Method of packaging with shrink film lid

Abstract: A package (11) with improved clarity and a thinner lidstock includes a product support member (12) having a cavity formed therein; a product (10) disposed in the cavity; and an oriented, heat shrinkable lidstock film (14) disposed over the product, and sealed to the product support member. A method of packaging a product includes the steps of providing a product support member having a cavity formed therein, and a flange (16) around the perimeter of the member; placing the product in the cavity formed by the product support member; placing an oriented, heat shrinkable film over the product; sealing the oriented, heat shrinkable film to the flange of the product support member; and cutting at least some of the oriented heat shrinkable film extending beyond the perimeter of the product support member. The lidstock film optionally can be peeled apart after the package has been made, for example to peel an oxygen impermeable portion from a permeable substrate.

Description: The present invention relates to a method of packaging a food product, especially a meat product, in packages having a tray and lidstock, in which the lidstock of the package comprises a barrier shrink film. It is common practice in packaging many goods, including food items, to use a thermoformed tray. The tray provides a cavity into which a food or other product can be placed. In some applications, instead of thermoforming a web, a preformed tray is used. This can be made from a variety of materials; typical is foamed polystyrene. A non-forming web (lidstock), typically a laminate, is fed from a roll across the tray, and covers the product. Sometimes, the non-forming web is sealed to the tray edges to form the finished package. Sometimes the lidstock includes an oxygen barrier layer to provide longer shelf life to the packaged product. To complement the oxygen barrier feature of some lidstocks, and provide a means to adhere the lidstock to the tray, some trays have a film or layer of oxygen barrier material adhered to the interior cavity of the tray. This is done in such a way that the lidstock can be sealed to the oxygen barrier film of the tray. This barrier layer is sometimes supplied by adhering a flexible oxygen barrier film or layer to an e.g. polystyrene foam sheet prior to thermoforming into trays. Alternatively, the oxygen barrier film is adhered to the tray after the tray has been made. US Patents 4,847,148 and 4,935,089 (Schirmer) disclose examples of this. Commercially sold lidstocks suffer from several shortcomings. They tend to have relatively poor optical properties. This means that the aesthetic appearance of the overall package is diminished. Also, these materials are relatively thick, and therefore raise waste disposal problems. Where modified atmosphere is used in the interior of the package, the food article oftens absorbs some of-the gas, resulting in a loose lidstock. A round or oval package containing a bottom portion with one or more compartments and a peel-off lid is disclosed in US-A-5,353,985 and EP-A-0,498,760. It is indicated that uniaxially or biaxially oriented films may be used in the bottom portion or lid. However this does not address difficulties with the aesthetic appearance of the packaging. The inventor has discovered that a trayed package can be made with a shrinkable lidstock, including an oxygen barrier layer. This lidstock provides improved clarity and tightness in the finished package, and a downgauged lidstock which uses less material. The present invention affords a method for packaging meat and other products wherein the aesthetic properties of the package are substantially improved. This result is accomplished while substantially maintaining the overall performance and function of the package in terms of protection of the packaged product. The present invention pertains to a method of packaging a food product comprising: (a) providing a product support member comprising a tray having a flange around the perimeter of the tray; (b) placing the food product on the tray; (c) placing over the product a biaxially oriented, heat shrinkable lidstock film including an oxygen barrier layer, the film having a clarity of at least 50% (ASTM D 1746) and a thickness of less than about 51 µm (2 mils); (d) heat sealing the film to the flange ; and (e) cutting away at least some of the film extending beyond the perimeter of the product support member, and heating such that the heated film shrinks back to the flange and forms a bead thereon. In a preferred embodiment, a package comprises a foamed polymeric tray having a first surface, said surface defining a cavity formed therein for receiving a food product, and a flange disposed around the periphery of the tray; a thermoplastic film liner adhered to the first surface and the flange of the tray, the film liner comprising an oxygen barrier material; a food product disposed in the cavity; and an oriented, heat shrinkable film disposed over the product, and heat sealed to the thermoplastic film liner in the region of the flange of the foamed tray, the oriented, heat shrinkable film forming a bead along the flange, the film comprising outer layers comprising an olefinic polymer, and an intermediate layer comprising an oxygen barrier material. The oriented, heat shrinkable film most preferably does not extend beyond the flange of the foamed tray. The present invention is advantageous in that it offers a package with better optics than conventional packages. It also provides a package with a neatly trimmed lidstock around the perimeter of the package, along the tray flange, by eliminating excess film overhang. The invention uses a lidstock that offers good package tightness during storage. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic cross-sectional view of a package produced according to the present invention, the package having a product therein. FIG. 2 illustrates an enlarged view of a portion of the package illustrated in FIG. 1. FIG. 3 illustrates a schematic plan view of the package illustrated in FIG. 1. FIG. 4 illustrates an alternative embodiment of the present invention, the package having a peelable shrinkable lidstock. DEFINITIONS As used herein, the phrase "product support member" refers to a component of a package on or in which a product is directly or indirectly placed. Meat products are typically supported on a tray-like package component, typically comprising expanded polystyrene sheet material, which may be thermoformed into a tray or other shape, for supporting the meat product. As used herein, the phrase "over the product" refers to the position of a package component which is over the product when the product or tray is in an upright position. As used herein, the phrase "liner" refers to a film, laminate, web, or coating used to line or cover either the interior or exterior surface of a tray or other product support member. If on the interior surface, the liner will typically be in direct contact with the product. "Interior surface" herein is the surface which forms or defines the cavity or space into or onto which the product is placed. As used herein, "perimeter" refers to the outer edge, when viewed in plan view, of the relevant element, e.g. product support member, flange, liner, or oriented heat shrinkable lidstock. As used herein, "EVOH" refers to ethylene vinyl alcohol copolymer. As used herein, the term "oriented" refers to a polymer-containing material which has been stretched at an elevated temperature (the orientation temperature), followed by being "set", while in the stretched configuration, by cooling the material while substantially retaining the stretched dimensions. Upon subsequently heating unrestrained, unannealed, oriented polymer-containing material to its orientation temperature, heat shrinkage results. As used herein, the term "olefinic", "polyolefin" or the like refers to any polymerized olefin, which can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted. More specifically, included in the term are homopolymers of olefins, copolymers of olefins, copolymers of an olefin and a non-olefinic comonomer copolymerizable with the olefin, such as vinyl monomers, modified polymers thereof, and the like. Specific examples include polypropylene homopolymer, polyethylene homopolymer, poly-butene, ethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer (EVA), ethylene/ethyl acrylate copolymer, ethylene/butyl acrylate copolymer, ethylene/methyl acrylate copolymer, ethylene/acrylic acid copolymer, ethylene/methacrylic acid copolymer, modified polyolefin resin, ionomer resin, polymethylpentene, etc. As used herein, the phrase "ethylene/alpha-olefin copolymer" refers to such heterogeneous materials as linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); as well as homogeneous polymers such as TAFMER (TM) ethylene/alpha olefin copolymers supplied by Mitsui Petrochemical Corporation and metallocene-catalyzed polymers such as EXACT (TM) materials supplied by Exxon. These materials generally include copolymers of ethylene with one or more comonomers selected from C 1 to C 10 alpha-olefins such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. LLDPE, as used herein, has a density usually in the range of from about 0.91 grams per cubic centimeter to about 0.94 grams per cubic centimeter. Other ethylene/alpha-olefin copolymers, such as the long chain branched homogeneous ethylene/alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY (TM) resins, are also included as another type of ethylene/alpha-olefin copolymer useful in the present invention. As used herein, the phrase "ionomer resin" refers to a product of an ionic polymerization, i.e., a polymer containing interchain ionic bonding. Preferably, the ionomer comprises at least one member selected from the group consisting of a thermoplastic resin based on metal salt of an alkene/acid copolymer; more preferably, a thermoplastic resin based on metal salt of ethylene/acid copolymer; still more preferably, ethylene/methacrylic acid copolymer. As used herein, the term "ionomer" also includes ethylene/acrylic acid copolymer and ethylene/acid/acrylate terpolymer. As used herein, the terms "core" or "intermediate", as applied to multilayer films, refer to any internal film layer which has a primary function other than serving as an adhesive or compatibilizer for adhering two layers to one another. Usually, a core or intermediate layer provides the multilayer film with a desired level of strength, i.e., modulus, and/or optics, and/or abuse-resistance, and/or oxygen impermeability. As used herein, the phrase "tie layer" refers to any internal layer having the primary purpose of adhering two layers to one another. As used herein, the term "barrier", and the phrase "barrier layer", as applied to films and/or film layers, is used with reference to the ability of a film or film layer to serve as a barrier to one or more gases. Oxygen barrier layers, i.e., O 2 barrier layers, can comprise, for example, ethylene/vinyl alcohol copolymer, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyacrylonitrile, etc. As used herein, the term "peelable" refers to the capability of removing one or more layers of a multilayer film by manually peeling back the layers along a plane or interface of relatively low bond strength. Clarity is measured according to ASTM D 1746. Tensile strength, elongation, and modulus are measured according to ASTM D 882. Tear propagation is measured according to ASTM D 1938. Shrink tension is measured according to ASTM D 2838. Free shrink is measured according to ASTM D 2732. Oxygen transmission rate is measured according to ASTM D 3985. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrated package 11 having meat product 10 therein, the meat product being on tray 12. Oriented, heat shrinkable lidstock film 14 encloses product 10 on tray 12. Film 14 is heat sealed to the tray 12 at flange 16. A bead 18 marks the edge of film 14. Figure 2 is an enlargement of the portion of the package of Figure 1 enclosed in the circle of Fig 1. Like parts are identified by the same numbering as in Figure 1. The oriented, heat shrinkable lidstock film 14 is further depicted as a three layer film in which outer layers 20a and 20b enclose an intermediate layer 22. Any suitable monolayer or multilayer film can be used for lidstock film 14, provided that it is biaxially oriented, heat shrinkable, has oxygen barrier properties, a clarity of at least 50% (ASTM D 1746) and a thickness of less than about 51 µm (2 mils). More preferably, the biaxially oriented heat shrinkable lidstock film is a multilayer film including a layer comprising an oxygen barrier polymer to extend the shelf life of the packaged article. In general, this multilayer film can comprise from 2 to 20 layers; preferably, from 3 to 10 layers; and more preferably, from 4 to 8 layers. Preferably, the oriented, heat shrinkable lidstock film used in the present invention has a total thickness (i.e., a combined thickness of all layers), of from 2.5 to 51 µm (0.1 to 2 mils, 1 mil equals 0.001 inch); more preferably, from 7.6 to 38 µm (0.3 to 1.5 mils); and still more preferably, from 10.2 to 30 µm (0.4 to 1.2 mils). Oriented, heat shrinkable lidstock film 14 comprises any suitable polymer or combination of polymers. Preferred are olefinic outer layers 20a and 20b, and e.g. EVOH, saran (vinylidene chloride copolymer), nylon (polyamide), polyethylene terephthalate ("PET") or other suitable oxygen barrier material for intermediate layer 22. Suitable tie layers can be used as needed to bond adjacent layers together. Especially preferred materials are BDF 2001 and BDF 2050, sold by W.R.Grace & Co.-Conn. These and other suitable films are described in US Patents 4,724,185, 4,726,984, 4,755,419, 4,828,928, 4,839,235, and 5,004,647. Both BDF materials are biaxially oriented, heat shrinkable films, and have a core layer of ethylene vinyl alcohol copolymer and nylon; skin layers of a blend of ethylene octene copolymer and ethylene vinyl acetate copolymer, and intermediate layers of an anhydride grafted olefinic copolymer Examples of suitable materials for oriented, heat shrinkable lidstock film 14, and especially the outer layers of the film, include such olefinic materials as ethylene/vinyl acetate copolymer, ionomer, ethylene/alpha-olefin copolymer, especially homogeneous ethylene/alpha-olefin copolymer, ultra low density polyethylene ("ULDPE"), ethylene/n-butyl acrylate copolymer ("EnBA"), ethylene/methyl acrylate copolymer ("EMA"), low density polyethylene, and plasticized polyvinyl chloride. SSD-351 (TM) stretch olefin film, obtainable from W.R. Grace & Co.-Conn., of Duncan, S.C., and SSD-310 (TM) stretch olefin film, also obtainable from W.R. Grace & Co.-Conn., of Duncan, S.C., are also suitable films for use in the present invention. The latter product is described in US Patent 4,617,241. Preferred oriented, heat shrinkable lidstock films are at least partially crosslinked, preferably by electronic crosslinking. Figure 2 illustrates a thermoplastic film liner 17. Like lidstock film 14, thermoplastic film liner 17 can comprise any suitable material, such as those indicated above for lidstock film 14. Thermoplastic film liner 17 functions to allow or facilitate the sealing of lidstock film 14 to the tray 12 in the flange region 16 of the tray. Film liner 17 also preferably includes an oxygen barrier layer, such as those identified above for film 14. Thermoplastic film liner can be a monolayer film or a multilayer film. It can have any total thickness desired, so long as the film provides the desired properties for the particular packaging operation in which the film is used. A sequence of making the package is as follows. A tray is provided, with if necessary or beneficial a thermoplastic film liner adhered by any suitable means to its interior surface, as shown in Figure 2. A meat or other product is placed in the cavity formed by the tray. An oriented, heat shrinkable lidstock material is placed over and sealed to the tray in the flange area of the tray. A knife 30 or equivalent means is brought down near the outer edge of the tray, or within the flange region of the tray. Some or all of the excess film material extending beyond the edge of the tray or flange is then cut away. If a heated cutting means is used, the heat of the heated knife causes the remaining oriented heat shrinkable film to shrink back in the flange area of the tray, and form a bead 18 along the flange. Figure 3 illustrates the inventive process in schematic plan view. The outer dashed lines represent the original spacial extent of excess lidstock film 14 before cutting; the bead 18 is shown along the perimeter of the tray flange after cutting and heating film 14, and subsequent shrink back occurs. Arrows appearing around the perimeter of the tray show the direction of shrink back after cutting and heating. In general, any suitable product support member comprising a tray may be used, either alone, or optionally in combination with one or more supplemental product support members. Preferably, a tray is used. More preferably, the tray comprises a thermoformed foam sheet, or a thermoformed or molded rigid sheet tray, or any other support member which may be preformed or formed in-line during packaging. In general, the product support member may comprise any suitable material as known to those of skill in the art, such as polyolefin; preferably, the support member comprises at least one member selected from the group consisting of polyvinylchloride, polystyrene, polypropylene, polyethylene terephthalate, and cellulose; more preferably, tray 12 comprises polystyrene; still more preferably, tray 12 comprises polystyrene foam. Conventional processes and packaging equipment well known in the art can be used to accomplish each of the basic steps discussed above. The step of cutting/heating to induce shrink back can be done by modifying conventional packaging equipment, or providing additional equipment to cut the excess lidstock film that extends beyond the edge of the tray flange, and heat the film to cause shrinkback into or on the flange area. A hot knife or other suitable cutting/heating means such as hot wire or laser can be used. Thus, film 14 is sealed to tray 12 at the perimeter thereof, preferably in a flange area, and preferably films 14 and 17 are preferably heat-sealed to each other around the perimeter of tray 12. Although the process of the present invention is useful for the packaging of any product, the process is especially suited to the packaging of meat products such as ground beef. The present invention is further illustrated by the following examples and data. Unless stated otherwise, all percentages, parts, etc., are by weight. EXAMPLE 1 Several tests were conducted to evaluate 100 gauge BDF-2050 (Example 1) as a lidstock, and compare it with a conventional lidstock believed to have a polyethylene terephthalate substrate as a sealant with saran and ethylene vinyl acetate copolymer as additional layers (Comparative Example 1). Packages were made on a Ross 580 machine. In the case of the film of Example 1, the machine was modified by placing teflon tape on top of the heating plate in the upper chamber. Alternatively, the seal bars could be recessed to prevent premature shrinkage of the BDF film. After the packages were made, they were advanced to a station where a mechanical knife cut the excess film. Because this was not a heated knife, the remaining film along the edge of the package did not shrink back to form a bead. These particular tests were intended only to establish some basic fitness-for-use data. Three fitness-for-use criteria were used to see whether the oriented, heat shrinkable BDF film was comparable in performance with conventional lidstock. These were shelf-life test, drop test, and shaker test. The shelf life test using ground beef was conducted to compare Example 1 and comparative Example 1 in terms of gas, color, and microbial counts. Packages containing one pound of ground beef (ground in the packaging lab) in foamed polystyrene trays having an inner surface lined with a barrier film were vacuum/gas flushed with 80% oxygen/20% carbon dioxide. The barrier film liner had the following film structure: a sealant layer (the film layer to be sealed to the BDF lidstock in the flange area of the tray) of LLDPE; a tie layer of an anhydride modified polyolefin; an EVOH layer; another tie layer; and a layer of ethylene methyl acrylate copolymer for bonding to the foamed polystyrene tray. Fifteen packages were made for each type of lidding film and evaluated over an 11 day period. The result was that in general there were no differences between the two lidding films. Over time, the oxygen concentration of the package with BDF film was higher than with the conventional lidstock, but the differences were not significant. There were no significant differences in color values except on the last day, when the packages with BDF had significantly greater red color as measured by Hunter "a" value. No significant differences in total aerobic plate counts were seen. The conclusion is that in terms of desired product shelf life, the oriented, heat shrinkable film of example 1 is fit-for-use as a lidstock in combination with a barrier lined foam tray and a modified atmosphere. The drop tests used the same type of barrier lined foam trays. Packages were made with the BDF film lidstock. Each package was over-pressured with gas, and contained a one (1) pound water bag. The packages were stacked 12 to a case (4 columns, 3 deep). A total of 8 cases (96 packages) were dropped 3 feet each. Each package was evaluated for damaged seals or film. Two additional cases were stored for one week at 2°C (35°F) and dropped to determine the effect of cold storage on the seals. Seal conditions were 132°C (270°F) for 1.3 seconds. Gas flush time was 0.65 seconds. The result was that none of the 96 packages dropped were damaged in any way. The shaker tests used the same type of barrier lined foam trays. Packages were made with the BDF film lidstock. Each package was over-pressured with gas, and contained a one (1) pound water bag. The packages were stacked 12 to a case (4 columns, 3 deep). A total of six cases (72 packages) were vibrated over a one hour period using a simulated truck program. Packages were then evaluated for seal/film damage. Seal and gas flush conditions were the same as used in drop testing. The shaker testing was done to anticipate any problems in seal integrity or film delamination during transportation. If the overlap of film on the flange is pulled with enough force, the BDF film will delaminate rather than lift off the flange seal area. The result was that none of the 72 packages tested had damaged seals or exhibited any type of delamination. Clarity and thickness values for Example 1 and Comparative Example 1 appear in Table 1 below. Also included is an additional Comparative Example 2, which is a conventional, commercial lidstock available from the assignee. The lidstock of Comparative Example 2 has an LLDPE/EVA/EVA sealant bonded at the EVA layer to a saran coated polyester. Example Clarity (%) Gauge µm (mils) 1 79 30/(1.2) comp. 1 35 81/(3.2) comp. 2 29 66/(2.6) Oriented heat shrinkable lidstock films of the present invention have a clarity of at least 50%, preferably at least 60%. Clarity is measured per ASTM D 1746. EXAMPLE 2 A shrink film having the construction: polyolefin/tie/EVOH/tie/polyolefin is adhered to a foamed polystyrene tray having an oxygen barrier film adhered to the interior cavity of the tray. EXAMPLE 3 A shrink film having the construction: polyolefin /tie/polyamide/EVOH/polyamide/tie/polyolefin is adhered to a foamed polystyrene tray having an oxygen barrier film adhered to the interior cavity of the tray. EXAMPLE 4 A shrink film having the construction: was adhered to a foamed polystyrene tray having a film having an oxygen barrier material adhered to the interior cavity of the tray. The package was made on a Ross 580 machine. The machine was modified by placing teflon tape on top of the heating plate in the upper chamber. After the packages were made, they were advanced to a station where a mechanical knife cut the excess film. This was not a heated knife, and the remaining film along the edge of the package did not shrink back to form a bead. Thus, with this mechanical cut, excess film overhung the tray flanges. It was discovered that this film could be peeled back to remove some of the layers from the multilayer shrink film lidstock. Peel was initiated at one corner of the extended portion of the shrink lidstock. It is believed that the oxygen barrier portion of the film, including the EVOH and both polyamide layers (herein "impermeable portion"), was peeled from the film. This left the tie and polyolefin layers adhered to the tray. These remaining layers, referred to herein as the permeable substrate, have relatively high oxygen transmission. For end-use applications such as case-ready beef, it is desirable to package and store a meat product in a package having good initial oxygen barrier properties, and then, when the package is put in a retail display case, remove the oxygen barrier component to create an oxygen permeable package and promote blooming (onset of red color) in the meat product. The package of example 4 provides a peelable shrink film lidstock for such a package. For peelable embodiments, the bond between the sealant layer of the lidstock and the support member has a strength which is greater than the force required to peel the impermeable portion from the permeable substrate. In this manner, the impermeable portion can be peeled from the permeable substrate and the product will continue to be fully contained within the package. The peel force between the permeable substrate and impermeable portion is preferably between 0.0002 and 0.44 N/mm (0.001 and 2.5 lb/inch). A more preferred peel force between the two portions is between 0.0009 and 0.35 N/mm (0.005 and 2 lb/inch), most preferably between 0.0017 and 0.26 N/mm (0.01 and 1.5 lb/inch). A peel force falling within these ranges provides a balance between sufficient adhesion to prevent premature film separation, e.g., during manufacture, shipping and storage, and sufficient peelability so that the two portions can be separated without tearing or otherwise compromising the permeable substrate. A peel force of more than about 0.44 N/mm (2.5 lb/inch) results in a lidstock film that is more difficult to peel, or can result in unintended separation of the entire lidstock from the support member. On the other hand, a peel force of less than about 0.0002 N/mm (0.001 lb/inch) creates a greater likelihood of premature delamination of the film. Figure 4 is like Figure 2, but shows a peelable shrink lidstock film 14 further depicted as a four layer film in which sealant layer 20a and outer layer 20b enclose an intermediate layer 22 and oxygen barrier layer 23. The impermeable portion represented in the drawing by outer layer 20b and oxygen barrier layer 23, is peeled away from the permeable portion represented by sealant layer 20a and intermediate layer 22. If desired, a suitable tab, header, or the like can be placed at one end of the package to initiate peel. In Example 4, the outer polyolefin layers were a blend of about 70% LLDPE (Dowlex 2045.04 from Dow), 24 % linear medium density polyethylene (LMDPE) (Dowlex 2037 from Dow), and about 6% slip additives. Polyamide 1 was nylon 6,66 (Ultramid C 35 from BASF) and Polyamide 2 was nylon 6,12 (Grilon CF 6S from Emser). Tie 1 and Tie 2 were both anhydride-grafted polyolefinic adhesives (Bynel CXA 4104 from Du Pont.). Table 2 below shows several properties of the shrink lidstock of Example 4 compared with other films, and including the interlaminar bond strength between the Tie 1 and Polyamide 1 layers (noted in the Table 2 as "Tie 1 -PA 1 ) and the Tie 2 and Polyamide 2 layers (noted as "Tie 2 -PA 2 "). It is compared with standard BDF 2050 and other films. The table shows that the tie/polyamide interfaces offer significantly lower interlaminar adhesion ("bond strength") making the film of Example 4 especially preferred for peelable shrink lidstock applications. In Table 2: "BDF 2050 1 " refers to a standard heat shrinkable film as described hereinabove; "BDF 2050 2 " refers to a standard heat shrinkable film as described hereinabove, but which has been annealed (heat set) such that the final layflat width of the annealed film is 4% less than the layflat width of the film before annealing; "BDF 2050 3 " refers to a standard heat shrinkable film as described hereinabove, but which has been annealed such that the final layflat width of the annealed film is 8% less than the layflat width of the film before annealing; and Example 5 is a shrink film like that of Example 4, but which included a small amount of ethylene vinyl acetate copolymer in the outer layers. PROPERTY BDF 2050 1 BDF 2050 2 BDF 2050 3 EXAMPLE 4 EXAMPLE 5 Tensile strength (psi x 1000) long. 13 14 13 17 18 Elongation (%) long. 86 91 82 94 94 Modulus (psi x 1000) long. 94 96 67 133 134 Tensile strength (psi x 1000) trans. 11 11 11 16 18 Elongation (%) trans. 136 114 114 79 70 Modulus (psi x 1000) trans. 89 90 92 131 143 Tear Property (grams) long. 42 19 16 13 19 Tear Property (grams) trans. 12 32 33 10 36 Bond Strength Tie 1 -PA 1 (lb/inch) 0.14 0.19 0.13 0.02 0.02 Bond Strength Tie 2 -PA 2 (lb/inch) 0.15 0.19 0.16 0.02 0.03 Peak Load (lb) 19 18 21 25 28 Gradient (lb/inch) 32 29 34 43 46 Energy at Break (ft-lbs.) 0.4 0.4 0.4 0.5 0.6 Shrink Tension trans. lb/in. 2 @ 82°C (180°F) 471 385 285 569 569 93°C (200°F) 518 467 397 619 573 104°C (220°F) 596 456 404 617 629 116°C (240°F) 515 448 413 615 553 127°C (260°F) 492 457 414 644 652 Free Shrink trans. % @ 82°C (180° F) 16 14 9 14 15 98°C (200°F) 23 22 20 20 21 104°C (220°F) 31 32 30 25 29 116°C (240°F) 58 59 56 42 44 127°C (260°F) 64 65 63 55 54 Five packages were prepared in which the lidstock film of Example 4 was sealed in each case to a foamed polystyrene tray. The lidstock film of each package was peeled back, leaving behind a permeable substrate. The oxygen transmission rate (OTR) of this substrate was measured using an OX-TRAN measuring device at 23°C (73°F) at 0% relative humidity (ASTM D 3985). The results are shown below in Table 3. SAMPLE OTR GAUGE cc @ STP/24 hours,m 2 ,atmosphere µm/(mils) 1 16,800 9.9/(0.39) 2 20,100 9.4/(0.37) 3 19,700 9.1/(0.36) 4 16,300 9.7/(0.38) 5 17,100 9.7/(0.38) SSD 310 13,700 16.3/(0.64) SSD 310 11,600 18.3/(0.72) The interlaminar bond strength of peelable embodiments of the shrink film lidstock of the present invention can vary depending on the exact composition of the specific film, method of production, and the like. Table 4 shows four lip seal readings taken for each of five packages. For each package, four specimens were taken; each had a small (approx. 25mm (1 inch) long by 25mm (1 inch) wide) section of the foamed tray, and adhered thereto, a small (approx. 25mm (1 inch) long by 25mm (1 inch) wide) section of the lidstock film of Example 4. Using an Instron tester, peel was initiated by pulling the foamed section with the permeable substrate adhered thereto, from the impermeable portion of the lidstock. This was done for each of the 20 samples. Table 4 records the force required to initiate peel in the flange seal area of each specimen. Table 5 records the peel force required to continue the delamination of what is believed to be the Tie 2 -PA 2 interface of the lidstock, for each of the 20 samples. SAMPLE LOAD AT MAX. (lb/inch) 1 1.6 2 1.2 3 1.8 4 2.3 5 2.1 6 1.4 7 1.3 8 0.7 9 1.3 10 0.8 11 1.8 12 1.3 13 1.0 14 1.8 15 1.4 16 0.7 17 1.3 18 0.9 19 1.3 20 0.9 Mean 1.3 SAMPLE AVG. LOAD Between limits (lb/inch) 1 0.015 2 0.014 3 0.016 4 0.006 5 0.010 6 0.002 7 0.003 8 0.004 9 0.009 10 0.010 11 0.015 12 0.009 13 0.015 14 0.022 15 0.033 16 0.024 17 0.024 18 0.019 19 0.021 20 0.013 Mean 0.014 S.D. 0.008 Packages made in accordance with the present invention can optionally include modified atmosphere in the cavity formed by the support member and shrink lidstock. For meat packaging applications where a red color is desired at the time the package is made, and where the lidstock has an oxygen barrier component, a high oxygen atmosphere having in excess of 20% oxygen is sometimes preferred. For embodiments such as peelable lidstock, where the lidstock has an oxygen barrier component, an atmosphere with a predominance of nitrogen and carbon dioxide is sometimes preferred. This latter embodiment provides extended shelf life of a meat product during distribution and storage, and the capability of then peeling away the impermeable portion when the package is displayed for sale at a retail outlet. Removal of the impermeable portion allows oxygen to enter the package interior through the permeable substrate, causing the meat to bloom.

Claims: A method of packaging a food product comprising: (a) providing a product support member (12) comprising a tray having a flange (16) around the perimeter of the tray; (b) placing the food product (10) on the tray; (c) placing over the product a biaxially oriented, heat shrinkable lidstock film (14) including an oxygen barrier layer, the film (14) having a clarity of at least 50% (ASTM D 1746) and a thickness of less than about 51 µm (2 mils); (d) heat sealing the film (14) to the flange (16); and (e) cutting away at least some of the film (14) extending beyond the perimeter of the product support member (12), and heating such that the heated film shrinks back to the flange and forms a bead (18) thereon. A method according to claim 1, wherein step (e) is performed using a cutting/heating means. A method according to claim 2, wherein the cutting/heating means is a hot knife (30), hot wire or laser. A method according to any one of claims 1 to 3, further comprising providing a product support member (12) having a thermoplastic film liner (17) adhered to the flange (16), and sealing the film (14) to the thermoplastic film liner in the region of the flange (16). A method according to any one of claims 1 to 4, wherein the film (14) is peelable. A method according to any one of claims 1 to 5, wherein the film (14) comprises two adjacent film layers (22, 23), said layers being peelable from each other at a peel force of between 0.0018 and 4.38 N/cm (0.001 and 2.5 pounds per inch). A method according to claim 6 further comprising peeling the two adjacent film layers (22,23) apart. A method according to any one of claims 1 to 7, wherein the film (14) comprises outer layers of an olefinic polymer and an intermediate layer comprising an oxygen barrier material. A method according to any one of claims 1 to 8, wherein the film (14) is at least partially cross-linked. A method according to any one of claims 1 to 9, wherein the product support member (12) comprises a foamed tray. A method according to any one of claims 1 to 10, wherein the product support member (12) comprises at least one member selected from the group consisting of polyvinylchloride, polystyrene, polypropylene, polyethylene terephthalate, and cellulose. A method according to any one of claims 1 to 11, wherein the product support member (12) includes a thermoplastic film liner (17) adhered to an inner surface of the tray. A method according to claim 12, wherein the thermoplastic liner comprises an oxygen barrier material. A method according to any one of claims 1 to 13, wherein the film (14) does not extend beyond the flange (16). A method according to any one of claims 1 to 14, wherein the food product is a meat product.

Inventors: KOCKER PATRICK N, MUDAR KIMBERLY A, KOCKER, PATRICK, N., MUDAR, KIMBERLY A.
Applicants: CRYOVAC INC, CRYOVAC, INC.
Application year: 1996
Main classification: B65D77
IPC codes: B65D77, B65D17, B65D71