Shrink flat film process

The source of compression in the replicated network is a volume contraction of the electrochemically deposited material on heating. This is confirmed by thickness measurements of flat films (Fig. 2.22) before and after high temperature processing. Since the film cannot shrink in the lateral direction (without fracturing from the substrate), all compression is taken up by vertical compression. 

The double-bubble process involves the extrusion and blowing of a tube of molten plastic in a downward direction. The tube is then cooled, most often using a water bath, reheated to just below the melt temperature, and reinflated. The reinflation along with the increase in haul-off speed provides biaxial orientation. Typically the next step is annealing to relieve thermal stresses and stabilize the film. The double-bubble process is most often applied to PP film, but is also used with multilayer PP or PE-based films. One of the major advantages is that this process can deliver a high-clarity film with precise shrink characteristics and very uniform flatness. 

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