Split barrier layers help offset curling
Another approach that can be taken to eliminate curling is to split the barrier layer.. In this case, the unbalanced forces in the moisture-sensitive layers will tend to offset each other and help to maintain a flat, curl-free film.
As advances in coextrusion and orientation of coextruded films continues, there are many opportunities to produce new high-performance films in the barrier field and real opportunities to potentially replace existing flavor- and aroma-barrier coatings with barrier coextrusions. To date, most tenter-oriented polypropylene (OPP) and polyester (OPET) films are comprised of polymers from the same general polymer family, i.e.: homopolymer and copolymers of PP or PET.
But as polymer technologies advance, there are opportunities to combine and stretch polymers of dissimilar composition such as nylon and EVOH as in US Patent Application 2015/0118461 A1. Some cast and double-bubble, oriented films like this exist today for use in thermoforming and heat-shrinkable meat packaging. But films of this nature can be prone to curl and, to go further, the source of curl must be examined and overcome.