Microwave packaging bag and method for manufacturing a microwave packaging bag

Abstract

To suppress the occurrence of bursting or popping sounds when heating in a microwave oven. [Solution] The microwave packaging bag has a vapor-permeable portion formed in a part of the sealed portion where the peripheral edge of the laminated sheet is heat-sealed, allowing steam to pass through. The laminated sheet has a base layer, a heat-adhesive resin layer, and a dry laminate layer. The vapor-permeable portion has an easily peelable portion made of a laminate strength-reducing varnish whose laminate strength is lower than the laminate strength of the base layer and the dry laminate layer, and a plurality of holes that penetrate at least the base layer in the thickness direction.

Description

Technical Field

[0001] The present invention relates to a packaging bag for a microwave oven and a method for manufacturing the packaging bag for a microwave oven.

Background Art

[0002] There is a packaging bag made of a plastic film, which contains food and is sealed, and then distributed in a sealed state. Among this type of packaging bag, there is one that is compatible with a microwave oven and can be directly heated in the microwave oven while in a sealed state. When heating a packaging bag in a sealed state in a microwave oven, the internal pressure of the packaging bag increases and it bulges due to the water vapor evaporated from the food during heating and the thermal expansion of the air inside the packaging bag.

[0003] Regarding the packaging bag compatible with a microwave oven, an invention has been proposed in which a foamed ink layer composed of foamed ink is laminated as an intermediate layer on the part where the pressure of the plastic film is released, and the foamed ink layer is configured to vent steam from between the layers or the interface (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of a configuration in which a foamed ink layer is formed in the intermediate layer of a plastic film, if a material that is easy to stretch is selected as the base material layer inside both resin layers sandwiching the foamed ink layer, especially when the base material layer is a polyolefin-based resin, it may rupture.

[0006] The present invention aims to provide a microwave packaging bag that, even if the base material layer is made of a polyolefin resin that is easily stretchable, is configured to reliably release internal steam and air to the outside when the internal pressure rises during microwave heating, thereby suppressing the occurrence of bursting or popping noises. [Means for solving the problem]

[0007] To achieve the above objective, the microwave packaging bag of the present invention has a storage space for containing contents. The microwave packaging bag has a sealed portion formed by heat-sealing at least a part of the peripheral edge of laminated sheets arranged front to back, and a permeable portion formed in a part of the sealed portion that allows steam from the storage portion to pass through. The laminated sheet has a base layer, a heat-adhesive resin layer arranged inside the base layer, and a dry laminate layer that adheres the base layer and the heat-adhesive resin layer. The permeable portion has an easily peelable portion formed between the base layer and the dry laminate layer and composed of a laminate strength reducing varnish that is lower than the laminate strength between the base layer and the dry laminate layer, and a plurality of holes that penetrate at least the base layer in the thickness direction in the portion of the laminated sheet that constitutes the permeable portion. [Effects of the Invention]

[0008] According to the microwave packaging bag of the present invention, when the internal pressure increases during heating in a microwave oven, the steam and air inside are quickly released, thereby suppressing the occurrence of bursting or popping noises. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a rear view of an example of a microwave-safe packaging bag 1. [Figure 2] Figure 2 is an exploded perspective view of the microwaveable packaging bag 1 shown in Figure 1. [Figure 3] Figure 3 is a plan view of the resin sheet used in the packaging bag shown in Figure 1. [Figure 4]Figure 4 shows the raw material being unwound from the raw material roll before it is formed into a resin sheet. [Figure 5] Figure 5 is a cross-sectional view of the vicinity of the vapor-permeable portion of the resin sheet in the first embodiment. [Figure 6] Figure 6 is an enlarged cross-sectional view showing the steam vent portion of the microwave packaging bag of the first embodiment. [Figure 7] Figure 7 is a flowchart showing an example of the manufacturing process for microwaveable packaging bags. [Figure 8] Figure 8 is an enlarged cross-sectional view of the steam vent portion of the microwave packaging bag according to the second embodiment. [Figure 9] Figure 9 is an enlarged cross-sectional view of the steam vent of another example of the microwave packaging bag of the second embodiment. [Figure 10] Figure 10 shows a modified example of the shape of the holes in the steam passage section. [Figure 11] Figure 11 shows a modified example of the shape of the holes in the steam passage section. [Modes for carrying out the invention]

[0010] <First Embodiment> Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a rear view of an example of a microwave oven packaging bag 1. Figure 2 is an exploded perspective view of the microwave oven packaging bag 1 shown in Figure 1. Figure 3 is a plan view of the resin sheet 10 used in the packaging bag shown in Figure 1. Figure 4 is a diagram showing the raw material 20 being unwound from the raw material roll 201 before it is formed into the resin sheet 10. Figure 5 is a cross-sectional view of the vicinity of the steam-permeable portion 23 of the resin sheet in the first embodiment.

[0011] The microwave packaging bag 1 is a so-called pillow-type packaging bag, and is rectangular when viewed from the back. The microwave packaging bag 1 has a back seal portion 21 and an end seal portion 22. The back seal portion 21 and the end seal portion 22 are formed by heat bonding a part of the resin sheet 10 that makes up the microwave packaging bag 1. The back seal portion 21 is formed in the center of the short side of the back of the microwave packaging bag 1 and extends in the longitudinal direction. The end seal portion 22 extends along both sides in the longitudinal direction of the microwave packaging bag 1.

[0012] As shown in Figure 2, the microwave packaging bag 1 is made up of a single rectangular resin sheet 10. The resin sheet 10 has a first strip-shaped portion 101 that is located at both ends in the longitudinal direction and formed along the short side, and a second strip-shaped portion 102 that is located at both ends in the short direction and formed along the long side.

[0013] The resin sheet 10 is bent so that the heat-adhesive resin layers 12 of the first strip-shaped portions 101 at both ends in the longitudinal direction come into contact with each other. The first strip-shaped portions 101 are then heated and pressurized to heat-bond them. As a result, the resin sheet 10 is formed into a cylindrical body 100 with a back seal portion 21. In the cylindrical body 100, the second strip-shaped portions 102 are positioned at both openings (see Figure 2).

[0014] Then, the contents S are placed inside the cylindrical body 100, and the heat-adhesive resin layers 12 of the second strip-shaped portions 102 located at both openings of the cylindrical body 100 are brought into contact with each other. By heating and pressurizing, the second strip-shaped portions 102 are heat-bonded. This forms the end seal portion 22. As a result, a microwave-safe packaging bag 1 is formed in which the contents S are contained in the storage portion 103 and sealed.

[0015] When looking at the packaging bag 1 for a microwave oven from the front and back, a steam vent portion 23 is formed at a portion where the back seal portion 21 of the end seal portion 22 intersects with the front and back. To explain further, a back seal portion 21 is formed on a part of the end seal portion 22. And the end seal portion 22 is formed by arranging and thermally bonding the second strip portion 102 in the front and back directions. And the steam vent portion 23 is formed on the second strip portion 102 on the side opposite to the side where the back seal portion 21 of the end seal portion 22 is arranged.

[0016] As shown in FIG. 2 etc., the steam vent portion 23 is formed at the central portion in the longitudinal direction of the second strip portion 102. The steam vent portion 23 is configured to release the air and steam inside the accommodating portion 103 to the outside when the pressure inside the accommodating portion 103 rises. Details of the steam vent portion 23 will be described later.

[0017] Next, the detailed configuration of the resin sheet 10 will be described. The resin sheet 10 has a laminated structure in which a heat - adhesive resin layer 12 (see FIG. 4) described later is laminated on the inner - side surface. As shown in FIG. 5, the resin sheet 10 has a structure in which a base material layer 11, a dry - laminate layer 13, and a heat - adhesive resin layer 12 are laminated in order from the outside to the inside of the packaging bag 1 for a microwave oven.

[0018] The base material layer 11 is formed of, for example, polypropylene (PP) with a thickness of about 20μm. The polypropylene constituting the base material layer 11 can be, for example, a uniaxially or biaxially stretched polypropylene (OPP) film. The biaxially stretched polypropylene (OPP) film used for the base material layer 11 in this embodiment has, for example, a breaking strength in the MD direction described later of 100 MPa and a breaking elongation of 300% at a temperature of 80°C. Also, the breaking strength in the MD direction at a temperature of 100°C is 80 MPa and the breaking elongation is 400%.

[0019] The heat-adhesive resin layer 12 is formed, for example, from polyethylene (PE) with a thickness of approximately 40 μm. Examples of polyethylene that can constitute the heat-adhesive resin layer 12 include linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). In addition, inorganic agents such as titanium dioxide and carbon black may be contained in these films. This can impart light-shielding properties to the laminate. The heat-adhesive resin layer 12 is composed of a resin that has a tensile elongation at break in the MD direction of 10 percent to 100 percent at a 100°C environment, and has the characteristic of being relatively difficult to stretch and easy to break in a heated environment.

[0020] The base material layer 11 and the heat-adhesive resin layer 12 are bonded together by the dry laminate layer 13. The dry laminate layer 13 is made of a material such as urethane with a thickness of approximately 3 μm. In other words, the base material layer 11 and the heat-adhesive resin layer 12 are bonded together by the dry laminate layer 13 formed by the dry lamination method.

[0021] Furthermore, a printing layer 15 for printing patterns, etc., is formed at a predetermined position on the lower surface (heat-adhesive resin layer 12 side) of the base layer 11. The printing layer 15 may also be provided on the upper surface (outside) of the base layer 11. The printing layer 15 is formed to a thickness of approximately 1-3 μm by ink placed at a predetermined position on the base layer 11. On the lower surface (inside) of the base layer 11, a layer with a transparent vapor-deposited film, a barrier coat layer using polyvinyl alcohol (PVA), etc., may be formed. Examples of transparent vapor-deposited films include those formed from silica or alumina.

[0022] As shown in Figure 4, the resin sheet 10 is formed by cutting a continuous, long roll of raw material 20 with the same layer structure at a predetermined pitch P. When the raw material 20 is cut at the predetermined pitch P, the portion of the resin sheet 10 adjacent to the cutting line 202 is the second strip portion 102. The raw material 20 is provided as a roll of raw material 201 wound into a roll shape. The resin sheet 10 is formed by pulling the raw material 20 from the roll of raw material 201 and cutting it. The direction in which the raw material 20 is pulled from the roll of raw material 201 is defined as the film pulling direction (MD direction), and the direction perpendicular to the MD direction is defined as the TD direction.

[0023] In the resin sheet 10, a vapor-permeable portion 23 is formed in the central part of the second strip-shaped portion 102 in the TD direction, adjacent to the cutting line 202. The breaking strength of the base layer 11 of the resin sheet 10 in the MD direction is different from the breaking strength in the TD direction. More specifically, the breaking strength of the base layer 11 in the TD direction is higher than the breaking strength in the MD direction. Also, the elongation of the base layer 11 in the MD direction is greater than the elongation in the TD direction. Furthermore, the breaking strength of the base layer 11 in the MD and TD directions decreases with increasing temperature, while the elongation (deformation) increases with increasing temperature.

[0024] As shown in Figure 3, the resin sheet 10 constituting the microwave packaging bag 1 is formed such that end seal portions 22 are arranged at both ends in the MD direction. When the microwave packaging bag 1 is heated, the base material layer 11 of the resin sheet 10 stretches more in the MD direction than in the TD direction and is more prone to tearing in the MD direction.

[0025] Next, the configuration of the steam-permeable section 23 of the resin sheet will be described. Figure 6 is an enlarged cross-sectional view of the steam-permeable section of the microwave packaging bag of the first embodiment.

[0026] As shown in Figures 5 and 6, an easy-peel portion 14 is positioned between the base material layer 11 and the dry laminate layer 13 in the vapor-permeable portion 23. The easy-peel portion 14 may be formed between the printed layer 15 and the dry laminate layer 13, or the printed layer 15 may not be placed in the area where the easy-peel portion 14 is formed, and the easy-peel portion 14 may be formed in direct contact with the base material layer 11.

[0027] The easily peelable portion 14 is a part that reduces the lamination strength between the base material layer 11 and the dry laminate layer 13 of the vapor-permeable portion 23. In this embodiment, the easily peelable portion 14 is formed with a lamination strength-reducing varnish. The lamination strength-reducing varnish reduces the lamination strength between the base material layer 11 and the dry laminate layer 13.

[0028] As the varnish that reduces the laminate strength, an ink containing a release agent, a foaming ink in which the gas in the microcapsules contained in the ink foams up due to the heat and pressure during filling and sealing, and a brightness ink containing aluminum paste can be appropriately selected. The easily peelable portion 14 may also be constructed by applying multiple coats of ink such as silver ink, pearl ink, or white ink. In this case, the application amount is preferably 3 g / m2·dry or more.

[0029] Furthermore, the ink selected when applying multiple coats of ink to form the easily peelable portion 14 may be selected to match the design formed by the printed layer 15. In particular, when the easily peelable portion 14 is formed in direct contact with the substrate layer 11, the easily peelable portion 14 may be made to form part of the design formed by the printed layer 15. The easily peelable portion 14 may also be formed by printing in the same way as or at the same time as the printed layer 15.

[0030] Multiple holes 3 are formed in the vapor-permeable section 23, penetrating the base material layer 11 and the dry laminate layer 13 in the thickness direction. For example, the holes 3 are cylindrical and penetrate from the upper surface (outer surface) to the lower surface (inner surface) of the base material layer 11. Note that the shape of the holes 3 is just an example and is not limited to a cylindrical shape. In addition, in the resin sheet 10 of this embodiment, the holes 3 also penetrate the dry laminate layer 13. Note that the holes 3 may not reach the dry laminate layer 13, and may be configured so that a part of them is formed in the dry laminate layer 13, that is, the ends of the holes 3 reach the middle part of the dry laminate layer 13, or the holes 3 may penetrate the resin sheet 10, that is, penetrate the heat-adhesive resin layer 12. The holes 3 only need to penetrate at least the base material layer 11.

[0031] However, as will be explained in detail later, it is preferable for the holes 3 in the resin sheet 10 to penetrate to the heat-adhesive resin layer 12 due to the manufacturing process. Even if the holes 3 penetrate to the heat-adhesive resin layer 12, most of the holes 3 will be closed when the end seal is formed by heat sealing. As a result, the holes 3 will be formed in the base layer 11, the dry laminate layer 13, and a portion of the heat-adhesive resin layer 12 that was not completely filled during heat sealing. Alternatively, the holes may penetrate two layers of the resin sheet 10 after the end seal has been formed by heat sealing and then heat-welded.

[0032] In the steam-permeable section 23, the multiple holes 3 are arranged with spacing in the MD direction and the TD direction. Some or all of the holes 3 are provided so as to penetrate the easy-peel section 14 in the thickness direction of the resin sheet 10. In the microwave packaging bag 1, heating generates steam inside the containment section 103 and the gas filled inside expands. As a result, the base material layer 11 deforms in the MD direction and the TD direction. Because the holes 3 are formed in the base material layer 11, the displacement in the MD direction and the TD direction due to thermal deformation is discontinuous due to the holes 3.

[0033] Thus, in the steam-permeable section 23, the easily peelable section 14 and the multiple holes 3 are formed, making it easier to peel the base material layer 11 from the dry laminate layer 13, that is, the base material layer 11 from the heat-adhesive resin layer 12, compared to other parts of the end seal section 22, and suppressing deformation of the base material layer 11.

[0034] <Manufacturing process for microwaveable packaging bag 1> The manufacturing process of the microwave packaging bag 1 with the above configuration will be explained with reference to the drawings. Figure 7 is a flowchart showing an example of the manufacturing process of the microwave packaging bag 1. As shown in Figure 7, a printed layer 15 is formed on the lower surface of the resin film (see Figure 5) that constitutes the base layer 11 made of biaxially oriented polypropylene (printing process: S101). An easy-peel portion 14 is formed by applying a laminate strength reducing varnish to the lower surface of the printed layer 15 in the portion of the base layer 11 where the vapor-permeable portion 23 is formed (easy-peel portion formation process: S102).

[0035] A dry laminate layer 13 is formed on the lower surface of the base layer 11 where the printed layer 15 and the easily peelable portion 14 are formed (dry laminate layer formation step: step S103). As a result, the dry laminate layer 13 is formed on the inner surface of the base layer 11.

[0036] Subsequently, a heat-adhesive resin layer 12 is formed on the inner surface (bottom surface) of the dry laminate layer 13 (heat-adhesive resin layer formation step: step S104). Then, a hole 3 is formed in the portion of the second strip-shaped portion 102 where the vapor-permeable portion 23 is formed, so as to penetrate at least the base material layer 11, the printed layer 15, and the easily peelable portion 14, and preferably the dry laminate layer 13 and the heat-adhesive resin layer 12 (hole formation step: step S105). The hole 3 is configured to penetrate the base material layer 11, the printed layer 15, the easily peelable portion 14, and the dry laminate layer 13 from top to bottom, but is not limited to this. The hole 3 only needs to be configured to penetrate at least the base material layer 11. The hole 3 may be formed by a mechanical processing method using a machining center, or by a chemical method. Here, it is assumed that the hole 3 is formed by drilling using a machining center.

[0037] In this way, a raw material roll 20 is produced from a biaxially oriented polypropylene resin film before forming the resin sheet 10. Subsequently, a raw material roll 201 is formed by winding the raw material roll 20 into a roll shape (winding process: step S106).

[0038] The manufacturing apparatus described so far forms a printed layer 15 and an easily peelable section 14 on the resin film constituting the base layer 11, and then laminates a heat-adhesive resin layer 12 via a dry laminate layer 13. After this, the raw material roll 201 is transferred to the apparatus for manufacturing packaging bags, where a resin sheet 10 is formed, and then a microwave-safe packaging bag 1 is manufactured. Note that if the process of laminating each of the above layers onto the resin film and the process of manufacturing the packaging bag, which will be described later, are carried out as a series of processes, the winding process may be omitted.

[0039] As shown in Figure 4, the raw material 20 is cut at a predetermined pitch P in the MD direction (cutting step: step S107). The raw material 20 may be cut mechanically using a blade, or it may be cut by irradiating it with laser light. In addition, a wide range of cutting methods that can accurately cut along the cutting line 202 can be used. The resin sheet 10 is formed by cutting the raw material 20 in the cutting step S107. In order to cut accurately in the cutting step, cutting lines may be provided on the raw material 20 at a predetermined pitch P. In this case, the cutting step can be configured to cut along the cutting line.

[0040] The rectangular resin sheet 10 is positioned with its first strip-shaped portions 101 at both ends in the TD direction abutted together (sheet bending process: step S108). At this time, the sheets are positioned so that the heat-adhesive resin layers 12 of the first strip-shaped portions 101 are in contact with each other. Then, by heating and pressurizing the abutted first strip-shaped portions 101, the first strip-shaped portions 101 are heat-bonded, and a back seal portion 21 is formed (heat bonding process: step S109). As a result, a cylindrical body 100 is formed from the resin sheet 10.

[0041] Second strip-shaped portions 102 are positioned at the ends of both openings of the cylindrical body 100. In this state, the second strip-shaped portion 102 positioned at one end of one opening is placed on top of the other. At this time, the inner surfaces of the second strip-shaped portions 102 come into contact with each other. The heat-adhesive resin layers 12 of the second strip-shaped portions 102 come into contact with each other, and by heating and pressurizing the second strip-shaped portions 102, the front and back second strip-shaped portions 102 are heat-bonded together (heat bonding process: step S110).

[0042] As a result, the cylindrical body 100 becomes a bag-like shape with one opening closed. After the contents S are placed inside the cylindrical body 100 through the closed opening, the second strip-shaped portions 102 located at the ends of the opening are heat-bonded together (heat bonding step: step S111). In the heat bonding step of step S111, the same process as in the heat bonding step of step S110 is performed. This forms a microwave-safe packaging bag 1 with the contents S contained in the storage portion 103 and sealed.

[0043] In the manufacturing process of the microwave packaging bag 1 described above, one of the second strip-shaped portions 102 is heat-sealed to close one opening of the cylindrical body 100, the contents S are placed inside, and the other second strip-shaped portion 102 is heat-sealed. However, the process is not limited to this. For example, the contents S may be placed inside the cylindrical body 100, and then the second strip-shaped portions 102 forming both openings may be heat-sealed. In the microwave packaging bag 1, the air inside the containment portion 103 may be removed, or the containment portion 103 may be filled with an inert gas such as nitrogen gas.

[0044] <Regarding steaming during heating of microwave packaging bag 1> When the microwave-safe packaging bag 1 is heated in a microwave oven, the pressure inside the containment section 103 increases due to the thermal expansion of the air inside the containment section 103 and the steam generated by the evaporation of moisture contained in the contents S. As the pressure inside the containment section 103 increases, the microwave-safe packaging bag 1 swells, and the stress acting on the resin sheet 10 increases. The stress acting on the resin sheet 10 is concentrated near the end seal section 22.

[0045] The resin sheet 10 expands significantly (stretches) due to heating and the increase in pressure inside the containment section 103. As described above, the base layer 11 is made of polypropylene (PP), and the heat-adhesive resin layer 12 is made of polyethylene (PE). The base layer 11 is made of a material that is easily stretched, and the heat-adhesive resin layer 12 is made of a material that is relatively easy to break when heated. Therefore, when the microwave packaging bag 1 is heated in a microwave oven, the heat-adhesive resin layer 12 and the base layer 11 deform. The base layer 11 elongates more in the MD direction than in the TD direction. The end seal section 22 is elongated and extends along the TD direction. When the base layer 11 deforms due to the increase in pressure inside the containment section 103, the deformation (displacement) in the MD direction is greater than the deformation (displacement) in the TD direction in the steam-permeable section 23.

[0046] If the packaging bag does not have a ventilation section 23, the heat-adhesive resin layer 12 will rupture if a force exceeding its breaking strength is applied to it due to the increase in internal pressure in the containment section 103. In addition, the base layer 11 will also deform due to the increase in internal pressure in the containment section 103. At this time, the base layer 11 is stretched at a high temperature, but because the base layer 11 has a high tensile elongation rate at high temperatures, the film thickness becomes thinner, and the base layer 11 ruptures following the rupture of the heat-adhesive resin layer 12. For example, the stress acting on the heat-adhesive resin layer 12 due to the increase in internal pressure in the containment section 103 is concentrated at the boundary with the end seal section 22. Within the end seal section 22, a greater stress acts on the central part of the heat-adhesive resin layer 12 in the TD direction than on both ends in the TD direction. Therefore, rupture is more likely to occur near the central part of the end seal section 22 in the TD direction.

[0047] If the heat-adhesive resin layer 12 and the base layer 11 rupture while the internal pressure of the containment section 103 is high, the air and steam inside the containment section 103 will be forcefully ejected to the outside. At this time, the contents S contained in the containment section 103 may be ejected to the outside, guided by the ejection of air and steam. Also, if the base layer 11, which is a stretched film, ruptures, a popping sound may occur when air and steam are ejected, even if the contents S are not ejected. In either case, the convenience for the user is reduced.

[0048] In contrast, the microwave packaging bag 1 according to this embodiment has a steam-permeable section 23 in the central part of the TD direction where stress tends to concentrate in the end seal section 22. The steam-permeable section 23 has a plurality of holes 3, and an easy-peel section 14 printed with a laminate strength-reducing varnish that reduces the laminate strength is placed between the base material layer 11 and the heat-adhesive resin layer 12.

[0049] In the steam passage section 23, the resin sheet 10 deforms due to the increase in pressure inside the containment section 103. At this time, in the steam passage section 23, the lamination strength between the base material layer 11 and the heat-adhesive resin layer 12 is weak, so the base material layer 11 and the heat-adhesive resin layer 12 each deform.

[0050] In the vapor-permeable section 23, the presence of an easily peelable section 14 divides the base layer 11 into a dry laminate layer 13 and a heat-adhesive resin layer 12. As a result, the dry laminate layer 13 and the heat-adhesive resin layer 12 rupture from the seal edge 221 of the end seal section 22 due to thermal expansion. Since the heat-adhesive resin layer 12 is an unstretched film, the popping sound associated with its rupture is milder compared to that of a stretched film and is less likely to be perceived as a popping sound. In other words, in the vapor-permeable section 23, the resin sheet 10 is divided in the thickness direction by the easily peelable section 14 compared to the part of the end seal section 22 where the vapor-permeable section 23 is not formed, thus suppressing the deformation of the base layer 11 due to the deformation of the heat-adhesive resin layer 12.

[0051] Furthermore, in the microwave packaging bag 1, the lamination strength is reduced in the steam-permeable section 23 by the easy-peel section 14, and the presence of holes 3 minimizes deformation due to thermal expansion of the easily stretchable base material layer 11.

[0052] Furthermore, if the base layer 11, which is made of a polyolefin material that is easily stretchable, does not have holes 3, the base layer 11 will become thinner due to thermal expansion in the MD direction before the steam can be discharged to the outside, leading to rupture. As a result, a burst will occur. However, if the base layer 11 is made of a material such as biaxially oriented polyester or biaxially oriented polyamide, which has a tensile elongation in the MD direction of less than 300% at a 100°C environment, it is not necessary to provide holes 3.

[0053] A fractured portion 120 (see Figure 6) is formed due to the stress in the heat-adhesive resin layer 12 and the decrease in tensile strength resulting from the reduction in thickness due to thermal deformation of the heat-adhesive resin layer 12. However, since the base layer 11 is provided with an easily peelable portion 14, the displacement associated with the deformation of the heat-adhesive resin layer 12 and the dry laminate layer 13 is not easily transmitted, and even if the heat-adhesive resin layer 12 and the dry laminate layer 13 fracture, the base layer 11 will not fracture.

[0054] As a result of the formation of the fractured section 120, high-temperature steam generated in the containment section 103 penetrates through the fractured section 120 to the boundary between the dry laminate layer 13 and the easily peelable section 14. In the steam-permeable section 23, holes 3 are formed that penetrate the base material layer 11 and the dry laminate layer 13. Therefore, the steam that penetrates to the boundary between the dry laminate layer 13 and the easily peelable section 14 is discharged to the outside through the holes 3.

[0055] Some of the steam passing through the hole 3 flows into the area where the easily peelable section 14 is formed. The easily peelable section 14 is made of a laminate strength-reducing varnish. Therefore, the easily peelable section 14 is peeled off by the incoming high-temperature steam. In other words, the substrate layer 11 and the heat-adhesive resin layer 12 are separated in the area where the easily peelable section 14 is located.

[0056] Therefore, due to the aforementioned effect of the laminate strength-reducing varnish, the air and steam inside the containment section 103 that flowed into the vapor-permeable section 23 are discharged from the holes 3, but any remaining air and steam are also discharged from between the base material layer 11 and the heat-adhesive resin layer 12.

[0057] The same applies even if the pore portion 3 is not formed up to the dry laminate layer 13.

[0058] In other words, in the microwave packaging bag 1, by having a steam-permeable portion 23 in the central part of the TD direction where stress tends to concentrate in the end seal portion 22, rupture is suppressed in parts other than the end seal portion 22 and the nearby steam-permeable portion 23.

[0059] Furthermore, because the steam passage section 23 has the above-described configuration, steam can be discharged while suppressing the rupture of the base material layer 11 due to an increase in the internal pressure of the containment section 103. As a result, even if the internal pressure of the containment section 103 increases due to heating in a microwave oven, the scattering of contents S and the generation of a rupture sound due to the rupture of the base material layer 11 can be suppressed.

[0060] Furthermore, it is preferable that the total cross-sectional area of ​​the holes 3 has a cross-sectional area that can achieve a flow rate sufficient to cause peeling by the easily peelable portion 14 with steam flowing between the base material layer 11 and the dry laminate layer 13 of the vapor-permeable portion 23 when the heat-adhesive resin layer 12 ruptures. For example, the area ratio of the holes 3 to the vapor-permeable portion 23 can be 1% or more and less than 50%.

[0061] In this embodiment, the steam passage 23 is formed at the point where both end seal portions 22 intersect with the back seal portion 21, but is not limited to this. The steam passage 23 may be formed at the point where one end seal portion 22 intersects with the back seal. Furthermore, the portion where the steam passage 23 is formed is not limited to the point where the end seal portion 22 intersects with the back seal portion 21, but may be formed at a position offset from the point where the end seal portion 22 intersects with the back seal portion 21. In addition, the steam passage 23 may be formed in the middle portion in the longitudinal direction of the back seal portion 21. Moreover, a plurality of steam passages 23 may be formed in the microwave packaging bag 1. It is preferable that the steam passage 23 is formed near the point where stress concentrates in the heat-adhesive resin layer 12 when the internal pressure of the containment portion 103 increases.

[0062] In this embodiment, the microwave packaging bag 1 is a pillow-type packaging bag, but is not limited thereto. For example, it can be widely used for packaging bags constructed by heat-sealing predetermined positions of overlapping resin sheets, such as a gusset type with a gusset on the side, a three-sided sealed type made by folding a single resin sheet and heat-sealing three sides, a four-sided sealed type made by overlapping two resin sheets and heat-sealing the periphery, and a self-standing type with a bottom.

[0063] In this embodiment, the steam vent section 23 of the microwave packaging bag 1 is configured to release air and steam from inside the containment section 103 to the outside through the holes 3. However, the invention is not limited to this configuration, and the base layer 11 may be configured such that cracks are formed to increase the flow rate as air and steam flow out. Here, a crack configuration could be such that the holes 3 connect to each other and the opening slowly enlarges.

[0064] <Second Embodiment> The microwave packaging bag of the second embodiment will be described with reference to the drawings. Figure 8 is an enlarged cross-sectional view of the steam vent 24 of the microwave packaging bag 1A of the second embodiment. As shown in Figure 8, the microwave packaging bag 1A differs from the microwave packaging bag 1 in that it has a steam vent 24. The other parts of the microwave packaging bag 1A are the same as those of the microwave packaging bag 1. Therefore, in the microwave packaging bag 1A, the same reference numerals are used for parts that are substantially the same as those of the microwave packaging bag 1, and detailed descriptions of the same parts are omitted.

[0065] In the microwave packaging bag 1A, the steam vent portion 24 is provided at the point where the back seal portion 21 of the end seal portion 22 intersects. The steam vent portion 24 is provided with a hole portion 4. In the steam vent portion 24, the hole portion 4 is formed to penetrate the heat-adhesive resin layer 12.

[0066] In the manufacturing process for microwave packaging bag 1A, as shown in Figure 7, after forming the heat-adhesive resin layer in step S104, the hole-forming step in step S103 is performed to form the holes.

[0067] As described above, even when a microwave-safe packaging bag 1A having a steam-through section 24 with a hole 4 that penetrates the end seal section 22 is heated in a microwave oven, air and steam from the containment section 103 can be easily discharged through the hole 4. In addition, the expansion of the base material layer 11 is suppressed by the hole 4. Therefore, the rupture of the microwave-safe packaging bag 1A can be suppressed.

[0068] Alternatively, after sealing the end seal portion 22 in step S110 or step S111, the hole forming step in step S103 to form the hole portion 5 may be performed to manufacture the microwave packaging bag 1B. With this configuration, the hole portion 5 penetrates the end seal portion 22 in which the steam vent portion 25 is formed (see Figure 9). As a result, steam can be easily released from the hole portion 5 in the microwave packaging bag 1B, and the rupture of the base material layer 11 can be suppressed.

[0069] <Variation> Figures 10 and 11 show modified shapes of the holes in the steam passage section 23. As shown in Figure 10, the holes 3B may be formed in the shape of a slit. The slit-shaped holes 3B may be, for example, perforated. In this case, the length of one hole is preferably 3 mm or less. Also, as shown in Figure 11, the holes 3C may be arranged in a shape that moves further apart from each other as you move from one end to the other, a so-called V-shape. Other shapes are also acceptable.

[0070] Assuming that the gap between the holes may rupture during steaming, the distance between the unperforated slits should preferably be 3 mm or less, and the total length over which the base material ruptures when steaming through the holes should preferably be 6 mm or less. If it exceeds 6 mm, it will be perceived as a popping sound.

[0071] Although the heat-adhesive resin layer 12 described above is formed of polyethylene (PE), the heat-adhesive resin layer 12 may also be formed of polypropylene (unoriented polypropylene: CPP) instead of polyethylene film. Furthermore, the heat-adhesive resin layer 12 is not limited to polyethylene or polypropylene, but can be made from a wide range of heat-adhesive polyolefin materials.

[0072] In a resin sheet, if each layer is made of polyolefin, the microwave packaging bag can be constructed as a monoolefin. This is advantageous for recycling the microwave packaging bag.

[0073] Although embodiments of the present invention have been described above, the present invention is not limited thereto. Furthermore, various modifications can be made to the embodiments of the present invention, as long as they do not depart from the spirit of the invention. [Industrial applicability]

[0074] According to the present invention, a packaging bag that can be used for cooking in a microwave oven can be provided. [Explanation of Symbols]

[0075] 1. 1A Microwave-safe packaging bags 3, 3A, 4 holes 10, 10A resin sheet 11 Base material layer 12 Heat adhesive resin layer 13. Dry Laminate Layer 14. Easily peelable area 15 Printing layer 20 Original fabric 201 Roll of raw material 21 Spine seal section 22 End seal section 221 Seal edge section 23, 24 Steaming section 100 cylindrical body 101 First band-shaped section 102 Second band-shaped section 103 Storage Unit S contents

Claims

1. A microwaveable packaging bag having a compartment for containing contents, A sealed portion formed by heat-sealing at least a portion of the peripheral edge of the laminated sheets arranged front and rear, It has a steam passage formed in a part of the seal portion that allows steam from the containment portion to pass through, The aforementioned laminated sheet is A base layer and A heat-adhesive resin layer is disposed inside the aforementioned base material layer, It has a dry laminate layer that bonds the substrate layer and the heat-adhesive resin layer, The aforementioned steaming section includes, An easily peelable portion is disposed between the base material layer and the dry laminate layer and is composed of a laminate strength reducing varnish in which the laminate strength between the base material layer and the dry laminate layer is lower than the laminate strength between the base material layer and the dry laminate layer. A microwave packaging bag having a plurality of holes that penetrate at least the base material layer in the thickness direction in the portion of the laminated sheet that constitutes the steam-permeable portion.

2. The microwave packaging bag according to claim 1, wherein both the base material layer and the heat-adhesive resin layer are made of polyolefin resin.

3. The microwave packaging bag according to claim 1, wherein in the steam-permeable portion, the holes penetrate the dry laminate layer.

4. The microwave packaging bag according to claim 1, wherein in the steam-permeable portion, the hole penetrates the heat-adhesive resin layer.

5. The microwave packaging bag according to claim 1, wherein the base layer is made of a resin that exhibits a tensile elongation at break of 300 percent or more in the MD direction under conditions of 100°C.

6. The microwave packaging bag according to claim 1, wherein the heat-adhesive resin layer is made of a resin having a tensile elongation at break of 10 percent to 100 percent in the MD direction at a 100°C environment.

7. A method for manufacturing microwave packaging bags, which are formed to have a storage section capable of holding articles, which is sealed at a sealing portion, A step to form an easily peelable portion is to apply a laminate strength reducing varnish, in which the laminate strength between the base material layer and the dry laminate layer is lower than the laminate strength between the base material layer and the dry laminate layer, to the portion on one side of the resin sheet constituting the base material layer where a permeable portion is formed, thereby forming an easily peelable portion. A dry laminate layer formation step in which a dry laminate layer is formed on one surface of the resin sheet, A hole forming step is to form a hole that penetrates at least the base material layer in a portion of the sealing portion which is a steam passage portion formed to allow steam generated in the containment portion to pass through, A heat-adhesive resin layer formation step is performed on the surface of the dry laminate layer opposite to the substrate layer, A sheet arrangement step of arranging the resin sheets so that the heat-adhesive resin layers are arranged facing each other, A method for manufacturing a microwave-safe packaging bag, comprising a heat bonding step of heat bonding a predetermined portion of the resin sheet to form the sealed portion.

8. A method for manufacturing microwave packaging bags, which are formed to have a storage section capable of holding articles, which is sealed at a sealing portion, A step to form an easily peelable portion is to apply a laminate strength reducing varnish, in which the laminate strength between the base material layer and the dry laminate layer is lower than the laminate strength between the base material layer and the dry laminate layer, to the portion on one side of the resin sheet constituting the base material layer where a permeable portion is formed, thereby forming an easily peelable portion. A dry laminate layer formation step in which the dry laminate layer is formed on one surface of the resin sheet, A heat-adhesive resin layer formation step is performed on the surface of the dry laminate layer opposite to the substrate layer, A hole-forming step is to form holes that penetrate the base material layer, the dry laminate layer, and the heat-adhesive resin layer in a portion of the seal portion that is formed, which is a portion in which a steam-passing portion is formed to allow steam generated in the containment portion to pass through, A sheet arrangement step of arranging the resin sheets so that the heat-adhesive resin layers are arranged facing each other, A method for manufacturing a microwave-safe packaging bag, comprising a heat bonding step of heat bonding a predetermined portion of the resin sheet to form the sealed portion.

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