Advanced Thermoforming, 2nd Edition

Chapter 32Multilayer Films for Thermoforming Applications

Multilayer films are applied when, for example, there is demand for improved product protection, extension of the shelf life of a packaged product, and scarce material usage. For these reasons multilayer films for thermoforming applications must possess the following capabilities:

• High oxygen, gas, water vapor, and aroma barrier
• High product neutrality
• Light protection and UV barrier
• Excellent thermoformability and sealability
• Good mechanic characteristics
• Good printability
• Peelability

Another characteristic concerning applications for convenience food should be temperature resistance. The above‐described requirements are fulfilled through the use of different polymer materials. In order to reduce costs for certain applications, multilayer films can be used but with each layer consisting of the same type of plastic. For the inner layer of the film, recycled material is often used. So‐called double films are used when large film thicknesses or an even distribution of the mechanical characteristics are desired. Double films are assembled from the same basic raw material.

Another application area for the use of multilayer film results when it is necessary to sterilize the packaging material, as is the case in many applications. With form, fill, and seal machines, mainly three sterilization methods are used: treatment with hydrogen peroxide (H₂O₂), container sterilization with heat, and the neutral aseptic system (NAS ...