Advanced Thermoforming, 2nd Edition

Chapter 22Optimizing a Thermoforming Process for Packaging

Written in cooperation with Rudi Salmang, Terneuzen, The Netherlands

Thermoforming is achieved by heating and stretching a polymeric film/sheet until it duplicates the surface of a mold. Stretching may be achieved by means of a mechanical plug or by means of air pressure or vacuum, or combinations thereof. Evaluating the performance of different resins in thermoforming processes has been very difficult and sometimes subjective due to the nature of the process itself; that is, isolating the results and main effect of each step of the process is very difficult.

In a plug‐assisted thermoforming process, typically used in producing deep draw articles, the film is stretched initially by a plug, which may provide up to 90% of the total volume deformation, and then air pressure (or vacuum) generates the last 10% or more of the required deformation, until the film touches the mold walls and cools.

The stretching of the film begins with the plug contacting the film and pushing it into the mold cavity. The film “sticks” to the plug in the initial place of contact while the remaining noncontacting film is stretched. It should be noted that plug temperature has a great influence on this process, and although plug temperature is not typically measured, it must reach a level of equilibrium to obtain consistency in the final articles.

Cooling of the film occurs as a result of increasing the surface area and reducing the thickness ...