AU672776B2 - Hermetic seal for trayed product - Google Patents

Description

I~.k l~ i~iP--LII~ IYLj EPrm~l~l)l L-l

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): W. R. Grace Co.-Conn.

ADDRESS FOR SERVICE: o o oo r

D

r r r D o DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Hermetic seal for trayed product The following statement is a full description of this invention, including the best method of performing it known to me/us:r r r r o u r r NI 0 f- 4 BACKGROUND OF THE INVENTION This invention relates to a sealed tray system providing a hermetic enclosure which is a liquid-tight container or a liquid-tight and air-tight container for packaging products, preferably food products such as meats. The present invention also pertains to a method of packaging a product in the sealed tray system.

Laminates of various types of thermoplastic synthetic resinous layers have been widely used in the packaging and .:.container industry. Containers and packaging have been made from multiple layers including gas-impermeable layers or films if of barrier material, adhesive layers and layers of rigid material. i As the rigid material, high impact foamed polystyrene has found wide acceptance. Various thermoplastic resin materials such as those described in U.S. Patent Nos. 4,332,858 and H 4,558,099 have been known to possess excellent impact resistance and beat resistance. Other suitable foamed or unfoamed .of: materials, such as the rigid polyvinyl chloride (PVC) sheet as Sdisclosed in U.S. Patent No. 3,748,218, have been used to form rigid layers based on their excellent mechanical properties.

However, such rigid materials typically are sufficiently po- S rous so as to have a high degree of gas transmission. Thuz, in applications requiring a hermetic seal such as food packaging, the rigid material is, on its food-contact side, laminated with a flexible plastic layer or film of a gas-impervious material to provide a barrier against undesirable gas permeation into the package. i 3/920326.2/OLDFLDR la

I

.ro 7. A method of packaging a product in a sealed tray I"Barrier" is a term of art used in the plastics industry to refer to plastics that are a barrier to gas permeation, usually oxygen permeation. Some oxygen will still come through the flexible 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 flexible films are a good barrier to liquids. Thus, to avoid confusion with the conventional use i in the plastics industry of the word barrier,, when it is intended to refer to a barrier to liquid, the term "liquid- j tight" or "liquid-impermeable" or "liquid impervious" will be used.

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

a p a One type of laminate commonly used in food packaging is made of a layer of saran or another barrier plastic material sandwiched between two layers of rigid polystyrene. U.S.

Patent Nos. 3,748,218 and 4,659,785 disclose packaging laminates wherein an intermediate layer is centrally located between two or more layers of rigid material.

Another known type of laminate used as a container includes an outer (exterior) rigid layer and an inner (interior) barrier layer which faces the product in the container.

U.S. Patent Nos. 3,793,135, 3,798,103, 4,076,570, 4,111,349 and 4,832,775 describe formed packaging or container laminates wherein a barrier film forming the interior surface exposed to contact by food or other contents is backed by an underlying rigid substrate.

3/920326.2/OLDFLDR

IT!

1: Other known packaging systems utilize the barrier film as a lid. For example, U.S. Patent Nos. 3,328,196 and 4,055,672 describe packaging systems in which an impervious lid may be sealed 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 accomplished with standard adhesives. Such lamination is disclosed in many of the patents mentioned above. The disclosures of all of these patents are incorporated herein by reference. On the other hand, known packages i 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 appearance. j Furthermore, when overwrap or film-type lids are used "o to enclose the contents of conventional containers made of foamed polystyrene absent any laminated layer of barrier film, an excellent seal hermetically enclosing the tray and product 4 contained therein is difficult 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 i prone to leakage, 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 necessary for sealing that the product be below the rim so that the S° lid may be sealed in place.

OBJECTS AND SUMMARY OF THE INVENTIO1 An object of the invention is to provide a package or container tray system which ces the above-mentioned I disadvantages of the known systems.

A! 3/920326.2/OLDFLDR T NT I p r 4 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 exterior surface or bottom layer of the tray and which also includes an inner or interior layer of rigid iiaterial, whereby an overwrap of flexible fluid-impermeable film can be sealed to the bottom barrier layer to form an effective seal. By definition, it is intended by "fluid-impermeable" or "fluid-impervi- I 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 c:i t made from polyvinylidene chloride, ethylene vinyl alcohol copolymer, or nylon, as mentioned above.

Additionally, 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 advantageously inhibited from leaking from the package, while a durable exterior fluid-impermeable layer is provided effectively to prolong shelf-life and S* freshness of the packaged product.

i i. Thus, the tray of the invention allows for the use of an air-permeable flexible film layer which is liquid-tight whereby a tray is obtained which breathes while also preventing substantial leakage of liquids from the tray package. A sealed tray which is liquid-tight but air-permeable is desirable 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-shrink version, may also be employed.

Therefore, the present invention provides a sealed tray system for packaging a product, comprising a product; a tray for holding said product, said tray having a top and a bottom, and said tray including at least one interior layer including a rigid layer, said rigid layer defining the tray top and (ii) a fluid-impervious exterior layer laminated to said at least one interior layer said fluid-impervi- S ous layer defining the tray bottom; and 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 disposed between said fluid-impervious sealing film and said tray top.

The present invention also provides a method of packag- S ing a product in a sealed tray system, comprising: placing S a product on top of a tray, said tray comprising 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 exterior layer forming the bottom of the tray; and 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.

3/920326.2/OLDFLDR i These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. la shows a side view in cross-section of a tray system according to one embodiment of the invention, wherein a sealing film is sealed to the exterior fluid-impermeable layer to form a dual-layer seal.

Fig. Ib shows a bottom view of the tray system embodiment shown in Fig. la.

Figs. 2a through 2e show an alternative embodiment of a tray system, wherein a fluid-impermeable quadruple layer is formed. Fig. 2a illustrates the tray with product 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 exterior fluid impermeable layer of the bottom of the tray forming a tube about the tray of product.

Fig. 2c illustrates the tray system after two opposing portions 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 of 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 sealing film portions have been sealed to the sealing film on the bottom of the tray.

DESCRIPTION OF PREFERRED EMBODIMENTS |j' The sealed tray system of the invention advantageously comprises a product, a tray for holding said product, and a I fluid-impervious sealing film for forming a product enclosure. The tray has a top and bottom and the tray includes (a) 3/920326.2/OLDFLDR 6

T

at least one interior layer including a rigid layer, said rigid layer defining the tray top, and a fluid-impermeable exterior layer laminated to the at least one interior layer, said fluid-impermeable exterior layer defining the tray bottom. The sealing film is sealed to the exterior layer, whereby 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 liquids. This depends on the product being packaged. For packaging 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-impermeable and gas-impermeable.

In use, a product may be packaged by a method comprising 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 S fluid-tight seal around the product by overwrapping the product with a fluid-impervious film and sealing the film to the exterior layer.

4 In one preferred embodiment the sealed tray system shown in Figs. la and Ib, the tray 1 is a two-layer laminate.

The system includes a tray I formed from a laminate of a S rigid interior layer 1A and an exterior layer lB on the tray bottom that is a barrier to oxygen as well as being liquid-im- 0 permeable. The system also includes a fluid-impervious sealing film 2 for overwrapping a product 3, such as meat.

As shown in Fig. Ib, all of the edges 2A, 2B of overwrap sealing film 2 are sealed to the exterior layer 1B at a suitable point inside the perimeter 1C of the tray bottom.

The film 2 thus overlaps portions of the exterior barrier layer IB, forming a dual-fluid-impermeable tray system. Film 2 forms one of the duo and exterior 1B forms the other.

3/920326.2/OLDFLDR 7

I.K-

4 1 It is not illustrated, but it is understood that the film 2 may be sealed so that the entire bottom of the tray is covered by the film, thereby providing a dual fluid-impermeable layer across the entire tray bottom. Alternatively, a portion of the surface area of the exterior layer 1B may remain uncovered by the film 2. When employing an air-permeable liquid-tight layer 1B, the film edges 2A, 2B are preferably sealed to leave a suitable area of the exterior layer uncovered providing sufficient breathability for the product 3.

In the quadruple fluid-impermeable embodiment depicted i in Figs. 2a through 2e, the film 2 is first positioned over the tray 1 containing product 3 as shown in Fig. 2a. Then, edges 2A of sealing film 2 are brought toward each other to form a tube about the tray as shown in Fig. 2b. Then, essentially simultaneously, edges 2A are sealed to the exterior 1B of the tray 1 in region 2C as the sealing film 2 is made snug and taut about the tray 1 as shown in Figs. 2c and 2d (except region 2C on the exterior 1B of the tray 1 cannot be seen in Figs. 2c and 2d, but can be seen on the bottom view of tray 1 in Fig. 2e). After the sealing film edges 2A are sealed to the exterior layer 1B as shown in Figs. 2c and 2d, sealing film 2 is then sealed to itself as shown in Fig. 2e. Thus, the entire tray 1 and product 3 may be advantageously enclosed by the film 2, forming a quadruple-fluid-impermeable surface on the bottom of the packaged tray by means of the overlapping film 2 and the exterior layer lB.

According to one method of making the embodiment shown in Figs. 2a through 2e, a piece of film 2 of a suitable size is placed on top of the tray 1 and product 3 where tray 1 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 1B at center seal area 2C, thereby encircling 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 the open ends of the film tube) are brought around the underside of the tray 1 and are heat-sealed to the film 2 surface J 3/920326.2/OLDFLDR already sealed to the exterior layer 1B to form the packaged product as shown in Fig. 2e.

In alternative embodiments of the tray element 1, a plurality of interior layers may be laminated to the exterior fluid-impermeable layer 1B, with at least one of the interior layers being formed from a rigid material 1A. For example, the interior layers may include an interior barrier 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 x 16" may be used. Similarly, the thicknesses of the layers are selected depending on the materials used for the layers and the end use.

A suitable rigid material, for example a foam such as of polystyrene, may be used as a rigid interior layer. In one embodiment of the two-layer tray for poultry packaging, the rigid interior layer preferably contains a polyethylene polymer, such as a linear or non-linear polyethylene having a density below about 0.95 g/cm 3 so the tray breathes.

Any suitable liquid-tight flexible plastic material or liquid-tight and air-tight flexible plastic material may be used to formt the fluid-impermeable exterior layer, such as a polymer of polyvinylidene chloride (PVDC) or hydrolyzed ethylene vinylacetate (EVOH). Hydrolyzed ethylene vinyl acetate 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 from the package while preventing entry of air from the surroundings into the sealed package.

3/920326.2/OLDFLDR 9 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 preventing leakage of liquids. Preferably, the liquid-impervious and air-permeable layer of this embodiment is made of a polyethylene polymer such as a polyethylene polymer having a low density below about 0.95 g/cm 3 or a linear polyethylene polymer having a low density about about 0.95 g/cm 3 or blends thereof.

The tray component 1 of the system is formed by laminating the interior layer(s) 1A to the exterior layer 1B 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 1B. Preferably, particularly for poultry packaging, the sealing film or overwrap 2 is a multi-ply coextruded polyolefin film having stretch and shrink capabilities, such as heat-sealable SSD-310 or SSD-350 anti-fog film manufactured 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 having a low density below about 0.95 g/cm 3 with an oxygen barrier layer of, polyvinylidene chloride (PVDC) or hydrolyzed ethylene vinylacetate (EVOH) thereon.

The product 3 to be packaged, for example a food article 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/OLDFLDR I 1 Y r1 1 *r around to the bottom of the tray. Any suitable type of film overwrapping machine, such as the so-called elevator or inline types, may be used to overwrap the product 3 with the sealing film 2. The film 2 is then sealed to the exterior layer 1B on the tray bottom and optionally to itself, depending on how many fluid-impermeable layers it is desired to have on the tray bottom. The overwrap film 2 may be sealed around the tray bottom at any suitable location so long as an effective seal is formed on the tray bottom which completely encloses the perimeter 1C of the tray (see, Figs. lb and 2b).

The edges 2A, 2B of the overwrap film 2 may be sealed at a suitable location inside the perimeter 1C of the tray bottom as shown in Fig. lb. Alternatively, 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 edges 2B could touch each other or overlap, as the edges 2A are shown overlapping.

Suitable means known in the art may be used to seal the overwrap film 2 to the tray's exterior barrier layer 1B, such as PVC sealing machinery manufactured by Packaging Machinery Corp, or OSSID Corp., or 3069D and 3069F Sealer-Coolers manufactured by the Cryovac Division of W.R. Grace Co.-Conn.

0 For example, using a 3069D or 3069F Sealer-Cooler, o4 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 passing the trays through the Sealer-Cooler at a speed of about 52 feet per minute. While the trays are on the underlying conveyor belt, an overlying pressure 5<ans is conveyed at the same speed as the conveyor belt so as to apply vertical pressure to the top of the trays.

3/920326.2/OLDFLDR 11

F-"

The overlying pressure means may be an overhead conveyor belt made of a series of foam rubber pads encased in pockets 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 I the specific packaged product. For example, an inflatable bladder may be used adjustably to apply pressure to the interior side of an overhead conveyor belt, thus adjusting the pressure applied by the exterior side of the overhead belt to the packaged product traveling underneath on the underlying conveyor 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 the overlying pressure means, so that sufficient contact is maintained bet tween the package bottom and the underlying belt without damaging the product.

4I In the Sealer-Cooler, the underlying conveyor belt transports the overwrapped trays over a plate heated to a temperature appropriate for the type of sealing film used, about 250 0 F (121 0 C) to 300 0 F (149C) for SSD film, then over a cooled plate to set the seal between the exterior layer and sealing film. The cooled plate may be a baffled plate a o through which about 1/2 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 hermetic seal between the barrier layer and overwrap film can be effected without damage during transport.

3/920326.2/OLDFLDR 12 13 Additionally, 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 rather 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, available from the Formpac Unit of Cryovac, was used. SSD-310 was sealed to the tray bottom by overwrapping the tray with SSD- St w310, and then passing this through a 3069F Sealer-Cooler on a a bottom polytetrafluoroethylene belt. The belt with the tray t itt passed over a heat plate with a surface temperature of 250aF (121 0 Pressure was applied to the top with an overhead i soft belt consisting of a series of foam rubber pads encased in belt material. This overheat belt is adjustable vertically to vary the amount of pressure to the top of the tray. Next, the tray on the bottom belt was passed over a plate cooled by circulating 0.5 gallon of cold tap water per minute through it. The seal between the SSD film and the barrier layer of the tray was cooled and set as it passed over the cooler o° .plate. Both belt speeds were 52 feet/minute. This was then o repeated with SSD-350.

Although the invention has been described with reference to preferred embodiments, the invention is not limited thereto. Rather, the scope of the invention is defined by the appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any oIer integer or group of integers.

of any other integer or group of integers.

-v RA4/ ro s- .I

Claims (13)

1. A sealed tray system for packaging a product, comprising: a product; a tray for holding said product, said tray having a top and a bottom, and said tray including 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 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 recited 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. S6. A sealed tray system as recited in claim 1, wherein said exterior layer is impermeable to air as well as liquids.

I 3/920326.2/OLDFLDR 14 p.-

7. A method of packaging a product in a sealed tray system, comprising: placing a product on top of a tray, said tray comprising 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 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. i

11. A method of packaging a product as recited in claim 7, wherein the exterior layer is impermeable to air as well as liquids. I j h 3/920326.2/OLDFLDR P:\OPERPHH35180-93.247 319196 16

12. A sealed tray system substantially as hereinbefore described with reference to the drawings and/or Examples.

13. A packaging method substantially as hereinbefore described with reference to the drawings and/or Examples. DATED this 3rd day of September, 1996. -'no 4 0 0 00 *0 So 0 '4 0 4 to go S 0 4 o C 0 0 0 *400 00 0* 0* .00. o 0 o 04 40 00 0 0 0 0 W. R. GRACE CO.-CONN. By its Patent Attorneys DAVIES COLLISON CAVE r 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, 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 improv-.; T shelf-life and enhances the aesthetic appeal of the pa:o,' ''product. 4 *9 94 I *a 9 o r b o 3/920326.2/OLDFLDR LL i. i Li~ L