Heatsealability of Flexible Web Materials in Hot-Bar Sealing Applications

Abstract

Heatsealability of flexible web materials is critical to the economics of their use on commercial form-fill-seal machines. Our objective was to determine which factors in the heatsealing process affect seal strength significantly and should be included when testing for heatsealability A recently-available precision laboratory heat sealer was used to study the response of low density polyethylene (LDPE) coextruded film and high density polyethylene/ethylene vinyl acetate-polybutylene (HDPE/EVA-PB) coextruded film to sealing die configuration, plus the usual variables of temperature, time and pressure. Interface temperature and dwell time were confirmed as primary factors in controlling heatseal strength. Pressure normal to the seal surface had little effect above the level required to flatten the web for good contact. Serrated dies moderately improved seal strength of HDPE/EVA-PB at high die force, but had no advantage with LDPE. Variables in measuring seal strength were critical in interpreting results, particularly with serrated dies Results were gen erally compatible with the theory of chain-end diffusion.