Meaning
Coextruded plastic structures containing several distinct layers of different polyolefin resins are designed to combine the specific performance advantages of each resin into a single thin web. Using a polyethylene multilayer film allows converters to optimize properties like puncture resistance, sealing temperature, and optical clarity in a single run. These films are produced by combining the output of several extruders through a single feedblock and die.
This approach avoids the need for secondary lamination steps, reducing production costs.
Layer Architecture
Standard commercial films typically utilize three to nine layers to achieve a balance of properties. In a typical polyethylene multilayer film, the outer layer is selected for high heat resistance to prevent sticking to the packaging jaws, while the inner layer is formulated for low-temperature sealing. The core layers often consist of linear low density polyethylene to provide toughness and stretchability.
This specialized architecture ensures that each zone of the film performs its intended function without compromise. Adjusting the thickness ratio of these individual layers during coextrusion allows manufacturers to tune the stiffness of the final product to match specific packaging machinery.
Functional Customization
Barrier resins or recycled materials can be incorporated into the core layers to minimize material costs or prevent oxygen transmission. Incorporating these different polymers into a polyethylene multilayer film requires the use of tie layers to prevent delamination of incompatible resins. These adhesive layers ensure a strong bond between the polar and non-polar polymers.
The resulting structure maintains its integrity even when subjected to severe flexing or deep-draw thermoforming.
Mechanical Performance
Tension and puncture tests demonstrate the superior mechanical properties of these coextruded structures compared to single-layer alternatives. The interface between the coextruded layers acts to arrest micro-cracks, preventing them from propagating through the entire thickness of the film. This behavior allows packaging engineers to down-gauge the film, reducing the amount of plastic used per package while maintaining the necessary load-bearing capacity.
