Abstract:
A molded plastic bulk container for the storage, transport and handling of large quantities of bulk material such as fruit. The container includes:  
     (a) a base which may be internally concave;  
     (b) a number of walls, for example four, extending upwardly from the base,  
     wherein at least one, and preferably all, of the walls is adapted to have an internally concave configuration under a neutral load, i.e. when the container is empty.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to a plastic container for storage, transport and general handling of large quantities of bulk material such as food products, including fruit.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is recognized that a primary aim of bulk containers is to provide the most efficient ratio between the internal volume and the cubed external volume (“the volume ratio”). According to conventional wisdom, this is achieved with a container having straight, planar sides and being of a square or rectangular configuration. In smaller containers this is found to be an effective design capable of achieving the stated aim.  
           [0003]    However, in larger containers of the type considered in the present case there is a need to resist the tendency of the container&#39;s support surfaces to bow outwards under the considerable load placed thereon. It has been generally considered that if the walls and floor were to be permitted to bow outwardly then the external dimensions of the container required to be maintained within strict tolerances would be at variance with generally accepted standards. This would inevitably lead to space problems in storage, transport and general handling.  
           [0004]    The most common method employed to address this problem is to reinforce the walls and floor of the container with struts and ribs which are effective to maintain the planar configuration of the surfaces. These ribs are made of considerable thickness (e.g., about 40 mm) adequate to further impart sufficient rigidity to resist the distortive forces of the load. Consequently, known plastic containers have traditionally been made with deep reinforcing ribs and walls and floors of considerable thickness to resist the tendency to bulge. As space is taken up by the ribs the resultant container has a volume ratio which is reduced relative to the potential volume ratio if it was possible to overcome the problem of bulging.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to ameliorate the aforementioned disadvantages of the prior art or at least provide a useful alternative thereto.  
           [0006]    Accordingly in one aspect of the invention there is provided a molded plastic bulk container including:  
           [0007]    (a) a base; and  
           [0008]    (b) walls extending upwardly from the base,  
           [0009]    wherein at least one of the base or one of the walls is adapted to have an outwardly curved configuration under a neutral load.  
           [0010]    In line with conventional bulk containers, the container may comprise a base with four walls and, optionally, a lid. The walls may have equal dimensions. Where the container has four walls, a first pair of opposing walls may have different dimensions compared to a second pair of opposing walls. The first pair of opposing side walls may be longer, higher or thicker than the second pair of opposing side walls.  
           [0011]    The container may be formed as a unitary structure. The container may be made up of two or more separately formed components. The separately formed components may be later affixed together to form the container. The components may be attached by sonics, heat or friction welding or press-fitting.  
           [0012]    Preferably the container is integrally formed in a single molding process. The container may be made using a variety of plastics possessing the necessary properties of strength, abrasion resistance, food contact safety, UV resistance and the like. An example of a suitable polymer is high density polyethylene.  
           [0013]    The base may be planar as in conventional bulk containers or may have a curved configuration. The base may have an outwardly curved configuration, whereby the surface of the base bulges or bows outwardly thereby to define a substantially concave interior surface.  
           [0014]    Where the base is substantially planar, as in conventional bulk containers, the base must necessarily be reinforced with strengthening ribs. However, where the base has an internally concave configuration the need for reinforcing ribs may be substantially reduced, although not necessarily entirely dispensed with, and the thickness of the base may also be substantially reduced. Moreover, the internal volume of the container, and hence its produce capacity, is increased by making available the area below side edges of the base which are normally reserved for the insertion of forklift tines. Accordingly, in a preferred embodiment the container has an internally concave base whereby the depression extends into the area intermediate the area reserved for insertion of the forklift tines.  
           [0015]    The concave base may be radially contoured to provide an irregularly concave base. The base may have a central deep bowl inclined radially upwardly towards the lower edge of each wall of the container. Preferably, however, the base is made with minimal thickness to save on material and is reinforced by ribs as is conventional in the art. Where a concave base is used, the need for reinforcing ribbing has been found to be reduced because of the geometrically stronger shape of the concave base compared to the conventional planar base.  
           [0016]    The reinforcing ribs of the base may be in the form of a square or rectangular grid pattern. The reinforcing ribs may be in the form of circular or radiating ribs extending outwardly from a center point of the base. The reinforcing ribs of the base may be a combination of a grid pattern and a circular or radiating pattern. Where a concave base is used, the reinforcing ribs may comprise a series of circular ribs of ever increasing diameter extending away from the center of the base. The concave base may comprise linear ribs radiating outwardly from an area central to the base towards the container walls.  
           [0017]    Preferably, the reinforcing ribs are located on the underside of the base. The underside of the base may be configured to provide runners for forklift tines. The runners may be solid or may be formed from reinforcing ribs. The runners may be substantially planar along their length. The runners may include upturned portions at one or both of their ends whereby to receive and guide the tine onto the runner and reduce the likelihood of a potentially damaging collision between the tine tip and another portion of the container.  
           [0018]    Some of the walls may be planar and reinforced with ribs as is standard in the art. Preferably all of the walls are adapted to have an outwardly curved configuration under a neutral load. A normal load may be considered the load applied to the bearing surfaces of the container including the base and the walls when the container is full of produce. A neutral load may be considered the load applied to the bearing surfaces of the container when the container is empty.  
           [0019]    The walls may be capable of flexing under a normal load. The walls may be substantially rigid and inflexible whereby they have a permanently outwardly curved configuration whether under load or not.  
           [0020]    As the force applied by a normal load has a tendency to urge conventional planar walls into an outwardly curved configuration, the molding of the walls with a permanent curved configuration may achieve similar strength properties as obtained by a conventional planar wall without the need for the reinforcing ribs required to achieve the necessary strength properties for the walls. Moreover, by having the walls in this curved configuration the walls may be molded with a far smaller thickness than conventional planar walls with ribs. For example, a conventional planar wall with ribs generally has a thickness of about 40 mm and requires substantial reinforcing ribbing. By contrast, a wall of the container of the present invention may be formed having a thickness of less than 40 mm, such as 30 mm to 40 mm, or 20 mm to 30 mm, or 10 mm to 20 mm, or 1 mm to 10 mm, preferably 3 mm to 6 mm and may require no ribbing at all on the majority of its surface. The curved wall may require no reinforcing ribs on its surface at all.  
           [0021]    As the cubed volume of the container is critical and generally must be rigidly constrained within certain standards, it is preferred that the curved walls do not bow beyond the limit of the cubed volume of the container.  
           [0022]    Each adjacent pair of walls may be joined at their junctions by corner posts. The corner posts may be partially or fully hollow, or internally porous. The corner posts may be L-shaped, square shaped, circular, rectangular, channel shaped or any other suitable shape in cross section. Preferably the corner posts are hollow, thereby to save on material costs. Preferably the corner posts are circular in cross section. Preferably the corner posts have an overall cylindrical configuration. The inventors have discovered that a cylindrical corner post molded to be hollow by the use of vertical inserts in the manufacturing process, provides a post using a minimal amount of material, whilst possessing optimum strength.  
           [0023]    The corner posts may be of a substantially constant cross section throughout their lengths. The corner posts may include top and bottom surfaces which are complementary, whereby the bottom surface is adapted to be seated on a complementary top surface. The top and bottom surfaces of the corner post may include a variety of complementary configurations well known to the person skilled in the art. The top of each corner post may include a planar part-circular support surface for seating a corner post base with a corresponding circular configuration.  
           [0024]    The top of the container may include an upstanding lip extending totally or partially around the periphery of the container. The lateral ribs may form corner ledges abutting the base of the lip at each corner. The corner post base may include a foot with an instep contoured to fit around the corner lip whereby the foot fits snugly onto the corner post top surface and corner lip.  
           [0025]    Adjacent the top surface of each corner post there may be a lateral ledge extending on one or both sides to improve the stability of the upper portion of the container and to maintain the curved structure overall. The lateral ledge may extend as bridges between the corner posts. The lateral ledge may taper towards the center of each adjacent wall. The lateral ledge may extend to a point intermediate the length of the top of each adjacent wall.  
           [0026]    Accordingly, in a preferred form of the invention the container may comprise four outwardly curved walls and a minimally reinforced internally concave base together with four hollow cylindrical corner posts. Such a container represents a structure having considerable strength, being lightweight, and requiring lower amounts of material compared to prior art containers. It may be apparent to a person skilled in the art that the geometry of this shape of the container generates a volume or capacity comparable to a conventional bin with generally flat, planar walls and base. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    The invention will now be described in the following non limiting description of one embodiment of the invention, in which:  
         [0028]    [0028]FIG. 1 is a perspective view of the top side of a container according to the invention;  
         [0029]    [0029]FIG. 2 is a perspective view of the underside of the container;  
         [0030]    [0030]FIG. 3 shows side elevation part sections of the container on the entry side and the foot side; and  
         [0031]    [0031]FIG. 4 shows a part plan view and a part underside plan view of the container. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    [0032]FIG. 1 shows an embodiment of the invention comprising a bulk container integrally formed by a single molding process. The container  1  includes a base  10 , four walls  12   a ,  12   b  extending substantially vertically therefrom and four corner posts  14  interposed at each of the junctions of each pair of walls  12   a  , 12   b  and a continuous upstanding lip  16  extending around the periphery of the upper region of the container  1 .  
         [0033]    The walls  12   a ,  12   b  curve outwardly. The lower edge  22  of each of opposed walls  12   a  extends along an arc connected at either end to feet  42  whereby the lower edge  22  lies in the horizontal plane extending between the feet  42  as best shown in FIG. 2. The lower edge  22  is configured to receive either individual corner feet  42  or to receive a single longitudinal foot  23   c  extending between the feet  42  along the sides of the container  1  corresponding to walls  12   a . The longitudinal foot  23   c  has an internal linear edge  23  and a curved outer edge  23   a  which generally follows the contour of the wall  12   a . Inset into the outer edge  23   a  is a recess  23   b  to avoid transfer of loads onto the walls  12   a ,  12   b.    
         [0034]    The lower edge  24  of opposed walls  12   b  is raised, relative to lower edge  22  to enable forklift tines (not shown) to be received under the container  1 . The lower edge  24  follows a similar curved contour to the wall  12   b , which contour is of a substantially constant cross section extending from the lower edge  24  to the upper edge  26   b  of the wall  12   b.    
         [0035]    The posts  14  are substantially hollow cylindrical structures extending from a lower end  41  up to a top post surface  44 . The top post surface  44  is generally of a circular planar configuration adapted to snugly receive a corresponding foot  42  of an identical container  1  to be seated thereon when vertically adjacent containers  1  are to be stacked one on top of the other.  
         [0036]    To conform to the corner portion  18  of the lip  16 , the foot  42  of each corner post  14  is provided with a recess in the form of an instep  46  to enable vertically adjacent containers  1  to be stably stacked one on top of the other.  
         [0037]    Extending in the same plane as top post surface  44  are pairs of laterally extending reinforcing ledges  48  which taper towards the center area of the top wall edges  26   a ,  26   b . The lateral reinforcing ledges  48  improve the lateral stability of the top region of the container  1  and provide a lateral bridge between the top edges  26   a ,  26   b  and the upstanding lip  16  without requiring side molds or inserts during the molding process.  
         [0038]    The base  10  as best shown in FIGS. 2 and 3 includes a central bowl region  2  extending radially upwardly to meet the walls  12   a ,  12   b  at their lower regions but above lower wall edges  22 ,  24 . The base  10  is gradually stepped whereby there is provided a steep inclination region  4  towards the center  2  and a shallower inclination in the outer regions  6  of the base  10  as shown in FIG. 3. The shallower region  6  is adapted to accommodate a pair of opposed runners  8  extending in parallel direction adjacent opposed walls  12   a  under the base  10 .  
         [0039]    The central area  4  of the base  10  includes reinforcing ribs  2   a  having a radiating pattern corresponding to the contour of the bowl shaped base  10 . The radiating pattern includes a series of circular reinforcing ribs  2   b  of increasing diameter extending away from the center portion  2  and linear reinforcing ribs  2   c  radially extending outwardly from the center portion  2 . The radiating reinforcing ribs  2   a  extend to the lower edges  24  of walls  12   b  and the internal edge  8   a  of each runner  8 .  
         [0040]    The central area  2  is configured to depend downwards to within 12.5 mm of the plane occupied by the lowermost points of the container  1 , thereby to maximize the internal volume of the container  1  and make use of the space between the runners  8 .  
         [0041]    Each runner  8  is formed from a rectangular grid pattern of reinforcing ribs presenting a sufficiently smooth running surface for forklift tines to slide underneath. The runners  8  have upturned ends  9  thereby to facilitate the entry of a forklift tine.  
         [0042]    The container according to the above described exemplary embodiment of the invention has a range of superior properties compared to conventional bulk containers.  
         [0043]    In containers with internally planar surfaces, the produce tends to apply forces of unequal distribution to the supporting and wall surfaces whereby bruising or other damage to the produce is likely to occur. The inky concave surfaces of the container of the invention provide for a more even distribution of the forces applied by the produce, thereby to minimize damage to the produce.  
         [0044]    The geometry of the corner posts being in the form of hollow circular columns provides a structure more resistant to buckling than the conventional L-shaped posts and is also most cost effective with regard to capital costs for tooling.  
         [0045]    The internal surfaces of the container are permitted to “bulge” outwardly, thereby to take up the space intermediate the corner posts which is normally lost in a conventional container.  
         [0046]    The bowl shaped base depending into the space normally reserved under the base for insertion of forklift tines provides a container with an increased capacity in that the volume ratio is increased.  
         [0047]    One embodiment of the invention also may provide an easily stackable container which is not only convenient but may be essential in particular commercial applications.  
         [0048]    The preferred embodiment is considerably lighter than conventional plastic bulk containers due to the use of less material per unit.  
         [0049]    The container of the invention may be easier to mold in manufacture than conventional containers because the need for reinforcing ribs for the side walls may be dispensed with, the reinforcing ribs of the base may be substantially reduced in number and depth and the cylindrical post construction may be easier to form in the molding process than conventional post designs.  
         [0050]    In particular, the cycle time involved in the manufacturing process may be considerably shortened as the deep reinforcements of conventional plastic bulk containers tend to slow down the cycle. In fact, the elimination of the reinforcing ribs normally required for the container walls may result in once cycle of the manufacturing process being completely eliminated. That is the side movement of the mold to release the reinforcing ribs on a conventional plastic bulk container&#39;s walls may be dispensed with.  
         [0051]    It will be appreciated that many modifications and variations may be made by those skilled in the art to the embodiments described without departing from the spirit or scope of the invention.