Tie Layer

A tie layer is part of the finished film, not a coating added to the outside. In a structure such as PE/tie/EVOH/tie/PE, it sits between polyethylene (PE) and ethylene vinyl alcohol (EVOH) so the barrier layer stays attached to the surrounding film. The exact resin depends on the two materials it has to join.

The material used to make that layer is often sold separately as adhesive resin pellets or granules. A film producer feeds that purchased resin into an extruder with the other resins; the coextrusion process turns it into an internal layer of the finished web. Buying tie-layer granules and buying coextruded barrier film are different transactions.

For example, Dow describes an anhydride-modified polyethylene adhesive resin supplied as pellets for coextrusion with EVOH, nylon, and PE. That is an example of a possible tie resin, not a universal match for every film. Selection also depends on processing conditions, neighboring resin grades, target bond strength, and what happens after the film is printed, sealed, or flexed. A trial should test adhesion in the finished structure rather than assume a resin name guarantees it.

A buyer specifying PE and EVOH in one film asks the film producer which tie resin will join those layers and what bond test will confirm the finished structure stays together.

The tie layer contributes adhesion; it does not replace a barrier layer or prove the package is ready for use. Prime Film Extrusion describes co-extruded film as the finished product. Tie-layer resin pellets are an input to that process, not a separate finished film offering.

A tie layer shows up wherever two resins will not stick to each other on their own. These three structures cover most of them.
1. PE / tie / EVOH / tie / PE ... an oxygen barrier film for meat, cheese and foods that spoil in air.
2. PE / tie / nylon ... a tough, puncture resistant film for vacuum packaging.
3. PE / tie / nylon / EVOH / nylon / tie / PE ... a seven layer film when a package needs both a strong barrier and toughness.

If you are buying tie layer granules so you can make barrier film, price the finished film too. Prime Film runs co-extruded structures of three to seven layers in Orlando. We buy the resins, choose the tie layer for the materials it has to join and test the bond in the finished film.

Structures outside our lines are made by partner extruders we manage. You still get one quote and one engineer to talk to.