Apparatus for sealing a hem in a moving web of film

In a machine for making draw tape bags having front and back panels from thermoplastic film including apparatus for heat sealing a pair of hems in a moving web of the thermoplastic film, each of the hems comprising folded opposing layers of the web in the front and back panels comprising:

• structure including a first two-sided surface having the moving web passing on one side of said surface and an edge of the web wrapped around said surface on the other side of said surface forming a first hem in the two layers of the web in the front panel in the direction of movement of the web prior to leaving said surface, said structure having an opening in said surface extending along the path of movement of the first hem;
• means for feeding a draw tape into the first hem while the web in the front panel is on said surface;
• means carried by said structure on said other side of said surface for engaging the layer of the first hem wrapped around said other side for maintaining the moving web of film in the front panel tightly around said surface and against the opposite sides thereof to avoid formation of wrinkles in the film during the heat sealing of the first hem;
• first means supported adjacent said opening in said first surface for heat sealing together the two web layers in the first hem in the direction of movement of the web while the web is moving and prior to the sealed first hem leaving said surface, said first heat sealing means comprising a first plurality of heated rollers mounted in tandem in the direction of the movement of the web and supported at said one side of said first surface, said first rollers being positioned to extend through said opening in said surface;
• said structure including a second two-sided surface having the moving web passing on one side of said surface and an edge of the web wrapped around said surface on the other side of said surface forming a second hem in the two layers of the web in the back panel in the direction of movement of the web prior to leaving said surface, said structure having an opening in said surface extending along the path of movement of the second hem;
• means for feeding a draw tape into the second hem while the web in the back panel is on said surface,
• means carried by said structure on said other side of said surface for engaging the layer of the second hem wrapped around said other side for maintaining the moving web of film in the back panel tightly around said surface and against the opposite sides thereof to avoid formation of wrinkles in the film during the heat sealing of the second hem;
• second means supported adjacent said opening in said second surface for heat sealing together the two web layers in the second him in the direction of movement of the web while the web is moving and prior to the sealed second hem leaving said surface, said second heat sealing means comprising a second plurality of heated rollers mounted in tandem in the direction of movement of the web and supported at said one side of said second surface said second rollers being positioned to extend through said opening in said surface;
• and
• backup means positioned between said first and second surfaces in alignment with said openings and cooperating with said pluralities of heated rollers to press together the opposing layers of film in each of the hems for heat sealing the hems while the web is moving and prior to the sealed hems leaving the respective surfaces.