Packaging bags

Abstract

To provide a packaging bag capable of easily forming a steam vent seal part in bag-making filling without using a special bag-making filling device.SOLUTION: According to the present invention, a packaging bag in which a film is welded at a seal part is provided. The seal part includes a steam vent seal part that forms a steam flow path as an internal pressure rises. The film comprises a modified region in which the surface of the film has been treated by corona discharge. The steam vent seal part is a portion where the modified region and a surface facing the same are welded.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a packaging bag suitable for heating the contents in a microwave oven. [Background technology]

[0002] Patent Document 1 discloses a packaging bag constructed by welding a flexible film at a seal portion. This packaging bag is provided with a steam release seal portion to allow the escape of steam generated when the contents are heated in a microwave oven. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2013 / 100058 issue Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, a steam release seal portion is formed by providing a seal portion at the seam portion that is curved and protrudes in an approximately V-shape toward the inside of the packaging bag, but it is not easy to form a steam release seal portion of this configuration in an apparatus (bag making and filling apparatus) that continuously performs bag making and filling of the contents.

[0005] The present invention has been made in consideration of the above circumstances, and provides a packaging bag in which a steam release seal portion can be easily formed during the bag making and filling process without using a special bag making and filling device. [Means for solving the problem]

[0006] According to the present invention, there is provided a packaging bag constructed by welding a film at a seal portion, the seal portion having a steam release seal portion that forms a steam flow path as the internal pressure increases, the film having a modified area where the surface of the film has been corona discharge treated, and the steam release seal portion is a portion where the modified area and its opposing surface are welded together.

[0007] In the packaging bag of the present invention, the steam release seal portion is formed by utilizing the fact that the seal strength at high temperatures decreases in the modified area that has been treated with corona discharge. Therefore, the steam release seal portion can be easily formed during the bag making and filling process without using special bag making and filling equipment.

[0008] Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other. Preferably, in the packaging bag described above, the sealed portion comprises an upper horizontal seal portion arranged to close the upper side of the packaging bag, and a lower horizontal seal portion arranged to close the lower side of the packaging bag, and the modified region is arranged in a stripe shape across the upper horizontal seal portion, the lower horizontal seal portion, and the non-sealed portion between them. Preferably, in the packaging bag described above, the film is a laminated film in which a base film and a sealant film are laminated, the sealant film has a laminate surface on the base film side and a seal surface opposite the laminate surface, the modified area is a seal surface modified area in which the seal surface has been corona discharge treated, and the laminate surface is provided with a laminate surface modified area in which the laminate surface has been corona discharge treated. Preferably, in the packaging bag described above, the laminate surface modified region has an area larger than that of the sealing surface modified region. Preferably, the method for manufacturing the packaging bag described above includes a corona discharge treatment step, in which corona discharge treatment is performed so that the surface energy of the sealing surface modified area is greater than the surface energy of the laminate surface modified area. Preferably, the method for manufacturing the packaging bag described above includes a corona discharge treatment step, in which a corona discharge treatment is performed on the laminate surface to form the laminate surface modified area, and then a corona discharge treatment is performed on the seal surface to form the seal surface modified area. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a front view of a packaging bag 1 according to one embodiment of the present invention (for convenience, the bag is shown in a state where no contents are filled). [Diagram 2] FIG. 2A is an exploded view showing the layer structure of film 2 used in producing packaging bag 1, and FIG. 2B shows film 2 as viewed from sealing surface 2d. [Diagram 3] FIG. 2 is a block diagram showing the manufacturing process of a corona discharge treated sealant film 12. [Figure 4] FIG. 1 is a configuration diagram of a bag making and filling machine 100. [Diagram 5] 5 is an enlarged view of the vicinity of a transverse sealing machine 116 of the bag making and filling machine 100 of FIG. 4, showing a state in which a transverse seal portion 32 is being formed by the transverse sealing machine 116. FIG. [Figure 6] 5, the horizontal sealing machine 116 is opened, and the horizontal sealing unit 32 moves to the position of the press / cutter 118. [Figure 7] 6, the state in which the horizontal seal portion 32 is being clamped by the press / cutter 118 is shown. [Figure 8] This shows the state after the press / cutter 118 and the squeezing rollers 115 are opened from the state shown in FIG. [Figure 9] This shows the state after the squeezing rollers 115 are closed after the contents W are further added from the state shown in FIG. [Figure 10] This shows a state after the contact portion 5a has moved from the state in FIG. 9 to the position of the horizontal sealer 116. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0011] 1. Packaging bag 1 1 and 2, a packaging bag 1 according to one embodiment of the present invention is constructed by welding a film 2 at a sealed portion 3. The sealed portion 3 includes a steam release sealed portion 4 that forms a steam flow path as the internal pressure of the packaging bag 1 increases.

[0012] Packaging bag 1 is intended for heating the contents in packaging bag 1 in a microwave oven, and as the contents are heated, the moisture in the contents turns to steam, causing an increase in the internal pressure of packaging bag 1. Because steam release seal portion 4 has a weaker seal strength than the other parts of seal portion 3, when the internal pressure of packaging bag 1 increases, the seal is broken at steam release seal portion 4 and a steam flow path is formed. Steam is released to the outside from this steam flow path, preventing damage to packaging bag 1 due to an excessive increase in internal pressure.

[0013] The seal portion 3 includes a vertical seal portion 31 and a horizontal seal portion 32. The vertical seal portion 31 is formed by bending the film 2 into a cylindrical shape and welding the film 2 at the overlapping portion where both side edge portions of the film 2 are overlapped. In this embodiment, the vertical seal portion 31 is of a palm-to-palm type in which the inner surfaces of the film 2 are welded together. By forming the vertical seal portion 31 in the film 2, the cylinder 5 is formed.

[0014] The horizontal seal portion 32 includes an upper horizontal seal portion 32a and a lower horizontal seal portion 32b. The upper horizontal seal portion 32a and the lower horizontal seal portion 32b are provided so as to close the upper and lower sides of the cylindrical body 5, respectively. The horizontal seal portions 32a, 32b are preferably formed along the upper and lower ends of the cylindrical body 5, respectively. The horizontal seal portions 32a, 32b are preferably formed so as to be perpendicular to the vertical seal portion 31. The horizontal seal portions 32a, 32b can each be formed by heat-sealing the cylindrical body 5.

[0015] As shown in FIG. 2, the film 2 has a modified region 7 in which the surface of the film 2 has been subjected to a corona discharge treatment. The modified region 7 is provided on the sealing surface (the surface to be welded) 2d of the film 2. The modified region 7 is formed so that a part or the whole of the modified region 7 overlaps with the region in which the sealed portion 3 is to be formed. In the modified region 7, polar groups such as hydroxyl groups and carbonyl groups are formed by the corona discharge treatment. The area where the modified region 7 and its opposing surface are welded has low seal strength at high temperatures, so this area becomes the steam release seal portion 4. The opposing surface may or may not be subjected to a corona discharge treatment.

[0016] As shown in Fig. 1, the value of [width W1 in the left-right direction of the steam release seal portion 4 / width W2 in the left-right direction of the horizontal seal portions 32a, 32b] is, for example, 0.05 to 0.8, and preferably 0.1 to 0.3. If this value is too small, steam may not be properly released, and if this value is too large, steam may be released too quickly, resulting in insufficient heating of the contents. Specifically, this value may be, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8, and may be within a range between any two of the values ​​exemplified here.

[0017] The modified region 7 is provided in a stripe shape across the upper horizontal seal portion 32a, the lower horizontal seal portion 32b, and the non-sealed portion 8 therebetween. In this case, the steam release seal portion 4 is provided in each of the horizontal seal portions 32a, 32b, so that steam can be released smoothly. In addition, the modified region 7 provided in the non-sealed portion 8 has good surface wettability, so that the film 2 is less likely to fog up in the modified region 7 of the non-sealed portion 8, and the visibility of the contents is excellent. Furthermore, such stripe-shaped modified region 7 can be easily formed by continuously performing a corona discharge treatment on the film moving in the longitudinal direction.

[0018] As shown in FIG. 2A, the film 2 is preferably a laminated film having a base layer 2a and a sealant layer 2b, and more preferably has an adhesive layer 2c between the base layer 2a and the sealant layer 2b.

[0019] The base material layer 2a is disposed so as to be exposed on the outer surface of the packaging bag 1, and the sealant layer 2b is disposed so as to be exposed on the inner surface of the packaging bag 1. The sealant layers 2b are heat-sealed to each other to form the vertical seal portion 31 and the horizontal seal portions 32a and 32b.

[0020] The base layer 2a is made of a material having excellent strength and high impact resistance. For example, polyamide is used as the base layer 2a. The adhesive layer 2c is a layer for bonding the base layer 2a and the sealant layer 2b so as to be laminated together, and for example, polyethylene is used as the adhesive layer 2c.

[0021] The polyamide of the base layer 2a preferably contains an aromatic polyamide, because in this case, the barrier property of the base layer 2a is excellent. There are no particular limitations on the aromatic polyamide, but it is possible to use a resin containing 70 mol % or more of polyamide structural units composed of xylylenediamine and an α,ω-aliphatic dicarboxylic acid having 6 to 12 carbon atoms in the molecular chain. Specific examples include homopolymers such as polymetaxylylene adipamide, polymetaxylylene pimelamide, polymetaxylylene azelamide, polyparaxylylene azelamide, and polyparaxylylene decanamide, and copolymers such as metaxylylene / paraxylylene adipamide copolymer, metaxylylene / paraxylylene pimelamide copolymer, metaxylylene / paraxylylene azelamide copolymer, and metaxylylene / paraxylylene sepacamide copolymer, with polymetaxylylene adipamide (hereinafter referred to as "MXD6") being preferred as it has excellent basic properties such as strength and gas barrier properties, and is relatively easily available industrially.

[0022] The sealant layer 2b can be made of a resin having excellent heat-sealing properties, for example, polyethylene (for example, linear low-density polyethylene).

[0023] The film 2 can be formed by laminating a base layer 2a having a thickness of 10 μm to 20 μm, for example 15 μm, an adhesive layer 2c having a thickness of 10 μm to 30 μm, for example 20 μm, and a sealant layer 2b having a thickness of 30 μm to 50 μm, for example 40 μm, and the film 2 usually has a thickness of 50 μm to 100 μm.

[0024] The film 2 is preferably a laminated film in which a base film 11 constituting the base layer 2a and a sealant film 12 constituting the sealant layer 2b are laminated. The base film 11 and the sealant film 12 are preferably bonded to each other via an adhesive layer 2c by using an extrusion lamination method. The base film 11 and the sealant film 12 may be heat-sealed without the adhesive layer 2c.

[0025] The corona discharge treatment for forming the modified region 7 may be carried out after the laminate film is formed, or the laminate film may be formed using the corona discharge treated sealant film 12 .

[0026] Here, the surface of the sealant film 12 on the base film 11 side is referred to as a laminating surface 12a, and the surface opposite to the laminating surface 12a is referred to as a sealing surface 12b.

[0027] The corona-discharge-treated sealant film 12 preferably has a laminate surface modified region 7a where the laminate surface 12a is corona-discharge-treated, and a sealing surface modified region 7b where the sealing surface 12b is corona-discharge-treated. The sealing surface modified region 7b becomes the modified region 7. By providing the laminate surface modified region 7a, the adhesion between the sealant film 12 and the base film 11 or the adhesive layer 2c is improved.

[0028] As shown in Fig. 2, the value of [width W3 of the sealing surface modified region 7b in the left-right direction / width W4 of the sealant film 12 in the left-right direction] is, for example, 0.02 to 0.4, and preferably 0.05 to 0.2. The width W3 of the sealing surface modified region 7b in the left-right direction coincides with the width W1 of the steam release seal portion 4, so if this value is too small, steam may not be properly released, and if this value is too large, steam may be released too quickly, resulting in insufficient heating of the contents. Specifically, this value is, for example, 0.02, 0.05, 0.1, 0.2, 0.3, or 0.4, and may be within a range between any two of the values ​​exemplified here.

[0029] The laminate surface modified region 7a preferably has a larger area than the seal surface modified region 7b. The value of [area of ​​laminate surface modified region 7a / area of ​​seal surface modified region 7b] is, for example, 1.1 to 30, specifically, for example, 1.1, 1.5, 2, 3, 4, 5, 10, 15, 20, 25, 30, and may be within a range between any two of the numerical values ​​exemplified here. Preferably, the width in the left-right direction of the modified regions 7a and 7b is constant along the longitudinal direction of the sealant film 12, and in this case, the area ratio of the modified regions 7a and 7b coincides with the ratio of the left-right widths of the modified regions 7a and 7b.

[0030] From the viewpoint of suppressing delamination, it is preferable that the laminate surface modified region 7a is formed in as wide an area as possible of the laminate surface 12a, and it is more preferable that it is provided on the entire laminate surface 12a. The value of [area of ​​the laminate surface modified region 7a / area of ​​the laminate surface 12a] is, for example, 0.2 to 1, specifically, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and may be within a range between any two of the numerical values ​​exemplified here.

[0031] Here, a method for producing the corona discharge treated sealant film 12 will be described with reference to Fig. 3. This method includes a corona discharge treatment step.

[0032] First, a circular film 14 is extruded from a circular slit of a die 13 and is sandwiched between a pair of rollers 15 to be flattened into a flat film 16 .

[0033] Next, corona discharge is induced in the gap between the anode 17a and cathode 17b of the corona discharge treatment device 17, to perform corona discharge treatment on the outer surface of the flat film 16. In this embodiment, two corona discharge treatment devices 17 with differently positioned anode 17a and cathode 17b are used to perform corona discharge treatment on both sides of the flat film 16. The cathode 17b is, for example, in the shape of a roller.

[0034] Next, both edges of the flat film 16 turned by the turning rollers 19 are cut by a cutter (not shown) to separate the flat film 16 into two films 20, which are then bifurcated by using a turning roller 21. Note that after cutting one edge of the flat film 16, the flat film 16 may be opened to form a single film.

[0035] Next, the surface of each film 20 that corresponds to the inner surface of the flat film 16 is subjected to a corona discharge treatment using a corona discharge treatment device 17, and then wound into a roll to obtain a film roll 12r of the sealant film 12.

[0036] Through the above steps, a sealant film 12 is obtained in which both sides have been subjected to a corona discharge treatment. In the above description, the corona discharge treatment is incorporated into the manufacturing process of the sealant film 12, but the step of performing the corona discharge treatment may be performed after the manufacturing of the sealant film 12 is completed. Alternatively, one side of the sealant film 12 may be subjected to a corona discharge treatment before the sealant film 12 is wound into a roll, and then the other side of the sealant film 12 may be subjected to a corona discharge treatment by roll-to-roll. In the above description, the sealant film 12 is manufactured by the inflation method, but the sealant film 12 may be manufactured by another method such as the T-die method.

[0037] The laminate surface corona discharge treatment for forming the laminate surface modified region 7a and the seal surface corona discharge treatment for forming the seal surface modified region 7b may be performed in either order, but it is preferable to perform the seal surface corona discharge treatment after the laminate surface corona discharge treatment. In general, the degree of corona discharge treatment decreases the longer the time has passed since the film was formed. For this reason, the later the corona discharge treatment is performed, the stronger the conditions of the corona discharge treatment required to achieve the desired surface state must be. Methods for strengthening the conditions of the corona discharge treatment include increasing the energy of the corona discharge treatment and lengthening the time of the corona discharge treatment.

[0038] The effect of the corona discharge treatment is most pronounced on the treated surface, but also on the opposite surface. Therefore, the effect of the corona discharge treatment on the sealing surface is also pronounced on the laminate surface 12a, and the effect of the corona discharge treatment on the laminate surface is also pronounced on the sealing surface 12b. The former may have a slight effect on the laminate strength, but is unlikely to be a major problem. On the other hand, the latter affects the seal strength at the seal portion 3, which makes it difficult to set the sealing conditions, and when peeling at the steam release seal portion 4, peeling is likely to occur between the sealant layer 2b and the base layer 2a, rather than at the adhesive interface between the sealant layers 2b. For this reason, it is desirable to minimize the effect of the latter. Also, the effect on the opposite surface becomes greater as the conditions of the corona discharge treatment on the treated surface become stronger.

[0039] From the above viewpoints, in order to make the conditions of the corona discharge treatment on the laminate surface as weak as possible, it is preferable to carry out the corona discharge treatment on the laminate surface before the corona discharge treatment on the seal surface.

[0040] In addition, the corona discharge treatment is preferably performed such that the surface energy of the laminate surface modification region 7a is smaller than the surface energy of the seal surface modification region 7b. This further reduces the influence of the corona discharge treatment on the laminate surface on the seal surface 12b. The surface energy can be evaluated, for example, by measuring the dyne level using a dyne pen (e.g., manufactured by ARCOTEST). In one example, the dyne level of the seal surface modification region 7b is 42 dynes, and the dyne level of the laminate surface modification region 7a is 38 dynes.

[0041] 2. Bag-making and filling method Next, a bag-making and filling method using the film 2 will be described with reference to FIGS. 4 to 10. This method can be implemented using a vertical bag-making and filling machine 100.

[0042] <S1: Film bending step> First, the film 2 fed out from the roll-shaped web F is guided to the former 112 via a plurality of pay-off rollers 120 and 121. A sensor 119 is arranged in the path from the roll-shaped web F to the former 112, and it detects the registration marks printed at regular intervals in the length direction of the film 2, enabling the film 2 of a certain length to be fed out at regular time intervals on the track of the bag-making and filling machine 100. While passing through the former 112, the film 2 is curved into a cylindrical shape, and the both side edges of the curved tip overlap with each other. An overlapping portion is formed at the overlapping part.

[0043] <S2: Longitudinal seal step> Next, the overlapping portion of the film 2 is heat-sealed by the longitudinal sealer 113 to form the longitudinal seal portion 31. The longitudinal sealer 113 includes a pair of seal rollers, and in accordance with the timing when the film 2 moves at regular time intervals, while sandwiching the overlapping portion of the film 2 with the pair of seal rollers, the pair of seal rollers are rotated in opposite directions to each other to perform heat-sealing while feeding out the film 2. By forming the longitudinal seal portion 31 on the film 2, the cylindrical body 5 is formed.

[0044] <S3: Horizontal Sealing Process> Next, by rotating the feed roller 114, the cylindrical body 5 is moved downstream by a predetermined length. As shown in FIGS. 5 to 6, a predetermined position of the cylindrical body 5 is heat-sealed by the horizontal sealer 116 to form the horizontal seal portion 32. The horizontal seal portion 32 is configured by connecting the upper horizontal seal portion 32a of the downstream packaging bag 1 and the lower horizontal seal portion 32b of the upstream cylindrical body 5, and is divided vertically in the cutting process described later. The horizontal sealer 116 includes a pair of seal bars 116a, and heat-sealing is performed by clamping the predetermined position with the pair of seal bars 116a for a predetermined time. In the film 2, the modified region 7 is formed in a streak shape along the longitudinal direction of the film 2. No matter at which position of the film 2 the horizontal seal portion 32 is formed, the horizontal seal portion 32 is formed overlapping the modified region 7. The portion where the horizontal seal portion 32 overlaps the modified region 7 becomes the steam vent seal portion 4.

[0045] <S4: Cutting Process> Next, by rotating the feed roller 114, as shown in FIG. 6, the horizontal seal portion 32 is moved to the position of the press-cutter 118. The press-cutter 118 includes a pair of bars 118a.

[0046] Next, as shown in FIG. 7, the press-cutter 118 is closed to clamp and cool the horizontal seal portion 32, and the horizontal seal portion 32 is cut with a cutter blade (not shown) and divided vertically. As shown in FIG. 8, the upper horizontal seal portion 32a of the downstream packaging bag 1 and the lower horizontal seal portion 32b of the upstream cylindrical body 5 are formed. When the horizontal seal portion 32 of the downstream packaging bag 1 is cut, it falls onto the conveyor 130.

[0047] <S5: Filling Process> Next, as shown in FIG. 8, when the squeezing roller 115 is opened, the content W that was introduced from the hopper 111 in the previous process and accumulated on the upper side of the squeezing roller 115 falls to the lower side of the squeezing roller 115. Since the lower lateral seal portion 32b is formed in the cylindrical body 5, the fallen content W is filled into the cylindrical body 5. A forming device 123 is arranged around the cylindrical body 5, and the outer shape of the cylindrical body 5 is defined by the circumferential surface of the cylindrical body 5 coming into contact with the forming device 123.

[0048] Next, the content W is further introduced into the cylindrical body 5. When the content W in the cylindrical body 5 reaches the position of the sensor 122, as shown in FIG. 9, the squeezing roller 115 is closed, thereby dividing the content W into an upper portion and a lower portion of the squeezing roller 115. The content in the lower portion of the squeezing roller 115 is the content for one bag of the packaging bag 1. Also, by closing the squeezing roller 115, an adhering portion 5a is formed on the cylindrical body 5, and a bag portion 5b is formed between the adhering portion 5a and the lower lateral seal portion 32b. The packaging bag 1 is formed by forming an upper lateral seal portion 32a above the bag portion 5b.

[0049] <S6: Feeding Process> Next, while the squeezing roller 115 is kept closed, the feeding roller 114 is rotated to move the adhering portion 5a to the position of the horizontal sealing machine 116 as shown in FIG. 10. After that, by performing the horizontal sealing process in the same manner as in S3, a horizontal seal portion 32 can be formed at a position (adhering portion 5a) higher than the portion (bag portion 5b) filled with the content W.

[0050] After this, by repeating the steps S1 to S6, the packaging bag 1 filled with the content W can be continuously manufactured.

[0051] The above steps produce a packaging bag 1 filled with the contents W. The steam release seal portion 4 is formed at the portion where the horizontal seal portion 32 overlaps the modified region 7, and therefore the steam release seal portion 4 can be easily formed without using a special device. The steam release seal portion 4 is formed at both the upper horizontal seal portion 32a and the lower horizontal seal portion 32b. However, for example, the welding strength at the lower horizontal seal portion 32b may be made higher than the welding strength at the upper horizontal seal portion 32a so that only the portion where the upper horizontal seal portion 32a overlaps the modified region 7 becomes the steam release seal portion 4 (the portion where the lower horizontal seal portion 32b overlaps the modified region 7 has too high a welding strength to become the steam release seal portion 4). The welding strength can be changed by changing the pressing force, seal width, seal temperature, etc. of the seal bar 116a. The horizontal seal portions 32a and 32b may be formed using separate seal bars.

[0052] 3.Other configurations In the above embodiment, the overlapping portion is of a palm-sealed type, but it may be of an envelope-sealed type. The packaging bag may be of a three-sided seal, four-sided seal, gusseted type, or the like. The steam release seal portion 4 may be provided at any position in the seal portion 3, for example, in the vertical seal portion 31. In this case, the modified region 7 is formed so that a part or the whole of the modified region 7 overlaps with the region where the vertical seal portion 31 is formed. [Explanation of symbols]

[0053] 1: Packaging bag 2: Film 2a: Base material layer 2b: sealant layer 2c: Adhesive layer 2d: Sealing surface 3: Seal part 4: Steam release seal 5: Cylindrical body 5a: Adhesion part 5b: Bag part 7: Modified area 7a: Laminate surface modification area 7b: Sealing surface modified area 8: Non-sealed part 11: Base film 12: Sealant film 12a: Laminated surface 12b: Sealing surface 12r: Film roll 13: Die 14: Circular film 15: Laura 16: Flat film 17: Corona discharge treatment device 17a: Anode 17b: Cathode 19: Turning Roller 20:Film 21: Turning Roller 31: Vertical seal part 32: Horizontal seal section 32a: Upper horizontal seal 32b: Lower horizontal seal 100: Bag making and filling machine 111: Hopper 112:Forma 113: Vertical sealing machine 114: Feed roller 115: Squeezing roller 116: Horizontal sealing machine 116a: Seal bar 118: Press and cutter 118a: Bar 119: Sensor 120: Feed roller 121: Feed roller 122: Sensor 123: Molding equipment 130: Conveyor F: Rolled raw material W: Contents

Claims

1. A method for manufacturing a packaging bag, comprising: The packaging bag is configured by welding a film at a seal portion, The seal portion includes a steam release seal portion that forms a steam flow path as the internal pressure increases, The film has a surface that is subjected to a corona discharge treatment to provide a modified region, and is a laminated film in which a base film and a sealant film are laminated, The sealant film has a lamination surface on the base film side and a sealing surface opposite to the lamination surface, The modified area is a seal surface modified area in which the seal surface is subjected to a corona discharge treatment, The laminate surface is provided with a laminate surface modification region in which the laminate surface is subjected to a corona discharge treatment; The steam release seal portion is a portion where the modified region and its opposing surface are welded together, The method includes a corona discharge treatment step, In the corona discharge treatment step, the surface energy of the sealing surface modified region is made larger than the surface energy of the laminate surface modified region, The method includes performing a corona discharge treatment on a laminate surface to form the laminate surface modified region, and then performing a corona discharge treatment on a seal surface to form the seal surface modified region.

2. 2. The method of claim 1 , The method, wherein the laminate surface modification region is larger in area than the seal surface modification region.

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