Welding thermoplastic wrappers - by moving wrapper folds past a hot surface

摘要

System for trapping the folded ends of wrapped packages between guide plates leading to a pair of heated panels covered by films which move past at the same rate as the packages while the folds are heated. Esp. for sealing wrappers made of thermoplastic (polypropylene) films or coated with a heat sealing adhesive (polyvinylidene chloride-acrylonitrile copolymers). The moving films prevent drag or adhesion from disturbing the folds before the weld sets. Allow greater heat transfer periods with quicker pack throughputs than transverse reciprocating hot jaw welders. In example equipment moving films were continuous webs of polyethylene terephthalate 500 mm thick driven round two PTFE rollers and past a heater support frame with bevelled faces for accepting the incoming packs.