HF welding of polyolefin films with low dielectric loss factor - by using polyolefin films which are laminated on outer non-weld, side with polymer of high dielectric loss factor and m.pt. above that of polyolefin

摘要

A process is claimed for welding and unwelding polyolefin films with low dielectric loss factor (DLF) (I) by means of HF welding appts. The films (I) used in the process have a layer of polymer (II) with high DLF and m.pt. above that of (I) inseparably bonded to the outer surface of (I) on the opposite side of the weld. Pref. films (I) are polyethylene (PE) or polypropylene (PP), or one is PE and the other is PP. (II) is a layer of polyamide (PA), thermoplastic polyurethane or polyester, which is laminated with (I) by coextrusion, the thickness of (II) being adjusted according to the thickness of (I) and its m.pt., i.e. to 20-100 (pref. 20-50)% of the thickness of (I). Conventional welding units are used, with frequency 10-200 MHz and contact times of 2-10 secs. ADVANTAGE - The process enables polymer films with low DLF to be directly welded or unwelded by the HF welding technique without using insulating layers and PVC interlayers (which must not stick to the film to be welded and must be heat-stable over many welding cycles).