FILM, PACKAGE, AND CONTENTS-CONTAINING PACKAGE

Abstract

A film is used in a package in which the internal pressure of a container increases when heated in a microwave oven, and the internal pressure is reduced by releasing internal steam. The film includes: an outer layer film molecularly oriented by biaxial stretching; an inner layer film that is laminated to the outer layer film and heat-sealable; one or more orientation relaxation portions formed in the outer layer film, and a breaking portion provided at a position which the one or more orientation relaxation portions face with a predetermined distance and configured to rupture when the internal pressure of the container is increased in the microwave oven. At least the breaking portion omits a printed layer between the outer layer film and the inner layer film.

Description

FIELD

The present invention relates to a film, a package, and a contents-containing package, which release steam generated when the packaged contents are heated in a microwave oven.

BACKGROUND

A type of package is known in which its sealed contents are heated in a microwave oven. However, when the contents are heated in the microwave, the internal pressure increases. For this reason, another type of package is known that is equipped with means for automatically releasing steam during microwave heating to reduce the internal pressure in the package.

For example, Jpn. Pat. Appln. KOKAI Publication No. 2019-64642 discloses a package and a film capable of releasing steam during microwave heating by providing a breaking portion that includes non-oriented portions arranged opposite to each other across an oriented portion of a crystalline stretched oriented film.

For example, Jpn. Pat. Appln. KOKAI Publication No. 2017-74965 discloses a package and a film capable of steaming food without excessively releasing steam.

SUMMARY

A film according to one embodiment of the present invention is a film used for a package in which an internal pressure of a container increases when heated in a microwave oven, and steam is released to reduce the internal pressure. The film includes an outer layer film molecularly oriented by biaxial stretching, an inner layer film laminated to the outer layer film and capable of being heat-sealed, one or more orientation relaxation portions formed in the outer layer film, and a breaking portion formed at a position which the one or more orientation relaxation portions face at a predetermined distance, and configured to rupture when the internal pressure of the container increases during microwave heating. At least in the breaking portion, a printed layer is omitted between the outer layer film and the inner layer film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the structure of a package according to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating an example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 and illustrates the layer structure of a film used in the package.

FIG. 4 is a perspective view illustrating the package heated in a microwave oven as an example of use.

FIG. 5 is a plan view illustrating an example of the structure of an orientation relaxation portion and a breaking portion provided for the package.

FIG. 6 is a plan view illustrating another example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 7 is a plan view illustrating another example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 8 is a plan view illustrating another example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 9 is a plan view showing another example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 10 is a plan view showing another example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 11 is a plan view illustrating another example of the structure of three or more orientation relaxation portions and a breaking portion provided for the package.

FIG. 12 is a plan view illustrating another example of the structure of three or more orientation relaxation portions and a breaking portion provided for the package.

FIG. 13 is a plan view illustrating another example of the structure of three or more orientation relaxation portions and a breaking portion provided for the package.

FIG. 14 is a perspective view illustrating the structure of a package according to a second embodiment of the present invention.

FIG. 15 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a third embodiment of the present invention.

FIG. 16 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a fourth embodiment of the present invention.

FIG. 17 is a perspective view illustrating the structure of the package.

FIG. 18 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a fifth embodiment of the present invention.

FIG. 19 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a sixth embodiment of the present invention.

FIG. 20 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a seventh embodiment of the present invention.

FIG. 21 is a perspective view illustrating the structure of a package according to an eighth embodiment of the present invention.

FIG. 22 is a perspective view illustrating the structure of a package according to a ninth embodiment of the present invention.

FIG. 23 is a perspective view illustrating the structure of the package.

FIG. 24 is a cross-sectional view schematically illustrating the layer structure of a film used in a package according to a tenth embodiment of the present invention.

FIG. 25 is a plan view illustrating an example of the structure of a pair of orientation relaxation portions and a breaking portion provided for the package.

FIG. 26 is a plan view illustrating an example of a structure of a pair of orientation relaxation portions and a breaking portion provided for a package according to the eleventh embodiment of the present invention.

DETAILED DESCRIPTION

A package 1 using a film 11 according to the first embodiment of the present invention will be described with reference to FIG. 1 through FIG. 13.

FIG. 1 is a perspective view illustrating the structure of the package 1 according to the embodiment of the present invention, FIG. 2 is a plan view illustrating an example of the structure of a pair of orientation relaxation portions 21a and a breaking portion 13 provided for the package 1, and FIG. 3 is a cross-sectional view schematically illustrating the layer structure of the film 11 used in the package 1. FIG. 4 is a perspective view illustrating, as an example of use, a state in which the package 1 is heated in a microwave oven.

The package 1 is a packaging container that packages contents 200 inside. The package 1 is a microwave oven heating container designed to hold the contents 200 for heating in a microwave oven. As shown in FIG. 1, in the present embodiment, the package 1 is a package composed of a multilayer film 11 with a biaxially stretched oriented film 21 on its outer surface and formed into a bag shape. The package 1 is, for example, a pillow packaging bag formed by placing the contents 200 inside the bag-shaped film 11, and sealing the ends with a sealed portion 12.

As a specific example, the package 1 includes a film 11 having a laminated structure with a biaxially stretched oriented film 21 on the outer surface side, a sealed portion 12 formed by forming the film 11 into a bag shape and heat-sealing the ends, and a breaking portion 13 provided for the film 11 and breakable when the internal pressure increases. The contents 200 mentioned here are moisture-containing items that are to be heated in a microwave oven, such as food to be cooked in a microwave oven, and a hand towel to be heated in the microwave oven.

The film 11 is used as at least part of the packaging material that forms the package 1. The film 11 is configured, for example, in a rectangular shape that can be formed into a bag shape. The layer structure of the film 11 includes, from the outer surface side of the package 1, a biaxially stretched oriented film 21, an adhesive layer 22, and a sealant film 23. The film 11 may also include a printed layer 24 between the biaxially stretched oriented film 21 and the sealant film 23. The film 11 may include the printed layer 24 on the outer surface of the biaxially stretched oriented film 21. The layer structure of the film 11 is not limited to this and may consist of two or more layers, with at least one layer including the biaxially stretched oriented film 21.

The biaxially stretched oriented film 21 includes an orientation relaxation portion 21a, which is formed by heating a portion of the film to a predetermined temperature near its melting point or higher. The orientation relaxation portion 21a constitutes a portion of the breaking portion 13. The orientation relaxation portion 21a is configured in various shapes, depending on the structure of the breaking portion 13.

The biaxially stretched oriented film 21 is a crystalline stretched oriented film. The biaxially stretched oriented film 21 is configured, for example, from a general-purpose biaxially stretched film, such as a biaxially stretched PET film, a biaxially stretched nylon film, or a biaxially stretched PP film, or a composite film of these. Other suitable examples of the biaxially stretched oriented film 21 include a biaxially stretched film having barrier properties, such as a biaxially stretched PVA film or a biaxially stretched EVOH film, and a co-extruded biaxially stretched film including barrier resin, such as PP/EVOH/PP, NY/EVOH/NY and NY/MXD-NY/NY, in the intermediate layer thereof. Additionally, a general-purpose biaxially stretched film coated with a PVA-based, PVDC, or PAA-based barrier resin, or a hybrid coated film in which an inorganic substance is dispersed within the above-mentioned barrier resin, can be suitably used as the biaxially stretched oriented film 21. The thickness of the biaxially stretched oriented film 21 is preferably 12 μm or more and 50 μm or less.

This is because if the thickness of the biaxially stretched oriented film 21 is less than 12 μm, there is a risk that the physical strength of the package 1 may decrease, and it becomes technically challenging to produce the film, leading to increased costs. If the thickness of the biaxially stretched oriented film 21 exceeds 50 μm, the film 11 including the biaxially stretched oriented film 21 becomes difficult to stretch. It should be noted that the thickness of the biaxially stretched oriented film 21 is not limited, as long as the breaking portion 13 can break or rupture due to the shape of the orientation relaxation portion 21a.

The orientation relaxation portion 21a is formed by heating the biaxially stretched oriented film 21 to a predetermined temperature near its melting point or higher, thereby relaxing or eliminating its orientation. In other words, the biaxially oriented film 21 of the film 11 includes an orientation portion 21b that is not heated to a predetermined temperature near its melting point or higher, and an orientation relaxation portion 21a that is heated to the predetermined temperature near the melting point or higher and that is formed in part of the orientation portion 21b. The predetermined temperature near the melting point varies depending on the biaxially oriented film 21, but it is at least a temperature sufficient to relax the orientation and achieve the desired relationship between the tensile elastic modulus and breaking elongation of the orientation relaxation portion 21a and the orientation portion 21b.

Let it be assumed that the tensile elastic modulus in the molecular orientation portion of the film 11 is E1 and the tensile elastic modulus in the molecular orientation relaxation portion is E2. In this case, the relationship between the tensile elastic modulus E1 of the orientation portion 21b and the tensile elastic modulus E2 of the orientation relaxation portion 21a is, for example, 0<E2/E1<0.5. The molecular orientation portion of the film 11 refers to the portion of film 11 which includes the biaxially stretched oriented film 21, the adhesive layer 22, and the sealant film 23, and in which the orientation portion 21b of the biaxially stretched oriented film 21 is present. The molecular orientation relaxation portion of the film 11 refers to the portion of the film 11 where the orientation relaxation portion 21a of the biaxially stretched oriented film 21 is present.

For example, in the case where the biaxially stretched oriented film 21 of the present embodiment is a biaxially stretched PET film, the tensile elastic modulus E1 of the molecular orientation portion of the film 11 is approximately 2000 MPa, and the tensile elastic modulus E2 of the molecular orientation relaxation portion is approximately 200 MPa. In this case, E2/E1 is approximately 0.1, which is a value less than 0.5.

As a method for heating the biaxially stretched oriented film 21 to form the orientation relaxation portion 21a within the biaxially stretched oriented film 21, laser beam heating, hot plate heating, impulse heating, or near-infrared heating is preferred.

For example, the laser beam heating and the near-infrared heating may have the advantage of allowing non-contact heating of the biaxially stretched oriented film 21, but the laser light heating is preferred because it enables localized heating. Additionally, if the biaxially stretched oriented film 21 has poor laser light absorption and the orientation relaxation portion 21a is difficult to form, a laser light-absorbing material may be blended into the material of the stretched oriented film 21 in advance to enhance its laser light absorption. Alternatively, the biaxially stretched oriented film 21 can be coated with a laser light-absorbing material.

As for the type of laser light, it is preferable to use a carbon dioxide laser, which is relatively well-absorbed by most resin materials used in the biaxially stretched oriented film 21. The laser light-absorbing material can be suitably selected depending on the type of laser light. These heating methods can be suitably selected based on the material of the biaxially stretched oriented film 21.

In the case of hot plate heating or impulse heating, it is preferable to perform a treatment such as Teflon® surface treatment on the pressing head so that the resin of the molten biaxially stretched oriented film 21 or part of the resin of the sealant film 23 does not adhere to the pressing head. For example, in the case of hot plate heating, the orientation relaxation portion 21a is formed by pressing a heated head (hot plate), set to a temperature at or above a predetermined level near the melting point of the biaxially stretched oriented film 21, against the film 21 to melt and heat it.

Whether or not the orientation relaxation portion 21a is properly formed can be determined by inspecting the formed biaxially stretched oriented film 21. As inspection methods, techniques such as crystallinity measurement using X-ray diffraction, FT-IR (Fourier transform infrared spectroscopy), or DSC (differential scanning calorimetry) can be employed in addition to the use of an orientation viewer equipped with polarizing plates.

For example, the breaking elongation of the orientation portion 21b of such a biaxially stretched oriented film 21 is set to 200% or less, and the breaking elongation of the orientation relaxation portion 21a is set to 300% or more.

The adhesive layer 22 can be appropriately selected from general dry lamination adhesives used for food. However, since the package 1 is to be heated in a microwave oven, it is preferable that the adhesive layer 22 be heat resistant. From the perspectives of performance and cost-effectiveness, the thickness of the adhesive layer 22 is preferably 2 μm to 5 μm.

The sealant film 23 is, for example, an unstretched low-density polyethylene (LDPE) film, an unstretched linear low-density polyethylene (LLDPE) film, an unstretched polypropylene (PP) film, an unstretched polyethylene terephthalate film, or the like. The thickness of the sealant film 23 is preferably 10 μm or more and 100 μm or less. More desirably, the thickness of the sealant film 23 is 20 μm or more and 60 μm or less.

This is because if the thickness of the sealant film 23 is less than 10 μm, the practical strength of the package 1 may be insufficient, and the sealed portion 12 may break easily due to vibrations during transportation or impact from dropping. If the thickness of the sealant film 23 exceeds 100 μm, it may be less stretchable, which may lead to issues with the reliability of steam release.

The printed layer 24 is provided, at least, in the region of the breaking portion 13, and may be applied to part of the film 11 or may not be applied to any part of the film 11. In other words, the printed layer 24 is located in the region where the orientation portion 21b, which is positioned between the orientation relaxation portions 21a that form the breaking portion 13, is provided. Furthermore, the printed layer 24 is provided in regions other than the region between the biaxially stretched oriented film 21 and the adhesive layer 22 and the region between the adhesive layer 22 and the sealant film 23.

As a specific example, as shown in FIG. 3, the printed layer 24 is provided between the biaxially stretched oriented film 21 and the sealant film 23, except in the region where the breaking portion 13 is provided. For example, the printed layer 24 is provided between the biaxially stretched oriented film 21 and the adhesive layer 22, except in the breaking portion 13, which is the orientation portion 21b between the two orientation relaxation portions 21a of the biaxially stretched oriented film 21.

The sealed portion 12 is formed by heat-sealing (thermal bonding) the film 11 at its ends.

The breaking portion 13 is formed by the orientation portion 21b arranged between the orientation relaxation portions 21a facing each other. That is, the breaking portion 13 is provided in part of the film 11 and extends in a linear or curved pattern. It is formed either by a single orientation relaxation portion 21a, shaped with two portions facing each other with a predetermined distance therebetween, or by a plurality of orientation relaxation portions 21a arranged to face each other, so that it is formed by the orientation portion 21b existing between the orientation relaxation portions 21a. That is, the breaking portion 13 is formed by arranging portions of the orientation relaxation portion 21a to face each other, with the orientation portion 21b of the biaxially stretched oriented film 21, which is kept below its melting point, interposed between them. In other words, the orientation portion 21b of the biaxially stretched oriented film 21, which retains its orientation, is interposed.

As a specific example, as shown in FIG. 2 and FIG. 5 through FIG. 13, the orientation relaxation portion 21a has short sides and long sides, and one or more of such portions are provided. In a case where one orientation relaxation portion 21a is provided, the short sides thereof face each other with a predetermined distance therebetween, as shown in FIG. 5, or the short sides and the long sides face each other with a predetermined distance therebetween.

In a case where two orientation relaxation portions 21a are provided, the short sides of the two orientation relaxation portions 21a face each other with a predetermined distance therebetween, as shown in FIG. 2 and FIG. 6 through FIG. 8, or the short side of one orientation relaxation portion 21a faces the long side of the other orientation relaxation portion 21a with a predetermined distance therebetween, as shown in FIG. 9 and FIG. 10. Similarly, in a case where three or more orientation relaxation portions 21a are provided, the short sides of any two orientation relaxation portions 21a or the short sides and the long sides of three or more orientation relaxation portions 21a face each other with a predetermined distance therebetween, as shown in FIG. 11 through FIG. 13. In a case where a plurality of orientation relaxation portions 21a are provided in the breaking portion 13, it is preferable that the orientation relaxation portions 21a have the same size and shape as shown in FIG. 2, but they may have different sizes and shapes as shown in FIG. 13 as long as the breaking portion 13 is configured to break.

Specifically, the breaking portion 13 is formed by one or more heated orientation relaxation portions 21a of the biaxially stretched oriented film 21, which are positioned with a predetermined distance therebetween and adjacent to each other across the orientation portion 21b of the biaxially stretched oriented film 21 that retains its orientation. The predetermined distance mentioned here can be set appropriately as long as the breaking portion 13 can break and form a steam port 21c when heated in a microwave oven, but is preferably less than 5 mm. In addition, the long sides and the short sides need not be straight but may be curved. In other words, the breaking portion 13 is configured in a shape in which the orientation relaxation portion 21a extends in any direction, and one end of one orientation relaxation portion 21a faces another portion of the same orientation relaxation portion 21a or part of another orientation relaxation portion 21a, with a predetermined distance therebetween. In addition, as long as the breaking portion 13 can break and form a steam port 21c, part of the orientation portion 21b, which is sandwiched between the orientation relaxation portions 21a facing each other, may undergo orientation relaxation.

Possible shapes of one orientation relaxation portion 21a include a circular ring or a polygonal ring with a portion cut out, as shown in FIG. 5. Two orientation relaxation portions 21a may be linear, with their short sides facing each other linearly or at a predetermined angle, as shown in FIG. 2, FIG. 6 and FIG. 7, or may be T-shaped with a short side of one of them facing a long side of the other, as shown in FIG. 9 and FIG. 10. In addition to being linear, the two orientation relaxation portions 21a may also be wavy, as shown in FIG. 8. Three or more orientation relaxation portions 21a may be arranged such that their longitudinal directions are aligned in one direction, as shown in FIG. 12 and FIG. 13, or may be arranged in the circumferential direction around the breaking portion 13, as shown in FIG. 11.

In consideration of manufacturing costs and other factors, it is preferable that the orientation relaxation portions 21a be formed as a pair of rectangles elongated in one direction, with their short sides facing each other, as shown in FIG. 2. The orientation relaxation portions 21a shown in FIG. 2 have a short side length of 0.5 to 10 mm and a long side length of 3 to 100 mm, and the short side length is preferably set to a range shorter than the long side length, and is appropriately selected depending on the size of the bag and the structure of the laminate. The distance between the facing short sides of the two orientation relaxation portions 21a is set to be less than 5 mm, and more desirably to be 0.5 to 3.0 mm, and is appropriately selected depending on the size of the bag and the structure of the laminate.

This is because if the dimensions of the orientation relaxation portions 21a are less than this range, the range of expansion is too narrow and steam release may not be properly performed. If the dimensions exceed this range, the strength of the bag may decrease and the gas barrier properties may decrease significantly. Furthermore, if the distance between the facing short sides of the two orientation relaxation portions 21a is less than the specified range, the tips of the facing orientation relaxation portions 21a may merge, preventing the formation of the steam port 21c and causing the package 1 to burst. On the other hand, if the distance exceeds the specified range, the region between the facing short sides of the two orientation relaxation portions 21a will not be able to stretch, causing the breaking portion 13 to fail to rupture. This also risks preventing the formation of the steam port 21c and causing the package 1 to burst.

Next, a method for manufacturing the above-described package 1 will be described.

First, a portion of the film 11 is heated to a predetermined temperature near the melting point of the biaxially stretched oriented film 21 or higher, thereby eliminating the orientation in that portion of the biaxially stretched oriented film 21 and forming an orientation relaxation portion 21a with a predetermined shape. As a specific example, the portion of the film 11 is irradiated with laser light, such as a carbon dioxide laser, at an output sufficient to heat the biaxially stretched oriented film 21 to a predetermined temperature near its melting point or higher.

Next, the laser light is scanned to trace the shape of an orientation relaxation portion 21a to be formed. For example, in a case where a pair of orientation relaxation portions 21a are to be formed, the laser light is scanned to trace the shape of one of the orientation relaxation portions 21a, the irradiation of the laser light is stopped, and the laser light is again irradiated to the position where the other orientation relaxation portion 21a is to be formed. Then, the laser light is scanned to trace the shape of the other orientation relaxation portion 21a. At this time, it is sufficient for the orientation of the orientation relaxation portion 21a to be relaxed; it is not necessary to irradiate the laser light until it becomes unoriented and the orientation is completely eliminated, though it may be unoriented. Through these steps, the portion of the film 11 is heated to form the orientation relaxation portions 21a. As a result, the film 11 having a breaking portion 13 formed in a portion thereof is manufactured.

The film 11 thus formed is formed into a bag shape, and contents 200 are placed inside the bag. Next, the ends of the film 11 are heat-sealed to form a sealed portion 12, thereby manufacturing a sealed bag-shaped package 1 in which the contents 200 are contained (a contents-containing container for microwave heating). It should be noted that any manufacturing method can be used for the package 1 as long as it can contain the contents 200 inside. For example, the package may be heat sealed except for a portion to form a partially open bag shape, and then filled with the contents 200 through the opening, and then the opening heat-sealed. Alternatively, the contents 200 may be placed on the film 11, then shaped into a bag, and heat-sealed.

Next, a method of using the above package 1 will be described.

The package 1 containing the contents 200 is placed in a microwave oven, and the contents 200 are then heated in the microwave oven. When the contents 200 are heated in the microwave oven, steam is generated from the contents 200, causing the internal pressure to increase, the package 1 to expand, and the film 11 to stretch. When the film 11 stretches, the breaking portion 13 located between the facing short sides of the orientation relaxation portion 21a, or between the facing short and long sides, ruptures. As a result, the steam inside the package 1 escapes to the outside, reducing the internal pressure and releasing the steam. The steam generated from the contents 200 may contain alcohol vapor.

The function in which the breaking portion 13 ruptures and steam is released from the package 1 will be described in detail. When the package 1 containing the moisture-containing contents 200 is heated in a microwave oven, steam is generated from the contents 200, the internal pressure increases, and as a result, the package 1 expands. Since LDPE, LLDPE, CPP, etc. used as the sealant film 23 are usually unstretched and are therefore unoriented, they have lower tensile strength and larger breaking elongation values than those of stretched films. On the other hand, the biaxially stretched oriented film 21 usually has high tensile strength and small breaking elongation values, so that the film 11 formed by laminating the biaxially stretched oriented film 21 and the sealant film 23 is difficult to stretch.

However, the orientation relaxation portion 21a of the biaxially stretched oriented film 21 is the region where the orientation of the biaxially stretched oriented film 21 is relaxed or in an unoriented state, and therefore has a lower tensile strength than the orientation region, which is the orientation portion 21b of the biaxially stretched oriented film 21. In addition, the tensile elastic modulus E2 of the molecular orientation relaxation portion of the film 11 is lower than the tensile elastic modulus E1 of the molecular orientation portion. When the internal pressure increases, the package 1 expands, and the film 11 stretches, the film 11 in the region of the orientation relaxation portion 21a stretches in the width direction due to stress concentration.

At this time, the film 11 in the region of the orientation relaxation portion 21b located between the facing short sides or between the facing short and long sides of the orientation relaxation portion 21a also stretches in response to the stretching of the region of the orientation relaxation portion 21a. However, the region of the orientation relaxation portion 21a has a larger breaking elongation value and a lower tensile elastic modulus. As a result, due to the difference in breaking elongation and tensile elastic modulus between the orientation relaxation portion 21a and the orientation portion 21b, when the film 11 stretches to a certain extent, the breaking portion 13, which includes the orientation portion 21b located between the facing short sides or between the facing short and long sides of the orientation relaxation portion 21a, ruptures before other portions of the film 11, creating a small hole that releases steam. The small hole serves as a steam port 21c, through which steam is released from the package 1.

In addition, even if the film 11 includes the printed layer 24, at least in the region of the breaking portion 13, only the adhesive layer 22 is provided between the biaxially stretched oriented film 21 and the sealant film 23, and the printed layer 24 is not provided between the biaxially stretched oriented film 21 and the sealant film 23. Since the adhesive layer 22 ensures strong adhesion between the biaxially stretched oriented film 21, which is the outer layer film, and the sealant film 23, which is the inner layer film, interlayer delamination can be prevented between the biaxially stretched oriented film 21 and the sealant film 23 in the breaking portion 13 even when the internal pressure of the package 1 increases.

In other words, if the printed layer 24 is located between the biaxially stretched oriented film 21 and the sealant film 23, the adhesion between the biaxially stretched oriented film 21 and the sealant film 23 deteriorates, and interlayer delamination is more likely to occur.

In the film 11 of the embodiment, however, the printed layer 24 is not provided between the biaxially stretched oriented film 21 and the sealant film 23 at least in the breaking portion 13. Therefore, in the film 11 of the embodiment, the adhesion between the biaxially stretched oriented film 21 and the sealant film 23 in the breaking portion 13 is favorably strong, preventing interlayer delamination. As a result, stress concentration occurs at the boundary between the molecular orientation relaxation portion (the orientation relaxation portion 21a) and the molecular orientation portions (the breaking portion 13 and the orientation portion 21b) located adjacent to the molecular orientation relaxation portion (orientation relaxation portions 21a), allowing the biaxially stretched oriented film 21 and the sealant film 23 to break favorably at the breaking portion 13. Therefore, the package 1 can prevent so-called bag breakage, in which the breaking portion 13 does not break and the portion other than the breaking portion 13 breaks.

With the package 1 configured in this manner, the short sides or the short and long sides of the orientation relaxation portion 21a are arranged in the film 11, with an orientation portion 21b of a predetermined width sandwiched between them to form a breaking portion 13. Additionally, no printed layer 24 is provided between the biaxially stretched oriented film 21 and the sealant film 23 in the breaking portion 13. Thus, the package 1 can rupture in the breaking portion 13 during microwave heating to allow internal steam to release.

In the package 1 and film 11 of the embodiment described above, the printed layer 24 between the biaxially stretched oriented film 21 and the sealant film 23 is not provided in the breaking portion 13, so that interlayer delamination of the film 11 is prevented in the breaking portion 13, ensuring stable steam release during microwave heating.

The present invention is not limited to the embodiment described above. In the embodiment described above, as an example where the film 11 of the package 1 does not have a printed layer 24 between the biaxially stretched oriented film 21 and the sealant film 23 in the breaking portion 13, a structure was described in which the printed layer 24 is provided between the biaxially stretched oriented film 21 and the sealant film 23 except in the region where the breaking portion 13 is located. Specifically, the printed layer 24 was described as being positioned between the biaxially stretched oriented film 21 and the adhesive layer 22. However, this structure is not restrictive in any way.

Other embodiments of the film 11 of the package 1 will be described below. In the examples described below, the films 11 differ from the film 11 of the above-mentioned embodiment in terms of the presence, absence, or position of the printed layer 24. Therefore, similar components are assigned the same reference numerals, and a detailed description of the structures will be omitted. In each of the films 11 of the examples described below, the printed layer 24 between the biaxially stretched oriented film 21 and the sealant film 23 is not provided at least in the breaking portion 13. Therefore, interlayer delamination between the outer layer film (biaxially stretched oriented film 21) and the inner layer film (sealant film 23) can be prevented in the breaking portion 13.

As in the second embodiment shown in FIG. 14, the film 11 of the package 1 may be configured without the printed layer 24. In other words, the film 11 may be composed of the biaxially stretched oriented film 21, the adhesive layer 22, and the sealant film 23.

As in the third embodiment shown in FIG. 15, the film 11 of the package 1 may be configured such that the printed layer 24 is provided on the outer surface of the biaxially stretched oriented film 21, covering at least both the orientation relaxation portion 21a and the orientation portion 21b including the breaking portion 13. The printed layer 24 may be applied to the entire surface of the orientation portion 21b, i.e., to the entire surface of the film 11, or it may be omitted in certain portions of the orientation portion 21b.

As in the fourth embodiment shown in FIG. 16 and FIG. 17, the film 11 of the package 1 may be configured such that the printed layer 24 is not provided on the outer surface of the biaxially stretched oriented film 21 in the region where the orientation relaxation portion 21a and the breaking portion 13 are provided, but on the orientation portion 21b other than the orientation relaxation portion 21a and the breaking portion 13. The printed layer 24 may be applied to the entire region of the orientation portion 21b, excluding the orientation relaxation portion 21a and the breaking portion 13. Additionally, as shown in FIG. 17, the printed layer 24 may be applied to regions other than the region including the orientation relaxation portion 21a and the breaking portion 13; for example, it may be applied excluding the region surrounding the orientation relaxation portion 21a and the breaking portion 13.

As in the fifth embodiment shown in FIG. 18, the film 11 of the package 1 may be configured such that the printed layer 24 is provided on the outer surface of the biaxially stretched oriented film 21 and a protective film 25 is provided on the outer surface of the printed layer 24. That is, the film 11 may have a multilayer structure including the biaxially stretched oriented film 21, the adhesive layer 22, the sealant film 23, the printed layer 24, and the protective film 25. For example, the protective film 25 may be formed of the above-mentioned material used for the biaxially stretched oriented film 21 and the sealant film 23, or may be formed of another material. The printed layer 24 may be applied to the entire surface of the biaxially stretched oriented film 21, selectively omitted around the breaking portion 13, omitted around both the orientation relaxation portion 21a and the breaking portion 13, or applied to the entire surface except for specific regions. In the example of FIG. 18, the printed layer 24 is provided such that it avoids the breaking portion 13. Furthermore, as shown in FIG. 18, the protective film 25 is not provided at least in the breaking portion 13, but is provided on the outer surface side of the biaxially stretched oriented film 21 in such a manner as to avoid the breaking portion 13. The protective film 25 may be provided in such a manner as to avoid the orientation relaxation portion 21a and the breaking portion 13, or it may be provided in such a manner as to avoid the orientation relaxation portion 21a, the breaking portion 13, and the peripheries of the orientation relaxation portion 21a and the breaking portion 13.

As in the sixth embodiment shown in FIG. 19, the film 11 of the package 1 may be configured such that the printed layer 24 is provided on the outer surface of the biaxially stretched oriented film 21, excluding the region of the breaking portion 13.

As in the seventh embodiment shown in FIG. 20, the film 11 of the package 1 may be configured such that the printed layer 24 is provided between the biaxially stretched oriented film 21 and the sealant film 23, specifically, between the biaxially stretched oriented film 21 and the adhesive layer 22, except in the region where the breaking portion 13 and the orientation relaxation portion 21a are provided.

As another example, the film 11 of the package 1 may be configured such that that the printed layer 24 is provided on the outer surface of the biaxially stretched oriented film 21 and between the biaxially stretched oriented film 21 and the sealant film 23, as long as the printed layer 24 between the biaxially stretched oriented film 21 and the sealant film 23 is not provided at least in the breaking portion 13.

Furthermore, the package 1 is not limited to that described in connection with the above-described embodiments. For example, in the above-described examples, a structure was described in which the breaking portion 13 and one or more orientation relaxation portions 21a constituting the breaking portion 13 are provided in the film 11, but this structure is not restrictive in any way. For example, as in the eighth embodiment shown in FIG. 21, the film 11 does not have a breaking portion 13 or an orientation relaxation portion 21a but has an opening 11a in a portion thereof, and the package body 1 may be formed by heat-sealing a film piece 14, which includes a breaking portion 13 and one or more orientation relaxation portions 21a constituting the breaking portion 13, to that opening 11a to seal it.

In the examples described above, the package 1 is a bag-shaped package, but this is not restrictive in any way. For example, like the package 1A according to the ninth embodiment shown in FIG. 22 and FIG. 23, the package 1A may be composed of a bottomed cylindrical resin container 15 and a lid 16 that covers the opening of the resin container 15, and the lid 16 may be made of a film 11. That is, the package 1A uses the film 11 with the breaking portion 13 as the lid that covers the opening of the resin container 15.

The resin container 15 is configured, for example, as a rectangular pyramid, a polygonal pyramid, or a cone-shaped bottomed cylindrical shape, and has a flange portion 15a at the opening. The lid 16 is adhered, by heat sealing, to the flange portion 15a of the resin container 15 in which the contents 200 are contained. The lid 16 is composed of a film 11 formed in the outer shape of the flange portion 15a, and the breaking portion 13 is arranged in the center.

The package 1A configured in this manner produces the same advantages as the package 1 described above.

In the examples described above, the film 11 is configured such that the orientation relaxation portion 21a is formed in the biaxially stretched oriented film 21 by laser heating. However, for example, as in the film 11B of the tenth embodiment shown in FIG. 24 and FIG. 25, a laser light-absorbing portion 26 may be provided in a portion of the film 11B in order to form the orientation relaxation portion 21a. For example, the laser light absorption portion 26 is a portion of the film 11B with high absorbance of the laser light that is irradiated onto it. For instance, the laser light absorption portion 26 is formed by printing ink or similar materials with high absorbance of laser light. As a specific example, the laser light-absorbing portion 26 is a black printed portion made with ink containing carbon black, which enhances laser absorbance. The laser light-absorbing portion 26 is provided, for example, on the outer surface of the biaxially stretched oriented film 21 or between the biaxially stretched oriented film 21 and the sealant film 23. Specifically, it is formed on the surface of the biaxially stretched oriented film 21 facing the adhesive layer 22, in the region where the orientation relaxation portion 21a is to be formed, prior to the formation of the orientation relaxation portion 21a. In a case where the laser light-absorbing portion 26 is provided between the biaxially stretched oriented film 21 and the sealant film 23, the laser light-absorbing portion 26 is not provided at least in the region where the breaking portion 13 is to be formed. FIG. 24 shows an example in which the laser light-absorbing portion 26 is provided on the outer surface of the biaxially stretched oriented film 21.

The film 11B includes orientation relaxation portions 21a which are formed in the biaxially stretched oriented film 21 by heating the laser light-absorbing portion 26 to a predetermined temperature near its melting point or higher by laser light, and a breaking portion 13 is formed between the orientation relaxation portions 21a. The orientation relaxation portions 21a can be configured in various shapes, depending on the structure of the breaking portion 13.

In the film 11B configured in this manner, ink containing carbon black or the like is first printed on the outer surface of the biaxially stretched oriented film 21 in the region where an orientation relaxation portion 21a is to be formed, and a laser light-absorbing portion 26 is formed thereby. For example, in a case where a pair of orientation relaxation portions 21a, which are elongated in one direction and aligned longitudinally, are formed, two rectangular laser light-absorbing portions 26, also elongated in the same direction and aligned longitudinally, are formed. These are positioned either within the region of the orientation relaxation portions 21a or within a region slightly larger in the width direction.

Next, the biaxially stretched oriented film 21 and the sealant film 23 are adhered to each other via the adhesive layer 22. Subsequently, the laser light output device 100 is adjusted to output the laser light 101 at a level that does not heat the biaxially stretched oriented film 21 to a predetermined temperature near its melting point or higher and that heats the laser light-absorbing portion 26 to a predetermined temperature near its melting point or higher. Then, the laser light output device 100 is controlled to scan the laser light-absorbing portion 26.

At this time, as indicated by the arrow in FIG. 25, the laser light 101 is scanned from one laser light-absorbing portion 26 to the other laser light-absorbing portion 26 through the orientation portion 21b located between the pair of laser light-absorbing portions 26. As a result, in the region of the laser light-absorbing portion 26, the biaxially stretched oriented film 21 is heated to its melting point to form the orientation relaxation portion 21a, and in the region where the laser light-absorbing portion 26 is not provided, the biaxially stretched oriented film 21 does not melt and remains oriented. Through these steps, the film 11B for use in the package 1 is manufactured, and can be used for either one of the packages 1 and 1A.

The film 11B configured in this manner provides the same advantages as the film 11 according to the first embodiment. Furthermore, since the laser light-absorbing portion 26 is located in the region where the orientation relaxation portions 21a are to be formed, the film 11B requires only a single scan of the laser light 101, as shown in FIG. 25.

Specifically, two scans of the laser light are required to form two orientation relaxation portions 21a. However, as with the film 11B, the laser light-absorbing portion 26 is provided and the output of the laser light 101 is adjusted such that the biaxially stretched oriented film 21 melts only at the laser light-absorbing portion 26. Thus, two orientation relaxation portions 21a can be formed in a single scan. In this way, the number of scans of the laser light 101 can be reduced, improving both the production efficiency of film 11B and the accuracy of the orientation relaxation portions 21a to be formed.

In the above examples, a description was given of the case where the package 1 and films 11 and 11B have breaking portions 13 between the facing alignment relaxation portions 21a, but this is not restrictive in any way. As shown in the eleventh embodiment in FIG. 26, the film 11C may have a structure in which the breaking portion 13 includes a continuous portion 21f that connects the short sides or the short and long sides of the facing orientation relaxation regions 21a. This continuous portion 21f is a region that is rendered unoriented by melting the biaxially stretched orientation film 21. The continuous portion 21f constitutes part of the breaking portion 13. The continuous portion 21f is provided in part of the orientation portion 21b located between the facing short sides or between the facing short and long sides of the orientation relaxation portions 21a. In other words, the continuous portion 21f is configured such that its width is smaller than the width of the short sides of the orientation relaxation portions 21a.

A method for manufacturing the film 11C configured in this manner will be described. For example, ink containing carbon black or the like is first printed on the outer surface of the biaxially stretched oriented film 21 in the region where an orientation relaxation portion 21a is to be formed, and a laser light-absorbing portion 26 is formed thereby. For example, in a case where a pair of orientation relaxation portions 21a, which are elongated in one direction and aligned longitudinally, are formed, two rectangular laser light-absorbing portions 26, elongated in the same direction and aligned longitudinally, are formed. These are positioned either within the region of the orientation relaxation portions 21a or within a region slightly larger in the width direction.

Next, the biaxially stretched oriented film 21 and the sealant film 23 are adhered to each other via the adhesive layer 22. Subsequently, the laser light output device 100 is adjusted to output the laser light 101 at a level that heats the biaxially stretched oriented film 21 to a predetermined temperature near its melting point or higher. Then, the laser light output device 100 is controlled to scan the laser light-absorbing portion 26.

At this time, the laser light 101 is scanned in a single process from one laser light-absorbing portion 26 to the other laser light-absorbing portion 26 through the alignment portion 21b located between the pair of laser light-absorbing portions 26. As a result, in the region of the laser light-absorbing portions 26, the biaxially stretched oriented film 21 is heated to its melting point, forming an orientation relaxation portion 21a with a large width in the short-side direction. In regions where the laser light-absorbing portions 26 are not present, a continuous portion 21f with a smaller width than that of the orientation relaxation portion 21a is formed. Through these processes, the film 11C for use in the package 1 is manufactured, and it can be used in packages of any shape, such as package 1 or 1A.

The film 11C configured in this manner is similar to the film 11 according to the first embodiment in that the continuous portion 21f breaks at the breaking portion 13 of the film 11 during microwave heating, forming the steam port 21c. This is because when the internal pressure of the package 1, 1A increases during microwave heating and the biaxially stretched oriented film 21 stretches, the continuous portion 21f breaks first, since the width of the continuous portion 21f is smaller than the width of the orientation relaxation portion 21a and the absolute value of the amount of stretch is smaller in the continuous portion 21f than in the orientation relaxation portion 21a.

It should be noted that the method of forming the orientation relaxation portion 21a and the continuous portion 21f is not limited to laser light heating, and methods such as hot plate heating, impulse heating, and near-infrared heating can also be used. Additionally, the film 11C need not be provided with the laser light-absorbing portion 26.

The present invention is not limited to the above-mentioned embodiments. For example, in connection with the above examples, a description was given of the structure in which the package includes a pillow packaging bag for the package 1, and a resin container 15 and a lid 16 for the package 1A, but the present invention is not limited to this structure. As long as the package includes a sealed space for containing the contents 200, the films 11, 11B, and 11C are stretchable in accordance with an increase in the internal pressure of the package 1 or 1A, and the breaking portion 13 is breakable, the shape of the package can be appropriately determined, and the film 11 can be used for the package. Other examples of the shape of the package include a three-side-sealed flat pouch, a half-fold-sealed flat pouch, a gusseted pouch, and a standing pouch.

In connection with the above examples, a description was given of an example in which the film 11 has a higher breaking elongation value in the region of the orientation relaxation portion 21a than in the orientation portion 21b, and in which the relationship between the tensile elastic modulus E1 in the molecular orientation portion of the film 11 and the tensile elastic modulus E2 in the molecular orientation relaxation portion satisfies 0<E2/E1<0.5. However, the film 11 may be configured such that either the breaking elongation of the orientation relaxation portion 21a and the orientation portion 21b or the tensile elastic modulus E2/E1 satisfies the above-mentioned relationship.

That is, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made in the implementation stage without departing from the gist of the invention. In addition, the embodiments may be implemented by combining them as appropriate, in which case the combined advantages are obtained. Furthermore, the above-described embodiments include various inventions, and a variety of inventions can be derived by selectively combining components disclosed in connection with the embodiments. For example, if the object is achieved and the advantages are attained even after some of the components disclosed in connection with the embodiments are deleted, the structure made up of the resultant components can be extracted as an invention.

REFERENCE SIGNS LIST

• • 1, 1A . . . Package, 11, 11B, 11C . . . Film, 11a . . . Opening, 12 . . . Sealed Portion, 13 . . . Breaking Portion, 14 . . . Film Piece, 15 . . . Resin Container, 15a . . . Flange Portion, 16 . . . Lid, 21 . . . Biaxially Stretched Oriented Film, 21a . . . Orientation Relaxation Portion, 21b . . . Oriented Portion, 21c . . . Steam Port, 21f . . . Continuous Portion, 22 . . . Adhesive Layer, 23 . . . Sealant Film, 24 . . . Printed Layer, 25 . . . Protective Film, 26 . . . Laser Light-Absorbing Portion, 100 . . . Laser Light Output Device, 101 . . . Laser Light, 200 . . . Contents

Claims

1. A film used for a package in which an internal pressure of a container increases when heated in a microwave oven, and steam is released to reduce the internal pressure, the film comprising: an outer layer film molecularly oriented by biaxial stretching;an inner layer film laminated to the outer layer film and capable of being heat-sealed;one or more orientation relaxation portions formed in the outer layer film; anda breaking portion formed at a position which the one or more orientation relaxation portions faces with a predetermined distance, and configured to rupture when the internal pressure of the container increases during microwave heating,wherein at least in the breaking portion, a printed layer is omitted between the outer layer film and the inner layer film.

2. The film according to claim 1, wherein the printed layer is provided between the outer layer film and the inner layer film in at least part of a region excluding the breaking portion.

3. The film according to claim 1, wherein the printed layer is provided on an outer surface side of the outer layer film.

4. The film according to claim 3, wherein the printed layer provided on the outer surface side of the outer layer film is located in a region excluding the breaking portion.

5. The film according to claim 1, wherein the printed layer between the outer layer film and the inner layer film is omitted in the breaking portion and the orientation relaxation portions.

6. A package wherein the film as recited in claim 1 is used as at least part of a packaging material.

7. The package according to claim 6, wherein the printed layer is provided between the outer layer film and the inner layer film in at least part of a region excluding the breaking portion.

8. The package according to claim 6, wherein the printed layer is provided on an outer surface side of the outer layer film.

9. The package according to claim 8, wherein the printed layer provided on the outer surface side of the outer layer film is located in a region excluding the breaking portion.

10. The package according to claim 6, wherein the printed layer between the outer layer film and the inner layer film is omitted in the breaking portion and the orientation relaxation portions.

11. The package according to claim 6, wherein inner layer films are heat-sealed together to form a bag-like structure for accommodating contents, and the orientation relaxation portions and the breaking portion are disposed in a region that constitutes the bag-like structure.

12. The package according to claim 6, comprising: the film, anda container body including a flange around an opening and configured to contain contents,wherein the inner layer film of the film is heat-sealed to the flange to cover the opening, and the orientation relaxation portions and the breaking portion are arranged at a position facing the opening.

13. A contents-containing package comprising: the package as recited in claim 6, andcontents contained within the package.