| 摘要 |
Between the two housings (1, 18), and below and parallel to the film (F), there is provided a frame (7) having openings (8) with shapes and dimensions suitably greater than the shapes and dimensions in plan view of the underlying trays (V) to be packaged, supported by any means such that, during the closure of the housings (1, 18), this frame (7) interacts with sealing means and contributes to the formation of a main chamber (29) delimited by the upper edge of the tray and by the film above this edge, which is initially connected to the inner chambers (19, 2, 102) of the two housings (1, 18), to enable the air to be removed from these chambers and to form the desired level of vacuum therein, while, in the next step, said main chamber (29) is isolated from the inner chambers of the two housings, so that the process gases for preserving the product can be injected directly into this main chamber, while a corresponding quantity of atmospheric air is directed into said inner chambers of the housings (1, 18) to counterbalance the pressures on the opposite faces of the film which, when the process gases have been fed in, is welded to the edge of the tray and is cut outside this edge by means associated with the upper housing, the whole arrangement being such that, at the end of the cycle, when the housings (1, 18) are opened, no large quantities of process gases are dispersed into the atmosphere, as would be the case in the prior art. |
