Evaluation of the Ultrasonic Sealing Performance of Flexible Films with Polyolefin Seal Layer

Abstract

Recent studies have shown advantages of ultrasonic sealing over heat conductive sealing, namely sealing through contamination, decreased energy consumption, no need for thick peel layers. Up to now there is no efficient systematic methodology to determine the optimal settings for the ultrasonic sealing of flexible films. Besides that, almost no literature is available about the specific permeation of the seal area in a package. In this study, seal strength, compaction and/or energy consumption are investigated as determining parameters in optimizing the ultrasonic sealing (USS) performance of flexible packaging films. These parameters are used to evaluate the ultrasonic seal performance of polyolefin monolayer and multilayer materials – 60 μm monolayer polyethylene (PE) and polypropylene (PP) polyolefin films, laminated films of 24 μm polyethylene terephthalate (PET) or oriented polyamide (OPA) with 40 μm PE seal layer. These materials are sealed with a 35 kHz ultrasonic sealer at 15 different settings of force, amplitude and time to calculate the optimum settings and to evaluate the ultrasonic seal performance. Besides that, the oxygen transmission rate (OTR) of ultrasonically sealed commercial pouches and flat films with and without the presence of a high barrier layer, ethylene vinyl alcohol (EVOH) or aluminum (Alu), in PET laminates with a PE sealing layer, is evaluated. This is measured with a Mocon OX-TRAN® device. The optimization method is validated and ready for implementation. Metallocene linear low density polyethylene with C6 branches (mLLDPE-C6) and random copolymer polypropylene (raco PP) are selected as ultrasonic best performing polyolefin monolayers because of respectively mainly a lower energy consumption and a broader seal window compared to other tested films. PET was selected as the best performing laminate for ultrasonic sealing because of the lower energy consumption compared to OPA laminates. Ultrasonic seal strengths of OPA and PET laminates were similar. Strong ultrasonic seals have no impact on the OTR. This is illustrated by the OTR-results of high barrier PET/Alu/PE pouches at normal and extreme ultrasonic settings, respectively 0.66±1.56x104 and 0.48±2.9x10-4 cc/package.day.