Abstract:
The present invention relates to improved packages which include a rigid or semi-rigid tray having a single thermoplastic overwrap comprising a polymeric laminate surrounding the tray and having a front panel and an opposing back panel. The inventive packages also include a continuous seal circumscribing a recessed cavity of the tray which comprises a heat seal formed by heat sealing a portion of the front panel to the peripheral flange of the tray. Advantageously, when the tray is removed from the overwrap, a portion of the first film separates from the laminate and remains peelably sealed to the flange of the tray and thus, may serve as a lidding film for the container. Since the recessed cavity is still covered, the container may then be placed directly in a microwave or conventional oven to thaw and/or cook the food container within the package without first removing the lidding film.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to packages including a tray surrounded by a single thermoplastic overwrap and particularly to ovenable packages having a single peelable thermoplastic overwrap heat sealed to the tray that provides a lidding film which separates from the overwrap and remains peelably sealed to the flange of the tray when the tray is removed from the overwrap. 
     Various concerns arise in connection with the manufacture and use of food and non-food packages. One area of concern is with respect to the cost of packaging components and the efficiency that they are assembled with the food items. For example, current packaging containers for microwavable meals include a tray on which a food item is supported and a separate plastic lidding film which is heat sealed to the rim of the tray to seal the food item within the package. The lidding film is normally sealed to the container in order to prevent leakage of fluids from within the container and also prevent ingress and egress of gases into and out of the container. Lidding films also help retain the moisture content, nutritional value, flavor, texture and appearance of the food. A lidding film is often used to cover a tray in microwave packages to prevent food from splattering inside the oven and helps to control the temperature inside the package during the heating process. Typically, a separate paperboard sleeve-type overwrap or paperboard carton is required which surrounds the sealed tray and provides a surface for product information and/or cooking instructions. It would be highly desirable to minimize the cost of the packaging components by eliminating the paperboard sleeve-type overwrap or paperboard carton. 
     There is a need in the art for improved packages that address at least some of the above concerns, and which are simple in construction, can be made easily and inexpensively manufactured. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is concerned with packages which include a rigid or semi-rigid tray having a base and at least one sidewall extending from the base thereby forming a recessed cavity; wherein the at least one sidewall comprises a peripheral flange extending generally perpendicularly from the at least one sidewall and which circumscribes the recessed cavity. The inventive packages also include a single thermoplastic overwrap comprising a polymeric laminate surrounding the tray and having a front panel and an opposing back panel having a longitudinal seal disposed underneath the base of the tray, a first leading end seal positioned substantially transverse to the longitudinal seal, and an opposing second trailing end seal positioned substantially transverse to the longitudinal seal. The overwrap further includes an exterior surface and an interior surface, a first side edge, an opposing second side edge, a front panel and an opposing back panel comprising a longitudinal seal, a first leading end seal positioned substantially transverse to said longitudinal seal, and an opposing second trailing end seal positioned substantially transverse to the longitudinal seal 
     The packages also include a peelable seal continuously circumscribing the recessed cavity which comprises an inner perimeter defined by a heat seal formed by heat sealing a portion of the front panel to the peripheral flange. The packages further comprise a first film integrally formed in polymeric laminate which forms the interior surface of the overwrap, and a second film also integrally formed in the laminate which forms the exterior surface of the overwrap. 
     Advantageously, when the tray is removed from the overwrap, a portion of the first film separates from the laminate and remains peelably sealed to the flange of the tray and thus, may serve as a lidding film for the container. Since the recessed cavity is still covered, the container may then be placed directly in a microwave or conventional oven to thaw and/or cook the food container within the package without first removing the lidding film. The consumer thus avoids having to handle the raw product or to clean a container in which the food would have otherwise been placed for heating or cooking. Because this portion of the first film is peelably affixed to the flange, the consumer may also simply dispose of the remaining film after heating or cooking the food by peeling the film away from the tray. 
     Optionally, the packages of the present invention are self-venting whereby a venting means permits the portion of the first film which separates from the laminate and remains peelably sealed to the flange of the tray when the tray is removed from the overwrap to rupture and release steam in response to heat and/or overpressure generated during heating of a food item in a microwave oven. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an isometric top perspective view f one preferred embodiment of the present invention. 
         FIG. 2  depicts an isometric bottom perspective view of one preferred embodiment of the present invention. 
         FIG. 3  depicts one embodiment of a thermoplastic overwrap of the present invention taken through section A-A of  FIG. 1 . 
         FIG. 4  depicts an isometric top perspective view of the present invention illustrating a portion of first film which separates from overwrap and remains peelable attached to the tray when removing the tray from the overwrap. 
         FIG. 5  depicts an isometric top perspective of a package of the present invention illustrating one embodiment of a pattern of perforations in a first film. 
         FIG. 6  depicts a cross-sectional view of a general embodiment of a thermoplastic overwrap of the present invention sealed to a tray and illustrating one embodiment of a pattern of perforations in a first film taken through section A-A of  FIG. 5 . 
         FIG. 7  depicts an isometric top perspective of a package of the present invention illustrating another embodiment of a pattern of perforations in a first film. 
         FIG. 8  depicts an isometric top perspective of a package of the present invention illustrating one embodiment of a pattern of perforations in a first film and one embodiment of a pattern of perforations in a second film 
         FIG. 9  depicts a cross-sectional view of a general embodiment of a thermoplastic overwrap of the present invention sealed to a tray and illustrating one embodiment of a pattern of perforations in a first film and one embodiment of a pattern of perforations in a second film taken through section A-A of  FIG. 8 . 
         FIG. 10  depicts an isometric top perspective of a package of the present invention illustrating one embodiment of a pattern of perforations in a first film and one embodiment of a pattern of perforations in a second film. 
         FIG. 11  depicts a cross-sectional view of one embodiment of a first film of the present invention. 
         FIG. 12  depicts an isometric top perspective of one embodiment of a means for venting internal pressure from inside said package comprising a pattern of perforations. 
         FIG. 13  depicts a cross-sectional view of one embodiment of a self-venting means taken through section A-A of  FIG. 12 . 
         FIG. 14  depicts an isometric top perspective of another embodiment of a means for venting internal pressure from inside said package comprising a heat-sealable release coating applied to an area of the peelable heat seal. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     Referring now more particularly to  FIGS. 1-2  of the drawings, a preferred embodiment of package  10  embodying the present invention is shown. The package  10  comprises a rigid or semi-rigid tray  20  having a recessed cavity  30  and a peripheral flange  40  circumscribing recessed cavity  30 . The tray  20  can be made of any suitable material, however, it is preferred that the tray  20  be made of a plastic that can withstand exposure to the heating and/or cooking environment of a microwave oven. Most preferably, the plastic is polypropylene or crystallized polyethylene terephthalate (“CPET”) although other plastics, such as, amorphous polyethylene terephthalate (“APET”) or polystyrene may be used. It should be recognized that tray  20  may also be formed from multilayer plastic films which provide an exterior heat sealable surface, and oxygen and/or moisture barrier properties. In a preferred embodiment of the present invention, tray  20  includes an exterior heat sealable surface which can be heat sealed to an overwrap. 
     The tray  20  has a base  21  and a sidewall  22  extending from the base  21  which forms recessed cavity  30 . The sidewall  22  of tray  20  terminates at peripheral flange  40  which circumscribes recessed cavity  30 . It will be appreciated that tray  20  may be of the shape as shown in  FIGS. 1-2  or any other shape, such as, for example, rectangular, square, circular or polygon depending on both functional and aesthetic requirements. It will also be appreciated that tray  20  may have any depth as desired depending upon type and amount of food product container therein. It will be further appreciated that tray  20  may be configured to include two or more recessed cavities depending again on both functional and aesthetic requirements. 
     As depicted, a single thermoplastic overwrap  50  comprises a polymeric laminate  80  and encloses tray  20  and includes a front panel  51  and an opposing back panel  52  (shown in  FIG. 2 ). Front panel  51  includes an inner surface and an outer surface. Back panel  52  is disposed underneath the base  21  of tray  20  and includes a longitudinal seal  70  (shown in  FIG. 2 ). Preferably, longitudinal seal  70  is a heat seal or cold seal, and more preferably, a heat seal. Longitudinal seal  70  may be configured as either a fin seal or lap seal, and preferably as a fin seal. As used herein, the term “heat seal” refers to welding or melting of two polymeric surfaces together by the application of heat and pressure. It will be appreciated by those skilled in the art that heat seals may be hermetic seals meaning that they prevent the ingress of air and/or moisture through the seal. Thermoplastic overwrap  50  further comprises a first leading end seal  71  positioned substantially transverse to the longitudinal heat seal  70 , an opposing second trailing end seal  72  positioned substantially transverse to the longitudinal seal  70 , a first side edge  73 , and an opposing second side edge  74 . As depicted, first side edge  73  and an opposing second side edge  74  are each positioned between first leading end seal  71  and opposing second trailing end seal  72 . Preferably, first leading end seal  71  and opposing second trailing end seal  72  are each a heat seal or cold seal, and more preferably, a heat seal. Preferably, first leading end seal  71  and opposing second trailing end seal  72  are each configured as a fin seal. 
     Front panel  51  includes a continuous peelable seal  75  which continuously circumscribes the recessed cavity  30  and comprises a perimeter defined by heat seal  76  formed by heat sealing a portion  53  of front panel  51  to the peripheral flange  40 . It will be appreciated that this portion of front panel  51  covers recessed cavity  30  which then seals any food item within container  10 . This reduces the cost of packaging by eliminating the need for a separate lidding film. Portion  53  also provides a relatively smooth surface for printing of indicia. Printing onto portion  53  may include graphics or colors to make package  10  more attractive to a potential consumer. Alternatively, portion  53  may be transparent and used for viewing of the food item contained within package  10  by a consumer. In addition, back panel  52  may be used to place other indicia, such as mandated by local food labeling laws, as well as, cooking instructions which may be desired to be placed on the package  10 . In this way, the extra cost of a separate printed paperboard overwrap sleeve or a separate paperboard carton can now be eliminated by printing directly onto to front panel  51  and/or back panel  52  of package  10 . 
     Thermoplastic overwrap  50  may comprise a material which will not melt or otherwise deteriorate during heating of the food items in a microwave oven. Preferably, thermoplastic overwrap  50  is constructed from a material that will sufficiently not retain heat to prevent discomfort or burning to the consumer upon handling following microwave cooking. It will be appreciated that the choice of materials used to form overwrap  50  may be determined by the nature of the food items to be packaged in the package  10 . For example, packaging of refrigerated foods. overwrap  50  must by substantially impermeable to gases and/or water vapor. Packaging for refrigerated foods will often include oxygen barrier materials such as one or more layers of polyamide and ethylene vinyl alcohol copolymer. The constructions of the overwrap of the invention will be discussed in greater detail below. 
       FIG. 3  is a cross-sectional view of an example of a preferred embodiment of a thermoplastic overwrap  50  comprising a polymeric laminate  80  heat sealed to tray  20  at flange  40  thereby creating a peelable seal  75 . As depicted, laminate  80  includes a multilayer structure formed by lamination of a first film  201  to a second film  202  via an adhesive layer  204 . As depicted, there is a release lacquer  203  printed in-register (or non-contiguously) on first film  201  such that release lacquer  203  is in direct contact with less than the entire surface of second film  202 . Overwrap  50  will include an interior surface  51   a  and an exterior surface  51   b.    
     In accordance with an important aspect of the present invention, the removal of tray  20  from overwrap  50  may be achieved by tearing front panel  51  away from back panel  52  or cutting by across overwrap  50  near first leading end seal  71  with a pair of scissors. With front panel  51  separated from back panel  52 , the consumer may simply grasp tray  20  and pull front panel  51  away from the tray, thereby separating a portion of first film  210  from laminate  80  which remains peelably sealed to flange  40  and functions as a lidding film thereafter as illustrated in  FIG. 4 . With the overwrap  50  removed and a lidding film  210  covering tray  20 , the consumer may then place the tray inside a microwave oven to thaw and/or cook the food items as desired. 
     To facilitate the removal of tray  20  from overwrap  50 , first film  201  may comprise a pattern of perforations  205  within first film  201  located between the peelable seal  75  and at least one of the first side edge  73 , opposing second side edge  74 , first leading end seal  71  or opposing second trailing end seal  72 . Perforations may be formed as continuous, intermittent or a combination of continuous and intermittent segments of scoring, cutting or perforations. Pattern of perforations  205  may be formed by any mechanical and/or optical scoring, cutting or perforating methods known in the art. One example of a scoring technique which may be used to assist in the formation of perforations is optical ablation using a laser source. Laser scoring is well-known in the art. Preferably, pattern of perforations  205  has a depth of the entire thickness of first film  201 . As illustrated in  FIGS. 5 and 6 , one embodiment of a pattern of perforations  205  (identified as bold dashed lines in  FIGS. 6 and 7 ) comprises a first discrete linear line  205   a  positioned adjacent to said first side edge  73 , and a second discrete linear line  205   b  positioned adjacent to said opposing second side edge  74 .  FIG. 7  illustrates another embodiment pattern of perforations  205  in first film  201  comprising a continuous line  205   c  substantially circumscribing said peelable seal  75 . 
     To further assist in the opening of overwrap  50 , there may be a pattern of perforations  206  within second film  202  in addition to pattern of perforations  205  within first film  201 . Preferably, pattern of perforations  206  (identified as bold dotted lines in  FIGS. 9 and 10 ) within second film  202  are also located between peelable seal  75  and at least one of first side edge  73 , opposing second side edge  74 , first leading end seal  71  or opposing second trailing end seal  72  as noted for pattern of perforations  205  in first film  201 . Preferably, pattern of perforations  206  has a depth of the entire thickness of second film  202 . As shown in FIGS,  8  and  9 , one embodiment of a pattern of perforations  206  comprises a first discrete linear line  206   a  positioned adjacent to said first side edge  73 , and a second discrete linear line  206   b  positioned adjacent to said opposing second side edge  74  in addition to the first and second discrete lines  205   a  and  205   b  in first film  201 .  FIG. 10  illustrates another embodiment pattern of perforations  206  in second film  202  comprising a continuous line  206   c  substantially circumscribing said peelable seal  75  in additional to the continuous line  205   c  in first film  201 , 
     In one embodiment, package  10  includes a pattern of perforations  205  in only first film  201  as depicted in  FIG. 7 . In another embodiment, package  10  includes a pattern of perforations  205  in first film  201  and a pattern of perforations  206  within second film  202  as depicted in  FIG. 10 . 
     In one embodiment, first film  201  is a multilayer film comprising any number of layers depending on the functional properties desired, First film  201  may comprise any polyolefin including, but not limited to, polyethylene, preferably, low density polyethylene, and more preferably, linear low density polyethylene, ethylene vinyl acetate copolymer, polypropylene or combinations thereof. In one embodiment, first film  201  is a three-layer film as illustrated in  FIG. 11 . Preferably, first film  201  comprises an exterior heat sealing layer  201   a . Such exterior heat sealing layers may comprise ethylene/vinyl acetate copolymer or polypropylene. Preferably. first film  201  comprises a second layer  201   b  in contact with the exterior heat sealing layer comprising a blend of polybutene and a polyolefin. Suitable polyolefins include, but not are limited to ethylene/vinyl acetate copolymer and polyethylene. First film  201  may also comprise a third layer  201   c  in contact second layer  201   b.    
     First film  201  may be formed by coextrusion of one or more polymeric materials by cast coextrusion or blown coextrusion techniques. Preferably, first film  201  is formed by blown coextrusion methods. The total thickness of first film  201  is generally from about 12.7 μm (0.5 mil) to about 254 μm (10 mil), typically from about 25.4 μm (1 mil) to about 127 μm (5 mil), most typically from about 50.8 μm (2 mil) to about 63.5 μm (2.5 mil). 
     Package  10  may further comprise a means for venting internal pressure from inside said package. One such means may include a pattern of perforations  211  having a depth of the entire thickness of the first film  201 . Preferably, pattern of perforations  211  is located within portion of first film  201  which separates from the overwrap and remains peelably attached to the tray. Perforations may include one or more scored or cut segments within portion of first film  210  as illustrated in  FIGS. 12 and 13 . The number and size of the perforations may vary depending upon amount of internal pressure generated within the package. Another means for venting internal pressure may comprise a portion of the pee able seal comprising a heat-sealable release coating Preferably, a heat-sealable release coating  212  (shown in  FIG. 14 ) is applied within a predetermined area of peelable seal  75  between the inner surface of the overwrap  51   a  and flange  40 . Release coating  212  may comprise a solvent-based printable heat-sealable release coating. An example of a commercially available solvent-based printable heat-sealable release coating is PROXSEAL J9660MN supplied by Henkel Corporation (Cary, N.C.). 
     In a preferred embodiment, second film  202  comprises an oriented thermoplastic material. Examples of suitable oriented thermoplastic materials include, but are not limited to oriented polyethylene terephthalate, oriented polypropylene and oriented polyamide. Preferably, film  202  is oriented, more preferably, uniaxially oriented in either the machine direction or transverse direction and more preferably, biaxially oriented in both the machine direction and the transverse direction. Preferably, film  202  is a biaxially oriented polyethylene terephthalate film which is heat annealed to render the film substantially non-heat shrinkable, e.g., a film having a heat shrinkage of less than about 15%, more preferably, less than 10% and most preferably, less than 5% in either the machine and/or transverse direction. The total thickness of film  202  is generally from about 36 gauge to 142 gauge (or 9.14 microns to 36.10 microns), typically, from 42 gauge to about 92 gauge (or about 10.67 microns to about 23.37 microns). 
     In accordance with the present invention, first film  201  may be a multilayered film which includes oxygen barrier materials that provides an oxygen transmission rate of less than about 1.0 cm 3 /100 in 2 /24 h at 73° F., 0% RH and 1 atm (or about 15.5 cm 3 /m 2 /24 h at 23° C., 0% RH and 1 atm), preferably, less than about 0.5 cm 3 /100 in 2 /24 h at 73° F., 0% RH and 1 atm (or about 7.75 cm 3 /m 2 /24 h at 23° C., 0% RH and 1 atm), and most preferably, about 0.2 cm 3 /100 in 2 /24 h at 73° F., 0% RH and 1 atm (or about 3.1 cm 3 /m 2 /24 h at 23° C., 0% RH and 1 atm). In accordance with the present invention, second film  201  includes water barrier materials, such as a polyolefin, particularly, polyethylene which provides a water vapor transmission rate less than about 1.0 g/100 in 2 /24 h at 73° F., 90% RH and 1 atm (or about 15.5 g/m 2 /24 h at 23° C., 90% RH and 1 atm) and preferably, about 0.2 g/100 in 2 /24 h at 73° F., 90% RH and 1 atm (or about 3.1 g/m 2 /24 h at 23° C., 90% RH and 1 atm). First film  201  may comprise both oxygen barrier materials and water barrier materials. 
     WORKING EXAMPLES 
     The following example illustrates a certain particular embodiment of a polymeric laminate suitable for use as an overwrap in the present invention and is not to be interpreted as limiting. In the following example, resin composition percentages are based on the total weight of each film layer. 
     Example 1 
     Example 1 is one embodiment of a polymeric laminate suitable for use as a thermoplastic overwrap of the present invention having a general structure  80  as illustrated in  FIG. 3 . In this example, first film  201  is a three-layer film which was adhesively laminated to a second film  202  via an adhesive layer  204 . A release lacquer  203  is printed in-register (or non-contiguously) onto first film  201  such that release lacquer  203  is in direct contact with less than the entire surface of second film  202 , First film  201  was formed by blown-film coextrusion methods. Second film  202  was purchased as free-standing film. In this example, first film  201  has thickness of about 2.0 mil and a structure and layer compositions as described below and as illustrated in  FIG. 11 . Reported below is the basis weight of the layer relative to the total film weight and the layer composition.
         Layer 1 (Sealant): 5%; 100 wt.- % ethylene/vinyl acetate copolymer (EVA)-Petrothene NA442 having a5% vinyl acetate content (Equistar Chemicals, LP, Houston, Tex., USA)   Layer 2: 5%; 83 wt.- % ethylene/vinyl acetate copolymer (EVA)-Petrothene NA442 having a5% vinyl acetate content (Equistar Chemicals, LP, Houston, Tex., USA) and 17 wt.- % polybutene (PB)-polybutene-1 PB 8640M having a random copolymer of butene-1 and low ethylene content (LyondellBasell Industries Holdings, B.V., The Netherlands)   Layer 3: 90%; 60 wt.- % ultra low-density polyethylene (ULDPE)-ATTANE® 4701 copolymer supplied by Dow Chemical Company, Midland, Mich.), 35 wt.- % linear low density polyethylene ExxonMobil™ LLDPE 1001.32 (ExxonMobil Chemical Company, Houston, Tex.), and 5% processing additives.       

     A release lacquer  203  was printed in-register (or non-contiguously) on first film  201 . If the release lacquer is a solvent-borne material, it is then dried through a drying oven. Following the application of the release lacquer, first film  201  is then scored, cut and/or perforated to provide the pattern of perforations in the first film. A reverse printed 48 gauge mono-layer second film  202  was then bonded with a laminating adhesive  203  to the lacquered first film  201  The mono-layer second film  202  was a biaxially oriented polyethylene terephthalate (OPET) free-standing substrate (SKYRO® SP65 supplied by SKC, Inc., Covington, Ga.). After the lamination has been completed, the second film  202  is then scored, cut and/or perforated to provide the pattern of perforations in the second film. 
     After formation of the overwrap, the tray may then be filled with a food product and the overwrap placed over the tray and sealed to the flange of the tray. Preferably, overwrap is sealed to the tray such that a continuous seal is formed circumscribing the perimeter of the recessed cavity Preferably, the overwrap is sealed as a heat seal. Heat sealing can be achieved by bringing the surface of the overwrap into contact the surface of the flange and then applying sufficient heat and pressure to a predetermined area of the two surfaces to cause the contacting surfaces to become molten and intermix with one another, thereby forming as essentially inseparable fusion bond between the two surfaces in the predetermined area when the heat and pressure are removed therefrom and the area is allowed to cool. In one embodiment, the heat seal of the overwrap to the flange of the tray is a non-hermetic heat seal. In another embodiment, the heat seal of the overwrap to the flange of the tray is a hermetic heat seal. Once the overwrap is sealed to the flange of the tray, the overwrap is folded around the tray and a longitudinal seal is formed underneath the base of the tray. Preferably, the longitudinal seal is configured as a fin seal. Alternatively, the longitudinal seal can be configured as a lap seal. Sealing the overwrap underneath the base of the tray forms the front panel and the opposing back panel of the package. It is preferred to form the longitudinal seal as a heat seal. 
     After forming the longitudinal seal, a first leading end seal positioned substantially transverse to the longitudinal seal and an opposing second trailing end seal positioned substantially transverse to the longitudinal seal are then formed. Preferably, each of the end seals are formed as fin seals by heat sealing the inner surfaces of the front and back panels together which extend beyond the perimeter of the tray. After the end seals are formed, the leading end and trailing end of the overwrap are cut to individualize each package. 
     In an alternative method, the overwrap is first folded around the tray and a longitudinal seal is formed underneath the base of the tray. After forming the longitudinal seal, a first leading end seal positioned substantially transverse to the longitudinal seal and an opposing second trailing end seal positioned substantially transverse to the longitudinal seal are then formed. Following formation of the ends seal, the overwrap is then heat sealed to the flange of the tray. The heat sealing of the overwrap to the tray flange may be accomplished such a manner known to those skilled in the art so that either a hermetic or non-hermetic heat seal is formed. 
     Once package has been individualized, a separate label-type pull-tab may then be adhesively applied to the removable portion of the package at a location near or on a line of weakness. Preferably, the pull-tab is placed at a location which generally corresponds to the mid-point on the line of weakness. The pull-tab may have at least a first edge which is permanently affixed to the removable portion of the front panel. The pull-tab may further have an opposing second edge which is peelably affixed to the front panel of the package.