Patent Publication Number: US-6213294-B1

Title: Packaging system for preserving perishable items

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation-in-part of applicant&#39;s patent applications U.S. Ser. No. 09/342,844, filed on Jun. 29, 1999, U.S. Pat. No. 6,112,890, which in turn was a continuation-in-part of U.S. Ser. No. 09/182,754, filed on Oct. 29, 1998, now U.S. Pat. No. 6,023,915. 
    
    
     TECHNICAL FIELD 
     A packaging system for preserving perishable items which comprises a tray made from open-cell foam, an oxygen absorber, a barrier bag enclosing said tray, and a pressure valve connected to said barrier bag. 
     BACKGROUND OF THE INVENTION 
     In U.S. Pat. No. 5,698,250 of Gary R. DelDuca et al., which is assigned to Tenneco Packaging Inc., a “modified atmospheric package” was claimed. This package contained “ . . . an oxygen scavenger activated with an activating agent . . . . ” According to the patentees, the oxygen scavenger is necessary because “Low-level oxygen systems relying upon evacuation techniques to diminish oxygen levels suffer from several disadvantages . . . the evacuation techniques render it difficult to remove any oxygen within a previously wrapped package such as an overwrapped meat tray . . . . The trapped oxygen raises the residual oxygen level in the package and can also cause billowing and subsequent damage to the package during evacuation” (see lines 3-15 of column 2 of this patent). The entire disclosure of this patent is hereby incorporated by reference into this specification. Furthermore, each of the prior art references cited during the prosecution of this patent are also hereby incorporated by reference into this specification. 
     It is an object of this invention to provide an improved packaging system for preserving perishable items. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention, there is provided a packaging system for preserving a perishable item comprised of a tray comprised of open-cell foam, an oxygen absorber, a bag enclosing said tray, and a pressure relief valve operatively connected to such bag. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood by reference to the following detailed description thereof, when read in conjunction with the attached drawings, wherein like reference numerals refer to like elements, and wherein: 
     FIG. 1 is a sectional view of one preferred packaging system of the invention; 
     FIGS. 2A,  2 B,  2 C,  2 D, and  2 E schematically illustrate one means of preparing and using the packaging system of FIG. 1; 
     FIG. 3 is a sectional view of a portion of the tray used in the system of FIG. 1; 
     FIG. 4 is a sectional view of one preferred barrier bag which may be used in the packaging system of FIG. 1; and 
     FIG. 5 is a graph illustrating the oxygen concentrations in a specified packaging material over time with two systems, one of which uses a conventional foam tray, and the other of which uses the open-cell foam tray of this invention; 
     FIG. 6 is a sectional view of another preferred packaging system of the invention; 
     FIG. 7 illustrates a process for making a packaging system in which the barrier bag expands during the process; 
     FIG. 8 illustrates a process for limiting the extent to which the barrier bag can expand during the process; and 
     FIG. 9 is a graph illustrating how the use of granulated carbon dioxide affects the preferred process. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the first part of this specification, and by reference to FIGS. 1-5, one preferred packaging system of the invention will be described. 
     In the second part of this specification, and by reference to FIG. 6, another preferred packaging system of the invention will be described. 
     In the third part of this specification, and by reference to FIGS. 7-10, certain preferred processing steps which may be used in making the packaging systems of this invention will be described. 
     One Preferred Packaging System of the Invention. 
     FIG. 1 is a sectional view of one preferred packaging system  10  which is comprised of a tray  12  which, in the preferred embodiment depicted, includes flanges  14  around the perimeter of such tray  12 . A perishable good or goods  15  is disposed within tray  12 . 
     The perishable goods which may advantageously be protected by the packaging system  10  of this invention include oxygen-sensitive food such as, e.g., red meat (veal, beef, pork, etc.), pasta, cooked food, and the like. Alternatively, one may preserve perishable non-food items such as photographic film, computer components, inorganic materials susceptible to oxidation, etc. 
     In the preferred embodiment depicted in FIG. 1, a skin layer  19  is contiguous with and attached to the bottom surface of the tray and preferably up the side of the tray to the flanges  14 . 
     In the preferred embodiment depicted in FIG. 1, a gas permeable film material  18 , which may include slits or perforations  20 , covers the perishable goods  15 . This skin layer  19  is illustrated more clearly in FIG.  3 . 
     Referring again to FIG. 1, it will be seen that the tray  12  which is overwrapped with gas permeable film material  18  is disposed within a barrier bag  22  which surrounds the tray  12  and which preferably is made of a substantially impermeable material. This barrier bag is attached to a one-way valve  24 , which will be described in greater detail elsewhere in this specification. 
     From about 10 to about 150 grams of solid carbon dioxide  16 , which may be in the form a flakes, one or more pellets, an irregular shape, etc., are disposed outside of tray  12  but within barrier bag  22 . 
     The barrier bag  22 , prior to the time it is sealed, contains an opening  23 . 
     FIG. 2A is a sectional view of tray  12  attached to skin layer  19 . The tray  12  is comprised of at least 90 weight percent of foam material. In one preferred embodiment, the foam material is open-cell foam which contains at least about 20 volume percent of open cells. 
     As is known to those skilled in the art, an open-cell cellular plastic is a cellular plastic in which there is a substantial number of interconnected cells; see, e.g., A.S.T.M. D883. Reference also made by had to U.S. Pat. No. 5,798,409 (open cell foams of polystyrene and polyurethane), U.S. Pat. No. 5,784,845 (open cell foam material made from alkenyl aromatic polymer material), U.S. Pat. No. 5,646,193 (rigid open cell foam material), U.S. Pat. Nos. 5,557,816, 5,475,890, 5,434,024 (open cell foam material of polyvinyl chloride, or polyisocyanate, or polyphenol, or polypropylene), U.S. Pat. Nos. 5,348,587, 5,343,109, 5,239,723, 5,139,477 (polyethylene open cell foam material), U.S. Pat. Nos. 4,739,522, 4,395,342 (open cell foam material made from cellulose acetate, or phenol-formaldehyde, or cellular rubber), etc. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     It is preferred that the open cell foam material be made from a resin selected from the group consisting of polyethylene, polyvinyl chloride, polyacrylonitrile (such as the “BAREX” resin sold by the British Petrolem/Amoco company), poly(ethylene terephthalate), polystyrene, rubber-modified polystyrene, ethylenepolystyrene, interpolymers (such as “INDEX” interpolymers sold by Dow Chemical Corporation of Midland Mich.), polypropylene, polyurethane, polyisocyanurate, epoxy, urea formadehyde, rubber latex, silicone, fluropolymer or copolymers thereof or blends thereof, and in general any other suitable resin, resin mixture, or any foamable composition which can be made with an open cell structure such as, e.g., matrials made using a silane peroxide catalyst system (sold by the Sentinel Foam company or Hyanis, Mass.). 
     As is well known to those skilled in the art, one may vary the degree to which a foam material contains open-cell structure by the process taught by applicant in his 1977 article entitled “Controlling the Properties of Extruded Polystyrene Foam.” This article was presented at the Proceedings of the International Conference on Polymer Processing, which was held at the Massachusetts Institute of Technology, Cambridge, Mass., in August 1977. This proceedings were published in 1977 in a book edited by Nam P. Suh and Nak-Ho Sung entitled “Science and Technology of Polymer Processing” (The MIT Press, Cambridge, Mass., 1977); and a description of means to control the concentration of open cells appeared on page  410  of this book. In particular, the correlation between the concentration of open cells produced in the foam and the melt temperature of the resin/blowing agent mixture used, was discussed. 
     Referring again to FIG. 2A, the tray  12  is comprised of foam material which contains at least about 20 volume percent of open cells. In one preferred embodiment, the foam material contains at least about 30 volume percent of open cells. It is even more preferred that the foam material contain from about 30 to about 90 volume percent of open cells and, even more preferably, from about 45 to about 90 volume percent of open cells. The extent to which a foam material contains open-cell foam may be determined by A.S.T.M. Standard Test D2856-94, “Test Method for Open-Cell Content of Rigid Cellular Plastics by the Air Pycnometer.” 
     The open-cells in the foam contain a gas phase with gases which are substantially identical to the gases in ambient air. Thus, the open-cells generally contain a gas phase comprised of from about 19 to about 22 volume percent of oxygen (depending upon the altituide) and from about 78 to about 81 volume percent of nitrogen. In general, such gas phase contains from about 20.5 to about 21 volume percent of oxygen and from about 79 to about 79.5 volume percent of nitrogen. 
     FIGS. 2B,  2 C,  2 D,  2 E,  2 F, and  2 G illustrate how use the tray depicted in FIG. 2A to make the structure depicted in FIG. 1, For the sake of simplicity of representation, much of the detailed description of the tray contained in FIG. 2A has been omitted from FIGS. 2B,  2 C, 2 D,  2 E,  2 F, and  2 G. 
     After the tray  12  has been fabricated (see FIG.  2 A), the good or goods  15  are placed in the tray and then wrapped either manually or automatically with a gas permeable film material  18 , or other suitable means, to holds the goods  15  in place, thereby forming wrapped tray  30  (see FIG.  2 C). 
     The open-cell foam material which comprises tray  12  have as an average cell diameter of from about 0.001 to about 0.020 inches and, more preferably, from about 0.002 to about 0.008 inches. In preferred embodiment, the cell diameter of such cells is from about 0.003 to about 0.007 inches. 
     The average cell diameter of a foam may be determined in accordance with the procedure described in applicant&#39;s U.S. Pat. Nos. 3,953,739 and 4,329,052, the disclosures of which are hereby incorporated by reference into this specification. One may also use one or more of the methods disclosed in other United States patents, such as, e.g., U.S. Pat. Nos. 5,912,729, 5,817,704, 5,810,964, 5,798,065, 5,795,680, 5,790,926, 5,786,401, 5,770,634, 5,7532,717, 5,912,729, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     Referring again to FIG. 1A, the tray  12  has walls with a thickness  21  of from about 0.025 to about 0.350 inches and, preferably, from about 0.040 to about 0.15 inches. In one embodiment, the thickness  21  is from about 0.04 to about 0.1 inches. The thickness of the sidewalls  23  and  25  of tray  12  may be equal to or less than the thickness of the bottom surface  27  of tray  12 . In one embodiment, the thickness of sidewalls  23  and  25  is from  25  to about 50 percent of the thickness of the bottom surface  27 . 
     In one preferred embodiment, illustrated in FIG. 2A, the bottom surface  27  of tray  12  forms an interior angle ( 29  or  31 ) between sidewalls  23  or  25  of from about 10 to about 85 degrees and, preferably, from about 25 to about 50 degrees. Angles  29  and  31  may be the same or different. 
     Referring again to FIG. 2A, the tray  12  preferably has a density of from about 0.5 to about 50 pounds per cubic foot and, preferably from about 1 to about 10 pounds per cubic foot, and more preferably from about 1.5 to about 6 pounds per cubic foot. It is even more preferred that the density be from about 2.0 to about 5.0 pounds per cubic foot. In one embodiment, the density of tray  12  is from about 2 to about 3 pounds per cubic foot. 
     Referring again to FIG. 2A, it will be seen that tray  12  is attached to a skin  19 ; the means for attaching this skin  19  will be discussed elsewhere in this specification. The thickness of skin  19  is preferably from about 0.0005 to about 0.01 inches and, more preferably, from about 0.002 to about 0.005 inches. 
     In FIGS. 2B through 2G, tray  12  is depicted in various combination with other elements. However, for the sake of simplicity of representation, many of the details of tray  12  depicted in FIG. 2A have been omitted in these latter Figures. 
     As is illustrated in FIG. 2B, the perishable goods  15  are placed within tray  12 , either manually or automatically. In one embodiment, not illustrated, an absorbent pad is placed between the goods  15  and the bottom of the tray in order to absorb excess juices exuded from the goods  15 . 
     Referring to FIG. 2C, a gas permeable film material  18  adapted to pass both oxygen and carbon dioxide is wrapped around the entire tray  12 . The film material may be adhered to the tray because of its “cling properties,” and/or it may be heat-treated to cause it to adhere to the tray; in each either event, the film  18  is contiguous with the sides and the bottom of tray  12  and encloses the perishable goods  15 . Thus, as is disclosed in U.S. Pat. No. 5,698,250, the film  18  may contain additives which allow the film to cling to itself. This film generally has a thickness ranging from about 0.5 mil to about 1.5 mils. 
     These gas-permeable films are well known to those skilled in the art and are described, e.g., in U.S. Pat. Nos. 5,888,597, 5,885,699, 5,852,152 (ethylene/vinyl acetate film and ethylene/acrylic acid film), U.S. Pat. Nos. 5,840,807, 5,839,593, 5,804,401, 5,780,085, 5,759,712, 4,056,639, 4,011,348, 3,867,558, 3,857,981, 3,728,135, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     In one preferred embodiment, film  18  is a polyvinyl chloride film supplied by the Borden Packaging and Industrial Products company of North Andover, Mass. as “Resinite.” This film  18  has an oxygen permeability of from about 1100 to about 1400 cubic centimeters per 100 square inches per 24 hours, as measured by the Mocon Controls Oxtran  100  machine measured at 23 degrees Centigrade. The film has a carbon dioxide permeability of from about 12,400 to about 13,4000 cubic centimeters per 100 square inches per 24 hours as measured by a Linde Cell at 23 degrees Centigrade and 1 atmosphere pressure. 
     In the preferred embodiment depicted in FIG. 2C, film  18  is comprised of perforations  33 ,  35 ,  37 , and  39 . In this embodiment, it is preferred that each of such perforations have a maximum cross-sectional dimensional of less than about 0.05 inches. When such perforations are present, it is preferred that from about 1 to about 4 of them occur per square inch of surface. 
     Referring to FIG. 2D, the wrapped tray  30  (see FIG. 2C) is wrapped in an oxygen barrier bag  22  which, in the preferred embodiment depicted, is preferably shaped similarly to a typical bag with an open end into which to insert the wrapped tray. Such oxygen barrier bags are well known to those skilled in the art and are described, e.g., in U.S. Pat. Nos. 5,862,947, 5,855,626, 5,811,027, 5,799,463, 5,798,055, 5,780,085, 5,753,182, 5,711,978, 5,700,554, 5,667,827, 5,583,047, 5,573,801, 5,573,797, 5,529,833, 5,350,622, 5,346,644, 5,227,255, 5,203,138, 5,195,305, 4,857,326, 4,605,175, 4,082,829, 3,953,557, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     In one preferred embodiment, the barrier bag described in column 4 of U.S. Pat. No. 5,698,250 may be used. This bag is commercially available as product number 325C44-EX861B from the PrintPak, Inc. company of Atlanta, Ga. 
     In another preferred embodiment, the barrier bag used is a biaxially oriented nylon film coated with an oxygen barrier coating (such as polyvinylidene chloride) and having a thickness of from about 0.00072 to about 0.00112 inches. Such a bag is commercially available from the Allied Signal Corporation (of New Jersey) as “Capron Emblem 1530” or “Capron Emblem 2530.” 
     Regardless of the particular barrier bag used, it is preferred that it have an oxygen permeability of less than 5 cubic centimeters per 100 square inches per 24 hours, as measured by a suitable gas permeability measuring device, such as the aforementioned Mocon Controls Oxtran 100 machine; measurements are taken under ambient conditions. This test method is well know, being described in A.S.T.M. Standard Test D-1434 “Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting.” Reference may also be had to U.S. Pat. Nos. 5,913,445, 5,882,518, 5,769,262, 5,684,768, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     Referring again to FIG. 2D, the barrier bag  22  is preferably operably connected to a pressure relief valve  24 . The pressure relief valve  24  is adapted to open and allow gas disposed within barrier bag  22  when the pressure within barrier bag  22  is from about 0.05 to about 1.0 pounds per square inch gauge and, more preferably, from about 0.1 to about 0.2 pounds per square inch gauge. In an even more preferred embodiment, the valve  24  is adapted to allow gas disposed within barrier bag  22  to vent to the outside when the pressure within such bag is from about 0.12 to about 0.14 pounds per square inch gauge. 
     The valve  24 , after it is has opened to vent gas from the barrier bag  22 , closes when the internal pressure drops within the range of from about 0.01 to about 0.04 pounds per square inch gauge. 
     Pressure sensitive gas valves for releasing gas from a sealed flexible pouch, such as valve  24 , are well known to those skilled in the art. See, for example U.S. Pat. Nos. 5,059,036, 5,419,638, 5,048,846, 4,653,661, 4,690,667, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     In one preferred embodiment, the pressure sensitive gas valve is sold by the Plitek, Inc. company of 681 Chase Avenue, Elk Grove Village, Ill. 60007; see, e.g., a publication by Plitek (entitled “Plitek Pressure Relief Valve”) which was published on Jul. 8, 1991. A copy of this publication is in the file history of U.S. Pat. No. 5,419,638 of Mark D. Jamison. 
     The valve  24  may be incorporated into the gas barrier bag  24  by conventional means such as, e.g., by means of the “CCL Model 230 Valve Applicator labelling system” which is sold by CCL Industries of 3070 Mainway, Units 16-19, Burlington, Ontario L7M3X1. This system is adapted to be secured to the side of a vertical form-fill and seal machine to apply self-adhesive valve labels to the plastic web on the forming tube section of the machine just prior to the seal and cut station. 
     Referring again to FIGS. 2D and 2E. after the sealed tray  30  is disposed within the barrier bag  22 , solid carbon dioxide  16  is charged into the barrier bag  22  prior to the time the bag is sealed. In general, from about 10 to about 150 grams of solid carbon dioxide is charged to barrier bag  22 . For a description of one use of such solid carbon dioxide in a barrier bag without a valve  24 , reference may be had to U.S. Pat. Nos. 5,731,023 and 5,737,905. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification. It should be noted that the amount of solid carbon dioxide used in the processes of these patents is substantially less than the amount of carbon dioxide generally used in applicant&#39;s process. In general, a sufficient amount of carbon dioxide is used to generate at least about 1.5 liters of gaseous carbon dioxide per kilogram of perishable goods  15 ; see, e.g., an article by N. Penney and R. G. Bell entitled “Effect of Residual Oxygen on the Colour, Odour and Taste of Carbon-Dioxide-Packaged Beef, Lamb and Pork . . . ” published in Meat Science 33 (1993) at pages 245-252. 
     Referring to FIG. 2E, after the solid carbon dioxide is disposed within barrier bag  22 , the bag is heat sealed by conventional means; see, e.g., U.S. Pat. Nos. 5,908,676, 5,799,463, 5,759,653, 5,332,121, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     In one embodiment, after the barrier bag  22  has been heat sealed, a vacuum is applied through valve  24  to remove air disposed within barrier bag  22 . 
     FIG. 3 is a sectional view, taken through line  3 — 3  of FIG. 1, of tray  12 . Referring to FIG. 3, and to the preferred embodiment depicted therein, it will be seen that tray  12  is comprised of open cell foam  50  to which is attached a skin layer  19  which is preferably comprised of a multiplicity of through-holes  52 ,  54 ,  56 ,  58 ,  60 , and  62 . These through holes have a maximum dimension (such as a maximum diameter) of from about 5 to about 40 mils and generally extend from the top surface  64  of the skin layer  19  to the top surface  66  of the open cell foam layer. 
     In another embodiment, not shown, no such through holes exist in the skin layer  19 . In either embodiment, however, the skin layer has a thickness  68  of from about 0.0005 to about 0.01 inches, and, preferably, from about 0.002 to about 0.005 inches. 
     As will be apparent to those skilled in the art, the structure depicted in FIG. 3 is a laminated structure with one or more skin layers  19  and/or  68 . Means for producing such a laminated structure are well known. Thus, by way of illustration, in the process of Example 4 of U.S. Pat. No. 4,510,031, a 0.2 millimeter thick sheet of an ethylene/propylene block copolymer having a density of 0.91 was heat laminated to both surfaces of a foamed sheet. Thus, by way of further illustration, laminates made by bonding a skin layer to a foam core are described in U.S. Pat. Nos. 5,882,776, 5,876,813, 3,633,459, and the like. Thus, by way of even further illustration, U.S. Pat. No. 4,098,941 discloses a process in which a skin layer is formed in situ on a foam core by heat treatment. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     The skin layers  19  and/or  68  may be adhered to the foam layer  50  by adhesive means, by heat lamination means, by coextrusion, by mechanical means, and by other conventional means known to those skilled in the art. The skin layer  19  and/or the skin layer  68  may consist essentially of unfoamed plastic (such as polystyrene, or rubber-modified polystyrene, or polyethylene or polypropylene, mixtures thereof, and the like), paper, and the like. In another embodiment, the skin layer  19  and/or the skin layer  68  may consist essentially of either open cell foam and/or closed cell foam. 
     Without wishing to be bound by any particular theory, applicant believes that the laminated structure possesses substantially more flexural strength than the unlaminated foam core and, in many cases, reaches or exceeds the structural strength of an unlaminated closed cell foam core, such as the ones described in U.S. Pat. No. 5,698,250. 
     Extrusion Process for Making the Foam Tray  12   
     Processes for making closed cell polystyrene foam are well known to those skilled in the art. See, e.g., the following United States patents, each of which named the applicant as an inventor: U.S. Pat. Nos. 5,356,944, 5,286,429, 4,747,983, 4,329,052, 4,022,858, 3,953,739, 3,879,507, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     Processes for modifying closed-cell polystyrene foam processes to make open cell foam are also well known to those skilled in the art. See, e.g., the article by applicant entitled “Controlling the Properties of Extruded Polystyrene Foam” given at the Proceedings of the International Conference on Polymer Processing held at The Massachusetts Institute of Technology, Cambridge, Mass. in August of 1977 which was published in a book entitled “Science and Technology of Polymer Processing,” edited by Nam P. Suh and Nak-Ho Sung (The MIT Press, Cambridge, Mass, 1977). Reference may also be had to U.S. Pat. Nos. 5,798,409, 5,784,845, 5,646,193, 5,557,896, 5,475,890, 5,434,024, 5,343,109, 5,239,723, 5,139,477, 4,739,522, 4,395,342, 4,259,373, 4,108,600, 4,107,876, 4,082,678, 4,079,170, 3,868,716, 3,844,286, 3,589,592, and the like. The disclosure of each of these United States patents is hereby incorporated by reference into this specification. 
     As is disclosed in these patents, the conventional process for making polystyrene foam, which is described in the aforementioned patents, uses the well documented extrusion process for producing cellular polystyrene foam in which a solution of a volatile blowing agent in molten polymer, formed in an extruder under pressure, is forced through an orifice into an ambient environment of temperature and pressure. The polymer simultaneously expands and cools under conditions that give it enough strength to maintain dimensional stability at the time corresponding to optimum expansion. Stabilization is due to cooling of the polymer phase to a temperature below its glass transition or melting point. Cooling is effected by vaporization of the blowing agent, gas expansion, and heat loss to the environment. 
     The polystyrene foam sheet thus produced is allowed to equilibrate with atmospheric gases for a period of from about 1 to about 5 days, at which time it is heat shaped into a container using conventional thermoforming equipment. 
     FIG. 4 is a schematic view of another system for preserving perishable goods in which a two compartment barrier bag comprised of compartment  102  and compartment  104  communicate with each other via an orifice  106 . A chunk of solid carbon dioxide  108  gradually sublimes causing gas to travel via arrows  110  and  112  and, when pressure has built up, to vent through valve  24 . The system of this FIG. 4 is very similar to the system depicted in FIG. 1, with the exception that it utilizes a two-compartment barrier bag rather than a single compartment barrier bag. 
     FIG. 5 is a graph presenting data generated from the experiments of the Examples described in applicant&#39;s copending patent application Ser. No. 09/342,844. 
     Another Preferred Packaging System of the Invention 
     FIG. 6 shows an packaging system  11  which is substantially identical to the packaging system  10  depicted in FIG. 1 but which differs from packaging system  10  in that it contains oxygen absorber  200 . 
     One may use any of the commercially available oxygen absorbers as oxygen absorber  200 . One preferred oxygen absorber  200  is an iron-based oxygen absorber such as, e.g., the iron-based absorbent described in U.S. Pat. No. 5,928,960. The entire disclosure of this United States patent is hereby incorporated by reference into this specification. 
     Further reference may be had to U.S. Pat. No. 5,262,375, which also discusses oxygen absorber packets. The entire disclosure of this patent is hereby incorporated by reference into this specification. 
     One oxygen absorber packet which may be used in the process of this invention is manufactured by Multiform Dessicants Incorporated of North Tonawanda, N.Y. It is believed that this absorber packet contains iron and silica gel. 
     Other iron-based oxygen absorbers also will work well as oxygen absorber  200 . 
     Referring again to FIG. 6, and in the preferred embodiment depicted therein, the solid carbon dioxide  16  preferably is in particulate form and has a particle size distribution such that at least about 90 weight percent of its particles are sized in the range from about 25 microns to about 1,000 microns and, more preferably, are sized in the range of from about 100 to about 500 microns. In one embodiment, at least about 90 weight percent of the carbon dioxide particles are in the range of from 200 to about 400 microns. 
     In the embodiment depicted in FIG. 6, it is preferred that the barrier bag  22  have an oxygen permeability of less than 10 cubic centimeters per 100 square inches per 24 hours, as measured by suitable gas permeability measuring device. 
     Referring again to FIG. 6, and in the preferred embodiment depicted therein, the tray  12  preferably has a water absorbency of at least about 200 percent. In the test used to determine water absorbency, a tray is weighed under ambient conditions and then immersed in water for a period of thirty minutes. Thereafter, the tray is removed from the water bath and weighed. The ratio of the weight of the “wet tray” to that of the “dry tray” is at least about 2.0/1.0 and, preferably, at least 2.5/1.0. A tray with the desired characteristics is commercially available form Vitembal S. A. of Remoulins, France, as the “Integral” absorbent tray. 
     A Process of Limiting the Expansion the Barrier Bag 
     FIG. 7 illustrates the condition of packaging system  11  (see FIG. 6) after the carbon dioxide  16  has sublimated and is released through valve  24 . Certain components of packaging system  11  have been omitted from FIG. 7 for the sake of simplicity of representation. 
     Referring to FIG. 7, it will be seen that barrier bag  22  has a height  202  which is substantially greater than the height of the barrier bag  22  depicted in FIG.  6 . As will be apparent to those skilled in the art, this occurs because the sublimation of the solid carbon dioxide produces a gaseous phase which increases the pressure within barrier bag  22 . Some of this pressure is vented to atmosphere via valve  24 , but some of the pressure causes barrier bag  22  to increase in volume. If the expansion of barrier bag  22  is unrestrained, and depending upon the concentration of the solid carbon dioxide  16 , the volume enclosed by barrier bag  22  could increase by as much as 1,500 percent. 
     When the packaging system  11  has a large volume, it is difficult to ship efficiently and is more cumbersome to use. 
     FIG. 8 illustrates a process for limiting the increase in volume of the barrier bag  22 . Referring to FIG. 8, it will be seen that the solid carbon dioxide  16  within barrier bag  22  causes sublimate to flow in the direction of arrow  204  through valve  24 . It also causes the barrier bag  22  to expand in volume, but such volume expansion is limited by the presence of constraint  206 . In the particular embodiment depicted, constraint  206  is comprised of opposing walls  208  and  210  which are separated by distance  202 . An orifice  212  disposed within wall  208  is adapted to receive valve  24  and to allow gas passing through valve  24  to exit the constraint  206 . Depending upon the extent of distance  202 , the extent to which the barrier bag  22  will be allowed to expand during sublimation of the solid carbon dioxide  16  can be controlled. 
     One may use any suitable means for controlling the expansion of the volume within barrier bag  22 . In one embodiment, not shown, wall  208  is hingeably attached at point  214  to wall  209  and may be rotated upwardly in the direction of arrow  216  and/or downwardly in the direction of arrow  218 , thereby varying the effective distance  202  between wall  208  and wall  210  at various points along such wall. Other suitable means for controlling the expansion of the volume within barrier bag  22  will be apparent to those skilled in the art. 
     Referring again to FIG. 8, and in the preferred embodiment depicted therein, the packaging device  11  constrained by constraint  206  is disposed within a vacuum chamber  300  comprised of a port  302 . Sublimate exiting constraint  206  through valve  24  then can exit vacuum chamber  300  through valve  304  in the direction of arrow  306 . 
     As will be apparent to those skilled in the art, the presence of a vacuum within vacuum chamber  300  facilitates the removal of oxygen from barrier bag  22 . It is preferred that the vacuum within vacuum chamber  300  be less than 10.0 millimeters of mercury absolute. This will cause the pressure within barrier bag to be less than about 10.0 millimeters of mercury absolute. 
     FIG. 9 is a graph presenting data from an experiment in which various processing parameters were varied. Utilizing a setup such as that disclosed in FIG. 2E, an experiment was conducted in which 53 grams of solid carbon dioxide, in the form of a block, were disposed within a barrier bag  22  with an internal volume of 250 cubic centimeters, and the bag was thereafter immediately heat sealed to isolate its interior volume from ambient conditions. Sublimate was then allowed to escape through valve  24 , and measurements were taken of the oxygen concentration within the barrier bag  22  at various points in time. This system took 60 minutes to reach an oxygen concentration as low as 500 parts per million. 
     The experiment described above was repeated, with the exception that 50 grams of carbon dioxide in particulate form was substituted for the 53 grams of carbon dioxide in block form. The particulate carbon dioxide had a particle size distribution such that at least 95 percent of its particles were within the range of 25 microns to 1,000 microns. Using these conditions, the system took only about 27 minutes to reach an oxygen concentration as low as 500 parts per million. 
     The experiment described above which used particulate carbon dioxide was substantially repeated, but only 49.2 grams of particulate carbon dioxide were used. Furthermore, instead of immediately sealing barrier bag  22  after charging the particulate carbon dioxide to it, the barrier bag was sealed five (5.0) minutes after the carbon dioxide was charged. Using these conditions, million. 
     Thus, it is apparent that, by using particulate carbon dioxide, and by not sealing the barrier bag  22  immediately after charging such carbon dioxide, the efficiency of the system can be increased by at least about 600 percent. Furthermore, it is advantageous, when using this improved process, to also utilize one or more of the improvements described in FIG.  8 . 
     It is to be understood that the aforementioned description is illustrative only and that changes can be made in the apparatus, in the ingredients and their proportions, and in the sequence of combinations and process steps, as well as in other aspects of the invention discussed herein, without departing from the scope of the invention as defined in the following claims.