Experimental investigations into fold cracking of double coated barrier dispersion coatings, TAPPICon24

The trend for replacing single use plastics with fibre-based barrier coated board packaging has prompted a significant amount of research. There are many proposed ways of providing suitable packaging for example for food service applications. Amongst these are dispersion coated barriers on board, as well as laminated boards which can be produced using conventional polyethylene (PE) or new biodegradable plastics. Minerals have also been shown to be suitable additives to these coatings for improving barrier performance through surface chemistry and by increasing the tortuosity of the pathway through the barrier layer. They also improve the cost effectiveness of the layer by lowering the material cost, potentially improving drying rate and also by improving hold out of the functional layers leading to a reduction in the amount of barrier coating needed to meet a given performance requirement. Minerals can also aid in the barrier handling in terms of rheology and reduced “stickiness” as well as blocking of the films. When incorporated as fillers into extruded films, improved adhesion of the film to the board has been reported [1].

One of the remaining challenges is the potential for cracking at the fold during converting and the loss of barrier performance that this can lead to. In this work we systematically looked at the impact of mineral type and level in a dispersion coating. We assessed the differences in performance resulting from different coating application methods for the precoat layer, by looking at the cracking tendency and loss of barrier functionality after folding for both the precoat alone and the final double coated sheets. Barrier results include moisture vapour transmission rate (MVTR), viscous vegetable oil and the fluid blue stain in industrial methylated spirits (IMS) and Cobb water absorption, both before and after folding.

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