JP5260084B2 - Square bottom bag that prevents film tearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a film of a square bottom bag from being torn from a position along a boundary part or a welding line when the square bottom bag drops, even if the square bottom bag has the welding line of a simple shape and is made of a film showing linear cuttability and easy cuttability in a widthwise direction. <P>SOLUTION: The curved welding lines 11 each having a curved part 18 are provided at right and left gusset fold portions 3, and four plastic films overlapping each other at the gusset fold portions 3 are integrally welded to each other. The curved part 18 is formed of at least two connected circular arc parts of a first circular arc part 19 and a second circular arc part 20 connecting with the first circular arc part. The curvature radius of the first circular arc part 19 has a curvature radius having an intersecting position having an intersection angle between an imaginary tangential line of the first circular arc part 19 and a linear welding line 4 at the lower end of a bag body of 45 degrees, between the right and left gusset fold portions 3. The curvature radius of the second circular arc part 20 is larger than that of the first circular arc part 19. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a square-bottom bag filled with liquid, powder, and granules, and more specifically, in the medical and pharmaceutical field, the exterior of a soft bag filled with a chemical solution such as physiological saline or electrolytic solution. The present invention relates to a square bottom bag that can be suitably used as a square bottom bag typified by a bag.

As shown in FIGS. 1 and 2, the conventional square-bottom bag 1 is formed of four plastics by gusseting the valley folds inward of the bag body 2 on the left and right sides of a tubular bag body 2 made of a plastic film. The bag body is provided with a gusset fold portion 3 in which films are overlapped, and only a linear weld line 4 is applied perpendicular to the tube flow direction (tube length direction) in the manufacturing process of the bag body 2. The lower end of 2 is closed.
And in the position of the linear welding line 4 in the lower end part of the bag body 2, in the right and left gusset folding portions 3, as described above, there are four plastic films (the front plastic film A, relative to the plastic film A). Plastic film B, plastic film C on the back side, plastic film D opposite to this plastic film C, see FIG. 2), and two plastic films are overlapped between the gusset folding portions 3. .
Therefore, a step is inevitably generated at the boundary portion 5 (the gusset intersection) between the overlapping portion of the four films and the overlapping portion of the two films. Therefore, it is difficult for the linear weld wire 4 to have a uniform weld line in strength. Further, when the square bottom bag 1 is used and the contents are stored and dropped, the boundary portion 5 is a collection point of the film, so stress concentrates on the boundary portion 5. Thus, there is a problem that the film easily breaks at the boundary portion 5.

As a technique aimed at solving the above problems, there is a technique described in Patent Document 1.
In the square bottom bag 1 in this technique, a linear welding wire 4 is provided at the lower end portion of the bag body 2 as shown in FIG. And, above the linear weld line 4 at the gusset folding portion 3, two sheets of plastic film A on the front of the square bottom bag and plastic film B opposite thereto, and the back of the square bottom bag A bent welding wire 6 is provided so that two sheets of a plastic film C and a plastic film D opposed thereto are welded. The bent weld line 6 is inclined at 45 degrees with respect to the height direction of the gusset fold portion 3, and is located at a position close to the outer end 8 side of the gusset fold portion 3 from the valley fold end 7 of the gusset fold portion 3. The straight weld line 4 is bent and then connected to the straight weld line 4. Further, a reinforcing welding wire 9 in which four films are integrated as an arc or a circle is provided between the welding line reaching the linear welding wire 4 from the bent portion of the bending welding wire 9 and the valley folding end 7. ing.

However, there is a problem that the shape of the welding wire of the square-bottom bag is complicated and the region where the welding wire exists is wide in the vertical direction of the bag body, so that the production efficiency is not good.
Further, when the plastic film used as the bag is a material having a straight-cut property and an easy-cut property along the width direction of the bag, the reinforcing welding wire 9 having an arc shape as shown in FIG. There was a problem that the film was easily torn at a position along the weld line 10 inclined 45 degrees of the bent weld line 6.
JP 2005-104572 A

  Therefore, the present invention makes the shape of the weld line simple, and even if it is a square bottom bag using a film having a straight cut property and an easy cut property in the width direction, the boundary portion and the weld wire when dropped. It is an object to prevent the film from tearing from a position along the line.

The present invention has been made to solve the above-mentioned problems, and the invention of claim 1 has a gusset fold portion of a valley fold inwardly on the left and right sides of a tubular bag body, and the lower end portion of the bag body is A square bottom bag closed by a linear weld line along the width direction of the bag, the bag being formed of a plastic film having a straight cut property and an easy cut property in the width direction of the bag body. In the bottom bag, each of the left and right gusset folding portions is provided with a curved welding line that reaches the outer end of the gusset folding portion from the valley folding end portion side of the gusset folding portion via the curved shape portion. four plastic film that overlaps with gusset fold parts of the left and right have been welded together by a line, the curved shape portion of each of the curved weld line is located in the valley folding end of the gusset fold parts At least two arc portions of one arc portion and a second arc portion continuous with the first arc portion are formed in series, and the radius of curvature of the first arc portion is the virtual tangent of the first arc portion. The radius of curvature between the left and right gusset folds is at the intersection point with the linear weld line, and the radius of curvature of the second arc portion is larger than the radius of curvature of the first arc portion. The square bottom bag which prevented the film tearing characterized by these is provided, The square bottom bag which prevented this film tearing is provided, and the said subject is eliminated.

  In the invention of claim 2, the welding line extending from the curved portion in the curved welding line to the outer end of the gusset folding portion is a linear shape inclined toward the lower end portion of the bag, and 2. The square bottom bag according to claim 1, wherein the bag is not crossed with the linear welding line.

  Further, the invention according to claim 3 is an angle for preventing film tearing according to claim 1 or 2, wherein the seal width of each of the linear weld line and the curved weld line is 1 mm or more and less than 3 mm. It is a bottom bag.

  The invention of claim 4 is as follows. A weld line is formed from the first arc portion to the lower end portion of the bag body along a direction perpendicular to the linear weld line, and the weld line perpendicular to the linear weld line is the linear weld line. It is a square bottom bag which prevented the film tear as described in any one of Claim 1 to 3 which becomes a position which the connection point connected to the wire | line and the connection point approached the outer end side from the valley folding end of the gusset folding part. .

  In the invention according to claim 5, a welding line is formed from the first arc portion to the lower end portion of the bag body along a direction perpendicular to the linear welding line, and is perpendicular to the linear welding line. The welding line is not connected to the linear welding line and is located in the vicinity, and the virtual extension line from the welding line and the linear welding line are in a direction perpendicular to the linear welding line; The square bottom bag according to any one of claims 1 to 3, wherein the crossing point is a position that is closer to the outer end side from the valley folding end of the gusset folding portion.

  According to a sixth aspect of the present invention, between the left and right gusset folds, a linear shape portion substantially parallel to the linear weld line and the both ends of the linear shape portion are curved toward the linear weld line side. The center welding line which consists of a curve-shaped part is located, and the two plastic films which overlap between the right and left gusset folding parts are welded integrally by this center welding line. It is a square bottom bag which prevented the film tear of description.

  A seventh aspect of the present invention is the square bottom bag according to any one of the first to sixth aspects, wherein the plastic film has a thickness of less than 150 μm.

(Effect of the invention of claim 1)
As described above, in the conventional square bottom bag, when dropped in a state in which the contents are accommodated, at the lower end of the gusset folding portion, the front film, the folded film facing the front film side, Each of the back film and the folded film facing the back film side opens so as to swell, and the tensile stress generated in those films is once at the intersection of the valley fold end of the gusset fold and the linear weld line. The film tears at this intersection.
On the other hand, according to the first aspect of the present invention, the curved weld line is formed on the linear weld line at the gusset folded portion by welding four plastic films. Even if the internal bag is dropped and the internal pressure is momentarily increased, the folded film at the lower end of the gusset fold does not open and the valley folds at the gusset fold. Tensile stress is not concentrated at the intersection between the end and the linear weld line, that is, at the boundary portion that is local. Therefore, it is possible to prevent film tearing from the boundary portion, and it is possible to provide a square bottom bag in which a film tear is prevented by a drop impact in a square bottom bag having a gusset shape.

  Further, the radius of curvature of the first arc portion is the radius of curvature between the left and right gusset folding portions at the intersection point between the virtual tangent of the first arc portion and the linear weld line. The impact applied to the first arc portion from the contents of this can be avoided by guiding the first arc portion along the virtual tangent line between the left and right gusset folds to prevent film tearing from the boundary. It became.

(Effect of the invention of claim 2)
According to the invention of claim 2, by forming the welding line toward the outer end side of the gusset folding portion toward the lower end side, the content that moves rapidly when falling is moved to the outer end side of the gusset folding portion. It was possible to prevent film tearing along the curved welding line.
Furthermore, the region where the welding line between the linear welding line and the curved welding line is provided can be narrowed in the vertical direction (tube length direction) of the bag body so that the square bottom bag can be manufactured efficiently. Become.
Furthermore, in the curved welding line, the welding line to the outer end side of the gusset folding portion can be gradually lowered to the lower end side of the bag body. Therefore, maintaining the distance from the linear weld line at the gusset fold portion becomes a capability, and stable manufacturing can be performed considering allowance for meandering and gusset folding during bag making.

(Effect of the invention of claim 3)
According to the invention of claim 3, the pressure at the time of welding is appropriately applied to the plastic film without being dispersed, and proper welding can be performed. Furthermore, a better seal appearance can be obtained.

(Effect of the invention of claim 4)
According to the invention of claim 4, even when the pressure from the contents increases on the lower end side of the bag body when the square-bottom bag containing the contents is dropped, the conventional linear welding of the valley folding end and the bottom part closing is performed. The film does not spread around the intersection (gazette intersection) with the line. Therefore, the film can be prevented from tearing by preventing the concentration of the tensile stress of the film at the intersection.

(Effect of the invention of claim 5)
According to the invention of claim 5, as in the effect of the invention of claim 4, even if the pressure from the contents increases on the lower end side of the bag body when the square bottom bag containing the contents falls, The film does not spread around the intersection of the valley folding end and the linear weld line at the bottom. Therefore, it is possible to prevent the film from tearing by preventing the concentration of the tensile stress of the film at the intersection.

(Effect of the invention of claim 6)
According to the invention of claim 6, between the left and right gusset folding portions, a central weld line composed of a linear shape portion and curved shape portions on both sides thereof is provided, and two sheets between the left and right gusset folding portions are provided. Since the plastic film is integrally welded, the pressure can be released in the direction perpendicular to the resin flow direction of the plastic film (X direction in FIG. 9) even if the internal pressure increases momentarily as described above. Thus, it is possible to further reduce the concentration of stress at the gusset intersection, which is the intersection of the valley folding end and the linear weld line of the bottom closure.

(Effect of the invention of claim 7)
When the thickness of the plastic film is 150 μm or more, the suitability for folding the gusset is poor, and it becomes difficult for the resin melted at the position of the welding line to fill the film step at the boundary portion. The suitability for folding the gusset is kept good, and the resin of the plastic film is properly melted even at the boundary portion, so that the step at the boundary portion is surely filled.

Next, the present invention will be described based on the embodiments shown in FIGS. 1 to 4 are denoted by the same reference numerals, and the description thereof is omitted.
In the square bottom bag 1 of the present invention, as shown in FIG. 5, a curved welding line 11 is provided on the lower end side of each of the left and right gusset folding portions 3 so as to be above the linear welding line 4. A plastic film 12 provided on the front surface of the bag body 2 at the gusset folding portion 3, a plastic film 13 that is folded so as to be opposed to the plastic film 12 on the front surface, and the bag. Four films of a plastic film 14 on the back of the body 2 and a plastic film 15 folded so as to face the plastic film 14 on the back are integrally welded.

The curved welding wire 11 is connected to the linear welding wire 4 at one end of the gusset folding portion 3 on the valley folding end 7 side, and the other end reaches the outer end 8 of the gusset folding portion 3. . On the valley folding end 7 side, not the position of the valley folding end 7 in the linear welding wire 4 but the position close to the outer end 8 side from the valley folding end 7 as the connection point 16, the linear welding line. 4 is connected to the welding line 4 and is connected to the welding line 4 at right angles. A curved shape portion 18 having a curved shape toward the outer end 8 side is connected to the connecting portion 17, and the curved weld line 11 reaches the outer end 7 side via the curved shape portion 18. Yes.
In this embodiment, the curved portion 18 is formed by two arc portions of a first arc portion 19 and a second arc portion 20 being continuous, and is located on the valley folding end 7 side of the gusset folding portion 3. The first arc portion 19 is connected to the connecting portion 17, and the second arc portion 20 is connected to the first arc portion 19 at a position on the outer end 8 side with respect to the first arc portion 19.
As described above, the curved shape portion 18 is a combination of two arc portions 19 and 20 that are continuously bent from the connecting portion 17 to the outer end 8 side, and the direction of the end portion of the curved shape portion 18 on the outer end 8 side. Is in a direction that is perpendicular to the outer end 8 or that is inclined toward the lower end. And the welding line 21 in the part ranging from this curve-shaped part 18 to the said outer side end 8 of the gusset folding part 3 is made into the linear shape which inclines toward the lower end part of the bag body 2, Furthermore, a linear welding line 4 is not crossed.

The radius of curvature R1 of the first arc portion 19 of the curved shape portion 18 is determined from the intersection position 23 where the intersection angle θ between the virtual tangent line 22 of the first arc portion 19 and the linear weld line 4 is 45 degrees. The radius of curvature is between the gusset folds 3. Furthermore, the curvature radius R2 of the second arc portion 20 is made larger than the curvature radius R1 of the first arc portion 19.
In the case of a square-bottom bag used for the purpose of storing physiological saline in a pharmaceutical product, for example, the radius of curvature R1 at the first arc portion 19 is 2.5 mm, and the radius of curvature R2 at the second arc portion 20 is It can be 41 mm.

As the plastic film in the square-bottom bag 1 of this embodiment, when the square-bottom bag is used for the purpose of containing physiological saline in a pharmaceutical product as described above, A laminated film of density polyethylene / linear low density polyethylene + cyclic olefin copolymer / linear low density polyethylene (thickness ratio 1/1/1, total thickness 100 μm) can be suitably used. In addition, the thickness of the said plastic film made into the laminated film shall be less than 150 micrometers.
In the embodiment, the seal width of each of the linear welding wire 4 and the curved welding wire 11 is 1 mm or more and less than 3 mm.

  FIG. 7 shows an example of use of the square bottom bag 1 of the present embodiment. The lower end portion of the bag body 2 is closed by the linear welding wire 4 and the linear shape is formed at the gusset folding portion 3. The curved welding wire 11 having one end connected to the linear welding wire 4 is provided above the welding wire 4. Then, a stored item (for example, a soft bag) 24 is accommodated in the bag body 2, and a linear weld line 25 extending in the width direction of the bag body 2 at a position away from the upper end portion of the bag body 2 by a required distance. Is provided to close the upper portion of the bag body 2. In FIG. 7, reference numeral 26 denotes a handle hole, and 27 denotes a notch, which is torn from the notch 27 so that the stored item 24 can be taken out.

In the above-described embodiment, the welding line 17 that is perpendicular to the linear welding line 4 is formed from the first arc portion 19 of the curved welding line 11, and the welding line that is perpendicular is connected to the connection line 17. Although it is connected to the linear welding wire 4 as the portion 17, the present invention is not limited to this embodiment, and the first arc portion 19 is perpendicular to the linear welding wire 4. The weld line portion may be disconnected from the linear weld line 4. The embodiment will be described next.
FIG. 8 shows an example in which the welding line from the first arc portion 19 is not connected to the linear welding line 4, and the other points are the same as those of the above-described embodiment. That is, a welding wire perpendicular to the linear welding wire 4 is formed from the first arc portion 19 toward the linear welding wire 4, and the formed perpendicular welding wire is used as the extension portion 28. . And the lower end part of the extension part 28 is not connected to the linear weld line 4 and is located in the vicinity, and the virtual extension line 29 from the extension part 28, the linear weld line 4 and the intersection 30 are the gusset folding portion. 3 is provided so as to be closer to the outer end 8 side from the valley folding end 7.

  In this way, the welding line (extension 28) from the first arc portion 19 in the curved welding line 11 is perpendicular to the linear welding line 4 and is directed to the intersection 30 and linear welding. Even if it is not connected to the line 4, the impact applied to the first arc part 19 from the contents accommodated in the bag body 2 when dropping is applied along the virtual tangent line 22 of the first arc part 19. Thus, it can be guided so as to be guided between the left and right gusset folding portions, and concentration of stress on the boundary portion 5 (intersection of the gusset) can be prevented.

FIG. 9 shows still another embodiment. In the embodiment shown in FIG. 9, the curved welding line 11 provided in the left and right gusset folding portions 3 is the same as that in the embodiment shown in FIG. 8, but between the left and right gusset folding portions 3. A welding wire 31 is provided, and the front plastic film 12 and the back plastic film 14 which are overlapped with each other between the left and right gusset folding portions 3 are integrally welded at the central welding wire 31.
The central weld line 31 is formed by aligning the height position with the uppermost position of the left and right curved weld lines 11 in the bag body height direction, and a linear shape part 32 substantially parallel to the linear weld line 4 and the linear shape part. It comprises a curved portion 33 that is curved in an arc shape from both ends of 32 toward the linear welding wire 4 side. Each of the left and right curved shape portions 33 is not connected to the linear welding wire 4 in the same manner as the end portion processing of the extension 28 in the left and right curved welding wires 11.

The central weld line 31 is on both sides, that is, the curved portion 33 does not reach the position corresponding to the valley folding end 7 of the gusset folding portion 3, and each curved portion 33 is equidistant from the valley folding end 7. positioned. The virtual tangent line 22 of the first arc portion 19 of the left and right curved weld lines 11 is preferably non-intersecting with the center weld line 31.
In this way, the two plastic films 12 and 14 between the left and right gusset folding portions 3 are integrally welded by the central welding line 31 at the position of the central welding line 31, and the contents made of liquid or the like are put therein. Even when the impact when dropping the bag body is directed to the bottom side of the bag body between the gusset folds, the impact pressure is distributed along the central weld line 31, and the conventional bottom of the bag body It has a tremendous effect in reducing stress concentration at the gusset intersection due to spreading.
It is preferable that the seal width of the central weld line 31 is the same as the seal width of the curved weld line 11.

Next, the square-bottom bags in the present invention are designated as Examples 1 and 2, and seven types of square-bottom bags of Examples 1 and 2 and Comparative Examples 1 to 5 which are square-bottom bags having the following configurations are manufactured. And examined.
Example 1
(Structure of plastic film): linear low density polyethylene / linear low density polyethylene + cyclic olefin copolymer / linear low density polyethylene (thickness ratio 1/1/1, total thickness 100 μm)
As the linear low density polyethylene, Ube Maruzen Polyethylene Co., Ltd. product name Umerit 4040F (density 0.937 g / cm ² ) was used.
The cyclic olefin was carried out in a 20 wt% dry blend only in the intermediate layer.
(Shape of weld line): The shape shown in FIG. The seal width between the linear weld line and the curved weld line was 1 mm.

Example 2
(Configuration of plastic film): Same as Example 1.
(Shape of weld line): The shape shown in FIG. 9 provided with a central weld line. The seal widths of the linear weld line, the curved weld line, and the central weld line were all 1 mm.

Comparative example 1
(Configuration of plastic film): Same as Example 1.
(Shape of weld line): Only the linear weld line shown in FIG. 1 was used. The seal width of the linear weld line was 3 mm.

Comparative example 2
(Configuration of plastic film): Same as Example 1.
(Shape of weld line): Only the linear weld line shown in FIG. 1 was used. The seal width of the linear weld line was 1 mm.

Comparative example 3
(Configuration of plastic film): Same as Example 1.
(Shape of weld line): The shape shown in FIG. The seal width of the straight welded wire, the bent welded wire, and the reinforcing welded wire was 3 mm.

Comparative example 4
(Configuration of Plastic Film): The same layer configuration as in Example 1 was used, and the total thickness of the film was 120 μm.
(Shape of weld line): Only the linear weld line shown in FIG. 1 was used. The seal width of the linear weld line was 3 mm.

Comparative example 5
(Configuration of Plastic Film): The same layer configuration as in Example 1 was used, and the total thickness of the film was 150 μm.
(Shape of weld line): Only the linear weld line shown in FIG. 1 was used. The seal width of the linear weld line was 3 mm.

<Test>
(Gazette shape)
As Examples 1 and 2 and Comparative Examples 1 to 5, square-bottom bags having left and right gusset folding portions with a folding width of 68 mm and a size of 430 mm × 192 mm were made.

(Drop bag test)
The square bottom bags of Examples 1 and 2 and Comparative Examples 1 to 5 are filled with 2 L of tap water and sealed with an impulse sealer in a state where air is removed as much as possible.
From the height of 100 cm, it was dropped horizontally on the concrete (so that the bottom of the corner did not hit the concrete surface first), and the number of times until the rupture and the rupture location were evaluated (number of test bags = 3).
* Rupture locations are indicated by the symbols shown in the figure.

(Gazette suitability)
Folding suitability was evaluated using an offline gusset machine.

(Seal strength)
Sealing was carried out with a bag making machine, and the sealing strength of a portion where four films were overlapped and a portion where two sheets were overlapped was measured.
Peeling angle: 90 degrees Peeling speed: 300 mm / min
Testing machine: Tensile testing machine (Orientec)
* The four-ply portion of Examples 1 and 2 was a curved portion. The two-layer overlap part of Example 2 measured the linear shape part of the center welding line. The four-ply portion of Comparative Example 3 was measured with the weld line 10 in the shaded area in FIG.

  In the embodiment shown in FIG. 8 as well, the same structure as that of the plastic film in Example 1 is used, and the first arc portion side of each curved welding line is not connected to the linear welding line. The bag is made and the same test is performed. Since the result was the same as Example 1, it was not described in Table 1.

  As shown in Table 1, in the square bottom bag of the present invention, the suitability of the gusset is good and the sealing strength can be secured appropriately. Furthermore, since the bag is not broken during the drop test, it can be judged that it is favorable for reliably preventing the tearing of the film at the position of the weld line.

  The present invention is effective as an exterior bag for housing a soft bag containing physiological saline.

It is explanatory drawing which shows the linear welding line in the state which looked at the side surface of the conventional square bottom bag. It is explanatory drawing which shows the cross section of the tube which comprises the bag body of the square bottom bag of FIG. It is explanatory drawing which shows the linear welding wire in the state which looked at the side surface of the square bottom bag which is another prior art example, a bending welding wire, and a reinforcement welding wire. It is explanatory drawing which expands the boundary part of the bag body lower end part in the prior art example of FIG. 3, and shows a welding line. It is explanatory drawing which shows the linear welding line in the state seen from the side surface of an example of the square bottom bag which prevented the film tear based on this invention, and a curvilinear welding line. It is explanatory drawing which expands the boundary part of the bag body lower end part in an example of this invention, and shows a welding line. It is explanatory drawing which shows the use condition in an example of this invention. It is explanatory drawing which shows the other example of this invention. It is explanatory drawing which shows the other example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Square bottom bag 2 ... Bag body 3 ... Gazette folding part 4 ... Linear welding line 7 ... Valley folding end of a gusset folding part 8 ... Outer edge of a gusset folding part 11 ... Curved welding line 16 ... Connection point 17 ... Connection part 18 ... Curve-shaped part 19 ... First arc part 20 ... Second arc part 21 ... Inclined weld line 22 ... Virtual tangent line 23 ... Intersection point 28 ... Extension part 29 ... Virtual extension line 30 ... Intersection point 31 ... Center welding Line 32 ... Linear shape portion 33 ... Curve shape portion R1 ... curvature radius of the first arc portion R2 ... curvature radius of the second arc portion θ ... intersection angle

Claims (7)

It is a square-bottom bag that has a gusset fold part that is folded inwardly on the left and right sides of the tubular bag body, and the lower end portion of the bag body is closed by a linear welding line along the bag width direction. In the square bottom bag made of a plastic film having a linear cut property and an easy cut property in the width direction of the bag body,
Each of the left and right gusset folding portions is provided with a curved welding line that reaches the outer end of the gusset folding portion from the valley folding end portion side of the gusset folding portion via the curved shape portion. The four plastic films that overlap at the gusset folding part are welded together,
The curved portion of each of the curved welding lines includes at least two arc portions, a first arc portion located on the valley folding end side of the gusset folding portion and a second arc portion continuing to the first arc portion. Are formed in a row,
The radius of curvature of the first arc portion is a radius of curvature with the intersection position of the virtual tangent of the first arc portion and the linear weld line between the left and right gusset folding portions,
A square bottom bag for preventing film tearing, wherein the radius of curvature of the second arc portion is larger than the radius of curvature of the first arc portion.   The welding line extending from the curved shape portion to the outer end of the gusset folding portion in the curved welding line is a linear shape inclined toward the lower end portion of the bag body, and does not intersect the linear welding line. The square bottom bag which prevented the film tear of Claim 1 made into.   The square bottom bag which prevented the film tear of Claim 1 or 2 which made each seal width | variety of the said linear welding line and the curvilinear welding line 1 mm or more and less than 3 mm.   A weld line is formed from the first arc portion to the lower end portion of the bag body along a direction perpendicular to the linear weld line, and the weld line perpendicular to the linear weld line is the linear weld line. The square bottom bag which prevented the film tear as described in any one of Claim 1 to 3 which becomes a position which connected to the line and the connection point has approached the outer end side from the trough folding end of the gusset folding part.   A welding line is formed from the first arc portion to the lower end portion of the bag body along a direction perpendicular to the linear welding line, and the welding line perpendicular to the linear welding line is a linear welding line. The intersection of the virtual extension line from the welding line and the linear welding line that is located in the vicinity and is perpendicular to the linear welding line is a valley of the gusset folding portion. The square bottom bag which prevented the film tear as described in any one of Claim 1 to 3 which becomes a position which approached the outer side end from the folding end.   Between the left and right gusset folds, a central weld line is formed of a linear portion that is substantially parallel to the linear weld line and a curved portion that is curved toward the linear weld line from both ends of the linear portion. The square bottom which prevented the film tear as described in any one of Claim 1 to 5 where two plastic films which overlap between the right and left gusset folding parts are integrally welded by this center welding line bag.   The square bottom bag which prevented the film tear as described in any one of Claim 1 to 6 whose said plastic film is thickness less than 150 micrometers.

Images