Thermoforming snap-back

Figure 10.8 Vacuum snap-back thermoforming (reprinted with permission from [1])...

Amorphous materials can be thermoformed with less residual stress than semi-crystalline resins. Retained volume is nearly 100 percent for monolayer COC-LLDPE films with COC content between 15 and 30 weight percent. This result reflects the amorphous nature of COC which is imparted into the films, even at relatively small amount. Less stress means less post-form shrinkage or snap-back, giving the flexible package the appearance of a rigid one. Film structures with high LDPE content tend to have lower retained volume. Formed cavities from other semicrystalline materials, such as nylon and PP, usually suffer some loss in volume. 

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