and a side surface 112b, and a flange portion 113 that spreads outward in the horizontal direction from the upper end of the side surface 112b. The lid material 114 is joined to the upper surface of the flange portion 113 of the container body 112 via a seal portion 116. The lid material 114 may include the above-mentioned packaging material 30 having at least one high-stiffness polyester film. By forming the lid material 114 using the above-mentioned packaging material 30, it is possible to give the lid material 114 excellent puncture strength. This makes it possible to suppress the lid material 114 from being torn when a sharp member with a pointed tip comes into contact with the lid material 114. In addition, if the container with lid 110 is dropped, it is possible to prevent the container with lid 110 from being damaged and the contents from leaking out.

The sealant layer 70 of the packaging material 30 constituting the lid material 114 may have easy peel properties. That is, the sealant layer 70 of the packaging material 30 constituting the lid material 114 may have a first layer 71 mainly composed of polyethylene or polypropylene, and a second layer 72 containing a mixed resin of polyethylene and polypropylene and constituting the inner surface 30x.

In this application, products for packaging items, such as bags 10 and lidded containers 110, are also referred to as packaging products.

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, loop stiffness, and drop strength of the packaging material 30 of the present invention were evaluated using Examples A1 to A3, Comparative Examples 1 to 3, Examples B1 to B3, and Examples C1 to C3.

(Example A1)
A high-stiffness polyester film (hereinafter also referred to as a high-stiffness PET film) made of PET and having a loop stiffness of 0.0017 N or more was prepared as the first biaxially stretched plastic film 40. Next, a printing layer having a thickness of 1 μm was formed on the surface of the high-stiffness PET film.
Specifically, XP-55 manufactured by Toray Industries, Inc. was used as the high stiffness PET film. The thickness of the high stiffness PET film was 16 μm. The measured loop stiffness of the high stiffness PET film was 0.0021 N in both the machine direction and the perpendicular direction. The Young's modulus of the high stiffness PET film in the machine direction was 4.8 GPa, and the Young's modulus of the high stiffness PET film in the perpendicular direction was 4.7 GPa.
The tensile strength of the high stiffness PET film in the machine direction was 292 MPa, and the tensile strength of the high stiffness PET film in the perpendicular direction was 257 MPa. The tensile elongation of the high stiffness PET film in the machine direction was 107%, and the tensile elongation of the high stiffness PET film in the perpendicular direction was 102%. In this case, the tensile strength of the high stiffness PET film in the machine direction divided by the tensile elongation was 2.73 [MPa/%], and the tensile strength of the high stiffness PET film in the perpendicular direction divided by the tensile elongation was 2.52 [MPa/%].
The heat shrinkage of the high stiffness PET film in both the machine direction and the perpendicular direction was 0.4%.

A biaxially stretched PET film with a thickness of 12 μm was prepared as the second biaxially stretched plastic film 50. The biaxially stretched PET film used had approximately the same tensile strength in the machine direction (MD) and the perpendicular direction (TD).

In addition, an unstretched polypropylene film ZK500 manufactured by Toray Advanced Film Co., Ltd. was prepared as the sealant layer 70. ZK500 contains the above-mentioned propylene-ethylene block copolymer. The thickness of the sealant layer 70 was 60 μm.

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 biaxially oriented plastic film 40, the second biaxially oriented plastic film 50, and the sealant layer 70 were laminated in this order by dry lamination to produce the packaging material 30. The printed layer was laminated so that it faced the surface side of the second biaxially oriented plastic film 50. For the first adhesive layer 45 and the second adhesive layer 55, a two-component polyurethane adhesive (base: RU-40, hardener: H-4) manufactured by Rock Paint Co., Ltd. was used. The base RU-40 is a polyester polyol. The thickness of the first adhesive layer 45 and the second adhesive layer 55 was 3 μm. The overall thickness of the packaging material 30 was 95 μm.

[Evaluation of puncture resistance]
Next, the puncture strength of the packaging material 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 instrument. Specifically, as shown in FIG. 19, 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 a test piece of the packaging material 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 packaging material 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 puncture strength of the packaging material 30. The environment during the measurement was a temperature of 23° C. and a relative humidity of 50%. As a result, the puncture strength was 16.7 N.

[Evaluation of loop stiffness]
The loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 was also measured. A measuring device, No. 581 Loop Stiffness Tester (registered trademark) LOOP STIFFNESS TESTER DA type manufactured by Toyo Seiki Seisakusho, was used. The environment during the measurement was a temperature of 23°C and a relative humidity of 50%. As a result, the loop stiffness in the machine direction of the packaging material 30 was 0.134 N, and the loop stiffness in the perpendicular direction was 0.108 N.

[Evaluation of Drop Strength]
Next, the bag 10 was produced using the packaging material 30 as the surface film 14, the back film 15, and the lower film 16, and the drop strength of the bag 10 was evaluated. Specifically, the bag 10 shown in FIG. 15 was produced using the packaging material 30. The height S1 of the bag 10 was 160 mm, and the width S2 was 147 mm. The height S3 of the folded lower film 16, i.e., the height from the lower end of the bag 10 to the folded-back portion 16f, was 46 mm. The width S4 of the side seal portion 13a was 7.0 mm. Next, 200 g of water was filled into the bag 10 through the opening 11b of the upper portion 11 as the content. After that, the upper portion 11 was heat-sealed to form the upper seal portion 11a. The width S5 of the upper seal portion 11a was 10.0 mm. In this manner, a plurality of bags 10 shown in FIG. 15 containing 200 g of water were produced.

In the process of producing the bag 10, a heat sealer TP-701-A manufactured by Tester Sangyo Co., Ltd. was used as a heat sealing device for forming the sealed portions such as the upper sealed portion 11a, the lower sealed portion 12a, and the side sealed portion 13a. The heat sealing conditions were as follows.
Heat seal temperature: 220°C
Heat sealing time: 1.0 seconds Heat sealing pressure: 0.1 MPa

Then, the bag 10 containing the water was subjected to a heat sterilization treatment. Specifically, the bag 10 was subjected to a spray-type retort treatment. The retort temperature was 121°C, and the retort time was 30 minutes.

Next, some of the bags 10 after the heat sterilization treatment were stored for one week in an environment at 3° C. After that, the following steps A1 to A4 were successively carried out.
Step A1: The bag 10 stored in an environment at 3° C. is taken out.
Step A2: The bag 10, with the back film 15 facing downward, is dropped repeatedly 10 times from a height of 120 cm.
Step A3: The bag 10, which is held so that the lower portion 12 faces downward, is dropped repeatedly 10 times from a height of 120 cm.
Step A4: It is confirmed whether the bag 10 is broken or not.
The time required to continuously carry out steps A1 to A4 on one bag 10 was about 2 minutes.

The above-mentioned steps A1 to A4 were performed on 10 bags 10, and the number of bags 10 that were not broken was counted, which was 10. In other words, the pass rate was 10/10. In the following explanation, the pass rate of the drop test performed on packaging containers stored for one week in an environment of 3°C is also referred to as the low-temperature drop test pass rate.

In addition, some of the bags 10 after the heat sterilization treatment were stored for one week in an environment of 25° C. After that, the following steps B1 to B4 were continuously carried out.
Step B1: The bag 10 stored in an environment at 25° C. is taken out.
Step B2: The bag 10, with the back surface film 15 facing downward, is dropped repeatedly 10 times from a height of 120 cm.
Step B3: The bag 10, with the lower portion 12 facing downward, is dropped repeatedly 10 times from a height of 120 cm.
Step B4: It is confirmed whether the bag 10 is broken or not.
The time required to continuously carry out steps B1 to B4 on one bag 10 was about 2 minutes.

The above-mentioned steps B1 to B4 were performed on 10 bags 10, and the number of bags 10 that were not broken was counted, which was 10. In other words, the pass rate was 10/10. In the following explanation, the pass rate of the drop test performed on packaging containers stored for one week in an environment of 25°C is also referred to as the room temperature drop test pass rate.

(Example A2)
A packaging material 30 was produced in the same manner as in Example A1, except that the biaxially stretched PET film used as the second biaxially stretched plastic film 50 in Example A1 was used as the first biaxially stretched plastic film 40, and the high-stiffness PET film used as the first biaxially stretched plastic film 40 in Example A1 was used as the second biaxially stretched plastic film 50. The overall thickness of the packaging material 30 was 95 μm.

Next, the puncture strength and loop stiffness in the machine direction and perpendicular direction of the packaging material 30 were measured in the same manner as in Example A1. As a result, the puncture strength was 16.5 N, the loop stiffness in the machine direction was 0.132 N, and the loop stiffness in the perpendicular direction was 0.110 N.

Next, in the same manner as in Example A1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example A1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example A1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

(Example A3)
As in Example A1, a biaxially stretched PET film was prepared as the first biaxially stretched plastic film 40. Then, a transparent deposition layer and a gas barrier coating film were formed on the surface of the biaxially stretched PET film as follows. Then, a printing layer having a thickness of 1 μm was formed on the surface of the gas barrier coating film.

The method for forming the transparent deposition layer and the gas barrier coating film is described below. First, a roll of biaxially stretched PET film was prepared. Next, the biaxially stretched PET film was subjected to oxygen plasma treatment, and then a transparent deposition layer containing aluminum oxide and having a thickness of 12 nm was formed on the oxygen plasma-treated surface. The oxygen plasma treatment and film formation process are described in detail below.

In the oxygen plasma treatment, plasma was introduced from a plasma supply nozzle under the following conditions in a plasma pretreatment chamber onto the surface of the biaxially stretched PET film on which a transparent deposition layer was to be formed, and the biaxially stretched PET film transported at a transport speed of 400 m/min was subjected to plasma pretreatment. As a result, an oxygen plasma-treated surface was formed on the surface of the biaxially stretched PET film on which a transparent deposition layer was to be formed.
[Oxygen plasma pretreatment conditions]
Plasma intensity: 200 W·sec/ ^m2
Plasma formation gas ratio: oxygen/argon = 2/1
Voltage applied between pretreatment drum and plasma supply nozzle: 340 V
Vacuum level in pre-treatment section: 3.8 Pa

In the film formation process, a transparent deposition layer containing aluminum oxide having a thickness of 12 nm was formed on the oxygen plasma-treated surface of the biaxially stretched PET film by vacuum deposition using aluminum as a target in a film formation chamber into which the biaxially stretched PET film was continuously transported from the plasma pretreatment chamber. A reactive resistance heating method was adopted as the heating means for the vacuum deposition method. The film formation conditions were as follows.
[Aluminum oxide film formation conditions]
・Vacuum degree: 8.1×10 ^-2 Pa
Conveying speed: 400 m/min
Oxygen gas supply amount: 20,000 sccm

Subsequently, a gas barrier coating film was formed on the transparent deposition layer. Specifically, 385 g of water, 67 g of isopropyl alcohol, and 9.1 g of 0.5N hydrochloric acid were mixed and adjusted to pH 2.2, and 175 g of tetraethoxysilane as a metal alkoxide and 9.2 g of glycidoxypropyltrimethoxysilane as a silane coupling agent were mixed with the solution while cooling to 10° C. to prepare solution A.
Solution B was prepared by mixing 14.7 g of polyvinyl alcohol having a polymerization degree of 2,400 and a saponification degree of 99% or more as a water-soluble polymer, 324 g of water, and 17 g of isopropyl alcohol.
Subsequently, the liquid A and the liquid B were mixed in a weight ratio of 6.5:3.5. The solution thus obtained was used as a coating agent for a gas barrier coating film.

The above-prepared gas barrier coating film coating agent was applied to the above-prepared transparent deposition layer by spin coating. The transparent deposition layer was then heated in an oven at 180°C for 60 seconds to form a gas barrier coating film with a thickness of approximately 400 nm on the transparent deposition layer. In this way, a barrier laminate film having a biaxially stretched PET film, a transparent deposition layer, and a gas barrier coating film was obtained.

As the second biaxially stretched plastic film 50, a high-stiffness PET film was prepared in the same manner as in Example A1. As the sealant layer 70, an unstretched polypropylene film ZK500 manufactured by Toray Advanced Film Co., Ltd. was prepared in the same manner as in Example A1.

Next, in the same manner as in Example A1, the first biaxially oriented plastic film 40 provided with the transparent deposition layer, the gas barrier coating film, and the printed layer, the second biaxially oriented plastic film 50, and the sealant layer 70 were laminated in that order by dry lamination to produce the packaging material 30. The printed layer was laminated so that it faced the surface side of the second biaxially oriented plastic film 50. The overall thickness of the packaging material 30 was 95 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.8 N, the loop stiffness in the machine direction was 0.132 N, and the loop stiffness in the perpendicular direction was 0.110 N.

Next, in the same manner as in Example A1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example A1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example A1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

(Comparative Example 1)
The packaging material 30 was produced in the same manner as in Example A1, except that an unstretched polypropylene film ZK207 manufactured by Toray Advanced Film Co., Ltd. was used as the sealant layer 70. The thickness of the sealant layer 70 was 70 μm. The overall thickness of the packaging material 30 was 105 μm.

ZK207 has a high tensile modulus. 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 39,000 when the thickness is 50 μm, and 40,800 when the thickness is 60 μm. The product of the tensile modulus of ZK207 (MPa) and the thickness (μm) in the perpendicular direction is 31,500 when the thickness is 50 μm, and 33,600 when the thickness is 60 μm.

ZK207 also has low tensile elongation. 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, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 15.6 N, the loop stiffness in the machine direction was 0.182 N, and the loop stiffness in the perpendicular direction was 0.153 N.

Next, in the same manner as in Example A1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example A1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example A1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test was 7/10, and the pass rate for the room-temperature drop test was 9/10.

(Comparative Example 2)
A packaging material 30 was produced in the same manner as in Comparative Example 1, except that the biaxially stretched PET film used as the second biaxially stretched plastic film 50 in Comparative Example 1 was used as the first biaxially stretched plastic film 40, and the high-stiffness PET film used as the first biaxially stretched plastic film 40 in Comparative Example 1 was used as the second biaxially stretched plastic film 50. The overall thickness of the packaging material 30 was 105 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 15.4 N, the loop stiffness in the machine direction was 0.180 N, and the loop stiffness in the perpendicular direction was 0.155 N.

Next, in the same manner as in Example A1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example A1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example A1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test was 7/10, and the pass rate for the room-temperature drop test was 9/10.

(Comparative Example 3)
A packaging material 30 was produced in the same manner as in Example A1, except that the biaxially stretched PET film used as the second biaxially stretched plastic film 50 in Example A1 was used as the first biaxially stretched plastic film 40. The overall thickness of the packaging material 30 was 91 μm.

Then, the puncture strength of the packaging material 30 was measured in the same manner as in Example A1. As a result, the puncture strength was 13.7 N.

Next, in the same manner as in Example A1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example A1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example A1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

The layer structures and evaluation results of the packaging materials 30 of Examples A1 to A3 are shown together in Figure 20. The layer structures and evaluation results of the packaging materials 30 of Comparative Examples 1 to 3 are shown together in Figure 21. In Figures 20 and 21, the "Layer Structure" column lists the components of the packaging material 30 from top to bottom, starting with the outer layer.

As can be seen from a comparison between Examples A1 to A3 and Comparative Example 3, when the packaging material 30 contains a high stiffness polyester film, the puncture strength of the packaging material 30 can be increased compared to when the packaging material 30 does not contain a high stiffness polyester film. Specifically, the puncture strength can be increased to 14.0 N or more. In Examples A1 to A3, the puncture strength of the packaging material 30 was 16.0 N or more.

As can be seen from Examples A1 to A3, when the loop stiffness of the packaging material 30 in at least one direction was less than 0.150 N, the pass rate of the low-temperature drop test and the pass rate of the room-temperature drop test conducted after retort processing were both 10/10. In Examples A1 to A3, the loop stiffness of the packaging material 30 in both the flow direction and the vertical direction was less than 0.150 N. On the other hand, as can be seen from Comparative Examples 1 and 2, when the loop stiffness of the packaging material 30 in the flow direction and the vertical direction was 0.150 N or more, some bags 10 broke in the drop test. From these findings, it is believed that the loop stiffness of the packaging material 30 being less than 0.150 N and the packaging material 30 having appropriate flexibility contributes to improving the drop strength of the bag 10 after retort processing.

(Example B1)
As in Example A1, a high-stiffness PET film having a thickness of 16 μm was prepared as the first biaxially stretched plastic film 40. Then, as in Example A3, a transparent deposition layer and a gas barrier coating film were formed on the surface of the first biaxially stretched plastic film 40. Then, a printing layer having a thickness of 1 μm was formed on the surface of the gas barrier coating film.

As the second biaxially stretched plastic film 50, a biaxially stretched PET film with a thickness of 12 μm was prepared, as in Example A1.

In addition, a sealant film (thickness 50 μm) made of a mixed resin containing low-density polyethylene and linear low-density polyethylene and having a melting point of 105°C was prepared as the sealant layer 70.

Then, the first biaxially oriented plastic film 40, the second biaxially oriented plastic film 50, and the sealant layer 70 were laminated in this order by dry lamination to produce the packaging material 30. The printed layer was laminated so that it faced the surface side of the second biaxially oriented plastic film 50. For the first adhesive layer 45 and the second adhesive layer 55, a two-component polyurethane adhesive (base: RU-40, hardener: H-4) manufactured by Rock Paint Co., Ltd. was used. The base RU-40 is a polyester polyol. The thickness of the first adhesive layer 45 and the second adhesive layer 55 was 3 μm. The overall thickness of the packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.5 N, the loop stiffness in the machine direction was 0.111 N, and the loop stiffness in the perpendicular direction was 0.121 N.

Next, a bag 10 containing 200 g of water was produced using the packaging material 30 in the same manner as in Example A1, except that the heat sealing temperature of the heat sealing device was set to 180°C. The bag 10 containing water was then subjected to a heat sterilization treatment. Specifically, the bag 10 was subjected to a boiling treatment. The boiling temperature was 95°C, and the boiling time was 60 minutes. The drop strength of the bag 10 after the heat sterilization treatment was evaluated in the same manner as in Example A1. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

(Example B2)
A packaging material 30 was produced in the same manner as in Example B1, except that the biaxially stretched PET film used as the second biaxially stretched plastic film 50 in Example B1 was used as the first biaxially stretched plastic film 40, and the high-stiffness PET film used as the first biaxially stretched plastic film 40 in Example A1 was used as the second biaxially stretched plastic film 50. The overall thickness of the packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.4 N, the loop stiffness in the machine direction was 0.114 N, and the loop stiffness in the perpendicular direction was 0.123 N.

Next, in the same manner as in Example B1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example B1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example B1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

(Example B3)
A packaging material 30 was produced in the same manner as in Example B1, except that a transparent deposition layer and a gas barrier coating film were not provided on the high-stiffness PET film constituting the first biaxially stretched plastic film 40. The overall thickness of the packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.5 N, the loop stiffness in the machine direction was 0.111 N, and the loop stiffness in the perpendicular direction was 0.121 N.

Next, in the same manner as in Example B1, a bag 10 containing 200 g of water was produced using the packaging material 30. Also, in the same manner as in Example B1, the bag 10 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example B1, the drop strength of the bag 10 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

The layer structure and evaluation results of the packaging material 30 of Examples B1 to B3 are shown in Figure 22. In Examples B1 to B3, the packaging material 30 contained a high-stiffness polyester film, so that the puncture strength of the packaging material 30 could be increased to 14.0 N or more. In Examples B1 to B3, the puncture strength of the packaging material 30 was 16.0 N or more.

As can be seen from Examples B1 to B3, when the loop stiffness of the packaging material 30 in at least one direction was less than 0.150 N, the pass rate of the low-temperature drop test and the pass rate of the room-temperature drop test conducted after the boiling process were both 10/10. In Examples B1 to B3, the loop stiffness of the packaging material 30 in both the flow direction and the vertical direction was less than 0.150 N. From these findings, it is believed that the fact that the loop stiffness of the packaging material 30 is less than 0.150 N and that the packaging material 30 has appropriate flexibility also contributes to improving the drop strength of the bag 10 after the boiling process.

(Example C1)
A packaging material 30 was produced in the same manner as in Example B1, except that a co-extruded film having a first layer 71 and a second layer 72 shown in FIG. 12 and having easy peel properties was used as the sealant layer 70. The first layer 71 was a layer made of polyethylene and had a thickness of 45 μm. The second layer 72 was a layer containing a mixed resin of polyethylene and polypropylene and had a thickness of 5 μm. As the polyethylene, a high-density polyethylene having a density of 0.950 g/cm ³ was used. As the polypropylene, an ethylene-propylene random copolymer was used. The mass ratio of polypropylene to polyethylene in the second layer 72 was 7:3. The thickness of the sealant layer 70 was 50 μm. The thickness of the entire packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.2 N, the loop stiffness in the machine direction was 0.112 N, and the loop stiffness in the perpendicular direction was 0.115 N.

Next, the packaging material 30 was used as the lid material 114 to produce the lidded container 110 shown in Figures 18A and 18B.

First, the container body 112 was prepared. An ethylene-propylene block copolymer was used as the material for constructing the container body 112. The inner dimension R1 of the flange portion 113 of the container body 112 was 60 mm, the outer dimension R2 of the flange portion 113 was 70 mm, and the height R3 of the container body 112 was 110 mm.

Next, 200 g of water was filled into the container body 112 as the contents, and then the lid 114 made of the packaging material 30 was heat sealed to the upper surface of the flange portion 113 of the container body 112 to form a sealed portion 116. The width R4 of the sealed portion 116 was 5 mm. In this manner, multiple lidded containers 110 containing 200 g of water as shown in Figures 18A and 18B were produced.

In the process of producing the lidded container 110, a heat sealer TP-701-A manufactured by Tester Sangyo Co., Ltd. was used as the heat sealing device for forming the sealed portion 116. The heat sealing conditions were as follows.
Heat seal temperature: 180°C
Heat sealing time: 1.5 seconds Heat sealing pressure: 0.5 MPa

Then, the covered container 110 containing the water was subjected to a heat sterilization process. Specifically, the covered container 110 was subjected to a spray-type retort process. The retort temperature was 121°C, and the retort time was 30 minutes.

Next, some of the multiple lidded containers 110 after the heat sterilization treatment were stored for one week in an environment of 3° C. After that, the following steps C1 to C3 were successively carried out.
Step C1: The lidded container 110 stored in an environment at 3° C. is taken out.
Step C2: The lidded container 110, which is held so that the side surface 112b is parallel to the horizontal direction, is dropped twice repeatedly from a height of 60 cm.
Step C3: Check whether water is leaking from the lidded container 110.

The above-mentioned steps C1 to C3 were performed on 10 lidded containers 110, and the number of lidded containers 110 that did not leak water was counted, which was 10. In other words, the pass rate for the low-temperature drop test was 10/10.

In addition, some of the multiple lidded containers 110 after the heat sterilization treatment were stored for one week in an environment of 25° C. After that, the following steps D1 to D3 were continuously carried out.
Step D1: The lidded container 110 stored in an environment at 25° C. is taken out.
Step D2: The lidded container 110, which is held so that the side surface 112b faces horizontally, is dropped twice repeatedly from a height of 60 cm.
Step D3: Check whether water is leaking from the lidded container 110.

The above-mentioned steps D1 to D3 were performed on 10 lidded containers 110, and the number of lidded containers 110 that did not leak water was counted, which was 10. In other words, the room temperature drop test pass rate was 10/10.

(Example C2)
A packaging material 30 was produced in the same manner as in Example C1, except that the biaxially stretched PET film used as the second biaxially stretched plastic film 50 in Example C1 was used as the first biaxially stretched plastic film 40, and the high-stiffness PET film used as the first biaxially stretched plastic film 40 in Example C1 was used as the second biaxially stretched plastic film 50. The overall thickness of the packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.3 N, the loop stiffness in the machine direction was 0.114 N, and the loop stiffness in the perpendicular direction was 0.119 N.

Next, in the same manner as in Example C1, a lidded container 110 containing 200 g of water was produced using the packaging material 30 as the lid material 114. Also, in the same manner as in Example C1, the lidded container 110 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example C1, the drop strength of the lidded container 110 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

(Example C3)
A packaging material 30 was produced in the same manner as in Example C1, except that a transparent deposition layer and a gas barrier coating film were not provided on the high-stiffness PET film constituting the first biaxially stretched plastic film 40. The overall thickness of the packaging material 30 was 85 μm.

Next, in the same manner as in Example A1, the puncture strength and the loop stiffness in the machine direction and the perpendicular direction of the packaging material 30 were measured. As a result, the puncture strength was 16.2 N, the loop stiffness in the machine direction was 0.112 N, and the loop stiffness in the perpendicular direction was 0.115 N.

Next, in the same manner as in Example C1, a lidded container 110 containing 200 g of water was produced using the packaging material 30 as the lid material 114. Also, in the same manner as in Example C1, the lidded container 110 containing water was subjected to a heat sterilization treatment. Also, in the same manner as in Example C1, the drop strength of the lidded container 110 after the heat sterilization treatment was evaluated. As a result, the pass rate for the low-temperature drop test and the pass rate for the room-temperature drop test were both 10/10.

The layer structure and evaluation results of the packaging material 30 of Examples C1 to C3 are shown in Figure 23. In Examples C1 to C3, the packaging material 30 contained a high-stiffness polyester film, so that the puncture strength of the packaging material 30 could be increased to 14.0 N or more. In Examples C1 to C3, the puncture strength of the packaging material 30 was 16.0 N or more.

As can be seen from Examples C1 to C3, when the loop stiffness of the packaging material 30 in at least one direction was less than 0.150 N, the pass rate of the low-temperature drop test and the pass rate of the room-temperature drop test conducted on the lidded container 110 after retort processing were both 10/10. In Examples C1 to C3, the loop stiffness of the packaging material 30 in both the flow direction and the vertical direction was less than 0.150 N. From these findings, it is believed that the fact that the loop stiffness of the packaging material 30 is less than 0.150 N and that the packaging material 30 has appropriate flexibility also contributes to improving the drop strength of the lidded container 110 after retort processing.

10 Bag 11 Upper part 12 Lower part 12a Lower seal part 13 Side part 13a Side seal part 14 Surface film 15 Back film 16 Lower film 17 Storage part 18 Contents 20 Steam release mechanism 20a Steam release seal part 25 Easy-open means 26 Notch 30 Packaging material 32 Printed layer 34 Vapor deposition layer 36 Gas barrier coating film 40 First biaxially stretched plastic film 45 First adhesive layer 50 Second biaxially stretched plastic film 55 Second adhesive layer 70 Sealant layer

Claims (10)

A packaging material comprising, in order from the outer surface side to the inner surface side, at least a first biaxially oriented plastic film, a second biaxially oriented plastic film, and a sealant layer,
The first biaxially oriented plastic film and the second biaxially oriented plastic film contain polyester as a main component,
One of the first biaxially oriented plastic film and the second biaxially oriented plastic film is a high stiffness polyester film having a loop stiffness of 0.0017 N or more in at least one direction;
The packaging material has a puncture strength of 14.0 N or more. The packaging material according to claim 1, wherein the first biaxially oriented plastic film and the second biaxially oriented plastic film each contain polyethylene terephthalate as a main component. The packaging material according to any one of claims 1 to 2, comprising a deposition layer located on the surface of the first biaxially oriented plastic film or the surface of the second biaxially oriented plastic film, and a gas barrier coating film located on the deposition layer. The packaging material according to any one of claims 1 to 3, wherein the loop stiffness in one direction of the packaging material is less than 0.150 N. The packaging material according to any one of claims 1 to 4, wherein the puncture strength of the packaging material is 16.0 N or more. The packaging material according to any one of claims 1 to 5, wherein the sealant layer is a single-layer sealant film containing a propylene-ethylene block copolymer. The packaging material according to any one of claims 1 to 5, wherein the sealant layer contains polyethylene having a melting point of 100°C or higher. The packaging material according to any one of claims 1 to 5, wherein the sealant layer has a first layer mainly composed of polyethylene or polypropylene, and a second layer located on the inner side of the first layer and containing a mixed resin of polyethylene and polypropylene. A retort pouch comprising the packaging material according to any one of claims 1 to 8. A microwave pouch having a storage portion,
A packaging material according to any one of claims 1 to 8;
a seal portion joining inner surfaces of the packaging material together, the seal portion including a steam release seal portion that peels off due to an increase in pressure in the containing portion.