Plug Assisted Thermoforming of Multilayer Sheet

SPECIAL GUEST POST: Sven Engelmann, Dipl. -Ing. Director of Research & Development, EBB Microparts, Crailsheim, Germany

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

The quality of a thermoformed part depends not only on even material distribution but also on the minimum thickness of the barrier layer. In other words, for the thermoformed part, the complete thickness of the film as well as the thickness of the barrier layer are important.

Multilayer films for forming- filling and sealing (FFS) applications mostly consist of carrier layers, barrier layers, heat sealing layers and adhesive layers.

A common multilayer film with high barrier characteristics against oxygen is PP / EVOH / PP, consisting of polypropylene outer layers, two adhesive layers, and the EVOH barrier layer. Often these films do also have a sealing layer so the thermoformed package can be sealed with a lid film. This sealing layer can also provide reseal properties which allow the package to be resealed after being opened for the first time.

One can imagine that several layers made from different polymers are difficult to thermoform. The different layers do have different forming temperatures and different coefficients of friction. The sealing layer will start to get sticky already at low temperature since that is required for fast cycle times when being processed in the sealing station of the packaging machine.

That means that the plug assist material should be able to cope with this. Otherwise the sealing layer will be scratched apart from the film compound. Hytac WFT or FLXT can prevent this and are therefore good plug assist materials for thermoforming multilayer sheet.

Sven Engelmann has a distinguished career in polymer science and thermoforming technology. Prior to EBB, Sven was a development engineer for thermoforming technology and polymer materials at Illig and the Director of Polymer Technology at Gerhard Schubert GmbH, a leading designer and manufacturer of innovative form/fill/seal technologies.. In addition to his work in the private sector, he is a lecturer at the University of Stuttgart and the Aalen University of Applied Sciences where he teaches “Basics of Thermoforming.” He is the author of numerous articles published in both the US and Europe on thermoforming, polymer processing and injection molding. His recent book, Advanced Thermoforming, can be purchased on Amazon. He can be contacted via s.engelmann@ebb-microparts.de