Packaging bag

Abstract

The present invention provides a packaging bag for microwave ovens whereby steam generated when heating the contents of said bag can be vented reliably and suitably by means of a simple configuration, without having to provide flaps formed in a pressed-palms shape (pressed-palms section).　According to the present invention, there is provided a packaging bag comprising, in the peripheral surface thereof, first and second surfaces that face each other, an opening that is open upward, and an opening / closing member configured to open / close the opening, wherein the opening / closing member has a first engaging member and a second engaging member, and defining an upper region and a lower region to be regions where the second engaging member faces the second surface, the upper region has a portion where the seal strength per unit width between the second engaging member and the second surface is relatively small, and in a region of the lower region that overlaps said portion in the vertical direction, the second engaging member and the second surface are not heat-sealed, or are heat-sealed to a lower seal strength per unit width than said portion.

Description

packaging bag

[0001] The present invention relates to a self-standing packaging bag for use in a microwave oven, which is made by forming a flexible film into a bag shape.

[0002] Patent Document 1 discloses a packaging bag for use in a microwave oven that has an openable and closable fastening portion.

[0003] JP 2016-137929 A

[0004] The packaging bag of Patent Document 1 allows any content to be heated by opening the joint and placing the content to be heated inside the packaging bag. In the configuration of Patent Document 1, steam generated when the content is heated is discharged to the outside through a steam release seal provided on a flap (gable portion) formed in a gable shape.

[0005] However, some bag making machines do not have the function of providing folded flaps (gable portions) on packaging bags. Therefore, a simple mechanism for venting steam generated when heating contents in microwave packaging bags is desired, without providing folded flaps (gable portions). Moreover, even if the steam vent mechanism is simple in configuration, it is still required to have the ability to reliably and effectively vent steam pressure inside the packaging bag to the outside.

[0006] The present invention has been made in consideration of the above circumstances, and provides a packaging bag for use in a microwave oven that has a simple structure and does not require any flaps (gable portions) formed in a gable shape, and that can reliably and suitably release steam that is generated when the contents are heated.

[0007] According to the present invention, the following inventions are provided: [1] A packaging bag for use in a microwave oven, made of a flexible film formed into a bag shape, the packaging bag having a peripheral surface portion, the peripheral surface portion having first and second surfaces facing each other, an opening that opens upward, and an opening / closing member configured to open and close the opening, the opening / closing member having a pair of engaging members consisting of a first engaging member and a second engaging member, the first engaging member being heat-welded to the first surface, and an area where the second engaging member faces the second surface, the upper and lower sides of which are defined as an upper region and a lower region, respectively, across a position where the second engaging member engages with the first engaging member, the upper region has a portion where the welding strength per unit width between the second engaging member and the second surface is relatively low, and in an area vertically overlapping with the portion in the lower region, the second engaging member and the second surface are not heat-welded or are heat-welded so that the welding strength per unit width is lower than that of the portion in the lower region. [2] The packaging bag according to [1], wherein the upper region comprises an upper central region in the center of the left-right direction of the packaging bag and upper end regions located on both sides of the upper central region, the second engaging member is heat-sealed to the second surface in both the upper central region and the upper end regions, and the upper central region has a smaller welding strength per unit width than the upper end regions, the lower region comprises a lower central region in the center of the left-right direction of the packaging bag and lower end regions located on both sides of the lower central region, the second engaging member is heat-sealed to the second surface in the lower end regions, and the second engaging member is not heat-sealed to the second surface in the lower central region or is heat-sealed so that the welding strength per unit width is smaller than that of the upper central region, and the lower central region overlaps with the upper central region in the up-down direction of the packaging bag and is wider than the upper central region in the left-right direction of the packaging bag. [3] The packaging bag according to [2], wherein the length of the lower central region in the left-right direction of the packaging bag is 1.5 times or more the length of the upper central region. [4] The packaging bag according to [2] or [3], wherein the second engaging member is not heat-welded to the second surface in the lower central region.[5] A packaging bag according to any one of [2] to [4], wherein the lower central region is configured to cover the entire left-right area of ​​the inside of the packaging bag.

[0008] According to the present invention, a packaging bag for microwave oven use can reliably and effectively release steam generated when the contents are heated, without providing any folded flaps (gable portions) in the bag, using a simple structure. Therefore, packaging bags for microwave oven use can be manufactured even using a bag making machine that does not have the function of providing folding flaps (gable portions) on packaging bags.

[0009] FIG. 3A is a perspective view of the packaging bag 1 of the first embodiment of the present invention with contents placed therein. It is a plan view of the packaging bag 1 of FIG. 1. FIG. 3A is a cross-sectional view taken along line A-A in FIG. 2, FIG. 3B is an enlarged view of region B in FIG. 3A, and FIG. 3C shows the state in which the opening / closing member 23 of FIG. 3B is open. It is a view showing the welding state of the upper region 23a3 and the lower region 23a4 of the base 23a1 of the front-side engaging member 23a. FIG. 5A is a side view of the peripheral wall film 20b. FIG. 5B is a view showing the state in which a portion of the peripheral wall film 20b has been cut and the bottom film 20a has been inserted into the cut portion. FIG. 6A is a view showing the manufacturing process of the packaging bag 1 by welding the peripheral wall film 20b and the bottom film 20a, and FIG. 6B is a view showing the state in which the opening / closing member 23 has been inserted between the front portion 3 and the back portion 4. Fig. 7A shows the front seal bar 10a and the rear seal bar 10b welding the peripheral wall film 20b, the front engaging member 23a, and the rear engaging member 23b, and Fig. 7B is a perspective view showing the schematic configuration of the front seal bar 10a. Fig. 8A is a diagram explaining the contact state between the front seal bar 10a and the peripheral wall film 20b in the upper region 23a3, Fig. 8B is a diagram explaining the contact state between the front seal bar 10a and the peripheral wall film 20b in the lower region 23a4, and Fig. 8C is a diagram showing the welding state in the upper region 23a3 and the lower region 23a4 of the base 23a1 of the front engaging member 23a. Fig. 9A is a plan cross-sectional view of the vicinity of the opening / closing member 23 showing the state in which heated steam is discharged from the packaging bag 1, and Fig. 9B is a side cross-sectional view showing the state in which heated steam is discharged from the packaging bag 1. 1 is a perspective view of a packaging bag 1 according to another embodiment of the present invention, in which a tear-opening portion 24 is provided above an opening / closing member 23. FIG. 2 is a view showing an example of another embodiment of the present invention, in which a fixed portion S5 is provided between a strong seal area S1 and a weak seal area S2.

[0010] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0011] 1. First Embodiment 1-1. Structure of Packaging Bag 1 As shown in FIGS. 1 to 3C, packaging bag 1 in this embodiment of the present invention is a free-standing packaging bag for use in a microwave oven, in which a flexible film is formed into a bag shape. Packaging bag 1 has a bottom portion 2 and a peripheral portion 21 extending from bottom portion 2. Peripheral portion 21 has a front portion 3 and a back portion 4 facing each other, and an opening 22 that opens upward. Front portion 3 and back portion 4 are welded to each other at their left and right ends (hereinafter also referred to as side ends). Bottom portion 2 is welded (heat sealed) to front portion 3 and back portion 4. In this way, the bottom portion 2, front portion 3, and back portion 4 are welded to each other, forming the film into a bag shape.

[0012] In this disclosure, the top, bottom, left, and right of Fig. 2 will be described as the top, bottom, left, and right of the packaging bag 1. Specifically, the bottom surface portion 2 side will be the lower side, and the front surface portion 3 (and back surface portion 4) side will be the upper side. Also, the left and right sides when the front surface portion 3 is placed in front will be the left and right sides of the packaging bag 1. Furthermore, the front surface portion 3 side will be the front side, and the back surface portion 4 side will be the rear side.

[0013] As shown in FIGS. 1 to 3C, an opening / closing member 23 is provided on the peripheral surface 21 of the packaging bag 1.

[0014] 3B and 3C, the opening / closing member 23 is configured to be able to open and close the opening 22. The opening / closing member 23 includes a front-side engaging member 23a and a rear-side engaging member 23b that are engageable with each other. The front-side engaging member 23a is fixed to the inner surface of the front face portion 3. The rear-side engaging member 23b is fixed to the inner surface of the rear face portion 4. The welded state between the front-side engaging member 23a and the front face portion 3 and the fixed state (welded state) between the rear-side engaging member 23b and the rear face portion 4 will be described later.

[0015] 3C, the front engaging member 23a includes a base 23a1 and a hook portion 23a2 protruding from the base 23a1, and the rear engaging member 23b includes a base 23b1 and a hook portion 23b2 protruding from the base 23b1.

[0016] Base portion 23a1 is fixed to front surface portion 3 via upper region 23a3 and lower region 23a4. Base portion 23b1 is fixed to back surface portion 4 via upper region 23b3 and lower region 23b4. Hook portions 23a2 and 23b2 can be engaged with and disengaged from each other. As shown in FIG. 3B , opening 22 is closed by engaging hook portions 23a2 and 23b2, and as shown in FIG. 3C , opening 22 is opened by disengaging hook portions 23a2 and 23b2.

[0017] The upper regions 23a3, 23b3 and the lower regions 23a4, 23b4 are respectively disposed above and below the engagement position (engagement position of the hook portions 23a2, 23b2) between the front side engagement member 23a and the rear side engagement member 23b.

[0018] 4, in the upper region 23a3, the base 23a1 is heat-sealed to the front surface 3 in strong seal regions S1 (corresponding to the upper end regions) on both sides except for the central region in the left-right direction of the packaging bag 1. The base 23a1 is weakly welded to the front surface 3 in a weak seal region S2 (corresponding to the upper central region) in the central region. The weak seal region S2 is configured so that the weld strength per unit width is smaller than that of the strong seal region S1 so that it can be peeled off by steam pressure generated when the contents of the packaging bag 1 are heated.

[0019] Meanwhile, in the lower region 23a4, the base portion 23a1 is heat-sealed to the front surface portion 3 in strong seal regions S3 (corresponding to the lower end regions) at both left and right ends of the packaging bag 1. In addition, the base portion 23a1 is not welded to the front surface portion 3 in an unsealed region S4 (corresponding to the lower central region) sandwiched between the strong seal regions S3.

[0020] In Fig. 4, the left-right length of the strong seal region S3 roughly corresponds to the weld width of the left-right ends of the front and back portions 3 and 4 (the left-right length of side edge welds 12, which will be described later). Therefore, an unsealed region S4 is provided across the entire left-right area inside the packaging bag 1. However, the configurations of the strong seal region S3 and the unsealed region S4 are not limited to those shown in Fig. 4. The unsealed region S4 is intended to apply a concentrated force in the peeling direction to the weak seal region S2 when the packaging bag 1 is heated, so the left-right length of the unsealed region S4 only needs to be greater than the left-right length of the weak seal region S2.

[0021] The unsealed region S4 is positioned so as to overlap the weak seal region S2 in the vertical direction and is wider than the weak seal region S2 in the horizontal direction. Considering the need to efficiently apply a peeling force to the weak seal region S2 when the packaging bag 1 expands due to the pressure of the heated steam, the horizontal length of the unsealed region S4 is preferably at least 1.5 times the horizontal length of the weak seal region S2. The horizontal length of the unsealed region S4 can be, for example, 1.5 to 5 times the horizontal length of the weak seal region S2. Specifically, the horizontal length of the unsealed region S4 can be, for example, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5 times the horizontal length of the weak seal region S2, or it can be any ratio within a range between any two of the values ​​exemplified here.

[0022] The unwelded portion in the unsealed region S4 preferably extends from the lower end of the base portion 23a1 to the upper end of the hook portion 23a2. In other words, in the unsealed region S4, the base portion 23a1 is preferably welded to the front surface portion 3 only at a portion above the hook portion 23a2. With this configuration, when the packaging bag 1 expands, a force that attempts to peel the base portion 23a1 of the front-side engaging member 23a from the front surface portion 3 is more easily applied to the weak seal region S2.

[0023] By providing such a large unsealed portion in the lower region 23a4, the force for breaking the seal is more likely to be concentrated on the weak seal region S2 in the upper region 23a3 when the packaging bag 1 expands. As a result, peeling between the base portion 23a1 and the front surface portion 3 is promoted in the weak seal region S2, and the steam pressure inside the packaging bag 1 can be reliably and suitably released to the outside.

[0024] On the other hand, as described above, the base portion 23b1 is fixed to the back portion 4 via the upper region 23b3 and the lower region 23b4. Although not shown, the base portion 23b1 is heat-sealed to the back portion 4 in the upper region 23b3 and the lower region 23b4 over the entire area in the left-right direction of the packaging bag 1. The heat-sealing between the base portion 23b1 and the back portion 4 is similar to the heat-sealing in the strong seal region S1 described above.

[0025] In this embodiment, the rear-side engaging member 23b corresponds to the first engaging member of the present invention, and the front-side engaging member 23a corresponds to the second engaging member of the present invention. Also, the rear portion 4 corresponds to the first surface, and the front portion 3 corresponds to the second surface. However, this is not limiting, and the present invention can be suitably implemented even if the front-side and rear-side configurations are interchanged.

[0026] Fig. 2 is a plan view of the packaging bag 1. The plan view means that the packaging bag 1 is flattened without any contents inside the packaging bag 1 and viewed in this state from a direction perpendicular to the front surface 3 of the packaging bag 1. As shown in Fig. 2, the packaging bag 1 is formed so as to be symmetrical with respect to a center line in the left-right direction.

[0027] The length H1 of the packaging bag 1 in the up-down direction can be, for example, 12 to 25 cm. Specifically, H1 is, for example, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, or 25 cm, and may be within a range between any two of the values ​​exemplified here.

[0028] The packaging bag 1 has side edge welds 12 at its side edges, welding the front surface 3 and the back surface 4 together. This fixes the front surface 3 and the back surface 4 together in the front-to-rear direction. Furthermore, the packaging bag 1 has bottom edge welds 13 at its bottom edge, welding the bottom surface 2 and the front surface 3, and the bottom surface 2 and the back surface 4 together.

[0029] The lower end welded portion 13 is the area below the center line E, and welds the bottom portion 2 to the front portion 3, and the bottom portion 2 to the back portion 4 at the side and bottom ends of the packaging bag 1 (the area surrounded by the dotted line in Figure 2).

[0030] The manufacturing procedure for the packaging bag 1 will be briefly described below with reference to FIGS. 5A to 6B.

[0031] First, as shown in FIG. 5A, one peripheral wall film 20b is folded.

[0032] 5A and 5B, the bottom film 20a folded into a V shape is inserted into the open side of the folded peripheral wall film 20b. Then, as shown in FIGS. 5B to 6A, the bottom film 20a and the peripheral wall film 20b are welded together, and the end opposite the welded portion is cut away, thereby forming the bottom portion 2, the front portion 3, and the back portion 4.

[0033] 6B , an opening / closing member 23 is inserted between the front portion 3 and the rear portion 4 near the cutout (near the upper ends of the front portion 3 and the rear portion 4), and the opening / closing member 23 is fixed to the inner surfaces of the front portion 3 and the rear portion 4. Here, the opening / closing member 23 is inserted after the bottom film 20a and the peripheral wall film 20b are welded, but the opening / closing member 23 may be inserted before the bottom film 20a. Furthermore, the processes of welding the bottom film 20a and the opening / closing member 23 to the peripheral wall film 20b may be performed separately or simultaneously.

[0034] Thereafter, the front portion 3 and the back portion 4 are welded together to form the side edge welds 12. When the side edge welds 12 are formed, the opening / closing member 23 is also crushed and welded, forming the strong seal area S3.

[0035] Here, the bottom film 20a and the peripheral wall film 20b are preferably laminated films having a base layer and a sealant layer, and more preferably have an adhesive layer and a printed layer between the base layer and the sealant layer.

[0036] The base material layer is disposed so as to be exposed on the outer surface of the packaging bag 1, and the sealant layer is disposed so as to be exposed on the inner surface of the packaging bag 1. The sealant layers are welded (heat sealed) together to form a welded portion.

[0037] The substrate layer is made of a material that has excellent strength and high impact resistance, such as polyamide, polyolefin, polyethylene, or polyester.

[0038] The adhesive layer is a layer for adhering the base layer and the sealant layer so as to laminate them together.

[0039] The sealant layer can be formed from a resin with excellent weldability. The sealant layer can be formed from a polyolefin resin such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, or ethylene-propylene block copolymer. More specifically, unstretched polypropylene or linear low-density polyethylene can be used. The film constituting the sealant layer is preferably one that can be cut linearly in the MD direction.

[0040] As an example, in this embodiment, the structure is as follows: base material layer: oriented nylon (25 μm) / printing layer / adhesive layer (dry laminate) / sealant layer: LLDPE (60 μm).

[0041] Next, the fixing of the opening / closing member 23 shown in FIG. 6B to the front surface 3 and the rear surface 4 will be described in more detail with reference to FIGS. 7A to 8C.

[0042] 7A, the front-side engaging member 23a is heat-sealed by the front-side seal bar 10a connected to the front-side heater, while the rear-side engaging member 23b is heat-sealed by the rear-side seal bar 10b connected to the rear-side heater.

[0043] As shown in Fig. 7B, the front seal bar 10a has multiple regions (10a1, 10a2, 10a3, 10a4) of different heights. The multiple regions (10a1, 10a2, 10a3, 10a4) are designed to have different pressing forces during heat sealing and different heat seal strengths (welding strength per unit width). For ease of explanation, in Fig. 7B, the area of ​​the peripheral wall film 20b (corresponding to the front portion 3) corresponding to the size of a single packaging bag 1 is hatched.

[0044] As shown in Figure 7A, in the heat welding process, with a heat-resistant sheet 11 made of fluororesin or the like interposed between the front-side engaging member 23a and the rear-side engaging member 23b, the front-side seal bar 10a and the rear-side seal bar 10b sandwich and weld the peripheral wall film 20b (corresponding to the front portion 3), the front-side engaging member 23a, the rear-side engaging member 23b, and the peripheral wall film 20b (corresponding to the rear portion 4).

[0045] As shown in FIG. 8A , the area of ​​the front seal bar 10a where the upper region 23a3 is heat-sealed includes a weak seal area 10a3 and a strong seal area 10a4. The weak seal area 10a3 is located in a position corresponding to the center of the packaging bag 1 in the left-right direction. The weak seal area 10a3 is configured to be approximately 0.5 mm lower in height than the strong seal area 10a4. The height difference between the weak seal area 10a3 and the strong seal area 10a4 is, for example, 0.3 to 0.7 mm. Specific examples of this height difference include 0.3, 0.4, 0.5, 0.6, and 0.7 mm, and may be within a range between any two of the values ​​shown here.

[0046] As shown in FIG. 8B , the area of ​​the front seal bar 10a where the lower region 23a4 is heat-sealed includes a strong seal area 10a1 and an unsealed area 10a2. The unsealed area 10a2 is positioned to cover the entire left-right area of ​​the inside of the packaging bag 1. The unsealed area 10a2 is configured to be approximately 1.0 mm lower in height than the strong seal area 10a1. The height difference between the unsealed area 10a2 and the strong seal area 10a1 is, for example, 0.8 mm or greater. The value of this height difference is, for example, 0.8 to 1.3 mm, specifically, for example, 0.8, 0.9, 1.0, 1.1, 1.2, or 1.3 mm, and may be within a range between any two of the values ​​exemplified here.

[0047] 8A and 8B, a weakly sealed area S2 having a steam venting function can be formed in the center of the upper area 23a3, as shown in Fig. 8C. Also, the strongly sealed areas S3 at both ends of the lower area 23a4 can be firmly heat-sealed, while the unsealed areas S4 sandwiched between the strongly sealed areas S3 can remain unsealed.

[0048] 9A and 9B, steam generated when the contents of the packaging bag 1 are heated in a microwave oven escapes to the outside through the gap between the front engaging member 23a and the front portion 3, preventing an excessive increase in pressure inside the packaging bag 1. Since the packaging bag 1 is configured so that the force required to break the seal is easily concentrated in the weak seal region S2 of the upper region 23a3, there is no need to provide a separate steam release seal portion or the like.

[0049] The welding strength per unit width of the weak seal region S2 in the upper region 23a3 shown in FIG. 8C is preferably set so that the peel strength according to JIS K6854 is approximately 10 N / 15 mm width or less. The peel strength is, for example, 3 to 10 N / 15 mm width, specifically, 3, 4, 5, 6, 7, 8, 9, or 10 N / 15 mm width, and may be within a range between any two of the values ​​exemplified here. When the horizontal length of the weak seal region S2 is increased, the peel strength is preferably set to a value close to 10 N / 15 mm width, and when the horizontal length of the weak seal region S2 is decreased, the peel strength is preferably set to a value close to 3 N / 15 mm width. The horizontal length of the weak seal region S2 is preferably 1 to 7 cm, more specifically, 1, 2, 3, 4, 5, 6, or 7 cm, and may also be within a range between any two of the values ​​exemplified here, for example, 4 cm.

[0050] 8C, the welding strength per unit width in the strong seal regions S1 and S3 of the upper region 23a3 is preferably set to, for example, a peel strength of approximately 20 N / 15 mm width according to JIS K6854. The peel strength is, for example, 15 to 30 N / 15 mm width, and more specifically, for example, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 N / 15 mm width, and may be within a range between any two of the values ​​exemplified here.

[0051] If steam can be reliably and suitably released from weak seal region S2 of upper region 23a3, there is no need to provide a separate steam release seal portion, gable portion, or the like in packaging bag 1. Therefore, even if a microwave oven packaging bag is manufactured using a bag making machine that does not have the function of providing a gabled flap (gable portion) on a packaging bag, problems with using the microwave oven packaging bag can be prevented.

[0052] 2. Other Embodiments

[0053] The packaging bag 1 described in the first embodiment may have a tearing portion 24 provided above the opening / closing member 23, as shown in FIG. 10 . The tearing portion 24 is a portion for opening the packaging bag 1. In this embodiment, the tearing portion 24 includes a tear initiation portion 24a, which serves as a starting point for tearing the peripheral portion 21, and a perforation line 24b, which is a printed line indicating the area where the opening should be cut. The packaging bag 1 may be opened by tearing the peripheral portion 21 starting from the tear initiation portion 24a, or by cutting the peripheral portion 21 along the perforation line 24b using a cutting tool such as scissors. The tear initiation portion 24a is a portion that facilitates tearing the peripheral portion 21 and is formed, for example, by a notch or cut. One of the tear initiation portion 24a and the perforation line 24b may be omitted. The tearing portion 24 may also have another configuration that enables the packaging bag 1 to be opened. For example, instead of the cut lines 24b, half-cut lines extending in the circumferential direction of the peripheral surface portion 21 may be provided, or a strip of film may be arranged so as to extend in the circumferential direction of the peripheral surface portion 21. The strip of film is welded to the peripheral surface portion 21, and by grasping and pulling an end of the strip of film, it is possible to tear the peripheral surface portion 21 along the strip of film.

[0054] If the upper side of the tearing portion 24 is heat-sealed, the packaging bag 1 will not leak even if it is distributed with liquid seasoning or the like inside. When using the packaging bag 1, the user tears the tearing portion 24 and then opens the opening / closing member 23, allowing food ingredients such as meat or vegetables to be placed in the packaging bag 1 and mixed with the liquid seasoning or the like. The opening / closing member 23 can then be closed and the food ingredients inside the packaging bag 1 can be heated by heating in a microwave oven.

[0055] Furthermore, as shown in FIG. 11 , a fixed portion S5 having a higher welding strength per unit width than the strong seal region S1 may be provided between the strong seal region S1 and the weak seal region S2. The fixed portion S5 preferably has a welding strength per unit width of at least 30 N / 15 mm width, as measured by JIS K6854. The fixed portion S5 is preferably provided adjacent to one end of the weak seal region S2. The side where the fixed portion S5 is provided is less susceptible to tearing, while the opposite side is more susceptible to tearing. Therefore, the location of the fixed portion S5 can control the direction in which the upper region 23a3 peels when the weak seal region S2 tears. The fixed portion S5 can be formed, for example, by adjusting the shape of the front seal bar 10a so that the pressure applied during heat sealing is locally increased. However, the fixed portion S5 may also be formed by other methods, such as locally increasing the temperature during heat sealing.

[0056] Although the above describes the embodiments, the technical concepts of the present disclosure can also be employed in the following aspects. Instead of the unsealed region S4 described above, a weakly sealed region (corresponding to the lower central region) may be provided. If the seal of this weakly sealed region is easily broken when the packaging bag 1 expands, it will have the same effect as the unsealed region S4, and therefore will not pose a problem in practical use of the packaging bag 1. The welding strength per unit width of this weakly sealed region is preferably smaller than that of the weakly sealed region S2 (upper central region), and more preferably, it is set to a level that is substantially unwelded (e.g., a peel strength of less than 3 N / 15 mm width according to JIS K6854). The peripheral portion 21 may have a pair of side portions between the front portion 3 and the back portion 4. In this case, the front portion 3 and the back portion 4 are welded to the respective pair of side portions to form a substantially rectangular peripheral portion 21. In the above embodiment, the bottom portion 2 is made of a film folded into a V-shape, but this is not limited to this form. For example, it may be made of a film folded into a W-shape. The method for manufacturing the packaging bag 1 is not limited to the method described in the above embodiment.

[0057] 1: packaging bag, 2: bottom surface, 3: front surface, 4: back surface, 10a: front seal bar, 10a1: strong seal area, 10a2: unsealed area, 10a3: weak seal area, 10a4: strong seal area, 10b: back seal bar, 11: heat-resistant sheet, 12: side edge welded portion, 13: bottom edge welded portion, 20a: bottom film, 20b: peripheral wall film, 21: peripheral surface, 22: opening, 23: opening / closing member, 23a: front side seal Joint member, 23a1: base, 23a2: hook portion, 23a3: upper region, 23a4: lower region, 23b: rear engaging member, 23b1: base, 23b2: hook portion, 23b3: upper region, 23b4: lower region, 24: opening portion, 24a: tear start portion, 24b: cut line, B: region, E: center line, S1: strong seal region, S2: weak seal region, S3: strong seal region, S4: unsealed region, S5: fixed portion

Claims

1. A packaging bag for use in a microwave oven, made of a flexible film formed into a bag shape, the packaging bag having a peripheral surface, the peripheral surface having first and second surfaces opposing each other, an opening that opens upward, and an opening / closing member configured to open and close the opening, the opening / closing member having a pair of engaging members consisting of a first engaging member and a second engaging member, the first engaging member being heat-sealed to the first surface, and the upper and lower areas of the area where the second engaging member faces the second surface, sandwiching the position of engagement with the first engaging member, are defined as the upper area and the lower area, respectively, the upper area has a portion where the welding strength per unit width between the second engaging member and the second surface is relatively small, and in an area that overlaps in the vertical direction with the portion in the lower area, the second engaging member and the second surface are not heat-sealed or are heat-sealed so that the welding strength per unit width is smaller than that of the portion in the lower area.

2. A packaging bag according to claim 1, wherein the upper region comprises an upper central region in the left-right center of the packaging bag and upper end regions located on either side of the upper central region, the second engaging member is heat-sealed to the second surface at both the upper central region and the upper end regions, and the upper central region has a smaller welding strength per unit width than the upper end regions, the lower region comprises a lower central region in the left-right center of the packaging bag and lower end regions located on either side of the lower central region, the second engaging member is heat-sealed to the second surface at the lower end regions, and is not heat-sealed to the second surface at the lower central region or is heat-sealed so that the welding strength per unit width is smaller than that at the upper central region, and the lower central region overlaps with the upper central region in the up-down direction of the packaging bag and is wider than the upper central region in the left-right direction of the packaging bag.

3. A packaging bag according to claim 2, wherein the length of the lower central region in the left-right direction of the packaging bag is at least 1.5 times the length of the upper central region.

4. A packaging bag according to claim 2 or 3, wherein the second engaging member is not heat-welded to the second surface in the lower central region.

5. A packaging bag according to claim 4, wherein the lower central region is configured to cover the entire inside of the packaging bag in the left-right direction.

Images