Patent Publication Number: US-7585528-B2

Title: Package having an inflated frame

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to packaging having a chamber portion for containing a product and an inflated frame surrounding the chamber, and to methods of making such packaging. 
     It is common in food packaging operations for a food product (e.g., fresh meat) to be placed on a rigid tray (e.g., a thermoformed expanded polystyrene tray having a central depressed area and a surrounding peripheral flange). A thermoplastic film may then be positioned over the food and heat sealed to the peripheral flange to hermetically enclose the food product. 
     However, a high percentage of the final packaging costs for such packaging systems is due to the relatively high cost of such trays. Further, there are costs and inconveniences associated with transporting and storing the trays before their use in the packages. Also, such trays add to the volume of packaging waste material with which the consumer must deal after opening the package. 
     SUMMARY OF THE INVENTION 
     The present invention addresses one or more of the aforementioned problems. 
     A package for containing a product includes top and bottom opposing flexible chamber sheets. These sheets are sealed together in a selected chamber seal zone to define a watertight chamber portion that is capable of containing the product. A hollow frame circumscribes the chamber portion. The frame supports the chamber portion when the frame is inflated. 
     A process of packaging includes the following steps: 1) providing a base web comprising a flexible sheet material; 2) placing a product on the base web; 3) positioning over the product a lid web comprising a flexible sheet material; 4) sealing the lid web to the base web at a selected chamber seal zone to form a chamber portion enclosing the product; and 5) sealing the lid web to the base web at one or more selected frame seal zones to form a hollow frame circumscribing the chamber portion and adapted to support the chamber portion when the frame is inflated. 
     The need for a rigid tray may be eliminated by the inventive package, so that the package may be considered “tray-less.” 
     These and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the detailed description of the invention and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a package of the present invention having the frame in an inflated state and a modified atmosphere in the chamber portion; 
         FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a plan view of one embodiment of the package of the present invention wherein the frame in interrupted by seals; 
         FIG. 4  is a plan view of another embodiment of the package of the present invention; 
         FIG. 5  is a representative schematic of a process line for making a package of the present invention; 
         FIG. 6  is a plan view of a further embodiment of the package of the present invention wherein the chamber portion containing the packaged product can be detached from the outer frame; 
         FIG. 7  is a plan view of a package of the present invention having a frame inflation passageway and a chamber inflation passageway; 
         FIG. 8  is a representative sectional view of a package of the present invention having a thermoformed base sheet; 
         FIG. 9  is a representative sectional view of a package of the present invention having a thermoformed base sheet and a thermoformed lid sheet; 
         FIG. 10  is a representative sectional view of the vacuum/gas-flush/sealing/inflation chamber of  FIG. 5  in the chamber open mode; 
         FIG. 11  is a representative sectional view of the vacuum/gas-flush/sealing/inflation chamber of  FIG. 5  in the chamber close mode; 
         FIG. 12  is a representative sectional view of the vacuum/gas-flush/sealing/inflation chamber of  FIG. 5  in the chamber portion seal mode; 
         FIG. 13  is a representative sectional view of the vacuum/gas-flush/sealing/inflation chamber of  FIG. 5  in the frame seal mode; 
         FIG. 14  is a representative sectional view of the vacuum/gas-flush/sealing/inflation chamber of  FIG. 5  in the chamber open mode with a formed package of the present invention; 
         FIG. 15  is a representative sectional view of a thermoforming station; 
         FIG. 16  is a representative sectional view of another thermoforming station; 
         FIG. 17  is a representative schematic of an alternative process line for making a package of the present invention; 
         FIG. 18  is a representative sectional view of a preferred thermoformed base sheet suitable for the manufacture of a package of the present invention; 
         FIG. 19  is a plan view of a base web thermoformed as illustrated in  FIG. 18 ; 
         FIGS. 20   a ,  20   b , and  20   c , are plan views of packages of the present invention equipped with different easy-opening features. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1  and the sectional view of the same package at  FIG. 2 , package  10  comprises a chamber portion  12  circumscribed by a hollow frame  14 . The chamber portion  12  may be, and preferably is, “watertight” (i.e., does not permit leakage or permeation of liquid water except if subjected to structural discontinuity) and further it may be, and preferably is, “airtight” or “hermetic” (i.e., does not permit permeation of oxygen at a rate above 1000 cubic centimeters (at standard temperature and pressure) per square meter per day per 1 atmosphere of oxygen pressure differential measured at 0% relative humidity and 23° C., unless subjected to structural discontinuity). Chamber portion  12  is capable of or adapted to contain product  16 . The chamber portion  12  may include a top chamber sheet  18  and a bottom chamber sheet  20 , which may be juxtaposed and sealed together at a chamber seal zone  22  to form the chamber portion  12 . The terminology “top” and “bottom” sheets as used in this application includes the sense of one sheet of material folded over upon itself to form the top and bottom sheets. 
     Hollow frame  14 , which is shown in an inflated state, circumscribes chamber portion  12 . The frame  14  is adapted to support the chamber portion  12  when the frame  14  is inflated. Frame  14  may be inflated with any fluid material, such as liquids, flowable powders or, preferably, with gases. 
     Frame  14  may be in form of a continuous tube surrounding chamber portion  12 , as shown in  FIG. 1 , or said continuous tube may be interrupted by one or more seals  23 , as illustrated in  FIG. 3 . 
     When frame  14  is interrupted by more than one seal, said seals create two or more discrete frame chambers  25 . The advantage of having discrete chambers clearly resides in the possibility that one chamber of the frame may deflate without deflating the entire frame. Preferably in this embodiment the seals interrupting the frame are two or more and are disposed symmetrically along the frame in order to avoid or prevent as much as possible any distortion of the end package. Preferably, in case of packages of substantially rectangular or square shape, as illustrated in  FIG. 3 , said seals are positioned in the corners. 
     In a further embodiment, illustrated in  FIG. 4 , said one or more seals  23  may contain continuous or discontinuous (serrated) cuts  123 . The advantage of this embodiment resides in the possibility for the end user to easily open the package by grasping by hands the two edges of the frame that are separated by cut-seals  123  and tearing them apart, thus using the cut-seal as a notch. This can be done with or without prior deflation of the frame, in case of a single cut-seal, or of the two discrete chambers  25  of the frame that are adjacent to the cut-seal used as the package notch. 
     Frame  14  may include a top frame sheet  26  and a bottom frame sheet  28 , which may be juxtaposed and sealed together at a frame inner seal zone  30  and a frame outer seal zone  32  to form frame  14 . 
     As illustrated in  FIG. 2 , lid sheet  34  extends continuously from the frame to the chamber portion, thereby including both top chamber sheet  18  and top frame sheet  26 . Also as illustrated in  FIG. 2 , base sheet  36  extends continuously from the frame to the chamber portion, thereby including both bottom chamber sheet  20  and bottom frame sheet  28 . The lid sheet  34  may be formed from a lid web  38  ( FIG. 5 ) and the base sheet  36  may be formed from a base web  40  ( FIG. 5 ). As used herein, a “web” is a continuous length of sheet material handled in roll form, as contrasted with the same material cut into short lengths. 
     In order to support chamber portion  12  when frame  14  is inflated, frame  14  may be attached to the exterior perimeter of chamber portion  12 , for example, by one or more heat or adhesive seals, or by a tape (not shown) or other mechanical linkage attaching frame  14  to the chamber portion  12 . For example, as illustrated in  FIG. 2 , frame  14  is attached to the chamber portion  12  by virtue of lid sheet  34  and base sheet  36 , which extend continuously from frame  14  to chamber portion  12  to attach frame  14  to chamber portion  12 . Either or both of the lid and base sheets may extend continuously from the frame to the chamber portion to attach the frame  14  to the chamber portion  12 . 
     Frame inner seal zone  30  may be coextensive with chamber portion seal zone  22 , as illustrated in  FIGS. 1-2 . Alternatively, the frame inner seal zone  30  may be spaced apart from chamber portion seal zone  22  or may be adjacent to chamber portion seal zone  22 . If lid sheet  34  is sealed to base sheet  36  so that frame inner seal zone  30  is coextensive with chamber portion seal zone  22 , then the frame  14  and chamber portion  12  may share a common seal, as illustrated in  FIG. 2 . In such case, the frame inner seal zone  30  may be said to include or comprise chamber portion seal zone  22 —or chamber portion seal zone  22  may be said to include or comprise frame inner seal zone  30 . 
     The sheets (i.e., top and bottom chamber sheets, top and bottom frame sheets, lid and base sheets) may be sealed together at any of the seal zones (e.g., chamber seal zone  22 , the frame inner seal zone  30 , and the frame outer seal zone  32 ) by any method, such as heat sealing (e.g., conductance sealing, impulse sealing, ultrasonic sealing, dielectric sealing) or by application of a suitable adhesive (e.g., a UV-curable adhesive) (not shown) between the sheets in the applicable seal zone. Such methods and the relative equipment are well known to those of skill in the art. 
     As illustrated in  FIG. 6 , it is also possible to create a line of weakness  31 , embedded in the coextensive seal that separates chamber portion  12  from hollow frame  14 , or positioned between the chamber portion seal zone  22  and the frame inner seal zone  30 , in case these two zones are spaced apart. The presence of such a weakness line may allow detachability of chamber portion  12  containing the packaged product  16  from the inflated frame  14  if and when desired. This possibility might be particularly useful e.g. when it is necessary for the customer to reduce the size of the package to better store it at home. In  FIG. 6  the weakness line  31  is shown as a zig-zag serration embedded in a wide coextensive seal  22 - 30  separating chamber portion  12  from frame  14 . By breaking the serration it is thus possible to separate the sealed chamber portion  12  containing product  16  from the circumscribing frame portion  14 . In this embodiment, once the chamber portion is separated, it is also possible, if desired, to use the shaped edges of the zig-zag serration as a tear initiator to easy open the package. 
     As illustrated in another embodiment shown in  FIG. 7 , package  10  includes a frame inflation passageway  42  attached to frame  14  to provide access to the interior of hollow frame  14  for inflating the frame. Accordingly, frame inflation passageway  42  may be connected to one or more portions of frame  14  and be in fluid communication with the interior space of frame  14 . A chamber inflation passageway  44  may be attached to chamber portion  12  to provide access to the interior space of chamber portion  12  for introducing a modified atmosphere into the interior space of chamber portion  12 . Chamber inflation passageway  44  may be connected to one or more portions of chamber portion  12  and be in fluid communication with the interior space of chamber portion  12 . Examples of frame inflation passageway  42  and chamber inflation passageway  44  include sealable inflation passageways or one-way inflation valves, for example, as illustrated in U.S. Pat. No. 6,276,532 by Sperry et al, which is incorporated herein in its entirety by reference. 
     As illustrated in another preferred embodiment shown in  FIG. 8 , package  11  includes a thermoformed bottom chamber sheet  120  and a thermoformed bottom frame sheet  128 , which may be provided as thermoformed base sheet  136 . The thermoformed bottom chamber sheet  120  may provide a configuration adapted for convenient placement of, or conformance to, product  16  within chamber portion  12 . 
     As illustrated in still another preferred embodiment shown in  FIG. 9 , package  11  may include a thermoformed bottom chamber sheet  120  and a thermoformed bottom frame sheet  128 , which may be provided as thermoformed base sheet  136 , as well as a matching thermoformed top chamber sheet  118  and a thermoformed top frame sheet  126 , which may be provided as thermoformed lid sheet  134 . 
     The package of the present invention may be useful for the packaging of food as well as non-food products. 
     When a product  16  is packaged which is preferably stored under an atmosphere different from ambient air, package  10  ( 11 ) may conveniently include a modified atmosphere  24  in chamber portion  12 , so that product  16  may be packaged in said modified atmosphere  24 . A modified atmosphere may be useful, for example, to decrease the concentration of oxygen from that of ambient air or to increase the concentration of oxygen and carbon dioxide from that of ambient air in order to extend a packaged product&#39;s shelf-life or bloom color life. For example, in packaging meat, the atmosphere in the sealed package may comprise about 80% by volume oxygen and about 20% by volume carbon dioxide in order to inhibit the growth of harmful microorganisms and extend the time period in which the meat retains its attractive red (“bloom”) coloration. As used herein, the term “modified atmosphere” refers to a gas environment having a composition that is altered from that of ambient air for the purpose of extending the shelf life, enhancing the appearance, or reducing the degradation of a packaged product. 
     Examples of modified atmosphere  24  include gas environments having an oxygen concentration (by volume): 1) greater than about any of the following values: 30%, 40%, 50%, 60%, 70%, 80%, and 90%, 2) ranging between any of the preceding values (e.g., from about 30% to about 90%), 3) no more than about any of the following values: 15%, 10%, 5%, 1%, and 0%, and 4) ranging between any of the preceding values (e.g., from about 0% to about 15%). A modified atmosphere may also include gas environment having a carbon dioxide concentration of greater than about any of the following values: 10%, 20%, 30%, 40%, and 50% by volume. The modified atmosphere  24  may also include non-ambient amounts of one or more gases selected from e.g. argon, nitrogen, carbon monoxide, helium, and the like gases. 
     When a modified atmosphere  24  is employed, the package according to the present invention is particularly useful for the packaging of oxygen-sensitive items (i.e., items that are perishable, degradable, or otherwise changeable in the presence of oxygen). Examples of oxygen-sensitive products or items include red meat (e.g., beef, veal, and lamb), processed meat, pork, poultry, fish, cheese, and vegetables. Package  10  ( 11 ) may also include an absorbent pad (not shown) within chamber portion  12 , for example, to absorb meat purge and/or release moisture or fragrances. 
     As used herein, “the sheets” refers to any of the top and bottom chamber sheets  18  ( 118 ),  20  ( 120 ), top and bottom frame sheets  26  ( 126 ),  28  ( 128 ), and lid and base sheets  34  ( 134 ),  36  ( 136 ). Any of the sheets may comprise one or more layers of thermoplastic polymer materials such as for instance polyolefins, polystyrenes, polyurethanes, polyamides, polyesters, polyvinyl chlorides, ionomers and blends thereof. 
     Useful polyolefins include ethylene homo- and co-polymers and propylene homo- and co-polymers. Ethylene homopolymers include high density polyethylene (“HDPE”), a polyethylene with a density higher than 0.94 g/cm 3 , typically comprised between 0.94 and 0.96 g/cm 3 , medium density polyethylene (“MDPE”), a polyethylene with density typically comprised between 0.93 and 0.94 g/cm 3 , and low density polyethylene (“LDPE”) a polyethylene with density below 0.93 g/cm 3 . Ethylene copolymers include ethylene/alpha-olefin copolymers (“EAOs”) and ethylene/unsaturated ester copolymers (“copolymer” as used in this application means a polymer derived from two or more types of monomers, and includes terpolymers, etc.) 
     EAOs are copolymers of ethylene and one or more alpha-olefins, the copolymer having ethylene as the majority mole-percentage content. The comonomer may include one or more C 3 -C 20  α-olefins, such as one or more C 4 -C 12  α-olefins, preferably one or more C 4 -C 8  α-olefins. Useful α-olefins include 1-butene, 1-hexene, 5-methyl-1-pentene, 1-octene, and mixtures thereof. 
     EAOs include one or more of the following: linear medium density polyethylene (“LMDPE”), for example having a density of from 0.926 to 0.94 g/cm 3 , linear low density polyethylene (“LLDPE”), for example having a density of from 0.915 to 0.930 g/cm 3 , and very-low or ultra-low density polyethylene (“VLDPE” and “ULDPE”), for example having density below 0.915 g/cm 3 . Unless otherwise indicated, all densities herein are measured according to ASTM D1505. 
     The polyethylene polymers and copolymers may be either heterogeneous or homogeneous. As is known in the art, heterogeneous polymers have a relatively wide variation in molecular weight and composition distribution; whereas, homogeneous polymers have a relatively narrow variation in molecular weight and composition distribution. Heterogeneous polymers may be prepared with, for example, conventional Ziegler Natta catalysts. On the other hand, homogeneous polymers are typically prepared using metallocene or other single site-type catalysts. 
     Another useful ethylene copolymer is ethylene/unsaturated ester copolymer, which is the copolymer of ethylene and one or more unsaturated ester monomers. Useful unsaturated esters include vinyl esters of aliphatic carboxylic acids, containing from 4 to 12 carbon atoms (e.g., vinyl acetate), and alkyl esters of acrylic or methacrylic acid (collectively, “alkyl (meth)acrylate”), containing from 4 to 12 carbon atoms. 
     Useful propylene copolymer includes propylene/ethylene copolymers (“EPC”), which are copolymers of propylene and ethylene having a majority weight % content of propylene, such as those having an ethylene comonomer content of less than 10%, preferably less than 6%, and more preferably from about 2% to 6% by weight; and propylene-ethylene-butene terpolymers (or propylene-ethylene-higher a-olefin terpolymers) having a majority wt. % of propylene, such as those having a total amount of ethylene and butene (or ethylene and higher α-olefin) of less than 25 wt. %, preferably less than 20 wt. %. Also the propylene polymers can be heterogeneous or homogeneous. 
     Suitable polyamides are both homo-polyamides or co- (ter- or multi-)polyamides, which can be aliphatic, aromatic or partially aromatic. The homopolyamides are derived from the polymerisation of a single type of monomer comprising both the chemical functions which are typical of polyamides, i.e. amino and acid groups, such monomers being typically lactams of amino-acids, or from the polycondensation of two types of polyfunctional monomers, i.e. polyamines with polybasic acids. The co-, ter-, and multi-polyamides on the other hand are derived from the copolymerisation of precursor monomers of at least two (three or more) different polyamides, e.g. two different lactams, or two types of polyamines and/or polyacids, or a lactam on the one side and a polyamide and a polyacid on the other. Examples of suitable polyamides are PA 6, PA 6/66, PA 6/12, PA 6I/6T, PA MXD6, PA MXD6/MXDI, and the like polyamides. 
     Examples of useful polyesters include amorphous (co)polyesters, comprising an aromatic dicarboxylic acid, e.g. terephthalic acid, naphthalenedicarboxylic acid, and isophthalic acid, as the main dicarboxylic acid component and an aliphatic glycol, e.g., ethylene glycol, trimethylene glycol, tetramethylene glycol, optionally admixed with an alicyclic glycol, such as cyclohexane dimethanol, as the main glycol component. Polyesters with at least about 75 mole percent, more preferably at least about 80 mole percent, based on the total of the dicarboxylic acid component, of terephthalic acid may be preferred. 
     As reported above, any of the sheets may be mono- or multi-layered. If a sheet is multilayered, then the sheet may include one or more outer layers of a heat-sealable material to assist in heat sealing the sheets together, as is known in the art. Such a sealant layer may include one or more of the thermoplastic polymers discussed above. 
     It may be advantageous for any, or one or more, of the sheets to have gas (e.g., oxygen, carbon dioxide) barrier attributes to decrease the gas permeability of the sheet. Barrier attributes for the sheets may be useful, for example to increase the inflated life of frame  14 , to enhance the storage life of a packaged product  16  contained within chamber portion  12  that may degrade upon exposure to oxygen (e.g., red meat), and to help maintain a modified atmosphere  24  that may be contained within chamber portion  12 . 
     Any, or one or more, of the sheets may therefore comprise one or more materials (“barrier components”) that markedly decrease the oxygen or carbon dioxide transmission rate through the sheet and thus impart barrier attributes to the sheet. (Since carbon dioxide barrier properties generally correlate with oxygen barrier properties, only oxygen barrier properties are discussed in detail herein.) Examples of barrier components include: ethylene/vinyl alcohol copolymer (“EVOH”), polyvinyl alcohol (“PVOH”), vinylidene chloride polymers (“PVdC”), polyalkylene carbonate, polyester (e.g., PET, PEN), polyacrylonitrile (“PAN”), and polyamide. Preferred barrier materials are EVOH, PVDC, polyamides and blends of EVOH and polyamides. 
     EVOH may have an ethylene content of between about 20% and 40%, preferably between about 25% and 35%, more preferably about 32% by weight. EVOH may include saponified or hydrolyzed ethylene/vinyl acetate copolymers, such as those having a degree of hydrolysis of at least 50%, preferably of at least 85%. 
     Vinylidene chloride polymer (“PVdC”) refers to a vinylidene chloride-containing copolymer, that is, a polymer that includes monomer units derived from vinylidene chloride (CH 2 ═CCl 2 ) and monomer units derived from one or more of vinyl chloride, styrene, vinyl acetate, acrylonitrile, and C 1 -C 12  alkyl esters of (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methyl methacrylate). As is known in the art, one or more thermal stabilizers, plasticizers and lubricating processing aids may be used in conjunction with PVdC. 
     If a sheet is multilayered, then the one or more layers of the sheet that incorporate barrier components in an amount sufficient to notably decrease the oxygen permeability of the sheet are considered “barrier layers.” If the sheet is monolayered, then the barrier components may be incorporated in the sole layer of the sheet and the sheet itself may be considered a “barrier layer.” 
     A useful barrier layer includes that having a thickness and composition sufficient to impart to the sheet incorporating the barrier layer an oxygen transmission rate of no more than about any of the following values: 150, 100, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5 cubic centimeters (at standard temperature and pressure) per square meter per day per 1 atmosphere of oxygen pressure differential measured at 0% relative humidity and 23° C. All references to oxygen transmission rate in this application are measured at these conditions according to ASTM D-3985. For example, top and bottom chamber sheets  18  ( 118 ),  20  ( 120 ) as well as top and bottom frame sheets  26  ( 126 ), and  28  ( 128 ), may each have a thickness and composition sufficient to impart to each of the sheets any of the oxygen transmission rates previously recited. 
     When the modified atmosphere  24  in chamber portion  12  is free from oxygen and the packaged product  16  is particularly oxygen-sensitive, it may also be advisable to include an oxygen scavenging agent in the top and/or in the bottom chamber sheets  18  ( 118 ),  20  ( 120 ), in a layer in closer proximity to the packaged product than the gas-barrier layer. The oxygen scavenging agent present in said layer will react with the residual oxygen that is trapped in the package or that permeates into the package in spite of the gas barrier layer, thus maintaining the modified atmosphere  24  free from oxygen. The use of oxygen scavengers is described for instance in U.S. Pat. No. 5,350,622 while a general method of triggering the oxygen scavenging process is described in U.S. Pat. No. 5,211,875. The content of both these documents in its enterity is incorporated herein by reference. 
     The sheets may have any thickness suitable for the packaging application, preferably taking into consideration factors such as the desired inflation pressure of the frame and/or chamber portion, the tensile strength of the sheet material, the hoop stress resulting from the given inflated configuration of the frame and/or chamber portion, the amount of abuse expected for the application, whether the sheets are thermoformed or not and the desired gas permeation rate through the sheets. Useful sheet thickness ranges include from about 0.5 to about 10 mils, preferably from about 1 to about 9 mils, and more preferably from about 2 to about 8 mils. 
     Any or all of the sheets may have one or more of the characteristics selected from flexible, stretchable, extendable, and elastic. For example, a sheet may be stretched by inflation. The sheets preferably exhibit a Young&#39;s modulus sufficient to withstand the expected handling and use conditions. Young&#39;s modulus may be measured in accordance with one or more of the following ASTM procedures: D882; D5026-95a; D4065-89, each of which is incorporated herein in its entirety by reference. Any or all of the sheets may have a Young&#39;s modulus of at least about any of the following values: 100 MPa, 200 MPa, 300 MPa, and 400 MPa, measured at 100° C. The Young&#39;s modulus for the sheets may also range from about 70 to about 1000 MPa, and preferably range from about 100 to 500, measured at 100° C. 
     Any or all of the sheets may be oriented in either the machine (i.e., longitudinal) or the transverse direction, or in both directions (i.e., biaxially oriented), in order to reduce the permeability and to increase the strength and durability of the sheet. For example, the sheet may be oriented in at least one direction by a ratio of any of the following: at least 2.5:1, from about 2.7:1 to about 10:1, at least 2.8:1, at least 2.9:1, at least 3.0:1, at least 3.1:1, at least 3.2:1, at least 3.3:1, at least 3.4:1, at least 3.5:1, at least 3.6:1, and at least 3.7:1. 
     Any or all of the sheets may be heat shrinkable or non-heat shrinkable. If heat shrinkable, the sheets may have a total free shrink at 185° F. (85° C.) of at least about any of the following values: 5%, 10%, 15%, 40%, 50%, 55%, 60%, and 65%. The total free shrink at 185° F. (85° C.) may also be within any of the following ranges: from 40 to 150%, 50 to 140%, and 60 to 130%. The total free shrink is determined by summing the percent free shrink in the machine (longitudinal) direction with the percentage of free shrink in the transverse direction. For example, a sheet which exhibits 50% free shrink in the transverse direction and 40% free shrink in the machine direction has a total free shrink of 90%. It is not required that the sheet have shrinkage in both directions. The free shrink of the sheet is determined by measuring the percent dimensional change in a 10 cm×10 cm sheet specimen when subjected to selected heat (i.e., at a certain temperature exposure) according to ASTM D 2732, which is incorporated herein in its entirety by reference. The sheets may be annealed or heat-set to reduce the free shrink either slightly, substantially, or completely; however, a sheet may not be heat set or annealed once stretched if it is desired that the sheet have a high level of heat shrinkability. 
     In a preferred embodiment of the present invention the film is not heat-shrinkable. When, as in the package  11  liustrated in  FIGS. 8 and 9 , one or both of the base and lid sheets are at least partially thermoformed, preferably said thermoformable sheets are substantially non oriented and their thickness, before the thermoforming step, is preferably ≧2.5 mils, more preferably ≧3 mils. 
     One or more layers of any of the sheets used in the manufacture of the package of the present invention may include appropriate amounts of additives typically included to improve processability or performance of the thermoplastic materials, such as slip agents, antiblock agents, anti-oxidants, fillers, dyes, pigments, cross-linking enhancers, cross-linking inhibitors, radiation stabilisers, antistatic agents and the like agents. 
     In particular when the packaged product  16  is a food product, at least the top chamber sheet  18  ( 118 ) preferably incorporates or has dispersed in effective amounts of one or more antifog agents in the sheet resin before forming the resin into a sheet, and in the case of a multilayer sheet, in one or more of the layers of the sheet. The antifog agent may also be applied as an antifog coating to at least one surface of the sheet. Useful antifog agents and their effective amounts are well known in the art. 
     Any of the sheets, for example, the top chamber sheet  18  ( 118 ) and/or top frame sheet  26  ( 126 ), may be transparent to visible light to enable a consumer to see the packaged product in the areas where the sheet does not support a printed image (e.g., labeling information). “Transparent” as used herein means that the material transmits incident light with negligible scattering and little absorption, enabling objects (e.g., packaged product or print) to be seen clearly through the material under typical viewing conditions (i.e., the expected use conditions of the material). Also, any of the sheets may be opaque, colored, or pigmented. For example, the bottom chamber sheet  20  ( 120 ) and/or bottom frame sheet  28  ( 128 ) may be opaque, colored, or pigmented to provide a background for the packaged product  16  or to simulate the appearance of a conventional meat tray, or to hide the presence of an absorbing pad or of drip. 
     Useful films for forming the sheets may be selected from one or more of the films disclosed in International Patent Application Publication No. WO 01/68363 A1 published 20 Sep. 2001 entitled “Bi-Axially Oriented and Heat-Set Multilayer Thermoplastic Film for Packaging” and U.S. Pat. No. 6,299,984 issued 9 Oct. 2001 entitled “Heat-Shrinkable Multilayer Thermoplastic Film” (corresponding to EP 0 987 103 A1 published 22 Mar. 2000). Each of the foregoing publications is incorporated herein in its entirety by reference. 
     Another class of thermoplastic structures that proved useful for the manufacture of a package according to the present invention, particularly for the manufacture of a package as illustrated in  FIG. 8  and in  FIG. 9  wherein one or both of the base and lid sheets are thermoformed (or at least partially thermoformed), comprises laminates with an outer heat-sealing layer comprising an ethylene homo- or copolymer (e.g. LLDPE, VLDPE, homogeneous ethylene-α-olefin copolymers, LDPE, EVA, ionomers, etc.), a gas-barrier layer preferably comprising EVOH, and the other outer abuse resistant layer, comprising a polyamide, and preferably a polyamide with a melting point equal to or higher than 175° C. The thickness of this laminate, that can be obtained by heat- or glue-lamination of pre-formed layers or by coextrusion or extrusion coating, is generally comprised between 2 and 10 mils, preferably between 2.5 and 9 mils and more preferably between 3 and 8 mils. The structure typically comprises one or more inner bulk layers to reach the desired thickness, typically of low cost polyolefins, e.g. polyethylene and/or polypropylene resins. Tie layers, to improve the bond between the various layers and avoid delamination, might also be present, if needed or appropriate. 
     An example of a thermoplastic film structure of particular interest is the following nine layers structure with a total thickness of 150 microns (6 mils): 
     LLPDE1/LLDPE2/PP/PP/PP/PP/PP/EVOH/PA6 
     with the following partial thicknesses (μm) 13.5/30/6/21/15/21/6/15/22.5 
     wherein: 
     LLDPE1 is a linear low density polyethylene also containing slip and antiblock additives, used as the structure heat-sealable layer; 
     LLDPE2 is linear low density polyethylene; 
     PP is polypropylene; 
     EVOH is ethylene/vinyl alcohol copolymer; and 
     PA6 is Nylon 6, used as the outer abuse resistant layer. 
     In one embodiment the package  10  may be formed using packaging machine  74  ( FIG. 5 ). Packaging machine  74  includes base unwind mandril  45  that supports base web roll  46  so that base web  40  may be fed to vacuum/gas-flush/sealing/inflation chamber  48  (i.e., “seal chamber  48 ”). Lid unwind mandril  51  supports lid web roll  50  so that lid web  38  may also be fed to seal chamber  48 . 
     Seal chamber  48  includes top chamber casing  52  and opposing bottom chamber casing  54 . The top and bottom chamber casings are moveable relative each other to a chamber open mode, illustrated in  FIGS. 10 and 14 , and a chamber closed mode, illustrated in  FIGS. 11 ,  12  and  13 . In the chamber open mode, the top and bottom casings are spaced apart to allow the lid and base webs  38 ,  40  and product  16  to enter seal chamber  48 . In the chamber closed mode, top and bottom casings  52 ,  54  are proximate each other to form an enclosed chamber volume  68 . 
     Top chamber casing  52  may enclose and slideably receive both inner seal bar  56  and outer seal bar  58 . Bottom chamber casing  54  may support seal anvil  60 , which opposes both the inner and outer seal bars. Inner seal bar  56  and seal anvil  60  are moveable relative each other between an inner seal bar engaged position and an inner seal bar disengaged position. In the inner seal bar engaged position, illustrated in  FIGS. 12 and 13 , inner seal bar  56  and seal anvil  60  are proximate each other to define inner seal chamber volume 70 and outer seal chamber volume  72 . In the inner seal bar disengaged position, illustrated in  FIG. 11 , the inner seal bar  56  and seal anvil  60  are spaced apart. 
     Similarly, outer seal bar  58  and seal anvil  60  are moveable relative each other between an outer seal bar engaged position and an outer seal bar disengaged position. In the outer seal bar engaged position, illustrated in  FIG. 13 , outer seal bar  58  and seal anvil  60  are proximate each other. In the outer seal bar disengaged position, illustrated in  FIGS. 11 and 12 , the outer seal bar  58  and seal anvil  60  are spaced apart. 
     Seal chamber  48  includes a vacuum source  62 , a modified atmosphere source  64 , and an inflation gas source  66 , each of which is capable of controlled fluid communication with seal chamber  48 , as discussed further below. 
     Cutter  76  is downstream from the seal chamber  48 . Suitable cutters are well known in the art and include, for example, rotary cutters, knife cutters, cutting blades, and laser cutters. 
     In the operation of packaging machine  74 , the base web  40  is unwound from base web roll  46  supported by base unwind mandril  45  and is fed to the seal chamber  48 . The base web  40  may be pulled along by gripping chains (not shown) at two sides, as is known in the art. Product  16  may be placed on base web  40  before the web is fed to seal chamber  48 . Lid web  38  is unwound from lid web roll  50  supported by lid unwind mandril  51  and is also fed to seal chamber  48 . The lid web  38  may also be pulled along by gripping chains (not shown) at two sides, as is known in the art. At least a portion of lid web  38  may be positioned over product  16 , either before or after product  16  enters seal chamber  48 . 
     The lid and base webs  38 ,  40  on either side of product  16  are positioned between the top chamber casing  52  and bottom chamber casing  54  while the seal chamber  48  is in the chamber open mode ( FIG. 10 ). Next, the seal chamber  48  moves to a chamber closed mode so that top and bottom chamber casings  52 ,  54  engage, compress, or squeeze the lid and base webs  38 ,  40  between them and as a result form three essentially airtight enclosed chamber volumes: upper chamber volume  68  (which is a volume above web  38 ), lower chamber volume  69  (which is a volume below web  40 ), and intermediate chamber volume  67  (which is a volume between webs  38  and  40  enclosing product  16 ). ( FIG. 11 ) Optionally, upper and lower chamber volumes  68 ,  69  may be placed in fluid communication by appropriate piping, tubing, or other means, as is known in the art. 
     In the chamber closed mode ( FIG. 11 ), a vacuum may be pulled on the enclosed intermediate chamber volume  67  to evacuate a desired amount of enclosed ambient air through vacuum source  62 . Next, a modified atmosphere of a desired composition and amount may be introduced into intermediate chamber volume  67  through modified atmosphere source  64 . The modified atmosphere may be introduced at a temperature lower than the ambient temperature, so that upon later warming to ambient temperature, the modified atmosphere within chamber portion  12  may obtain an above-ambient pressure. 
     It may be desirable to maintain a balanced force on the upper and lower webs (i.e., avoid ballooning of the intermediate chamber volume  67 ) when introducing modified atmosphere into intermediate chamber volume  67 . To do so, the pressure in the upper and lower chamber volumes  68 ,  69  may be increased by introducing a gas (e.g., air or modified atmosphere) into those chamber volumes when introducing modified atmosphere into intermediate chamber volume  67 . 
     Subsequently, inner seal bar  56  and seal anvil  60  move to the inner seal bar engaged position ( FIG. 12 ) to compress lid and base webs  38 ,  40  between them and also to define inner seal chamber volume  70 , outer seal chamber volume  72 , and frame volume  73  (between the lid and base webs). The inner seal bar is heated to a temperature effective to heat seal the webs together in chamber seal zone  22  (see  FIG. 2 ). In so doing, chamber portion  12  is formed enclosing modified atmosphere  24  and product  16  (see  FIG. 2 ). 
     Next, an inflation gas is introduced into the frame volume  73  through inflation gas source  66 . Suitable inflation gas includes, for example, air, nitrogen, or modified atmosphere (including modified atmosphere having the same composition as that introduced through modified atmosphere source  64 , as discussed above). An amount of inflation gas is added to elevate the pressure within frame volume  73  to a desired amount, for example, a gauge pressure (wherein “gauge pressure” is the pressure difference between the system and the atmospheric pressure) of at least about any of the following values: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, and 1 bar; a gauge pressure of less than about 2 bar; and a gauge pressure ranging between any of the foregoing values (e.g., from about 0.2 bar to about 0.8 bar, and from about 0.3 bar to about 2 bar). 
     It may also be desirable to maintain a balanced force on the upper and lower webs (i.e., avoid premature ballooning of the frame volume  73 ) when introducing inflation gas into frame volume  73 . To do so, the pressure in the outer seal chamber volume  72  may be increased by introducing an inflation gas into that chamber volume when introducing inflation gas into frame volume  73 . 
     Turning to  FIG. 13 , outer seal bar  58  and seal anvil  60  move to the outer seal bar engaged position ( FIG. 13 ) to compress lid and base webs  38 ,  40  between them. The outer seal bar is heated to a temperature effective to heat seal the webs together in frame outer seal zone  32  (see  FIG. 2 ). In so doing, hollow frame  14  is formed enclosing the inflation gas at the elevated pressure. 
     Next, the inner and outer seal chamber volumes  70 ,  72  and lower chamber volume  69  may be vented to restore ambient pressure before opening the chamber. Then, the top and bottom chamber casings return to the chamber open mode, with inner seal bar  56  and seal anvil  60  in the disengaged position and outer seal bar  58  and seal anvil  60  in the disengaged position, as illustrated in  FIG. 14 . 
     Upon exposure to ambient pressure, frame  14  takes on an inflated condition since the pressure within frame  14  is greater than the ambient pressure. In taking on an inflated condition, frame  14  tries to pull away from chamber portion  12 , thus creating a tension that provides some stiffness or rigidity to the package  10  and to chamber portion  12  (containing the modified atmosphere) relative to the state where frame  14  is not inflated. The pressure within frame  14  may be any of the pressures mentioned above with respect to the pressure within outer seal chamber volume  72 . 
     Lid and base webs may be indexed forward so that cutter  76  ( FIG. 5 ) may sever the webs to release package  10 . The cutter may cut the webs, for example, by butt or die cuts as is known in the art. Although the cutter  76  is illustrated in  FIG. 5  as downstream from seal chamber  48 , the cutter may alternatively be located just upstream of the seal chamber  48 . The packaging machine  74  may operate in an indexed and/or essentially continuous manner, to produce numerous packages  10  from the lid and base web rolls. 
     The manufacture of a package  11  wherein either one or both of the lid and base sheets are thermoformed, as illustrated in  FIGS. 8 and 9 , involves the use of at least one thermoforming station to thermoform a portion of the base web  40  upstream from the point where product  16  is placed on the web and/or of the lid web  30  upstream the vacuum chamber  48 . Thermoforming stations and thermoforming methods are well known in the art, and include positive or negative vacuum forming and positive or negative compressed air forming, any of which may be used with or without mechanical pre-stretching and with or without plug assist. For example, the packaging machine illustrated in  FIG. 5  may be modified to include a thermoforming station, such as that represented by thermoform station  80  ( FIG. 15 ) having mold  82  and opposing plug  84 , which cooperate to form base web into a desired shape, such as the shape of the thermoformed base sheet  136  (which in  FIG. 8  includes thermoformed bottom chamber sheet  120  and thermoformed bottom frame sheet  128 ). Another example of a suitable thermoforming station is represented by thermoforming station  86  ( FIG. 16 ) having forming mold  88 , opposing hot plate  90 , and enclosing top and lower chambers  92 ,  94 . Thermoforming station  86  may also be used to form base web into a desired shape, such as the shape of the thermoformed base sheet  136  ( FIG. 8 ). Base web  40  may be formed into a series of tray shapes having flanges to facilitate the sealing of the lid web  38  to the base web  40 . The bottom frame sheet may or may not be thermoformed. Alternatively, only the frame sheets, bottom and/or top frame sheets, may be thermoformed while the chamber sheets are not. 
     In another, preferred, embodiment, package  10  ( 11 ) may be formed using the packaging machine schematically represented in  FIG. 17  and indicated as  100 . 
     In said Figure,  101  is the unwinding station for the base web roll, while  102  is the unwinding station for the lid web roll.  103  and  104  identify two separate thermoforming stations that can be excluded, if neither the base or the lid have to be thermoformed, or can be separately and independently actuated to provide for only the base web  40 , or only the lid web  38  or both base and lid webs at least partially thermoformed. 
     When at least one of the base and lid webs is thermoformed, a preferred profile of thermoforming is that indicated in  FIG. 18  for a base web. In said  FIG. 18 ,  136  is the overall thermoformed base sheet,  128  is the thermoformed bottom frame sheet,  109  is the outermost edge of the thermoformed bottom frame sheet  128 ,  120  is the thermoformed bottom chamber sheet, and  110  is the edge separating the thermoformed bottom frame sheet  128  from the thermoformed bottom chamber sheet  120 . In said  FIG. 18 ,  120 ,  128 , and  136  correspond to the items identified with the same numerals in package  11  of  FIGS. 8 and 9 , and  109  and  110  correspond to the same numerals in the plan view of the thermoformed web of  FIG. 19 . 
       105  is the station where product  16  is suitably positioned on the base web. When the base web  40  is thermoformed e.g. as in the embodiment of  FIG. 18 , product  16  is loaded into the thermoformed bottom chamber sheet. 
     The base web  40  loaded with product  16  and the corresponding lid web  38 , are then advanced to a vacuum/gas-flushing/sealing chamber schematically indicated by the numeral  106  (“first chamber”). Said first chamber  106  differs from chamber  48  described above essentially in that it does not include an inflation gas source. 
     In said first chamber  106 , if desired, it is possible to draw vacuum within chamber portion  12 , through a vacuum source  162 , and optionally introduce therein a suitably modified atmosphere  24 , through a modified atmosphere source  164 . Then moving the seal bars and the seal anvils into the engaged position, either in one single or two separate steps, all the seals of the end package  10  ( 11 ), i.e. the frame outer seal  32 , the frame inner seal  30  and the chamber portion seal  22 , are made. The thus obtained intermediate package, where product  16  is sealed within chamber portion  12 , either under vacuum or under the desired, optionally modified, atmosphere, and frame portion  14  is sealed but not yet inflated, is then passed to a second severing/inflating chamber  107  (“second chamber”). In said second chamber  107 , the webs are severed by suitable cutters, to separate the individual intermediate package, and then frame portion  14  is inflated by blowing the desired gas therein through a hole  108  which may be located either in the top frame sheet  26  ( 126 ) or in the bottom frame sheet  28  ( 128 ). Once frame portion  14  is inflated, hole  108  is closed or anyway separated from the inflated frame portion  14 , e.g. by heat-sealing, before the final package leaves said second chamber  107 . 
     Hole  108  is preferably created in one of the thermoforming stations  103  and  104 , in the loading station  105 , or in a separate dedicated station that can be positioned between the thermoforming and the product loading stations. 
       FIG. 19  represents a plan view of a suitably thermoformed base web entering the loading station  105 . In said  FIG. 19 ,  108  is the hole that will be used to inflate frame portion  14  in severing/inflating chamber  107 , and the double lines  109  and  110  are the edges of the thermoformed portions (the correspondence with the profile of  FIG. 18  is indicated by using the same numerals). The web also contains slits  111 , cut through the web, which are used for the optional steps of vacuumization and introduction of the modified atmosphere  24 . Preferably said slits  111  are cut through the web with the shape of a cross as illustrated in  FIG. 19 . The base web  40  loaded with product  16  is advanced to first chamber  106  where it is positioned so that slits  111  are immediately over a matrix containing orefices which are connected through a pipe positioned below the slits, to the source of vacuum  162 . Once the first vacuum chamber  106  is closed, clamping the base and lid webs inside, vacuum may be applied through said pipe and the edges of the slits  111 , indicated in  FIG. 19  as  111   a ,  111   b ,  111   c , and  111   d , are drawn down against the interior side of the pipe so as to enlarge the passage for the air. To prevent collapse of the lid web  38  over the base one  40 , due to the vacuumization of the space between the two, vacuum is drawn also from the top of the vacuum chamber to keep the lid web raised over the base web  40 . This can be done using a different or, as schematically illustrated in  FIG. 17 , the same vacuum source  162 . After the drawing of vacuum, the desired modified atmosphere  24  is injected into the first chamber  106  through the same slits  111 , by excluding the vacuum source  162  and actuating the modified atmosphere source  164 . Once the pressure of the gas forced upwardly through the slits  111  into the vacuum chamber has reached the desired value, the sealing mechanism within the chamber is arranged to seal the packages individually along closed lines of seal  32 ,  30 , and  22 , between the base web  40  and the lid web  38 , excluding the slits  111  and leaving hole  108  within the frame portion  14 . With reference to  FIG. 19 , preferably said closed lines will correspond to the double lines  109  and  110 . 
     The first chamber  106  is then opened and the sealed webs are advanced to the second chamber  107 , where suitable cutters sever the sealed webs to release the individual package. Air or any other desired gas is then blown into the frame portion  14  through a suitable nozzle, into register with the hole  108 , connected to an inflation gas source  166 . To keep hole  108  in correspondence with the nozzle, a hollow pressing device may suitably be employed. With reference to the particular embodiment illustrated in  FIG. 19 , where hole  108  communicates with frame portion  14  through a passage  112 , this in fact should be achieved without compressing the unsealed passage  112  that needs to be free to allow inflation of frame portion  14 . 
     Alternatively a small and flexible tube, still connected to the inflation gas source  166 , can be inserted into hole  108 , and used to inflate frame portion  14 . When a small tube is employed, it is also possible to connect it to a suitable pump and reservoir and inflate, and thus stiffen, frame portion  14  with any fluid, including liquids, such as water and aqueous solutions, and flowable powders. 
     As soon as frame portion  14  is inflated as desired, hole  108  is closed and/or the communication between hole  108  and frame portion  14  is closed, while the package is still in severing/inflating chamber  107 . This can be achieved by any means, such as for instance by applying a barrier label on top of the hole, by heat-sealing together the top sheet to the bottom sheet of the package in an area that includes at least the hole  108  and is larger than the hole, or by means of a closed seal line around the hole to eliminate any communication between hole  108  and frame portion  14 . With reference to  FIG. 19 , preferably hole  108  may be closed either by heat-sealing the passage  112  or by heat-sealing the top sheet to the bottom sheet in the whole area around hole  108  which is delimited in said Figure by the double lines and by the passage  112 . 
     In the embodiment illustrated in  FIG. 7 , modified atmosphere  24  is introduced into chamber  12  by the chamber inflation passageway  44 , which is sealed or otherwise closed afterwards. The frame  14  is inflated by introducing an inflation gas or the desired fluid through frame inflation passageway  42 , which is sealed or otherwise closed afterwards. 
     An end user may open package  10  ( 11 ), for example, by cutting top chamber sheet  18  ( 118 ) to provide access to product  16 . After removal of product  16 , the inflated frame  14  may be punctured to deflate it or the passageway  42 , if any, may be opened. The deflated package  10  ( 11 ) may then be ready for recycling. 
     The new package according to the present invention may however be fitted with easy opening features that may help the end user to open the package, and particularly the chamber portion  12  without resorting to the use of cutting or puncturing tools. 
     Examples of easy opening features applied to the new package are illustrated in  FIGS. 20   a, b , and  c.    
     As illustrated in  FIG. 20   a , the bottom chamber sheet  20  ( 120 ) or, preferably, the top chamber sheet  18  ( 118 ), may present a weakness line  113 , that may be e.g., a through cut, either continuous or discontinuous, or a line where the thickness of the web has been reduced so that a slight pressure may break the film, covered by an adhesive label  114  that has a non adhesive tab ( 114   a ) integral thereto so that it can be easily peeled off, when desired, by grasping said non adhesive tab with the fingers, peeling it off and thus leaving the weakness line exposed. 
     Alternatively, as illustrated in  FIG. 20   b , the top chamber sheet  18  ( 118 ) has secured to its outer surface a tab  115  made of resilient material comprising lines of weakening  116  defining a cutter  117  capable of piercing the top chamber sheet  18  ( 118 ) when pressed against it. To open the package, the tab is raised, the lines of weakening  116  are bent, broken or torn by the user to expose the cutting edge of the cutter  117  which is then pressed against the top chamber sheet to pierce it. Also in this case the easy opening feature can alternatively be positioned on the bottom chamber sheet  20  ( 120 ) even if it is clearly more visible to the user if positioned on the top chamber sheet. 
     In  FIG. 20   c  it is illustrated a preferred embodiment of the invention where a tear-open slit, either in the form of a continuous or discontinuous cut, is created in an area of the juxtaposed lid and base sheets, isolated from frame portion  14  and adjacent to the chamber seal zone  22 , said slit being almost perpendicular to the chamber seal  22 . The package illustrated in said Figure may conveniently be obtained using the packaging machine  100  of  FIG. 17  and the process illustrated above, where frame portion  14  is inflated through a hole  108  and the communication between frame portion  14  and hole  108  is then excluded by either heat-sealing the passage  112  or by heat-sealing together the lid and base sheets over the whole area around said hole which is delimited by the double lines and by the passage  112 . Said area is identified in  FIG. 20   c  with numeral  200 . Along the border of area  200  which are in contact with the frame inner seal zone  30  there is a serration  201  and area  200  is divided in two parts by a second serration  202  almost perpendicular to the chamber seal zone  22 . By pressing on this area it is thus possible to break the serrations  201  and  202  and pulling apart the two flaps thus created,  200   a  and  200   b , easily open chamber portion  12 . Alternatively, instead of serration lines it is possible to foresee cuts through the top and bottom webs. 
     The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents. Except in the claims and the specific examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material, reaction conditions, use conditions, molecular weights, and/or number of carbon atoms, and the like, are to be understood as modified by the word “about” in describing the broadest scope of the invention. Any reference to an item in the disclosure or to an element in the claim in the singular using the articles “a,” “an,” “the,” or “said” is not to be construed as limiting the item or element to the singular unless expressly so stated. All references to ASTM tests are to the most recent, currently approved, and published version of the ASTM test identified, as of the priority filing date of this application. Each such published ASTM test method is incorporated herein in its entirety by this reference.