| 摘要 |
1,217,457. Packaging. SAFEWAY STORES Inc. 4 June, 1969 [3 March, 1969], No. 28226/69. Heading B8C. A method of packaging a product between first and second sheets, 12, 31 of heat sealable material comprises moving the first sheet 12 along a path in steps, heating it at stations b, c, pressure forming it into a series of cups at station d, filling each cup at station d with product from a loader 22, forming slits in the sheet 12 between the cups at station g, sealing the second sheet 31 to the first sheet 12 around but not entirely around, the periphery of each cup at station h, evacuating each package and then filling it with a preservative gas such as carbon dioxide and/or nitrogen and a tracer gas such as octafluorcyclobutane and completely sealing the package at station i, subjecting each package to a pressure different from its internal pressure and sensing for the escape of gas from the package at station k and marking defective packages at station l. The sheet 12 is formed into cups by an endless chain of trays 17 and three gaskets 26, 27, 28 which are individually coupled to a vacuum supply; and lesser vacuum levels are applied to the gaskets 26, 27 prior to application of vacuum to the basket 28. The apparatus at station i for evacuating the package and filling it with preservative gas comprises an element 39 which presses the upper sheet 31 downwardly, a conduit 43 in communication with the package and a valve 44 for selectively supplying vacuum or preservative gas. The apparatus at station k for detecting a leaky package comprises a chamber 48 enclosing the package and evacuated through a passage 52. A gas detecting probe 53 or a tube leading to gas sensing equipment generates an electric signal across conductors 54 and a delay circuit 56 delays the signal for an interval substantially equal to the stepping time of the packages. Alternatively the preservative gas may be forced out of a leaky package by a resilient porous pad on the end of a piston, Figs. 4, 5 (not shown). The marking station l includes an electromagnetic device 57 connected to the delay circuit 56 and a marking member 62 located above the package. Apparatus for rejecting the defective packages may be provided. The packages are separated by a knife 66 and suction is applied at station r to withdraw the packages from the trays 17 and place them on a conveyer 72. A plurality of packages in an overwrapping container may be tested for leakage of the preservative gas by a method similar to that described for a single package. |
