Square bottom packaging bag and manufacturing method of square bottom packaging bag

Abstract

To provide a square bottom packaging bag that is less likely to warp and a method for manufacturing the square bottom packaging bag.SOLUTION: The square bottom packaging bag includes: a square-tubular side portion 11 made of a laminate A having at least an outermost layer made of a paper layer; and a bottom portion 12 that closes one end of the square-tubular opening of the side portion 11 by joining the side portion 11 to the bottom seal portion. The bottom portion 12 is made of a laminate B that is different from the laminate A that constitutes the side portion 11 and has an outermost layer made of a biaxially oriented film and an innermost layer made of a sealant layer and does not have paper, and the side portion 11 is formed by joining a pair of opposing flat portions and a pair of opposing side portions by four side seal portions, and in the outermost layer of the laminate A that constitutes the pair of opposing flat portions, there is no difference in the inclination of the molecular orientation of the film or the difference in thermal shrinkage of the film between the bottom seal portion and the four side seal portions. The other end of the square-tubular opening is an opening K, and when the opening K is open, the laminates of the side portion 11 overlap only at the four side seal portions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a packaging bag with a square bottom and a method for manufacturing the same. [Background technology]

[0002] Packaging bags made of soft films such as resins are sometimes used to package foods, medical products, miscellaneous goods, etc. A known example of such packaging bags is a square-bottom packaging bag having a pair of flat surfaces, a pair of side surfaces, and a bottom surface. There are various types of square-bottom packaging bags depending on the manufacturing method, such as the joining form of each surface portion constituting the packaging bag and the conveying direction of the soft film (for example, Patent Documents 1 and 2). In many cases, the square-bottom packaging bag is manufactured in a folded state into a flat shape, and the way in which the flat shape is folded varies from one type to another.

[0003] Patent Document 1 describes a method for manufacturing a rectangular tubular self-supporting bag (square-bottom packaging bag) from a laminate film such as a plastic film. In this method, a strip-shaped tubular body is intermittently fed one unit length at a time in a manufacturing method for a rectangular tubular self-supporting bag, and a cut is made in the back material and both side materials while leaving the front material. Then, the cut edge is folded back by the width of the fold of the side material, the bottom material is superimposed on the open surface, and only the left and right side edges of the bottom material are heat-sealed to the open surface. Further, the folded back piece is folded back together with the bottom material, the two edge portions of the bottom material are heat-sealed to the open surface, and the bag body with the bottom material attached is cut off from the strip-shaped tubular body. In the manufacturing method for a rectangular tubular self-supporting bag of Patent Document 1, the up-down direction of the self-supporting bag coincides with the flow direction of the laminate film.

[0004] Patent Document 2 describes a method for producing a packaging material (packaging bag with square bottom) from a laminate film such as a plastic film. In this method, the front wall, the rear wall and the side wall are each formed from separate material sections that are joined by welded seams. The material sections of the front wall and the rear wall are formed by first and second flat main material webs that overlap each other and are transported in a common first transport direction. Side folded sections are cut to length from a flat third material web that is folded and formed as a side folded web and transported in a second transport direction transverse to the first transport direction so as to be placed on one of the main material webs. A flat fourth material web that forms a separate material section that forms the bag bottom is integrated into at least one of the main material webs and then welded along a side edge that is transported parallel to the first transport direction and adjacent to the side folded section and both main material webs. In the method for producing a packaging material in Patent Document 2, the up-down direction of the packaging material is perpendicular to the flow direction of the laminate film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-334861 A [Patent Document 2] JP 2000-254984 A Summary of the Invention [Problem to be solved by the invention]

[0006] Conventionally, a laminated film such as a plastic film used for a square-bottom packaging bag shown in Patent Documents 1 and 2 has been used, in which a laminated film is provided on the outermost layer. However, when this laminated film is used to manufacture a square-bottom packaging bag, the square-bottom packaging bag may be folded and flattened immediately after manufacture, and warped at the four corners of the square-bottom packaging bag. This warping is generally called S-shaped curl. When this warping occurs, for example, when multiple square-bottom packaging bags are bundled and stored in a box or the like for shipping, the bags become bulky and difficult to store. In addition, when such warping occurs in the square-bottom packaging bag, it may be difficult to open the opening for filling when filling the square-bottom packaging bag with a filling material such as food. An object of the present invention is to provide a square-bottomed packaging bag that is less prone to warping than when a laminate having a stretched film as the outermost layer is used, and a method for manufacturing the square-bottomed packaging bag. [Means for solving the problem]

[0007] Thus, according to the present invention, there is provided a square-bottom packaging bag having a square-tubular side portion made of laminate A, at least the outermost layer of which is a paper layer, and a bottom portion which closes one end of the square-tubular opening of the side portion by joining the side portion and the bottom seal portion, wherein the bottom portion is made of laminate B which is different from laminate A which constitutes the side portion, and whose outermost layer is a layer made of a biaxially oriented film, and whose innermost layer is a sealant layer and does not have paper, and the side portion is formed by joining a pair of opposing flat portions and a pair of opposing side portions by four side seal portions, and in the outermost layer of laminate A which constitutes the pair of opposing flat portions, there is no difference in the inclination of the molecular orientation of the film or the difference in thermal shrinkage of the film between the bottom seal portion and the four side seal portions, the other end of the square-tubular opening is an opening, and when the opening is open, the laminates of the side portions overlap only at the four side seal portions. Here, the laminate A may further have an innermost layer and an intermediate layer made of a biaxially stretched film having a thickness of 6 μm or more and 50 μm or less.

[0008] Furthermore, according to the present invention, there is provided a method for producing a square-bottom packaging bag, in which a flat film and a side film are conveyed along the vertical direction of the packaging bag. Further, according to the present invention, there is provided a method for producing a packaging bag with a square bottom, in which a flat portion film is transported along the left-right direction of the packaging bag. Effect of the Invention

[0009] According to the present invention, it is possible to provide a square-bottomed packaging bag that is less prone to warping and a method for manufacturing a square-bottomed packaging bag. [Brief description of the drawings]

[0010] [Figure 1] 1A to 1C are diagrams illustrating an example of a configuration of a packaging bag according to the present embodiment. [Diagram 2] FIG. 2 is a diagram showing the packaging bag in a folded state. [Diagram 3] 13(a) to 13(c) are diagrams illustrating the bottom portion in more detail. [Figure 4] 1(a) to 1(c) are cross-sectional views of a laminate constituting a side surface portion. [Diagram 5] FIG. 1 is a diagram showing an S-shaped curl. [Figure 6] 1A to 1C are diagrams illustrating an example of a method for manufacturing a packaging bag. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. <Overall description of packaging bag> FIG. 1 is a diagram showing an example of the configuration of a square-bottom packaging bag 10 (hereinafter simply referred to as "packaging bag 10") in this embodiment. As shown in the figure, the packaging bag 10 of this embodiment includes a side portion 11 that constitutes the side surface of the packaging bag 10 and a bottom portion 12 that constitutes the bottom surface of the packaging bag 10. The side surface portion 11 has a rectangular tubular shape in which a pair of flat portions 11a and a pair of side portions 11b are alternately joined, and the two side portions 11b are disposed at positions opposite each other. The bottom surface portion 12 is joined to the side surface portion 11 so as to close one end of the rectangular cylindrical opening.

[0012] The flat portion 11a and the side portion 11b of the side portion 11 are joined by thermal welding of the laminated bodies that constitute them. As a result, the laminated bodies are thermally welded together to form side seal portions SL, SR that protrude outward. By providing such seal portions SL, SR on the side portion 11, the self-supporting ability of the packaging bag 10 is improved.

[0013] Moreover, the other end of the rectangular cylindrical opening of the side portion 11 opposite to the bottom portion 12 side that closes one end of the opening is an opening K. Then, the filling material can be filled into the packaging bag 10 through the opening K. The filling material is not particularly limited, but may be, for example, food, medical products, miscellaneous goods, etc. Then, by sealing the opening K after filling, the filling material filled in the packaging bag 10 can be distributed in a sealed state. Also, an opening 11c, which is a cut, is provided in the side seal portions SL and SR above the packaging bag 10. Then, a consumer can take out the filling material filled in the packaging bag 10 by tearing the side portion 11 from the opening 11c as a tear start portion.

[0014] The side portions 11b and the bottom portion 12 of the packaging bag 10 can be folded along predetermined fold lines. In the folded state, the two opposing flat portions 11a of the packaging bag 10 are close to each other, and the space inside the packaging bag 10 is almost eliminated. The packaging bag 10 has a flattened shape. On the other hand, when the side portions 11b and the bottom portion 12 are not folded but are stretched out, the packaging bag 10 is in an unfolded state, and in this state, the side portions 11 are in the shape of a rectangular tube.

[0015] FIG. 2 is a diagram showing the packaging bag 10 in a folded state. The side portion 11b is rectangular and extends in a direction connecting one end and the other end of the rectangular tube, and is folded in half at a fold line T to form a V-shape, with the apex V1 of the V projecting toward the inside of the packaging bag 10. In this case, the apexes V1 of the two side portions 11b face each other as shown in FIG.

[0016] 3(a) to (c) are diagrams illustrating the bottom portion 12 in more detail. FIG. 3(a) shows the bottom portion 12 in an extended state. As shown in the figure, the bottom portion 12 is rectangular and is folded so as to be convex toward the inside of the bag when the packaging bag 10 is folded. The bottom portion 12 has a fold line T which is a valley fold that is folded so as to be convex toward the inside of the bag, and a fold line Y which is a mountain fold that is folded so as to be convex toward the outside of the bag. In FIG. 3(a), the fold line T is shown by a dotted line, and the fold line Y is shown by a dashed line. The fold line T is formed in the middle between the pair of flat portions 11a, with a straight portion T1 which is parallel to the pair of flat portions 11a and terminates inside the peripheral portion of the bottom portion 12, and a V-shaped portion T3 which extends from both ends T2 of the straight portion T1 toward the corresponding corner of the bottom portion 12. Fold line Y extends substantially perpendicularly from both ends T2 of straight portion T1 of fold line T toward the short side of bottom portion 12. By folding bottom portion 12 so as to be convex toward the inside of the bag, bottom portion 12 is folded so that the pair of flat portions 11a approach each other, resulting in the state shown in FIG. In addition, in the folded state, the bottom surface portion 12 is folded into a trapezoidal shape in a plan view as shown in Fig. 2. If the upper side of this trapezoid corresponding to the straight line portion T1 is defined as the apex V2, the bottom surface portion 12 is folded while projecting the apex V2 toward the inside of the packaging bag 10, that is, toward the opening K. 2, the location where the side portion 11b folded in half into a rectangular shape and the bottom portion 12 folded into a trapezoid shape overlap is a triangular portion W. In this triangular portion W, the side portion 11b is folded and overlapped while being sandwiched between the bottom portion 12.

[0017] 3(c) is a diagram showing a bottom seal portion SD of the bottom portion 12. The bottom seal portions SD are provided along each of the four sides of the rectangular bottom portion 12, and join the bottom portion 12 to the flat portion 11a and the side portion 11b by thermal welding of the laminates constituting these portions.

[0018] <Description of Layer Structure of Side Portion 11 and Bottom Portion 12> Next, the layer configuration of the side surface portion 11 and the bottom surface portion 12 will be described. 4(a) to (c) are cross-sectional views of the laminate constituting the side surface portion 11. FIG. 4(a)-(b) show the cross-sectional structure of the laminate of the side surface portion 11 of the present embodiment, and Fig. 4(c) shows the cross-sectional structure of an example of a laminate of a side surface portion that is conventionally used. The lower side in the figure is the inside side of the packaging bag 10, and the upper side in the figure is the outside side of the packaging bag 10. The side surface portion 11 described here includes both the flat portion 11a and the side portion 11b. In the side of a conventional square-bottom packaging bag, a biaxially oriented film is used as the outermost layer in consideration of printability and strength. Printing is performed on the biaxially oriented film, and the printing layer Pr is often located on the inside of the biaxially oriented film. In this case, warping may occur at the four corners of the packaging bag immediately after production due to this biaxially oriented film. In detail, warping occurs in which one side curls up and the other side curls down at adjacent corners of the four corners. This is also called S-shaped curl.

[0019] FIG. 5 is a diagram showing an S-shaped curl. In this case, the flat portion of packaging bag 10J, which is a conventional packaging bag, curls upward on one side at the upper portion, which is the front side, and curls downward on the other side, which is the rear side. The sealed portions SLJ, SRJ, and SDJ are more rigid than the portions without the sealed portions SLJ, SRJ, and SDJ, and therefore are less likely to warp, but warping is likely to occur at the corners of the upper opening KJ, which is not sealed.

[0020] The warpage is believed to occur for the following reasons. During the production of the film, the biaxially stretched film is stretched by being pulled in the longitudinal and transverse directions, and the resin molecules are oriented in these directions. At this time, near the center of the width of the film, the orientation direction of the molecules coincides with the longitudinal or transverse direction of the film, but near the ends of the width, the orientation direction may not coincide with the longitudinal or transverse direction of the film, and may be inclined from these directions. In a conventional packaging bag 10J in which the side portion is formed from a laminate using a biaxially stretched film in the outermost layer, when a pair of flat portions are arranged opposite each other as shown in FIG. 1, the orientation directions of the molecules of the biaxially stretched film in the outermost layer of each flat portion are different, and it is considered that warping occurs when the difference is large. The same can be said about a pair of side portions. Furthermore, during the production of packaging bag 10J, in the heat sealing to form each sealed portion SLJ, SRJ, SDJ, the orientation directions of the biaxially stretched films in the outermost layers of a pair of opposing flat portions differ greatly, resulting in differences in thermal shrinkage and resulting in some portions of each sealed portion SLJ, SRJ, SDJ with large and small thermal shrinkage rates, which is also thought to be a cause of warping at the four corners of packaging bag 10J. As described above, warping is likely to occur at the corners of the upper opening KJ that are not sealed.

[0021] As a result, the four corners of the packaging bag 10J may be warped when the packaging bag 10J is in a folded state immediately after production. That is, the above-mentioned S-shaped curl occurs. When the S-shaped curl occurs, as described above, for example, a bundle of several tens of packaging bags 10J bundled together for shipping becomes bulky, and when the bundle is stored in a box or the like, it may be difficult to store. Furthermore, when filling the packaging bag 10J with a filling material such as food, the upper opening KJ for filling may become difficult to open. In particular, the S-shaped curl is likely to occur when the laminate constituting the side surface of the packaging bag 10J has a direction connecting one end and the other end of the rectangular cylindrical opening of the side surface aligned with the flow direction of the film constituting the laminate. In this embodiment, this problem is alleviated by using side portion 11 that does not use a biaxially stretched film for the outermost layer.

[0022] In the present embodiment, the laminate constituting the side surface portion 11 is a laminate A having an outermost layer 112 of paper. When printing is to be performed on the side surface portion 11, printing is performed on the outer surface side of the paper. Additionally, a coating may be applied to protect the print.

[0023] The type of paper that can be used as the paper constituting the outermost layer 112 may be appropriately selected depending on the appearance and shape of the product, and is not particularly limited. For example, kraft paper such as bleached kraft paper and one-sided glossy bleached kraft paper, coated paper made by coating kraft paper with paint, base paper for foil, fine paper, rayon paper, pure white roll paper, etc. can be mentioned. Among these, coated paper is preferable because it has strength, a smooth surface, and excellent printability. In addition, in the process of manufacturing the packaging bag 10, it is preferable that the amount of paper dust generated is small when cutting the packaging bag 10 into individual bags. In the case of paper that generates a small amount of paper dust, the appearance of the cut line is also good, so it is preferable. From this viewpoint, coated paper is also preferable. Furthermore, since the side portion 11b of the side portion 11 is folded, it is preferable that it has excellent folding suitability. From this viewpoint, kraft paper and pure white roll paper are preferable. The basis weight of the paper is 20 g / m 2 More than 70g / m 2 It is preferable that:

[0024] The innermost layer 111 of the laminate A constituting the side portion 11 is a sealant layer. The innermost layer 111 is a layer for forming the seal portions SL, SR, and SD by heat welding, and is made of an unstretched film made of synthetic resin or a synthetic resin extruded in a layered form. The material of the synthetic resin for forming the innermost layer 111 is not particularly limited as long as it is heat-weldable. For example, polyethylene (PE) resin, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methacrylic acid copolymer, polypropylene (PP) resin, ethylene-polypropylene copolymer, and other resins can be used. In addition, any of high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene can be used as the polyethylene resin. It is possible to use only one of these resins, or two or more of them in combination. Moreover, the thickness of the innermost layer 111 is preferably not less than 15 μm and not more than 200 μm.

[0025] The innermost layer 111 is disposed on the inner surface side of the packaging bag 10. As described above, when the laminate constituting the flat portion 11a and the laminate constituting the side portion 11b are alternately joined, the respective innermost layers 111 are joined by thermal welding. Also, when the laminate constituting the side portion 11 and the laminate constituting the bottom portion 12 are joined, the respective innermost layers 111, 121 are joined by thermal welding. For this reason, the innermost layers 111, 121 constituting each surface are preferably made of a resin capable of being thermally welded to each other, and are preferably made of the same type of resin.

[0026] The outermost layer 112 of the laminate A constituting the side surface portion 11 is paper. Therefore, there is no difference in the inclination of the molecular orientation of the biaxially stretched film or in the thermal shrinkage, and the above-mentioned S-shaped curl does not occur. As a result, a bundle of several tens of packaging bags 10 is not bulky for shipping, and the bundle fits easily when stored in a box or the like. Furthermore, when filling the packaging bag 10 with a filling material such as food, the opening for filling is easily opened. Even if the laminate A constituting the side surface portion 11 of the packaging bag 10 of the present invention has a direction connecting one end and the other end of the rectangular cylindrical opening of the side surface portion 11 and the flow direction of the film constituting the laminate A, the S-shaped curl does not occur. Furthermore, by using paper for the outermost layer 112 of the laminate A that constitutes the side surface portion 11, the amount of plastic used can be reduced, resulting in a packaging bag 10 with a smaller environmental impact. From this viewpoint, the weight of the paper that constitutes the outermost layer 112 preferably accounts for 50% or more of the weight of the packaging bag 10.

[0027] Furthermore, in the laminate A constituting the side surface portion 11 of the present embodiment, an intermediate layer 113 may be used between the paper of the outermost layer 112 and the innermost layer 111, if necessary.

[0028] The intermediate layer 113 is a layer that can impart functionality such as gas barrier properties, water vapor barrier properties, mechanical toughness, bending resistance, puncture resistance, impact resistance, abrasion resistance, and cold resistance, and may be a stretched film made of a synthetic resin, a deposition film in which a metal such as aluminum or magnesium, or an inorganic material such as silicon oxide or aluminum oxide is deposited on a stretched film, or a film in which a stretched film is coated with polyvinylidene chloride. Examples of synthetic resins that form the stretched film used in the intermediate layer 113 include films of polyethylene terephthalate (PET), polyamide, polyvinyl chloride, polycarbonate, polyvinyl alcohol, and saponified ethylene-vinyl acetate copolymer. These stretched films may be uniaxially stretched films or biaxially stretched films. When tearability is required, it is preferable to use a uniaxially stretched film stretched in the tear direction. Metal foils such as aluminum and magnesium can also be used. The thickness of intermediate layer 113 may be any thickness that can impart these functionalities, and is, for example, not less than 6 μm and not more than 50 μm.

[0029] A biaxially stretched film may be used as intermediate layer 113. When a biaxially stretched film is used as intermediate layer 113, S-shaped curl is less likely to occur than when a biaxially stretched film is used for outermost layer 112. This is because the outermost layer 112 made of paper is provided on the outside of the biaxially stretched film of intermediate layer 113, so that the influence of thermal shrinkage due to heat sealing is less.

[0030] It is preferable that the bottom portion 12 uses a laminate B using a biaxially stretched film instead of paper for the outermost layer 122. In this embodiment, when a laminate using paper for the outermost layer is used as the bottom portion 12, if a cutting process of the bottom portion 12 is performed before each sealing portion is applied when manufacturing the packaging bag 10 described later, paper powder from the paper during cutting is likely to be mixed into the inside of the packaging bag 10. In addition, as described in FIG. 3(a) in this embodiment, the folding method of the bottom portion 12 is complicated. And, in the case of the bottom portion 12 made of a laminate using paper for the outermost layer, the strength to be able to cope with this folding is likely to be insufficient. Therefore, it is preferable to use a laminate B using a biaxially stretched film for the outermost layer 122 for the bottom portion 12.

[0031] For the innermost layer 121 of the laminate B constituting the bottom surface portion 12, various materials can be used that are used for the innermost layer 111 of the laminate A constituting the above-mentioned side surface portion 11. However, from the viewpoint of thermal welding with the side surface portion 11, it is preferable to use the same type of material as that of the innermost layer 111 of the side surface portion 11.

[0032] The biaxially stretched film used for the outermost layer 122 of the laminate B constituting the bottom portion 12 may be made of polyester-based resins such as polyethylene terephthalate, polyamide-based resins, polypropylene-based resins, polycarbonate-based resins, or polyacetal-based resins. Only one of these resins may be used, but two or more of them may also be used in combination. Cellophane, nonwoven fabric, or the like may also be used in combination as necessary. In the examples given here, a biaxially stretched film is used, but a uniaxially stretched film may also be used. However, when printing is to be performed on this, printability is required, and therefore a uniaxially stretched film or a biaxially stretched film is preferable. Like the laminate A, the laminate B may also have an intermediate layer. The laminate A and the laminate B are both laminated by a known method such as a dry lamination method or an extrusion lamination method.

[0033] <Description of Manufacturing Method of Packaging Bag 10> Next, a method for producing the packaging bag 10 will be described. The method for producing the packaging bag 10 is not particularly limited, but for example, it is produced as follows. Here, we will give an example of a manufacturing method that includes a conveying step in which the conveying direction of the film of the laminate A that constitutes the side portion 11 of the packaging bag 10 is made to coincide with the direction connecting one end and the other end of the rectangular tubular opening of the side portion 11. A side surface film, which is a laminate A using paper for the outermost layer 112 and which constitutes the side surface portion 11 of the packaging bag 10, is prepared. Also, a bottom surface film, which is a laminate B using a biaxially stretched film for the outermost layer 122 and which constitutes the bottom surface portion 12 of the packaging bag 10, is prepared. The side film may be previously separated into a side film and a flat film, but may also be cut into two during the manufacturing process.

[0034] The side films are folded in half, and the bottom portion 12 is formed by cutting the bottom film into a rectangular shape and folding the bottom portion 12 into a trapezoidal shape in plan view as described above.

[0035] Next, the folded side films and bottom portion 12 are sandwiched between a pair of flat portion films at predetermined positions.

[0036] More detailed explanation will be given with reference to FIG. 6 shows an example of a manufacturing method for the packaging bag 10. An apparatus 200 in this manufacturing method has rolls 210 and 220, and the rolls 210 and 220 rotate to transport the fed film in the direction of arrow C. The direction of arrow C is the flow direction of the film that constitutes the laminate A. Here, a pair of long side films 11bF folded along the flow direction are transported so that the apexes V1 of their V shapes face each other, and are clamped by the folded portions at both ends of the bottom portion 12, which is folded into a trapezoidal shape when viewed in a plane. Then, a pair of flat films HF1, HF2 are fed between the rolls 210 and 220 from above and below. The side films 11bF and the bottom portion 12 are sandwiched between the flat films HF1 and HF2, and then the side seal portions SL, SR, and bottom seal portion SD are applied. As a result, the flat films HF1, HF2, the side films 11bF, and the bottom portion 12 are integrated to form a belt-shaped film BF.

[0037] Next, when two or more packaging bags 10 are manufactured in the width direction, the strip film BF is cut along the conveying direction, thereby forming a strip bag in which the packaging bags 10 are connected in the longitudinal direction. Furthermore, an opening 11c is formed by cutting a part of the side seal portions SL, SR. Then, the strip-shaped bag is cut in a direction perpendicular to the conveying direction below the bottom seal portion SD, whereby the strip-shaped bag is separated into individual packaging bags 10, and the packaging bags 10 are manufactured.

[0038] Here, in the case of a laminate containing paper, when cutting is performed in the manufacturing stage, paper powder is likely to come out from the cut surface, depending on the type of paper. The bottom surface portion 12 is cut from the bottom surface film before being sandwiched between the pair of flat surface films HF1 and HF2 to form the respective seal portions SL, SR, and SD. Therefore, when sandwiched between the pair of flat surface films HF1 and HF2, paper powder may get mixed into the inside of the strip film BF, and the paper powder may end up getting mixed into the inside of the packaging bag 10. Therefore, when forming the packaging bag 10 by this manufacturing method, it is preferable that the bottom surface portion 12 is a laminate not containing paper. In contrast, the flat surface portion 11a and the side portions 11b are cut after the respective seal portions are formed to become the strip film BF, so even if paper powder comes out by cutting, the paper powder will not get mixed into the inside of the packaging bag 10.

[0039] As shown in FIG. 6, in this embodiment, when the packaging bag 10 is placed with the bottom surface 12 facing downward, the flat film HF1, HF2, and the side film 11bF are conveyed along the vertical direction. When this manufacturing method is used for the flat film and the side film made of a laminate using a biaxially stretched film as the outermost layer, the flat film and the side film are conveyed along the vertical direction of the packaging bag, so that the above-mentioned S-shaped curl is particularly likely to occur. In this embodiment, even when the packaging bag 10 is manufactured by such a manufacturing method, the S-shaped curl can be suppressed. At least, it is preferable that the conveying direction of the flat film constituting the flat portion 11a of the side surface portion 11 coincides with the direction connecting one end and the other end of the rectangular tubular opening of the side surface portion 11, that is, along the vertical direction of the packaging body 10.

[0040] In the embodiment described above in detail, the side surface portion 11 is formed into a rectangular tube shape by bonding four sheets of film, but the number of sheets is not particularly limited. For example, a rectangular tube-shaped side surface portion may be formed by rolling and bonding one sheet of film. In this case, the side seal portion may be provided at the corner of the side surface portion as shown in FIG. 1, or may be formed within one of the faces. Furthermore, when the side seal portion is provided at the corner, it may or may not protrude outward as shown in FIG. 1. When using a flat film and a side film using a biaxially stretched film as the outermost layer, S-shaped curl is likely to occur when the manufacturing method shown in this embodiment is used in which the flat film and the side film are transported along the top-to-bottom direction of the packaging bag, so the effects of the present invention are more pronounced. However, the present invention is not limited to this manufacturing method, and the packaging bag may also be one in which the flat film is transported along the left-to-right direction of the packaging bag. In the embodiment described above in detail, the packaging bag 10 is folded in the manner shown in Figs. 1 to 3, but the folding manner is not limited to this, and other folding manners are also applicable.

[0041] Although the present embodiment has been described above, the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear from the claims that various modifications and improvements to the above embodiment are also included in the technical scope of the present invention. [Explanation of symbols]

[0042] 10...packaging bag, 11...side portion, 11a...flat portion, 11b...side portion, 12...bottom portion, 111, 121...innermost layer, 112, 122...outermost layer, 113...middle layer, SL, SR, SD...sealed portion, K...opening, Pr...printed layer, T, Y...fold line

Claims

1. A rectangular tubular side portion made of a laminate A having at least an outermost layer made of paper; a bottom surface portion that closes one end of a rectangular tubular opening of the side surface portion by joining the side surface portion and the bottom seal portion; A square bottom packaging bag having the bottom surface portion is composed of a laminate B which is different from the laminate A constituting the side surface portion, has an outermost layer made of a biaxially oriented film, has an innermost layer made of a sealant layer, and does not have paper; the side surface portion is configured by joining a pair of opposing flat surfaces and a pair of opposing side portions with four side seal portions; In the outermost layer of the laminate A constituting the pair of opposing flat surfaces, there is no difference in the inclination of the molecular orientation of the film, and there is no difference in the thermal shrinkage of the film in the bottom seal portion and the four side seal portions, The other end of the rectangular cylindrical opening is an opening portion, When the opening is open, the laminates of the side portions overlap only at the four side seal portions. A packaging bag with a square bottom.

2. 2. The square-bottom packaging bag according to claim 1, wherein the laminate A further comprises an innermost layer and an intermediate layer made of a biaxially oriented film having a thickness of 6 μm or more and 50 μm or less.

3. A method for producing the square bottom packaging bag according to claim 1, A method for manufacturing square-bottom packaging bags, in which a flat film and a side film are conveyed along the vertical direction of the packaging bag.

4. A method for producing the square bottom packaging bag according to claim 1, A method for manufacturing a square-bottom packaging bag, in which a flat film is transported along the left-right direction of the packaging bag.

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