WO1999042383A1

WO1999042383A1 - Article carrier and blank

Info

Publication number: WO1999042383A1
Application number: PCT/US1999/003187
Authority: WO
Inventors: Martinus C. M. Bakx
Original assignee: Mead Corp
Current assignee: Mead Corp
Priority date: 1998-02-19
Filing date: 1999-02-16
Publication date: 1999-08-26
Anticipated expiration: 2000-08-19
Also published as: AU3293299A; GB9803462D0; RO118580B1

Abstract

An article carrier of the basket type and a blank for forming an article carrier adapted to accommodate a plurality of articles, such as bottles, comprise a base (12), opposed side and end walls and an internal medial partition structure (24, 26, 42), handle means (H), wherein the internal medial partition structure (24, 26, 42) comprises at least one locking tab (100) to connect the base (12) to the internal medial partition structure (24, 26, 42).

Description

ARTICLE CARRIER AND BLANK

This invention relates to an article carrier, for example a basket type, adapted to accommodate a plurality of articles, such as bottles and to a blank for forming the carrier.

In known basket carriers for bottles there comprises a central (medial) partition structure which incorporates a handle structure by which the carrier can be lifted and carried and the bottles are arranged in rows on either side of the partition structure. Commonly, bottles are separated from one another by transverse partition panels extending from each side of the medial partition structure to the adjacent side wall of the carrier. Hence, in this type of arrangement the bottles are accommodated in individual cells of the carrier, although such cells are not essential.

An example of such a carrier is shown in US Patent No 4,927,009. This carrier includes side, end and bottom walls, and is adapted to receive articles grouped in two rows. Located between the two rows is a medial panel which connects the end walls and includes an opening to provide a handle by which the basket may be carried. In its usual form, this carrier also includes partition panels extending between the medial panel and the side walls, to define individual cells into which the articles may be placed.

Basket-style carriers are usually manufactured and shipped in a glued but collapsed condition. In one form, the end walls are folded at the medial panel, so that they are collapsed onto themselves to bring the side walls together in a flat collapsed condition. The medial panel is thus displaced longitudinally with respect to the side walls. For use, such as at a beverage bottling facility, the basket carrier is erected by separating the side and end panels and moving the medial panel back into a spaced aligned relationship with the side walls to define the article receiving cells and the set- up basket is available to be loaded with the articles to be carried.

There is a tendency for such carriers to collapse back to their original condition. Once the bottles have been loaded, it is not possible for the carton to collapse, but in the 2 period between erecting the carton and loading the bottles, it is necessary to prevent this occurrence. Nevertheless, the carton will tend to distort even when it is loaded.

It is known therefore to provide various lock arrangements to hold the carrier in erected condition. For example, a lock arrangement may be provided on the lower edge of the central medial panel to engage a notch formed in the bottom wall, as shown in US Patent No 4,187,944. Two such locks may also be provided, the locks engage each side of the bottom wall, as shown in US Patent No 4,336,878. As an alternative approach, it is known to provide a locking arrangement which engages an aperture in the bottom panel at a location intermediate the side edges. This type of locking arrangement may require additional means to keep the lock in engagement, such as the flap provided adjacent the aperture as shown in European Published Application No. 0 481 599 Al. This requires additional manipulation of the carrier during erecting to close the flap, and the flap manipulation weakens the folded connection for the flap, increasing the possibility of inadvertent disengagement of the lock during use.

Accordingly, a need still exists for a locking arrangement for a basket-style carrier which can be easily engaged as the carrier is erected, and that reliably and securely maintains its engagement during carrier loading and subsequent use.

The present invention has sought to overcome or at least mitigate the problems of the prior art.

One aspect of the invention provides an article carrier of the basket type adapted to accommodate a plurality of articles, for example bottles, which carrier comprises a base, opposed side and end walls, and an internal medial partition structure, wherein said medial partition structure comprises at least one locking tab extending downwardly to connect said base to said medial partition panel characterised in that said locking tab includes a pair of opposed locking edges and in that said base comprises adjacent first and second apertures each to receive and retain in locking engagement a separate one of said locking edges of said locking tab to connect said base and said medial partition structure. 3 According to one optional feature of this aspect of the invention, the locking tab may comprise a lock body, said lock body including one of said pair of opposed locking edges and a retaining tab spaced from and connected to the lock body by an intermediate portion which retaining tab defines the other of said pair of opposed locking edges.

According to another optional feature of this aspect of the invention, the first aperture may be co-operatively engaged with the lock body extending through said aperture whereby said intermediate portion is disposed beneath the base.

According to a further optional feature of this aspect of the invention, the retaining tab may be co-operatively engaged with the second locking aperture whereby an upper portion of said retaining tab is disposed above the base.

According to a yet further optional feature of this aspect of the invention, said medial partition structure further comprises at least one locking tab struck from a reinforcing panel and extending downwardly to connect said base to the medial partition panel, characterised in that said at least one locking tab includes a locking edge and in that said base comprises an aperture to receive and retain in locking engagement said locking edge to connect the base and the medial partition structure.

A second aspect of the invention provides a carton of the basket type adapted to accommodate a plurality of articles, for example bottles, comprising a base, opposed side and end walls, an internal medial partition structure, wherein said medial partition structure comprises at least one locking tab struck from a reinforcing panel and extending downwardly to connect said base to the medial partition panel, characterised in that said at least one locking tab includes a locking edge and in that said base comprises an aperture to receive and retain in locking engagement said locking edge to connect the base and the medial partition structure.

A third aspect of the invention provides a blank for forming an article carrier of the basket type comprising a single sheet of foldable material including panels for forming a base, opposed side and end wall panels, and a medial partition structure, said 4 medial partition structure comprises at least one locking tab extending downwardly to connect said base to the medial partition panel characterised in that said locking tab includes a pair or opposed locking edges and in that said base comprises a pair of adjacent apertures each to receive and retain in locking engagement a separate one of said locking edges of said locking tab to connect said base and said medial partition structure.

A fourth aspect of the invention provides a method for locking an article carrier adapted to accommodate a plurality of articles, for example, bottles, comprises a base, opposed side and end walls, and an internal medial partition structure, wherein said medial partition structure comprises at least one locking tab extending downwardly to connect said base to the medial partition panel, said locking tab includes a pair of opposed locking edges and said base comprises adjacent first and second apertures, which method comprising the steps of causing relative movement between said medial partition structure and said base to position said locking aperture beneath said locking tab; causing relative movement between said medial partition structure and said base to cause said locking tab to pass through said first aperture; and causing relative movement between said medial partition structure and said base inwardly to cause said locking tab to pass through said second aperture.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

FIGURE 1 is a plan view of an unfolded single blank of paperboard from which a basket carrier according to a first embodiment of invention is formed;

FIGURES 2a and b illustrate the detachable connection means in the blank of a first embodiment of the invention shown in Figure 1;

FIGURE 3 is a perspective view of an erected but unloaded bottle carrier formed from the blank shown in Figure 1 viewed from above and from one end; 5 FIGURE 4 is a perspective view of detachable connection means formed in a carrier of a second embodiment of the invention.

FIGURE 5 is a perspective view of an alternative detachable connection means in a carrier of a third embodiment of the invention.

Referring to the drawings, and in particular to Figures 1, 2a and 2b thereof, an article carrier is formed from a single blank 10 of paperboard or other suitable foldable sheet material which can be adapted to accommodate a plurality of articles, for example six bottles arranged in two rows of three bottles each. The carrier includes a base 12 which can be formed from first and second base panels 14, 16 hingably connected together along fold line 18. Base 12 comprises a first aperture 20 which in this embodiment is formed along fold line 18, as illustrated in Figure 2a. Preferably, a second aperture 22 is struck from base 12, being adjacent and spaced from first aperture 20 in a co-linear relationship. In one class of embodiments, the first and second apertures 20, 22 are adapted to engage detachable connection means as hereinafter described.

There further comprises a pair of medial panels 24, 26 forming part of the medial partition structure struck from an end portion of the blank 10 being hingably connected together along an interrupted central fold line 32. In this embodiment, one or both of medial panels 24, 26 are provided along their lower edge with a locking tab 25.

The locking tab extends downwardly and includes a pair of opposed locking edges 29,

31. Preferably, locking tab 25 comprises a substantially elongate "U" shaped hook 27, shown in more detail in Figure 2b. The locking tab 25 includes a lock body 33 which defines one of the locking edges 29 and a retaining tab 35 spaced from and connected to the lock body 33 by an intermediate portion 37. In this embodiment, the retaining tab

35 defines the other locking edge 31. It is envisaged the locking tab could be struck from other panels of the medial partition structure or, more generally, of the blank without departing from the scope of invention.

The outer panels of the carrier are formed from a series of panels which are hingably connected together. Thus, one row of articles are enclosed by outer panels 6 comprising end panel 30, side panel 32 and second end panel 34 formed to one side of central fold line 28. End panel 30 is foldably connected to medial panel 24 along fold line 36 which panels can be placed in a substantially perpendicular relationship. Side panel 32 and end panel 30 are foldably connected about fold line 38 wherein the aforesaid panels can be folded into a substantially perpendicular relationship. Along the opposing side edge of side panel 32 there is provided fold line 40 which interconnects second end panel 34 and side panel 32 to enable the aforesaid end panel and side panel to be placed in a substantially perpendicular relationship. As illustrated in Figure 1, end panel 34 is hingably connected to medial partition structure 42 along fold line 44. In this embodiment, base 12 is foldably connected to the lower edge of side panel 32 along fold line 46.

A second row of articles are enclosed by a further series of outer panels which substantially correspond to outer panels 30, 32 and 34. The outer panels comprise end panel 48 hingably connected to medial panel 26 along interrupted fold line 36; side panel 52 which is foldably connected to end panel 48 along fold line 54 such that the panels can be folded into substantially perpendicular relationships and a second end panel 56 is hingably connected to side panel 52 along the opposed side edge by fold line 58. Second end panel 56 is foldably connected to medial partition structure 42 along fold line 44. Optionally, a glue flap 60 is foldably connected about fold line 62 to the lower edge of side panel 52.

Turning to the construction of one example of a handle structure H, shown in Figures 1 and 3, there comprises a pair of handle panels 64, 66 foldably connected to medial partition structure 42 along fold line 44. Handle panels 64, 66 are separated from corresponding side and end panels 32, 34; 52, 56 by cut lines 65, 67 respectively which extend between fold lines 44 and 84. Handle panels 64, 66 are foldably connected together along central fold line 28. A hand receiving aperture 70 is desirably struck from a central portion of handle panel 64 and is provided with a tab 72 extending into hand aperture 70 which tab 72 is connected to the upper edge of hand receiving aperture 68 along fold line 74. Likewise, a corresponding hand receiving aperture 76 and tab 78 are struck from handle panel 66 which are located in a position symmetrical 7 about fold line 28, being substantially identical to hand receiving aperture 68 and tab

70.

Preferably, a pair of handle support panels 80, 82 adjacent in a longitudinal plane to handle panels 62, 64 are struck from the blank 10 and are foldably connected to medial panels 24, 26 respectively along fold line 84. In this embodiment, handle support panels are adjacent to and separated from handle panels 64, 66 by cut line 69. It is preferred that fold line 84 is formed at an angular relationship with fold line 36 so that in use the handle support panels 80, 82 can be folded into alignment with handle panels 64 and 66 respectively as hereinafter described. Handle support panels 80, 82 are connected together by fold line 86, which is positioned in a substantially perpendicular relationship to fold line 84. In this embodiment, handle support panels 80, 82 comprise a pair of apertures 88, 90 adapted to be aligned with hand receiving apertures 70, 76 respectively as shown in Figure 3.

Referring again to Figure 1, there is shown one embodiment of the medial partition structure 42 which is formed at one end of the blank and comprises a pair of partition panels 92, 94 foldably connected to respective ones of end panels 34, 56 along fold line 44. In use, partition panels 92, 94 form part of a central partition structure with panel 92 defining a lower central partition panel substantially midway between the base 12 and the handle panels 64, 66 and likewise, partition panel 94 providing an upper central partition panel. In this embodiment, there further comprises a reinforcing panel 96 foldably connected to reinforcing panel 94 along interrupted fold line 98. Reinforcing panel 96 is used to close the openings that are created when the partition panels 92, 94 and transverse partition panels are folded into position Preferably, a locking tab means 100 is provided which extends from an edge of reinforcing panel 96, which is defined in part by cut line 102. In use, the locking tab 100 extends downwardly and includes at least one locking edge.

Partition panels 92, 94 and reinforcing panel 96 can be interspaced by a series of transverse partition panels used to form the individual article receiving cells Cl to C3, shown in Figure 3. Thus in this embodiment, a secondary partition panel 104 is hingably connected to partition panel 92 along fold line 106. Secondary partition panel 8 104 extends into partition panel 94 and is separated from the aforesaid panel by lateral and longitudinal cut lines 108 and 110 respectively. Cut line 108 terminates at fold line

106. A transverse partition panel 112 is hingably connected to secondary partition panel 104 along one edge by fold line 114, and is separated from panels 104 and 92 by cut lines 116, 118 respectively. Cut line 116 extends from one end of fold line 114 to interrupted fold line 126 and cut line 118 extends from the opposing end of fold line

114 to a second part of interrupted fold line 126. An intermediate panel 120 is foldably connected to partition panel 92 along fold line 122 and to a second transverse panel 124 along fold line 126.

A second transverse partition panel 124 is connected to secondary partition panel 104 along fold line 126. Fold line 126 is preferably interrupted by cut line 128 which extends into transverse partition panel 124 to define a side edge of glue flap 130. Glue flap 130 is hingably connected to transverse partition panel 112 along interrupted fold line 132 and is separated therefrom by cut line 134, to define an opposite side edge. Cut line 134 extends between the two portions of fold line 132. Likewise, a second glue flap 136 is connected to an end edge of transverse partition panel 124 along fold line 138 which is preferably interrupted by cut line 140 to define a side edge of glue flap 136.

Preferably, a second pair of transverse partition panels 142, 144 are connected to partition panel 94 and reinforcing panels 96. As illustrated in Figure 1, transverse partition panel 142 is hingably connected to partition panel 94 along fold line 146 and is separated therefrom by opposed cut lines 148, 150 extending between fold line 146 and fold line 160. Transverse partition panel 144 is formed from partition panel 94 being hingably connected thereto and to reinforcing panel 96 along interrupted fold line 160.

A pair of glue flaps 152, 162 are provided, identical in shape and configuration as glue flaps 130 and 136 respectively. Thus, glue flap 152 is connected to the end edge of transverse partition panel 142 by fold line 154 which is preferably interrupted by cut line 158 to define a side edge of the glue flap. The opposing side edge is defined by cut line 161 which extends into transverse partition panel 144. Likewise, glue flap 9 162 is hingably connected to an end edge of transverse partition panel 144 along fold line 164 which is preferably interrupted by cut line 166 to define a side edge.

It is envisaged that the configuration of medial partition structure can be altered according to particular manufacturing requirements without departing from the scope of invention. For example, the transverse partition structure can be removed or reconfigured to vary the number of cells within the carrier.

Optionally, apertures 132, 134 are struck along fold lines 28 and 86 respectively to improve the folding operation during the carton set up process.

The second and third embodiments shown in Figures 4 and 5 respectively, are formed from blanks substantially the same as the blank described above and illustrated in Figure 1. Therefore, only the differences are described in more detail. The second embodiment shown in Figure 4, incorporates only one type of locking tab 25 connected to medial panel 26. Additionally, cut line 102 is substantially planar to define a lower edge of transverse partition panel 144 that is co-linear with fold line 98.

The third embodiment illustrated in Figure 5, incorporates the locking tab 100 only, extending from reinforcing panel 96 and the medial panel 26 does not include locking tab 25.

The construction of the completed carrier of any of the embodiments from a flat collapsed condition of the blank requires a series of sequential folding and gluing operations. It is envisaged that the folding process is not limited to that described below and can be altered according to particular manufacturing requirements.

Thus, handle support panels 80 and 82 are folded outwardly about fold line 84 and into a face to face relationship with upper portions of medial panels 24, 26. Thereafter, secondary partition panel 104 and transverse partition panels 112, 124 are folded about fold lines 106 and 122 respectively and into face to face relationship with the extended portion of partition panel 92. Secondary partition panel 104 and intermediate panel 120 are preferably secured to partition panel 92 by glue or other 10 suitable means known in the art. Reinforcing panel 96 is folded about fold line 98 and into a face contacting relationship with the second pair of transverse partition panels

142, 144, such that the locking tab 100 extends away from the second pair of transverse partition panels. Preferably, the portions of the partition panel 94 marked by hatched lines in Figure 1 are secured to the respective portions of reinforcing panel 96 by glue or other means known in the art. Likewise, glue is applied to the glue flaps 130, 136;

152, 162 and the medial partition structure 42 is folded about fold line 44 in an inward direction such that the glue flaps 130, 136; 152, 162 come into face contacting relationship with respective side walls 32 and 52.

The end structure comprising end panels 30 and 48 and medial panels 24, 26 together with handle support panels 80, 82 are folded inwardly, such that the end panels 30, 48 come into face contacting relationship with respective side walls 32, 52 and handle support panels 80, 82 are placed in a face to face relationship with outer handle panels 64 and 66 respectively. Handle support panels 80, 82 may be secured to the outer handle panels 64, 66 and the medial panel 24 is secured to partition panel 92 along an end portion by glue or other means known in the art. Likewise, it is preferred for the medial panel 26 to be connected to partition panel 94 and reinforcing panel 96 by glue or other means known in the art. In order to form a flat collapsed carton, the part constructed carrier is folded about central fold line 28 so that first and second partition panels 92 and 94 and medial panels 24 and 26 respectively come into face contacting relationship and are secured together by glue or other means known in the art. Thus, the carton is in a flat collapsed condition ready to be supplied to a packaging machine for final construction and loading. The shape of the carton is commonly referred to as an "arrow head" type of construction. However, it is envisaged that the outer carton panels could be adapted to form a "parallelogram" type basket carrier without departing from the scope of invention.

In use, the article carrier is erected by moving the outer edges of the collapsed carrier defined by fold lines 44 and 38, 54 inwardly toward each other thereby separating end panels 30 and 48 and 36 and 56 respectively and placing these panels in a substantially rectangular configuration, as shown in Figure 3. This folding operation also facilitates construction of the individual cells whereby transverse partition panels 11 112, 124 are caused to move out of alignment with first side panel 32 and partition panel 92 and are folded about fold lines 114, 132; 126, 138 respectively so that three cells Cl, C2, C3 are formed as illustrated in Figure 3. Similarly, transverse partition panels 142, 144 are caused to move out of alignment with second side panel 52 and partition and reinforcing panels 94, 96 and are folded about fold lines 146, 154; 160,

164 respectively, so that a further three cells (not shown) are formed. Figure 3 illustrates the position of the cells and medial partition structure 44 when the carton is in a set up condition.

In one class of embodiments, the base 12 is then formed by folding first and second base panels 14, 16 about fold line 46 and into substantially perpendicular relationship with side wall 32 respectively. Optionally, the end edge of base 12 is then secured to the glue flap to complete construction of the base. In other embodiments, the base 12 is formed after the articles have entered their respective cells through the open top or bottom of the carrier.

Thus, the carton can be in a glued and set up condition or a collapsed condition for transfer to an article loading facility.

The carton is then ready to receive articles (not shown) which are loaded by relative vertical movement between the articles and carrier during forward feed movement, well known in the art, by which bottles enter their respective cells through the open top of the carrier.

The erected carton can be maintained in a set up condition during the loading operation by the use of detachable connection means connecting the base to the carrier. Figures 4 and 5 each illustrate one type of detachable connection means. It will be appreciated that in the embodiment illustrated in Figures 1 to 3, the detachable connection means incorporating both types of detachable connection means illustrated in Figures 4 and 5. However, it is envisaged that only one of the above versions could be incorporated into a carrier, without departing from the scope of the invention. 12 Turning again to the construction of the first type of detachable connection means used in the first and second embodiments with reference to Figures 1, 2, 3 and 4, the locking tab 25 comprising the substantially elongate "U" shaped hook 27 with a pair of opposed locking edges 29, 31. The locking tab 25 is caused to be moved into alignment with and above locking aperture 20 by relative folding movement between the medial partition structure 44 and the base 12. Locking tab 25 is then caused to pass through the locking aperture 20. As the end and side panels are moved into perpendicular relationships, as shown in Figure 3, the retaining tab 35 is caused to pass through locking aperture 22, whereby locking edges 29 and 31 engage the portion of the base 12 intermediate apertures 20 and 22. In the first embodiment, only locking tab 100 which can be secured to the first hook means is also inserted in the first aperture 20 to provide additional support. Thus, the base is engaged with the carrier and the carrier is secured in a set up condition, so that loading can be completed and any unintended forces applied to the sides or ends of the carton will not result in the carton collapsing back to a flat collapsed condition. Furthermore, the detachable connection means maintains the carrier in a set up condition after loading. Of course, in those embodiments in which the base is formed after loading, the detachable connection means is provided to engage the base so as to maintain the carton in a set up condition.

In a third embodiment shown in Figure 5, the detachable connection means comprises the locking tab 100 extending from reinforcing panel 96 and first aperture 20 only, and the base panel is held in place by locking tab 100 being engaged with first aperture 20 as shown in Figure 5. Thus, the base panel is secured to the carton at a central location to the medial partition structure to maintain it in a set up condition.

In use, handle tabs 72, 78 of the carton are folded about hand panels to further secure handle panel structure H and the carton as shown in Figure 3.

A further problem with the prior art is the amount of board used to achieve a basket type carrier with individual dividing cells. The present invention enables an efficient use of board to be achieved as a long rather than wide blank can be used since the blank is joined along the side edges of the handle panels and the medial partition structure extends from the end panels. 13

It will be recognised that as used herein, the terms "top", "base" and "side" with respect to the panels of the carton (or carton blank) are relative terms, and that the carton (formed from the blank) may be re-oriented as necessary or as desired.

The present invention and its preferred embodiments relate to an article carrier which is shaped to provide satisfactory strength to hold the bottles securely but with a degree of flexibility so that the load transferred to the handle is absorbed by the carrier. The shape of the blank minimises the amount of paper board required. The carrier can be applied to an array of bottles by hand or automatic machinery. It is anticipated that the invention can be applied by a variety of carrier and not limited to those of the basket carrier type.

Claims

14 CLAIMS

1. An article carrier of the basket type adapted to accommodate a plurality of articles, for example bottles, which carrier comprises a base, opposed side and end walls, and an internal medial partition structure, wherein said medial partition structure comprises at least one locking tab extending downwardly to connect said base to said medial partition panel characterised in that said locking tab includes a pair of opposed locking edges and in that said base comprises adjacent first and second apertures each to receive and retain in locking engagement a separate one of said locking edges of said locking tab to connect said base and said medial partition structure.

2. An article carrier as claimed in claim 1 wherein the locking tab comprises a lock body, said lock body including one of said pair of opposed locking edges and a retaining tab spaced from and connected to the lock body by an intermediate portion which retaining tab defines the other of said pair of opposed locking edges.

3. An article carrier as claimed in claim 2 wherein the first aperture is cooperatively engaged with the lock body extending through said aperture whereby said intermediate portion is disposed beneath the base.

4. An article carrier as claimed in claim 2 or claim 3 wherein the retaining tab is co-operatively engaged with the second locking aperture whereby an upper portion of said retaining tab is disposed above the base.

5. An article carrier as claimed in any preceding claim wherein said medial partition structure further comprises at least one locking tab struck from a reinforcing panel and extending downwardly to connect said base to the medial partition panel, characterised in that said at least one locking tab includes a locking edge and in that said base comprises an aperture to receive and retain in locking engagement said locking edge to connect the base and the medial partition structure.

6. A carton of the basket type adapted to accommodate a plurality of articles, for example bottles, comprising a base, opposed side and end walls, an internal medial 15 partition structure, wherein said medial partition structure comprises at least one locking tab struck from a reinforcing panel and extending downwardly to connect said base to the medial partition panel, characterised in that said at least one locking tab includes a locking edge and in that said base comprises an aperture to receive and retain in locking engagement said locking edge to connect the base and the medial partition structure.

7. A blank for forming an article carrier of the basket type comprising a single sheet of foldable material including panels for forming a base, opposed side and end wall panels, and a medial partition structure, said medial partition structure comprises at least one locking tab extending downwardly to connect said base to the medial partition panel characterised in that said locking tab includes a pair or opposed locking edges and in that said base comprises a pair of adjacent apertures each to receive and retain in locking engagement a separate one of said locking edges of said locking tab to connect said base and said medial partition structure.

8. A method for locking an article carrier adapted to accommodate a plurality of articles, for example, bottles, comprising a base, opposed side and end walls, and an internal medial partition structure, wherein said medial partition structure comprises at least one locking tab extending downwardly to connect said base to the medial partition panel, said locking tab includes a pair of opposed locking edges and said base comprises adjacent first and second apertures, which method comprising the steps of: causing relative movement between said medial partition structure and said base to position said locking aperture beneath said locking tab; causing relative movement between said medial partition structure and said base to cause said locking tab to pass through said first aperture; and causing relative movement between said medial partition structure and said base inwardly to cause said locking tab to pass through said second aperture.