| 摘要 |
<p>Packages wrapped in impermeable film bags from within which residual air is evacuated are prepd. with an ancillary vacuum chamber in which a heating pressure differential can be maintained while the bag is being evacuated. The bag can thus be maintained in a distended state, so that the bag wall temp. can be adjusted by circulation of hot air within the chamber at an intermediate pressure before being applied to the surface of the contents by internal evacuation followed by repressurisation of the surrounding chamber. Used for mfr. of close-fitting packages, esp. if made from heat shrinkable films such as "Barrier Bag" (RTM), specifically a 3-ply laminate of films of ethylene-vinyl acetate, polyvinylidene chloride and irradiated ethylene vinylacetate, or of autofusible films made from layers of nylon (polyamide) and ethylene vinyl acetate. The bag temp. is adjusted and most of the thermal contraction can occur before the bag makes general contact with the pack contents, which tend to act as a heat sink and to inhibit sliding of the bag walls. Allows relatively high proportions of potential thermal contraction to be utilised.</p> |
