The shelf life, both refrigerated and at room temperature, of many food products can be greatly extended if the food product is in a substantially oxygen free environment. One way of achieving the oxygen free environment is to simply evacuate the package to a very high level of vacuum. However, when flexible packaging is involved the use of a high vacuum can distort, compact, and crush the enclosed product as the vacuum is applied. For example, bakery products can readily be squeezed or compressed so they lose their appeal. Shredded cheeses can be compacted to such an extent that they have to be re-shredded, Swiss cheese with its holes can be distorted, and chopped meat products can be undesirably pressed. Accordingly, it is one object of the present invention to provide an oxygen free package of flexible packaging material wherein the contents of the package are not crushed or compressed by pressure differential.
Gas flush packaging has been used as an alternative to high vacuum packaging and quite often nitrogen is the inert gas of choice. When a vacuum chamber is used to evacuate and then gas flush a package it has heretofore been found necessary to clamp the package or bag mouth around a nozzle. A typical example of this is shown in U.S. Pat. No. 3,714,754 which issued on Feb. 6, 1973 to E. L. Holcombe et al. In FIGS. 2 and 8 of the Holcombe patent is shown a bag whose mouth is clamped around a nozzle within a vacuum chamber and this type of nozzle and clamp can be used to inject an inert gas into a bag after the air within the bag has been first evacuated. A similar device is shown in Canadian Patent No. 934,714 which issued Oct. 2, 1973 having as inventors, Philip L. Reid and John T. Roberts. In this latter patent a clamped bag mouth is shown and also the use of a flexible diaphragm is shown in FIG. 2 where the diaphragm under the influence of pressure difference presses against the bagged product and helps force air out of the bag. Also, U.S. Pat. No. 4,457,122 which issued July 3, 1984 to J. Harold Atkins et al also the use of a diaphragm to press air from a bag enclosing a product within a vacuum chamber. In order to evacuate a heat shrinkable bag within a chamber, a partially evacuated bag has been clamped, the chamber pressure lowered so that the bag balloons away from the product, the bag pierced as it balloons, and then the bag resealed by heat sealing. A patent disclosing some of these features is United Kingdom Patent No. 2,094,745B which has a priority date of Mar. 18, 1981 and is assigned to W. R. Grace & Co. Also, U.S. Pat. No. 4,182,095 which issued Jan. 8, 1980 to Timothy T. Day and Canadian Patent No. 1,060,402 which issued Aug. 14, 1979 show somewhat related processes. Still another patent which shows the evacuation of a bag within a chamber is U.S. Pat. No. 4,164,111 which issued on Aug. 14, 1979 to Pietro Di Bernardo.
A method of arranging a plurality of vacuum chambers for a commercial, relatively high speed process is shown in U.S. Pat. No. 3,958,391 which issued on May 25, 1976 to Eitaro Kujubu and whose disclosure is incorporated herein by reference. Similar vacuum chamber machines which are sometimes termed as "rotary vacuum chamber machines" are also disclosed in U.S. Pat. No. 4,580,393 which issued Apr. 8, 1986 to Takao Furukawa and U.S. Pat. No. 4,586,328 which issued on May 6, 1986 to Takao Takai et al and the contents of these two patents are incorporated herein by reference.
It is a general object of the present invention to provide an improvement in the foregoing vacuum chamber machines and evacuation processes by providing a method and apparatus for making a gas flushed package. These and other objects will become readily apparent to those skilled in the art from the following summary of the invention, description of the drawings, and detailed description.