Abstract: A solvent-based adhesive is used to form a continuous, adhesively bonded and welded seam at the longitudinal edge portions of plastic film which have been overlapped. First, a bead of the adhesive is disposed on the edge portion of a web of film passing over an applicator roll. Next, as the film moves between the applicator roll and nip rolls, the adhesive dissolves a portion of the film to form a longitudinal channel having a generally semicircular cross-section. Then the edge portion is overlapped onto the other edge portion with the bead of adhesive between them. Finally the overlapped edge portions are squeezed between the nip rolls, so that the adhesive exudes laterally outward from the groove and is distributed smoothly between the overlapped edge portions, until the adhesive and dissolved film form a uniform band having a rounded hat-shaped cross-sectional profile.