JP7836639B2 - Packaging materials and packaging products comprising packaging materials - Google Patents

Description

This invention relates to packaging materials and packaged products comprising these packaging materials.

Conventionally, various packaging materials have been developed and proposed for packaging products that fill and package various items such as food and beverages, pharmaceuticals, chemicals, cosmetics, hygiene products, daily necessities, and others. These packaging materials include a plastic film as a base material. For example, Patent Document 1 discloses an example in which the packaging material comprises a base material containing polyethylene terephthalate and a base material containing nylon.

Japanese Patent Application Publication No. 8-242825

Nylon possesses high strength, but it also has the characteristic of easily absorbing moisture. Therefore, when a base material contains nylon, the moisture absorbed by the nylon may cause clouding of the base material.

This invention was made with these points in mind, and aims to provide a packaging material that is excellent in strength and less prone to clouding.

The present invention relates to a packaging material comprising a base material, a metal foil, and a sealant layer, in order from the outer surface to the inner surface,
The aforementioned substrate has only one biaxially oriented plastic film containing polyester as the main component,
The packaging material has a Young's modulus of 3800 MPa or more in one direction and in a direction perpendicular to the said one direction.

The puncture strength of the packaging material according to the present invention may be 15.0 N or higher.

In the packaging material according to the present invention, the Young's modulus of the packaging material in the aforementioned one direction may be 4000 MPa or more.

In the packaging material according to the present invention, the thickness of the biaxially oriented plastic film may be 14 μm or more and 30 μm or less.

In the packaging material according to the present invention, the biaxially oriented plastic film may contain 90% by mass or more of polyethylene terephthalate.

In the packaging material according to the present invention, the sealant layer may contain polypropylene as its main component.

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 present invention relates to a packaged product comprising the packaging material described above.

According to the present invention, it is possible to provide a packaging material that is excellent in strength and less prone to clouding.

This is a front view showing a bag according to an embodiment of the present invention. This is a cross-sectional view showing an example of the layer structure of the packaging materials that make up the bag. This is a plan view showing an example of a loop stiffness measuring instrument. Figure 3 is a cross-sectional view of the loop stiffness measuring instrument along line IV-IV. This figure shows an example of a method for preparing test specimens used in loop stiffness measuring instruments. This is a diagram illustrating the process of attaching a test specimen to a loop stiffness measuring instrument. This is a diagram illustrating the process of forming a loop portion on a test specimen. This is a diagram illustrating the process of applying a load to the loop portion of the test specimen. This is a diagram illustrating the process of applying a load to the loop portion of the test specimen. This figure shows an example of the layer structure of a sealant layer. This figure shows an example of a method for filling a bag with contents. This is a front view showing one modified version of the bag. This is a longitudinal cross-sectional view showing an example of a packaged product including packaging materials. This is a plan view showing an example of a packaged product including packaging materials. This is a perspective view showing an example of a packaged product, including the packaging materials. This figure shows an example of a method for measuring puncture strength. This figure shows the evaluation results of the examples. This figure shows the evaluation results of the comparative example.

An embodiment of the present invention will be described with reference to Figures 1 to 11. Note that, for the sake of illustration and ease of understanding, the scale and aspect ratios of the drawings attached to this specification have been appropriately modified and exaggerated from those of the actual objects.

Furthermore, terms such as "parallel," "orthogonal," and "identical," as well as values for length and angle, used in this specification to specify shapes, geometric conditions, and their degrees, shall not be strictly interpreted, but rather shall be interpreted to include a range that allows for the expectation of similar functionality.

Figure 1 is a front view showing a bag 10 according to this embodiment. The bag 10 includes a storage section 17 for containing contents. Note that Figure 1 shows the bag 10 before contents are placed inside. The configuration of the bag 10 will be described below.

In this embodiment, the bag 10 is a so-called flat pouch made by joining the front film and the back film of the bag 10. The bag 10 includes an upper part 11, a lower part 12, and a pair of side parts 13, and has a substantially rectangular outline in the front view. The names such as "upper part,""lowerpart," and "side parts," as well as terms such as "upper" and "lower," merely describe the relative position and direction of the bag 10 and its components with respect to the state in which the opening for filling the contents is located at the top. The orientation of the bag 10 during transport and use is not limited by the names and terms used herein.

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. In this embodiment, the intended use of the bag 10 is that the consumer opens the bag 10 by tearing it along the first direction D1.

As shown in Figure 1, the bag 10 comprises a surface film 14 that constitutes the front surface and a back surface film 15 that constitutes the back surface.

Furthermore, the terms "front film" and "back film" mentioned above merely describe the division of each film according to its positional relationship, and the method of providing the film when manufacturing the bag 10 is not limited by these terms. For example, the bag 10 may be manufactured using a single film in which the front film 14 and the back film 15 are connected, or it may be manufactured using a total of two films: one front film 14 and one back film 15.

The surface film 14 and the back film 15 are joined together on their inner surfaces by a sealing portion. In the front view of the bag 10, such as in Figure 1, hatching is applied to the sealing portion.

As shown in Figure 1, the sealing portion has an outer edge sealing portion that extends along the outer edge of the bag 10. The outer edge sealing portion includes a lower sealing portion 12a extending along the lower part 12, and a pair of side sealing portions 13a extending along the pair of side portions 13. In the bag 10 before contents are placed inside, as shown in Figure 1, the upper part 11 of the bag 10 is an opening 11b. After contents are placed inside the bag 10, the upper sealing portion is formed and the bag 10 is sealed by joining the inner surface of the surface film 14 and the inner surface of the backing film 15 at the upper part 11.

The lower sealing portion 12a, the side sealing portion 13a, and the upper sealing portion are sealing portions formed by joining the inner surface of the surface film 14 to the inner surface of the backing film 15.

The method for forming the seal is not particularly limited, as long as the opposing films can be joined together to seal the bag 10. For example, the seal may be formed by melting the inner surfaces of the films by heating and welding them together, i.e., by heat sealing. Alternatively, the seal may be formed by bonding the inner surfaces of the opposing films together using an adhesive.

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

Furthermore, although not shown in the figures, the easy-open means 25 may include cuts or groups of scratches formed in the areas of the surface film 14 and back film 15 where the seal portion is formed. The group of scratches may, for example, include a plurality of through holes formed to penetrate the surface film 14 and/or back film 15. Alternatively, the group of scratches may include a plurality of holes formed on the outer surface of the surface film 14 and/or back film 15 without penetrating the surface film 14 and/or back film 15.

Layer structure of the surface film and back film Next, the layer structure of the surface film 14 and back film 15 will be described. Figure 2 is a cross-sectional view showing an example of the layer structure of the packaging material 30 that makes up the surface film 14 and back film 15.

As shown in Figure 2, the packaging material 30 comprises a base material 35, a first adhesive layer 45, a metal foil 50, a second adhesive layer 55, and a sealant layer 70 in this order. The base material 35 has only one biaxially oriented plastic film 40. The base material 35 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 side of the housing 17. The thickness of the packaging material 30 is, for example, 60 μm or more, may be 70 μm or more, 80 μm or more, or 90 μm or more. The thickness of the packaging material 210 may be 130 μm or less, 120 μm or less, or 110 μm or less.

The film constituting the packaging material 30, such as the biaxially oriented plastic film 40, and the packaging material 30 itself, have a flow direction and a perpendicular direction. If the sealant layer 70 is composed of a sealant film, the sealant layer 70 also has a flow direction and a perpendicular direction. The flow direction is the direction in which the film flows during film formation, and is known as the MD (Machine Direction). The perpendicular direction is the direction perpendicular to the flow direction, and is known as the TD (Transverse Direction). In the bag 10 shown in Figure 1, the direction in which the upper part 11 and lower part 12 extend is the flow direction, and the direction in which the side part 13 extends is the perpendicular direction.

The packaging material 30 in this embodiment is configured to have excellent puncture resistance. This prevents the bag 10 from tearing when a sharp object with a pointed tip comes into contact with it. In other words, the packaging product, such as the bag 10, made from the packaging material 30 can have puncture resistance.

The following describes each layer of the packaging material 30 in detail.

(Biaxially oriented plastic film)
The biaxially oriented plastic film 40 is a biaxially oriented film stretched in two predetermined directions. A biaxially oriented plastic film is a plastic film that has been intentionally stretched to improve the mechanical strength of the plastic film. The stretching direction of the biaxially oriented plastic film 40 is not particularly limited. For example, the biaxially oriented plastic film 40 may be stretched in the direction in which the side portion 13 stretches and in a direction perpendicular to the direction in which the side portion 13 stretches. Also, the stretching directions of each biaxially oriented plastic film 40 may be the same or different. The stretching ratio of each biaxially oriented plastic film 40 is, for example, 1.05 times or more.

In this embodiment, we propose using a biaxially oriented plastic film 40 that has a loop stiffness of 0.0017 N or more in at least one direction and contains polyester as the main component. In the following description, a biaxially oriented plastic film that has a loop stiffness of 0.0017 N or more in at least one direction and contains polyester as the main component will also be 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 flow direction (MD) or the perpendicular direction (TD). The high-stiffness polyester film may also have a loop stiffness of 0.0017 N or more in both the flow direction (MD) and the perpendicular direction (TD). By including the high-stiffness polyester film in the packaging material 30, the packaging material 30 can have excellent puncture strength. In this application, "main component" refers to the component that accounts for 51% by mass. The high-stiffness polyester film does not contain polyamide.
Preferably, the polyester is an aromatic polyester mainly composed of an aromatic polyester comprising 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, polyesters include polyethylene terephthalate (hereinafter also referred to as PET) and polybutylene terephthalate (hereinafter also referred to as PBT). Examples of high-stiffness polyester films include high-stiffness PET films containing 51% by mass or more of PET as the main component, and high-stiffness PBT films containing 51% by mass or more of PBT as the main component. The thickness of the high-stiffness polyester film is preferably 5 μm or more, more preferably 7 μm or more. Furthermore, 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 represents the rigidity of a film, such as a biaxially oriented plastic film. The measurement method for loop stiffness will be explained below with reference to Figures 3 to 9. The measurement method described below can be used not only for single-layer films such as biaxially oriented plastic films, but also for multi-layer films such as vapor-deposited films and laminated films. A vapor-deposited film is a film containing a single-layer film, such as a biaxially oriented plastic film, and a vapor-deposited layer formed on the single-layer film. A laminated film is a film containing multiple laminated films, such as the packaging material 30.

Figure 3 is a plan view showing the test specimen 80 and the loop stiffness measuring instrument 85, and Figure 4 is a cross-sectional view of the test specimen 80 and the loop stiffness measuring instrument 85 along line IV-IV in Figure 3. The test specimen 80 is a rectangular film having a long side and a short side. In this application, the length L1 of the long side of the test specimen 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, the No. 581 Loop Stiffness Tester (registered trademark) LOOP STIFFNESS TESTER DA type manufactured by Toyo Seiki Co., Ltd. can be used. The length L1 of the long side of the test specimen 80 is adjustable as long as the test specimen 80 can be gripped by the pair of chuck parts 86 described later.

The loop stiffness measuring instrument 85 includes a pair of chuck portions 86 for gripping a pair of long-side ends of the test specimen 80, and a support member 87 for supporting the chuck portions 86. The chuck portions 86 include a first chuck 861 and a second chuck 862. In the state shown in Figures 3 and 4, the test specimen 80 is positioned on the pair of first chucks 861, and the second chuck 862 has not yet gripped the test specimen 80 between itself and the first chuck 861. As will be described later, during measurement, the test specimen 80 is gripped between the first chuck 861 and the second chuck 862 of the chuck portion 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-deposited film, or a laminated film, is available before it is processed into a packaging product, the test specimen 80 may be prepared by cutting the film to be measured. Alternatively, the test specimen 80 may be prepared by cutting a packaging product made from the packaging material 30, such as a bag. Figure 5 shows an example of a method for preparing the test specimen 80 by cutting the surface film 14 or back film 15 of the bag 10. When measuring the loop stiffness of the packaging material 30 in the flow direction, the test specimen is prepared by cutting the surface film 14 or back film 15 of the bag 10 so that the long side of the test specimen aligns with the flow direction, as indicated by reference numeral 80A in Figure 5. When measuring the loop stiffness of the packaging material 30 in the vertical direction, the test specimen is prepared by cutting the surface film 14 or back film 15 of the bag 10 so that the long side of the test specimen aligns with the vertical direction, as indicated by reference numeral 80B in Figure 5.

A method for measuring the loop stiffness of a test specimen 80 using a loop stiffness measuring instrument 85 will be described. First, as shown in Figures 3 and 4, the test specimen 80 is placed on the first chuck 861 of a pair of chuck portions 86 arranged with a gap L3 between them. In this application, the gap L3 is set so that the length of the loop portion 81 (hereinafter also referred to as the loop length), which will be described later, is 60 mm. The test specimen 80 includes an inner surface 80x located on the side of the first chuck 861 and an outer surface 80y located on the opposite side of the inner surface 80x. When the test specimen 80 is made of packaging material 30, the inner surface 80x and outer surface 80y of the test specimen 80 coincide with the inner surface 30x and outer surface 30y of the packaging material 30. When the loop portion 81, which will be described later, is formed on the test specimen 80, the inner surface 80x is located inside the loop portion 81, and the outer surface 80y is located outside the loop portion 81. Next, as shown in Figure 6, the second chuck 862 is positioned on the test piece 80 so as to grip the long-side end of the test piece 80 between it and the first chuck 861.

Next, as shown in Figure 7, at least one of the pair of chuck portions 86 is slid on the support member 87 in a direction that reduces the distance between the pair of chuck portions 86. This allows a loop portion 81 to be formed on the test piece 80. The test piece 80 shown in Figure 7 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 the parts of the test piece 80 that are gripped by the pair of chuck portions 86. The pair of intermediate portions 82 are the parts of the test piece 80 located between the loop portion 81 and the pair of intermediate portions 82. As shown in Figure 7, 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 with 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 the point P1 where the loop portion 81 side surface of one second chuck 862 intersects with the test piece 80, and the point P2 where the loop portion 81 side surface of the other second chuck 862 intersects with the test piece 80. The aforementioned interval L3, ignoring the thickness of the test piece 80, is the length of the loop portion 81 plus 2 × t. t is the thickness of the second chuck 862 of the chuck portion 86.

Subsequently, as shown in Figure 8, the posture of the chuck portion 86 is adjusted so that the protrusion 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 faces horizontally. In the example shown in Figure 8, the protrusion direction Y of the loop portion 81 coincides with the thickness direction of the chuck portion. A load cell 88 is prepared at a distance Z1 from the second chuck 862 in the protrusion 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 toward the loop portion 81 of the test piece 80 at a speed V by a distance Z2 as shown in Figure 8. The distance Z2 is set so that, as shown in Figures 8 and 9, the load cell 88 contacts the loop portion 81, and then the load cell 88 pushes the loop portion 81 toward the chuck portion 86. 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 86, when the load cell 88 is pushing the loop portion 81 toward the chuck portion 86, is 10 mm. The speed V used to move the load cell 88 was set to 3.3 mm/second.

Next, as shown in Figure 9, the load cell 88 is moved a distance Z2 toward the chuck portion 86. While the load cell 88 is pressing against the loop portion 81 of the test piece 80, the load value applied from the loop portion 81 to the load cell 88 stabilizes, and then the load value is recorded. The load value obtained in this way is adopted as the loop stiffness of the film constituting the test piece 80. In this application, unless otherwise specified, the environment during loop stiffness measurement is a temperature of 23°C and a relative humidity of 50%.

By using a high-stiffness film having a loop stiffness of 0.0017 N or more in at least one direction as the biaxially oriented plastic film 40, the puncture strength of the biaxially oriented plastic film 40 can be increased. This allows the puncture strength of the packaging material 30 comprising the biaxially oriented plastic film 40 to be, for example, 15.0 N or more, more preferably 16.0 N or more, and even more preferably 17.0 N or more.

Examples of high-stiffness films include high-stiffness PET films containing 51% or more by mass of PET. The PET content in the high-stiffness PET film may be 80% or more by mass, 90% or more by mass, or 95% or more by mass. The thickness of the high-stiffness film is preferably 5 μm or more, more preferably 7 μm or more. The thickness may also be 10 μm or more, or 14 μm or more. Furthermore, the thickness of the high-stiffness film is preferably 30 μm or less, but may also be 25 μm or less, or 20 μm or less.

The desirable mechanical properties of high-stiffness polyester films will be further explained.
The puncture strength of the high-stiffness polyester film is preferably 10 N or higher, and more preferably 11 N or higher.

The tensile strength of the high-stiffness polyester film in at least one direction is preferably 250 MPa or more, and more preferably 280 MPa or more. For example, the tensile strength of the high-stiffness polyester film in the flow direction is preferably 250 MPa or more, and more preferably 280 MPa or more. Also, the tensile strength of the high-stiffness polyester film in the vertical direction is preferably 250 MPa or more, and 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, and more preferably 120% or less. For example, the tensile elongation of the high-stiffness polyester film in the flow direction is preferably 130% or less, and more preferably 120% or less. Also, the tensile elongation of the high-stiffness polyester film in the vertical direction is preferably 120% or less, and more preferably 110% or less.
Preferably, in at least one direction, the value obtained by dividing the tensile strength of the high-stiffness polyester film by its tensile elongation is 2.0 [MPa/%] or more. For example, the value obtained by dividing the tensile strength of the high-stiffness polyester film by its tensile elongation in the vertical direction (TD) is preferably 2.0 [MPa/%] or more, and more preferably 2.2 [MPa/%] or more. The value obtained by dividing the tensile strength of the high-stiffness polyester film by its tensile elongation in the flow direction (MD) is preferably 1.8 [MPa/%] or more, and more preferably 2.0 [MPa/%] or more.

Tensile strength and tensile elongation can be measured in accordance with JIS K7127. A tensile testing machine STA-1150 manufactured by Orientec Co., Ltd. can be used as the measuring instrument. A rectangular film cut from high-stiffness polyester film with a width of 15 mm and a length of 150 mm can be used as the test specimen. The initial distance between the pair of chucks holding the test specimen is 100 mm, and the tensile speed is 300 mm/min. The length of the test specimen is adjustable as long as it can be gripped by the pair of chucks. Unless otherwise specified in this application, the environment for measuring 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 an Orientec RTC-1310A tensile testing machine is used as the measuring instrument, and the initial distance between the pair of chucks holding the test specimen is 50 mm. When measuring the tensile strength and tensile elongation of the packaging material 30, a test specimen can be prepared by cutting the surface film 14 or back film 15 of the bag 10 so that the long side direction of the test specimen coincides with the flow direction or perpendicular direction, similar to the measurement of loop stiffness shown in Figure 5.

The thermal shrinkage rate of the high-stiffness polyester film in at least one direction is preferably 0.7% or less, and more preferably 0.5% or less. For example, the thermal shrinkage rate of the high-stiffness polyester film in the flow direction is preferably 0.7% or less, and more preferably 0.5% or less. The thermal shrinkage rate of the high-stiffness polyester film in the perpendicular direction is preferably 0.7% or less, and more preferably 0.5% or less. The heating temperature when measuring the thermal shrinkage rate 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 higher, and more preferably 4.5 MPa or higher. For example, the Young's modulus of the high-stiffness polyester film in the flow direction is preferably 4.0 GPa or higher, and more preferably 4.5 MPa or higher. The Young's modulus of the high-stiffness polyester film in the perpendicular direction is preferably 4.0 GPa or higher, and more preferably 4.5 GPa or higher.

Young's modulus can be measured in accordance with JIS K7127, similar to tensile strength and tensile elongation. A tensile testing machine STA-1150 manufactured by Orientec Co., Ltd. can be used as the measuring instrument. A rectangular film cut from high-stiffness polyester film, 15 mm wide and 150 mm long, can be used as the test specimen. The initial distance between the pair of chucks holding the test specimen is 100 mm, and the tensile speed is 300 mm/min. The length of the test specimen is adjustable as long as it can be gripped by the pair of chucks. Unless otherwise specified in this application, the environment for measuring 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 an Orientec RTC-1310A tensile testing machine is used as the measuring instrument, and the initial distance between the pair of chucks holding the test specimen is 50 mm. When measuring the Young's modulus of the packaging material 30, a test specimen can be prepared by cutting the surface film 14 or back film 15 of the bag 10 so that the long side direction of the test specimen coincides with the flow direction or perpendicular direction, similar to the measurement of loop stiffness shown in Figure 7.

In the manufacturing process of high-stiffness polyester film, for example, first, a plastic film obtained by melting and molding polyester is stretched to 3 to 4.5 times its original size in the flow direction and perpendicular direction at 90°C to 145°C, respectively, in a first stretching step. Next, the plastic film is stretched to 1.1 to 3.0 times its original size in the flow direction and perpendicular direction at 100°C to 145°C, respectively, in a second stretching step. Afterward, heat setting is performed at a temperature of 190°C to 220°C. Subsequently, a relaxation treatment (a process to reduce the film width) of approximately 0.2% to 2.5% is performed in the flow direction and perpendicular direction at a temperature of 100°C to 190°C. By adjusting the stretching ratio, stretching temperature, heat setting temperature, and relaxation treatment rate in these steps, a high-stiffness polyester film with the above-mentioned mechanical properties can be obtained.

According to this embodiment, by including a high-stiffness polyester film in the packaging material 30, excellent puncture resistance can be imparted to the packaging material 30 and the packaging product such as the bag 10 composed of the packaging material 30. This prevents, for example, the bag 10 from tearing when it comes into contact with a sharp object with a pointed tip. The puncture resistance of the packaging material 30 is preferably 15.0 N or higher, preferably 16.0 N or higher, and more preferably 17.0 N or higher. The method for measuring puncture resistance will be described in the examples below.

Furthermore, according to this embodiment, the Young's modulus of the packaging material 30 can be increased by including a high-stiffness polyester film in the packaging material 30. The Young's modulus of the packaging material 30 in both the unidirectional and unidirectional directions may be, for example, 3800 MPa or more, 3900 MPa or more, 4000 MPa or more, or 4100 MPa or more. For example, the Young's modulus of the packaging material 30 in the flow direction (MD) may be, for example, 3800 MPa or more, 3900 MPa or more, 4000 MPa or more, or 4100 MPa or more. Also, the Young's modulus of the packaging material 30 in the perpendicular direction (TD), which is perpendicular to the flow direction (MD), may be, for example, 3800 MPa or more, 3900 MPa or more, 4000 MPa or more, 4100 MPa or more, 4200 MPa or more, or 4300 MPa or more. A high Young's modulus of the packaging material 30 makes it less prone to stretching. Therefore, the processing accuracy of the packaging material 30 during the manufacturing process of packaging products such as bags 10 is improved. Furthermore, when using the packaging material 30 to manufacture a gusset-type bag 10, which is configured to be self-supporting as described later, the self-supporting ability of the bag 10 is improved. The Young's modulus of the packaging material 30 in the vertical direction (TD) may be higher than the Young's modulus of the packaging material 30 in the flow direction (MD).

In this embodiment, the loop stiffness of the packaging material 30 in at least one direction is, for example, 0.090 N or more, may be 0.100 N or more, may be 0.110 N or more, may be 0.120 N or more, or may be 0.130 N or more. For example, the loop stiffness of the packaging material 30 in the flow direction (MD) is, for example, 0.090 N or more, may be 0.100 N or more, may be 0.110 N or more, may be 0.120 N or more, or may be 0.130 N or more. Similarly, the loop stiffness of the packaging material 30 in the vertical direction (TD) is, for example, 0.090 N or more, may be 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 high, the packaging material 30 may be prone to tearing or other damage when the packaged product made of the packaging material 30 is dropped. Considering this point, the loop stiffness of the packaging material 30 in at least one direction may be less than 0.150 N or less than 0.140 N. For example, the loop stiffness of the packaging material 30 in the flow direction (MD) may be less than 0.150 N or less than 0.140 N. Similarly, 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.

(First adhesive layer)
The first adhesive layer 45 contains an adhesive for bonding a biaxially oriented plastic film 40 and a metal foil 50 by a dry lamination method. The adhesive constituting the first adhesive layer 45 is produced from an adhesive composition made by mixing a first composition containing a main agent and a solvent with a second composition containing a curing agent and a solvent. Specifically, the adhesive includes a cured product produced by the reaction of the main agent and the solvent in the adhesive composition.

Examples of adhesives include polyurethane. Polyurethane is a cured product produced by the reaction of a polyol as the main component with an isocyanate compound as the curing agent. Examples of polyurethane include polyether polyurethane and polyester polyurethane. Polyether polyurethane is a cured product produced by the reaction of a polyether polyol as the main component with an isocyanate compound as the curing agent. Polyester polyurethane is a cured product produced by the reaction of a polyester polyol as the main component with an isocyanate compound as the curing agent.

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

The material constituting the first adhesive layer 45 preferably has a higher thermal conductivity than the materials constituting the biaxially oriented plastic film 40, the metal foil 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 higher, and more preferably 3.0 W/m·K or higher. 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 containment section 17 is easily diffused in the planar direction of the packaging material 30 as it is transferred from the inner surface 30x to the outer surface 30y. This improves the heat dissipation of the packaging material 30, thereby suppressing the temperature rise of the packaging material 30. This prevents 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, more preferably 3 μm or more. Furthermore, the thickness of the first adhesive layer 45 is preferably 6 μm or less, more preferably 5 μm or less. By making the thickness of the first adhesive layer 45 3 μm or more, heat diffusion in the planar direction of the packaging material 30 becomes more easily achieved.

(Metal foil)
The metal foil 50 is located between the biaxially oriented plastic film 40 and the sealant layer 70. The metal foil 50 mainly contains a metal material. By including the metal foil 50 in the packaging material 30, the packaging material 30 can be given gas barrier properties that prevent the transmission of oxygen gas and water vapor, and light-shielding properties that prevent the transmission of visible light and ultraviolet rays.

Examples of the metallic materials constituting the metal foil 50 include aluminum. The aluminum content in the metal foil 50 may be, for example, 90% by mass or more, 95% by mass or more, or 98% by mass or more.

The thickness of the metal foil 50 is, for example, 5 μm or more, but may also be 6.5 μm or more, 8 μm or more, or 10 μm or more. Furthermore, the thickness of the metal foil 50 may be 20 μm or less, or 15 μm or less.

(Second adhesive layer)
When the sealant layer 70 is made of a sealant film, the second adhesive layer 55 includes an adhesive for bonding the metal foil 50 and the sealant film by a dry lamination method. Examples of adhesives for the second adhesive layer 55 include polyurethane, as in the case of the first adhesive layer 45. In addition to the configuration, materials, and properties described below, the same configuration, materials, and properties as those of the first adhesive layer 45 can be adopted for the second adhesive layer 55.

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 biaxially oriented plastic film 40, the metal foil 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 higher, and more preferably 3 W/m·K or higher.

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

Incidentally, as mentioned above, the isocyanate compounds that constitute the curing agent of the adhesive include aromatic isocyanate compounds and aliphatic isocyanate compounds. Of these, aromatic isocyanate compounds may leach components unsuitable for food applications under high-temperature environments such as heat sterilization. Furthermore, the second adhesive layer 55 is in contact with the sealant film. Therefore, if the second adhesive layer 55 contains an aromatic isocyanate compound, components leached from the aromatic isocyanate compound may adhere to the contents contained in the containment section 17 that is in contact with the sealant film.

Considering these issues, it is preferable to use a cured product formed by the reaction of a polyol as the main component and an aliphatic isocyanate compound as the curing agent as the adhesive constituting the second adhesive layer 55. This prevents components unsuitable for food use, which originate from the second adhesive layer 55, from adhering to the contents.

(Sealant layer)
Next, the sealant layer 70 will be described. The material constituting the sealant layer 70 can be one or more resins selected from polyethylene such as low-density polyethylene and linear low-density polyethylene, and polypropylene. The sealant layer 70 may be a single layer or a multi-layer layer. The sealant layer 70 may also be composed of an unstretched sealant film. Note that "unstretched" is a concept that includes not only films that are not stretched at all, but also films that are 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 the extent necessary for transport, but has not been intentionally stretched. The preferred mechanical properties of the sealant film will be explained further.
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 flow direction and the 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 flow 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, similar to the case of high-stiffness polyester film. A tensile testing machine STA-1150 manufactured by Orientec Co., Ltd. can be used as the measuring instrument. A rectangular piece of film, 15 mm wide and 150 mm long, can be used as the test specimen. The initial distance between the pair of chucks holding the test specimen is 100 mm, and the tensile speed is 300 mm/min.

The bag 10, made of packaging material 30, may be subjected to sterilization treatments at high temperatures, such as boiling or retorting. The sealant layer 70 preferably has heat resistance to withstand these high-temperature treatments. Retorting is a process in which the contents are filled into the bag 10, the bag 10 is sealed, and then the bag 10 is heated under pressure using steam or hot water. The temperature for retorting is, for example, 120°C or higher. Boiling is a process in which the contents are filled into the bag 10, the bag 10 is sealed, and then the bag 10 is heated in a water bath under atmospheric pressure. The temperature for boiling 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 perform retort processing of the bag 10 at a higher temperature, thereby shortening the time required for retort processing. Note that 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 film 40.

From the perspective of retort processing, a material primarily composed of propylene can be used as the material constituting the sealant layer 70. Here, a material "primarily composed of" propylene means a material with a propylene content of 90% by mass or more. Specific examples of materials primarily composed of propylene include polypropylene such as propylene-ethylene block copolymer, propylene-ethylene random copolymer, and homopolypropylene, or mixtures of polypropylene and polyethylene. Here, "propylene-ethylene block copolymer" refers to a material having the structural formula shown in formula (I) below. "Propylene-ethylene random copolymer" refers to a material having the structural formula shown in formula (II) below. "Homopolypropylene" refers to a material having the structural formula shown in formula (III) below.

When using a material primarily composed of propylene, and a mixture of polypropylene and polyethylene, the material may have a sea-island structure. Here, "sea-island structure" refers to a structure in which polyethylene is discontinuously dispersed within continuous regions of polypropylene.

From the perspective of boiling treatment, examples of materials constituting the sealant layer 70 include polyethylene, polypropylene, or combinations thereof. Examples of polyethylene include medium-density polyethylene, linear low-density polyethylene, or combinations thereof. For example, it is also possible to use the materials listed above as materials constituting the sealant layer 70 from the perspective of retort treatment. The materials constituting the sealant layer 70 have a melting point of, for example, 100°C or higher, more preferably 105°C or higher, more preferably 110°C or higher, and even more preferably 115°C or higher. When the sealant layer 70 contains polyethylene as the main component, a melting point of 100°C or higher can be achieved, for example, when the density of polyethylene is 0.920 g/ ^cm³ or higher. Furthermore, specific examples of sealant films for constituting a sealant layer 70 having a melting point of 100°C or higher include TUX-HC manufactured by Mitsui Chemicals Tohcello, L6101 manufactured by Toyobo, and LS700C manufactured by Idemitsu Unitech. Specific examples of sealant films for forming a sealant layer 70 having a melting point of 105°C or higher include NB-1 manufactured by Tamapoly. Specific examples of sealant films for forming a sealant layer 70 having a melting point of 110°C or higher include LS760C manufactured by Idemitsu Unitech and TUX-HZ manufactured by Mitsui Chemicals Tohcello. The polyethylene content in the sealant layer 70 is, for example, 70% by mass or more, and may be 80% by mass or more.

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 mainly composed of 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 tearing due to impact during a fall. Furthermore, the puncture resistance of the packaging material 30 can be improved.

The propylene-ethylene block copolymer includes, for example, a "sea" component made of polypropylene and an "island" component made of ethylene-propylene copolymer rubber. The sea component can contribute to improving the blocking resistance, heat resistance, rigidity, and seal strength of the propylene-ethylene block copolymer. The island component can 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 a propylene-ethylene block copolymer, the mass ratio of the polypropylene component (sea component) is higher than the mass ratio of the ethylene-propylene copolymer rubber component (island component). For example, in a propylene-ethylene block copolymer, the mass ratio of the polypropylene component (sea component) is at least 51% by mass, preferably 60% by mass or more, and more preferably 70% by mass or more.

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

Low-density polyethylene is polyethylene with a density of 0.910 g/ ^cm³ or more and 0.925 g/ ^cm³ or less. Medium-density polyethylene is polyethylene with a density of 0.926 g/ ^cm³ or more and 0.940 g/ ^cm³ or less. High-density polyethylene is polyethylene with a density of 0.941 g/ ^cm³ or more and 0.965 g/ ^cm³ or less. Low-density polyethylene can be 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 can be obtained, for example, by polymerizing ethylene at a medium or low pressure of 1 atmosphere or more and less than 1000 atmospheres.

Medium-density polyethylene and high-density polyethylene may partially contain copolymers of ethylene and α-olefins. Furthermore, even when polymerizing ethylene at medium or low pressure, medium-density or low-density polyethylene can be produced if it contains copolymers of ethylene and α-olefins. Such polyethylene is referred to as the linear low-density polyethylene described above. Linear low-density polyethylene is obtained by copolymerizing a linear polymer obtained by polymerizing ethylene at medium or low pressure with α-olefins to introduce short-chain branching. Examples of α-olefins include 1-butene ( _C4 ), 1-hexene ( _C6 ), 4-methylpentene ( _C6 ), and 1-octene ( _C8 ). The density of linear low-density polyethylene is, for example, 0.915 g/ ^cm³ or more and 0.945 g/ ^cm³ or less.

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

_R1 and _R2 are both H (hydrogen atom) or alkyl groups such as _{CH3 and C2H5} . Also, j and k are both integers of 1 or greater. Furthermore, j is greater than k. That is, in the α-olefin copolymer shown in formula (IV), the structure on the left including _R1 is the base. _R1 is, for example, H, _{and R2} is _, for example, _C2H5 .

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

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

Furthermore, the sealant layer 70 may further contain a thermoplastic elastomer. Using a thermoplastic elastomer can further enhance the impact resistance and puncture resistance of the sealant layer 70.

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 composed of at least one vinyl aromatic compound and a polymer block B mainly composed of at least one hydrogenated conjugated diene compound. Alternatively, the thermoplastic elastomer may be an ethylene-α-olefin elastomer. The ethylene-α-olefin elastomer is a low-crystallinity or amorphous copolymer elastomer, a random copolymer of 50-90% by mass of ethylene as the main component and α-olefin as the copolymer monomer.

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

One method for producing propylene-ethylene block copolymers involves polymerizing the raw materials, such as propylene and ethylene, using a catalyst. Suitable catalysts include Ziegler-Natta type catalysts and metallocene catalysts.

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

The following describes the preferred mechanical properties of a sealant film when the sealant layer 70 consists of a single layer sealant film containing a propylene-ethylene block copolymer.
The tensile elongation of the sealant film in the flow direction (MD) at 25°C is preferably 600% or more and 1300% or less. Furthermore, the product of the tensile elongation (%) of the sealant film in the flow direction (MD) and the thickness of the sealant film (μm) is preferably 35,000 or more and 80,000 or less. Furthermore, the tensile elongation of the sealant film in the vertical direction (TD) at 25°C is preferably 700% or more and 1400% or less. Furthermore, the product of the tensile elongation (%) of the sealant film in the vertical direction (TD) and the thickness of the sealant film (μm) is preferably 40,000 or more and 85,000 or less.
The tensile modulus of the sealant film in the flow direction (MD) at 25°C is preferably 400 MPa or more and 1100 MPa or less. Furthermore, the product of the tensile modulus (MPa) of the sealant film in the flow direction (MD) and the thickness of the sealant film (μm) is preferably 30000 or more and 55000 or less. Furthermore, 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. Furthermore, the product of the tensile modulus (MPa) of the sealant film in the perpendicular direction (TD) and the thickness of the sealant film (μm) is preferably 20000 or more and 45000 or more.
In the bag 10 shown in Figure 1, the first direction D1 corresponds to the flow direction (MD) of the sealant film. The second direction D2 corresponds to the perpendicular direction (TD) of the sealant film.

The tensile modulus and tensile elongation can be measured in accordance with JIS K7127. A tensile testing machine STA-1150 manufactured by Orientec Co., Ltd. can be used as the measuring instrument. In the bag 10 shown in Figure 1, the direction in which the upper part 11 and lower part 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 part 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 constructed such that the direction in which the upper part 11 and lower part 12 extend is the perpendicular direction of the film, and the direction in which the side part 13 extends is the flow direction of the film.

There are mainly two types of single-layer sealant films containing propylene-ethylene block copolymer.
The first type is an unstretched polypropylene film, such as ZK500, manufactured by Toray Film Processing Co., Ltd., which has high tensile elongation and impact resistance. Preferably, the first type of sealant film also has the characteristic of having low hot seal strength. This makes it possible to suppress the internal pressure of the containment section 17 from becoming excessive when the bag 10 is heated, and to suppress damage to the packaging material 30.
The second type is one with a high tensile modulus, such as the unstretched polypropylene film ZK207 manufactured by Toray Film Processing Co., Ltd. By using the second type of sealant film, the tearability when the consumer tears the bag 10 along the first direction D1 to open the bag 10 can be improved.

The product of the tensile elongation (%) of the first type of sealant film in the flow direction (MD) and the thickness (μm) of the sealant film is preferably 45,000 or more, more preferably 50,000 or more, and may be 55,000 or more, or 60,000 or more. Furthermore, the product of the tensile elongation (%) of the first type of sealant film in the vertical direction (TD) and the thickness (μm) of the sealant film is preferably 53,000 or more, and more preferably 60,000 or more. By having a high tensile elongation of the sealant film, it is possible to suppress the bag 10 from tearing due to impact when dropped or the like.
Furthermore, the product of the tensile modulus (MPa) of the first type sealant film and the thickness (μm) of the sealant film in the flow direction (MD) is preferably 38,000 or less, and more preferably 35,000 or less. Furthermore, the product of the tensile modulus (MPa) of the first type sealant film and the thickness (μm) of the sealant film in the vertical direction (TD) is preferably 30,000 or less, and more preferably 25,000 or less.

The product of the tensile modulus (MPa) of the second type of sealant film and the thickness (μm) of the sealant film in the flow direction (MD) is preferably 35,000 or more, more preferably 38,000 or more, and even more preferably 45,000 or more. Furthermore, the product of the tensile modulus (MPa) of the second type of sealant film and the thickness (μm) of the sealant film in the vertical direction (TD) is preferably 25,000 or more, more preferably 30,000 or more, even more preferably 35,000 or more, and may also be 38,000 or more. The sealant film having a high tensile modulus improves the tearability when opening the bag 10.
Furthermore, the product of the tensile elongation (%) of the second type sealant film in the flow direction (MD) and the thickness (μm) of the sealant film is preferably 55,000 or less, and more preferably 50,000 or less. Furthermore, the product of the tensile elongation (%) of the second type sealant film in the vertical direction (TD) and the thickness (μm) of the sealant film is preferably 60,000 or less, and more preferably 55,000 or less.

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

If the sealant layer 70 has easy-peel properties, as shown in Figure 10, the sealant layer 70 may include a first layer 71 located on the metal foil 50 side and a second layer 72 located inside the first layer 71 and constituting the inner surface 30x of the packaging material 30. Two main types of easy-peel sealant layers 70 are possible, such as Type A and Type B described below.

In the Type A sealant layer 70, the first layer 71 is a layer mainly composed of polyethylene, and the second layer 72 is a layer containing a mixed resin of polyethylene and polypropylene. In the second layer 72, the proportion of polypropylene is greater than the proportion of polyethylene. The mass ratio of polypropylene to polyethylene in the second layer 72 is 6:4 to 8:2.

When a packaging material 30 equipped with a type A sealant layer 70 is used in packaging products for heat sterilization purposes, it is preferable that the density of polyethylene in the sealant layer 70 be 0.940 g/ ^cm³ or higher.

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

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

In the Type B sealant layer 70, the first layer 71 is a layer mainly composed of polypropylene, and the second layer 72 is a layer containing a mixed resin of polyethylene and polypropylene. In the second layer 72, the proportion of polypropylene is greater than the proportion of polyethylene. The mass ratio of polypropylene to polyethylene in the second layer 72 is 6:4 to 8:2.

When a packaging material 30 equipped with a type B sealant layer 70 is used in packaging products for heat sterilization purposes, it is preferable that the density of polyethylene in the sealant layer 70 be 0.940 g/ ^cm³ or higher.

For the first layer 71 of the Type B sealant layer 70, for example, an ethylene-propylene block copolymer can be used as the polypropylene. For the second layer 72 of the Type B sealant layer 70, for example, an ethylene-propylene random copolymer can be used as the polypropylene.

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

Furthermore, the sealant layer 70 may be a resin layer formed on the inner surface of the metal foil 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 metal foil 50 and the sealant layer 70.

(Other layers)
The base material 35 of the packaging material 30 may further include a printed layer 32. In the example shown in Figure 2, the printed layer 32 is located on the surface of the biaxially oriented plastic film 40 that is on the side of the first adhesive layer 45.

The printing layer 32 is a layer on packaging products such as bags 10 to display information about the contents and packaging products, and to add aesthetic appeal. The printing layer can display letters, numbers, symbols, figures, and patterns. The printing layer includes a binder resin and coloring materials such as dyes and pigments dispersed in the binder resin. Gravure printing inks and flexographic printing inks can be used as materials for the printing layer. A specific example of a gravure printing ink is Finart, manufactured by DIC Graphics Corporation.

Next, an example of a method for manufacturing the packaging material 30 will be described.

First, prepare the biaxially oriented plastic film 40 and metal foil 50 described above. The biaxially oriented plastic film 40 may be provided with a printed layer 32 or the like, as needed.

Next, the biaxially oriented plastic film 40 and the metal foil 50 are laminated together via a first adhesive layer 45 using a dry lamination method. Then, the laminate containing the biaxially oriented plastic film 40 and the metal foil 50 is laminated together with a sealant layer 70 via a second adhesive layer 55 using a dry lamination method. This yields a packaging material 30 comprising the biaxially oriented plastic film 40, the metal foil 50, and the sealant layer 70.

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

In the dry lamination method, first, an adhesive composition is applied to one of the two films to be laminated. Next, the applied adhesive composition is dried to evaporate the solvent. Then, the two films are laminated together via the dried adhesive composition. Finally, the two laminated films are wound up and aged for 24 hours or more in an environment of, for example, 20°C or higher.

Next, a method for manufacturing a bag 10 using the packaging material 30 described above will be explained. First, a surface film 14 and a back film 15 made of the packaging material 30 are prepared. Subsequently, the inner surfaces of each film are heat-sealed to form sealing portions such as a lower sealing portion 12a and a side sealing portion 13a. The films joined together by heat sealing are then cut into an appropriate shape to obtain the bag 10 shown in Figure 1.

Next, the contents 18 are filled into the bag 10 through the opening 11b at the top 11. Specifically, as shown in Figure 11, the portion of the pair of side sealing portions 13a of the bag 10 closest to the top 11 is gripped by a pair of zipper portions 105. Furthermore, as indicated by arrow P in Figure 11, the zipper portions 105 are moved in a direction that narrows the distance between them in the width direction of the bag 10. This deforms the surface film 14 and back film 15 to form the opening 11b at the top 11. At this time, as shown in Figure 11, suction portions 106 may be attached to the outer surfaces of the surface film 14 and back film 15, and the suction portions 106 may be moved in the direction of arrow Q. This facilitates the formation of the opening 11b. Next, the contents 18 are filled into the bag 10 through the opening 11b. Afterward, the top 11 is heat-sealed to form the top sealing portion 11a. In this way, a sealed bag 10 containing the contents 18 can be obtained.

In this embodiment, the biaxially oriented plastic film 40 of the base material 35 of the packaging material 30 contains polyester as its main component. Therefore, compared to the case where the base material 35 is a biaxially oriented plastic film containing nylon as its main component, the moisture content in the base material 35 can be reduced. This suppresses the evaporation of moisture in the base material 35 during heat sealing, thereby preventing the formation of bubbles. This also suppresses the occurrence of cloudiness in the base material 35 caused by bubbles, making it easier to maintain the transparency of the base material 35.

The contents 18 are, for example, cooked foods containing moisture, such as curry, stew, or soup. The contents 18 may also contain ingredients with a high oil content, such as meat, fish, and seasonings for them. In addition to food, items that can be heated by methods such as boiling water can also be placed in the bag 10. Furthermore, contents that do not require heating may also be placed in the bag 10.

Next, the bag 10 containing the contents may be subjected to sterilization treatment such as boiling or retorting. In this embodiment, the biaxially oriented plastic film 40 of the base material 35 of the packaging material 30 contains polyester as its main component. Therefore, compared to the case where the base material 35 is a biaxially oriented plastic film containing nylon as its main component, the absorption of moisture by the base material 35 during sterilization treatment can be suppressed. This suppresses the occurrence of cloudiness caused by moisture in the base material 35, making it easier to maintain the transparency of the base material 35. Furthermore, it suppresses the increase in the static and dynamic friction coefficients of the outer surface 30y of the packaging material 30 due to moisture absorption by the base material 35. This prevents a decrease in the slipperiness of the packaging material 30 and the packaged product when they are exposed to a high-temperature, high-humidity environment.

Furthermore, in this embodiment, a high-stiffness polyester film is used as the biaxially oriented plastic film 40 of the base material 35 of the packaging material 30 constituting the bag 10. Therefore, the packaging material 30 and the bag 10 can be given excellent puncture resistance. This prevents, for example, the bag 10 from tearing when it comes into contact with a sharp object with a pointed tip. The puncture resistance of the packaging material 30 is preferably 15.0 N or higher, more preferably 16.0 N or higher, even more preferably 17.0 N or higher, and even more preferably 18.0 N or higher. The method for measuring puncture resistance will be described in the examples below.

Furthermore, in this embodiment, using a high-stiffness polyester film as the biaxially oriented plastic film 40 of the base material 35 makes it easier to increase the rigidity of the packaging material 30. When the packaging material 30 has rigidity, as shown in Figure 11, it becomes easier to form the opening 11b on the upper part 11 when moving the chuck portion 105. For example, the surface film 14 and the back film 15 become easier to deform into a curved shape that is convex towards the outer surface. This makes it easier to secure the opening width K of the opening 11b. Also, when the packaging material 30 constituting the surface film 14 and the back film 15 has rigidity, wrinkles are less likely to form on the surface film 14 and the back film 15. Therefore, the suction portion 106 easily adheres to the outer surfaces of the surface film 14 and the back film 15. This also contributes to securing the opening width K of the opening 11b.

Furthermore, in this embodiment, the packaging material 30 contains metal foil 50. This allows the packaging material 30 and the bag 10 to possess gas barrier properties that prevent the transmission of oxygen gas and water vapor, as well as light-shielding properties that prevent the transmission of visible light and ultraviolet light.

Next, the method for opening the bag 10 will be described. Consumers can open the bag 10 by tearing it along the first direction D1. To improve the tearability of the bag 10, it is preferable to use the second type of sealant film described above, which has a high tensile modulus.

It is possible to make various modifications to the embodiments described above. The following descriptions of modifications will be explained with reference to the drawings as needed. In the following descriptions and the drawings used therein, parts that can be configured similarly to the embodiments described above will be given the same reference numerals as those used for the corresponding parts in the embodiments described above, and redundant explanations will be omitted. Furthermore, if it is clear that the effects and advantages obtained in the embodiments described above can also be obtained in the modifications, the explanation may be omitted.

(A variation of the bag)
Figure 12 shows another example of a bag 10 comprising packaging material 30. The bag 10 shown in Figure 12 differs only in that it further comprises a lower film 16; otherwise, its configuration is substantially the same as that of the bag 10 shown in Figure 1. In the bag 10 shown in Figure 12, the same reference numerals are used for parts identical to those in the bag 10 shown in Figure 1, and detailed explanations are omitted.

The bag 10 shown in Figure 12 is a gusset-type bag configured to be self-supporting. In addition to the components of the bag 10 shown in Figure 1, the bag 10 includes a lower film 16 that constitutes the lower part 12. The lower film 16 is folded over at the folded portion 16f and positioned between the surface film 14 and the backing film 15. In this case, the sealing portion includes a lower sealing portion 12a that extends to the lower part 12. The lower sealing portion 12a includes a sealing portion formed by joining the inner surface of the surface film 14 and the inner surface of the lower film 16, and a sealing portion formed by joining the inner surface of the backing film 15 and the inner surface of the lower film 16.

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

Figures 13A and 13B are a longitudinal cross-sectional view and a plan view, respectively, showing a lidded container 110, which is an example of an application of the packaging material 30. The lidded container 110 comprises a container body 112 manufactured by sheet molding such as deep drawing or injection molding, and a lid material 114 joined to the container body 112. The container body 112 has a bottom surface 112a, a side surface 112b, and a flange portion 113 that extends horizontally outward 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 sealing portion 116. The lid material 114 may include the above-mentioned packaging material 30 having at least one high-stiffness polyester film. By constructing the lid material 114 using the above-mentioned packaging material 30, the lid material 114 can be given excellent puncture strength. This makes it possible to suppress the lid material 114 from tearing when a sharp object with a pointed tip comes into contact with the lid material 114.

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, which constitutes the inner surface 30x.

Figure 14 is a perspective view showing a container 120, an example of an application of the packaging material 30. The container 120 comprises an outer box 122 and a bag-in-box 124 housed within the outer box 122. The outer box 122 is constructed, for example, from corrugated cardboard. The bag-in-box 124 can contain contents such as water. The bag-in-box 124 may include the aforementioned packaging material 30 having at least one high-stiffness polyester film. By constructing the bag-in-box 124 using the aforementioned packaging material 30, the bag-in-box 124 can be given excellent puncture resistance. This prevents the lid material 114 from tearing if a sharp object with a pointed tip comes into contact with the bag-in-box 124.

The inside of the bag-in-box 124 may be cleaned with a cleaning solution containing hydrogen peroxide or the like. In this embodiment, the biaxially oriented plastic film 40 of the base material 35 of the packaging material 30 contains polyester as its main component. Therefore, compared to the case where the base material 35 is a biaxially oriented plastic film containing nylon as its main component, the occurrence of cloudiness in the base material 35 during cleaning can be suppressed, making it easier to maintain the transparency of the base material 35.

As shown in Figure 14, the bag-in-box 124 may be equipped with a spout 125 for dispensing the contents. In this case, the outer box 122 may have an opening 123 to expose the spout 125 to the outside of the outer box 122.

In this application, products for packaging articles, such as bags 10, lidded containers 110, and containers 120, are also referred to as packaging products.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention.

Examples 1-5 and Comparative Examples 1-3 evaluated the puncture strength, loop stiffness, tensile properties, appearance, and slipperiness of the packaging material 30 according to the present invention.

(Example 1)
As the biaxially oriented plastic film 40, a high-stiffness polyester film (hereinafter also referred to as high-stiffness PET film) was prepared, having a loop stiffness of 0.0017 N or more, containing 90% by mass or more of PET, and provided with a printed layer 32. 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 flow direction and the perpendicular direction. Furthermore, the Young's modulus of the high-stiffness PET film in the flow direction was 4.8 GPa, and the Young's modulus of the high-stiffness PET film in the perpendicular direction was 4.7 GPa.
Furthermore, the tensile strength of the high-stiffness PET film in the flow direction was 292 MPa, and the tensile strength of the high-stiffness PET film in the vertical direction was 257 MPa. In addition, the tensile elongation of the high-stiffness PET film in the flow direction was 107%, and the tensile elongation of the high-stiffness PET film in the vertical direction was 102%. In this case, the value obtained by dividing the tensile strength of the high-stiffness PET film in the flow direction by the tensile elongation was 2.73 [MPa/%], and the value obtained by dividing the tensile strength of the high-stiffness PET film in the vertical direction by the tensile elongation was 2.52 [MPa/%].
Furthermore, the thermal shrinkage rate of the high-stiffness PET film in both the flow direction and the perpendicular direction was 0.4%.

Furthermore, a 7 μm thick aluminum foil was prepared as metal foil 50.

Furthermore, as the sealant layer 70, an unstretched polypropylene film ZK500 manufactured by Toray Film Processing Co., Ltd. was prepared. ZK500 contains the aforementioned propylene-ethylene block copolymer. The thickness of the sealant layer 70 was 60 μm.

ZK500 has a higher tensile elongation compared to general unoriented polypropylene films. Specifically, the tensile elongation of ZK500 in the flow direction (MD) is 1180% when the thickness is 50 μm and 1100% when the thickness is 60 μm. Furthermore, 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 flow direction is 59,000 when the thickness is 50 μm and 66,000 when the thickness is 60 μm. Also, 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.

Furthermore, ZK500 has a lower tensile modulus compared to general unoriented polypropylene films. Specifically, the tensile modulus of ZK500 in the flow 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 flow 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.

Next, a packaging material 30 was prepared by sequentially laminating a biaxially oriented plastic film 40 with a printed layer 32, a metal foil 50, and a sealant layer 70 using a dry lamination method. The printed layer was laminated facing the metal foil 50. A two-component polyurethane adhesive (main component: RU-40, curing agent: H-4) manufactured by Rock Paint Co., Ltd. was used as the first adhesive layer 45 and the second adhesive layer 55. The main component, RU-40, is a polyester polyol. The thickness of the first adhesive layer 45 and the second adhesive layer 55 was 3 μm. The total thickness of the packaging material 30 was 90 μm.

[Evaluation of puncture resistance]
Next, the puncture strength of the packaging material 30 was measured in accordance with JIS Z1707 7.4. An A&D Tensilon universal material tester RTC-1310 was used as the measuring instrument. Specifically, as shown in Figure 15, a semicircular needle 90 with a diameter of 1.0 mm and a tip radius of 0.5 mm was inserted into a fixed test piece of packaging material 30 from the outer surface 30y side at a speed of 50 mm/min (50 mm per minute), and the maximum value of stress until the needle 90 penetrated the packaging material 30 was measured. The maximum value of 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 measurement was a temperature of 23°C and a relative humidity of 50%. As a result, the puncture strength was 17.3 N.

[Evaluation of tensile properties]
Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated. Specifically, the Young's modulus of the packaging material 30 in the flow direction and perpendicular direction was measured. The tensile properties of the packaging material 30 can be measured in accordance with JIS K7127. As the measuring instrument, an Orientec RTC-1310A tensile testing machine can be used. As the test specimen, a rectangular film cut from the packaging material with a width of 15 mm and a length of 150 mm can be used. The distance between the pair of chucks holding the test specimen at the start of measurement was 50 mm, and the tensile speed was 300 mm/min. The environment during measurement was a temperature of 23°C and a relative humidity of 50%. As a result, the Young's modulus in the flow direction was 4005 MPa, and the Young's modulus in the perpendicular direction was 4352 MPa.

[Evaluation of Loop Stiffness]
Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured. The measuring instrument used was the No. 581 Loop Stiffness Tester (registered trademark) LOOP STIFFNESS TESTER DA type manufactured by Toyo Seiki Co., Ltd. The measurement environment was 23°C and 50% relative humidity. As a result, the loop stiffness of the packaging material 30 in the flow direction was 0.112 N, and the loop stiffness in the perpendicular direction was 0.103 N.

[Evaluation of slipperiness]
Next, the slipperiness of the outer surface 30y of the packaging material 30 was evaluated. Here, the coefficient of friction of the outer surface 30y of the packaging material 30 was measured. Specifically, the static and dynamic coefficients of friction between the outer surface 30y of the packaging material 30 and the metal surface were measured. The measurements were performed using a TR-2 friction measuring instrument manufactured by Toyo Seiki Seisakusho Co., Ltd., in accordance with JIS K-7125. Aluminum was used as the metal constituting the metal surface.

The following describes the specific measurement method. First, the packaging material 30 was cut to create a test specimen measuring 70 mm in width and 152 mm in length. Next, the first and second measurements described below were performed using the test specimen.

In the first measurement, the test specimen was stored in a room at a temperature of 20–30°C and a humidity of 40–60% for at least 24 hours. Then, the test specimen was placed on a metal surface so that its outer surface was in contact with the metal surface. Next, a thread with a mass of 200 g, including a member measuring 63 mm in width and 63 mm in length, was placed on the test specimen. Subsequently, the test specimen was slid across the metal surface at a speed of 100 mm/min. The static and kinetic friction coefficients of the outer surface of the test specimen were calculated based on the force applied to the test specimen at the start of sliding and the force applied to the test specimen during the activity. The measurement environment was the standard condition specified in JIS K7100, with a temperature of 23°C and a humidity of 50%.

In the second measurement, the static and dynamic friction coefficients of the outer surface of the test specimen were measured in the same manner as in the first measurement, except that the test specimen was stored in a high-temperature constant-temperature chamber at 40°C and 90% humidity for 24 hours, and then placed on a metal surface. The measurement was performed within 5 minutes of removing the test specimen from the high-temperature constant-temperature chamber.

The ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less. In other words, there was almost no increase in the friction coefficient due to exposure of the test specimen to an environment of 40°C and 90% humidity.

[Evaluation of appearance]
Next, a bag 10 was made using the packaging material 30 as the surface film 14, back film 15, and bottom film 16, and the appearance of the bag 10 was evaluated. Specifically, first, a bag 10 as shown in Figure 11 was made 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 bottom film 16, that is, the height from the bottom end of the bag 10 to the folded portion 16f, was 46 mm. Next, 200 g of water was filled into the bag 10 as the contents through the opening 11b of the top 11. After that, the top 11 was heat-sealed to form the top seal portion 11a. In this way, multiple bags 10 as shown in Figure 11, each containing 200 g of water, were made.

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

Next, the bag 10, which had undergone heat sterilization, was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Example 2)
Packaging material 30 was prepared in the same manner as in Example 1, except that an unstretched polypropylene film ZK207 manufactured by Toray Film Processing Co., Ltd. was used as the sealant layer 70. ZK207 contains the propylene-ethylene block copolymer described above. The thickness of the sealant layer 70 was 70 μm. The total thickness of the packaging material 30 was 100 μm.

ZK207 possesses a high tensile modulus. Specifically, the tensile modulus of ZK207 in the flow direction (MD) is 780 MPa for a thickness of 50 μm and 680 MPa for a thickness of 60 μm. Furthermore, the tensile modulus of ZK207 in the perpendicular direction (TD) is 630 MPa for a thickness of 50 μm and 560 MPa for a thickness of 60 μm. Therefore, the product of the tensile modulus (MPa) and thickness (μm) of ZK207 in the flow direction is 39,000 for a thickness of 50 μm and 40,800 for a thickness of 60 μm. Also, the product of the tensile modulus (MPa) and thickness (μm) of ZK207 in the perpendicular direction is 31,500 for a thickness of 50 μm and 33,600 for a thickness of 60 μm.

Furthermore, ZK207 has low tensile elongation. Specifically, the tensile elongation of ZK207 in the flow 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 flow direction is 39,500 when the thickness is 50 μm and 43,800 when the thickness is 60 μm. The product of the tensile elongation (%) and thickness (μm) of ZK207 in the perpendicular direction is 51,000 when the thickness is 50 μm and 52,200 when the thickness is 60 μm.

Next, in the same manner as in Example 1, a packaging material 30 was prepared by sequentially laminating a biaxially oriented plastic film 40 with a printed layer, a metal foil 50, and a sealant layer 70 using a dry lamination method. The printed layer was laminated so that it faced the side of the metal foil 50.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 17.0 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 4113 MPa, and the Young's modulus in the perpendicular direction was 4235 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.131 N, and the loop stiffness in the perpendicular direction was 0.124 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Example 3)
Packaging material 30 was prepared in the same manner as in Example 1, except that unstretched polypropylene film ZK500R manufactured by Toray Film Processing Co., Ltd. was used as the sealant layer 70. The thickness of the sealant layer 70 was 50 μm. The total thickness of the packaging material 30 was 80 μm.

ZK500R possesses a high tensile modulus. Specifically, the tensile modulus of ZK500R in the flow direction (MD) is 980 MPa when the thickness is 50 μm. Furthermore, the tensile modulus of ZK500R in the perpendicular direction (TD) is 780 MPa when the thickness is 50 μm. Therefore, the product of the tensile modulus (MPa) and thickness (μm) of ZK500R in the flow direction is 49000 when the thickness is 50 μm. Also, the product of the tensile modulus (MPa) and thickness (μm) of ZK500R in the perpendicular direction is 39000 when the thickness is 50 μm.

Furthermore, ZK500R has low tensile elongation. Specifically, the tensile elongation of ZK500R in the flow direction (MD) is 770% when the thickness is 50 μm. The tensile elongation of ZK500R in the perpendicular direction (TD) is 870% when the thickness is 50 μm. Therefore, the product of the tensile elongation (%) and thickness (μm) of ZK500R in the flow direction is 38,500 when the thickness is 50 μm. The product of the tensile elongation (%) and thickness (μm) of ZK500R in the perpendicular direction is 43,500 when the thickness is 50 μm. Thus, in ZK500R, the product of the tensile modulus (MPa) and thickness (μm) of the sealant layer 70 in at least one direction is 42,000 or more.

Next, in the same manner as in Example 1, a packaging material 30 was prepared by sequentially laminating a biaxially oriented plastic film 40 with a printed layer, a metal foil 50, and a sealant layer 70 using a dry lamination method. The printed layer was laminated so that it faced the side of the metal foil 50.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 16.4 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3994 MPa, and the Young's modulus in the perpendicular direction was 4119 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.100 N, and the loop stiffness in the perpendicular direction was 0.101 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Example 4)
Packaging material 30 was prepared in the same manner as in Example 1, except that a polyethylene film with a thickness of 50 μm was used as the sealant layer 70. Low-density polyethylene with a density of 0.922 g/ ^cm³ was used as the polyethylene. The total thickness of packaging material 30 was 80 μm.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 15.4 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3898 MPa, and the Young's modulus in the perpendicular direction was 4002 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.092 N, and the loop stiffness in the perpendicular direction was 0.098 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Example 5)
A packaging material 30 was prepared in the same manner as in Example 1, except that the sealant layer 70 consisted of a first layer 71 and a second layer 72 as shown in Figure 10, and an easy-peel co-extruded film was used. The first layer 71 was a 45 μm thick layer made of polyethylene. The second layer 72 was a 5 μm thick layer containing a mixed resin of polyethylene and polypropylene. High-density polyethylene with a density of 0.950 g/ ^cm³ was used as the polyethylene. Ethylene-propylene random copolymer was used as the polypropylene. 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 total thickness of the packaging material 30 was 80 μm.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 15.8 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3928 MPa, and the Young's modulus in the perpendicular direction was 4080 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.096 N, and the loop stiffness in the perpendicular direction was 0.100 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Comparative Example 1)
The packaging material 30 was prepared in the same manner as in Example 1, except that a biaxially oriented PET film with a thickness of 12 μm was used as the base material 35 for the packaging material 30. The biaxially oriented PET film used had approximately the same tensile strength in the flow direction (MD) and the perpendicular direction (TD). The total thickness of the packaging material 30 was 86 μm.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 14.1 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3724 MPa, and the Young's modulus in the perpendicular direction was 3819 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.091 N, and the loop stiffness in the perpendicular direction was 0.087 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Comparative Example 2)
The packaging material 30 was prepared in the same manner as in Example 2, except that a biaxially oriented PET film with a thickness of 12 μm was used as the base material 35 for the biaxially oriented plastic film 40. The biaxially oriented PET film used had approximately the same tensile strength in the flow direction (MD) and the perpendicular direction (TD). The total thickness of the packaging material 30 was 96 μm.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 13.8 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3779 MPa, and the Young's modulus in the perpendicular direction was 3915 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.108 N, and the loop stiffness in the perpendicular direction was 0.101 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if any cloudiness had occurred. The result showed that no cloudiness had occurred.

(Comparative Example 3)
A packaging material 30 was prepared in the same manner as in Example 1, except that the base material 35 further includes a biaxially oriented nylon film (thickness 15 μm) located on the metal foil 50 side of the biaxially oriented plastic film 40. The total thickness of the packaging material 30 was 104 μm.

Next, the puncture strength of the packaging material 30 was measured in the same manner as in Example 1. The result showed a puncture strength of 18.4 N.

Furthermore, the tensile properties of the packaging material 30 in the flow direction and perpendicular direction were evaluated in the same manner as in Example 1. The results showed that the Young's modulus in the flow direction was 3645 MPa, and the Young's modulus in the perpendicular direction was 3382 MPa.

Furthermore, the loop stiffness of the packaging material 30 in the flow direction and perpendicular direction was measured in the same manner as in Example 1. The results showed that the loop stiffness in the flow direction was 0.136 N, and the loop stiffness in the perpendicular direction was 0.131 N.

Furthermore, the slipperiness of the packaging material 30 was evaluated in the same manner as in Example 1. As a result, the ratio of the static friction coefficient in the second measurement to the static friction coefficient in the first measurement was 1.05 or less. Similarly, the ratio of the dynamic friction coefficient in the second measurement to the dynamic friction coefficient in the first measurement was also 1.05 or less.

Furthermore, in the same manner as in Example 1, a bag 10 containing 200g of water was prepared using packaging material 30, and the bag 10 was subjected to heat sterilization. Subsequently, the heat-sterilized bag 10 was visually inspected to see if turbidity had occurred. The result showed that turbidity had occurred.

The layer structure and evaluation results of the packaging material 30 for Examples 1 to 5 are summarized in Figure 16. Similarly, the layer structure and evaluation results of the packaging material 30 for Comparative Examples 1 to 3 are summarized in Figure 17. In Figures 16 and 17, the "Layer Structure" column lists the components of the packaging material 30 from top to bottom, starting with the outermost layer. In the "Appearance" column of Figures 16 and 17, "great" means that no clouding occurred in the heat-sterilized bag 10, while "not good" means that clouding occurred in the heat-sterilized bag 10. Furthermore, in the "Slipperiness" column of Figures 16 and 17, "great" means that the ratio of the static friction coefficient and kinetic friction coefficient in the second measurement to the static friction coefficient and kinetic friction coefficient in the first measurement was 1.05 or less.

As can be seen from the comparison between Examples 1-5 and Comparative Examples 1-3, when the packaging material 30 contains a high-stiffness polyester film, the puncture strength of the packaging material 30 could be increased to a level equivalent to that when the packaging material 30 contains a nylon film. Specifically, it could be increased to 15.0 N or higher. In Examples 1, 2, and 3, the puncture strength of the packaging material 30 was 16.0 N or higher. Furthermore, in Examples 1 and 2, the puncture strength of the packaging material 30 was 17.0 N or higher.

Furthermore, as can be seen from the comparison between Examples 1-5 and Comparative Example 3, the absence of nylon film in the packaging material 30 suppressed the occurrence of cloudiness in the heat-sterilized bag 10.

10 Bag 11 Top 12 Bottom 12a Bottom seal part 13 Side part 13a Side seal part 14 Surface film 15 Back film 16 Bottom film 17 Storage part 18 Contents 25 Easy opening means 26 Notch 30 Packaging material 35 Base material 40 Biaxially oriented plastic film 45 First adhesive layer 50 Metal foil 55 Second adhesive layer 70 Sealant layer

Claims (10)

A packaging material comprising, in order from the outer side to the inner side, a base material, aluminum foil, and a sealant layer,
The packaging material constitutes a bag that is subjected to heat sterilization treatment.
The aforementioned substrate has only one biaxially oriented plastic film containing polyester as the main component,
The thickness of the aluminum foil is 15 μm or less.
A packaging material having a Young's modulus of 3800 MPa or more in one direction and in a direction perpendicular to the said one direction. The packaging material according to claim 1, wherein the thickness of the aluminum foil is 15 μm or less (except in cases where the thickness of the aluminum foil is 15 μm). The packaging material according to claim 1 or 2, wherein the puncture strength of the packaging material is 15.0 N or more. The packaging material according to any one of claims 1 to 3, wherein the Young's modulus of the packaging material in the aforementioned one direction is 4000 MPa or more. The packaging material according to any one of claims 1 to 4, wherein the thickness of the biaxially oriented plastic film is 14 μm or more and 30 μm or less. The packaging material according to any one of claims 1 to 5, wherein the biaxially oriented plastic film contains 90% by mass or more of polyethylene terephthalate. The packaging material according to any one of claims 1 to 6, wherein the sealant layer mainly comprises polypropylene. The packaging material according to any one of claims 1 to 6, 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 6, wherein the sealant layer comprises 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 bag comprising the packaging material described in any one of claims 1 to 9.