Patent Publication Number: US-9403337-B2

Title: Method for manufacturing a thermoplastic bag

Description:
BACKGROUND 
     1. Field of Invention 
     The invention relates generally to the field of thermoplastic manufacturing. In particular, but not by way of limitation, the invention relates to a method for manufacturing thermoplastic bags having a substantially flat and rectangular bottom. 
     2. Description of the Related Art 
     Many types of bags are known and used in commerce. For example, clothing, food, and other retailers commonly use bags at the point-of-sale (POS) to facilitate the transport of goods by the customer. Bag features vary according to intended use. For many applications, a flat-bottomed bag with carrying handles is desirable. Typically, such bags are constructed of paper. Paper bags have many shortcomings, however. For instance paper bags are not waterproof. In addition, paper bags are often more expensive to manufacture than thermoplastic bags. 
     SUMMARY OF THE INVENTION 
     The invention seeks to overcome one or more of the limitations described above by providing a method for manufacturing a flat-bottomed bag with carrying handles from thermoplastic film. In an embodiment of the invention, the method includes receiving a thermoplastic film tube, forming a first and second gusset in the tube, slitting along a crease of an interior fold of the first gusset, welding support structures in the first and second gussets, seam welding and cutting the tube to form a bag, and punching a portion of the first gusset to form a handle. The invention also provides a bag that is manufactured by the process. 
     These and other features are more fully described in the detailed description section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are described with reference to the following drawings, wherein: 
         FIG. 1  is a flow diagram of a bag-manufacturing process, according to a first and second embodiment of the invention; 
         FIG. 2A  is a plan view schematic of a slitting process and a welding process, according to a first embodiment of the invention; 
         FIG. 2B  is a plan view schematic of a slitting process and a welding process, according to a second embodiment of the invention; 
         FIG. 3A  is a sectional view of a gusseted polyethylene tube, according to the first embodiment of the invention; 
         FIG. 3B  is a sectional view of a gusseted polyethylene tube, according to the second embodiment of the invention; 
         FIG. 4  is a sectional view of a gusseted polyethylene tube, according to the first and second embodiments of the invention; 
         FIG. 5  is a sectional view of a gusseted polyethylene tube during a slitting process, according to the first and second embodiments of the invention; 
         FIG. 6  is a sectional view of a gusseted polyethylene tube during a welding process, according to the first and second embodiments of the invention; 
         FIG. 7A  is a plan view schematic of a cutting/welding process, according to the first embodiment of the invention; 
         FIG. 7B  is a plan view schematic of a cutting/welding process, according to the second embodiment of the invention; 
         FIG. 8A  is a plan view schematic of a punching process, according to the first embodiment of the invention; 
         FIG. 8B  is a plan view schematic of a punching process, according to the second embodiment of the invention; 
         FIG. 8C  is a plan view schematic of a punching process, according to a variation of the first embodiment of the invention; 
         FIG. 8D  is a plan view schematic of a punching process, according to a variation of the second embodiment of the invention; 
         FIG. 9A  is a plan view schematic of a completed bag, according to the first embodiment of the invention; 
         FIG. 9B  is a plan view schematic of a completed bag, according to the second embodiment of the invention; 
         FIG. 9C  is a plan view schematic of a completed bag, according to a variation of the first embodiment of the invention; 
         FIG. 9D  is a plan view schematic of a completed bag, according to a variation of the second embodiment of the invention; 
         FIG. 10A  is a perspective view of an opened bag, according to the first embodiment of the invention; 
         FIG. 10B  is a perspective view of an opened bag, according to the second embodiment of the invention; 
         FIG. 11  is a perspective view of an opened bag illustrating handle extension, according to the first and second embodiments of the invention; and 
         FIG. 12  is a perspective view of an opened bag with both handles extended, according to the first and second embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention are described with reference to  FIGS. 1-12 . Reference designators are reused for the same or similar features. The drawings are not to scale. Some features illustrated in the drawings have been exaggerated for descriptive clarity. Sub-headings are used in this section for organizational convenience but the disclosure of any particular feature(s) is/are not necessarily limited to any particular section or sub-section of this specification. 
     Manufacturing Process 
       FIG. 1  is a flow diagram of a bag-manufacturing process, according to a first and a second embodiment of the invention. After beginning in step  105 , the process receives a polyethylene (PE) tube in step  110 . Next, in step  115 , the process forms a first and a second gusset in the polyethylene tube, for example using gusseting wheels. In a first embodiment, and with reference to  FIGS. 2A and 3A , the first gusset  205  and the second gusset  210  are the same (or substantially the same) in width. In a second embodiment, and with reference to  FIGS. 2B and 3B , the gusseting is asymmetrical: the first gusset  215  being more narrow than the second gusset  220 . 
       FIG. 4  is a sectional view of a gusseted polyethylene tube, according to the first and second embodiments of the invention.  FIG. 4  illustrates that each of the gussets  205 ,  210 ,  215 , and  220  has a first layer  405 , a second layer  410 , a third layer  415 , and a fourth layer  420 . The first and the second layers  405 ,  410  form a first exterior fold; the third and the fourth layers  415 ,  420  form a second exterior fold; the second and the third layers  410 ,  415  form an interior fold.  FIG. 4  also illustrates a crease  425  of the interior fold and an un-gusseted portion  430  of the polyethylene tube. 
     In step  120 , the process slits along the crease  425  of the interior fold of the first gusset  205 ,  215 . With reference to  FIGS. 2A, 2B, and 5 , the slitting step  120  may be performed, for example, using a stationary knife  225  as the polyethylene tube is advanced (for example in web form on rollers) during manufacturing. 
     To provide reinforcement, the process welds a first and a second support structure in each of the first and second gussets in step  125 .  FIG. 2A  illustrates a plan view of the first support structure  230  in the first gusset  205 , and first support structure  240  in the second gusset  210 , according to the first embodiment. A second support structure  235  (not visible in  FIG. 2A ) in the first gusset  205  has a shape that is identical to the first support structure  230 . A second support structure  245  (not visible in  FIG. 2A ) in the second gusset  210  has a shape that is identical to the first support structure  240 . 
       FIG. 2B  illustrates a plan view of an alternative first support structure  250  in the first gusset  215 , according to the second embodiment of the invention. A second support structure  255  (not visible in  FIG. 2B ) in the first gusset  215  has a shape that is identical to the first support structure  250 . 
       FIG. 6  is a sectional view of a gusseted polyethylene tube during a welding process, according to the first and second embodiments of the invention. As shown therein, the first support structure  230 ,  240 , or  250  joins only the first and second gusset layers  405 ,  410 , and the corresponding second support structure  235 ,  245 , or  255  joins only the third and fourth gusset layers  415 ,  420 . 
     To achieve uniform shaping, the support structures in the first gusset are preferably aligned with the support structures in the second gusset. With respect to the first embodiment illustrated in  FIG. 2A , the first and second support structures  230 ,  235  (not shown) of the first gusset  205  and the first and second support structures  240 ,  245  (not shown) of the second gusset  210  are each centered about center line  260 . Preferably, center line  260  is disposed on the polyethylene tube to be equidistant from adjacent print registrations  275 . Also preferably, the width of support structures  230 ,  235  (not shown) in the first gusset  205  is approximately equal to the width of the support structures  240 ,  245  (not shown) in the second gusset  210 , as illustrated by width markers  265 ,  270 .  FIG. 2B  illustrates these same preferred alignment relationships for the second embodiment. 
     Cut/weld step  130  includes the formation of two seam welds to close bag sides. Cut/weld step  130  also includes cutting the bag from the polyethylene tube. These steps are preferably performed simultaneously to maximize production throughput. The seam welding and cutting in step  130  is performed in a lateral direction (i.e., across the polyethylene tube). With reference to  FIGS. 7A  (first embodiment) and  7 B (second embodiment), step  130  produces parallel seam welds  705  and  710  on either side of center line  260 . The cutting in step  130  is performed at center line  260 .  FIGS. 7A and 7B  also illustrate a seam weld  715  created in a prior execution of the cut/weld step  130 . 
     In step  135 , the process preferably transfers the bag separated in step  135  to a stack of bags. 
     In step  140 , the process removes a portion of the first gusset  205 ,  215  to form a handle in the bag. Step  140  may include, for instance, using a punch  805  as illustrated in  FIGS. 8A  (first embodiment) and  8 B (second embodiment) to produce void  905  shown in  FIGS. 9A  (first embodiment) and  9 B (second embodiment). In a variation of step  140 , the process could use a punch  810  illustrated in  FIG. 8C  (a variation of the first embodiment) and  8 D (a variation of the second embodiment) to form a void  910  that includes a tab  915  with a hole  920  as shown in  FIGS. 9C  (the variation of the first embodiment) and  9 D (the variation of the second embodiment). The process terminates in step  145 . 
     Other variations to the process illustrated in  FIG. 1  and described with reference to other figures herein are possible. For instance, the thermoplastic tube received in step  110  could be or include polypropylene (PP), a combination of PE and PP, or other thermoplastic composition, according to application requirements. Alternative embodiments may not include the un-gusseted portion  430  in the tube. Step  125  could produce support structures having shapes that are not consistent with those illustrated in  FIGS. 2A and 2B . Although seam welding and cutting are preferably performed simultaneously in cut/weld step  130  to maximize production throughput, these operations could be performed serially. Laser, water jet, or another cutting process could be used to remove a portion of the first gusset in step  140 . 
     Manufactured Bags 
       FIGS. 9A, 9B, 9C, and 9D  illustrate manufactured bags laying in a flat and unexpanded condition that can be produced by the process described with reference to  FIG. 1 .  FIGS. 10A, 10B, 11, and 12  illustrate opened bags where an expanded second gusset  210 ,  220  forms a floor of the bag.  FIG. 10A  shows supporting structures  230 ,  240  and seam weld  710  on one end of the bag, according to the first embodiment of the invention.  FIG. 10B  likewise illustrates supporting structures  250 ,  240  and seam weld  710  on one end of the bag, according to the second embodiment of the invention. Voids  905  are also visible in both  FIGS. 10A and 10B .  FIG. 11  illustrates how the first gusset  205 ,  215  is extended in a direction  1105  to convert the void  905  to a useable handle.  FIG. 12  shows a bag with both handles  1205  fully extended. 
     SUMMARY 
     Embodiments of the invention thus provide a method for manufacturing a thermoplastic bag having a flat bottom and handles. The resulting bag is waterproof and may be less expensive to manufacture than a paper bag alternative. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention.