CA2086481A1 - Hermetic seal for trayed product - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A sealed tray system is disclosed for hermetically packaging products such as meat. The system includes a tray for holding the product, the tray preferably being a laminate of a rigid interior layer of, e.g., a thermoplastic foam and an exterior layer of a liquid-impervious material such as polyethylene or a liquid- and gas-impervious material such as polyvinylidene chloride. An overwrap or sealing film is sealed to the exterior layer forming a leakproof package which improves the shelf-life and enhances the aesthetic appeal of the packaged product.
3/920326.2/SPECFLDRR

Description

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HERMETIC SEAL FOR TRAYED PRODUCT

BACKGROUND OF ~E INVE~T~ON
This invention relates to a sealed tray system provid-ing a her~etic enclosure which is a liquid-tight container or a liquid-tight and air-tight container for packaging products, preferably foad praducts such as~meats. The present invention also pertains to a method of packaging a product in the sealed tray system.

Læminates of various types of thermQplastic synthetic resinous layers have been widely used in the pacXaging and container industry. Containers and packaging have bee~ made from multiple layers includins ~as-impermeable layers or films of barrier material, adhesive layers a~d layers of rigid mate-rial. ~

~ s the rigid material,~ high impact foamed polystyrene has found wide accepta~ce Vaxious~thermoplasti~ resin ~ateri-als such as those described in U.S. Patent Nos. 4,332,858 and 4,558,09~ have ~een known to possess excellent impact resis-tance and heat resistance. Other suita~le foamed or un~oamed materials, such as the rigid polyvinyl chlorihe (PVC) sheet as disclosed in U.S. Patent No. 3,743,218, have been used to form rigid layers based on their e~cellent mechanical properties.
However, such ri~id materials t~pically are sufficiently pQ-rous so as to have a high degree of gas transmission. Thus, in applicatio~ requiring a hermetic seal such as food packag-ing, the riyid material is, on its foad-cQntact side, lami~at-ed with a flexi~le plastic layer or film of a gas-impervious material to provide a barrier against undesirable gas permea-tion into the package.

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"Barrier" is a term of art used in the plastics indus-try to refer to plastics that are a barrier to gas permeation, usually oxygen permeation. Some oxygen will still come through the flexib~e plastic film, but the oxygen transmission will be extremely low for those films characterized as good oxygen barriers~ Typical flexible plastic films that are known as good oxygen barriers are those made of polyvinylidene chloride resin, ethylene vinyl alcohol resin, or nylon resin.
Virtually all plastic ~lexible films are a good barrier to liquids. Thus, to avoid confusion with the conventional use in the plastics industry of the word barrier, when it is in-tended to reer to a barrier to li~uid, the term "liquid-tight" or "liquid-impermeable" or "liquid impervious" will be used.

As the protective barrier film, sheets made from gas-impermeable polyvinylidene chloride (commonly known as saran which, in the U.S., is not a trademar~ but has become generic) have been preferred. U.S. Patent Nos. 3,458,392, 3,654,069 and 4,335,181 disclose exemplary multi-layer systems of rigi~
layers laminate~ to plastic film.

One type of laminate commonly used in food packaging is made of a layer of saran or another barrier plastic materi-al sandwiched between two layers o rigid polystyrene. U.S.
Patent Nos. 3,748,218 and 4,659,785 disclose packaging lami-nates wherein an intermediate layer is centrally located be-tween two or more layers of rigid material.

Another known t~pe of laminate used as a container includes an outer (extericr) rigid layer and an inner linteri-or) barrier layer which faces the product in the container.
U.S. Patent Nos. 3,793,135, 3,798,103, 4,376,570, 4,111,349 and 4,832,775 describe formed packaging or container laminates wherein a barrier film ~orming the interior surface exposed to contact by food or other contents is backed by an underlying riyid substrate.

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~ ther known packaging systems utilize the barrier film as a lid. For example, U.S. Patent NosO 3,328,196 and 4,055,672 describe packaging systems in which an impervious lid may be seal~d to the edge or lip of a tray or container to envelope the product.

Lamination of a flexible film to a rigid material is known, and can be ac~omplished with standard adhesives. S~ch lamination is disclosed in many of the patents mentioned above. The disclosures of all of these patents are incorporat-ed herein by reference. On the other hand, known packages having the barrier layer on the inside of the package are undesirably susceptible to wicking of liquids and moisture from the environment externally of the package, which can exacerbate spoilage or contamination, resulting in decreased product shelf-life as well as an unpleasing aesthetic appear-ance.

Furthermore, when overwrap or fllm~type lids are used to enclose the contents of conventional con ainers made of foamed polystyrene absent any laminated layer of barrier film, an excellent seal hermetically enclosing the tray and product contained therein is dif:ficult to obtain. The overwrap or lid does not seal well to the tray, which consists of-the rigid foamed layer, such as a foamed polystyrene. Conventional packages wherein an overwrap film is sealed to itself are prone to leakage, e.g., of meat juices (purge), and allow entry of air leading to loss of freshness and spoilage of the packaged product. Moreover, in typical package systems having a rigid lid and adhesive sealant inside the rim, it is neces-sary for sealing that the product be below the rim so that the lid may be sealed in place.

OB~ECTS AND SUFM~RY OF T ~

~ n object of the in~ention is to provide a package or container tray sys~em which overcomes the above-mentioned disadvantages of the known systems.
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., .~.. : . , ;, Another object of this invention is to provide a tray system including a tray having an exterior fluid-impermeable layer and a rigid support layer laminated to the fluid-imperme-able layer, and an impervious film or overwrap sealed to the layer whereby the contents of the tray are enclosed in a liq-uid~-tight, and preferably also a gas-tight, manner.

An additional object of the present invention is to provide a tray laminate of an outer barrier having excellent durability as well as impermeability and an inner layer of a rigid material having desirable mechanical characteristics.

A further object of the invention is to provide a sealed tray system which may be used effectively to package a product while providing an aesthetically pleasing appearance.

By the present invention, an advantageous tray system is obtained which includes a layer of a flexible plastic film which is liquid-impervious and preferably is also a barrier layer, said flexible plastic film forming the outer or exteri-or surface or bottom layer of the tray and which aIso includes an inner or interior layer of -rigid material, whereby an overwrap of flexible fluid-impermea~le film can be sealed to the bottom barrier layer to form an e~fective seal. -By defini-tion, it is intended by "fluid-impermeable`' or "fluid-impervi-ous" to mean that the flexible film is always impermeable to liquid, and may also be impermeable~to gas. When it is also impermeable to gas, then it is a barrier film, such as one made rom polyvinylidene chloride, ethylene vinyl alcohol copolymer, or nylon, as mentioned above.

~ dditionally, by means of the laminated tray of the present invention, an absorptive pad in the tray interior may be provided whereby liquids, such as blood from a meat product lying on the tray, may be advantayeously inhibited from leak-ing from the package, whiIe a durable exterior fluid-imperme-able layer is provided effectively to prolong shelf-life and freshness of the packaged product.
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Thus, the tray of the invention allows for the use o~
an air-permeable flexible film layer which is liquid-tight whereby a tray is obtained which breathes while also prevent-ing substantial leakage o~ llguids from the tray package. A
sealed tray which is liquid-tight but air-permeable is desir-able in packaging some products, such as poultry. A typical such flexible film is the heat-shrinkable film disclosed in U.S. Patent 4,617,241, issued October 14, 1986 to Walter B.
Mueller, and this film is sold commercially by Cryovac under the Sales Code SSD-310, and also in an anti fog version under the Sales Code SSD-350. Such a film, but in a non-shrinX
version, may also be employed.

Thereore, the present invention provides a sealed tray system for packaging a product, comprising (a) a product;
Ib~ a tray for holding said product, said tray having a top and a bottom, and said tray including ~i) at least one interi-or layer including a rigid layer, said rigid layer defining .the tray top and (ii) a fluid-.impervious exterior layer lami-nated to .said at least one interior layer said fluid-impervi-ous layer defining the tray bottom; and (c) a fluid-impervious sealing film for forming:a fluid-tight enclosure of the prod-uct, the sealing film being sealed to said exterior layer, whereby said pxoduct ic dispo~ed between said fluid-impervious sealing film and said tray top.

The present invention also provides a method of packag-ing a product in a sealed tray system, comprising: ~a) placing a product on top of a tray, said tray comprising (i) at least one interior layer including a rigid layer, said rigid layer forming the tray top and (ii) a fluid-impervious exterior layer laminated to said at least one interior layer, the exte-rior layer forming the bottom of the tray; and (b) forming a fluid-tight seal around the product by overwrapping the prod-uct with a fluid-impervious sealing film and sealing the seal-ing f ilm to the exterior layer.

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These and other objects and advantages of the inven-tion will become apparent from the foll3wing detailed descrip-tion of the preferred embQdiments.

BRIEF DESCRIPTION 0~ THE DRAWINGS

Fig. la shows a side view in cross-section of a tray system accoxding to one embodiment of the invention, wherein a sealing film is sealed to the exterior fluid-impermeable layer to form a dual-layer sealO

Fig. lb shows a bottom view o~ the tray system embodi-ment shown in Fig. la.

Figs. 2a th~ough 2e show an alternative embodiment of a tray system, wherein a fluid-impermeable quadruple layer is formed. Fig. 2a ill~strates the tray with produ~t and the sealing film is positioned over this~prior to being sealed to the tray. In Fig~ 2b, edges of the sealing film are about to be sealed to the exterlor fluid impermeable layer of the bot-tom of the tray forming a tube about the tray of product.
Fig. 2c illustrates the tray system after two opposing por-tions of the sealing film having been sealed to the exterior fluid impermeable layer of the tray and before the~other two opposing portions of the sealing film have been sealed to the sealing film. Fig~ 2d is a cross-section o~ 2c.

Fig. 2e shows a bottom view of the fluid impermeable quadruple-layer tray system embodiment of Figs. 2c and 2d, after the other two opposing seali~g film portions have been sealed to the sealing film on the bottom of the tray.

DESCRIPTION OF PREFERRED EMBO~IME~TS

The sealed tray system of the invention advantageously comprises a product, a tray for holding said product, and a fluid-impervious sealing film for forming a product enclo-sure. The tray has a top and bottom and the tray inc~udes ~a~
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., ; , : .: - . : , : . : . : , at least one interior layer including a rigid layer, said ri~id layer defining the tray top, and (b) a fluîd~-impermeable exterior layer laminated to the at least one interior layer, said fluid-impermeable exterior layer defining the tray bot-tom. The sealing film is sealed to the exterior layer, where-by said product is disposed between said fluid-impermeable sealing film and said tray top. In the preferred embodiment, the exterior layer is impermeable to gases as well as liq-ui~s. This depends on the product being packaged. For packag-ing poultry, the exterior layer and the sealing film should both be liquid-impermeable but gas-permeable. For packaging fresh red meat, on the other hand, both should be liquid-imper-meable and gas-impermeable.

In use, a product may be packaged by a method compris-ing placing a product on top of a tray comprising at least one interior layer including a rigid layer which forms the tray top and a fluid-tight exterior layer laminated to at least one interior layer forming the tray bottom. Then is formed a fluid-tight seal around the product by overwrapping the prod-uct with a fluid-impervious film and sealin~ the film ~o the exterior layer.

In one preerred embodiment of the sealed tray system shown in Figs. la and lb, the tray 1 is a two-layer laminate.
The system includes a tray 1 formed from a laminate of a rigid interior layer lA and an exterior layer lB on the tray bottom that is a barrier to oxygen as well as being li~uid-im-permeable. The system also includes a fluid-impervious seal-ing film 2 for overwrapping a product 3, such as meat.

~ s shown in Fig. lb, all of the edges 2~, 2B of overwrap sealing film 2 are sealed to the exterior layer lB at a suitable point inside the perimeter lC of the tray bottom.
The film 2 thus overlaps portions of the exterior barrier layer lB, forming a dual-fluid-impermeable tray system. Film 2 forms one of the duo and exterior lB forms the other.

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It is not illustrated, ~ut it is understood that the film 2 may be sealed so that the entire bottom of the tray is covered by the film, therehy providing a dual fluid-imperme able layer across the entire tray bottom. Alternatively, a portion of the surface area of the exterior layer lB may re-main uncovered by the film 2. When employing an air-permeable liquid-tight layer lB, the ilm edges 2A, 2B are preferably sealed to leave a suita~le area o~ the exterior layer uncov~
ered providing suf~icient breathability for the product 3.

In the quadruple fluid-impermeable embodiment depicted in Figs. 2a through 2e, the film 2 is irst positioned over the tray l containing product 3 as shown in Fig. 2a. ~hen, edges 2A of sealing film 2 are brou~ht toward each other to form a tube about the tray as shown in Fig. 2b. Then, essen-tially simultaneously, edges 2A are seal~d to the exterior lB
of the tray l in region 2C as the sealing film 2 is made snug and taut about the tray l as shown in Figs. 2c and 2d ! except region 2C on the exterior lB of the tray l cannot be seen in Figs. 2c and 2d, but can be seen on the bottom view of tray l in Fig. 2e). After the sealing ~ edges 2A are sealed to the exteriQr layer lB as~ shown in Figs. 2c and 2d, sealin~
ilm 2 is then sealed to itself as shown in Fig. 2e. Thus, the entire tray l and product 3 may be advanta~eously enclosed by the film 2, formlng a ~uadruple-fluid-impermeable suxface on the bottom of the packaged tray by means of t~.e overlapping film 2 and the exterior layer lB.

According to one method of rnaking the embodiment shown in Figs. 2a through 2e, a piece of film 2 of a suitable si7e is placed on top of the tray l and product 3 where tray l is holding product 3, and then the film 2 is wrapped around the product and tray. Two opposing film edges 2A are heat-sealed to the exterior layer lB at center seal area 2C, thereby encir-cli~g the tray 1 in a tube of the film 2 as shown in Figs. 2b, 2c, and 2d. Then, the other two opposing film edges 2B ti.e., the open ends of the film t~e) are brought around the under-side of the tray l and are heat-sealed to the film 2 surface 3/920326.2/SPECF1DR

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already sealed to the exterior layer lB to form the packaged product as shown in Fig. 2e.

In alternative em~odiments of the tray element 1, a plurality of interior layers may be laminated to the extexior fluid-impermeable layer lB, with at least one of the interior layers being formed from a rigid material lA. For example, the interior layers may include an interior barrler layer sandwiched between rigid foam layers. Optionally, on the innermost interior layer which faces the packaged product there may be a suitable absorptive material (not shown in the drawings) to absorb liquids from the product 3.

The dimensions of the tray 1 are selected to suit the product 3 to be packaged, as known in the art. For example, for a large family-size package of poultry, a tray measuring 10" x 16" may be used. Similarly, the thicknes~es of the layers are selected depending on the materials used for thP
layers and the end use.

A suitable rigid material~ for example a fo~m such as of polystyrene, may be~used as a rigid interior layer. In o~e embodiment of the two-layer tray for poultry packaging, the rigid interior layer preferably contains a polyethylene poly-mer, such as a linèar or non-linear polyethylene having a density below about 0.95 g/cm3, so the tray breathes.

Any suitable liquid-tight flexible plastic material or liquid-tight and air-tight flexible plastic material may be used to form the fluid-impermea~le exterior layer, such as a polymer of polyvinylidene chloride (PVDC~ or hydrolyzed ethylene vinylacetate (EVOH). Hydrolyzed ethylene vinyl ace-tate copolymer is also known as ethylene vinyl alcohol copolymer. In one embodiment, the fluid-impermeable exterior layer is impervious to liquids. The fluid-impervious layer helps prevent leakage of liquids rom the package while pre-venting entry of air from the surrounding~ into the sealed package.
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In another embodiment for packaging products such as poultry, the fluid-impermeable exterior layer is liquid-tight but air-permeable, to allow the package to breathe while pre-venting leakage of liquids. Preferably, the liquid-impervious and air-permeable layer of this embodiment is made of a poly-ethylene polymer such as a polyethylene polymer having a low density below about 0.95 g/cm3 or a linear polyethylene polymer having a low density about about 0.95 g/cm3 ~ or blends thereof.

The tray component 1 of the system is formed by lami-nating the interior layer(s) lA to the exterior layer lB using conventional laminating equipment and techniques. The layers of the tray are laminated together using means known in the art.

In preferred embodiments, the overwrap film 2 is a fluid-tight material which is heat-sealable to itself as well as the barrier layer lB. Preferably, particularly for poultry packaging, the sealing film or overwrap 2 is a multi-ply coextruded polyolefin film having stretch and shrink capabili-ties, such as heat-sealable SSD-310 or SSD-350 anti-fog film manu~actured by W. R. Grace & Co.-Conn., Cryovac Division.
Alternatively, particularly for fresh red meat packaging a barrier-coated substrate may be used as the overwrap, such as a substrate of linear or non-linear polyethylene polymer hav-ing a low density below about 0.95 g/cm3 with an oxygen baxrier layer of, e.g., polyvinylidene chloride (PVDC) or hydrolyzed ethylene vinylacetate (EVOH) thereon.

The product 3 to be packaged, for example a food arti-cle such as fresh or frozen meat, is placed on the top side of tray 1. The product may extend above the rim of the tray, to provide the packaged product with a pleasing full-product appearance.

To form the sealed enclosure, the film overwrap 2 may be brought over the product 3 lying on the tray 1, down and 3/920326.2/SPECFLDR

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around to the bottom of the tray. Any suitable type o~ film overwrapping machine, such as the so-called elevator or in-line types, may be used to overwrap the product 3 with the sealing film 2. The film 2 is then sealed to the exterior layer lB on the tray bott~m and optionally to itself, depend-ing on how many fluid-impermeable layers it is desired to have on the tray bottom. The overwrap film 2 may be sealed ~round the tray bottom at any suitable locatlon so long as an effec-tive seal is formed on the tray bottom which completely enclos es the perimeter lC of the tray (see, e.g., Figs. lb and 2b).

The edges 2A, 2B of the overwrap film 2 may be sealed at a suitable location inside the perimeter lC of the tray bottom as shown in Fig. lb. ~lternati~ely, as shown e.g. in Figs. 2a through 2e, the overwrap film edges 2A, 2B may be sealed to enclose the tray completely in the overwrap, thereby providing a fluid-impermeable multi-ply which protects the package bottom against wear and provides an excellent seal.
It is not illustrated in Fig. 2e, but it is understood that the film 2 could be large enough so that the ed~es 2B could touch each other or overlap, as the edges 2A are shown overlap~
ping.

- Suitable means known in the art may be used to seal the overwrap film 2 to the tray's exterior barrier layer lB, such as PVC sealing machinery manufactured by Packa~ing Machin-ery Corp, or OSSID Corp., or 3069D and 3069F Sealer-Coolers manufactured by the Cryovac Division of W.R. Grace & Co.-Conn.

For example, using a 3069D or 3069F Sealer-Cooler, sealing may be effected by placing trays of food, with the overwrap film 2 on top and around but not sealed to the tray, on a thin Teflon~R) or fiberglass conveyor belt and passlng the trays through the Sealer-Cooler at a speed of about 52 feet per minute. While the trays are on the underlying convey-or belt, an overlying pressure means is conveyed at the same speed as the conveyor belt SQ as to apply vertical pressure to the top of the trays.
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The overlying pressure means may be an overhead convey-or belt made of a series of foam rubber pads encased i~ pock-ets of belting material, to provide a soft pressure surface lying on top of the trays which gently applies pressure to maintain optimal contact between the trays and the underlying belt. Other suitable overlying pressure means may be used, such as one or more pressure rollers having a soft surface Means known in the art are provided to adjust the pressure applied by the overlying pressure means to the overwrapped trays transported on the underlying belt to suit the specific packaged product. For example, an inflatable bladder may be used adjustably to apply pressure to the interi-or side of an overhead conveyor belt, thus adjusting the pres-sure applied by the ex~erior side of the overhead belt to the packaged product traveling underneath on the underlying convey-or belt. Other known pressure-adjusting devices, such as hydraulic cylinders or adjustable springs, may be used to adjust the pressure applied to the product by .he overlying pressure means, so that sufficient contact is maintained be-tween the package ~ottom and the underlying belt without damag-ing the product.

In the Sealer-Cooler, the underlying con~eyor belt transports the overwrapped trays over a plate heated to a temperature appropriate for the type of sealing film used, e.g., about 250QF (121C) to 300F ~149~) for SSD film, then over a cooled plate to set the seal hetween the exterior layer and sealing film. The cooled plate may be a baffled plate through which a~out lf2 gallon per minute of cold tap water is circulated to effect even heat transfer over the surface of the plate.

By means of the above-described Sealer-Cooler, a her-metic seal between the barrier layer and overwrap film can be effected without damage during transport.

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~ dditionally, by means of the present invention, a more durable and fluid-tight seal may be advantageously achieved in comparison with conventional seals wherein overwrap film is sealed to itself xather than the bottom of a tray.

Also, an overwrap was tried on a tray, but with no food product in the tray. It is understood this could have been done with food in the tray. A commercially available foamed polystyrene tray covered with a barrier material, avail-able from the Formpac Unit of Cryovac, was usedO SSD-310 was sealed to the tray bottom by ovexwrapping the tray with SSD-310, and then passing this through a 3069F Sealer-Coo~er on a bottom polytetrailuoroethylene belt. The belt with the tray passed over a heat plate with a surface temperature of 25aF
(121C). Pressure was applied to the top with a~ overhead soft belt consisting of a series of foam rubber pads encased in belt matexial. This overheat belt is adjustable vertic~lly to vary the amount of pressure to the top of the tray. Next, the tray on the bottom belt was passPd over a plate cooled by circulating 0.5 gallon of cold tap water per minute through it. The seal between the SSD~ ~il~ and the barrier layer of the tray was cooled and set s it passed over the cooler plate. Both belt speeds were ~2 ~eetlminute. This was then repeated with SSD 350.

~ lthough the invention has been described with reer-ence to preferred embodiments, the invention is not limited thereto. Rather, the scope of the invention is defined by the appended claims.

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Claims (11)

1. A sealed tray system for packaging a product, comprising:
(a) a product;
(b) a tray for holding said product said tray having a top and a bottom, and said tray including (i) at least one interior layer including a rigid layer, said rigid layer defin-ing the tray top and (ii) a fluid-impervious exterior layer laminated to said at least one interior layer said fluid-imper-vious exterior layer defining the tray bottom; and (c) a fluid-impervious sealing film for forming a fluid-tight enclosure of the product, the sealing film being sealed to said exterior layer, whereby said product is dis-posed between said fluid-impervious sealing film and said tray top.

2. A sealed tray system as recited in claim 1, wherein said rigid layer contains polystyrene foam or a polyethylene polymer.

3. A sealed tray system as recited in claim 1, wherein said exterior layer contains polyvinylidene chloride polymer, hydrolyzed ethylene-vinylacetate polymer, or nylon polymer.

4. A sealed tray system as reciter in claim 1, wherein said sealing film is heat-shrinkable.

5. A sealed tray system as recited in claim 1, wherein said sealing film is sealed to itself and to said exterior layer.

6. A sealed tray system as reciter in claim 1, wherein said exterior layer is impermeable to air as well as liquids.

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7. A method of packaging a product in a sealed tray system, comprising:

(a) placing a product on top of a tray, said tray comprising (i) at least one interior layer including a rigid layer, said rigid layer forming the tray top and (ii) a fluid-impervious exterior layer laminated to said at least one inte-rior layer, the exterior layer forming the bottom of the tray;
and (b) forming a fluid-tight seal around the product by overwrapping the product with a fluid-impervious sealing film and sealing the sealing film to the exterior layer.

8. The method of claim 7, further including sealing the sealing film to itself.

9. A method of packaging a product as recited in claim 7, wherein all of the edges of the sealing film are sealed to the exterior layer.

10. A method of packaging a product as recited in claim 7, wherein two opposing portions of the sealing film are sealed to the exterior layer and the remaining portions of the sealing film are sealed to a surface of the sealing film.

11. A method of packaging a product as recited in claim 7, wherein the exterior layer is impermeable to air as well as liquids.

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