Coating & Laminating Master and Expert solutions from Bobst
Overcoming the technical complexities of developing and manufacturing sustainable high barrier flexible packaging that is recycle-ready is a major challenge, even more so since the market looks for new solutions with the same performance as traditional multi-material non-recyclable packaging. This report from Bobst looks at some solutions.
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t has become imperative to work all along the value chain. All processes from resin production to film extrusion, through to ensuring barrier functionality of the substrate, printing, laminating, and pouch making, all operations must be optimized to handle the production and processing of novel substrates. Let us take the oneBARRIER PrimeCycle solution developed by Bobst, namely the offering of recycle-ready high barrier transparent AlOx-based or opaque AluBond- based full PE mono-material substrates. As indicated, the projects’ success requires the optimisation of each step of the production process: O Optimisation of the resin used for the film extrusion and their chemistry to offset polyolefins (PE) non-polarity, along with the optimization of the sealant web
O Optimisation of the extruded film via MDO orientation to improve the mechanical and optical properties
O Optimisation of the primer coating and of the vacuum deposition process for the transparent AlOx GEN II or the opaque AluBond, and of the subsequent printing and conversion processes.
What are the advantages for converters adopting Bobst integrated equipment and process package solution for production of recycle-ready high barrier packaging? For converters, the oneBARRIER PrimeCycle process advantages are manyfold: the knowledge of both coating and vacuum metallizing equipment technology and processes, topcoat formulations and conversion know-how from one single supplier offers advantages in terms of seamless
workflow integration. The oneBARRIER equipment package comprises the Bobst Expert K5 vacuum metallizer and, depending on the converter’s productivity needs, the Bobst oneBARRIER Expert coater or the oneBARRIER Master coater.
The seamless integration of the workflow of different equipment is essential to ensure the continuous and consistent machinability of polyolefin-based substrates in terms of both machine productivity performance and the quality of the end product. This owes to the critical issues that need to be overcome during processing: heat-sensitivity, extensibility, non- polar nature, and poor barrier performance of polyolefin-based films.
The first step is to apply a primer layer. When developing this solution, several different trials were run on a oneBARRIER Expert coater to find the primer formulation that would work best combined with the most suitable coating technology: namely a formulation able to provide oxygen and water vapour barrier, confer good polarity for the subsequent deposition of the metal layer, and achieve a good adhesion level between the non-polar base film and the primer layer and a coating method that avoids the formation of foam when metered at high speed.
The coater/laminator’s web tension from the unwinder to the rewinder and the drying tunnel temperature are other critical points that must be mastered to ensure the optimum thermal load to avoid defects in the MDOPE extensible film during the process. This is achieved via the hybrid tunnel with 2-sided optimised airflow system which enables high water-evaporation while maintaining the film at low temperature.
The 3-zone tunnel confers web stability at hight speed processing.
The clear AlOx GEN II or the opaque AluBond deposition process is carried out on a Bobst Expert K5 vacuum metallizer. AlOx GEN II is the latest process that has been developed specifically for polyolefin substrates to achieve higher transparency and a higher barrier level. AluBond is a hybrid coating technology that vastly improves anchoring properties to the base substrate providing an improved barrier performance.
Here, the same critical issues relating to heat- sensitivity, extensibility and low polarity have been overcome by unique technical solutions. The combination of the large 700 mm diameter cooling drum, with a dual zone gas wedge and a larger coating window, greatly contribute to putting minimum thermal stress on the film.
Web handling and tension control is very precise and managed by load cells, not torque. Dedicated solutions and an optimized web path enable achievement of very low web tension on the rewind section and prevent overstretching and damaging of the substrate that could cause a loss of barrier. Improvement of coating adhesion and of barrier performance is taken care of by a plasma pre-treatment which is ideally suited to MDO PE film because of its low thermal impact. The barrier performance resulting from the oneBARRIER PrimeCycle process for recycle- ready monomaterial packaging is equal to the performance of a non-recyclable multi- material structure, such as metallized PET, with the bond strength compliant with market requirement.
As a machine manufacturer offering end- to-end flexible packaging solutions, Bobst can go further in delivering converters solutions, including gravure or CI flexo printing and lamination, for optimum product protection that maximise quality, sustainable operation, productivity, and market acceptance whose perfect integration reduces the risk of defective packaging substrates.
Xwww.bobst.com
16
May 2022
www.convertermag.com
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