Rounded corner locking carton lid
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to folding carton lids, and more particularly to a liquid-tight, locking, paperboard carton lid having rounded corners for use with a carton of similar shape. 
     2. Description of the Prior Art 
     Applicant is unaware of any prior art patent that discloses a one-piece, liquid-tight, paperboard carton lid having an absolutely flat top wall with straight side and end walls and rounded corner walls joined to the top wall by a gusset arrangement formed in the manner of the present invention. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a one-piece paperboard carton lid having straight side and end walls joined to each other by rounded corner walls. 
     A more specific object of the invention is the provision, in a carton of the type described, of a liquid-tight, rounded corner construction. 
     Another specific object of the invention is the provision of a unique gusset arrangement for joining the corner edges of a carton top wall to the upper edges of carton side and corner walls. 
    
    
     These and other objects of the invention will be apparent from an examination of the following description and drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a blank of foldable sheet material from which the carton lid illustrated in FIGS. 5 and 6 may be formed; 
     FIG. 2 is a top plan view of one end of the blank illustrated in FIG. 1, with portions of the structure folded into a position different from that shown in FIG. 1; 
     FIGS. 3 and 4 are fragmentary perspective views of the structure illustrated in FIG. 2, but illustrating two stages in the formation of the carton lid from the blank illustrated in FIGS. 1 and 2; 
     FIGS. 5 and 6 are perspective views of a completely erected carton lid embodying features of the invention, as seen from the inside and outside, respectively; and 
     FIG. 7 is a fragmentary view similar to FIG. 1, but illustrating a slightly modified form of the invention. 
     It will be understood that, for purposes of clarity, certain elements may have been intentionally omitted from certain views where they are believed to be illustrated to better advantage in other views. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings for a better understanding of the invention, it will be seen that the rounded corner, locking carton lid, indicated generally at L in FIGS. 5 and 6, may be formed from the unitary blank B of foldable sheet material, such as coated paperboard, illustrated in FIG. 1. 
     The lid L, as best seen in FIGS. 3-6, includes a flat top wall panel 10, having side walls 12, and end walls 14, depending therefrom. Side walls 12, include center portions 12a, and end portions 12b, which are curved around from the center portions 12a at the end of the carton, to provide rounded corner walls 16. 
     Each of the side walls 12 includes a side wall panel 20, foldably joined at its upper edge along a fold line 21, to related side edge of top wall panel 10. 
     Each side wall also includes a lock flange first panel 22, foldably joined along a fold line 23 to an outer edge of side wall panel 20, and a lock flange second panel 24, foldably joined along a fold line 25 to an outer edge of lock flange first panel 22. 
     It will be seen that each of the end walls 14 includes an outer panel 30, which is foldably joined along a fold line 31 to a related end edge of top wall panel 10, and an inner panel 32, which is foldably joined along a fold line 33 to an outer edge of related outer panel 30. 
     In order to provide the unique, leak-proof, rounded corners for the carton lid, the diagonally angled corner edges of top wall panel 10 are connected to the upper edges of the side wall end portions 12b by means of novel corner gussets 40. 
     Each of the gussets 40 includes a pair of generally triangular first and second sections 42 and 44, respectively, which are foldably joined to each other on a fold line 47. 
     First section 42 is foldably joined to the top wall panel on a fold line 43, and second section 44 is foldably joined on a fold line 45 to the related end portion of side wall panel 20. It will be noted that fold line 45 is an extension of fold line line 21, which joins the side wall outer panel 20 to top wall panel 10. 
     The fold lines defining each corner gusset 40 are formed by embossing or debossing to facilitate folding of blank B in order to form the carton lid L, as best seen in FIGS. 3 and 4. 
     Fold line 43, which joins the gusset first section 42 to the top wall panel 10 is shown as a diagonal or angled line between the related side and end edges of top wall panel 10. This may be a straight line or may have two sections which form an angle with each other or may be curved slightly. When the side walls are folded downwardly from the top wall panel angled corner edges, and the end portions are folded inwardly from the center portions, the sections of each gusset lie in face-to-face relation with each other against the inner side of the related side wall end portion, and the side wall end portions form curved corner walls 16. 
     In erecting the carton, before side wall panels 20 are folded downwardly from the top wall panel, the locking flange is first formed. This is accomplished by folding flange second panel 24 inwardly 180 degrees against the inner surface of flange first panel 22, as illustrated in FIG. 2. Flange first panel 22 is then folded 180 degrees inwardly against the inner surface of related side wall panel 20. The side wall panels 20 can then be folded downwardly 90 degrees from top wall panel 10. 
     At this point the end portions 12b of the side wall panels are folded inwardly under the corner and end edges of top wall panel 10, with the ends of the related end portions in substantially abutting relationship, as shown in FIG. 3. 
     End wall panels 30 are then folded downwardly from the top wall panel, and the end wall inner panels are folded back upwardly to enclose the end portions of the side wall panels, as illustrated in FIGS. 3 and 4. Inner end panel 32 is preferably adhesively secured to the end portions of the side wall panels to complete the formation of the carton lid. 
     Thus, it will be seen that the novel construction provides a unique, rounded corner, locking carton lid having a flange adapted to interlock with a related flange on a folding carton having a similar contour. 
     Turning now to FIG. 7 of the drawings, it will be seen that a slightly modified form of the invention is shown. In this embodiment certain parts of the structure which correspond to those the previous embodiment have been identified by related numerals. In this embodiment, the flange consists of only one panel, 122, which is foldably joined along fold line 123 to the lower edge of side wall panel 120. 
     This lid functions in the same manner as that of the first embodiment, except that the flange is one ply thinner than the flange of the previous embodiment.