The sealing behavior of new mono‐polyolefin and paper‐based film laminates in the context of bag form‐fill‐seal machines

Abstract

Heat sealing behavior of mono-polyolefins and paper-based materials is drastically different from conventional multilayer plastic laminates. This paper presents the effect of sealing conditions on Hot-Tack and Cold-Tack for an oriented polypropylene (OPP)-based polyolefin laminate with either polyethylene (PE) or cast polypropylene (CPP) sealing layer and two different barrier paper materials carrying a thin acrylic copolymer sealing layer. The investigations include pressure, temperature, time, jaw pattern, and climate conditions (moisture). It is shown that the monopolyolefins reach comparable Hot-Tack and Cold-Tack ranges compared with the reference polyethylene terephthalate (PET)-aluminum (Al)-PE laminate. The CPP laminate exhibits a narrow sealing window near the range in which shrinkage is observed. While for the polyolefins temperature plays the main role, the sealing of paper materials turned out to be dependent on pressure, time, and moisture content in paper. Due to a rupture through the polymer thin coating, the Cold-Tack is dominated by a delamination of paper and coating. Consequently, the Cold-Tack is drastically lower than with PETAl -PE laminate. Monopolypropylene films exhibit extremely narrow sealing window, which shall be taken into the design consideration of bag formfill-seal (FFS) machines. Polymer coated paper can be potentially used at high-speed FFS; however, special attention shall be paid to moisture content control and filling.

The effect of flexible sealing jaws on the tightness of pouches made from mono‐polyolefin films and functional papers

“…The OPP materials exhibit shrinkage beginning at 140°C. The temperatures providing enough seal strength start at 100°C for the OPP/PE and at 120°C for the OPP/CPP material 6 . This is in an expected range and corresponds almost with the results of Tsujii et al 12 The rhodamine tests show that the OPP/PE laminate offers tight seals starting at 120°C but within high sealing times.…”

“…The transfer to the full scale with slight increase of sealing time towards 0.8 s provided tight seals also for the OPP/CPP laminate starting at 150°C (Figure 10, right). The onset temperature measured for this laminate at 143°C gives an indication of starting melt flow and interdiffusion at the seal surface 6 . Comparable results for onset and melting temperature were reported for a CPP layer by Kang et al 3 However, this temperature setting still leads to considerable shrinkage.…”

“…At 150°C, the CPP still shows no melt flow (Figure 9, left) whereas the PE layer is properly molten and shows a good filling of the layer jump gap (Figure 9, right). The missing melt flow of the CPP layer is most likely originating from its almost similar melting temperature at 165°C compared with the OPP carrier layer, which was reported in Hauptmann et al 6 …”

“…The important issue for the application of the material and sealing process is the sealing time limitation allowing for economically feasible production. It was reported in Hauptmann et al 6 that sealing pressure and moisture need to be seen in interaction with the applied sealing temperature when the sealing time is in a range between 0.3 and 0.5 s. This sealing time range reflects the operational production condition. Hot‐Tack and Cold‐Tack testing reveal intact sealant to sealant surface bonding relocating the crack into the paper layer.…”

“…However, Hot‐Tack and Cold‐Tack values were observed in a tolerable range. The relaxation of the material at temperatures around 150°C is likely to be the reason for the shrinkage reported by 6 . With further integration of a barrier layer using metallized OPP, both polyolefin variants can only prevent additional material effort if the sealing layer is reduced compared with PET laminates.…”