Active packaging and microlayer extrusion come together in the new "active microlayer" film technology where layer multiplication is applied not only to the barrier polymer but also to active components such as oxygen absorbers or desiccants. Flat-die manufacturer Extrusion Dies Industries LLC (EDI) says the patent-pending technique adds a new dimension of oxygen and moisture control to food packaging, with the company feeling that it will extend barrier properties beyond the limits of standard test procedures.
EDI has already demonstrated that dividing and recombining the barrier layer to create many micro-barrier layers can significantly increase the shelf life of retort and hot-fill containers, stand-up pouches, and vacuum skin packaging. Now researchers at EDI's Technology Center have gone further and incorporated active components in layers outside the barrier core and then multiplied those layers as well.
Gary D. Oliver, EDI's VP of technology, says the combination of what can be dozens of barrier and active layers appears to be greater than standard tests for oxygen and moisture ingress are designed to measure. "After encountering numerous active-component layers, oxygen is largely absorbed before it even reaches the barrier layer," Oliver said. The same is true of moisture, which is mostly gone before it gets a chance to degrade a barrier material like ethylene-vinyl alcohol [EVOH]. [Read more from Oliver on layer multiplication here].
Layer multiplication technology (LMT) creates film or sheet has the same composition and thickness of a conventional coextrusion but can be comprise of a hundred or more microlayers, instead of three to 11 layers of standard thickness. The heart of the technology is a special tool that takes the sandwich from a feedblock and divides and recombines the layers, creating multiples of the original multilayer structure.
Below, how a typical active microlayer structure could be produced in the form of polypropylene (PP) sheet with a 1.25-mm thickness:
- Four extruders produce melt streams of 1) the PP outer material, or skin; 2) the same PP skin material, but incorporating an active component such as an oxygen scavenger; 3) an adhesive or "tie" layer material; and 4) a barrier polymer such as EVOH.
- Feedblock No. 1 receives the "active component containing" skin material, along with the tie and barrier materials, and forms a five-layer sandwich: active-component / tie / barrier / tie / active component. This sandwich will evolve into the inner core of the finished sheet.
- Layer multiplier. This special tool built by EDI receives the five-layer sandwich from Feedblock No. 1 and divides and recombines it to form multiple repetitions of the structure-for example, four repetitions, resulting in a 20-layer structure consisting of micro-layers.
- Feedblock No. 2 receives the 20-microlayer structure and the melt stream of PP outer material, diverting the PP into two skin layers over the microlayer core.
- Extrusion die. In the manifold of the die, the sandwich from Feedblock No. 2 is transformed into sheet of target width.