Plastic film welded together from two pieces to give uniform joint

摘要

A plastic film is formed from at least two pieces (5), each with areas (10) joined together to form a seam(16) with a flange (17) below the visible film pieces (5) and a uniform joint line (19) on the visible side (18). The flange (17) has an area (21) with a regularly spaced toothed profile lateral to the joint and running along the joint line (19). The profiled area (21) is below a short flange (20) at the base of the joint line (19) ensuring the toothed profile does not show on the visible face of the film (5). In a process for joining two thermoplastic films (5), the films (5) are heated at the joining area (10) and pressed together to form the toothed profile area (21) and the non-profiled flange (20). Process equipment comprises two punches (1) moving relative to each other, each with a film-supporting face (4) and a punch face (2). A flat area adjacent to each film-supporting area (4) runs into the punch face (2) whose profiled area(21) has projections (14) and corresponding recesses (15), those on opposing punch faces (2) being complimentary to each other.