Patent Publication Number: US-2021187891-A1

Title: Method for making a plastic bag

Description:
TECHNICAL FIELD 
     The present invention relates to a method for making a plastic bag. 
     BACKGROUND ART 
     A plastic bag includes a sealed region formed along whole or part of its edge so as to ensure its sealability. 
     A method for making such a plastic bag is disclosed, for example, in Patent documents 1-3. For example, the method superposes at least two films on each other. The method then heat-seals the films to each other to form a sealed region. The method then cuts the films by unit of the bag with a cutter, thereby making the plastic bag. In this step, the films are cut along the sealed region, and thereby an edge of the sealed region of the plastic bag is formed by a cut edge resulting from the cutting. 
     Cutting the films along the sealed region using a sharp edged tool such as a cutter results in the sealed region having a very sharp cut edge. Due to this, when the plastic bag is shifted to a hand holding the plastic bag, the cut edge of the sealed region may hurt the hand. Like this, there is a danger that the cut edge of the sealed region may hurt, for example, a hand. 
     CITATION LIST 
     Patent Document 
     
         
         [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2011-020719 
         [Patent Document 2] Japanese Unexamined Patent Application Publication No. H11-320708 
         [Patent Document 3] Japanese Patent Publication No. 3733085 
       
    
     PROBLEM TO BE SOLVED BY THE INVENTION 
     An object of an aspect of the present invention is to provide a method for making a plastic bag with increased safety. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a method for making a plastic bag having an edge. The plastic bag includes a sealed region. The sealed region is formed along part or whole of the edge of the plastic bag by a section in which at least two plastic films are sealed to each other. The edge of the plastic bag includes a sealed edge of the sealed region. The method includes: heat-sealing the films to each other to form the sealed region; cutting the films such that part or whole of the sealed edge is formed by a cut edge; and heating an area formed by the cut edge of the sealed edge to smooth the area. 
     The method may include, while conveying a plurality of plastic bags in a state that the plastic bags are stacked with each other, heating the area of each of the plastic bags to smooth the area. 
     The method may include heating the area to smooth the area while cooling an intermediate part of the plastic bag. 
     The sealed edge may include a sealed corner edge part of the plastic bag. In the method, the sealed corner edge part may be formed by the cut edge, and the sealed corner edge part may be heated to be smoothed. 
     The sealed edge may include a sealed side edge part of the plastic bag. In the method, the sealed side edge part may be formed by the cut edge, and the sealed side edge part may be heated to be smoothed. 
     The sealed edge may include a sealed side edge part of the plastic bag. In the method, a gusset and two sheet panels may be used as the films. The method may further include interposing the folded or bent gusset between the sheet panels. The method may include: heat-sealing the sheet panels and the gusset to each other to form the sealed region; cutting the sheet panels and the gusset at a position of the sealed region such that the sealed side edge part is formed by the cut edge; and heating the sealed side edge part to smooth the sealed side edge part. 
     In the method, a side gusset or bottom gusset may be used as the gusset. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a plastic bag according to an implementation. 
         FIG. 2  is a side view schematically illustrating an example of an apparatus for making plastic bags. 
         FIG. 3  describes a making method according to an implementation of the present invention. 
         FIG. 4  illustrates a tip part of a punch blade. 
         FIG. 5  describes smoothing of a sealed edge (cut edge). 
         FIG. 6  describes an example of a smoothing step. 
         FIG. 7A  is a plan view schematically illustrating an example of a smoothing device, and  FIG. 7B  is a partial sectional side view of the device of  FIG. 7A . 
         FIG. 8  is a partial sectional side view illustrating another example of the smoothing device. 
         FIG. 9  illustrates another arrangement of the device of  FIG. 7A . 
         FIG. 10  is a front view of a plastic bag according to an implementation. 
         FIG. 11A  is a front view of a plastic bag according to another implementation, and  FIG. 11B  is an enlarged partial sectional view of  FIG. 11A . 
         FIG. 12  describes a making method according to another implementation of the present invention. 
     
    
    
     IMPLEMENTATIONS 
     A method for making a plastic bag according to implementations of the present invention will now be described with reference to the accompanying drawings. In each of the implementations, same or similar elements are indicated by same reference numerals, and the explanation thereof is omitted as much as possible. Elements illustrated in the Figures are not drawn to scale, but only to illustrate operation. 
     [First Implementation] 
     As illustrated in  FIG. 1 , a plastic bag  1  (hereinafter sometimes simply referred to as “bag”) is made of plastic film. The bag  1  includes films  11  and  12  opposed to each other (hereinafter sometimes referred to as “first sheet panel  11 ” and “second sheet panel  12 ”). Each of the films  11  and  12  of the implementation is a plastic film having a laminated structure. Inner surfaces of the films  11  and  12  are made of the sealant such as polyethylene, polypropylene, etc. Outer surfaces of the films  11  and  12  are made of the base such as nylon, PET (polyethylene terephthalate), etc. 
     The bag  1  includes an edge  100  along its periphery. The edge  100  of the bag  1  includes four side edge parts  140 ,  150  and  160  each having a linear shape, and four corner edge parts  170  joining the side edge parts  140 ,  150  and  160  and each having a rounded and protruding shape. 
     The bag  1  further includes a sealed region  13  formed along part or whole the edge  100 . The sealed region  13  is formed by a section in which at least two films are sealed to each other. In the implementation, the sealed region  13  is formed along part of the edge  100 . The sealed region  13  includes two sealed parts  14  (hereinafter sometimes referred to as “first sealed parts  14 ”) formed along two opposite side edge parts  140 , and a sealed part  15  (hereinafter sometimes referred to as “second sealed part  15 ”) formed along one side edge part  150  of the remaining opposite side edge parts  150  and  160 . In the implementation, each of the sealed parts  14  and  15  is formed by a section in which the two films  11  and  12  are sealed to each other. 
     Therefore, the edge  100  of the bag  1  in the implementation includes a sealed edge  130  of the sealed region  13  and the open side edge part  160  (that is, non-sealed side edge part). The sealed edge  130  includes the three sealed side edge parts  140  and  150 , and the four sealed corner edge parts  170 . The open side edge part  160  is used when filling contents in the bag  1 . 
     A method for making a plastic bag  1  of  FIG. 1  according to an implementation will be described.  FIG. 2  illustrates an example of a bag making apparatus  2  for implementing the method. The apparatus  2  includes a feeding device  3 , a heat seal device  4  and a cutting device  5 . As described below, the cutting device  5  includes a punch blade for forming the corner edge parts  170 , a cutter for cutting the films  11  and  12  in a feed direction Y and a cutter for cutting the films  11  and  12  in a direction perpendicular to the feed direction Y. 
     The two continuous films  11  and  12  (the first and second sheet panels) are intermittently fed with the feeding device  3 , that is, being repeatedly fed and paused at predetermined intervals. The films  11  and  12  are superposed on each other with the feeding device  3 . The feed direction Y of the continuous films  11  and  12  is the longitudinal (continuous) direction thereof. 
     The films  11  and  12  are then heat-sealed to each other with the heat seal device  4  during every pause, and thereby the sealed region  13  is formed as illustrated in  FIG. 3 . The heat seal device  4  generally includes a longitudinal seal mechanism and a cross seal mechanism. In the implementation, the second sealed part  15  is formed with the longitudinal seal mechanism, and the first sealed part  14  is formed with the cross seal mechanism. 
     After heat-sealing of the films  11  and  12 , the films  11  and  12  are cut with the cutting device  5 , and thereby the edge  100  of the bag  1  is formed by the cut edge resulting from the cutting. Thus, the shape of the bag  1  is completed. 
     As illustrated in  FIG. 4 , the cutting device  5  of the implementation includes a punch blade  50  and a receiving blade (not shown) for receiving the punch blade  50 . A tip part  500  of the punch blade  50  has a shape of the combined four corner edges  170 . The receiving blade includes the hole having a shape corresponding to the tip part  500 . The punch blade  50  is moved vertically by the driving mechanism (not shown) with respect to the receiving blade, to cut (punch) the films  11  and  12  in conjunction with the receiving blade. 
     The films  11  and  12  are cut (punched) with the punch blade  50  during every pause, and thereby the sealed corner edges  170  are formed by the cut edge resulting from the cutting. 
     As illustrated in  FIG. 3 , the cutting device  5  further includes two cutters  51  for cutting the films  11  and  12  in the feed direction Y. The films  11  and  12  are cut (slit) with one cutter  51  along the second sealed part  15  during every feed, and thereby the sealed side edge part  150  is formed by the cut edge resulting from the cutting. 
     The films  11  and  12  are cut (slit) with the other cutter  51  in the feed direction Y during every feed, and thereby the open side edge part  160  is formed by the cut edge resulting from the cutting. 
     The cutting device  5  further includes an additional cutter (not shown) for cutting the continuous films  11  and  12  in the width direction thereof (a direction perpendicular to the feed direction Y). This cutter includes, for example, a pair of an upper blade and a lower blade for shearing the films  11  and  12  in a direction perpendicular to the feed direction Y. The films  11  and  12  are cut (sheared) along the first sealed part  14  with the cutter during every pause, and thereby the sealed side edge part  140  is formed by the cut edge resulting from the cutting. 
     Every time the continuous films  11  and  12  are cut in the width direction thereof along the sealed part  14 , the bag  1  is shaped. At least a part (in the implementation, whole) of the sealed edge  130  ( FIG. 1 ) of the sealed region  13  is formed by the cut edge resulting from the cutting of the films  11  and  12 . 
       FIG. 5  illustrates a cross section of the sealed region  13  (sealed part  14  or  15 ) of the bag  1 . In the sealed region  13  after passing through the cutting device  5 , the films  11  and  12  are integrated with each other due to melting of the sealant. As illustrated in  FIG. 5 , the sealed edge  130  ( 140 ,  150 , or  170 ) is sharp since it is formed by a cut edge resulting from physical cutting with an edged tool such as a cutter. In particular, the sealed side edge part  140  in the implementation is very sharp since it is formed by the cut edge resulting from the shearing. Therefore, there is a risk that the sealed edge  130  may hurt a hand. For this, the apparatus  2  further includes a smoothing device  6  ( FIG. 2 ) disposed downstream of the cutting device  5 . 
     The smoothing device  6 , in the implementation, includes a heat unit for heating the sealed edge  130 . The heat unit is, for example, a hot air generator. The hot air generator includes a main body configured to generate hot air and a nozzle which is attached to the main body and from which hot air is blown. 
     The nozzle is preferably attached to the main body in an interchangeable manner. It is, therefore, possible to attach to the main body a nozzle having the optimal shape suitable for the kind of the film or the arrangement of the hot air generator. As a result, the following smoothing step can be performed efficiently. 
     The bag  1  is conveyed from the cutting device  5  to the smoothing device  6 . An area formed by the cut edge, of the sealed edge  130  (in the implementation, whole of the sealed edge  130 ) is heated to be smoothed with the smoothing device  6 . In the implementation, hot air is blown from the nozzle to the sealed edge  130 , and thereby the sealed edge  130  is heated to be smoothed with the hot air. In other words, the sealed side edge pasts  140  and  150  and the sealed corner edge parts  170  are heated to be smoothed. 
     “To smooth” means to eliminate a sharp shape of an object to make it a smooth shape. Therefore, the smoothing step according to an implementation of the present invention is a step of making an area formed by the cut edge of the sealed edge  130  smooth as illustrated in  FIG. 5  by heat-melting the area of the sealed edge  130 . The same is applied to the following implementations. As a result of the smoothing step, the smooth sealed edge  130  can be formed. 
     The open side edge part  160  is not included in the sealed region  13 . However, the open side edge part  160  may be smoothed, since it is formed by a cut edge. 
     The condition for smoothing the cut edge differs depending on material of the base and material of the sealant of the laminate films  11  and  12 . The tip of the cut edge resulting from the cutting (especially shearing) of the films  11  and  12  is made of the bases of the films  11  and  12 . Therefore, smoothing can be achieved by heating the cut edge to a temperature equal to or higher than the melting point of the base. For example, when the base is PET, heating to a temperature equal to or higher than 260° C., which is the melting point of PET, is required for smoothing. When the base is nylon, heating to a temperature equal to or higher than 215° C., which is the melting point of nylon, is required for smoothing. 
     Since the melting point of the sealant is lower than that of the base, not only the base but also the sealant changes to a molten state during smoothing. However, appropriate adjustment of the heating time and the heating temperature can easily prevent the sealant from melting too deeply. In addition, due to surface tension, the melted sealant can also be easily prevented from flowing out. 
     The bag  1  of  FIG. 1  is made via the above smoothing step. In a subsequent step, the contents are filled in the bag  1  from the open side edge part  160 . After filling, the films  11  and  12  may be heat-sealed to each other along the open side edge part  160 , and thereby the sealed part  16  is formed as illustrated in  FIG. 10 . Thus, the sealed side edge part  160  is formed. In addition to this, a spout  19  may be provided at a position of the sealed part  16 . 
     As described above, there is a high risk that the cut edge may hurt a hand. In the implementation, the area formed by the cut edge of the sealed edge  130  is smoothed by heating. Therefore, even if the plastic bag  1  is shifted to a hand holding the plastic bag  1 , the sealed edge  130  does not hurt the hand. The safety of the plastic bag  1  is very high. 
     After the smoothing step, a cooling step of cooling the area formed by the cut edge of the sealed edge  130  and its surrounding part with air may be performed. This improves the quality of smoothing. For example, air is applied to the both surfaces of the bag  1  to cool the area formed by the cut edge of the sealed area  130  and its surrounding part. Using air cooled with a refrigerant, for example, enhances the effect. 
     [Second Implementation] 
     This implementation, while conveying a plurality of the plastic bags  1  stacked with each other, heats the area formed by the cut edge of the sealed edge  13  of each bag  1  to smooth the area using the smoothing device  6 . 
     The smoothing device  6  of the implementation is configured to heat the sealed edge  130  not with hot air but with thermal radiation. As illustrated in  FIG. 6 , the heat unit  60  of the smoothing device  6  includes a heater instead of the hot air generator. The heater includes a heat source  600  such as an infrared light source. The heat source  600  is, for example, a halogen lamp. In this implementation, the heat source  600  has a longitudinal direction and is oriented perpendicular to the conveyance direction X of the bag  1 . The heat source  600  may be oriented in the conveyance direction X of the bag  1 . 
     The bag  1  is shaped with the cutting device  5  as in the first implementation. Subsequently, a certain number of the bags  1  are stacked with each other. The stacked bags  1  are then conveyed in the direction X with a conveyor (not shown) to pass adjacent to the heat unit  60  at an appropriate speed. While the stacked bags  1  are passing adjacent to the heat unit  60 , the sealed edge  130  (that is, the sealed side edge part  140  or  150 ) of each bag  1  is heat-melted with the heat unit  60  to a temperature equal to or higher than the melting point of the material of the films  11  and  12 , and thereby smoothed. 
     The conveyance speed of the bag  1  affects heat-smoothing. If the conveyance speed is fast, increasing the heat energy to the cut edge enables heating the cut edge to a temperature equal to or higher than the melting point of the base to smooth the cut edge. The heat energy of the above-described hot air generator or heater can easily be adjusted. Therefore, it is possible to appropriately smooth the cut edge while conveying the bag  1 , by adjusting the heat energy to the cut edge and the conveyance speed of the bag  1  in consideration of the melting point of the material of the film. 
     [Third Implementation] 
     This implementation heats the area formed by the cut edge of the sealed edge to smooth the area while cooling an intermediate part of the bag  1 . 
     As illustrated in  FIG. 7A , the smoothing device  6  of the implementation includes two heat units  60  disposed to be opposed to each other in a direction perpendicular to the conveyance direction X of the bag  1 .  FIG. 7B  schematically illustrates one heat unit  60  viewed from the direction of the arrow Y in  FIG. 7A . In the implementation, each of the heat units  60  is a heater including a heat source  600 . Alternatively, the heat unit  60  may be a hot air generator. The heat units  60  are disposed such that each of them is opposed to any one of the side edge parts  140 ,  150 ,  160  of the bag  1  while the bag  1  is passing through the smoothing device  6 . 
     The smoothing device  6  further includes cool units  61  provided for each of the heat units  60  and configured to cool an intermediate part of the bag  1 . The cool units  61  are disposed near the corresponding heat unit  60 . The cool units  61  are disposed such that they are opposed to an intermediate part of the bag  1  while the bag  1  is passing through the smoothing device  6 . 
     Each of the cool units  61  includes two coolers  610  opposed to each other. The coolers  610  are disposed such that the bag  1  passes between the coolers  610  and that the coolers  610  are opposed to an intermediate part of the bag  1  while the bag  1  is passing. Each of the coolers  610  has a passage  611  through which the refrigerant passes. The passage  611  extends in the conveyance direction X of the bag  1 . 
     After the bag  1  is shaped with the cutting device  5 , the bag  1  is conveyed with a conveyor (not shown) to the smoothing device  6 . When the bag  1  is conveyed through the smoothing device  6  as illustrated in  FIG. 7A , the heat units  60  heat the sealed side edge part  150  and the non-seal side edge part  160  of the bag  1  to smooth the edge parts  150  and  160 . At the same time, the cool units  61  cool the both surfaces of the intermediate part of the bag  1 . In particular, the cool units  61  efficiently cool regions close to the side edge parts  150  and  160 . 
     Therefore, the area formed by the cut edge of the seal edge part  130  is smoothed with the heat units  60  while the intermediate part of the bag  1  is cooled with the cool units  61 . This enables preventing a region except the edge  100  of the bag  1  (namely, the intermediate part of a bag) from scorching due to heat. 
     Gas may be used as the refrigerant, and the intermediate part of the plastic bag  1  may be cooled by spraying the gas directly on the intermediate part. For this, the smoothing device  6  in  FIG. 8  uses cooled air as the refrigerant gas. Each of the coolers  610  has at least one blowout hole  612  extending from the refrigerant passage  611 . In the implementation, a plurality of blowout holes  612  is arranged side by side in the conveyance direction X ( FIG. 7A ) of the bag  1 . Air is blown out from each blowout hole  612  through the passage  611 , applied to the intermediate part of the bag  1  while the bag  1  is passing through the smoothing device  6 , and thereby the intermediate part is cooled with air. 
     The smoothing device  6  is disposed downstream of and next to the cutting device  5 , and the conveyance direction X of the bag  1  is parallel to the feed direction Y of the continuous films  11  and  12 . Therefore, the side edge parts  150  and  160  are smoothed, whereas both of the sealed side edge parts  140  are not smoothed. 
     In order to smooth both of the sealed side edge parts  140 , as illustrated in  FIG. 9 , the conveyance direction X of the bag  1  may be turned 90 degrees from the feed direction Y with a conveyor disposed downstream of the cutting device  5 , and then the bag  1  may pass through the smoothing device  6 . Thereby, both of the sealed side edges  140  are heated to be smoothed with the smoothing device  6 . 
     Instead of the above, for example, only one heat unit  60  may be disposed such that it is opposed to one side edge part to be smoothed while the plastic bag  1  is being conveyed. 
     [Fourth Implementation] 
     This implementation makes a bag  1  of  FIG. 11A . The bag  1  further includes, as an additional film, at least one gusset  18  for increasing the capacity of the bag  1 . The gusset  18  of the implementation is a bottom gusset. The gusset  18  is folded in half, interposed between the films  11  and  12 , and extends along the sealed side edge part  150  of the bag  1 . 
     As illustrated in  FIG. 11B , the sealed part  15  includes a first sealed portion  15   a  formed by a section in which the first sheet panel  11  and one side part  181  of the gusset  18  are sealed to each other, and the second sealed portion  15   b  formed by a section in which the second sheet panel  12  and the other side edge  182  of the gusset  18  are sealed to each other. Accordingly, the sealed side edge part  150  includes the first edge portion  150   a  of the first sealed portion  15   a  and the second edge portion  150   b  of the second sealed portion  15   b.    
     The gusset  18  of the implementation is a plastic film having a laminated structure same as those of the sheet panels  11  and  12 . The inner surface (that is, the surface facing the sheet panel) of the gusset  18  is made of the sealant, whereas the outer surface of the gusset  18  is made of the base. 
     For example, a continuous gusset  18  is used as illustrated in  FIG. 12 . The gusset  18  in a folded state is supplied with a gusset supplying mechanism (not shown) to the continuous first and second sheet panels  11  and  12 . The gusset  18  is then interposed between the first and second sheet panels  11  and  12  when the first and second sheet panels  11  and  12  are superposed on each other with a feeding device  3  ( FIG. 2 ). At this time, the gusset  18  is positioned along one side of the continuous first and second sheet panels  11  and  12 . 
     Subsequently, the first and second sheet panels  11  and  12  and the gusset  18  are heat-sealed with the heat-seal device  4  ( FIG. 2 ), and thereby the sealed region  13  is formed. In this step, the first and second sheet panels  11  and  12  and the gusset  18  are heat-sealed to each other with the longitudinal seal mechanism, and thereby the sealed part  15  is formed. In other words, the first sheet panel  11  and the one side part  181  are heat-sealed to each other, and thereby the first sealed portion  15   a  is formed. Furthermore, the second sheet panel  12  and the other side part  182  are heat-sealed to each other, and thereby the second sealed portion  15   b  is formed. 
     Subsequently, the first and second sheet panels  11  and  12  and the gusset  18  are cut with the cutting device  5  ( FIG. 2 ), and thereby the bag  1  is shaped. In this step, the first and second sheet panels  11  and  12  and the gusset  18  are cut along the sealed part  15  with one cutter  51 , and thereby the sealed side edge portion  150  is formed by the cut edge resulting from the cutting. In other words, each of the first and second edge portions  150   a  and  150   b  is formed by the cut edge. 
     Subsequently, the sealed edge  13  is heated to be smoothed with the smoothing device  6 . In this step, the first and second edge portions  150   a  and  150   b  are heated to be smoothed. Thus, the bag  1  of  FIG. 11  is made. Thereafter, a filling step may be performed as in the other implementations. 
     When the first and second sheet panels  11  and  12  and the gusset  18  are cut, strong crimping force is added to these films. As a result, the first and second edge portions  150   a  and  150   b  can adhere to each other. This is referred to as “blocking”. 
     The folded gusset  18  always has restoring stress which is exerted in a direction of folding back. Since the blocked first and second edge portions  150   a  and  150   b  are melted due to heat when being heated to be smoothed, they disengage with each other due to the stress. Thus, the blocking can be eliminated at the same time of smoothing. 
     The blocking is conventionally and typically eliminated by using the expansion of the bag in accordance with the filling of the contents. However, in the case where the blocking is strong, it can fail to be eliminated even if the bag is filled with contents. As a result, the bag can fail to be filled with contents due to the failure of the expansion of the bag. Thus, it is very advantageous to be able to eliminate the blocking by using the heat during smoothing as described above. 
     Although the bottom gusset is exemplified as the gusset  18 , the gusset  18  may be a side gusset provided along the sealed side edge part  140 . Instead of the folded gusset  18 , a bent gusset  18  may be used. In this case, the blocking can also be eliminated during smoothing, since the restoring stress is exerted on the gusset  18 . 
     If too many bags  1  are stacked, the weight of the stacked bags  1  exceeds the restoring stress of the gusset  18 . Consequently, when the stacked bags  1  are subjected to a smoothing process all at once, the blocking may not be eliminated. Therefore, the number of bags  1  to be stacked should be adjusted as appropriate. 
     Although the preferred implementations according to the present invention are described, the present invention is not limited to the above implementations. 
     In the above implementations, the bag  1  is shaped every time the continuous films  11  and  12  are cut in the width direction thereof. More than two bags  1  may be shaped every time the continuous films  11  and  12  are cut in the width direction thereof. Even in this case, the cut edge of each bag  1  can be smoothed if the heat units  60  are appropriately disposed. 
     The sealed region  13  may have a section in which more than three films are stacked with and sealed to each other. In this case, since the rigidity of the sealed edge  130  is high, it is very advantageous to smooth the sealed edge  130 . 
     A bag other than ones illustrated in the implementations (for example, a plastic bag with a chuck) may be made. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
       1  plastic bag 
       100  edge of the plastic bag 
       11  film (first sheet panel) 
       12  film (second sheet panel) 
       13  sealed region 
       130  sealed edge 
       14  sealed part 
       140  sealed side edge part 
       15  sealed part 
       150  sealed side edge part 
       160  open side edge part 
       170  sealed corner edge part 
       18  film (gusset) 
       6  smoothing device 
       60  heat unit 
       600  heat source 
       61  cool unit 
       610  cooler 
       611  passage for refrigerant 
       612  blowout hole for refrigerant gas 
     X conveyance direction of the plastic bag 
     Y feed direction of the continuous film