Abstract:
A carton comprises first and second panels disposed in an overlapping relationship, and an interlocking arrangement for interconnecting the first and second panels. The interlocking arrangement comprises a slit formed in the first panel, and a tab projecting from the free end edge of the second panel and received in the slit. The slit includes a main slit portion disposed generally along the free end edge of the first panel, an intermediate slit potion emanating from an end of the main slit portion and extending away from the free end edge of the first panel, and a terminal slit portion emanating from the intermediate slit portion and extending away from the main slit portion to be disposed generally along the free end edge of the first panel. The tab comprises an ear protruding from at least one of the opposite side edges of the tab. The carton is characterised in that a fold line is disposed between the intermediate and terminal slit portions such that an engaging flap is defined by the fold line and the intermediate and terminal slit portions and connected to the first panel along the fold line. The carton is also characterised in that the ear of the tab is disposed in engagement with the engaging flap.

Description:
This is a continuation of international application No. PCT/US00/08701, filed Feb. 4, 2000, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a carton for packaging articles such as beverage cans, bottles, bricks and the like and more particularly to a slide type lock or panel-interlocking means for interconnecting two panels for forming a carton wall. 
     Slide type locks or slide-type panel-interlocking means have been well known in the field of package-manufacturing industry. A slide type lock comprises a tab and a slit. The tab is formed, for example, on an edge of a carton panel while the slit is defined in another panel. The tab is inserted into the slit and locked in the slit to interconnect the two carton panels. For slide locks to become reliable, it is essential that the tab and the slit be arranged to prevent undesired disengagement from each other. One of the conventional approaches for preventing the disengagement is to provide a crank-shaped section at each end of the slit and an outwardly projecting ear at each side edge of the tab. When inserted into such a slit, the tab is engaged at its ears with the carton material adjacent to the crank-shaped sections, which effectively prevents disengagement of the tab from the slit. Examples of the cartons taking such an approach are disclosed in U.S. Pat. Nos. 1,333,102; 3,064,877; 3,186,545; 3,305,161; 3,341,908; and 3,655,117, U.S. Design Patent No. 229,485, and French Patent No. 1,424,536, which are hereby incorporated by reference. 
     A drawback of the cartons using the above approach is that the material around the crank-shaped sections lacks structural flexibility, which not only interferes with smooth insertion of the tab but also causes the slit to remain slightly opened when the material is deformed due to the insertion of the tab. If remaining deformed after the insertion of the tab, the material around the crank-shaped sections is unlikely to function to prevent disengagement of the tab. 
     What is needed, therefore, is a carton having a slide-type lock wherein the tab insertion is facilitated and the tab-and-slit engagement is highly reliable to maintain the integrity of the carton. 
     SUMMARY OF THE INVENTION 
     According to the invention in one form, a carton having an improved slide-type lock is provided. The carton comprises first and second panels in an overlapping relationship, and an interlocking means for interconnecting the first and second panels. The interlocking means comprises a slit formed in the first panel, and a tab projecting from the free end edge of the second panel and received in the slit. The slit includes a main slit portion disposed generally along the free end edge of the first panel, an intermediate slit potion emanating from an end of the main slit portion and extending away from the free end edge of the first panel, and a terminal slit portion emanating from the intermediate slit portion and extending away from the main slit portion to be disposed generally along the free end edge of the first panel. The tab comprises an ear protruding from at least one of the opposite side edges of the tab. The carton is characterised in that a fold line is provided between the intermediate and terminal slit portions such that an engaging flap is defined by the fold line and the intermediate and terminal slit portions and connected to the first panel along the fold line. The carton is also characterised in that the ear of the tab is disposed in engagement with the engaging flap. 
     The above arrangement is of utility because when the tab is being inserted into the slit, the engaging flap is easily thrust aside by the tab due to the fold line. This facilitates insertion of the tab into the slit. The arrangement is further of utility because when the tab is fully inserted, the flap having been cleared by the tab is allowed to easily recover from the folded position because of the flexibility provided by the fold line. Without the fold line, the folded material tends to remain folded and hardly returns by itself to the initial unfolded position. The flap having returned to the unfolded position is ready to engage the ear of the tab to serve as a stopper for preventing the tab from coming out of the slit. 
     In a preferred form of the invention, the slit may further include an expansion slit portion emanating from the terminal slit portion and extending away from the free end edge of the first panel. The expansion slit portion serves to expand the end area of the slit when the first panel is manipulated to open the slit to facilitate insertion of the tab. 
     In another preferred form of the invention, the ear of the tab may be disposed adjacent to the free end edge of the second panel with a space therebetween so that the ear is provided with an edge defined for engagement with the engaging flap. This further insures that the engaging flap serve as the stopper. 
     In another preferred form of the invention, the first panel may include a panel body and a foldable panel portion connected to the panel body along a fold line, and the main slit portion may be formed in the foldable panel portion. In this form of the invention, it is further preferred that the intermediate slit portion is formed also in the foldable panel portion while the terminal slit portion is disposed in general alignment with the fold line between the panel body and the foldable panel portion. Such an arrangement allows the slit to wide open when the foldable panel is folded with respect to the panel body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a bottom, right and front perspective view of a carton of the first embodiment according to the invention; 
     FIG. 2 is a top, right and front perspective view, partially cut away, of the carton of FIG. 1, showing the carton without the packaged articles; 
     FIG. 3 is an enlarged fragmental plan view of the carton blank from which the carton of FIG. 1 is erected; 
     FIG. 4 is a plan view of the entire carton blank in FIG. 3; 
     FIG. 5 is an enlarged plan view of the slits in FIG. 4 wherein all the other parts of the carton blank have been omitted and not shown; 
     FIG. 6 is an enlarged fragmental plan view of a carton blank from which a carton of the second embodiment of the invention may be erected; 
     FIG. 7 is an enlarged plan view of the slits in FIG. 6 wherein all the other parts of the carton blank have been omitted and not shown; 
     FIG. 8 is an enlarged fragmental plan view of a carton blank from which a carton of the third embodiment of the invention may be erected; and 
     FIG. 9 is an enlarged fragmental plan view of a carton blank from which a carton of the fourth embodiment of the invention may be erected. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4 shows a carton blank for forming a carton of the first embodiment according to the present invention. The blank  1  is rectangular in shape and formed of paperboard. The blank is of a size such that it can package two articles of the same shape. At the middle of the rectangular blank  1 , there is provided an elongate rectangular top wall  2 . A pair of side walls  4 A and  4 B are connected to the opposite side edges of the top wall  2  along fold lines  3 A and  3 B respectively. The fold line  3 A is interrupted by tabs  5  and comprises three separate portions  3   a,    3   b  and  3   c  wherein the portions  3   a  and  3   c  are located adjacent to the opposite longitudinal edges of the blank  1  while the portion  3   b  is located intermediate the portions  3   a  and  3   c.  Each of the fold line  3 B and the fold line portions  3   a,    3   b  and  3   c  may be a continuous score line. Otherwise, it may be formed of a row of short cut lines or a combination of short score lines and short cut lines. 
     The tabs  5  and  5  are formed from the side wall  4 A and joined to the top wall  2 . The tabs  5  have a shape corresponding to the shape of a part of the top of each article to be packaged in the carton. A pair of openings  6  and  6  are formed in the side wall  4 A adjacent respectively to the tabs  5  to expose a part of each article. Each opening  6  is essentially diamond-shaped and extends from the fold line  3 A to a fold line  8 A at an intermediate position along the vertical length of the side wall  4 A. The top wall  2  is formed with a tear strip  7  for facilitating removal of the articles from the carton. The fold line  8 A is aligned with the lower edges of the openings  6  and  6  so that the upper half of the side wall  4 A may be disposed at an angle with respect to the lower half thereof when the blank is erected into a carton. The side wall  4 B is formed with a fold line  8 B similar and parallel to the fold line  8 A. The location of the fold line  8 B is such that the elevation of the fold line  8 B is slightly lower than that of the fold line  8 A upon formation of the carton. 
     Bottom lap panels  10 A and  10 B are connected respectively to the side walls  4 A and  4 B along fold lines  9 A and  9 B. The bottom lap panels  10 A and  10 B in combination form a composite bottom wall  10  when the carton is erected. Each of the fold lines  9 A and  9 B may be a continuous score line. Otherwise, the fold lines  9 A and  9 B each may be formed of a row of spaced short cut lines, or a combination of short score lines and short cut lines. The bottom lap panel  10 A is a form of the first panel as in the appended claims while the bottom lap panel  10 B is a form of the second panel. 
     Three tabs  11   a,    11   b  and  11   c  protrude from the free end edge of the bottom lap panel  10 B. These tabs are arranged along the free edge at equal spacings. The end tabs  11   a  and  11   c  each has a configuration which is a mirror image of the other tab. Each end tab  11   a  and  11   c  has an arched outline  12  including an outer side edge  12 A along which there is formed an essentially U-shaped notch  13  that defines a hook  14  having a tip end  15 . The hook  14  is a form of the ear as in the appended claims. In addition, sloping edge portions  16  are formed along the free end edge of the lap panel  10 B at the locations adjacent to the opposite longitudinal edges of the blank  1 . Due to the sloping edge portions  16 , the width of the lap panel  10 B gradually decreases toward the longitudinal edges of the blank  1 . 
     The intermediate tab  11   b  also has an arched outline  12 . Essentially U-shaped notches  13  and  13  are formed along the opposite side edges  12 A and  12 B of the tab  11   b,  respectively. These notches  13  and  13  define a pair of hooks  14  having respective tip ends  15 . Each of these hooks  14  is a form of the ear as in the appended claims. The hooks  14  of the tabs  11   a,    11   b  and  11   c  are of the same configuration except for their orientations. 
     The bottom lap panel  10 A has three slits  17   a,    17   b  and  17   c  for receiving the tabs  11   a,    11   b  and  11   c,  respectively. These slits  17   a,    17   b  and  17   c  are disposed along the free end edge of the lap panel  10 A at the location corresponding to the tabs  11   a,    11   b  and  11   c.  The distance between the opposite ends of each slit  17   a,    17   b  and  17   c  is generally equal to, or slightly greater than, the maximum transverse size of the each tab  11   a,    11   b  and  11   c  along the fold line  9 B. 
     The end slits  17   a  and  17   c  each has a configuration that is a mirror image of the other slit. Each end slit  17   a  and  17   c  includes a main slit portion that is disposed generally along, and arcuately curved convexly toward, the free end edge of the lap panel  10 A. The main slit portion of each end slit includes at its longitudinally intermediate position a rounded protrusion  18  serving as a guide means for facilitating insertion of the associated tab  11   a  or  11   c.  Each end slit  17   a  and  17   c  further includes at the outer end thereof an intermediate slit portion  20   a  and a terminal slit portion  20   c.  As shown in FIG. 3, the intermediate slit portion  20   a  emanates from the respective main slit portion and extends away from the free end edge of the bottom lap panel  10 A. The terminal slit portion  20   c  emanates from the intermediate slit portion  20   a  and extends away from the main slit portion along the free end edge of the bottom lap panel  10 A. However, a rounded comer slit portion  20   b  may be provided to interconnect the intermediate and terminal slit portions  20   a  and  20   c.  The intermediate and terminal slit portions  20   a  and  20   c  and optionally the comer slit portion  20   b,  in combination, form a crank-shaped section  19 . 
     The bottom lap panel  10 A further includes a triangular engaging flap  21  near the crank-shaped section  19  of each end slit  17   a  and  17   c.  The two sides of each engaging flap  21  are defined by the intermediate and terminal slit portions  20   a  and  20   c  of the adjacent slit. Each engaging flap  21  is joined to the lap panel  10 A along a fold line  22  so that it is easily foldable with respect to the lap panel  10 A. More specifically, each flap  21  is defined or surrounded by the respective fold line  22  and the adjacent intermediate and terminal slit portions  20   a  and  20   c.  The fold line  22  may comprise a continuous score line or one or more cut lines. 
     The intermediate slit  17   b  also includes a main slit portion that is arcuately curved convexly toward the free end edge of the bottom lap panel  10 A. The main slit portion of the intermediate slit  17   b  is provided at its mid position with a rounded protrusion  18  and at its each end with a crank-shaped section  19 . Each crank-shaped section  19  of the intermediate slit  17   b  is virtually identical to that of each end slit  17   a  and  17   c,  and thus the description thereof is omitted. A triangular engaging flap  21  is also provided near each crank-shaped section  19  of the intermediate slit  17   b.  Each engaging flap  21  of the intermediate slit  17   b  is virtually identical to those provided near the respective crank-shaped sections of the end slits  17   a  and  17   c,  and thus the description thereof is omitted. 
     The bottom lap panel  10 A includes a foldable panel portion  24  connected along an interrupted fold line  23 . The fold line  23  extends across the lap panel  10 A while interrupted by the slits  17   a,    17   b  and  17   c.  As a result, the main slit portion of each slit  17   a,    17   b  and  17   c  is located in the foldable panel portion  24 . The intermediate slit portion  20   a  of each slit is also located in the foldable panel portion  24  whereas the terminal slit portion  20   c  is arranged in general alignment with the fold line  23 . 
     The tabs  11   a,    11   b  and  11   c  mate respective with the slits  17   a,    17   b  and  17   c  to constitute a panel-interlocking means. 
     The operation of the interlocking means is now described hereinafter. 
     To set up a carton  1 A as in FIGS. 1 and 2 from the blank shown in FIG. 4, two articles “A” in an inverted orientation are placed on the top wall  2  of the blank  1 . The blank  1  is then folded along the fold lines  3 A,  3 B,  8 A,  8 B,  9 A and  9 B to bring the bottom lap panels  10 A and  10 B to positions close to each other. The foldable portion  24  of the lap panel  10 A is folded inwardly or downwardly of the panel  10 A along the fold line  23  to open the slits  17   a,    17   b  and  17   c.  The tabs  11   a,    11   b  and  11   c  of the bottom lap panel  10 B are then inserted into the opened slits  17   a,    17   b  and  17   c,  respectively. While the tabs  11   a,    11   b  and  11   c  are inserted, the triangular engaging flaps  21  are thrust aside by the tabs  11   a,    11   b  and  11   c  whereupon they are folded inwardly or downwardly about their respective fold lines  22 . Because of this yielding disposition of the flaps  21 , the insertion of the tabs  11   a,    11   b  and  11   c  is achieved easily without substantial resistance of the material of the bottom lap panel  10 A. When fully inserted, the tabs  11   a,    11   b  and  11   c  clear the respective flaps  21  and release them from the thrusting force. The released flaps  21  then recover from their respective folded positions and return to their original unfolded positions due to the flexibility provided by the fold lines  22 . The flaps  21  having returned to the unfolded position are ready to engage the hooks  14  of the tabs  11   a,    11   b  and  11   c  to serve as a stopper as will be described later. The tabs  11   a,    11   b  and  11   c  having been inserted into their respective slits  17   a,    17   b  and  17   c  connect the lap panels  10 A and  10 B together and retain the carton  1 A in the erected form as shown in FIGS. 1 and 2. 
     If the erected carton undergoes external force, one or more of the tabs  11   a,    11   b  and  11   c  may be pulled outwardly of the respective slits. However, the engaging flaps  21  as in the unfolded positions would engage the hooks  14  of the tabs  11   a,    11   b  and  11   c  to prevent withdrawal of the tabs from the slits. This assures that the carton  1 A is held in the erected condition while the articles “A” are packaged therein. 
     Having been described, the arrangement of the present invention facilitates insertion of the tabs  11   a,    11   b  and  11   c  into the slits  17   a,    17   b  and  17   c  and still effectively prevents disengagement of the tabs from the respective slits. 
     FIG. 6 illustrates a blank for forming a carton of the second embodiment according to the invention. The interlocking means in FIG. 6 differs from that in FIG. 3 in that the terminal slit portion  20   c  of each slit in FIG. 6 extends somewhat into the foldable panel portion  24  such that the terminal slit portion  20   c  is slightly inclined to the fold line  23 . It further differs from the interlocking means in FIG. 3 in that an expansion slit portion  20   d  is provided at the outer end of each terminal slit portion  20   c  and extends away from the free end edge of the bottom lap panel  10 A. The remainder of the interlocking means in FIG. 6 is virtually identical to that in FIG. 3, and thus the description thereof is omitted. However, the slits  17   a,    17   b  and  17   c  in FIG. 6 are also shown in FIG. 7 without the other parts of the blank to clarify their shapes and structures. Due to the terminal and expansion slit portions  20   c  and  20   d,  the slits  17   a,    17   b  and  17   c  in FIG. 6 provide larger openings therealong when the foldable panel portion  24  is folded about the fold line  23 . This facilitates insertion of the associated tabs  11   a,    11   b  and  11   c  into the slits  17   a,    17   b  and  17   c.    
     FIG. 8 illustrates a blank for forming a carton of the third embodiment according to the invention, which is a modified form of the blank in FIG.  3 . The interlocking means in FIG. 8 differs from that in FIG. 3 in that each slit  17   a  (not shown),  17   b  and  17   c  has no rounded protrusion at its longitudinally mid position. The remainder of the interlocking means in FIG. 8 is virtually identical to that in FIG.  3 . FIG. 8 suggests that the arcuate slits  17   a,    17   b  and  17   c  by themselves can serve as guide means for facilitating insertion of the associated tabs  11   a,    11   b  and  11   c  without the assistance of the rounded protrusions. 
     FIG. 9 illustrates a blank for forming a carton of the fourth embodiment according to the invention, which is a modified form of the blank in FIG.  6 . The interlocking means in FIG. 9 differs from that in FIG. 6 in that each slit  17   a  (not shown),  17   b  and  17   c  has no rounded protrusion at its longitudinally mid position. The remainder of the interlocking means in FIG. 9 is virtually identical to that in FIG.  6 . FIG. 9 also suggests that the arcuate slits  17   a,    17   b  and  17   c  by themselves can serve as guide means for facilitating insertion of the associated tabs  11   a,    11   b  and  11   c  without the assistance of the rounded protrusions. 
     It will be readily appreciated that although the three pairs of tab and slit are employed in each of the preceding embodiments, more or less than three pairs of tab and slit may be used to interconnect two panels or panel portions of a carton. For example, the tab  11   b  and slit  17   b  may be omitted from the carton of each embodiment to connect the respective panel portions by the other two pairs tab and slit only. 
     It will be also appreciated that the panels or panel portions to be interconnected by the interlocking means are not limited to the bottom lap panels but include a pair of top lap panels for forming a carton top wall, a pair of side lap panels for forming a carton side wall, a pair of end closure flaps for forming a carton end wall and the like.