Multilayer Flexible Packaging Structures

Layer-multiplying coextrusion represents an advanced polymer processing technique for combining two or more polymers in a layered configuration with controlled structure. It is a continuous processing technique capable of producing films economically. Coextrusion is an industrial process used to produce sheets and films that are suitable for food packaging. In this process, two or more polymers are extruded simultaneously from individual extruders. The melted polymers are delivered from extruders to a feedblock to be shaped and combined. Then, the melt flow is directed to the die to spread, become thin, and distribute uniformly to form the coextruded film. The main problem in coextrusion is to simultaneously process polymers of different rheological properties, which may cause problems such as interfacial instability and encapsulation that significantly affect the quality of the product. 

Multilayer film structures that provide high barrier levels to oxygen, water vapor, aromas/ flavors, and/or UV light for food applications usually contain a combination of barrier, bulk, and sealant films. Structures that use aluminum foils as a barrier or graphic substrate are usually excluded from this group. The thickness of the entire structure is usually less than 0.25 mm (0.010 in.), including the printed layer, bulk, barrier, tie, and sealant layers.

A single layer capable of working as a barrier film is very rare. The true value is created when the barrier film is a component that enables the effective performance of the final packaging film. Lists of polymers used to. manufacture common barrier, bulk, tie layer, or sealant films have been provided in the following paragraphs The specific action of each barrier material has been described. Different subtypes of the bulk layer plastics, such as PE, which are used to construct multilayer structures, have been listed.

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