Co-extrusion runs multiple resin streams through a single die at the same time, fusing them into one film while each layer keeps doing its own job. A structure might use one layer for oxygen barrier, another for puncture resistance, a tie layer to bond materials that would not otherwise adhere, and an outer layer tuned for sealing or print. The result is a film engineered to a spec, not a film that happens to meet one.
Tie layers are the part of the structure customers rarely think about but that make the whole thing possible. Many high-performance barrier resins, like EVOH or nylon, will not bond directly to polyethylene. A tie layer sits between them and chemically bridges the two, so the structure holds together through printing, filling, sealing, and the life of the package instead of delaminating in the field.
A common structure for oxygen-sensitive products runs PE/tie/EVOH/tie/PE: polyethylene on both outer layers for seal strength and cost, EVOH in the center for oxygen barrier, and tie layers bonding the EVOH to the PE on each side. We adjust layer ratios, resin selection, and total layer count based on the barrier level, clarity, and cost target a product actually needs, rather than defaulting to the heaviest structure available.
Running three, five, seven, or more layers requires tight control over each extruder's output and the die's layer distribution, since an uneven layer can defeat the barrier it was added to provide. Our lines are set up to hold that balance across the full width and length of a run.