This invention relates to boxes especially for the transport of food and in particular relates to a box construction enabling the boxes to form a stable stack.

Boxes for the transportation of foods such as fresh vegetables and fruits often comprise relatively shallow rectangular box portions having raised opposite end portions.

Our European patent publication number 0 548 173 discloses a box of this general type having reinforced corners produced during its manufacture.

The present invention seeks to provide a modified form of this general type of box which enables it to form stable stacks, for instance up to 4 metres high.

According to the present invention there is provided a box for the transport of food which comprises one or more tapered tabs projecting above the general plane of its upper surface and, on its lower surface, in positions corresponding to the tabs, an equivalent number of detents.

The tabs are preferably formed from the blank from which the box is made and project upwardly from the general plane formed by the top of the box walls. The extent of projection need only be relatively small, in the order of a few millimetres. Preferably, the tabs extend up to the top of the bottom sheet in the stacked box immediately above. This is to ensure that in the event of jolting, e.g. during transport, the tabs are retained in the coresponding detents. The tabs are tapered so that they are narrower at their top portions than they are further down. The detents will normally comprise a correspondingly shaped hole in the bottom of the box or the box wall capable of receiving the whole of the tab therein. The

tapering of the tab makes it easier to locate the top of the tab into the detent but as the tab enters the detent it substantially fills it, thus cutting down, or preferably eliminating, relative movement between adjacent stacked boxes. In this way boxes can be stacked, according to the weight of their load, to a stack height many times the box height.

Preferably, the box of the invention is constructed as described in our above mentioned European patent publication 0 548 173 and has corner reinforcements. However, it is preferred that the end portions 16 as described in the above publication are of the same height as the walls 14 and that the platforms formed by the top portions 18 are dispensed with entirely.

The boxes of the invention may be produced of any material but it is preferred to produce them from a plastics material and in particular a corrugated plastics material. Where plastics materials are employed, they are preferably polyolefin plastics.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a box in accordance with European patent publication number 0 548 173;

Figure 2 is a partial view on an enlarged scale of a corner; and

Figure 3 is a perspective view on an enlarged scale of another tab configuration.

Referring to the drawings, in particular Figures 1 and 2, a box generally designated 10 is produced in accordance with our European patent publication 0548173, the entire contents of which are incorporated herein by reference. Like numerals

are employed for like parts. However, in the present case, the blank portion 18 and 20 is omitted completely and the end portion 16 is of a height equivalent to that of the walls 14. Curved reinforcements 11 are formed in each corner of the box 10 in accordance with the method described in the above European patent publication. The plane portion 30 of the flap 26 is modified so as to have a cut out portion 13 and a tab portion 15. The tab portion 15 extends above the general plane of the top of the box as defined by the tops of the side walls 14 and end walls 16. Moreover the tab portion 15 tapers to a point (or more properly an edge) 17.

In a position in the base 12 of the box 10 corresponding to the position of the tab 15 there is provided a detent 19 in the form of a hole in the base 12. The hole 19 is of the same cross-sectional area as the widest portion of the tab 15. Although only one tab and detent may be provided, it is preferred to provide at least two for stability, and for convenience a tab/detent pair at each corner.

The edge 17 may be produced on the tab 15 by means of hot sealing where the box is made from the preferred corrugated plastics material sheet, or some other suitable method such as crushing and gluing where corrugated cardboard is employed.

In use, as seen best from figure 2, when the box illustrated is placed on top of a second box (shown in shadow in figure 2) the tab 15 of the lower box locates within the detent 19. Ease of location is improved by the tab 15 tapering to the point 17. However, once the tab 15 has been located within the detent 19 a further downward movement of the upper box causes the tab 15 completely to fill the detent 19 thereby reducing or eliminating relative movement between the two boxes. In this way a very stable stack of boxes can be built up.

In figure 3 another configuration of tab is illustrated. In this the tab 15 is rounded to a central edge portion 17 during

the sealing operation. There is also a seal 21 down the sdie of the tab 15. This shape is more effeicient in that it makes it easier to insert the tab 15 into the detent 19.

While it is preferred to use the construction of the invention with boxes having corner reinforcements as described in our above mentioned European patent publication, it will be appreciated that the invention is not so-limited, and the tapered tab and detent system can be employed with other forms of box to provide stable stackability.