Abstract:
A clamshell container comprising a tray and a cover formed from a blank; the tray including a bottom and four curved side walls foldable upward from the four edges of the bottom along arcuate fold lines, the tray walls having defined corners inwardly offset relative to the center points of the walls; and a cover provided with corresponding walls, at least three of which are folded from arcuate fold lines along corresponding edges of a cover top panel and which define depending arcuate cover walls and a cover with a maximum width at transverse centerlines between opposed sets of walls and minimum widths at corners defined by the cover walls; the cover pivotally closing over the tray with the arced walls of the tray received within the arced walls of the cover and engaging therewith.

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119(e) 
       [0001]    Applicant claims the benefit of priority of Provisional Patent Application No. 60/857,801, filed on Nov. 9, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Clamshell containers of paperboard and like sheet materials have long been known and used as takeout cartons for foodstuffs, particularly although not exclusively in fast food establishments. As will be recognized, such containers are, for the most part, of a square configuration intended to generally conform to and principally package hamburgers and other foodstuffs of similar shapes. 
         [0003]    Because of the planar nature of the paperboard panels which fold from a blank to define the container, and as the typical hamburger is round, the conventional clamshell container includes rather large defined interior air spaces about a received hamburger, particularly at the corners of the container. Such air spaces have been found to be a substantial source of heat loss from any warmed or heated foodstuff. Likewise, the lack of an effective seal between the lid and tray of the conventional paperboard clamshell container can also be a potential source of substantial heat loss. However, little attention has heretofore been directed to addressing the heat loss problem in such containers. 
         [0004]    Another factor to be considered in the formation of paperboard containers is the amount of paperboard material used. Basically, as a container for foods, the paperboard itself must be of high quality and be food compatible leak proof to a degree, structurally stable, etc. Such material is quite expensive. Thus, any reduction in the blank material required to form the container is highly desirable. As a practical matter, such blanks are normally cut in groups by a single impression or “hit” of the die. In view of the huge numbers of such disposable cartons utilized each year, in the hundreds of millions, any reduction in material, scrap or waste in the forming of the blanks can result in substantial savings and significant economical and ecological advantages. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention, in an acknowledged extremely crowded art, has several important objects which are considered to advance the art in a patentably significant manner. 
         [0006]    Two principal and interrelated objects involve an economically significant reduction in the material used in the formation of the container, and the formation of a container with enhanced heat retention capabilities. 
         [0007]    In achieving the above objects, it is also an intention of the present invention to provide a container which presents an attractive contemporary appearance with contoured lines and, as desired, an enhanced surface display area. 
         [0008]    Inasmuch as a substantial loss of heat from a received product results from the rather large corner air spaces provided in the conventional or traditional clamshell container, the present invention specifically provides for the reduction of these air spaces by utilizing concave walls as opposed to the more conventional planar or flat walls. Basically, both the tray walls and at least the majority of the lid or cover walls are concavely arced from about the tray bottom and cover top to define an area generally corresponding to that of a circular hamburger bun. 
         [0009]    The opposed ends of each tray wall panel arc inwardly and are joined, at corners, appreciably inwardly spaced from a similar corner-forming joinder were the walls panels joined at right angles as in the conventional planar configuration of a traditional clamshell. As an example, in comparison to a conventional container tray of approximately four inches by four inches, an arc from the central section of each wall to each end thereof sufficient to inwardly offset the corner forming end portions ⅛ inch will reduce the length of the side edge of the formed tray a total of ¼ inch. As compared to the traditional clamshell, this in turn will reduce each corner air space, on a radial line bisecting the formed corner, approximately 25%. The reduction in the corner air spaces, while in no way affecting the reception of the hamburger or like foodstuff within the container, will inherently enhance the heat retention capability of the closed container. With similar structural enhancements of the cover of the tray, the length of the opposed sides of each clamshell forming blank can be reduced as much as ½ inch. Such a savings in material, when producing literally millions of such blanks and containers, as noted above, is of tremendous significance both ecologically and economically, particularly when considering the single use disposable nature of the clamshell containers. Thus, it will be recognized that the two principal objects of the invention are achieved, that of substantially reducing the space within the container and the heat loss arising therefrom, and a significant reduction in the material required in the formation of the blank and container, all without affecting the basic function of the clamshell as a means for retaining a common foodstuff. 
         [0010]    As will be recognized as the invention is further explained and illustrated, in bringing together the ends of adjoining wall portions to define the reduced air spaces, corner angles of slightly greater than 90° are formed. This will allow minor although significant modifications in the joined ends of the walls which will provide for elimination of additional paperboard material for further savings. 
         [0011]    The various objects and advantages residing in the present invention will be better appreciated from the following more detailed description and drawings presented for illustration of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1A  is a cross-sectional view of a typical prior art clamshell container with a hamburger sandwich illustrated in phantom lines therein; 
           [0013]      FIG. 1B  is a similar cross-sectional view taken through the clamshell container of the present invention and illustrating the inwardly shifted corners providing the reduced internal air spaces and enhanced sealing between the tray and lid walls; 
           [0014]      FIG. 2A  illustrates the prior art blank from which the traditional container of  FIG. 1A  is folded; 
           [0015]      FIG. 2B  illustrates the improved blank of the present invention from which the container of  FIG. 1B  is folded; 
           [0016]      FIG. 3  is an enlarged detail view of a typical tray corner area as indicated on  FIG. 2B  superimposed on a phantom line showing of the corresponding corner area of the prior art container; 
           [0017]      FIG. 4  illustrates a nested layout allowed by the blank of the present invention for the simultaneous formation of multiple blanks with a single die impression; 
           [0018]      FIG. 5  is a perspective view of the clamshell container of the invention with the lid or cover open; and 
           [0019]      FIG. 6  is a perspective view of the closed clamshell container with the rather taller cover front wall presenting a significant display panel. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0020]    Referring now more specifically to the drawings,  FIGS. 1A and 2A  illustrate the traditional prior art clamshell container includes a tray  10  and a lid or cover  12  integrally joined and folded from a single blank  14 . The tray  10 , referring both to the folded container and the blank  14 , includes a flat rectangular bottom or bottom panel  16  sized to, in the preferred embodiment, receive a hamburger sandwich as suggested in the phantom line showings. Opposed planar tray side panels  18  are integral with opposed side edges of the bottom panel  16  along linear fold lines. Similarly, opposed planar front and rear tray wall panels  20  and  22  are integral with the front and rear edges of the tray bottom along linear fold lines. 
         [0021]    The cover  12  is similarly formed with a rectangular top or top panel  24 , opposed side walls  26  integral with opposed side edges of the top panel  24  along linear fold lines, and opposed planar front and rear cover walls  28  and  30  also integral with the top panel and foldable relative thereto along linear fold lines. The rear walls  22  and  30  of the tray and cover are integrally joined along a linear hinge forming fold line  32  for a selective opening and closing of the cover. As is traditional, appropriate glue and latch tabs  34  will be used in assembling the container and securing the folded tray and container walls at the respective corners. 
         [0022]    Noting the cross sectional detail of  FIG. 1A  in particular, it will be seen that a traditional container formed from flat panels along straight fold lines, as above described, while capable of receiving and carrying takeout foods, is not particularly effective in retaining heat. This is due both to rather large air spaces  36  provided at the various corner areas of the tray and cover, and in light of the less than effective sealing of the cover walls with the tray walls, resulting in spaces or gaps as suggested at  38 . 
         [0023]    Referring now to the present invention, attention is directed to  FIGS. 1B and 2B , and initially to the blank  39  illustrated in  FIG. 2B . As with the prior art blank  14 , the blank  39  includes both a tray  40  and a cover  42 . While the blank  39  also includes all of the basic components of the prior art blank  14 , including top and bottom panels, peripheral walls, glue flaps, and the like, significant differences exist with regard to the structure and relationship of the components to each other. 
         [0024]    More particularly, the opposed side walls  44  of the tray  40  are integral with the opposed side edges of the tray bottom  46  along arcuate fold lines  48  which are convex relative to the tray bottom  46 . The fold lines  48  each include opposed end portions  50  distinctly inwardly offset relative to the central section or center point  52  of the corresponding fold line  48 . It will be appreciated that the maximum transverse width of the tray bottom  46  will be between the central points  52  of the opposed side walls fold lines  48 . As suggested by the phantom line showing of the hamburger, this transverse width will be essentially equal to the transverse width of the prior art carton or container. However, as will be noted and as is particularly significant, the transverse width between aligned and opposed end portions  50  of the two fold lines  48  will be appreciably reduced while at the same time in no way interfering with the space required for the accommodation of the hamburger. 
         [0025]    The front and rear walls  52  and  54  of the tray  44  are similarly foldably joined to the front and rear edges of the tray bottom  46  along arcuate fold lines  56 . The fold lines  56 , as with the fold lines  48 , have the opposed and aligned end portions  58  thereof inwardly offset with the transverse distance between the front and rear fold lines  56  being at a maximum spacing at the center points and at a minimum spacing at the fold line end portions  58 . 
         [0026]    The adjoining end portions of the fold lines  48  and  56  and the associated wall panels define the four corners  60  of the tray  40 . The corners  60  formed by the joined wall panel ends are inwardly offset and defining an obtuse angles, that is an angle greater than 90°, as opposed to the right angle corners  62  formed by the joined panel ends of the conventional carton tray  10 . In this regard, note the enlarged detail of  FIG. 3  and the overlay relationship shown therein for purposes of illustration. The space  64  between the fold lines of the conventional tray and the inwardly offset end portions  50  and  58  of fold lines  48  and  56  represents a reduction in the material required in the formation of the blank  39  which is substantial. For example, in a container tray of conventional size, approximately 4 inches by 4 inches, a ⅛ inch radius arc from the center point of each fold line to each corner, that is an arc which will inwardly offset each corner of each fold line ⅛ inch from the center point thereof, will result in a space saving and reduction of material equal to ⅛ inch for a total of ¼ inch in the edge dimension of the tray both along the sides and across the front and rear thereof. In addition to the significant material reduction, it will also be noted that by in effect inwardly offsetting the corners, the corner spaces about the hamburger are also reduced. Using the ⅛ inch reduction noted above, this space reduction will produce a reduction of approximately 25% between the new corner position and the received hamburger. Note the dimension line  66  in  FIGS. 2B and 3 . Incidentally, in addition to the savings in material uniquely produced by the inward offsetting of the corner construction, and noting the detail of  FIG. 3  in particular, additional material reduction, as suggested at  68 , will also occur at the ends of the wall panels and the interposed glue flaps and latching lugs which will be defined to accommodate the repositioned corners. 
         [0027]    Referring now more specifically to the container cover  42 , and noting in particular the blank  39 , as in the conventional container, the cover includes a top or top panel  70 , opposed side walls  72 , a front wall  74  and a rear wall  76 . The cover top  70  has opposed side edges defined by convex fold lines  78  with end portions  80  inwardly offset from corresponding center points  82 . The side walls  72  are integral with and fold relative to the top  70  along these fold lines  78 . A similar convex fold line  84 , with end portions  86  inwardly offset from corresponding center point  88  define the forward edge of the top  70  for a folding of the cover front wall  74 . The rear wall  76  of the cover is folded relative to the rear edge of the top  70  along a linear or straight fold line  90 . A similar straight fold line  92  is formed between the joined outer edges of the tray and cover rear walls  54  and  76  to define a hinge therebetween. The use of such straight fold lines at these particular fold points is desired to prevent a buckling action as the clamshell container is closed. 
         [0028]    It is intended that the dimensional reduction in length and width of the cover  42 , and hence the material saving, closely correspond to that previously described with regard to the tray portion  40  of the container. As such, and in order to accommodate the straight rear wall fold line  90 , the radii of the side wall and front wall fold lines  78  and  84 , and the inward offset of the end portions thereof from the corresponding center points may slightly differ from those of the tray side and rear wall fold lines  48  and  56 . Thus, referring to the example of dimensions referred to above, a similar reduction in the cover edge length of approximately ¼ inch will result in a total blank edge length reduction of ½ inch, a very appreciable savings in material when considering the millions of such blanks produced yearly. It will also be recognized that the inward offsetting of the edge portions of the cover fold lines  78  and  84  will, in the closed container, similarly and effectively reduce the cold air space at the interior corners of the closed container. 
         [0029]    As is the case with regard to the tray  40 , in the cover  42 , the transverse distances between the two sets of the generally parallel fold lines is greatest at the center points thereof with the transverse distances reduced at the aligned corner portions. In accommodating the straight rear edge fold line  90  of the top  70  while maintaining the desired edge length reductions as previously noted, this can be achieved by utilizing a shorter radius in defining the side wall fold lines  78  and a greater radius in defining the front wall fold line  84  as compared to the radii utilized for the fold lines  48  and  56  of the tray  40 . 
         [0030]    Referring again to the tray portion of the blank in  FIG. 2B , the tray side walls  44  are preferably formed with arced or convex outer edges and extend, in the closed carton as suggested in  FIG. 1B , higher within the corresponding cover side walls  72 . The outer edge of each cover side wall  72  is defined by a complimentary concave cut reducing the height thereof an amount equal to the corresponding height increase of the tray side walls, thus not conflicting with the overall material reduction desired in the present invention. 
         [0031]    Noting  FIG. 4  and the partial layout of multiple blanks for utilization of a single die cut, it will be appreciated that the reverse positioning of adjacent blanks and the complementary configurations of the outer edges of the tray and cover side walls allow for a single “hit” or die cut, thus simplifying manufacture and reducing excess or waste material to a minimum. 
         [0032]    A similar complementary configuration will be noted in the preferred front walls  52  and  74  of the tray and cover wherein the outer edge of the tray front wall  52  is concave and relatively shorter than the front wall of a conventional clamshell container. At the same time, the front wall  74  of the cover is substantially taller and includes a convex outer edge, the configuration of which corresponds to that of the concave outer edge of the tray front wall  52 . This also allows for a single die cut between adjacent blanks in the formation of the blanks. 
         [0033]    The formation of the walls as above described is preferred and provides particular advantages over the prior art “flat panel” container. More particularly, the taller front wall  74  of the cover, as noted particularly in  FIG. 6 , provides, in conjunction with the curvature of the wall itself, an enlarged display area for logos, designs or any appropriate attractive indicia. The extended height of the cover front wall and the curvature thereof in conjunction with the curvature of the tray front wall ensures a positive continuous engagement of the upper edge of the front tray wall  52  against the inner surface of the elongate overhanging cover front wall  74 . Such a relationship also occurs between the overlapping side walls of the tray and cover as will be appreciated from the schematic cross sectional view of  FIG. 1B  wherein the convex upper edges of the tray side walls, initially at the highest center points thereof, engage against the inner surfaces of the cover side walls with the continuing closing movement of the cover causing a slight inward flexing of the tray side walls until full engagement of the tray side wall upper edges with the inner surfaces of the cover side walls is achieved and the appropriate latching means engaged. This avoids and eliminates the air gap normally experienced in flat-wall containers of the conventional type as illustrated in  FIG. 1A . In addition, in utilizing this relationship, it has been found that the cover  44  will actually seat lower on the tray, eliminating unnecessary interior air space and avoiding the undesirable cooling effect thereof. 
         [0034]    It will also be appreciated that the finished container itself, particularly when closed as illustrated in  FIG. 6  presents an attractive appearance derived from the smoothly curving or arcing contours as viewed from both the front and sides, providing a distinctive appearance desirable for product and/or provider identification. 
         [0035]    The foregoing describes a preferred embodiment of the invention and is considered illustrative of the principles of the invention. In the description above, the front wall of the container is described as being concave and the front wall of the cover as convex. If desired, and still within the scope of the invention, these shapes could be reversed or even have a straight line cut. It is to be understood that as modifications and changes may occur to those skilled in the art, it is not desired to limit the invention to the exact construction as shown and described. Rather, all suitable modifications and equivalents may be resorted to as falling within the spirit and scope of the invention as set forth in the appended claims.