Plastic bag

Abstract

In the present invention, when there are an oblique-line seal part and a top seal part on one surface of a plastic bag having a sheet valley-folded at a folding line, the intersection of the inner edge line on the inner edge side in the width direction of the oblique-line seal part and the inner edge line on the inner edge side in the width direction of the top seal part is within a range from the folding line toward the center in the crossing direction of the top seal part, and the distance in the crossing direction from the folding line to the intersection is 0-15 mm.

Description

plastic bags

[0001] The technology of the present disclosure relates to plastic bags.

[0002] Japanese Patent Application Laid-Open Nos. 10-250747 and 2012-121611 disclose plastic bags capable of containing liquids and the like. The plastic bags described in these publications are formed by sealing four sheets together by heat welding. At least one surface of the plastic bag is formed by bonding together the four sheets by heat welding the oblique sides of adjacent mountain-shaped regions with the peaks of the mountain-shaped regions facing each other. The heat-sealed seal includes oblique side seal portions that run along the two oblique sides of the mountain-shaped regions and a peak seal portion that extends at the peak in a direction intersecting the two oblique side seal portions.

[0003] In such plastic bags, stress tends to concentrate at the intersection of the hypotenuse seal and the apex seal, which can easily cause leaks, where the contents, such as liquids, leak out due to peeling of the sheet. Depending on the application of the plastic bag, leakage of the contents can cause serious contamination or lead to poor product quality. Therefore, preventing leaks in such plastic bags is an important issue.

[0004] However, most of these plastic bags are single-use. While various methods for preventing leaks, such as adding additional components, are possible if the cost is high, single-use bags often face limitations that prevent additional costs, creating a strong demand for low-cost methods of preventing leaks.

[0005] The technology disclosed herein provides a plastic bag that can effectively prevent leaks while keeping costs down.

[0006] The plastic bag according to the technology of the present disclosure is formed by sealing a plurality of sheets, including four sheets, namely, a first sheet, a second sheet, a third sheet, and a fourth sheet, by heat welding, and is a plastic bag that changes from a folded state in which the sheets are folded to an unfolded state in which the sheets are unfolded to form an internal storage space. In the unfolded state, at least one surface is formed by bonding together the oblique sides of adjacent mountain-shaped regions of the four sheets with the peaks of the mountain-shaped regions facing each other and heat welding them together. In the folded state, the mountain-shaped regions of the first sheet and the second sheet face each other, and the mountain-shaped regions of the third sheet and the fourth sheet are folded inward along a fold line passing through the peaks between the opposing first sheet and second sheet, and further, the heat-sealed seal portion is a diagonal seal portion and a peak seal portion. When viewed in a plane in the folded state, the oblique side seal portion is a seal portion that seals the respective inner surfaces of the oblique side portions of the mountain-shaped regions of the opposing first and second sheets and the respective inner surfaces of the oblique side portions of the mountain-shaped regions of the valley-folded third and fourth sheets, and the apex seal portion is a seal portion that extends in a cross direction that intersects the respective fold lines and the respective oblique side seal portions of the third and fourth sheets, and seals the respective inner surfaces of the opposing first and second sheets between the respective fold lines, and in each of the third and fourth sheets, the intersection of the inner edge line on the inner edge side in the width direction of the oblique side seal portion and the inner edge line on the inner edge side in the width direction of the apex seal portion is within an inner range that starts from the fold line and heads toward the center in the cross direction of the apex seal portion, and the distance in the cross direction from the fold line to the intersection point is 0 mm to 15 mm.

[0007] More preferably, the distance is between 0 mm and 10 mm.

[0008] The thickness of the sheet is preferably 120 μm or more.

[0009] The sheet is preferably a sheet in which a plurality of resin layers are laminated.

[0010] The plurality of resin layers preferably contain polyethylene and polyethylene terephthalate.

[0011] Preferably, the plurality of resin layers further contain nylon.

[0012] The capacity is preferably 50 L or more.

[0013] It is preferably used in bioprocesses.

[0014] According to the technology of the present disclosure, it is possible to effectively suppress leaks while suppressing costs.

[0015] 1 is a diagram showing the appearance of an example of a plastic bag. FIG. 1 is a diagram showing an example of how a plastic bag transitions from a folded state to an unfolded state. FIG. 2 is a diagram showing an example of the arrangement of four sheets when manufacturing a plastic bag. FIG. 3 is a diagram showing an example of a cross section of a sheet. FIG. 4 is a diagram showing how heat welding occurs. FIG. 5 is a diagram showing an example of a sealing procedure. FIG. 6 is a diagram showing how cutting occurs after sealing. FIG. 7 is a plan view of a plastic bag in a folded state. FIG. 8 is a diagram showing four mountain-shaped regions that make up the front of the plastic bag in a separated state. FIG. 9 is a diagram showing an example where an intersection point is on the fold line. FIG. 10 is a diagram showing an example where an intersection point is inside the fold line. FIG. 11 is a diagram showing tension acting on a vertex. FIG. 12 is a diagram showing a comparative example. FIG. 13 is a graph showing an example of experimental results. FIG. 14 is a diagram explaining a test piece used in the experiment. FIG. 15 is a diagram explaining a tensile test. FIG. 16 is a diagram showing how delamination occurs. FIG. 17 is a graph showing another experimental result. FIG. 18 is a graph showing yet another experimental result. FIG. 19 is a diagram showing the shear force applied to the interface of a resin layer when the sheet is thick. FIG. 19 is a diagram showing the shear force applied to the interface of a resin layer when the sheet is thin.

[0016] As shown in Figure 1, a plastic bag 10 according to the technology of the present disclosure is used, for example, in bioprocessing applications such as the production of biopharmaceuticals and vaccines. The plastic bag 10 contains process solutions used in each step of the bioprocess. Examples of process solutions include cell suspensions, culture media, culture media additives, and buffers used in cell culture. In bioprocessing, preventing contamination is important to ensure the quality of the product, so the plastic bag 10 is single-use.

[0017] The plastic bag 10 has a three-dimensional storage space therein for storing a process solution. The plastic bag 10, for example, has a substantially rectangular parallelepiped shape and includes a front surface 10F, a back surface 10B, a top surface 10U, a bottom surface 10L, and two side surfaces 10S. For example, the top surface 10U and the bottom surface 10L are provided with ports 12 for connecting tubes 11. The tubes 11, for example, supply and discharge the process solution to and from the plastic bag 10. The positions and number of ports 12 shown in FIG. 1 are merely examples and can be changed as appropriate.

[0018] The capacity of the plastic bag 10 is, for example, approximately 500 L. Considering the need to process a relatively large volume of process solution, such as in a bioprocess involving perfusion culture of cells, the capacity is preferably 50 L or more. A capacity of approximately 100 L to 1000 L is more preferable.

[0019] As an example, the plastic bag 10 is formed by heat-sealing four plastic sheets S (see FIG. 3). The heat-sealed seals include side seals ES, oblique seals EH, and a peak seal EP. The side seals ES extend from the front surface 10F toward the rear surface 10B, and are located at the boundaries between the top surface 10U, bottom surface 10L, and two side surfaces 10S. The oblique seals EH are located on the front surface 10F, and form a cross shape with an intersection near the center of the front surface 10F. The four oblique seals EH intersect at one end near the center of the front surface 10F, and the other ends extend toward the four corners of the front surface 10F and connect to the side seals ES at the other end. The peak seal EP is located near the center of the front surface 10F.

[0020] The areas of the front surface 10F defined by the four oblique seal portions EH are generally mountain-shaped, and hereinafter, each area will be referred to as a mountain-shaped area MA1, MA2, MA3, and MA4. As will be described later, each of the mountain-shaped areas MA1 to MA4 is a part of one of the four sheets S. The front surface 10F is formed by bonding the four sheets S together by placing the peaks of the mountain-shaped areas MA1 to MA4 of each sheet S face-to-face and then thermally welding the oblique sides of adjacent mountain-shaped areas MA1 to MA4 together (see FIG. 9). The oblique seal portions EH are located at positions corresponding to one of the oblique sides H1 to H4 of each of the mountain-shaped areas MA1 to MA4 (see FIG. 9), and the apex seal portion EP is located near the intersection of the four oblique seal portions EH and corresponds to the peaks PK1, PK2, PK3, and PK4 of each of the mountain-shaped areas MA1, MA2, MA3, and MA4 (see FIG. 9). Although not shown in the drawings, the rear surface 10B is similar to the front surface 10F. When it is not necessary to distinguish between the mountain-shaped regions MA1 to MA4, the oblique portions H1 to H4, and the apex portions PK1 to PK4, they will also be referred to as the mountain-shaped regions MA, the oblique portions H, and the apex portions PK.

[0021] As shown in FIG. 2 , the plastic bag 10 changes from a folded state in which the sheet S is folded to an unfolded state in which the sheet S is unfolded to form a three-dimensional storage space inside. In FIG. 2 , the upper part shows the folded state in which the plastic bag 10 is folded. In the folded state, four sheets S are stacked on top of each other, resulting in a substantially flat shape. The plastic bag 10 changes to an unfolded state in which a three-dimensional storage space (in this example, a rectangular parallelepiped) is formed inside by blowing gas into the interior of the plastic bag 10, for example, through a port 12. The middle part shows the state in which gas injection has begun from the folded state, resulting in a slight expansion. The bottom part shows a state in which gas injection has progressed further, approaching the unfolded state. Further gas injection causes the plastic bag 10 to reach the unfolded state shown in FIG. 1 .

[0022] A method for manufacturing the plastic bag 10 will be described below with reference to Figures 3 to 7. As shown in Figure 3, the plastic bag 10 is made up of four sheets S, namely, a first sheet S1, a second sheet S2, a third sheet S3, and a fourth sheet S4, and is formed by sealing these four sheets S by thermal welding. Here, when it is not necessary to distinguish between the first sheet S1 to the fourth sheet S4, the sheets S will simply be referred to as sheets S.

[0023] Each sheet S is, for example, rectangular. When the capacity of the plastic bag 10 is 500 L, the size of the sheet S is, for example, approximately 1690 mm in long sides and approximately 870 mm in short sides. Because the plastic bag 10 has a relatively large capacity, the thickness of each sheet S is preferably 120 μm or more, for example, approximately 190 μm to 210 μm. If the thickness of the sheet S is thin, the water vapor transmission rate decreases. The reason why a thickness of 120 μm or more is preferable is to ensure the water vapor transmission rate required for bioprocessing. When the plastic bag 10 is made of the sheet S, water vapor transmission through the sheet S tends to be large. In bioprocessing, changes in the concentration of the aqueous solution that is the content due to water evaporation can become a problem. Therefore, it is highly necessary to suppress water vapor evaporation, and water vapor transmission rate is important. By making the thickness of the sheet S 120 μm or more, the water vapor transmission rate required for bioprocessing can be ensured. The water vapor transmission rate is approximately 1.00 [g / (m ２ ·day)] or less, and more preferably 0.77 [g / (m ２ ·day)] or less. For example, the water vapor transmission rate of the sheet S used in this example is 0.86 [g / (m ２ ·day)], and when the thickness is 205 μm, it is 0.51 [g / (m ２ If the thickness is 120 μm or more, the water vapor permeability is 0.77 [g / (m ２ ·day)] or less can be ensured, and if the thickness is about 190 μm to 210 μm, the water vapor permeability is 0.77 [g / (m ２ ・day) or less can be ensured.

[0024] 4, each sheet S is, for example, a sheet in which multiple resin layers are laminated. For example, the multiple resin layers include a polyethylene (PE) layer and a polyethylene terephthalate (PET) layer. Furthermore, the resin layers may include oriented nylon (ONY) resin and ethylene-vinyl alcohol copolymer (EVOH) resin.

[0025] When manufacturing the plastic bag 10, the four sheets S are arranged as shown in Figure 3. The first sheet S1 and the second sheet S2 face each other, and the third sheet S3 and the fourth sheet S4 are folded inward along the fold line LO between the first sheet S1 and the second sheet S2. In this overlapping state, each sheet S is heat-sealed.

[0026] As shown in FIG. 5 , a sheet group SS, which is made up of four overlapping sheets S, is first heat-sealed along the long sides of the sheet group SS by heat welding using a heat sealer 21, forming side seals ES. The length of the heat sealer 21 is, for example, approximately 1500 mm. As shown in FIG. 3 , the third sheet S3 and the fourth sheet S4 are valley-folded along the fold lines LO between the first sheet S1 and the second sheet S2. Therefore, outside the fold lines LO, the first sheet S1 and the second sheet S2 are not in direct contact, and the third sheet S3 and the fourth sheet S4 are respectively folded and interposed between them. Therefore, the long edge edges of the first sheet S1 and the second sheet S2 do not contact each other, but rather contact the third sheet S3 or the fourth sheet S4. That is, one long side edge of the first sheet S1 is sealed to one long side edge of the third sheet S3, and the other long side edge is sealed to one long side edge of the fourth sheet S4. One long side edge of the second sheet S2 is sealed to the other long side edge of the third sheet S3, and the other long side edge is sealed to the other long side edge of the fourth sheet S4. This forms four side seals ES.

[0027] In Figure 6, the top row shows the state in which the side seals ES have been formed as shown in Figure 5. After the side seals ES have been formed by sealing the edges of the long sides, the oblique seals EH are formed as shown in the middle row of Figure 6. The oblique seals EH are also formed by thermal welding using the heat sealer 21. As described above, the first sheet S1 and the second sheet S2 are not in direct contact outside the fold line LO. Therefore, in the area where the third sheet S3 is interposed, the first sheet S1 is sealed to the third sheet S3, and the second sheet S2 is also sealed to the third sheet S3. In the area where the fourth sheet S4 is interposed, the first sheet S1 is sealed to the fourth sheet S4, and the second sheet S2 is also sealed to the fourth sheet S4. The same applies to the back side 10B. This forms four oblique seals EH on the front side 10F of the plastic bag 10 and four oblique seals EH on the back side 10B.

[0028] Furthermore, after the oblique side seal portion EH is formed, the lower row shown in Figure 6 is sealed by heat welding in the cross direction intersecting with the oblique side seal portion EH. In this example, the cross direction is the short side direction of the sheet group SS. Between the two fold lines LO, the inner surfaces of the opposing first sheet S1 and second sheet S2 are in direct contact with each other. The apex seal portion EP is a seal portion that seals the inner surfaces of the first sheet S1 and second sheet S2. The apex seal portion EP is formed on both the front side 10F and the back side 10B.

[0029] After the sheet group SS has been sealed by heat welding, as shown in Figure 7, for example, the four corners 23 outside the oblique side seal portion EH are cut. Also, for example, the outer edge 24 of the apex seal portion EP is also cut. This completes the plastic bag 10 shown in Figures 1 and 2. Figure 7 shows the folded state of the plastic bag 10. After the plastic bag 10 is completed, the port 12 shown in Figures 1 and 2 is attached, but the port 12 is omitted from Figure 8 and subsequent figures for convenience.

[0030] Fig. 8 shows the folded plastic bag 10 as viewed from above from the first sheet S1 side. The first sheet S1 forms the mountain-shaped area MA1, which is a part of each of the front surface 10F and the back surface 10B, and the top surface 10U when the plastic bag 10 is unfolded. Fig. 9 shows the configuration of the front surface 10F of the plastic bag 10 with the first sheet S1 to the fourth sheet S4 separated.

[0031] In Figure 8, the area inside the two fold lines LO indicated by the symbol A1 is the area where the first sheet S1 and the second sheet S2 are in direct contact, as described above. This area A1 is a two-ply area where only the first sheet S1 and the second sheet S2 overlap when the plastic bag 10 is folded. On the other hand, the area outside each of the two fold lines LO indicated by the symbol A2 is an area where the valley-folded third sheet S3 or the valley-folded fourth sheet S4 is interposed between the first sheet S1 and the second sheet S2, as described above. If the valley-folded third sheet S3 and the valley-folded fourth sheet S4 are counted as two sheets each, this area A2 is a four-ply area where four sheets S, including the first sheet S1 and the second sheet S2, overlap when the plastic bag 10 is folded.

[0032] As shown in FIG. 9 in addition to the plan view of the folded state in FIG. 8 , in the mountain-shaped region MA1 of the first sheet S1, one of the two oblique sides H1 is sealed to the oblique side H3 of the mountain-shaped region MA3 of the valley-folded third sheet S3 on its inner surface, and the other of the two oblique sides H1 is sealed to the oblique side H4 of the mountain-shaped region MA4 of the fourth sheet S4 on its inner surface. This sealed portion is the oblique side seal portion EH. Similarly, in the mountain-shaped region MA2 of the second sheet S2 facing the first sheet S1, one of the two oblique sides H2 is sealed to the oblique side H3 of the mountain-shaped region MA3 of the valley-folded third sheet S3 on its inner surface, and the other of the two oblique sides H2 is sealed to the oblique side H4 of the mountain-shaped region MA4 of the fourth sheet S4 on its inner surface. This sealed portion is also the oblique side seal portion EH.

[0033] In addition, the top seal portion EP extends in a cross direction intersecting the respective fold lines LO and the respective oblique side seal portions EH of the third sheet S3 and the fourth sheet S4, and is a seal portion that seals the inner surfaces of the opposing first sheet S1 and second sheet S2 between the respective fold lines LO.

[0034] 10, in each of the third sheet S3 and the fourth sheet S4, the intersection P1 of the inner edge line LH on the inner edge side of the width direction of the oblique side seal portion EH and the inner edge line LP on the inner edge side of the width direction of the apex seal portion EP is within the range inward from the fold line LO toward the center in the cross direction of the apex seal portion EP, and the distance D in the cross direction from the fold line LO to the intersection point is 0 mm to 15 mm. The inner range toward the center in the cross direction refers to the range between the two fold lines LO, including the area on the two fold lines LO. This range corresponds to the width of the double-ply region A1.

[0035] The example shown in Figure 10 shows an example where the distance D is 0 mm, and the intersection point P1 is on the fold line LO. In other words, in this case, if the intersection point between the fold line LO and the inner edge line LP of the apex seal portion EP is P0, the intersection point P1 coincides with point P0. On the other hand, the example shown in Figure 11 shows an example where the distance D is a value greater than 0, and the distance D is positive. When the distance D is positive, this means that the intersection point P1 is located inside the two fold lines LO, i.e., point P0. When the distance D is positive, this is hereinafter referred to as an inward shift, meaning that the intersection point P1 is shifted inside point P0.

[0036] As shown in Figure 12, point P0 is located on the fold line LO and is the vertex of the mountain-shaped area MA3 of the third sheet S3. Hereinafter, point P0 will be referred to as the vertex P0. Note that vertex P0 also exists on the mountain-shaped area MA4 side of the fourth sheet S4, which has another fold line LO.

[0037] When the plastic bag 10 is in an unfolded state, tension acts on the third sheet S3 in the direction indicated by the downward arrow in the mountain-shaped region MA3 shown in FIG. 12. When such tension acts, tension F acts on the apex P0. Experiments have shown that when tension F is concentrated on the apex P0, delamination occurs in each sheet S sealed at the oblique side seal portion EH and the apex seal portion EP. Delamination between each sheet S is delamination between the multiple resin layers that make up the sheet S shown in FIG. 4. This delamination can cause the contents to leak. The same applies to the apex P0 of the fourth sheet S4.

[0038] To prevent this leak, in the plastic bag 10, the distance D in the crossing direction of the intersection point P1 is set to 0 mm to 15 mm, so that the position of the intersection point P1 is set within the range inside the two fold lines LO, as shown in Figures 10 and 11. By setting the position of the intersection point P1 in this manner, the vertex P0 is located within the oblique side seal portion EH, and it is thought that the force acting on the vertex P0 is not concentrated at the vertex P0 but is dispersed along the inner edge line LH of the oblique side seal portion EH. The plastic bag 10 of the present disclosure suppresses delamination and leaks caused by delamination by dispersing the tension F in this way.

[0039] In contrast, in the comparative example shown in Figure 13, the intersection point P1 is located outside each folding line LO and is outside the inner range starting from the folding line LO toward the center of the apex seal portion EP in the intersecting direction. In other words, the value of the distance D from the folding line LO to the intersection point P1 is below 0, a negative value, because it is outside the folding line LO, unlike the example of inward shift shown in Figure 11. The comparative example shown in Figure 13 means that the intersection point P1 is outside point P0 on the folding line LO. When the distance D is negative, this is referred to as an outward shift, meaning that the intersection point P1 is shifted outward from the apex P0.

[0040] 10 and 11, in the case of an outward displacement where the intersection point P1 is shifted outward from the vertex P0, the vertex P0 is displaced from the oblique side seal portion EH. In this case, the tension F acting on the vertex P0 is concentrated at the vertex P0 without being dispersed to the oblique side seal portion EH. As described above, the concentration of the tension F at the vertex P0 can cause delamination of the sheets S sealed at the oblique side seal portion EH and the apex seal portion EP, resulting in leakage of the contents.

[0041] FIG. 14 is a graph showing an example of experimental results. The example shown in FIG. 14 shows the results of tensile strength measurements when the distance D is shifted inward and outward from the position of the intersection point P1, where the distance D is 0 mm as shown in FIG. 10, i.e., the position where the intersection point P1 and the vertex P0 coincide. In the example shown in FIG. 14, the width of the double-layered region A1 is 25 mm. The tensile strengths when the distance D is +5 mm and +15 mm are shown as inward shifts, and the tensile strengths when the distance D is -5 mm and -15 mm are shown as outward shifts. As shown in the graph in FIG. 14, the tensile strength is lower in the case of outward shifts than in the case of inward shifts, including when the distance D is 0 mm.

[0042] The tensile strength measurements were carried out in accordance with JIS Z0238:1998. The tensile tester used was a digital force gauge manufactured by Imada Co., Ltd., model number ZTS-1000N, and the motorized test stand model number MX2-1000N-L-V750. Using this tensile tester, an experiment was carried out under the conditions shown below, and the experimental results shown in Figure 14 were obtained. In Figure 14, the error bars BE indicate the variation in the measured values ​​at each position.

[0043] The experimental conditions were as follows. First, as shown in FIG. 15 , a test piece TP was prepared by cutting out a portion of a plastic bag 10, including the oblique seal portion EH, the apex seal portion EP, and the vertex P0, and the experiment was performed on the prepared test piece TP. The test piece TP was rectangular, with the longitudinal direction along the fold line LO. The center of the short side (width direction) of the test piece TP was the fold line LO, with half of the area in the short side direction being a two-ply area A1 and the remaining half being a four-ply area A2. One end of the test piece TP in the longitudinal direction had an area including the oblique seal portion EH, the apex seal portion EP, and the vertex P0. The example shown in FIG. 15 is an example in which the intersection point P1 and the vertex P0 coincide, similar to FIG. 8 . In the test piece TP used in the experiment, the thickness of each sheet S was 205 μm. The resin layer of each sheet S was composed of four layers: a PET layer, an ONY layer, an EVOH layer, and a PE layer. The plastic bag 10 has a capacity of 500 L. The heat sealer 21 is an impulse sealer (AS series: length 1500 mm) manufactured by Masui Giken Co., Ltd., and the welding conditions are 190° C. for 3 seconds.

[0044] As shown in FIG. 16 , the test piece TP was set on the base (not shown) of a tensile tester (not shown) with the above specifications, and the two-ply region A1 was fixed with a fixture 26. Then, one end of the sheet S4 having the fold line LO in the four-ply region A2 was gripped by a chuck (not shown) of the tensile tester. In this state, a tensile force DF was applied to the sheet S4 at a tensile speed of 500 mm / min so that the force was applied to the vertex P0, and the tensile strength of the test piece TP was measured. Multiple samples of the test piece TP were prepared by varying the position of the intersection point P1, and similar tensile tests were performed on these samples with different positions of the intersection point P1. Under these experimental conditions, the experimental results shown in FIG. 14 were obtained.

[0045] Furthermore, leak tests were conducted on test samples of each plastic bag 10 with the intersection point P1 positioned differently, as shown in Figure 14. The leak tests were conducted on two types of plastic bags 10, one with a capacity of 500 L and the other with a capacity of 1000 L. First, the plastic bag 10 was inflated with a hydrogen / nitrogen mixed gas until the internal pressure reached approximately 5.0 kPa, and then a dedicated probe was used to detect leaks while maintaining that pressure. Furthermore, for the 1000 L plastic bag 10, a liquid leak test was conducted by pouring water into the plastic bag 10 up to 105% of its nominal capacity, and checking for any leaks of the contents.

[0046] In the experimental results shown in Fig. 14, no leaks occurred when the distance D was inwardly displaced, including 0 mm. In contrast, intralayer delamination and leaks occurred when the distance D was outwardly displaced.

[0047] It has also been found that the tensile strength does not decrease even with inward displacement up to a value of 15 mm for the distance D. Therefore, the upper limit of the distance D is preferably 15 mm.

[0048] Figure 17 shows the state of delamination. As shown in Figure 17, when the same tensile strength was applied to both the inner and outer misalignment, delamination occurred in the outer misalignment.

[0049] Figure 18 shows the results of another experiment different from that shown in Figure 14. The experimental conditions for Figure 18 were almost the same as those for Figure 14. The difference is that in Figure 18, the width of the double-layered region A1 is 100 mm, which is wider than in Figure 14. In the graph shown in Figure 18, the tensile strength is lower for outer misalignment than for inner misalignment, including those where the distance D is 0 mm.

[0050] Figure 19 shows the results of yet another experiment. The experimental conditions in Figure 19 differ from those in Figure 14 in that the width of the two-ply region A1 is 100 mm, as in Figure 16 . Also, in Figure 19 , the manufacturer of the heat sealer 21 is different from that in Figure 14 ; in Figure 19 , an impulse sealer (model: LOS-1000-10W) manufactured by Fuji Impulse Co., Ltd. is used. The experimental results in Figure 19 show that the tensile strength is higher when the outer misalignment is -2 mm than when the distance D is 0 mm and when the inner misalignment is +2 mm and +8 mm. However, the length of the error bar BE, which indicates the magnitude of the variation in measurement error, is relatively long when the outer misalignment is used, suggesting that the influence of measurement error is also significant in the experimental results in Figure 19 . Furthermore, when comparing the outer misalignment and the inner misalignment, the greater the outer misalignment, the greater the drop in tensile strength; however, the same effect is seen when the inner misalignment is used. In other words, the tensile strength drops sharply in the direction of the outward misalignment. Therefore, even if the tensile strength can be ensured when the outward misalignment is slight, assuming that there is a manufacturing error in the distance D, it is considered that excluding the outward misalignment and limiting it to the inward misalignment has the advantage of ensuring average quality and yield, etc. Therefore, as described above, the distance D that defines the position of the intersection P1 is preferably in the range of 0 mm to 15 mm.

[0051] Furthermore, according to experiments, although leakage does not occur, when the distance D exceeds 10 mm, delamination may occur in the sheet S. Therefore, the range of the distance D is more preferably 0 mm to 10 mm.

[0052] Furthermore, the effect of the technology disclosed herein in suppressing interlayer delamination of the sheet S is greater as the thickness of the sheet S increases. Figures 20 and 21 are diagrams illustrating the shear force generated at the interface of each resin layer due to changes in the thickness of the sheet S. The thickness T1 of the sheet SA shown in Figure 20 is thicker than the thickness T2 of the sheet SB shown in Figure 21, i.e., T1 > T2.

[0053] When a bending force is applied to the sheet SA shown in Figure 20, a tension force FA1 acts on the outer PET layer of the sheet SA, and a contraction force FA2 acts on the PE layer inside the center line of the sheet SA in the thickness direction. In this case, a shear force corresponding to the difference between the tension force FA1 and the contraction force FA2 acts on the interface. This causes delamination.

[0054] 20, in the sheet SB shown in FIG. 21, a shear force corresponding to the difference between the tension FB1 and the contraction force FB2 acts on the interface of the sheet SB. Here, because the sheet SA is thicker than the sheet SB, the difference between the tension FA1 and the contraction force FA2 is greater than the difference between the tension FB1 and the contraction force FB2. Therefore, the thicker the sheet S, the greater the shear force at the interface, making delamination more likely to occur. Therefore, the thicker the sheet S, the greater the need to distribute the tension acting on the vertex P0. Therefore, the technology disclosed herein is considered to be more effective the thicker the sheet S.

[0055] As described above, the plastic bag 10 according to the technology of the present disclosure is a plastic bag formed by heat-sealing multiple sheets S, including four plastic sheets, namely, first sheet S1, second sheet S2, third sheet S3, and fourth sheet S4, and is a plastic bag that changes from a folded state in which the sheets S are folded to an unfolded state in which the sheets S are unfolded to form an internal storage space (see FIGS. 1 and 2). As shown in FIGS. 1 and 9, in the unfolded state, at least one surface (for example, the front surface 10F and the back surface 10B) is formed by bonding together the apexes PK of the mountain-shaped regions MA of each of the four sheets S1 to S4 by heat-sealing the oblique sides H of adjacent mountain-shaped regions MA with each other, with the apexes PK facing each other. 2, 3, 8, and 9, in the folded state, the mountain-shaped regions MA of the first sheet S1 and the second sheet S2 face each other, and the mountain-shaped regions MA of the third sheet S3 and the fourth sheet S4 are folded inward along the fold line LO passing through the apex PK between the opposing first sheet S1 and the second sheet S2. Furthermore, as shown in FIGS. 1, 8, and 9, the heat-sealed seal includes two seals: a diagonal seal EH and a peak seal EP. As shown in FIGS. 8 and 9, in a plan view of the folded state, the diagonal seal EH seals the inner surfaces of the diagonal sides E of the mountain-shaped regions MA of the opposing first sheet S1 and the second sheet S2 and the diagonal sides E of the valley-folded mountain-shaped regions MA of the third sheet S3 and the fourth sheet S4. The top seal portion EP extends in a cross direction intersecting the fold lines LO and the oblique side seal portions EH of the third sheet S3 and the fourth sheet S4, and is a seal portion that seals the inner surfaces of the opposing first and second sheets between the fold lines LO.Furthermore, as shown in Figures 10 and 11, in each of the third sheet S3 and the fourth sheet S4, the intersection P1 of the inner edge line LH on the inner edge side in the width direction of the oblique side seal portion EH and the inner edge line LP on the inner edge side in the width direction of the apex seal portion EP is within the inner range starting from the fold line LO toward the center of the apex seal portion EP in the crossing direction, and the distance D in the crossing direction from the fold line LO to the intersection point P1 is 0 mm to 15 mm.

[0056] This configuration allows for the distribution of tension F acting on the vertex P0 where the fold line LO and the inner edge line LP intersect. This prevents delamination of the sheet S and leakage resulting from delamination. Because the above configuration involves devising the position of the intersection P1, costs can be reduced compared to adding new leak prevention components. As a result, the above configuration effectively prevents leakage while keeping costs down. When the plastic bag 10 is for single use, cost reduction is important, so the technology of the present disclosure is particularly effective.

[0057] Moreover, from the viewpoint of further suppressing delamination, the distance D that defines the position of the intersection point P1 is more preferably 0 mm to 10 mm.

[0058] In order to ensure sufficient water vapor permeability, the thickness of the sheet S is preferably 120 μm or more.

[0059] Furthermore, when the sheet S is a sheet having multiple resin layers laminated thereon, the technology of the present disclosure for suppressing delamination is particularly effective. While the above embodiment has been described using an example of a laminated sheet S having multiple resin layers, the sheet S may also be a single layer. It is believed that the effect of dispersing the tension F acting on the vertex P0 can be expected to have a certain effect in terms of suppressing leaks even when a single-layer sheet S is used.

[0060] The multiple resin layers include polyethylene (PE) and polyethylene terephthalate (PET). The PE layer is relatively soft, and the PET layer is relatively hard. When these resin layers with different elastic moduli are combined, the difference in elongation rate makes delamination at the interface between the layers more problematic. Therefore, the technology of the present disclosure is more necessary than when resin layers with similar hardness are combined.

[0061] The multiple resin layers further contain nylon. Nylon has high tear strength. When such nylon layers with different physical properties are further combined, interlayer delamination becomes even more of a problem. Therefore, in such cases, the technology of the present disclosure is even more necessary.

[0062] Furthermore, when the capacity of the plastic bag 10 is 50 L or more, the tension F acting on the apex P0 is greater than when the capacity is less than 50 L, increasing the risk of leakage. Therefore, the technology of the present disclosure, which has the effect of dispersing the tension F acting on the apex P0, is more effective the larger the capacity of the plastic bag 10.

[0063] The plastic bag 10 is also used in bioprocessing. In bioprocessing applications, preventing contamination and fouling is often a critical issue compared to other applications. Single-use is also common in bioprocessing applications. Therefore, the technology of the present disclosure, which can effectively prevent leaks while keeping costs down, is particularly effective in bioprocessing applications.

[0064] In the above embodiment, the plastic bag 10 has a generally rectangular parallelepiped shape in the unfolded state, but it may have a polyhedron other than a hexahedron. Furthermore, the front surface 10F and the back surface 10B of the plastic bag 10 each have four angle-shaped areas MA1-MA4, an oblique side seal portion EH, and an apex seal portion EP. However, only the front surface 10F or only the back surface 10B may have such a surface, and at least one such surface is sufficient.

[0065] Also, as shown in FIG. 7, an example has been described in which unnecessary portions on the outside of the oblique side seal portion EH are cut off, but this does not necessarily have to be done.

[0066] Furthermore, although the example in which the plastic bag 10 is made up of four sheets S has been shown, the number of sheets S may be more than four.

[0067] The above embodiment further discloses the following: [Supplementary Item 1] A plastic bag formed by sealing a plurality of sheets including four plastic sheets, i.e., a first sheet, a second sheet, a third sheet, and a fourth sheet, by heat welding, the bag changing from a folded state in which the sheets are folded to an unfolded state in which the sheets are unfolded to form an internal storage space, wherein in the unfolded state, at least one surface is formed by bonding together the oblique sides of adjacent mountain-shaped regions of the four sheets with the peaks of the mountain-shaped regions facing each other and heat welding them together, wherein in the folded state, the mountain-shaped regions of the first sheet and the second sheet face each other, and the mountain-shaped regions of the third sheet and the fourth sheet are folded inward along a fold line passing through the peaks between the opposing first sheet and second sheet, and further, the heat-sealed seal includes two seals, i.e., a diagonal seal and a peak seal, and wherein, when the folded state is viewed from above, The oblique seals seal the inner surfaces of the oblique sides of the mountain-shaped regions of the opposing first and second sheets and the oblique sides of the mountain-shaped regions of the valley-folded third and fourth sheets, the apex seal extends in a cross direction intersecting the fold lines and the oblique seals of the third and fourth sheets and seals the inner surfaces of the opposing first and second sheets between the fold lines, and the third and fourth sheets each have an inner edge line of the oblique seal on the inner side in the width direction of the oblique seal and an inner edge line of the apex seal on the inner side in the width direction of the apex seal, and the third and fourth sheets each have an inner edge line of the inner side in the width direction of the oblique seal on the inner side in the width direction of the apex seal, and the distance from the fold line to the intersection in the cross direction is 0 mm to 15 mm. [Appendix 2] The plastic bag according to appendix 1, wherein the distance is 0 mm to 10 mm. [Appendix 3] The plastic bag according to appendix 1 or 2, wherein the sheet has a thickness of 120 μm or more.[Supplementary Item 4] The plastic bag according to any one of Supplementary Items 1 to 3, wherein the sheet is a sheet in which a plurality of resin layers are laminated. [Supplementary Item 5] The plastic bag according to Supplementary Item 4, wherein the plurality of resin layers include polyethylene and polyethylene terephthalate. [Supplementary Item 6] The plastic bag according to Supplementary Item 5, wherein the plurality of resin layers further include nylon. [Supplementary Item 7] The plastic bag according to any one of Supplementary Items 1 to 6, wherein the capacity is 50 L or more. [Supplementary Item 8] The plastic bag according to any one of Supplementary Items 1 to 7, wherein the plastic bag is used in a bioprocess.

[0068] The above-described description and illustrations are a detailed explanation of the parts related to the technology of the present disclosure and are merely an example of the technology of the present disclosure. For example, the above description of the configuration, functions, actions, and effects is an explanation of an example of the configuration, functions, actions, and effects of the parts related to the technology of the present disclosure. Therefore, it goes without saying that unnecessary parts may be deleted, new elements may be added, or replacements may be made to the above-described description and illustrations within the scope of the gist of the technology of the present disclosure. Furthermore, to avoid confusion and facilitate understanding of the parts related to the technology of the present disclosure, the above-described description and illustrations omit explanations of common technical knowledge that do not require particular explanation to enable the implementation of the technology of the present disclosure.

[0069] In this specification, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" means that it may be only A, only B, or a combination of A and B. Furthermore, in this specification, the same concept as "A and / or B" is also applied when three or more things are expressed by connecting them with "and / or."

[0070] The disclosure of Japanese Patent Application No. 2024-121455, filed on July 26, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A plastic bag formed by sealing a plurality of sheets, including four sheets, a first sheet, a second sheet, a third sheet, and a fourth sheet, by heat welding, and which changes from a folded state in which the sheets are folded to an unfolded state in which the sheets are unfolded to form an internal storage space; in the unfolded state, at least one surface is formed by bonding together the oblique sides of adjacent mountain-shaped regions of the four sheets with the peaks of the mountain-shaped regions facing each other, and in the folded state, the mountain-shaped regions of the first sheet and the second sheet face each other, and the mountain-shaped regions of the third sheet and the fourth sheet are folded inward along a fold line passing through the peaks between the opposing first sheet and second sheet, and further, the heat-sealed seal includes two seals, a diagonal seal and a peak seal; and when the folded state is viewed in a plane, a plastic bag in which the oblique side seal portion is a seal portion that seals the inner surfaces of the oblique side portions of the mountain-shaped regions of the opposing first and second sheets and the oblique side portions of the mountain-shaped regions of the valley-folded third and fourth sheets, the apex seal portion extends in a cross direction that intersects the fold lines and the oblique side seal portions of the third and fourth sheets, and seals the inner surfaces of the opposing first and second sheets between the fold lines, and in which the intersection of the inner edge line of the inner edge side of the oblique side seal portion in the width direction and the inner edge line of the inner edge side of the apex seal portion in the width direction is within an inner range starting from the fold line toward the center of the apex seal portion in the cross direction, and the distance in the cross direction from the fold line to the intersection point is 0 mm to 15 mm.

2. The plastic bag according to claim 1, wherein the distance is between 0 mm and 10 mm.

3. The plastic bag according to claim 1, wherein the thickness of the sheet is 120 μm or more.

4. The plastic bag according to claim 1, wherein the sheet is a sheet in which a plurality of resin layers are laminated.

5. The plastic bag according to claim 4, wherein the plurality of resin layers include polyethylene and polyethylene terephthalate.

6. The plastic bag according to claim 5, wherein the plurality of resin layers further includes nylon.

7. The plastic bag according to claim 1, having a capacity of 50 L or more.

8. The plastic bag according to claim 1, which is used in a bioprocess.

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