Thermoplastic bag produced with a back seam welder

Abstract

A thermal welder is configured to weld a back seam of a bag formed of thermoplastic sheet material. The welder may include a weld heater and a compression mechanism downstream of the weld heater to compress the sheet material to form the back seam. The welder may also include a weld breaker downstream of the compression mechanism to break apart incidental welds which are formed adjacent the back seam.

1 . A thermoplastic bag produced by a method comprising the steps of:
 providing flexible thermoplastic sheet material having a longitudinally extending first edge segment and an opposed longitudinally extending second edge segment;   forming an overlap region in the sheet material by placing the first edge segment over and beyond the second edge segment;   forming the sheet material into a tubular configuration comprising first and second superimposed panels, wherein the second panel includes the overlap region, and the overlap region overlays a portion of the first panel;   moving the sheet material downstream;   heating the sheet material along the overlap region with a weld heater;   compressing the first and second edge segments together with a compression mechanism downstream of the weld heater to form a longitudinally-extending welded back seam extending along the overlap region; and   as the sheet material is moving downstream in the tubular configuration, breaking incidental welds extending between the welded back seam and the portion of the first panel overlaid by the welded back seam with a weld breaker which extends downstream of the compression mechanism between the welded back seam and the first panel.   
     
     
         2 . The thermoplastic bag as defined in  claim 1 , wherein the bag comprises a thermoplastic tube having a top seam, a bottom seam and only a single seam extending between the top seam and the bottom seam; and wherein the single seam is the welded back seam formed where the first segment and the second segment overlap along the overlap region. 
     
     
         3 . The thermoplastic bag as defined in  claim 1 , further comprising:
 a first broken weld located on an inner surface of the second panel; and   a second broken weld located on the inner surface of the first panel; and   wherein the first broken weld comprises material that extends downwardly from the inner surface of the second panel and the second broken weld comprises material that extends upwardly from the inner surface of the first panel.   
     
     
         4 . The thermoplastic bag as defined in  claim 3 , wherein the first broken weld is located opposite the second broken weld. 
     
     
         5 . The thermoplastic bag as defined in  claim 1 , further comprising:
 a single top seam sealing together a top edge of the first panel and the second panel.   
     
     
         6 . The thermoplastic bag as defined in  claim 5 , wherein the top seam seals a top edge of the back seam to the first panel. 
     
     
         7 . The thermoplastic bag as defined in  claim 1 , further comprising:
 a single bottom seam sealing together a bottom edge of the first panel and the second panel.   
     
     
         8 . The thermoplastic bag as defined in  claim 7 , wherein the bottom seals seal a bottom edge of the back seam to the first panel. 
     
     
         9 . The thermoplastic bag as defined in  claim 1 , further comprising:
 a first gusset extending along a first side of the bag; and   a second gusset extending along a second side of the bag.   
     
     
         10 . The thermoplastic bag as defined in  claim 9 , wherein the back seam is located a distance inwardly away from each of the first gusset and the second gusset. 
     
     
         11 . The thermoplastic bag as defined in  claim 9 , further comprising:
 a single top seam sealing together a top edge of the first panel to the second panel, said top seam extending across and sealing a top end of each of the first gusset, the back seam and the second gusset.   
     
     
         12 . The thermoplastic bag as defined in  claim 11 , wherein the top seam is a thermally welded top seam. 
     
     
         13 . The thermoplastic bag as defined in  claim 9 , further comprising:
 a single bottom seam sealing together a bottom edge of the first panel to the second panel, said bottom seam extending across and sealing a bottom end of each of the first gusset, the back seam and the second gusset.   
     
     
         14 . The thermoplastic bag as defined in  claim 13 , the bottom seam is thermally welded.