Abstract:
A method of forming a stackable plastic box blank is described. A net of hinged elements are formed from a first plastic material. A plurality of panels are formed from a second plastic material, with the panels located between the individual elements of the net. The individual panels are then bonded or fused to the hinge elements.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a box blank and a method of forming same. 
     DESCRIPTION OF RELATED ART 
     Containers, such as boxes, are ubiquitous and essential for storage, packaging and transport of various goods and products. Cardboard boxes are generally preferred over boxes made of other materials such as plastic and various blanks for transport of cargo because they are lighter, less bulky and recyclable. Such boxes may also be formed as a blank, to minimize volume when empty and which is assemblable to form the box. However, the inherent disadvantages of cardboard boxes are that they are prone to damage and have weak hinges and are thereby unsuitable for stacking and containing heavy loads. Moreover, cardboard boxes normally require adhesive taping of the flaps covering the top of the box to prevent therm from caving in or opening up. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved box blank. 
     According to the invention in the first aspect there is provided a box blank formed from plastics material and comprising a plurality of hinge elements connecting a plurality of panels for forming sides of the box, the hinge elements and panels being formed from different plastics material. 
     The hinge elements are preferably formed by plastics material having greater toughness but less rigidity than the plastics material forming the panels to provide structure advantages for both components which could not be achieved with a box blank of a single material. 
     The hinge elements are further preferably formed from a plastics material having a melt index less than the material from which the panels are formed and have a plurality of projections formed thereon. 
     According to the invention in the second aspect there is provided a method of forming a box blank comprising the steps of: forming a net of hinge elements of a first plastics material; and forming panels of a second plastics material in the spaces between elements of the net. 
     Preferably the net is placed in an injection mould with the second plastics material being injected into said spaces to form the panels. Preferably the injection moulding process is separately controlled for each panel so that the panels are formed evenly. 
     The net is preferably formed from the first plastics material having a melt index less than the melt index of the second plastics material so that the second plastics material when injected melts the skin of the first plastics material so that the plastics material fuse together to form the box blank. 
     Preferably the net is provided with a plurality of projections formed thereon which act, firstly, to help reduce surface tension effects when the second material is injected and, form islands to which the second material can attach itself. Furthermore, the projections project slightly above the level of the panels once formed and when formed from a less rigid material, create an anti-slide panel to assist in frictional contact between the boxes when stacked. 
     According to the invention in the third aspect there is provided a box blank comprising a plurality of panels connected by hinge elements, the panels including structural panels forming the sides of the box and load bearing panels, the load bearing panels being connected to the structural panels by hinge elements formed parallel to the intended direction of load bearing support provided by the load bearing panels. 
     With the box blank constructed in accordance with the third, aspect of the invention, the load bearing panels provided additional columnal support to the structural panels without an intervening hinge element in the direction of intended, load support which might be subject to stress leading to consequent failure. 
    
    
     BRIEF DESCRPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective view of a net used for reinforcing hinge regions of a box blank being an embodiment of the invention. 
     FIG. 2 is a cross-sectional view taken along line C-C′ in FIG.  1 . 
     FIG. 3 is a perspective view of a box blank showing use of the net. 
     FIGS. 4A,  4 B and  4 C depict progressively the flow of molten plastics along the net shown in FIG. 1 resulting in the formation of a hinge element to be used in the blank as shown in FIG.  3 . 
     FIG. 5A depicts in more detail the blank of FIG.  3 . 
     FIGS. 5B,  5 C,  5 D and  5 E depict progressively how the blank may be folded to form a box. 
     FIG. 6 is a sectional view of part of two such boxes stacked on top of each other. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1 an injection—moulded net  2  formed as a single piece of material, preferably made of rubber-modified polypropylene is shown. The quantity of elastomer in the rubber-modified polypropylene is preferably such as not to cause problems if the blank is regranulated in one piece. Net  2  is used for the purpose of forming the hinges of a box blank. A first injection mould is used to manufacture net  2 . Pressures and temperatures involved in the injection moulding process follow known techniques. 
     Net  2  is symmetrical along axes A-A′ and B-B′, and has a ladder-like appearance. It comprises two elongate rectangular strips  8  and  10  of equal length placed parallel to each other and joined together by four shorter rectangular strips  12 ,  14 ,  16  and  18  parallel to each other, perpendicular to strips  8  and  10  and separated from each other by a predetermined spacing. The spacing between the shorter strips is dependent on the dimensions of the box required. The elongate edges of strips  12 ,  14 ,  16  and  18  are formed of unequal dimensions and strips  8  and  10  bear discontinuities  19  along their outer edges to enable strips  12 ,  14 ,  16  and  18  to be easily folded along their lengths. Net  2  is preferably of a constant thickness. 
     FIG. 2 depicts an exploded view of the cross-section C-C′ and shows panels  4  and  6  of net  2  bearing equally spaced convex projections  20  arranged in four rows along the width of strips  8 ,  10 ,  12   14 ,  16  and  18 . 
     To form the blank, net  2  is placed in a second injection mould (not shown) having a shape to produce box blank  35  as shown in FIG.  3 . Once net  2  is placed in the mould, molten plastics, preferably a copolymer polypropylene with a melt index between  15 - 20  and marginally higher than the rubber-modified polypropylene used for net  2 , is then injected to fill in the mould. Multiple injection points are used for injection of the molten copolymer polypropylene in the spaces in between net  2  to ensure a controlled and even flow of the molten copolymer polypropylene, with the injection being separately controlled at each injections point to fill the spaces simultaneously. The molten copolymer polypropylene follows a laminar flow, originating from injection points in the spaces in between the elements of net  2  and moves outwards from the injection points towards the edges of net  2 . Thereafter and as shown in FIGS. 4A,  4 B and  4 C, the molten polypropylene flows over the net  2  but only as far as an edge of the mould between  32 ,  34 . Since the rubber-modified polypropylene of net  2  has a marginally lower melt index, it melts partially on contact with the molten copolymer polypropylene, such that both materials fuse to form a blank, at the same time preserving the structure of net  2 . The flow of the molten copolymer polypropylene is stopped by the mould once it reaches lines  32  and  34  along each of the strips  8 ,  10 ,  12 ,  14 ,  16  and  18 ; as shown in FIG.  4 C. 
     The convex projections  20  of net  2  aid in laminar flow of the molten copolymer polypropylene by breaking up its panel tension and increase the grip of net  2  on the copolymer polypropylene and ensure the strength of blank  35 . The convex projections  20  also marginally protrude from panels  36  and  38  of blank  35  as shown in the plan view of FIG.  4 C. 
     Blank  35 , as depicted by FIG. 5A, therefore has hinge elements  70 ,  72 ,  74 ,  76 ,  78 ,  80 ,  82 ,  84 ,  86 ,  90 ,  92 ,  94 ,  96  and  98  which are formed by the unfilled spaces between the lines  32  and  34 , of FIG. 4B, along the strips of net  2 , the hinge elements connecting the thus formed panels  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64 ,  66  and  68 . The panels comprise structural panels  40 ,  44 ,  48 ,  50 ,  52 ,  54 ,  56 ,  58 ,  60 ,  64 ,  66  and  68  joining the sides and closure of the box and load bearing panels  42 ,  46 ,  62  and  66 , the use of which is detailed hereinafter with reference to FIG.  6 . 
     As depicted by FIG. 5A, panel  54  is moulded such that it contains one concavity  120  near each of its four corners. The concavities  120  are formed such that they appear as convex projections on the reverse side of panel  54 . Panels  50  and  58  also contain similar concavities  120  near hinge elements  80  and  86  respectively. Panel  42  contains a concavity  122 , formed near the corner formed by edge  105  and hinge element  72 , with diametrically opposite ends cut away. Concavity  122  appears as a convex projection on the reverse side of panel  42 . Panels  46 ,  62  and  66  contain similar concavities  122  near the corners formed by edge  107  and hinge element  76 , edge  115  and hinge element  92  and edge  117  and hinge element  96  respectively. Panels  44  and  64  contain rectangular openings  124  at either end of edges  135  and  137  respectively. Openings  124  are formed such that the convex projections of concavities  122  snap fit into them. Panels  44  and  64  contain further U-shaped openings  126  located adjacent to their rectangular openings  124 . Panels  44  and  64  also contain rectangular openings  132  with rounded corners and lengths running parallel to hinge elements  74  and  94 . Panels  40 ,  48 ,  60  and  68  each contain one U-shaped slit and a circular indentation  130 . The U-shaped slits are formed such that they result in U-shaped sections  128  that snap fit into U-shaped openings  126 . Circular indentations  130  are formed such that convex projections of concavities  122  snap fit into them. Panels  50  and  58  each possess two V-shaped projections  142  and two V-shaped receptacles  144 . 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E progressively illustrate how the blank  35  may be folded in a particular manner to form the box. Panels  44  and  64  are folded towards each other through an angle of ninety degrees along hinge elements  74  and  94  respectively. Panels  42  and  62  are also folded towards each other through an angle of ninety degrees along hinge elements  72  and  92  respectively. Similarly panels  46  and  66  are also folded towards each other through an angle of ninety degrees along hinge elements  76  and  96  respectively. At this stage blank  35  should resemble FIG.  5 B. Panels  52  and  56  are then folded towards each other angle through an angle of ninety degrees along hinge elements  82  and  84  respectively. Edges  102  and  104  of panels  42  and  46  respectively will then be aligned with hinge element  74  such that edges  106  and  108  meet. Similarly edges  112  and  114  of panels  62  and  66  respectively will be aligned with hinge element  94  such that edges  116  and  118  meet. Blank  35  would then resemble FIG.  5 C. The convex projections of concavities  122  present on panels  42  and  46  are then snap fit into rectangular openings  124  on panel  44  thereby holding panels  42 ,  44  and  46  together. Similarly the convex projections of concavities  122  present on panels  62  and  66  are snap fit into rectangular openings  124  on panel  64  thereby holding panels  62 ,  64  and  66  together. Convex projections of concavities  122  further protrude out of rectangular openings  124  after snapping into them. 
     FIG. 5D shows how panel  50  is then folded through an angle of ninety degrees along hinge element  80  such that hinge element  70  is aligned along edge  105  of panel  42  and a portion of edge  135  of panel  44  and hinge element  90  is aligned along edge  115  of panel  62  and a portion of edge  137  of panel  64 . Similarly panel  58  is folded through an angle of 90 degrees along hinge element  86  such that hinge element  78  is aligned along edge  107  of panel  46  and a portion of edge  135  of panel  44  and hinge element  98  is aligned along edge  117  of panel  66  and a portion of edge  137  of panel  64 . The V-shaped projections  142  of panel  50  then fit into the corresponding V-shaped receptacles of flap  58  and vice-versa. Panels  40  and  48  are then folded through an angle of ninety degrees along hinge elements  70  and  78  such that their respective U-shaped sections  128  snap fit into the U-shaped openings of panel  44  at the same time allowing the convex projections of concavities  122  protruding out of panel  44  to snap fit into circular indentations  130 . Thus, panels  40 ,  42 ,  44 ,  46  and  48  are held together. Panels  60  and  68  are similarly folded through an angle of ninety degrees along hinge elements  90  and  98  and snap fit so that panels  60 ,  62 ,  64  and  68  are held together. A box is thus formed and is depicted in FIG.  5 E. Rectangular openings  132  with rounded corners may be used to grip and carry the box. 
     FIG. 6 illustrates two such boxes stacked on top of each other. The convex projections of concavities  120  on panels  50  and  58  of the lower box rest in concavities  120  of panel  54 . The two boxes are thus held in place and the upper box is prevented from sliding over the lower box. Moreover, the force exerted by the upper box on the lower box due to its weight is borne principally by load bearing panels,  46  (and like panels  42 ,  62  and  66 ) thereby reducing the pressure that would otherwise exist on the panels  44  and  64  (and like panels) and the hinges formed by the hinge elements  70 ,  78 ,  74 ,  90 ,  98  and  94 . The boxes are further prevented from sliding over each other by the additional friction created by the marginally protruding sections of convex projections  20  of net  2 . 
     When the boxes are in a collapsed state such as in FIG. 5A, they may be stacked on top of each other such that convex projections of concavities  120  on the panel of the lower box rest in the concavities  120  of the upper box thereby preventing the boxes from sliding over each other. 
     The embodiment of the invention described herein above is not to be construed as limitative. For example, although the box is described incorporating the reinforcing net, and a novel load-resistant structure, these features may be used independently. Furthermore, both the box and the reinforcing net may be constructed of materials other than polypropylene such as polythene. As such it is to be understood that modifications may be made to the embodiments described without departing from the scope of the invention.