Abstract:
Containers are disclosed, as well as multilayer films used in such containers, which advantageously maintain a high seal strength even after being subjected to hot-fill conditions for sterilization. These microwavable/ovenable containers ( 10 ) and multilayer films are also beneficially self-venting upon exposure to microwave heating when the internal container pressure exceeds a threshold value. These self-venting containers are also automatically self-sealing after the self-venting feature has ruptured and the container has cooled to room temperature. The self-venting self-sealing nature of these containers arises from particular film and sealing characteristics, in which the seal width differs in defined, self-venting self-sealing seal regions ( 13 A), relative to non-venting seal regions ( 13 B) of a given peripheral seal. Particular film materials and structural geometries of the self-venting self-sealing seal regions can be used to improve the location of venting and control of the vented gases, as well as, the resealability of the containers.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a container used for products introduced into the container while warm or hot, as appropriate, for sanitary packaging of the product. More particularly, the present invention relates to flexible “hot-fill” containers useable in microwave and/or oven cooking, which also have a self-sealing self-venting region which ruptures as a result of elevated temperatures and/or pressure, and then reseals after expelling excess pressure from inside the container. 
       BACKGROUND OF THE INVENTION 
       [0002]    Flexible containers used for filling processes with warm or hot food products, so called “hot-fill applications”, must address several fundamental concerns that are not present in conventional container applications. The ability to hot fill in sheet or film packages permits the foods to be stored without refrigeration. Commercial sterilization by hot filling imposes several additional restrictions on the choice of materials for the sheet or film structure. The heat seal must survive commercial hot-fill temperatures of above 170° F. (77° C.) and typically, between 170° F. to 212° F. (77° C. to 100° C.). The structure must not delaminate, shrink, or wrinkle as a result of the sterilization. The oxygen and water barrier properties must not be permanently adversely affected by the conditions of commercial sterilization. The structure must be adequately strong to permit handling of the package while still hot. The additional requirements imposed by hot filling rule out many of the materials and structures commonly used for non-restored film or sheet food packages. 
         [0003]    One of the current market trends in food packaging is convenience, which is driven by the growing number of single household consumers who, for various reasons, do not want to cook any more, and the demand on ready meals that just have to be reheated is therefore constantly growing. Such ready meals are often “hot-fill” packed in flexible pouches. These flexible hot-fill pouches are typically formed from one or more thermoplastic sheets sealed along the edges to form an interior space. These pouches can include an opening through which an item can be placed into the package. The opening of the pouch can then be sealed to enclose the item therein. Various seals used in sealing the container normally prevent gases, such as air and moisture vapor from entering or exiting the container. In general, some level of fluids is present in the interior of the packaging article. For instance, many food products themselves may have a relatively high water content. During heating, some of this moisture may vaporize and accumulate within the interior of the packaging article. Accumulation of water vapor may result in bursting of the packaging article, such as the lid or a seam of the packaging article. Such rupturing is usually undesirable because it typically occurs when a relatively high pressure has been obtained in the package. As a result, damage to the oven or to the user may occur. At the very least, rupturing of the packaging article may result in the splattering heated food products and/or liquids within the interior of the oven. Such splattered material can be difficult to clean. 
         [0004]    To prevent rupturing of the package, a self-venting feature is beneficial for the controlled release of internal pressure (which, in the oven environment, is not counterbalanced externally) to avoid sudden, undesirable bursting of the container and loss/splattering of its contents. Multilayer packaging materials, which rely on heat generated during the cooking process to melt a portion of the packaging film in order to provide a self-venting feature, are known in the art and described, for example, in U.S. Pat. No. 6,596,355. Such layered materials require the use of low-temperature melting resins within the multilayered structure. However, these low-temperature melting resins cannot withstand the elevated temperatures required by hot filling operation. However, once the self-venting feature has been opened, hot food or liquid may leak or spill out through the self-venting feature when the package is removed from the microwave oven causing burns to the consumer. 
         [0005]    Consequently, there remains a need in the art for materials useful in containers, including flexible pouches and plastic containers sealed with multilayer films, which are not only self-venting, but are reliably self-sealing. In other words, as soon as the expulsion of steam or air when acting on the container is released or sufficiently reduced, the exit flow channel of a seal-venting feature will automatically self-seal in order to prevent further fluid flow out of the package. Thus, leakage, spills or spoilage of the package contents can be avoided. This automatic self-sealing would be a significant advantage in flexible self-venting microwavable containers and particularly, in flexible self-venting microwavable containers that have enough durability to withstand hot-fill operations. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is associated with the discovery of containers, as well as multilayer films used in such containers, which permit the expulsion of the steam or air when heat and/or pressure is applied to the container and automatically self-seals to prevent further fluid flow, leakage, or spoilage of the contents of the container. Preferably, the self-venting self-sealing containers have enough durability to withstand hot-fill operations. Such hot-fill operations typically include a temperature in the range from about 170° F. (77° C.) to about 212° F. (100° C.). These containers and films are also beneficially self-venting upon exposure to microwave heating, when the internal container pressure exceeds a threshold value, and self-sealing upon cooling the container to room temperature and/or reducing the intemal pressure of the container. The self-venting and self-sealing nature of these containers arises from particular sealing characteristics, as described in greater detail below, in which the seal width differs in defined, self-venting self-sealing seal regions, relative to non-venting seal regions of a given peripheral seal. The self-venting and self-sealing nature of these containers further arises from the particular materials used in the sealant layer of the multilayer film used in such containers. Particular structural features and geometries of the self-venting, self-sealing seal regions can also be used to improve the location of venting and control of the vented gases. 
         [0007]    Embodiments of the invention are directed to a hot-fill container comprising a peripheral seal formed by a sealant layer of a multilayer film. The peripheral seal has at least one self-venting self-sealing seal region with a minimum venting seal width that is less than a minimum non-venting seal width of a non-venting seal region. In a preferred embodiment, at least one self-venting self-sealing seal region is located in a peripheral fin seal region. The peripheral seal includes all the same layers as in the multilayer film. A given peripheral seal, including its self-venting, self-sealing and non-venting seal regions, is generally formed from one type of multilayer film and one type of base material. Also, the self-venting self-sealing and non-venting seal regions are normally exposed to the same internal container environment. Therefore, with these factors being constant or approximately constant over a given peripheral seal, it is possible to vary the seal thickness and/or geometry in the different seal regions, in order to adjust the ease with which gas venting will occur and other venting characteristics. However, the practice of the present invention does not require these factors to necessarily be constant or substantially constant over the seal regions. 
         [0008]    The sealant layer of the multilayer film generally refers to the innermost layer that is exposed to the internal contents of the container, such as food. The sealant layer is used for bonding, at adjacent bonding surfaces, with itself or another material to form a peripheral seal, normally by heat sealing. According to particular embodiments, the sealant layer is free of wax. For example, representative multilayer films, and consequently the seals formed by such films, include any film having a sealant layer comprising polyethylene, preferably metallocene polyethylene, and more preferably, between 50% to 100% by weight relative to the total weight of the sealant layer of metallocene polyethylene. The base material may be a mono-layer or multilayer film. The other material may also be a second multilayer film of the same type or of a different type as the multilayer film. For example, in embodiments in which the retortable container is formed by folding a multilayer film upon itself and heat sealing the overlapping edges, the multilayer film and base material are necessarily the same, as are their adjacent sealing layers. 
         [0009]    Further embodiments of the invention are directed to a hot-fill container comprising a peripheral seal formed by a sealing layer of a multilayer film. The peripheral seal in a self-venting self-sealing seal region forms an inward protrusion relative to the peripheral seal in a non-venting seal region. As discussed above, the peripheral seal is formed by a sealant layer of a multilayer film wherein the sealant layer comprises polyethylene, preferably metallocene polyethylene, and more preferably, between 50% to 100% by weight relative to the total weight of the sealant layer of metallocene polyethylene. 
         [0010]    According to any of the above embodiments, the particular sealing characteristics advantageously provide a desired, self-venting self-sealing capability to the hot-fill containers. In representative containers, gas is discharged through one or more self-venting self-sealing seal regions, as described herein, when the pressure within the container exceeds a threshold pressure. This threshold pressure is generally at least 1 psig (i.e., 1 psi gauge pressure, or 1 psi above the ambient, surrounding pressure, generally atmospheric), and typically at least 2 psig, and in some cases at least 5 psig. Exemplary threshold pressures that cause the container to vent through a self-venting seal region are in the range from about 1 psig to about 5 psig. 
         [0011]    These and other embodiments and aspects relating to the present invention are apparent from the following Detailed Description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1   a  depicts plan views of representative containers having self-venting self-sealing and non-venting seal regions. 
           [0013]      FIG. 1   b  depicts a side of a multilayer film of the present invention wherein the film is folded to provide a fin seal. 
           [0014]      FIG. 2  depicts a close-up view of the self-venting self-sealing seal region of the container of  FIG. 1   a.    
           [0015]      FIGS. 3A-3D  depict geometries of alternative self-venting self-sealing seal regions. 
           [0016]      FIGS. 4A-4B  depict cross-sectional views of multilayer films that are suitable for retortable containers described herein. 
           [0017]      FIGS. 1   a - 4 B are intended to illustrate embodiments of the invention by way of example, and not by way of limitation. The features referred to in these figures are not necessarily drawn to scale and should be understood to present an illustration of the invention and/or principles involved. Some features depicted have been enlarged or distorted relative to others, in order to facilitate explanation and understanding. The same reference numbers are used throughout the figures to refer to similar elements and dimensions. Those skilled in the art will appreciate that features of self-venting self-sealing hot-fill containers, according to alternative embodiments of the invention, are determined, in part, by the intended application and also the environment in which they are used. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    According to representative embodiments of the invention, retortable containers have a peripheral seal proximate at least one edge. This edge can result, for example, from heat sealing overlapping portions of a single multilayer film, separate multilayer films, or a multilayer film and a container bottom that may be formed of a rigid or flexible plastic material. In the latter case, the container bottom often has a peripheral flange for sealing with the multilayer film, such that it covers the container bottom and thereby encloses the container. The container is self-venting meaning that gases can escape the container, preferably in a controlled manner, when a threshold pressure (e.g., from about 1 psig to about 5 psig) is reached within the container. Such a pressure is normally attained upon heating the container in a microwave oven to a sufficient temperature to vaporize water or ice in the packaged food and/or cause significant expansion of the enclosed gases. The container is also self-sealing meaning that when the container has reached a sufficient temperature and/or pressure to vaporize water and has expelled gas and/or liquid through the self-venting feature, the self-venting feature subsequently reseals upon itself after cooling to room temperature and/or after the internal pressure of the container has returned to ambient conditions. 
         [0019]    The escape of gases upon heating preferably occurs at defined, self-venting self-sealing seal regions having a particular construction (e.g., in terms of seal width) and geometry (e.g., an inward protrusion) that can be varied to adjust the venting characteristics, including the threshold pressure, as well as the direction and even velocity of the escaping vapors. 
         [0020]      FIG. 1   a  depicts an exemplary self-venting and self-sealing container  10  having peripheral ends seals  12 A and  12 B located at the opposite ends of the container and a peripheral fin seal  12 C located between peripheral ends seals  12 A and  12 B. 
         [0021]    As illustrated in  FIG. 1   b , container  10  may be formed by folding a multilayer film  100  to bring the peripheral longitudinal edges  5  and  6  together in a fin seal configuration to create peripheral folds  16  of the container. Peripheral fin seal  12 C is formed from heating and compressing overlapping layers of multilayer film  100  at the peripheral longitudinal edge  17 . Peripheral ends seals  12 A and  12 B may then be formed from heating and compressing overlapping layers of multilayer film  100  at the peripheral edges  15  of the container. In general, however, aspects of the invention discussed herein are broadly applicable to a wide variety of container types, including pouches having at least two, end heat seals and a fin seal. In a preferred embodiment, a pillow pouch is shown. 
         [0022]    Peripheral fin seal  12 C is characterized as having self-venting self-sealing fin seal regions  13 A and non-venting fin seal regions  138 , having differing seal widths along a width dimension that is perpendicular to the edge of the container along which the seal extends. Self-venting seal-sealing fin seal regions are marked in  FIGS. 1   a ,  2 - 3 D with diagonal line segments. 
         [0023]    In  FIG. 1   a , the division between self-venting, self-sealing and non-venting fin seal regions  13 A,  138  is shown with dashed lines extending through the peripheral seals, perpendicular to the container edges.  FIG. 2  more clearly shows the basis for this division, with the dashed lines extending through transition point P on the inner boundary  63  of peripheral fin seal  12 C. At transition point P, gas escaping the container must traverse a minimum distance D across peripheral fin seal  12 C that is at least as great as the minimum non-venting seal width  32  in non-venting seal region  13 B. Therefore, gas within self-venting self-sealing container  10  will require a higher pressure to escape at point P and at all other points along the inner boundary  63 B of non-venting fin seal region  13 B, compared to the relatively lower, threshold pressure required for gas to escape at points along the inner boundary  63 A of self-venting, self-sealing fin seal region  13 A. 
         [0024]    The venting of gas is thereby advantageously confined to one or more specific regions of peripheral fin seal  12 C, namely self-venting, self-sealing seal regions  13 A. Moreover, the threshold pressure at which venting occurs can be adjusted by varying the characteristics of the seal (e.g., thickness and seal strength) in self-venting self-sealing fin seal region  13 A. The venting of the container  10 , upon exposure to sufficient microwave heating, can therefore be achieved in a controlled and desirable manner, without significant disruption, splatter, and/or loss of the container contents, to the benefit of the end user. Unlike prior art systems that rely on thermal degradation, or melting, of a film layer to achieve a self-venting property, containers according to embodiments described herein may rely on the seal geometry, including regions of varying thickness, to establish a defined venting “profile.” Venting may be based on a more controllable mechanical, rather than thermal, breakage of peripheral fin seal  12 C. 
         [0025]    As illustrated in the close-up view, in  FIG. 2 , the minimum venting seal width  30  in self-venting self-sealing fin seal region  13 A is less than the minimum non-venting seal width  32  in non-venting seal region  13 B. The minimum venting seal width, corresponding to the minimum distance across the peripheral seal in self-venting self-sealing fin seal region  13 A, impacts the threshold pressure, or pressure within the container (e.g., under microwave heating conditions), at which the onset of venting (i.e., the exiting of gases from within the container) occurs. According to representative embodiments, minimum self-venting self-sealing fin seal width  30  is generally at most about 5 mm (0.20 in) (e.g., from about 0.5 mm (0.020 in) to about 5 mm (0.20 in)) and typically at most about 3.2 mm (0.125 in) (e.g., from about 2.4 mm (0.094 in) to about 1.2 mm (0.047 in)). The minimum non-venting non-sealing fin seal width  32  is generally at least about 1 mm (0.039 in) (e.g., from about 1 mm (0.039 in) to about 10 mm (0.39 in)) and typically at least about 3.2 mm (0.125 in) (e.g., from about 3.2 mm (0.125 in) to about 7.5 mm (0.30 in)). 
         [0026]    According to the embodiment of  FIG. 2 , peripheral fin seal  12 C in self-venting self-sealing seal region  13 A forms an inward protrusion relative to peripheral fin seal  12 C in non-venting seal region  13 B. This protrusion therefore extends toward the interior, for example the center, of the region defined by peripheral longitudinal edge  17  ( FIG. 1   a ) of container  10  in fin seal region  12 C.  FIG. 2  illustrates how this configuration (or inward protrusion) of self-venting self-sealing seal region  13 A, together with line  55  defined by edge  17  of the container in non-venting seal region  12 B, define protruded area  57 . Protruded area  57 , in turn, defines outer boundary  65  of self-venting self-sealing seal region  13 A. Protruded area  57  of  FIG. 2  includes a tear-droplet shape  61 , which is a substantially complete tear-droplet shape except for gas discharge opening  59 . In alternative embodiments, the protruded area may include a circle, a less complete circle, such as a semi-circle, or may include some other area bounded by a curved shape, such as an ellipse or partial ellipse (e.g., a semi-ellipse). Otherwise, the protruded area may be a polygon. 
         [0027]    The materials that are sealed to form edges  15  and  17  as discussed above (e.g., overlapping portions of a single multilayer film, separate multilayer films, or a multilayer film and a container bottom) may be absent from protruded area  57 , for example in the case where these materials are simply punched out from peripheral fin seal  12 C. According to other embodiments, these materials may be present in protruded area  57 , but in an unsealed condition, or at least partly unsealed. In this case, the unsealed materials (e.g., unsealed multilayer films) in protruded area  57  advantageously act as guides to direct exiting (vented) vapors, for example between the unsealed materials through discharge opening  59 . Preferably, these exiting vapors will therefore be directed out the side of container  10 , substantially in the plane in which peripheral fin seal  12 C resides. 
         [0028]    In any of such embodiments, in which protruded area further includes gas discharge opening  59  as shown in  FIG. 2 , the gas discharge opening is preferably smaller (e.g., of a smaller diameter), based on the minimum distance across this opening, relative to the diameter of a partial circle or relative to the smallest diameter (e.g., along the minor axis) of the partial ellipse. According to particular embodiments, the gas discharge opening (regardless of the shape of the protruded area) is generally at least about 2 mm (0.079 in) (e.g., from about 2 mm (0.079 in) to about 15 mm (0.59 in)), and typically at least about 4 mm (0.16 in) (e.g., from about 4 mm (0.16 in) to about 10 mm (0.39 in)). In comparison, the diameter of the partial circle or smallest diameter of the partial ellipse of the protruded area is generally at least about 7.5 mm (0.30 in) (e.g., from about 7.5 mm (0.30 in) to about 25 mm (1 in)) and typically at least about 10 mm (0.39 in) (e.g., from about 10 mm (0.39 in) to about 20 mm (0.79 in)). The use of a smaller gas discharge opening  59 , relative to the diameter of the partial circle or smallest diameter of the partial ellipse, can provide for a more “focused” direction of exiting vapors. 
         [0029]      FIGS. 3A-3D , however, illustrate inward protrusions in self-venting self-sealing seal regions having alternative geometries. In  FIG. 3A , the protruded area  57  includes a partial circle  61 , which is a substantially complete circle except for gas discharge opening  59 .  FIG. 3A  depicts the gas discharge opening that is smaller than the diameter a circular protruded area  57 . In alternative embodiments, the protruded area may include a less complete circle, such as a semi-circle, or may include some other area bounded by a curved shape, such as an ellipse or partial ellipse (e.g., a semi-ellipse). For example, in  FIGS. 3B and 3C  include a gas discharge opening that is the same as the diameter of a semi-circular protruded area  57  (or the same as an axis of an elliptical protruded area  57 ). In  FIG. 3D , the protruded area, defined by line  55  and inward protrusion of self-venting self-sealing venting seal region  13 A, is a polygon having an arrow shape. As illustrated in  FIGS. 3A ,  3 C and  3 D, inner boundary  63  of self-venting seal region  13 A has a shape that conforms substantially to the shape of the inward protrusion and consequently also to the shape of outer boundary  65 . In these embodiments, the venting seal width is substantially constant over at least a portion of inner and outer boundaries  63 ,  65  and therefore over at least a portion (e.g., the majority of, and possibly all) of the self-venting seal-sealing seal region. This substantially constant venting seal width, in particular, corresponds to the minimum venting seal width  30 . The use of a substantially constant venting seal width  30 , in this manner, adds predictability to the onset of venting, namely when a desired threshold pressure is sufficient to overcome the gas barrier corresponding to the minimum venting seal width  30 . 
         [0030]    However, it is also possible, as shown in  FIG. 3B  for inner boundary  63  and consequently self-venting seal region  13 A to have a shape that does not conform to the shape of inward protrusion. In this case, the venting seal width varies over at least a portion (e.g., the majority of, and possibly all) of the self-venting self-sealing fin seal region. In the embodiment of  FIG. 3B , the minimum venting seal width  30  may correspond to several discreet points X, Y, Z, on inner boundary  63 , at which mechanical breakage of the seal is likely to occur, upon exposure to pressure and heat from within the container, due to microwaving of its contents. As is apparent from the particular embodiment of  FIG. 3B , the protruded area  57  can include a partial circle or a partial ellipse, with inner boundary  63  of self-venting self-sealing fin seal region  13 A being formed by line segments. Overall, having regard for the present specification, those skilled in the art will appreciate that the specific characteristics (including geometries, materials, and seal thicknesses) of the self-venting seal region can be varied to achieve desired venting characteristics, in terms of threshold pressure, exiting gas direction, and stability. 
         [0031]    In addition, the multilayer films, as well as containers having such films, preferably have seal strength, stability, heat resistance, and oxygen and water vapor transmission properties that allow them to be subjected to hot-fill conditions without loss of desired functional characteristics. 
         [0032]    Representative conditions mimicking a hot-fill heat treatment, corresponding to the above seal strength and seal strength stability properties, include exposure of the container to (1) a temperature of between 170° F. to 212° F. (77° C. to 100° C.) for 2 to 20 seconds. Furthermore, multilayer films described herein also have acceptable heat resistance, in terms of not undergoing delamination. Preferably, no delamination of the film structure is observed after the film is subjected to 212° F. (100° C.) for 20 seconds. Further properties of representative films include a barrier-oxygen transmission rate of generally from about 0.16 cc/M 2 /day (0.01 cc/100 in 2 /day) to about 62 cc/M 2 /day (4 cc/100 in 2 /day), and typically from about 0.16 cc/M 2 /day (0.01 cc/100 in 2 /day) to about 1.6 cc/M 2 /day (0.1 cc/100 in 2 /day) at a temperature of 23° C. (73° F.), and/or a barrier-water vapor transmission rate of generally from about 0.47 g/M 2 /day (0.03 g/100 in 2 /day) to about 7.8 g/M 2 /day (0.5 g/100 in 2 /day), and typically from about 0.47 g/M 2 /day (0.03 g/100 in 2 /day) to about 3.9 cc/M 2 /day (0.25 g/100 in 2 /day) at a temperature of 100° C. (212° F.) and 90% relative humidity. 
         [0033]    The multilayer film comprises a sealant layer that forms a peripheral seal of the container, including the self-venting self-sealing and non-venting seal regions, as described above. In regions where the multilayer film is sealed (e.g., by heat), this sealant layer is bonded to a suitable base material, such as a mono-layer or multilayer film, for example comprising polyethylene. The base material may also be another multilayer film of the same type or of a different type. For example, if the multilayer film is folded upon itself and heat sealed at overlapping edges to provide a container volume bounded by non-sealed areas of the film, the multilayer film and base material, as well as the sealing layers being bonded, are necessarily the same. In regions where the multilayer film is not sealed, the sealing layer is the innermost layer, facing the interior of the container and often contacting the container contents, such as food, directly. 
         [0034]    A preferred sealant layer comprises (e.g., in a major amount of at least 50% by weight), or consists essentially of (1) a polyethylene or (ii) a blend of polyethylene. Preferred polyethylenes include metallocene polyethylenes. The term metallocene polyethylene denotes polymers obtained by copolymerizing ethylene and an alpha-olefin, such as propylene, butene, hexene or octene, in the presence of a monosite catalyst generally consisting of an atom of a metal which may, for example, be zirconium or titanium, and of two cyclic alkyl molecules bonded to the metal. More specifically, the metallocene catalysts are usually composed of two cyclopentadiene-type rings bonded to the metal. These catalysts are often used with aluminoxanes as cocatalysts or activators, preferably methylaluminoxane (MAO). Hafnium may also be used as a metal to which the cyclopentadiene is bound. Other metallocenes may include transition metals of groups IV A, V A and VI A. Metals of the lanthanide series may also be used. These metallocene polyethylenes may also be characterized by their M w /M n  ratio of &lt;3, preferably &lt;2. A more preferred sealant layer comprises from about 50% to about 100% by weight relative to the total weight of the sealant layer of a metallocene polyethylene. 
         [0035]    In one particular embodiment, the sealing layer comprises about 60.40% by weight of metallocene polyethylene, about 35.00% by weight linear low density polyethylene and about 4.00% by weight antiblock and slip additives. Suitable metallocene polyethylenes include, but not limited to, ATTANE® ultra low density polyethylene copolymers (Dow Chemical Company, Midland, Mich. USA). A particularly suitable metallocene polyethylene is ATTANE® 4701 copolymer having a density of 0.913 g/cm 3 , a melt flow index of 1.00 g/10 min, and a Vicat softening point of 94° C. 
         [0036]    The thickness of the sealing layer is generally from about 10 μm (0.39 mils) to about 500 μm (20 mils), and typically from about 50 μm (2 mils) to about 200 μm (7.9 mils). In addition to the sealing layer, the multilayer film further comprises an outer layer facing the exterior of the container and disposed furthest from the container contents. In the case of 2-layer films, the outer layer and sealing layer are adjacent and bonded directly to one another. In the case of films comprising further layers (i.e., 3 or more total layers), the outer and sealing layers are not adjacent, but separated by these further layers, being disposed therebetween. 
         [0037]    The total thickness of a representative, multilayer film used in a self-venting self-sealing, hot-fillable container, as described herein, is generally from about 51 μm (2 mils) to about 380 μm (15 mils), and typically from about 74 μm (2.9 mils) to about 150 μm (6 mils). 
         [0038]    In a preferred embodiment, a cross-sectional view of a representative 10-layer film  500 , for example, is depicted in  FIG. 4A , having the following layers, in order: an outer layer of biaxially oriented polyethylene terephthalate  501 , an anchor coat layer  502 , a polyethylene layer  503 , a second polyethylene layer  504 , a first polyethylene/ethylene vinyl acetate blend layer  505 , a first tie layer  506 , an ethylene vinyl alcohol copolymer layer  507 , a second tie layer  508 , a second polyethylene/ethylene vinyl acetate blend layer  509 , and a polyethylene sealant layer  510 . 
         [0039]    The cross-sectional view of  FIG. 4B  depicts the sealing between adjacent sealant layers  510 , in either the self-venting region or non-venting region of peripheral seal  12  of a container as described herein. Sealing occurs between two identical 10-layer films, or otherwise a single 10-layer film that has been folded (e.g., with the fold not shown but occurring beyond the left side of the page). In addition to sealant layers  510 , the films may also include other layers, as described above. 
         [0040]    Overall, aspects of the invention are directed to self-venting, hot-fillable containers and multilayer films suitable for use in such containers. Characteristics of the multilayer films, in combination with characteristics of the self-venting self-sealing seal regions, provide containers having desirable venting properties as described herein. Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes can be made in these containers and multilayer films without departing from the scope of the present invention. Mechanisms used to explain theoretical or observed phenomena or results, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims. 
         [0041]    The following examples are set forth as representative of the present invention. These examples are not to be construed as limiting the scope of the invention as other equivalent embodiments will be apparent in view of the present disclosure and appended claims. 
       Example 1 
       [0042]    Specifically, the film had the following structure, from the outer to the inner (sealing or food contact) layer
   Layer 1 (outer): (48 gauge) one-sided corona treated oriented polyethylene terephthalate (OPET)—Skyrol SP65 (SKC Inc., Covington, Ga. USA)   Layer 2 (anchor coat): water based lamination primer coat—Aquaforte 108W (Aqua Based Technologies, NJ, USA)   Layer 3: 100.00 wt-% low density polyethylene (LDPE)—Dow 4005 (Dow Chemical Company, Midland, Mich., USA)   Layer 4: 77.80 wt-% linear low density polyethylene (LLDPE)—Exact 3139 (ExxonMobil Chemical, Houston, Tex., USA)+10.00 wt-% low density polyethylene (LDPE)—Dow 4005 (Dow Chemical Company, Midland, Mich., USA)+12.20 wt-% additives   Layer 5: 60.00 wt-% ultra-low density polyethylene (ULDPE)—Attane NG 4701G (Dow Chemical Company, Midland, Mich., USA)+40.00 wt-% ethylene vinyl acetate copolymer (EVA) having a 12% mole vinyl acetate content—DuPont Elvax 3135X (E. I. du Pont de Nemours and Company, Wilmington, Del. USA)   Layer 6 (1 st  tie): 100 wt-% anhydride-modified, linear low density polyethylene (LLDPE) resins.—DuPont Bynel® 41E687 ((E. I. du Pont de Nemours and Company, Wilmington, Del., USA)   Layer 7: 100 wt-% ethylene vinyl alcohol copolymer (EVOH)—Soamol® ET3803 (Soarus L.L.C., Arlington Heights, Ill., USA)   Layer 8 (2 nd  tie): 100 wt-% anhydride-modified, linear low-density polyethylene (LLDPE) resins—DuPont Bynel® 41E687 (E. I. du Pont de Nemours and Company, Wilmington, Del., USA)   Layer 9: 60.00 wt-% linear low density polyethylene (LLDPE)—ExxonMobil™ 1001.32 (ExxonMobil Chemical, Houston, Tex., USA)+40.00 wt-% ethylene vinyl acetate copolymer (EVA) having a 5% mole vinyl acetate content—ExxonMobil™ LD 306.38 (ExxonMobil Chemical, Houston, Tex., USA)   Layer 10 (sealing): 60.40 wt-% ultra-low density polyethylene (ULDPE)—Attane NG 4701G (Dow Chemical Company, Midland, Mich., USA)+35 wt-% linear low density polyethylene (LLDPE)—ExxonMobil™ 1001.32 (ExxonMobil Chemical, Houston, Tex., USA) density polyethylene (LDPE)—Dow 608A (Dow Chemical Company, Midland, Mich. USA)+4.0 wt-% additives   
 
         [0053]    This 10-layer film was sealed with a first end seal, a second end seal and a fin seal to form a pillow pouch. The initial and propagation (average) re-tack seal strengths of the seal-venting self-sealing fin seal was evaluated for sample pouches after the pouch had been heated and the fin seal vented. The term “initial re-tack seal strength” refers to the force required to initiate the separation of a portion of the film from itself. The term “propagation re-tack seal strength” refers to the force required to continue the separation of a portion of the film from itself after the separation has been initiated. Values were measured according to ASTM-F88 with a crosshead speed of 2.12 cm/sec (5 in/min). The results of this testing are shown in Table 1 below. 
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                 TABLE 1 
               
             
             
               
                   
               
               
                 Retack Seal Strength 
               
               
                 (gram-force/inch) 
               
             
          
           
               
                   
                 Initial 
                 Propagation 
               
               
                   
                   
               
             
          
           
               
                   
                 Sample 1 
                 4061 
                 2334 
               
               
                   
                 Sample 2 
                 970 
                 457 
               
               
                   
                 Sample 3 
                 1583 
                 568 
               
               
                   
                 Sample 4 
                 1023 
                 628 
               
               
                   
                 Sample 5 
                 2359 
                 1459 
               
               
                   
                   
               
             
          
         
       
     
         [0054]    This 10-layer film was sealed with a first end seal, a second end seal and a fin seal to form a pillow pouch. The threshold pressure at which gas was discharged from the self-venting self-sealing fin seal region was evaluated for sample pouches. The results of this testing are shown in Table 2 below. 
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                 TABLE 2 
               
               
                   
               
               
                 Threshold Pressure 
               
               
                 (psi) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sample 1 
                 1.5 
               
               
                   
                 Sample 2 
                 1.8 
               
               
                   
                 Sample 3 
                 2.0 
               
               
                   
                 Sample 4 
                 2.4 
               
               
                   
                 Sample 5 
                 2.3