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Abstract
Flexible packaging films for highly sensitive products that are to be protected against moisture and oxygen need high barrier materials. In the food and pharmaceutical packaging industries, barrier films, which contain a single inorganic layer on top of a polymeric substrate, provide sufficient barrier. For the protection of more sensitive products, such as vacuum insulation panels, organic photovoltaic cells, or organic light emitting diodes, the barrier films are, however, not sufficient and multilayered structures of alternating inorganic and polymeric layers are required as encapsulation material to ensure sufficient product lifetime. One approach for the production of multilayered structures is the face-to-face lamination of two barrier films via lamination adhesives. Such multilayered structures are usually referred to as multilayered high-barrier laminates. Solvent-free, UV-curable, epoxy-based adhesives are promising candidates for multilayered high-barrier laminates. The adhesives best suited for multilayered high-barrier laminates are those that provide both high laminate bond strength as well as barrier performance. In this paper three different types of such adhesives are discussed in terms of their water vapor barrier and adhesion performance. The effects of the structural differences in the adhesives — chain mobility, crosslink density and surface energy — on the laminate bond strength and barrier performance are investigated. Laminate bond strength tests were performed and failure types and failure locations in the laminates were examined. The results suggest that the intrinsic barrier performance of the adhesive significantly affects the barrier performance of the laminate. On the other hand, the adhesive having the best barrier performance shows a weak adhesion performance. An appropriate adhesive was designed by adjusting the type of the flexibilizer and photoinitiator used in its formulation. This adhesive in combination with a barrier film having an enhanced surface energy shows at the same time a promising laminate bond strength as well as barrier performance.
Acknowledgements
This work has been supported by the OLATRONICS project ‘Development and integration of processes & technologies for the production of organic low-cost & large-area flexible electronics’, funded by the EU Commission under the 7th Framework Programme (Grant number: 216211). The authors thank Mr Wolfgang Lohwasser from Amcor Flexibles Neuhausen GmbH for the supply of the PET/SiOx type of the barrier film, Dr Nicolas Schiller from the Fraunhofer Institute for Electron Beam and Plasma Technology (FEP) for the PET/ZnSnOx type of the barrier film. We also thank Ms Brigitte Seifert, Ms Simone Drotboom, Mr Wolfgang Busch from the Materials Development Department of the Fraunhofer Institute for Process Engineering and Packaging (IVV) for the optical microscopy, SEM images, lamination of the barrier films and Dr Cornelia Stramm and Dr Klaus Noller for useful discussions during the course of this study.