Folding carton with improved thread and punch lock

A folding container such as a tray, carton or the like constructed of paperboard includes an interior end panel articulated to a bottom wall panel and including a relief slit to ensure full engagement of a thread and punch lock on first and second end panels articulated to opposite sidewall panels. The first locking end panel includes a locking assembly comprising a tongue and cooperating locking tab. The second locking end panel includes a receipt aperture for the lock assembly. When locked in overlapping relation, the tongue and tab are respectively threaded and snapped into the receipt aperture to provide secure engagement. The relief slit is substantially U-shaped with the open end of the U directed toward the lock assembly receipt aperture when the end panels are in overlapping relation. The relief slit extends substantially around the tab engaging edge of the lock assembly receipt aperture so as to provide sufficient relief for the full and complete engagement of the locking tab.

TECHNICAL FIELD 
The present invention relates generally to the packaging field and, more 
particularly, to a folding container, tray or carton having a thread and 
punch lock on an end panel locking structure that insures full and 
reliable locking engagement during each carton erecting cycle. 
BACKGROUND OF THE INVENTION 
Cartons, trays and other folding containers having end panel locking 
structures are known in the art. Particularly, the end walls of the carton 
are formed by overlapping end wall panels articulated to the side and 
bottom walls of the carton body and locked together with tongues, tabs and 
slits or the like. Boxes and cartons of this type are used to package a 
wide range of goods from, for example, cookies to automobile parts. 
U.S. Pat. No. 1,425,256 to Hickman et al discloses a berry container having 
an end panel locking structure. Overlapping end panels articulated to the 
carton sidewalls include a cooperating tab and slit structure providing 
locking action. A third, solid interior end panel articulated to the 
bottom wall provides increased strength to the carton. 
While the Hickman concept provides a strong and secure carton, it is not 
without its disadvantages. The Hickman carton is not designed for erection 
on the high speed carton forming and erecting machinery required to be 
economically competitive in the marketplace of today. Specifically, the 
solid interior end panel can sometimes provide a hinderance to secure 
engagement of the end lock. It has been found that the solid interior end 
panel resists proper overtravel of the locking tab as it is punched into 
position by the punch-in finger of the erecting machinery. Without 
complete engagement of the locking tab in the cooperating slit being 
assured, consistent carton erection cannot be obtained. 
U.S. Pat. No. 3,206,098 to Stenger et al provides a portion of the locking 
structure of the overlapping end panels extending above the upper limit of 
the solid interior end panel. This structure allows some relief and 
flexibility to aid in lock engagement. 
The Stenger carton, however, suffers from several disadvantages. The lock 
structure is complicated and often interferes with product loading and/or 
smooth operation of the hinged carton top. The upper edge portion of the 
lock presents a jagged edge that can hang on the product as it is being 
inserted, or catch the lower edge of the charlotte flaps on the top as the 
carton is being closed. Further, since the interior end panel does not 
extend along the entire depth, it does not provide the desired degree of 
isolation of the carton contents from outside elements as, for example, 
when packaging semi-exposed food products, such as butter patties. 
A need is, therefore, identified for a carton with an improved thread and 
punch lock on the overlapping end panels. 
SUMMARY OF THE INVENTION 
Accordingly, it is a primary object of the present invention to provide a 
folding container, tray or carton having an improved locking structure 
overcoming the above-described limitations and disadvantages of the prior 
art. 
Another object of the present invention is to provide a carton with a 
locking structure of added strength and reliability that also assures 
isolation of the carton contents from outside elements. 
Still another object of the present invention is to provide a carton with a 
locking structure that substantially eliminates interference with product 
loading and top closure. 
A further object of the present invention is to provide a carton with an 
end panel locking structure that is easier to erect and that ensures full 
engagement of the lock during each carton erecting cycle. 
Additional objects, advantages, and other novel features of the invention 
will be set forth in part in the description that follows and in part will 
become apparent to those skilled in the art upon examination of the 
following or may be learned with the practice of the invention. The 
objects and advantages of the invention may be realized and attained by 
means of the instrumentalities and combinations particularly pointed out 
in the appended claims. 
To achieve the foregoing and other objects and in accordance with the 
purposes of the present invention as described herein, an improved 
container, tray or carton formed from a single sheet of foldable material 
is provided. The carton includes a bottom wall panel and a pair of 
oppositely disposed sidewall panels articulated to the bottom wall panel. 
First and second locking end panels articulated to the sidewall panels are 
adapted to overlap each other and overlie an interior end panel when 
locked. The interior end panel articulated to the bottom wall panel 
provides additional strength to the container. The interior end panel 
further isolates the container interior and contents from outside elements 
all along the lock. Advantageously, relief means in the form of a slit in 
the interior end panel allows full engagement of the locking means of the 
first and second locking end panels during carton erection, as will be 
more fully explained below. 
Preferably, the first locking end panel includes a locking assembly. The 
locking assembly includes a tongue and cooperating locking tab 
longitudinally aligned along the end panel. The second locking end panel 
includes a lock assembly receipt aperture. When the tongue and tab are 
inserted and punched into the receipt aperture of the second locking end 
panel, secure locking action is provided through desirable four-point 
engagement. 
Preferably, the relief slit along the interior end panel is substantially 
U-shaped and in alignment with the locking tab. The open end of the U is 
directed toward the lock assembly receipt aperture when the end panels are 
in overlapping or erected position. In this position, the slit extends 
along the interior end panel adjacent the edge of the receipt aperture. 
Thus, the interior end panel provides the desired relief as the mechanical 
punch-in finger secures the lock structure, and at the same time provides 
the desired protection of the carton contents from outside elements along 
the entire lock. 
Still other objects of the present invention will become readily apparent 
to those skilled in this art from the following description wherein there 
is shown and described a preferred embodiment of this invention, simply by 
way of illustration of one of the modes best suited to carry out the 
invention. As it will be realized, the invention is capable of other 
different embodiments, and its several details are capable of 
modifications in various, obvious aspects all without departing from the 
invention. Accordingly, the drawings and descriptions will be regarded as 
illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is now made to FIG. 1 showing a tray blank 10 including the end 
panel thread and punch lock constructed in accordance with the principles 
of the present invention. The blank 10 is preferably formed from a single 
sheet of coated paperboard. The blank 10 has a generally elongated, 
rectangular shape and is formed having a bottom panel 12, a pair of side 
panels 14, 16 articulated to opposite sides of the bottom panel 12 at side 
panel fold lines 18, 20 respectively. An interior end panel 22 is 
articulated to each end of the bottom wall panel 12 along an end panel 
fold line 24. A first locking end panel 26 is articulated to each end of 
the side panel 14 along fold line 28 while a second locking end panel 30 
is articulated to each end of the sidewall panel 16 along the fold line 
32. The blank 10 is erected into a tray by folding the side panels 14, 16 
and end panels 22, 26 and 30 in overlapping relation as shown in the 
drawing figures and described in detail below. 
The first locking end panels 26 each include a lock assembly comprising a 
tongue 34 along the outer edge 36 and a cooperating locking tab 38 
longitudinally spaced from the tongue along a mid-portion of the panel. 
The tongue 34 and cooperating locking tab 38 of the first locking end 
panel 36 are received in an aperture 40 in the second locking end panel 30 
to securely lock the end panels of the tray or carton in the erected 
position. With both the tongue 34 and cooperating locking tab 38 received 
in the aperture 40, secure engagement is provided at at least four points 
42 (note FIG. 5). 
The interior end panels 22 each include a relief slit 44 of substantially 
U-shape and substantially in alignment with the locking tab 38. When 
folded into proper overlapping relation during tray or carton erection, 
the open end of the substantially U-shaped relief slit 44 is also directed 
toward and substantially surrounds one side of the receipt aperture 40 in 
the second locking end panel 30 (note FIG. 3). In fact, the relief slit 44 
is spaced from, but adjacent one edge 46 of the receipt aperture 40. Thus, 
it should be appreciated that the interior end panel 22 with relief slit 
44 provides firm backup to the edge 46 of the lock assembly receipt 
aperture 40, but at the same time allows inward travel of a punch-in 
finger (see FIG. 5A). This action allows reliable, full engagement of the 
locking tab 38 with the aperture edge 46. Further, the interior panel 22 
provides additional strength to the carton and support to the locking 
panels 26, 30. Since there is no opening in the panel 22 but only a slit 
44, the desirable isolation of the interior of the erected tray or carton 
is obtained. 
As shown in FIGS. 2 and 2B, the initial erecting and thread and punch lock 
engaging step comprises the upward folding (note action arrow A) of the 
interior end panel 22 along the fold line 24. Next, the sidewall panel 16 
is upwardly folded about the fold line 20 and the second locking end panel 
30 is folded inwardly, as shown in FIGS. 3, 3A and 3B (see action arrow 
B). 
The opposite sidewall panel 14 is now folded upwardly along the fold line 
18 to a position parallel to the now folded sidewall panel 16. The first 
locking end panel 26 is then folded inwardly (note action arrow C and 
FIGS. 4, 4A and 4B) to overlie the second locking end panel 30. The tongue 
34 is inserted or threaded through the lock receipt aperture 40 (note FIG. 
4B). 
The final lock securing step is shown in FIGS. 5, 5A and 6. The backup 
piece P of the automated high speed erecting machinery is inserted into 
the carton to engage one side of the interior end panel 22. The tab 
punch-in finger F is then moved in the direction of action arrow D to 
engage the locking tab 38 and snap the tab 38 past the edge 46 of the 
aperture 40. This locking action fully and completely provides the 
overlapping end panels 26, 30 with secure engagement at the four points 42 
(see FIG. 6). Advantageously, the relief slit 44 in the interior end panel 
22 allows the proper inward movement to the paperboard to assure full 
engagement of the locking tab 38. 
In summary, numerous benefits have been described which result from 
employing the concepts of the present invention. In particular, the full 
depth interior end panel 22 provides added strength to the carton and 
assures isolation of the carton contents from outside elements all along 
the lock. Additionally, the relief slit 44 in the end panel 22 simplifies 
the carton or tray erection process, and assures full and reliable 
engagement of the thread and punch lock during each carton erecting cycle. 
The foregoing description of the preferred embodiment of the invention has 
been presented for purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. Obvious modifications or variations are possible in light of 
the above teachings. The embodiment was chosen and described to provide 
the best illustration of the principles of the invention and its practical 
application to thereby enable one of ordinary skill in the art to utilize 
the invention in various embodiments and with various modifications as are 
suited to the particular use contemplated. All such modifications and 
variations are within the scope of the invention as determined by the 
appended claims when interpreted in accordance with the breadth to which 
they are fairly, legally, and equitably entitled.