Microwave packaging bags

Abstract

To provide a packaging bag for a microwave oven that prevents food having been cooked from being less delicious.SOLUTION: A packaging bag for a microwave oven is formed of laminates 20, 21 such that a pair of front and rear opposed body part sheets 2, 3 and a bottom face sheet 4 sandwiched in a two-folded manner between the body part sheets 2, 3 have a thermally adhesive resin layer 27 on respective internal surfaces. Both side end parts of the body part sheets 2, 3 are thermally bonded with a side end part thermal adhesive part 6. The bottom face sheet 4 is thermally bonded to the respective body part sheets 2, 3 with a lower thermally adhesive part 7. The bottom face sheet 4 is provided with a thermally softening region R having a thermally softening resin layer 25 softening at a lower temperature than the thermally adhesive resin layer 27 on an outer surface side of the thermally adhesive resin layer 27, opposite the one body part sheet 2. The lower thermally adhesive part 7 has its inner edge 7a formed downward convexly to have a top part 7b at a lower end. A penetration part 9 penetrating the lower thermally adhesive part 7 is provided opposite below the top part 7b, and the thermally softening region R covers the top part 7b and the penetration part 9 while an upper end crosses the inner edge 7a of the lower thermally adhesive part 7.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a packaging bag for a microwave oven that steams through heating.

Background Art

[0002] Conventional packaging bags for microwave ovens are disclosed in Patent Document 1. This packaging bag for a microwave oven includes a pair of body sheets (front and rear wall members) facing each other front and back, and a bottom sheet (gusset portion forming member) that is folded in two and sandwiched at the lower part of the body sheet. The body sheet and the bottom sheet are formed of a laminate having a heat - adhesive resin layer on the inner surface.

[0003] The opposing body sheets are heat - adhered at the upper end and both side ends by an upper heat - adhesive portion and side - end heat - adhesive portions. The bottom sheet is heat - adhered to the body sheet by a lower heat - adhesive portion having an inner edge formed in an arc shape. A gusset portion is formed by the bottom sheet, and the packaging bag for a microwave oven is self - standing. In the packaging bag for a microwave oven, a storage portion for food sealed by the upper heat - adhesive portion, side - end heat - adhesive portions, and lower heat - adhesive portion is formed.

[0004] In the laminate forming the bottom sheet, a heat - softening resin layer (laminate strength adjustment layer) that softens at a lower temperature than the heat - adhesive resin layer is provided facing one of the body sheets. The lower end of the heat - softening resin layer is arranged on the outer edge of the lower heat - adhesive portion, and the upper end intersects the inner edge of the lower heat - adhesive portion.

[0005] Food stored in the packaging bag for a microwave oven is cooked by heating in a microwave oven. When the heat - softening resin layer of the lower heat - adhesive portion softens due to heating and the heat - adhesive resin layer of the lower heat - adhesive portion peels off from the inner edge due to the increase in the internal pressure of the storage portion, and when the heat - adhesive resin layer facing the heat - softening resin layer of the lower heat - adhesive portion is cut, the heat - softening resin layer peels off and the peeling of the laminate progresses. When the peeling of the laminate reaches the lower end of the lower heat - adhesive portion, an opening is formed and steaming occurs, and the internal pressure of the storage portion decreases. Thereby, it is possible to prevent the rupture of the packaging bag for a microwave oven due to the increase in internal pressure.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-223626 (pages 6-12, Figure 4) [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, with the conventional microwave packaging bags described above, the heat-softening resin layer is provided across both ends of the bottom sheet, which can result in a larger opening during steaming. This leads to a larger amount of steam escaping from the opening, causing the food to become more flavorful and reducing its overall deliciousness.

[0008] The present invention aims to provide a microwaveable packaging bag that can prevent a decline in the deliciousness of cooked food. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a microwave packaging bag in which a pair of front and rear facing body sheets and a bottom sheet that is folded in half and sandwiched between the lower part of the body sheets are formed from a laminate having a heat-adhesive resin layer on its inner surface, the ends on both sides of the body sheets are heat-bonded by side end heat-bonding portions, and the bottom sheet is heat-bonded to each of the body sheets by a lower heat-bonding portion, The bottom sheet has a heat-softening region on the outer surface side of the heat-adhesive resin layer, which softens at a lower temperature than the heat-adhesive resin layer, and this region is provided opposite one of the body sheets. The inner edge of the lower heat-bonded portion is formed convex downwards and has a top at its lower end, and a penetrating portion is provided below the top that penetrates the lower heat-bonded portion. The aforementioned heat-softening region is characterized in that its upper end intersects with the inner edge of the lower heat-bonding portion, covering the top portion and the through-portion.

[0010] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the lower end of the heat-softening region is positioned above the lower end of the lower heat-sealing portion.

[0011] Furthermore, the present invention is characterized in that, in a microwave packaging bag having the above configuration, the thickness of the heat-adhesive resin layer of the bottom sheet is smaller than the thickness of the heat-adhesive resin layer of the body sheet.

[0012] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the heat-softening region is formed in a strip shape that crosses the bottom sheet.

[0013] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the perforation portion is provided only on one of the body sheets.

[0014] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the perforations are provided on both of the body sheets.

[0015] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the through portion is formed by a linear cut.

[0016] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the through portion is formed by a plurality of cuts.

[0017] Furthermore, the present invention is characterized in that, in the microwave packaging bag having the above configuration, the top portion is formed in a curved shape, and the notch is formed in a curved shape along the top portion. [Effects of the Invention]

[0018] According to the present invention, a through-hole is provided facing the top of the inner edge of the lower heat-bonding part, and the top and the through-hole are covered by a heat-softening region having a heat-softening resin layer. Therefore, when the heat-softening resin layer causes the laminate to peel and reach the through-hole during heat cooking, steam passes through. Thereby, the through-hole can be formed to an appropriate size to regulate the amount of steam outflow, and a decrease in the deliciousness of the heat-cooked food can be prevented.

Brief Description of the Drawings

[0019] [Figure 1] Perspective view showing the microwave oven packaging bag of the first embodiment of the present invention [Figure 2] Front view showing the microwave oven packaging bag of the first embodiment of the present invention [Figure 3] Cross-sectional view taken along line A-A of FIG. 2 [Figure 4] Exploded perspective view showing the microwave oven packaging bag of the first embodiment of the present invention [Figure 5] Schematic cross-sectional view showing the layer structure of the laminate forming the body sheet of the microwave oven packaging bag of the first embodiment of the present invention [Figure 6] Schematic cross-sectional view showing the layer structure of the laminate forming the bottom sheet of the microwave oven packaging bag of the first embodiment of the present invention [Figure 7] Front view showing the microwave oven packaging bag of the second embodiment of the present invention [Figure 8] Front view showing the microwave oven packaging bag of the third embodiment of the present invention [Figure 9] Front view showing the microwave oven packaging bag of the fourth embodiment of the present invention

Modes for Carrying Out the Invention

[0020] <First Embodiment> Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show a perspective view and a front view of the microwave oven packaging bag 1 of the first embodiment. FIG. 3 shows a cross-sectional view taken along line A-A of FIG. 2. Further, FIG. 4 shows an exploded perspective view of the microwave oven packaging bag 1.

[0021] The microwave packaging bag 1 has a pair of body sheets 2 and 3 formed by a laminate 20 (see Figure 5), and a bottom sheet 4 formed by a laminate 21 (see Figure 6). As will be described in detail later, the laminate 20 and laminate 21 have a heat-adhesive resin layer 27 on their inner surfaces. The body sheets 2 and 3 face each other front and back to form the body of the microwave packaging bag 1, and the bottom sheet 4 is positioned between the body sheets 2 and 3 to form the bottom of the microwave packaging bag 1.

[0022] The bottom sheet 4 is folded in half along the horizontal fold line D and sandwiched between the lower part of the body sheet 2 and the lower part of the body sheet 3. The ends on both sides of the body sheet 2 and the body sheet 3 are heat-bonded by the side edge heat-bonding parts 6. The bottom sheet 4 is heat-bonded to the body sheet 2 and the body sheet 3 below the side edge heat-bonding parts 6 by the lower heat-bonding part 7.

[0023] After filling the storage compartment 8, which has an opening at the top, with food, the upper ends of the body sheet 2 and body sheet 3 are heat-sealed by the upper heat-sealing section 5. As a result, the storage compartment 8 of the microwave packaging bag 1 is sealed by the upper heat-sealing section 5, the side heat-sealing sections 6 and the lower heat-sealing section 7. In addition, a gusset is formed by the bottom sheet 4, allowing the microwave packaging bag 1 to stand upright.

[0024] The inner edge 7a of the lower heat-bonded portion 7 is formed convex downwards, with a apex 7b at its lower end. In this embodiment, the inner edge 7a of the lower heat-bonded portion 7 is formed by a circular arc with a predetermined radius of curvature, and the apex 7b is positioned in the center in the left-right direction. However, the apex 7b may be positioned off-center in the left-right direction.

[0025] The lower heat-bonding portion 7 is provided with a through-hole 9 facing the top 7b of the inner edge 7a. The through-hole 9 is provided only in the lower heat-bonding portion 7 that heat-bonds one of the body sheets 2. The through-hole 9 is formed linearly by an incision made with a cutting blade. The through-hole 9 may be formed in a straight line or in a curved shape along the top 7b. The through-hole 9 may also be formed as a hole, but forming it linearly by an incision is more preferable because it does not generate any waste material.

[0026] Figure 5 is a schematic cross-sectional view showing the layer structure of the laminate 20 that forms the body sheet 2 and body sheet 3. The laminate 20 is formed by sequentially laminating a base material layer 23, a printing layer 24, an adhesive layer 26, and a heat-adhesive resin layer 27. The heat-adhesive resin layer 27 is placed on the inner surface side of the body sheet 2 and body sheet 3.

[0027] The base layer 23 is formed from a resin film such as nylon, polyester, or polyethylene terephthalate. The thickness of the base layer 23 is, for example, 5 μm to 30 μm. To improve heat resistance, it is more desirable to form the base layer 23 from a uniaxially oriented film or a biaxially oriented film. Alternatively, the base layer 23 may be formed by laminating multiple resin films of different materials. In this embodiment, nylon with a thickness of 15 μm is used as the base layer 23. A barrier layer formed by an oxide vapor deposition film may be provided on the inner surface side of the base layer 23.

[0028] The printed layer 24 forms a design on the substrate layer 23 by gravure printing, offset printing, letterpress printing, screen printing, etc. The thickness of the printed layer 24 is, for example, 1 to 3 μm.

[0029] The heat-adhesive resin layer 27 is laminated on the inner surface side of the printed layer 24 and is formed from a polyolefin film that can be melted and welded by heat. As the polyolefin film forming the heat-adhesive resin layer 27, unoriented polypropylene film (CPP), linear low-density polyethylene film (LLDPE), low-density polyethylene film (LDPE), high-density polyethylene film (HDPE), etc. can be used. Considering the vapor permeability stability and the sealing performance with the heat-adhesive resin of the bottom sheet 4, low-density polyethylene or linear low-density polyethylene with low elongation at break is preferred. The thickness of the heat-adhesive resin layer 27 is, for example, 20 to 80 μm. In this embodiment, a linear low-density polyethylene film with a thickness of 60 μm is used as the heat-adhesive resin layer 27 of the laminate 20.

[0030] The substrate layer 23 on which the printed layer 24 is printed and the heat-adhesive resin layer 27 are dry-laminated by an adhesive layer 26 made of polyurethane, acrylic, or other adhesives.

[0031] Figure 6 is a schematic cross-sectional view showing the layer structure of the laminate 21 that forms the bottom sheet 4. The laminate 21 is formed by sequentially laminating a base material layer 23, a printing layer 24, an adhesive layer 26, and a heat-adhesive resin layer 27. The heat-adhesive resin layer 27 is placed on the inner surface side of the bottom sheet 4. In addition, a partially heat-softening resin layer 25 is formed on the inner surface of the printing layer 24.

[0032] The base layer 23, printing layer 24, adhesive layer 26, and heat-adhesive resin layer 27 of the laminate 21 are formed in the same manner as the base layer 23, printing layer 24, adhesive layer 26, and heat-adhesive resin layer 27 of the laminate 20. In this case, the thickness of the heat-adhesive resin layer 27 of the laminate 21 that forms the bottom sheet 4 is smaller than the thickness of the heat-adhesive resin layer 27 of the laminate 20 that forms the body sheets 2 and 3. Furthermore, considering vapor permeability stability, low-density polyethylene or linear low-density polyethylene with low elongation at break is preferred for the heat-adhesive resin layer 27 of the laminate 21. In this embodiment, a linear low-density polyethylene film with a thickness of 30 μm is used as the heat-adhesive resin layer 27 of the laminate 21.

[0033] By reducing the thickness of the heat-adhesive resin layer 27 of the bottom sheet 4, the heat-adhesive resin layer 27 of the lower heat-bonded section 7 (see Figure 2) becomes easier to cut due to the increase in internal pressure during cooking, as described later. In addition, by increasing the thickness of the heat-adhesive resin layer 27 of the body sheets 2 and 3, pinholes caused by sliding during transport of the microwave packaging bag 1 can be prevented. At this time, since the bottom sheet 4 is covered by the body sheets 2 and 3, pinholes are less likely to occur even if the thickness of the heat-adhesive resin layer 27 is reduced.

[0034] The thermo-softening resin layer 25 is formed from a resin that softens at a lower temperature than the thermo-adhesive resin layer 27. For example, the thermo-softening resin layer 25 is formed from a resin mainly composed of one of the following: an ethylene-vinyl acetate copolymer resin, a polyamide-nitrated cotton resin, or a polyamide-nitrated cotton-polyethylene wax resin, all of which have a melting point of 60-90°C.

[0035] The thermo-softening resin layer 25 is provided at one of the lower ends of the folded bottom sheet 4 and faces one of the body sheets 2. The thermo-softening resin layer 25 is not formed on the other portion of the bottom sheet 4 that faces the body sheet 3. The thermo-softening resin layer 25 is formed inline on the base layer 23 together with the printing layer 24 by gravure printing or the like.

[0036] The thermo-softening resin layer 25 forms a strip-shaped thermo-softening region R (see Figure 2) on one lower end of the folded bottom sheet 4. The thermo-softening resin layer 25 is formed by solid printing within the thermo-softening region R. The thermo-softening resin layer 25 may also be formed by printing a large number of dots within the thermo-softening region R, or by printing in a grid pattern.

[0037] The bottom sheet 4 is formed by providing a heat-softening region R extending in the MD direction on a roll-shaped film forming the base layer 23, and then cutting the laminated body 21, after laminating the heat-adhesive resin layer 27, in a direction perpendicular to the MD direction. This allows the bottom sheet 4, which has a heat-softening region R at its lower end, to be easily formed by cutting the roll-shaped laminated body 21 at any position. For this reason, the heat-softening region R is formed in a strip shape that crosses both side edges of the bottom sheet 4.

[0038] The thickness of the heat-softening resin layer 25 is formed to be between 1 μm and 5 μm. If the thickness of the heat-softening resin layer 25 is less than 1 μm, aggregation and peeling of the heat-softening resin layer 25 will be less likely to occur when heated in a microwave oven. If the thickness of the heat-softening resin layer 25 exceeds 5 μm, the heat-softening resin layer 25 provided on the roll-shaped film will bulge, and that part will stretch, causing bag manufacturing defects and reducing the yield of microwave-safe packaging bags 1.

[0039] As shown in Figure 2 above, the upper end of the heat-softening region R intersects with the inner edge 7a of the lower heat-bonding portion 7, and the lower end of the heat-softening region R coincides with the lower end of the lower heat-bonding portion 7. In addition, the top 7b and the through portion 9 of the inner edge 7a are covered by the heat-softening region R.

[0040] In the microwave packaging bag 1 with the above configuration, the food stored in the microwave packaging bag 1 is heated and cooked in a microwave oven. Heating softens the thermoplastic resin layer 25 of the lower thermoplastic portion 7, and the rise in internal pressure of the storage portion 8 causes the thermoplastic resin layer 27 of the lower thermoplastic portion 7 to agglomerate and peel off from the inner edge. When the thermoplastic resin layer 27 facing the thermoplastic resin layer 25 of the lower thermoplastic portion 7 is cut, the thermoplastic resin layer 25 agglomerates and peels off, and the peeling of the laminate 21 progresses. When the peeling of the laminate 21 reaches the penetration portion 9, steam passes through, and the internal pressure of the storage portion 8 decreases.

[0041] This prevents the microwave packaging bag 1 from bursting due to increased internal pressure. Furthermore, the perforation 9 can be sized appropriately to regulate the amount of steam released. Therefore, it prevents a decrease in the deliciousness of the food due to excessive steam release, which can lead to an over-intensified flavor.

[0042] According to this embodiment, a through-hole 9 is provided on the inner edge 7a of the lower heat-bonded portion 7, opposite the top 7b, and the top 7b and the through-hole 9 are covered by a heat-softening region R having a heat-softening resin layer 25. Therefore, when heating, the peeling of the laminate 21 progresses in the heat-softening resin layer 25 and reaches the through-hole 9, allowing steam to pass through and reducing the internal pressure of the storage portion 8. This makes it possible to form the through-hole 9 to an appropriate size to regulate the amount of steam that flows out, and to prevent a decrease in the deliciousness of the cooked food.

[0043] Furthermore, because the thickness of the heat-adhesive resin layer 27 of the bottom sheet 4 is smaller than the thickness of the heat-adhesive resin layer 27 of the body sheets 2 and 3, the heat-adhesive resin layer 27 of the bottom sheet 4 is more easily cut during heating. This makes it possible to more reliably prevent the microwave packaging bag 1 from bursting due to an increase in internal pressure.

[0044] Furthermore, since the heat-softening region R is formed in a strip shape that crosses the bottom sheet 4, the roll-shaped laminate 21 can be cut at any position to easily form a bottom sheet 4 having the heat-softening region R.

[0045] Furthermore, since the through-hole 9 is provided only on one of the body sheets 2, a microwave-safe packaging bag 1 can be easily realized in which the top portion 7b and the through-hole 9 are covered by the heat-softening region R.

[0046] Furthermore, through-holes 9 facing each other below the top portion 7b may be provided in both body sheets 2 and 3. The through-holes 9 on body sheet 3 are not necessary for steam passage, but the through-holes 9 on body sheet 2 can be easily formed by processing the through-holes 9 on the lower heat-sealed portion 7 while body sheets 2 and 3 are overlapping.

[0047] Furthermore, since the through-hole 9 is formed by linear cuts, it is possible to prevent foreign matter from entering the storage section 8 due to the removal of waste material.

[0048] Furthermore, if the notch forming the penetration portion 9 is formed in a curved shape along the curved top portion 7b, the distance between the top portion 7b and the penetration portion 9 can be made uniform. As a result, even if the peeling position of the laminate 21 varies, the time until steaming can be made uniform, and the rupture of the microwave packaging bag 1 can be prevented more reliably.

[0049] <Second Embodiment> Next, Figure 7 shows a front view of the microwaveable packaging bag 1 of the second embodiment. For ease of explanation, the same reference numerals are used for parts that are the same as those in the first embodiment shown in Figures 1 to 6 above. In this embodiment, the arrangement of the heat softening region R differs from that of the first embodiment. The other parts are the same as those in the first embodiment.

[0050] The upper end of the heat-softening region R of the laminate 21 of the bottom sheet 4 intersects with the inner edge 7a of the lower heat-bonding portion 7, similar to the first embodiment. The lower end Rb of the heat-softening region R is positioned above the lower end of the lower heat-bonding portion 7. The top 7b and the through portion 9 of the inner edge 7a of the lower heat-bonding portion 7 are covered by the heat-softening region R.

[0051] When food stored in the microwave-safe packaging bag 1 is heated, the heat-adhesive resin layer 27 facing the heat-softening resin layer 25 is cut, causing the heat-softening resin layer 25 to aggregate and peel off, and the peeling of the laminate 21 progresses. When the peeling of the laminate 21 reaches the penetration 9, steam leaks out from the penetration 9. At this time, even if the peeling of the laminate 21 progresses at a position away from the penetration 9, the peeling stops at the lower end Rb of the heat-softening region R, and then reaches the penetration 9. This makes it possible to more reliably restrict the formation of a large opening at the lower end of the lower heat-adhesive portion 7, which would increase the amount of steam leaking out.

[0052] According to this embodiment, since the lower end Rb of the heat-softening region R is positioned above the lower end of the lower heat-bonding portion 7, the amount of steam outflow can be reliably controlled.

[0053] <Third Embodiment> Next, Figure 8 shows a front view of the microwave packaging bag 1 of the third embodiment. For convenience of explanation, the same reference numerals are used for parts that are the same as those in the first embodiment shown in Figures 1 to 6 above. In this embodiment, the shape of the through-hole 9 differs from that of the first embodiment. The other parts are the same as those in the first embodiment.

[0054] The upper end of the heat-softening region R of the laminate 21 of the bottom sheet 4 intersects with the inner edge 7a of the lower heat-bonding portion 7, similar to the first embodiment. The through portion 9 faces below the top portion 7b and is formed in a perforated manner by arranging multiple cuts made by the cutting blade in the left-right direction.

[0055] This allows for the regulation of steam outflow, similar to the first embodiment. Furthermore, since the penetration portion 9 consists of multiple notches, the size and number of notches can be easily adjusted, allowing for more precise control of the steam flow rate. In addition, in the first embodiment shown in Figure 2, the body sheet 2 is prone to tearing when a downward force is applied to the penetration portion 9, which consists of notches. In contrast, in this embodiment, the penetration portion 9 is formed in a perforated manner by multiple notches, thus preventing the body sheet 2 from tearing when a downward force is applied to the penetration portion 9. The notches forming the penetration portion 9 may also be arranged along the curved top portion 7b.

[0056] In this embodiment, as in the second embodiment, the lower end Rb of the heat-softening region R (see Figure 7) may be positioned above the lower end of the lower heat-bonding portion 7.

[0057] <Fourth Embodiment> Next, Figure 9 shows a front view of the microwaveable packaging bag 1 according to the fourth embodiment. For convenience of explanation, the same reference numerals are used for parts that are the same as those in the first embodiment shown in Figures 1 to 6 above. In this embodiment, the shape of the through-hole 9 differs from that of the first embodiment. The other parts are the same as those in the first embodiment.

[0058] The upper end of the heat-softening region R of the laminate 21 of the bottom sheet 4 intersects with the inner edge 7a of the lower heat-bonding portion 7, similar to the first embodiment. The through portion 9 is located below the top portion 7b and is formed by multiple cuts made by the cutting blade in the left-right and up-down directions.

[0059] This allows for the regulation of steam outflow, similar to the first embodiment. Furthermore, since the penetration portion 9 consists of multiple notches, the size and number of notches can be easily adjusted, allowing for more precise control of the steam flow rate. In addition, in the first embodiment shown in Figure 2, the body sheet 2 is prone to rupture when a downward force is applied to the penetration portion 9, which consists of notches. In contrast, in this embodiment, since the penetration portion 9 is formed by multiple notches, it is possible to prevent the body sheet 2 from rupturing when a downward force is applied to the penetration portion 9. The notches forming the penetration portion 9 may also be arranged along the curved top portion 7b.

[0060] In this embodiment, as in the second embodiment, the lower end Rb of the heat-softening region R (see Figure 7) may be positioned above the lower end of the lower heat-bonding portion 7. [Industrial applicability]

[0061] According to the present invention, it can be used in microwave packaging bags that are heated for cooking. [Explanation of Symbols]

[0062] 1 Microwave-safe packaging bag 2, 3 Torso seats 4. Bottom sheet 5 Upper thermal bonding part 6 Side edge heat-bonded part 7 Lower thermal adhesive part 7a Inner border 7b Top 8 Storage compartments 9 Penetration 20, 21 Laminate 23 Base material layer 24 Printing layer 25 Thermosoftening resin layer 26 Adhesive layer 27 Heat adhesive resin layer D broken line R thermal softening region Rb bottom end

Claims

1. In a microwave packaging bag, a pair of front and rear facing body sheets and a bottom sheet that is folded in half and sandwiched between the lower part of the body sheets are formed from a laminate having a heat-adhesive resin layer on its inner surface, the ends of both sides of the body sheets are heat-bonded by side end heat-bonding portions, and the bottom sheet is heat-bonded to each of the body sheets by a lower heat-bonding portion, The bottom sheet has a heat-softening region on the outer surface side of the heat-adhesive resin layer, which softens at a lower temperature than the heat-adhesive resin layer, and this region is provided opposite one of the body sheets. The inner edge of the lower heat-bonded portion is formed convex downwards and has a top at its lower end, and a penetrating portion is provided below the top that penetrates the lower heat-bonded portion. The heat-softening region intersects the inner edge of the lower heat-bonding portion at its upper end and covers the top and the through portion. A microwave-safe packaging bag characterized in that the lower end of the heat-softening region is positioned above the lower end of the lower heat-sealing portion.

2. The microwave packaging bag according to claim 1, characterized in that the thickness of the heat-adhesive resin layer of the bottom sheet is smaller than the thickness of the heat-adhesive resin layer of the body sheet.

3. The microwaveable packaging bag according to claim 1 or 2, characterized in that the heat-softening region is formed in a strip shape that crosses the bottom sheet.

4. The microwave packaging bag according to any one of claims 1 to 3, characterized in that the through portion is provided only on one of the body sheets.

5. The microwave packaging bag according to any one of claims 1 to 3, characterized in that the aforementioned through-holes are provided on both of the body sheets.

6. The microwave packaging bag according to any one of claims 1 to 5, characterized in that the through portion is formed by a linear cut.

7. The microwave packaging bag according to claim 6, characterized in that the through portion is formed by a plurality of cuts.

8. The microwave packaging bag according to claim 6 or 7, characterized in that the top portion is formed in a curved shape and the notch is formed in a curved shape along the top portion.

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