Abstract:
A container made of an elastomer such as silicone with an integrated leak resistant seal. The seal incorporates press-fit elements with sizes and shapes sufficient to provide a strong seal that resists leakage of liquids from inside the container. The seal is integrated into the container and requires no external clips or clasps. Additional features are provided to facilitate opening such as extended flaps for pulling the sides open, and asymmetric cavities for press-fit elements to reduce the initial opening force. The container itself may be of asymmetrical shape, such as trapezoidal, to provide a wide opening along with a strong seal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One or more embodiments pertain to the field of storage and transport bags and containers and to seals for these bags and containers. More particularly, but not by way of limitation, one or more embodiments enable a shaped elastomeric bag with an integrated leak resistant seal. Embodiments may be used for storage, transport, and cooking of food, including liquids, and for other applications. Embodiments may be durable and reusable. Embodiments of the invention incorporate a leak resistant seal to provide enhanced sealing with a mechanism that is integrated into the container. 
     2. Description of the Related Art 
     Sealable bags and containers are well known in the art. For example, Ziploc® plastic bags have a zipper-like sealing mechanism integrated into the opening of the bag. More recent innovations have modified sealable bags to be more durable, reusable containers, often based on silicone materials. For example, both Munguia in US Patent Publication 2013/0105352 and LeBoeuf in US Patent Publication 2009/0110335 teach silicone food storage bags with seals. 
     A limitation of the existing art in sealable bags is that the integrated seal designs provide relatively weak sealing force. For example, Ziploc® bags are closeable, but they are not leak proof. This lack of leak resistance is a consequence of the relatively small sealing area and the simple track and groove shapes of the Ziploc® seal. LeBoeuf discloses a seal with a track and groove, but specifically notes that an additional mechanical clasp may be needed as an added method of closure. Hence the integrated sealing portion of the container disclosed in LeBoeuf may not be leak resistant without external clasping members. 
     This difficulty in providing an integrated leak resistant seal was taught in 1946 by Koeppel in U.S. Pat. No. 2,500,363. As Koeppel states: “Closures for containers of this nature have been formed in various ways, but when the opening in the bag or container is made sufficiently large to receive ice cubes or relatively large lumps of ice it is difficult to seal the opening effectively. Efforts have been made to overcome this difficulty by providing the container with a thickened portion about the mouth of the opening with complementary zig-zag or tongue and groove surfaces to form a seal. However, even such constructions are ineffective to prevent leakage unless they are pressed together with considerable force.” Koeppel then teaches a design using an external mechanical clip attached to a bag to provide the necessary sealing force. In this sense Koeppel arrives at a similar solution to LeBoeuf using an external clasp. 
     While use of external clips or mechanical clasps can provide seals, they are less convenient for the user and they require additional manufacturing cost and complexity. Therefore there is a need for an elastomeric container with an integrated leak proof seal, which does not require such additional elements to enhance sealing force. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the invention enable a shaped elastomeric container with an integrated leak resistant seal. Such a container may be used for example to store and transport liquids or solids or both, include food products. Embodiments of the invention may be of various shapes and sizes, including but not limited to rectangular, square, circular, trapezoidal, cylindrical, elliptical, polygonal, cubical, or any convenient shape for the intended use of the container. Embodiments of the invention utilize elastomers among their materials to provide properties such as flexibility, heat-resistance, microbial resistance, and ease of manufacturing. Other materials may be used as well for shaping, strengthening, decorating, or any other purpose. Some embodiments may employ silicone as one of the elastomers in the container. Silicone offers several potential advantages including non-toxicity, stick resistance, ability to be heated such as in an oven, ability to be frozen as in a freezer, and ability to be molded into various shapes in manufacturing processes. 
     Embodiments of the invention may include two parts of an enclosure, referred to as the top enclosure and the bottom enclosure. The top enclosure and bottom enclosure may be joined along some of their edges to form a container with an opening. The edge nearest the opening is referred to herein as the front edge; the edge opposite the front is referred to as the back edge. The edges running between the back and front are referred to as the left edge and the right edge. The joints between the parts of the enclosure may be made of an elastomer as well, or may be made of other materials. Any joining technique such as molding, gluing, taping, sewing, stapling, welding, or any other technique may be used to form the enclosure. The enclosure may partially surround an inner volume designed for the storage or transport of materials inside the container. In some embodiments the container may be sufficiently rigid so that this inner volume is present even when the container is empty. In other embodiments the container may be designed to collapse when empty so that the inner volume is not apparent unless items are inside the container. 
     Embodiments may have one or more edges of the enclosures fully or partially open for the insertion and removal of materials. Adjacent to or proximal to these open edges, embodiments may include a seal designed to close off the inner portion of the container that is utilized to open and close the container. In some embodiments the seal includes two elements called press-fit elements that are designed to press together and seal when closed. The press-fit elements are referred to herein as the top press-fit element and the bottom press-fit element. They may be located anywhere on the container where it is necessary or convenient to provide a seal. These press-fit elements may have complementary profiles that come together at a common boundary when the elements are pressed together. Various embodiments of the invention employ designs for the press-fit elements that contribute to the strength of the seal. In some embodiments the seal is designed for leak resistance. For example, some embodiments provide a seal that can hold one to two cups of water inside the container without leaking, even when the container is inverted with the seal pointing downwards. 
     In one or more embodiments the leak resistance of the seal is enhanced by utilizing sufficient material thickness in the press-fit elements. Thicker material in the press-fit elements increases the sealing force of the seal. In some embodiments the average material thickness of both the upper press-fit element and the lower press-fit element is at least 0.25 cm, in other embodiments, any value up to 0.5 cm, in other embodiments any value between 0.5 cm and 0.75 cm and in other embodiments 1.0 cm, when measured across the common boundary between the press-fit elements. Other embodiments may use even thicker material for greater sealing. Some embodiments do not rely on material thickness as a major factor for sealing strength, but instead or in addition use the shape of the press-fit elements to create enhanced leak-resistance. 
     In one or more embodiments of the invention the front edge of the enclosure may be longer than the back edge. For example, a container may be roughly trapezoidal in shape with the front edge longer than the back edge. Such embodiments may provide a benefit of a larger opening area for the insertion and removal of materials. This benefit may be particularly valuable when the press-fit elements of the seal utilize thick material, since the opening may pinch together at the left and right edges. 
     In one or more embodiments, the top press-fit element and the bottom press-fit element have one or more male or female elements that mate together to form part of the seal. Different embodiments may employ any convenient shapes, sizes, and numbers for these male and female elements. In some embodiments either the top press-fit element or the bottom press-fit element, or both, may have a vertical protrusion extending upward or downward into a corresponding cavity on the other press-fit element. In some embodiments one or more of the vertical protrusions may have one or more horizontal ridges emerging horizontally from the vertical protrusion. These ridges may be implemented to lock into place into corresponding indentations on the opposite press-fit element. Some embodiment use at least two horizontal ridges attached to a single vertical protrusion, spaced out vertically at different heights, to provide additional sealing force. Other embodiments may use only a single horizontal ridge, or no horizontal ridges. The shapes and sizes of the vertical protrusion and the horizontal ridges, if present, may differ across embodiments. For example, horizontal ridges may be triangular, circular, elliptical, square, rectangular, or any other shape extending horizontally from a vertical protrusion. In some embodiments a vertical protrusion may be at least 0.2 cm, e.g., 80%, or any other percentage of the overall thickness of the upper and lower press-fit elements, in other embodiments, any value between 0.4 cm and 0.6 and in other embodiments 0.8 cm tall. In some embodiments a horizontal ridge may be at least 0.1 cm wide or any other width, including any value greater than 0.1 cm, such as 0.2 cm or wider. 
     To achieve a leak resistant seal, one or more embodiments of the invention may incorporate press-fit elements of substantial size and material thickness. Such designs present a potential challenge in that the sealing elements may extend a considerable distance away from the top and bottom enclosures. To mitigate this effect, one or more embodiments of the invention may offset the top and bottom press-fit elements so that they are more centered along the horizontal plane of the container. In particular, in one or more embodiments, the top press-fit element or the bottom press-fit element, or both, may have cavities and protrusions that extend both above and below the center horizontal plane between the top and bottom enclosures. For example, a bottom press-fit element might have cavities below the center horizontal plane, and a vertical protrusion that extends above the center horizontal plane. Thus, one or more embodiments enable containers with leak resistant seals that have sealing elements better aligned or centered with the sides of the containers&#39; enclosures. Furthermore, thicker seals provide a tactile area in which to hold the container while minimizing the chance of dropping the container. Thus the seal is configured as a handle to hold the container in one or more embodiments when the seal is thick enough based on the coefficient of static friction and based on the shape of the seal in order to hold the desired contents securely. 
     In some embodiments of the invention the top and bottom press-fit elements may extend to portions of the left edge or right edge of the top and bottom enclosures. In such embodiments the opening mechanism for the container may incorporate a hinged area or similar design along the sides that allows the container to open wider than if it can only open on the front edge. Such embodiments may provide considerable convenience by making it easier for a user to insert items into the container or remove items from the container. 
     One or more embodiments of the invention may provide flaps or tabs extending from the front edge or the sides of the top and bottom press-fit elements. Such flaps or tabs may be used to hold the edges of the container in order to pull it open from its sealed position. These flaps may be of any convenient size or shape, and may be placed in any convenient location. In some embodiments for example, the flaps may be shaped roughly as an arc with the widest portion in the center of the front edge. In other embodiments the flaps may consist of simple tabs emerging from the center of the front edge or from other locations. In some embodiments there may be a bottom tab and a top tab, with the bottom tab longer than the top tab. Other embodiments may reverse this arrangement and may have a top tab that is longer than the bottom tab. In other embodiments the flaps or tabs may be of equal size. A longer flap or tab may provide a lever arm for the user when pulling the seal open, allowing the user to more easily open the seal. This feature may be particularly valuable for a very strong seal that is designed for leak resistance, since the user must have a mechanism to overcome the sealing force when opening the container. In one or more embodiments there may be a gap between the top flap and the bottom flap to make it easier for the user to grasp one or both of the flaps for opening. 
     In one or more embodiments the top or bottom press-fit element may incorporate a vertical protrusion surrounded by two cavities, one forward of the protrusion and one backward from the protrusion. In some embodiments the depths of these two cavities may be unequal. For example, in one or more embodiments a forward cavity may be shallower than a back cavity. A potential advantage of such an asymmetric shape for the press-fit element is that the force required to begin opening the seal from the forward edge may be less than the sealing force towards the back edge. This may facilitate opening by the user while maintaining a strong seal. Once the user has broken the seal at the forward cavity, the additional lever arm provided by the open portion of the press-fit element may be used to continuing opening the back part of the seal. 
     Embodiments of the invention may incorporate various shapes and sizes for the press-fit elements. In some embodiments the shape of the boundary between the top press-fit element and the bottom press-fit element may contribute significantly to the sealing force. Embodiments may use winding paths for the boundary with multiple changes of direction to improve the seal. Such winding paths provide two potential advantages. First, they can provide resistance to movement of the press-fit elements in multiple directions. Secondly, they can lengthen the distance that liquid must travel to escape from the seal, improving leak resistance. The direction of resistance to movement is quantified by the direction of the normal vector to the boundary surface. In some embodiments a boundary path may provide normal vectors that point in four different directions, including up, down, forward, and backward. Some embodiments may provide more or fewer normal vectors. The normal vectors are orthogonal to the surface whether planar or curved at a particular point along the plane or curve. In some embodiments the normal vectors to the boundary surface may point approximately in these four directions, but may point somewhere in all four quadrants of the vertical plane perpendicular to the back-to-front axis of the container. With normal vectors in all quadrants, the press-fit elements provide sealing forces in all directions. In other embodiments the winding path of the boundary may change directions multiple times to provide multiple normal vectors in all directions on different segments of the boundary path. For example, in one or more embodiments there may be at least three different segments of the boundary path with normal vectors in each of the four directions or four quadrants. Such paths further increase the sealing force. 
     In one or more embodiments the winding path of the press-fit boundary will be significantly longer than the straight-line back-to-front horizontal distance across the press-fit elements. This longer path improves the sealing by lengthening the path for liquids to travel out of the seal. For example, in some embodiments the length of the boundary path is at least twice as long as the horizontal back-to-front distance between the start and end of the boundary path. Other embodiments may utilize even longer boundary paths with greater distance ratios. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the ideas conveyed through this disclosure will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  illustrates a perspective view of an embodiment of the invention with the seal closed. 
         FIG. 2  illustrates the top and bottom enclosures and top and bottom press-fit elements of the embodiment shown in  FIG. 1 , for example in exploded view, when formed from one component or before attachment of portions of the top and bottom portions to one another. 
         FIG. 3  shows a side view of the top and bottom enclosures and top and bottom press-fit elements of  FIG. 2 . 
         FIG. 4  shows a side view of the enclosures and press-fit elements from  FIG. 3  relative to the center horizontal plane. 
         FIG. 5  illustrates a side view of the top and bottom press-fit elements of an embodiment of the invention, with their common boundary for example as shown with bold lines. 
         FIG. 6  illustrates detailed features of the lower press-fit element of an embodiment of the invention. 
         FIG. 7  illustrates a top view of an embodiment of the invention in which the front edge is longer than the back edge. 
         FIG. 8  illustrates the top and bottom press-fit elements of an embodiment of the invention in which a front vertical cavity is shallower than a back vertical cavity. 
         FIG. 9  illustrates the press-fit boundary of the embodiment of the invention shown in  FIG. 8 , along with horizontal normal vectors to the boundary. 
         FIG. 10  illustrates the press-fit boundary of the embodiment of the invention shown in  FIG. 8 , along with the vertical normal vectors to the boundary. 
         FIG. 11  illustrates the press-fit boundary of the embodiment of the invention shown in  FIG. 8 , along with the path length of the boundary. 
         FIG. 12  illustrates an embodiment of the invention in exploded view when formed from one component, or for example before attachment of at least a portion of the top and bottom element, with the seal&#39;s press-fit elements extending from the front edges to portions of the left and right edges of the enclosures. This embodiment also illustrates a top flap and a bottom flap extending forward from the seal. 
         FIG. 13  shows a close up view of the front of the embodiment shown in  FIG. 12 . 
         FIG. 14  illustrates another embodiment of the invention with the seal&#39;s press-fit elements extending from the front edges to portions of the left and right edges of the enclosures, and with top and bottom flaps configured with a vertical gap between them to facilitate grasping the flaps. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A shaped elastomeric container with an integrated leak resistant seal will now be described. In the following exemplary description numerous specific details are set forth in order to provide a more thorough understanding of the ideas described throughout this specification. It will be apparent, however, to an artisan of ordinary skill that embodiments of ideas described herein may be practiced without incorporating all aspects of the specific details described herein. In other instances, specific aspects well known to those of ordinary skill in the art have not been described in detail so as not to obscure the disclosure. Readers should note that although examples of the innovative concepts are set forth throughout this disclosure, the claims, and the full scope of any equivalents, are what define the invention. 
       FIG. 1  illustrates an embodiment of the invention with the container seal closed, shown in a perspective view. In some embodiments the container&#39;s materials may include elastomers, such as silicone or other rubbers or polymers. Other materials may be included in various embodiments. In some embodiments the body of the container may be rigid; in other embodiments it may be flexible. Embodiments that incorporate silicone offer a benefit of heat-resistance; thus for example such embodiments may be placed in an oven to heat food contained in the container. Some embodiments may be configured to be reused; other embodiments may be configured for single uses. 
       FIG. 1  shows an embodiment of a container with top enclosure  101  and bottom enclosure  102 . Top enclosure  101  has front edge  110 , back edge  111 , left edge  112  and right edge  113 . In the embodiment shown the top enclosure and the bottom enclosure are contiguous when formed from one element or joined via a seam along the back, left, and right edges for embodiments that utilize a plurality of components to form the apparatus. The front edges are not joined permanently, but are in contact when closed and are held closed via the sealing elements that extend forward from the front edges. Top and bottom enclosures may be formed or joined using integrated molding of both enclosures, or via various other methods to join elastomeric elements together. In some embodiments it is desirable that the joints between the top and bottom enclosures be continuous without gaps, so that the container can hold liquids without leaking. Furthermore, thicker seals such as seal  110  provide a tactile area in which to hold the container while minimizing the chance of dropping the container. Thus seal  110  is configured as a handle to hold the container in one or more embodiments, for example from the top, (right side as shown in  FIGS. 1, 12 and 14 ) when the seal is thick enough based on the coefficient of static friction of the material utilized to construct at least the seal portion of the container and based on the shape of the seal in order to hold the desired contents securely. 
       FIG. 2  shows an exploded view of  FIG. 1  with the top enclosure  101  and the bottom enclosure  102  shown separately. As in  FIG. 1 , top enclosure  101  has edges  110 ,  111 ,  112 , and  113 . Extending forward from front edge  110  of top enclosure  101  is top press-fit element  231 . In  FIG. 2  the edges of bottom enclosure  102  are also visible: front edge  210 , back edge  211 , left edge  212 , and right edge  213 . In the embodiment shown, the edges  210 ,  211 ,  212 , and  213  of the bottom enclosure are in contact with edges  110 ,  111 ,  112 , and  113  respectively of the top enclosure when the container is closed. In other embodiments edges of the top enclosure and bottom enclosure may not be fully in contact even when the container is closed, to enable flaps for opening or other structures with holes or attachment elements as one skilled in the art will recognize. Attached to the front edge of bottom enclosure  102  is bottom press-fit element  232 . In the embodiment shown, the press-fit elements extend forward from the front edges of the enclosure halves. In other embodiments these press-fit elements may be oriented differently; for example in some embodiments they may extend backwards from the front edges of the top and bottom enclosures. The specific location of the press-fit elements may be varied as long as they are able to mate together to seal the container. In some embodiments the press-fit elements may extend from the front edge to portions of the left or right edges of the top and bottom enclosures. 
     In the embodiment shown in  FIG. 2 , the top enclosure  101  and bottom enclosure  102  have curved shapes so that when they are joined together there is an inner volume enclosed by the container. In some embodiments the materials and shape of the enclosures may be sufficiently rigid that this volume is present even when the container is empty. In other embodiments the materials and shape may be more flexible, such that the top and bottom enclosures collapse against one another, as in a thin plastic bag, when the container is empty. 
       FIG. 3  shows a side view of the embodiment shown in  FIGS. 1 and 2 , with the top enclosure  101  and bottom enclosure  102  shown separately. This side view shows more clearly that the top press-fit element  231  and the bottom press-fit element  232  are shaped and oriented to fit together to provide a seal for the container. In this embodiment bottom press-fit element  232  has a protrusion with a triangular top that extends upward and that fits into a corresponding recess in top press-fit element  231 . Other embodiments may employ different shapes for the top and bottom press-fit elements. 
       FIG. 4  shows an annotated view of  FIG. 3 . Center horizontal plane  401 , running in this embodiment along the front-to-back axis, is the plane along which top enclosure  101  and bottom enclosure  102  are joined. In this embodiment the edges of the top enclosure  101  are located on the plane  401 , as are the edges of the bottom enclosure  102 . In other embodiments different shapes may be used so that edges need not all lie on a common plane. Portions of the top press-fit element  231  extend below plane  401  in this embodiment, and portions of the bottom press-fit element  232  extend above plane  401  in this embodiment. In other embodiments one or more of the press-fit elements may lie entirely on one side of the center horizontal plane.  FIG. 4  also shows that top enclosure  101  has a height  402  of its enclosed volume above the horizontal plane  401 , and that bottom enclosure  102  has a height  403  of its enclosed volume below the horizontal plane  401 . In this embodiment the top enclosure and the bottom enclosure are approximately mirror images of one another across the center horizontal plane. Other embodiments may employ other shapes, including shapes that are not mirror images or that do not have flat edges on a common horizontal plane. Different embodiments may provide various sizes and shapes for the volume enclosed by the container when it is closed. 
       FIG. 5  shows a close up side view of the top press-fit element  231  and bottom press-fit element  232  of the embodiment shown in  FIG. 4 . When closed and sealed, the press-fit elements meet at a common boundary  501 . In the embodiment shown, the bottom press-fit element has a center vertical protrusion with a groove on either side of the protrusion. The top press-fit element has a corresponding recess to accept the protrusion, and has protrusions extending downward to fit into the grooves of the bottom press-fit element. The thickness of the material of the press-fit elements is a significant factor contributing to the strength of the seal. In the embodiment shown in  FIG. 5 , the thickness varies across the press-fit elements. For example, near the back edge of the press-fit elements, bottom press-fit element has an edge thickness  504  and top press-fit element has an thickness  502 . In the center of the bottom protrusion, bottom press-fit element has a center thickness  505  and top press-fit element has a center thickness  503 . In one or more embodiments, the average material thickness of the top and bottom press-fit elements is at least 0.25 cm, in other embodiments, any value up to 0.5 cm, in other embodiments any value between 0.5 cm and 0.75 cm and in other embodiments 1.0 cm across their common boundary  501 . Material thickness at or in excess of these ranges can contribute to forming a leak-resistant seal when the enclosure is closed and sealed. For example, in one embodiment with average thickness of press-fit elements of about 0.8 cm, experiments have demonstrated a seal sufficient to contain 1 to 2 cups of water without leakage even when the container is held upside down (with the front facing downward) so that the water exerts pressure against the seal. 
     In some embodiments, the shapes and dimensions of the press-fit elements may also contribute significantly to the leak resistance of the seal.  FIG. 6  illustrates details of the bottom-press fit element  232  of the embodiment shown in  FIG. 5 . In this embodiment, vertical protrusion  601  extends upward from the bottom press-fit element, while cavities  606  and  607  are on either side of this vertical protrusion. Other embodiments may have different numbers and shapes of protrusions and cavities, configured as male elements and female elements that fit together when the seal of the container is closed. In some embodiments a main vertical protrusion, like protrusion  601 , may be located on the top press-fit element, rather than on the bottom press-fit element as in  FIG. 6 . As shown, the vertical protrusion is symmetrical, however, any asymmetrical shape may also be utilized so long as the seal is shaped for the desired leak resistance of the given implementation. 
     In the embodiment shown in  FIG. 6 , vertical protrusion  601  has two horizontal ridges  602  and  603  extending horizontally outward from the vertical protrusion. These ridges have triangular sloped upper surfaces to facilitate insertion into the corresponding cavities in the upper press-fit element. They also have flat horizontal lower surfaces that provide resistance to opening once the protrusion is inserted into the upper cavities. Other embodiments may have vertical protrusions with only one horizontal ridge, or with more than two horizontal ridges. In some embodiments vertical protrusions may have no horizontal ridges and other features of the shape or material of the press-fit elements may provide sufficient sealing force. 
     In the embodiment shown in  FIG. 6 , vertical protrusion  601  extends above the center horizontal plane  401 , and cavities  606  and  607  extend below the center horizontal plane  401 . This arrangement of the components of the press-fit element has the effect of centering the sealing elements relative to the top and bottom enclosures. Such a design may have a significant benefit for embodiments with relatively thick material in the press-fit elements, since otherwise the seal would potentially extend far above or below the outer surfaces of the top or bottom enclosures. For comparison, very thin plastic bags may have sealing elements that include a protrusion extending entirely above one side of the bag, with no corresponding cavities below that side of the bag. Such a design may be acceptable with very thin sealing elements, but such seals may not be as leak resistant as seals with thicker material. 
     The vertical protrusion  601  in  FIG. 6  has vertical height  604  above the cavities  606  and  607 , and the horizontal ridge  602  has width (measured back to front) of  605 . In one or more embodiments of the invention, one or more vertical protrusions have height  604  of at least 0.2 cm, e.g., 80%, or any other percentage of the overall thickness of the upper and lower press-fit elements, in other embodiments, any value between 0.4 cm and 0.6 and in other embodiments 0.8 cm. In other embodiments, one or more horizontal ridges extending from a vertical protrusion have width  605  of at least 0.1 cm wide or any other width, including any value greater than 0.1 cm, such as 0.2 cm or wider. Dimensions such as these exemplary values may contribute to a higher sealing force that causes the container to be leak resistant. Some embodiments may have a plurality of vertical protrusions or a plurality of horizontal ridges that provide sufficient aggregate sealing force even though individual vertical protrusions and horizontal ridges are below these exemplary dimensions. In one or more embodiments, the width of the seal may be varied to provide a higher or lower leak resistance capability. 
       FIG. 7  illustrates at top-view of an embodiment of the invention with top enclosure  101  shown. In this embodiment the length  701  of front edge  110  is larger than the length  702  of back edge  111 . The edges of top enclosure  101  therefore form roughly a trapezoid, rather than a rectangle. Such an embodiment offers the potential advantage that it is easier to place items into the opening of the container, or remove them from the container, because the opening along the front edge  110  is larger. Such a design may be particularly beneficial when the sealing elements are larger and thicker, since larger and thicker sealing elements may tend to pinch together at the left and right edges. 
       FIG. 8  illustrates a close up side view of the top and bottom press-fit elements of another embodiment of the invention. In this embodiment bottom press-fit element  232  has a vertical protrusion  601  and cavities  606  and  607  on either side of the vertical protrusion. This basic structure is similar to that of the embodiment shown in  FIG. 6 . However in the embodiment of  FIG. 8 , the vertical cavity  607  towards the back has depth  801  below center horizontal plane  401  that is greater than the depth  802  of the vertical cavity  606  towards the front. This asymmetry offers the potential advantage of reducing the amount of force needed to begin opening the seal from the front, while maintaining a deeper cavity towards the back to resist pressure from inside the container pressing against the seal. It therefore contributes to the leak resistance of the seal while mitigating the effect of this leak resistance on the force required by a user to open the container. Other embodiments may provide other asymmetric shapes with different arrangements and dimensions of cavities and protrusions to accomplish the same objective of a strong seal with a mitigated opening force. 
     Embodiments of the invention provide opposing surfaces of the top press-fit element and the bottom press-fit element to resist forces in multiple directions. These opposing surfaces in multiple directions contribute to the strength of the seal and the resistance of the seal to leaks. In one or more embodiments, opposing forces between the top and bottom press-fit elements exist in each of the four directions up, down, forward and backward (when viewed from a side view). In some embodiments the directions of opposing forces exist in all four quadrants of the plane perpendicular to the front edge, but may not be precisely along the vertical and horizontal axes. Such embodiments effectively provide opposing forces in all four directions since the vector sum of the actual forces includes components in the positive and negative vertical and horizontal directions. 
     In one or more embodiments, multiple segments of the common boundary provide resistance to forces in each direction. With multiple segments providing force resistance in various directions, the strength of the seal may be further increased. 
     The directions of the opposing forces between the top press-fit element and the bottom press-fit element are represented by the normal vectors to the common press-fit boundary between the top and bottom press-fit elements.  FIG. 9  illustrates this boundary  901  for the embodiment of the invention shown in  FIG. 8 . In  FIG. 9  several horizontal normal vectors are shown for this boundary. Normal vectors  902 ,  903 ,  904 , and  905  are horizontal towards the front. Normal vectors  906 ,  907 , and  908  are horizontal towards the back. In this embodiment, there are at least 4 normal vectors in the horizontal front direction, each on a different segment of the boundary, and there are at least 3 normal vectors in the horizontal back direction, each on a different segment of the boundary. 
       FIG. 10  illustrates vertical normal vectors for the embodiment shown in  FIG. 9 . In this embodiment, normal vectors  1001 ,  1002 , and  1002  are vertical pointing upwards, and normal vectors  1004 ,  1005 ,  1006 , and  1007  are vertical pointing downwards. Thus in this embodiment there are at least 3 normal vectors in the vertical up direction, each on a different segment of the boundary, and there are at least 4 normal vectors in the vertical down direction, each on a different segment of the boundary. 
       FIGS. 9 and 10  illustrate an exemplary embodiment of the invention with at least 3 different segments of the boundary having normal vectors in each of the directions forward, backward, up, and down. The embodiment shown has a winding boundary that changes direction multiple times to provide the forces in each direction. Other embodiments of the invention provide only a single segment for the normal vector in each of the four directions, or may provide more than 3 segments for the normal vector in each of the four directions. In some embodiments, there may be more segments providing normal vectors to forces in horizontal directions to increase the seal&#39;s resistance to horizontal pressure. Different embodiments of the invention may employ boundary path shapes optimized for the forces expected for the application of the container for this embodiment. In various embodiments the segments of the boundary may be flat, pointed, curved, segmented, or any combination thereof as appropriate for the application. 
     One or more embodiments of the invention provide leak resistance in part by utilizing a winding path for the boundary between the top press-fit element and the bottom press-fit element. When the seal is closed, liquids flowing through gaps in the seal must traverse this entire winding path. Hence a longer and more tortuous path increases the leak resistance of the seal. Different embodiments may employ various shapes for such a winding path.  FIG. 11  illustrates the boundary path for the embodiment shown in  FIG. 8 . The relative length of the different segments of the boundary are shown in  FIG. 11 ; for example the leftmost horizontal segment has length  1102  of 1.0. (The lengths shown are only relative to one another; they are not expressed in any specific units.) In the embodiment shown, the total length  1103  of the winding boundary path is 17.5. The horizontal distance  1101  between the start and end of the path is 7.0. Thus the path length is approximately 2.5 times the horizontal distance. This ratio of path length to horizontal distance is a quantification of the extent to which the boundary path winds and changes directions, which contributes to the sealing force and the leak resistance. Some embodiments of the invention, such as the one shown in  FIG. 11 , have a boundary path length of at least twice the horizontal distance between the start and end of the path. 
     Some embodiments of the invention utilize multiple techniques to enhance the leak resistance of the seal. For example, the embodiment shown in  FIG. 8  provides a winding boundary path of length more than twice the horizontal distance, as well as three or more normal vectors in each of the four directions up, down, backward, and forward. In some embodiments such techniques may be combined with a high average material thickness or other dimensional or material variations for the press-fit elements to further increase the leak resistance. 
     In one or more embodiments of the invention, the press-fit elements of the seal may extend to portions of the left edge or the right edge, or both, of the top and bottom enclosures.  FIG. 12  illustrates an embodiment in which the press-fit elements are located along the front edges and also along the front portions of the left and right edges.  FIG. 12  shows an exploded view of the top enclosure  101  and bottom enclosure  102 . In this embodiment top press-fit element  231  has portion  1201  that is proximal to left side  112 , and portion  1202  that is proximal to right side  113 . Similarly bottom press-fit element  232  has portion  1203  that is proximal to left side  212  and portion  1204  that is proximal to right side  213 . In the embodiment shown, the press-fit elements curve around the corners between the front edge and the left and right edges. In other embodiments the press-fit elements may form right angles at the corners, or may form any curved or polygonal shape to extend from the front edge to the left and right edges. Embodiments may employ curved shapes for the corners that may be circular, oval, elliptical, or any other shape. Embodiments may employ polygon shapes for the corners that may be rectangular, or they may use multiple segments with any angles between the segments. In some embodiments the press-fit elements may extend to only one of the left or right edges. A potential advantage of embodiments in which the press-fit elements extend to the left and right edges is that the opening of the container may be wider, simplifying insertion or removal of objects. 
     In one or more embodiments of the invention, the container may include a top flap or a bottom flap, or both, proximal to the opening. These flaps may be used for example for grasping the edges of the container when opening or closing the container.  FIG. 12  illustrates an embodiment of the invention with a top flap  1210  and a bottom flap  1211 . In some embodiments the shapes and sizes of the top flap and the bottom flap, if both are present, may be different. This is illustrated in  FIG. 12  where top flap  1210  forms an arc extending from approximately the middle third of the top front edge, while bottom flap  1211  extends along the entire bottom front edge.  FIG. 13  shows a close up view of the front of the embodiment illustrated in  FIG. 12 , shown in the closed position. As illustrated in  FIG. 13 , in this embodiment the bottom flap  1211  extends further forward than top flap  1210 . Embodiments that employ flaps of different sizes may facilitate opening by making it easier for a user to grasp one of the flaps to begin opening. Different embodiments may use different sizes and shapes of flaps, including symmetric designs with similar shapes for top and bottom flaps, and asymmetric designs as illustrated in  FIG. 13 . 
       FIG. 14  illustrates an embodiment of the invention with a vertical gap between the top flap and the bottom flap, to facilitate grasping the flaps for opening. In this embodiment top flap  1210  has a curved form that is vertically offset from bottom flap  1211  by distance  1401 . This shape may make it easier for a user to insert his or her fingers into the space between the flaps. In this embodiment bottom flap  1211  has a series of ridges running parallel to the front edge of the container, to aid in grasping the flap. In the embodiment shown in  FIG. 14 , the press-fit elements are located along the front edges and also along the front portions of the left and right edges. Top press-fit element  231  has portion  1201  that is proximal to left side  112 , and portion  1202  that is proximal to right side  113 . Similarly the bottom press-fit element extends to the left edge and the right edge. In this embodiment, the press-fit elements curve around the corners between the front edge and the left and right edges. 
     While the ideas herein disclosed have been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.