Fraunhofer-Publica

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.

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