Background of the Invention This invention relates to a carton accommodating a plurality of articles, such as yogurt pots, which may be arranged in groups provided in two or more tiers.

Some forms of yogurt pots or other like containers are relatively pliable and susceptible to deformation and crushing and lack any significant stacking strength. Hence, groups of such articles provided to be sold aε a unit can be relatively easily ruptured or deformed. Cartons have been used to accommodate those relatively vulnerable articles to protect them.

Some of the following patents concern the cartons which, when stacked one on another, would protect their contents to some extent.

U.S. Patent Nos. 4,084,740 (Lorenz) and 4,709,852 (Stoll) each discloses a stackable carton of a two-piece construction. The inner covering 10 of Lorenz has first tabs (see Figure 5) and first notches 75 while its outer covering 12 has top apertures 74 and second notches. The inner and outer coverings 100 and 10 of Stoll (see Figure 7) are provided respectively with first and second tabs 172 and 84 which in cooperation create anti-sliding means.

In U.S. Patent No. 3,489,314, positioning of the lid 31 on the container body 1 is facilitated by the projections 15 and the apertures 33.

U.S. Patent No. 3,744,700 discloses a carton having a pair of U-shaped coverings assembled together to form a fully enclosed carton. The tab 62.2 of one of the coverings is inserted into the slit 74.1 of the other covering to facilitate positioning of the one carton in respect to the other.

U.S. Patent No. 3,596,758 discloses a carton having partitions/beams 60 struck from a carton side wall 40 and folded into the positions between the articles within the carton.

U.S. Patent No. 4,747,487 discloses an arrangement of the flaps 2, 40, 41 and 42 for creating an anti-rocking corners of a carton.

U.S. Patent No. 3,596,758 discloses a carton having a side wall 36 and top and bottom walls 54 and 46 foldably joined to the upper and lower edges of the side wall 36. Article-retention flaps 60 are struck from the side wall 36 and folded inwardly, as shown in Figure 4, to the position where they are disposed vertically between the top and bottom walls 54 and 46. Other retention flaps 60 are struck from the other side wall 40 and folded inwardly of the carton. U.S. Patent No. 1,911,215 discloses a similar arrangement.

U.S. Patent No. 2,076,844, in Figures 10 and 12, illustrates a carton having article-retention flaps 37 and 38 formed from a top wall 39 and 40 and folded downward to extend entirely between the side walls 34 and 35.

U.S. Patent Nos. 2,711,819 and 3,394,860 each discloses a carton of a two-piece construction including an inner carton component comprising a medial wall and a pair of terminal walls. In U.S. Patent No. 2,711,819, for example, the medial wall 8 and 9 has article-retention flaps 12 and 13 struck therefrom and folded to the position where they extend entirely between the terminal walls 10 and 10. In U.S. Patent No. 2,411,819, Figure 3 shows a double-thickness carton wall having an inner panel, i.e., the medial wall 8 and 9, from which the flaps 12 and 13 are struck.

U.S. Patent No. 4,213,559 discloses a carton having a double-thickness wall comprising inner and outer panels 86 and 24. An article-retention flap 16 is formed from the inner panel 86. The aperture in the inner panel 86 defined by the retention flap 16 is covered by the outer panel 24.

Summary of the Invention The present invention seeks to provide a carton which has improved stacking strength and other strengthening to provide protection in vulnerable areas such as at the corners of the unit. In some of its forms, the invention seeks to provide a carton adapted to have improved stacking qualities so that a plurality of like such cartons can be inter-engaged to create a more stable stack. In one aspect of the invention, a carton comprises a lower blank and an upper blank. The lower blank comprises a bottom panel and a pair of inner side panels. The upper blank comprises a top panel and a pair of outer side panels. These upper and lower blanks are assembled together such that the inner and outer side panels create a pair of opposed side walls of a double wall structure. The upper blank also provides corner reinforcement for the packaged articles.

In another aspect of the invention, the upper and lower blanks do not necessarily create the double wall structure; however, each inner side panel is provided at its upper edge with a first tab and at its lower edge with a first notch while each outer side panel is provided at itε upper and lower edges respectively with a second tab and a second notch. The second tabs are struck from the top panel and thus define top apertures in the top panel. During the assembly of the carton, the first tabs are inserted into the top apertures of the upper blank to facilitate positioning of the upper blank with respect to the lower blank. In an assembled condition, the first and second tabs are in parallel abutting contact to create anti-sliding means while the first and second notches are in mutual registry to form an engaging slot. When two or more like cartons are stacked on top of another, the anti- sliding means of each lower carton is inserted into the engaging slot in the bottom of the upper adjoining carton εo that the cartons are stacked in a stable condition.

In another aspect of the invention, a carton has a side panel and a pair of top and bottom panels foldably joined to the upper and lower opposed edges of the side panel. The side panel has an article-retention flap struck therefrom and foldably joined thereto. The retention flap is folded inwardly to the position where it extends all the way between the top and bottom panels to reinforce the carton or to provide the carton with better structural stability. Such a retention flap is particularly useful for increasing stacking strength of the carton.

One aspect of the present invention provides a carton accommodating a plurality of articles which carton comprises a pair of blanks in which one blank provides a top panel and a pair of side panels of the carton whereas the other blank provides a base panel and a pair of side panels of the carton and wherein both the blanks include locating means at the top panel and at the base panel whereby a pair of like such cartons can inter-engage when stacked one on the other to enhance stability by resisting relative movement between the stacked cartons.

Another aspect of the present invention provides a carton accommodating a plurality of articles which carton comprises a pair of blanks in which one blank provides a top panel and a pair of side panels of the carton whereas the other panel provides a base panel and a pair of side panels of the carton and wherein at least one of the blanks include hinged flaps which extend inwardly of the carton and extend between said top and bottom panels thereby to enhance the stacking strength of the carton. Yet another aspect of the present invention provides a carton accommodating a plurality of articles which carton comprises a pair of blanks in which one blank provides a top panel and a pair of side panels of the carton whereas the other blank provides a base and a pair of side panels of the carton and wherein the side panels of both the blanks are disposed in overlapping relationship. The carton includes an end panel structures at its opposite

ends which provide reinforced corners of the carton. The end panel structures re provided by one of the blanks.

Brief Description of the Drawings An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows schematically a series of steps taken in forming a carton according to the invention from two blanks of foldable sheet material; Figure 2 is a plan view of one of the blanks for forming the carton of Figure l; and

Figure 3 is a plan view of the other blank for forming the carton of Figure 1.

Detailed Description of the Preferred Embodiment Referring first to Figures 1 and 2 of the drawings, there is shown a stack of containers P comprising two tiers t _{l t} t ₂ in which each tier has a group of articles formed in three rows of four articles per row. In this particular case the articles comprise soft walled plastic pots with top flanges by which the pots are connected together at their upper ends.

A lower blank or wrapper 10, shown in more detail in Figure 2 is formed from an elongate, relatively stiff (as compared to the upper wrapper 40) but foldable material such as corrugated board. Lower wrapper 10 comprises, in series, a first top flap 12, a first side panel 14, a bottom panel 16, a second side wall panel 18 and second top flap 20 hinged one to the next along transverse fold lines 22, 24, 26 and 28 respectively. Side panel 14 includes hinged flaps F _x and F ₂ which are hinged to side panel strips 14a and 14b of the side panel 14 along longitudinal fold lines 30 and 32 respectively. These flaps F ₁ and F ₂ are disposed on the opposite sides of the center panel strip 14c of the side panel 14. Likewise, side panel 18 includes hinged flaps F ₃

and F, which are hinged to side panel strips 18a and 18b of the side panel 18 along longitudinal fold lines 34 and 36 respectively. Flaps F ₃ and F ₄ are disposed on the opposite sides of the center panel strip 18c. Fold line 24 is interrupted by apertures H _x and H ₂ at the base end of side panel strips 14a and 14b and, similarly fold line 26 is interrupted by apertures H ₃ and H ₄ at the base end of side panel strips 18a and 18b to facilitate stable stacking as described below. For a like reason, tabs T,. and T ₂ are struck from top flap 12 along fold line 22 and tabs T ₃ and T ₄ are struck from top flap 20 along fold line 28.

In use the stack of articles are seated on base panel 16 as shown in Figure 1 and the flaps F _x - F, are inserted into the space between the endmost rows of articles in each tier and the next adjacent rows of articles. The flaps Fj - F _Λ extend the full height of the stack of articles and reinforce itε vertical stacking strength. As best seen at position C in Figures 1 the top flaps 12 and 20 are folded to overlie the tops of the adjacent articles in the upper tier t ₂ . As a result, the four tabs 1 ₁ - T„ protrude upwardly adjacent the corners of the stack. The lower wrapper 10 used in forming the carton is then in its correct position. In order to complete the carton, an upper blank or wrapper 40 is applied to the stack. The upper wrapper 40 is shown in more detail in Figure 3 and is formed from a single blank of paperboard or like foldable sheet material. The upper wrapper 40 comprises, in series, a first base flap 42, a first side panel 44, a top panel 46, a second side panel 48, and a second base flap 50 hinged one to the next along fold lines 52, 54, 56 and 58 respectively. At each of the opposite ends of side panel 44, a corner panels 60 and 60a are provided which are hinged to side panel 44 by fold lines 62 and 62a. Fold lines 62 and

62a are convergent in a direction from fold line 54 towards fold line 52. A side end panel 64 is hinged to corner panel 60 along fold line 66 and a side end panel 64a is hinged to corner panel 60a along fold line 66a. Both the fold lineε 66 and 66a extend parallel to the longitudinal axiε of the wrapper and thus, when the top wrapper 40 is put into position on the stack, the corner panels form divergent columns at the corners of the stack extending between the top and base of the stack. The other corner panels 68 and 68a are hinged to opposite endε of εide panel 48 along fold lineε 70 and 70a, respectively. Fold lines 70, 70a are convergent in a direction from fold line 56 towards fold line 58. A side end panel 72 is hinged to corner panel 68 along fold line 74 and a side end panel 72a is hinged to corner panel 68a along fold line 74a. Fold lines 74 and 74a are coincident with fold lines 66 and 66a at the opposite end of the blank.

A top end panel 76 is hinged along one of the opposite ends of top panel 46 along fold line 78 and a similar top end panel 76a is hinged to the other end of top panel 46 along fold line 78a. Top end panel 76 is hinged to side end panel 64 by means of a gusset panel 80 which is hinged to respective ones of those top and side end panels along fold lines 82 and 84. A similar arrangement is provided to hinge top end panel 76 to side end panel 72 by virtue of gusset panel 86 and fold lines 88 and 90. A like structure is provided at the opposite side of the blank in which like parts are designated by like reference numerals with the addition of suffix 'a'.

Apertures H ₅ and H ₆ interrupt fold line 52 and like apertures H ₇ and H _β interrupt fold line 58. When the wrapper 40 is properly applied to the stack, apertures H ₆ and H ₆ are brought into register with apertures H and H ₂ of lower wrapper 10, and apertures H ₇ and H _β are brought into registry with apertures H ₃ and H„. Likewise, tabs T ₅ and T ₆ which are struck from the top wall 46 along fold line 54

and tabs T ₇ and T _β which are struck from the top wall 46 along fold lines 56 co-operate with respective ones of tabs T _x to T ₄ upstanding from top flaps 12 and 20 of lower wrapper 10. The tab arrangement has two functions. First, correct positioning of the upper wrapper 40 upon the stack is facilitated because upstanding tabs T _λ - T ₄ of the lower wrapper 10 engage in the apertures which are defined by tabs T ₅ - T ₈ thus locating the top panel 46 on the top of the stack. Secondly, once thuε located, the tabε T _x T ₅ , T ₂ T ₆ , T ₃ T ₇ and T ₄ T _β are disposed in face abutting relationship, and thereby four pairs of upstanding locating projections τ ' to T ₄ ' are provided as shown at position E in Figure 1. These locating projections T _α ' to T ₄ ' are positioned εo as to respectively enter the four registered pairs of apertures Hi H ₅ , H ₂ H ₆ , H ₃ H ₇ and H ₄ H ₈ present in the base of a like carton when a plurality of such cartons are stacked one atop the other and thereby create a stable multi-carton stack in which relative sliding between the stacked cartons is discouraged.

When the upper wrapper is being applied to the stack of articles, as shown at position D in Figure 1, the side panels 44 and 48 are brought into overlapping relationship with side panelε 14 and 18 respectively of the lower wrapper 10 so that a double-skinned wall is provided at each side of the package to enhance protection of the contents. In order to enhance protection at the ends of the carton the side end wallε 64, 64a and 72, 72a are folded acroεε the ends of the carton thereby putting the corner panels 60, 60a and 68, 68a into position in which they extend between the top and bottom of the stack. Top end panel 76 is caused to be folded downwardly and secured (e.g., glued) to side end panels 64 and 72 by the tucking effect of gusset panels 80 and 86 and likewise top end panel 76a is secured to side end panels 64a and 72a by the tucking effect of gusset panels 80a and 86a. Thuε the vulnerable corners of the carton are protected against

impact. These reinforced corner structureε formed by the panels 64, 64a, 72, 72a, 76, 76a, 80, 80a, 86 and 86a improve rigidity of the carton which contributes to the stacking strength and resiεtε 'rocking' of the carton when in transit. In the completed form aε εhown at poεition E of Figure 1, the base flapε 42 and 50 of the upper wrapper 40 are secured (e.g., glued) to the bottom panel 16 of the lower wrapper 10 such that apertures H ₅ - H _β are in registry with apertures H - H ₄ . In order to facilitate carrying the carton a handle S is provided which comprises a strap 92 struck primarily from the top panel 46 of wrapper 40 and includes hand cushioning flaps 94 and 96 reεpectively.