Abstract:
A pallet includes a deck having columns supporting the deck. The deck includes a plurality of ribs extending downwardly from an upper sheet. A reinforcement sheet is secured to lower ends of the ribs. The reinforcement sheet is a coextruded sheet having a first material selected to bond well with the ribs and a second material selected for other improved physical properties. In the example disclosed herein, the second material is chosen for improved fire retardant properties. As one example, the reinforcement sheet can be vibration welded or hot plate welded to the lower ends of the ribs, thereby providing a strong weld between the reinforcement sheet and the ribs, which provides increased performance of the upper deck while the fire retardant layer of the reinforcement sheet provides fire retardant properties to one of the largest surfaces on the pallet.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to pallets. Pallets generally include an upper deck having columns below to support goods thereon above the floor. The columns also provide openings below the deck for the tines of a forklift. 
         [0002]    It has been proposed to add additives to the material of the pallet in order to improve its resistance to fire. However, these additives can cause other physical properties of the pallet to decrease, such as strength, toughness and stiffness. 
       SUMMARY OF THE INVENTION 
       [0003]    A pallet according to one embodiment of the present invention includes a deck supported at a distance above the floor by a plurality of columns The deck includes a plurality of ribs extending downwardly from an upper sheet. A reinforcement sheet is secured to lower ends of the ribs. The reinforcement sheet may be a plurality of coextruded sheets, one having a first material selected to bond well with the ribs and at least one other sheet of a second material selected for other improved physical properties. In one example disclosed herein, the second material is chosen for improved fire retardant properties. As one example, the reinforcement sheet can be vibration welded to the lower ends of the ribs, thereby providing a strong weld between the reinforcement sheet and the ribs. The reinforcement sheet provides increased performance of the upper deck while the fire retardant layer of the reinforcement sheet provides fire retardant properties to one of the largest surfaces on the pallet. 
         [0004]    These and other features of the application can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of a pallet according to one embodiment of the present invention. 
           [0006]      FIG. 2  is a front view of the pallet of  FIG. 1 . 
           [0007]      FIG. 3  is a side view of the pallet of  FIG. 1 . 
           [0008]      FIG. 4  is a top view of the pallet of  FIG. 1 . 
           [0009]      FIG. 5  is a bottom view of the pallet of  FIG. 1 . 
           [0010]      FIG. 6  is an exploded perspective view of the pallet of  FIG. 1 . 
           [0011]      FIG. 7  is a bottom perspective view of the exploded pallet of  FIG. 6 . 
           [0012]      FIG. 8  is a bottom perspective view of the upper deck of the pallet of  FIG. 1 . 
           [0013]      FIG. 9  is a bottom perspective view of the lower structure of the pallet of  FIG. 1 . 
           [0014]      FIG. 10  is a section view of the upper reinforcement sheet of the pallet of  FIG. 7 . 
           [0015]      FIG. 11  is a section view of the lower reinforcement sheet of the pallet of  FIG. 7 . 
           [0016]      FIG. 12  is a section view of an optional upper reinforcement sheet. 
           [0017]      FIG. 13  is a section view of an optional lower reinforcement sheet. 
           [0018]      FIG. 14  is a bottom exploded perspective view of a pallet according to an alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    A pallet assembly  10  according to one embodiment of the present invention is shown in  FIG. 1 . The pallet  10  generally includes an upper structure  12  and a lower structure  14 . The upper structure  12  includes an upper deck  16  having a generally planar upper support surface  18  and a plurality of column connectors  20  protruding downwardly therefrom. The lower structure  14  includes an integrally molded lower portion  22  including a plurality of columns  24  with runners  26  extending therebetween. 
         [0020]      FIGS. 2 and 3  are front and side views of the pallet assembly  10 .  FIG. 4  is a top view of the pallet assembly  10 . 
         [0021]      FIG. 5  is a bottom view of the pallet assembly  10 . As shown, the lower structure  14  includes a lower reinforcement sheet  30 , shaped to align with the runners  26  and the columns  24 . The upper structure  12  includes an upper reinforcement sheet  32  secured to the bottom thereof. 
         [0022]    An exploded view of the pallet assembly  10  is shown in  FIG. 6 . The upper structure  12  includes the upper deck  16 , reinforcement frame  36  and the upper reinforcement sheet  32 . The reinforcement frame  36  includes a plurality of elongated, hollow rods, preferably having a rectangular cross-section. The rods include peripheral rods  38  forming a periphery of the reinforcement frame  36  and optionally welded to one another. A longitudinal reinforcement rod  40  extends longitudinally along a center of the reinforcement frame  36  between opposite front and rear peripheral rods  38 . A lateral reinforcement rod  42  extends along a center-line between opposite side peripheral rods  38 . Optional angled reinforcement rods (not shown) may extend diagonally across each of the quadrants formed by the rods  38 ,  40 ,  42 . 
         [0023]    The upper reinforcement sheet  32  is generally a planar single piece of plastic extruded as a sheet and having peripheral column openings  46  around its periphery, including the corners, and a central column opening  48 . 
         [0024]    The lower structure  14  includes the lower portion  22  integrally injection molded as a single piece of plastic including the columns  24  and runners  26 . A lower reinforcement frame  50  includes a plurality of peripheral reinforcement rods  52  around a periphery, which may optionally be welded to one another. A longitudinal reinforcement rod  54  may extend along a center line longitudinally between two opposite peripheral reinforcement rods  52 . A lower reinforcement sheet  30  is generally shaped to align with the bottom of the lower portion  22 . 
         [0025]    Referring again to  FIG. 6 , although the pallet assembly  10  is illustrated with all of the reinforcements, the pallet assembly  10  can be configured with various combinations of the reinforcements depending on the application. For example, one configuration might not include any of the reinforcements at all. Another configuration would include only the peripheral reinforcement rods  52  and the longitudinal reinforcement rod  54  in the lower structure  14  and only the longitudinal reinforcement rod  40  in the upper structure  12 . Another configuration would include the peripheral reinforcement rods  52  and the longitudinal reinforcement rod  54  in the lower structure  14  and peripheral rods  38 , the longitudinal reinforcement rod  40  and the lateral reinforcement rod  42  in the upper structure  12 . Another configuration would include the peripheral reinforcement rods  52  and the longitudinal reinforcement rod  54  in the lower structure  14  and peripheral rods  38 , the longitudinal reinforcement rod  40 , the lateral reinforcement rod  42  and the angled reinforcement rods in the upper structure  12 . The various reinforcement rods can be different sizes (gauge), depending on the application, as are the channels in the bottoms of the deck and runners for receiving the rods. For example, the peripheral reinforcement rods  38  (and the corresponding channels in the upper deck  16 ) could have a smaller cross-section (e.g. ½″, which is less than half the total height of the upper deck  16 ) than the other rods and channels (e.g. ¾″). Therefore, when the channels are welded shut by the upper reinforcement sheet  32 , the upper deck  16  will be strong with or without the peripheral reinforcement rods  38 . 
         [0026]      FIG. 7  is an exploded bottom perspective view of the pallet assembly  10 . The upper deck  16  includes a plurality of ribs  56  extending downwardly from the upper sheet  18 . The lower portion  22  also includes a plurality of ribs  58  extending downwardly. 
         [0027]    A bottom perspective view of the upper deck  16  is shown in  FIG. 8 . The plurality of ribs  56  and the column connectors  20  protrude downwardly from the upper sheet  18 . Snap-fit connectors may be formed with the column connectors  20  for connecting to the columns  24  in a known manner. Peripheral ribs are provided along the periphery of the upper deck  16 . Openings are formed between some of the ribs  56  and column connectors  20  to accommodate the upper reinforcement frame  36  ( FIG. 7 ). 
         [0028]      FIG. 9  is a bottom perspective view of the lower portion  22  in which the columns  24  and runners  26  are integrally molded as a single piece of plastic, such as by injection molding. A plurality of ribs  58  extend downward. Openings may be formed through the ribs  58  to accommodate the lower reinforcement frame  50  ( FIG. 7 ). 
         [0029]    A cross-section of a portion of the upper reinforcement sheet  32  is shown in  FIG. 10 . A cross-section of a portion of the lower reinforcement sheet  30  is shown in  FIG. 11 . Each sheet  30 ,  32  includes a pair of coextruded sheets or layers  70 ,  72  that may optionally be then die-cut to the shapes shown. The upper layer  70  is formed of a material that matches the material of the upper deck  16  and the lower portion  22 . For example, the upper deck  16  and lower portion  22  may be injection molded of high density polyethylene, and the upper layer  70  may be high density polyethylene. However, “match” does not necessarily mean “identical”; rather, in this context “match” means that matched materials are selected to improve the bond between the two components. The matched materials improve the weld between the upper layer  70  and the upper deck  16  and lower portion  22  via vibration welding or hot plate welding (or adhesive, etc). The lower layer  72  is formed of a material with improved fire retardant properties (such as halogens, metal hydrates, intumescents or other additives). In a fire, the bottom surfaces of the pallet assembly  10 , including the bottom of the upper deck  16  and the bottom of the lower portion  22 , including the runners  26  is the most important area for fire retardant material. By coextruding the fire retardant material in the lower layer  72  with the upper layer  70  of a material that matches the structure to which the sheet is bonded, a good bond can be obtained while also obtaining good fire retardant characteristics. 
         [0030]      FIG. 12  is a section view of an optional upper reinforcement sheet  32  and  FIG. 13  is a section view of an optional lower reinforcement sheet  30 . Each sheet  30 ,  32  includes three (or more) coextruded sheets or layers  70 ,  72 ,  74  that may be die-cut or trimmed as needed. Again, the upper layer  70  is formed of a material that matches the material of the upper deck  16  and the lower portion  22 . For example, if the upper deck  16  and lower portion  22  are injection molded of high density polyethylene, then the upper layer  70  may be high density polyethylene. The matched materials improve the weld between the upper layer  70  and the upper deck  16  and lower portion  22  via vibration welding or hot plate welding (or adhesive, etc). The middle layer  72  is formed of a material with improved fire retardant properties (such as halogens, metal hydrates, intumescents or other additives). The lower layer  74  could match the upper layer  70  (and match the upper deck  16  and lower portion  22 ). Alternatively, the lower layer  74  may be another layer of fire retardant material (which may be the same or different material as that of the middle layer  72 ). As another option, one or more of the layers  72 ,  74  could have increased stiffness (e.g. through additives—in fact, the fire retardant additives increase stiffness too) which may increase the overall stiffness of the pallet  10 . This may also increase the brittleness of the layers  72 ,  74 ; however, because the sheets  30 ,  32  are spaced away from the perimeter of the pallet, they will be less subject to impact from fork tines, etc. 
         [0031]      FIG. 14  is a bottom exploded perspective view of a pallet  110  according to an alternative embodiment. The upper deck  16  and lower portion  22  may be the same as before. The upper reinforcement frame  136  is similar, but only includes ones cross-bar. A lower reinforcement frame is not shown, but could be the same as before. In this embodiment, there are two upper reinforcement sheets  132  secured to the ribs  56  of the upper deck  16  (again, via vibration or hot plate welding, adhesive, etc). The upper reinforcement sheets  132  do not cover the upper reinforcement frame  136 , but only cover the two large surfaces of the upper deck  16  between the upper reinforcement frame  136 . 
         [0032]    On the bottom ribs of the lower portion  22 , a plurality of lower reinforcement sheets  130  (show optionally overlapping) are welded or otherwise secured. Using the plurality of narrow lower reinforcement sheets  130  in this embodiment reduces the amount of material cut sheet to form the large openings in the single, large extruded of the first embodiment. 
         [0033]    Alternatively, the upper reinforcement sheets  132  and lower reinforcement sheets  130  could be injection molded (including the numerous apertures formed therein). In that case, there are several options for achieving improved fire resistance. First, the injection-molded plastic could include some fire retardant additive, such as magnesium hydroxide (MDH). Second, the injection-molded sheet  130 ,  132  could be a twin shot or multi-shot injection, such that the sheet  130 ,  132  has a matching upper layer and a fire retardant lower layer formed by different shots in the mold, such that the injection-molded sheets  130 ,  132  have an upper layer  70  (matching) and lower layer  72  (fire retardant) as in  FIGS. 10-11 . The injection-molded sheets  130 ,  132  could also have a third layer  74  (matching or some other property) as a bottom layer as in  FIGS. 12-13 , with all three layers formed in a multi-shot mold. As a third option, a fire retardant coating could be applied to one side of a mold prior to injection. The plastic is shot into the mold over the fire retardant coating. Again, the sheets  130 ,  132  include an upper layer  70  (matching) and lower layer  72  (fire retardant) as in  FIGS. 10-11 . 
         [0034]    Alternatively, the fire retardant layer may be added post injection molding by applying a coating to the bottom side of the injection molded layers (in which case the lower layers  72  of  FIGS. 10-11  would be the fire retardant coating and the upper layer  70  would be the injection molded layers). As yet another option, the fire retardant coating layer could also be added to an extruded sheet instead of coextruding the sheets. 
         [0035]    The fire retardant materials and additives described herein include intumescent type materials, Aluminum Hydroxide (ATH) and magnesium hydroxide (MDH). 
         [0036]    In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope. Alphanumeric identifiers in claimed method steps are for ease of reference in dependent claims and do not signify a required sequence of such method steps unless otherwise explicitly indicated.