Advanced Thermoforming, 2nd Edition

Chapter 23Analysis of Thermoforming Films

Written in cooperation with Manfred Reichert, Remshalden, Germany

23.1 GENERAL ANALYSIS OF THERMOFORMING FILMS¹

When packages (e.g., cups and bowls) are manufactured for the food industry on thermoform fill‐and‐sealing machines, the consumer expects consistently good quality packaging. So consistent machinability of the films used for the packaging on these machines must be guaranteed.

Currently, a multitude of plastic films exist. Depending on the application and the product, the best suited film is selected. For example, for the manufacture of yogurt cups, mostly PS (polystyrene) and PP (polypropylene) films are used. Delicate products that have a longer shelf life need to be packaged in multilayer films with a barrier layer that protects them mainly from ambient oxygen. Some examples are coffee cream, condensed milk, soups, convenience food, and baby food.

For consistent quality the film to be used must be specified exactly for each product. Thus the films must be first subjected to certain tests. Many tests exist, typically to obtain some basic facts:

• Free shrinkage measurements
• Thickness measurements (thickness of the complete film as well as the thicknesses of the individual layers)
• Tensile strength
• Surface texture appearance (gloss factor)
• Flame coloration (rapid test in order to determine the material)

Yet all test methods have only limited significance. Often thermoformers utilize films from different manufacturers that nominally ...