US20150360809A1 - Pallet and method of manufacture and use - Google Patents

Pallet and method of manufacture and use Download PDF

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Publication number
US20150360809A1
US20150360809A1 US14/735,779 US201514735779A US2015360809A1 US 20150360809 A1 US20150360809 A1 US 20150360809A1 US 201514735779 A US201514735779 A US 201514735779A US 2015360809 A1 US2015360809 A1 US 2015360809A1
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United States
Prior art keywords
pallet
bottom deck
board
boards
deck
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US14/735,779
Inventor
Richard McBride
Kevin L. Nichols
Brett M. Birchmeier
Andrew T. Graham
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Eovations LLC
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Eovations LLC
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Publication date
Priority to US201462010607P priority Critical
Application filed by Eovations LLC filed Critical Eovations LLC
Priority to US14/735,779 priority patent/US20150360809A1/en
Assigned to EOVATIONS, LLC reassignment EOVATIONS, LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GRAHAM, ANDREW T., MCBRIDE, RICHARD, BIRCHMEIER, BRETT M., NICHOLS, KEVIN L.
Publication of US20150360809A1 publication Critical patent/US20150360809A1/en
Abandoned legal-status Critical Current

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    • B65D19/00Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D19/0004Rigid pallets without side walls
    • B65D19/0053Rigid pallets without side walls the load supporting surface being made of more than one element
    • B65D19/0077Rigid pallets without side walls the load supporting surface being made of more than one element forming discontinuous or non-planar contact surfaces
    • B65D19/0089Rigid pallets without side walls the load supporting surface being made of more than one element forming discontinuous or non-planar contact surfaces the base surface being made of more than one element
    • B65D19/0093Rigid pallets without side walls the load supporting surface being made of more than one element forming discontinuous or non-planar contact surfaces the base surface being made of more than one element forming discontinuous or non-planar contact surfaces
    • B65D19/0095Rigid pallets without side walls the load supporting surface being made of more than one element forming discontinuous or non-planar contact surfaces the base surface being made of more than one element forming discontinuous or non-planar contact surfaces and each contact surface having a stringer-like shape
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Abstract

A pallet has a top deck coupled with a bottom deck through a plurality of spacer members. The bottom deck is provided as a sub-assembly comprising at least two lead bottom deck boards and at least one intermediate bottom deck board, each bottom deck board coupled with at least one other bottom deck board by a bottom deck joint, and wherein each board of the bottom deck sub-assembly is further coupled with at least one of the plurality of spacer members to couple the bottom deck sub-assembly with the top deck. At least one of the bottom deck lead boards are made from a fiber filled thermoplastic or oriented plastic composite material.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application claims the benefit of U.S. Provisional Patent Application No. 62/010,607, filed Jun. 11, 2014, which is incorporated herein by reference in its entirety.
  • TECHNICAL FIELD
  • This invention relates generally to pallets and more particularly to four-way entry pallets with improved resistance to damage.
  • BACKGROUND
  • Wood pallets are in widespread use for shipping products between manufacturers, distributors, and retailers. The vast majority of pallets in current use are constructed with a top deck formed of solid wood boards coupled with a bottom deck formed of solid wood boards. The top and bottom deck boards can be coupled together in a variety of ways to form the assembled pallet. Two-way entry pallets typically employ long stringers as spacer members for coupling the top deck boards and bottom deck boards, while four-way entry pallets (which are becoming more popular because of the greater ease of use that four-way entry allows) typically employ horizontal stringers to aid in holding and strengthening the top deck boards together and wood blocks as spacer members to couple the bottom deck boards to the top deck boards through the stringers. Wood pallets are typically of simple design and can be repaired when damaged in use. The Uniform Standard for Wood Pallets”, Copyright 2012, National Wooden Pallet and Container Association (referred to herein as the “NWPCA bulletin”), Alexandria, Va. 22314-2805, describes several types of conventional pallets.
  • The pool pallet system was developed as a means of controlling overall pallet usage cost and to limit destruction of timberlands used to provide wood for pallet construction. In the pool pallet system, a provider operates service centers to supply pallets and to receive returned pallets. When a pallet is returned to the service center, the pallet owner performs any needed repairs before returning the pallet to service. This process can continue as long as the pallet can, at a reasonable cost, be satisfactorily repaired and returned to service. Commonly used pool pallets have the advantage of being fabricated and repaired using common woodworking and fastening techniques that help make the pallet pool system cost-effective. This means the parts needing to be repaired can be readily deconstructed from the pallet. One particularly useful type of pallet used in the “pool” system is a 4-way entry block pallet with a full perimeter bottom deck.
  • Four-way entry pallets include a top deck, a bottom deck and spacer members. The top deck includes a pair of end members and a plurality of intermediate load supporting members. The bottom deck is provided with openings to accommodate the wheels of a hand transport. The top and bottom decks are separated by means of spacer members including longitudinally extending stringers on which are mounted spacer blocks, often of plywood or a composite material. The deck members, stringers and spacer blocks are typically mechanically fastened with, for example, nails or screws. Typically, nine blocks are installed at the corners of the pallet and intermediately of the end and side members to provide access to the pallet by the forks of a forklift or hand transport (pallet jack). In certain instances, the forks of a forklift truck can make contact with the lead boards of the decks and/or block members during alignment. If the force is significant, the lead boards and/or block members can be damaged. Many common types of pallet damage, and the requirement for their repair can be found in “Uniform Standard for Wood Pallets”, Copyright 2012 by the National Wooden Pallet and Container Association, Alexandria, Va. 22314-2805.
  • A number of suggestions have been made to reduce damage to lead boards for upper decks, including end-caps or protective parts for the access end of the pallet, multi-ply laminated boards (e.g. U.S. Publication No. 2011/0005435 to Renck et al.), pultruded boards (e.g. U.S. Publication No. 2006/0081158 to Ingham), and energy absorbing structures for the lead boards. However, because the added cost of these materials cannot typically be recovered, and because of the relative ease of repairing wood pool pallets, these improvements are not used widely in pool pallet systems of major North American pool pallet providers.
  • Another mode of damage is possible when a pallet jack is used to transport a pallet. A pallet jack, unlike a forklift, has forks that also serve as a base and includes wheels. In order to lift a pallet with a pallet jack, the fork is wheeled into the inner space of the pallet and then lifted, typically hydraulically. Hitting or running into the lower lead board can damage that board in the same manner as the lead board on the top deck of the pallet. Damage can also occur on the bottom deck of the pallet when a pallet jack is inserted into the pallet incorrectly so that the wheels of the pallet jack reside on a board of the bottom deck, rather than in the space designed for them. In this situation, the action of the forks of the pallet jack can force the top and bottom sections apart and can cause splitting or cracking of the boards of the bottom deck and can also lead to loss of an entire board if the mechanical fasteners fastening the board to the block spacer are pulled out.
  • When a pallet is entirely constructed of relatively cheap materials, these defects can be cost effectively managed by simply replacing the damaged board with another board of the same relatively cheap material. However, when pallets are constructed of combinations of material, for example, wood planks or boards and a relatively expensive energy attenuating lead board, such as a multi-ply laminated or a pultruded lead board, replacement of the lead board after damage and/or loss can become excessively costly. Thus these energy attenuating lead board materials are often undesirable even though they can reduce damage at the lead board position on a pallet deck and allow such a hybrid pallet a longer useful life.
  • SUMMARY
  • According to an embodiment of the invention, a pallet having a top deck comprising a first top deck lead board at a first end of the top deck and a second top deck lead board at a second end of the top deck, opposite the first, at least one intermediate board positioned between the first and second top deck lead boards, and a plurality of spacer members coupled with the top deck, the pallet comprises a bottom deck sub-assembly comprising: a first bottom deck lead board at a first end of the bottom deck sub-assembly and a second bottom deck lead board at a second end of the bottom deck sub-assembly, opposite the first, and at least one intermediate board extending between the first and second bottom deck lead boards and fastened to an adjacent first and second bottom deck lead board to form a joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards. The joint between the at least one intermediate board and the adjacent first and second bottom deck lead board has a joint strength in tension of 450 Newtons or greater and the bottom deck sub-assembly is coupled with the top deck through the plurality of spacer members to form the pallet. The first bottom deck lead board or the second bottom deck lead board can comprise an oriented plastic composite or fiber filled thermoplastic material.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • These and other features and advantages of the present invention will become better understood to those of ordinary skill in the art when considered in connection with the following description and drawings:
  • FIG. 1 is a perspective view from a top deck side of a conventional four-way entry block pallet.
  • FIG. 2 is a perspective view from a bottom deck side of a conventional four-way entry block pallet.
  • FIG. 3 is a vertical sectional view longitudinally taken along the line A-A of the pallet of FIG. 1 showing the position of a forklift of the low lift or pallet jack type inserted longitudinally into the pallet of FIG. 1 with the pallet jack wheels correctly aligned in the open space between bottom deck lead boards.
  • FIG. 4 is a vertical sectional view longitudinally taken along the line A-A of the pallet of FIG. 1 showing the position of a forklift of the low lift or pallet jack type inserted longitudinally into the pallet of FIG. 1 so that the pallet jack wheels are misplaced onto the lead board of the bottom deck of the pallet.
  • FIG. 5 illustrates a bottom deck sub-assembly according to an embodiment of the invention.
  • FIG. 6 is a partially exploded hybrid pallet having a bottom deck sub-assembly according to an embodiment of the invention.
  • FIG. 7A illustrates a bottom deck sub-assembly according to an embodiment of the invention.
  • FIG. 7B is an exploded view of the bottom deck sub-assembly of FIG. 7A according to an embodiment of the invention.
  • FIG. 8 is a partially exploded hybrid pallet having a bottom deck sub-assembly according to an embodiment of the invention.
  • FIG. 9 is a photograph illustrating pallet failure mode 1 for a conventional bottom deck structure having a test board made from an OPC material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 9, the heads of several of the nails coupling the test board to the spacer block have been pulled through the test board.
  • FIG. 10 is a photograph illustrating pallet failure modes 2 and 6 for a conventional bottom deck structure having a test board made from an OPC material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 10, several of the nails coupling the test board to the spacer block have been pulled out of the spacer blocks such that the test board can be removed by hand.
  • FIG. 11 is a photograph illustrating pallet failure mode 3 for a conventional bottom deck structure having a test board made from wood in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 11, the test board has split along its length, with the grain.
  • FIG. 12 is a photograph illustrating pallet failure mode 4 for a conventional bottom deck structure having a test board made from a wood plastic composite material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 12, the test board has split along its width.
  • FIG. 13 is a photograph illustrating pallet failure mode 5 for a conventional bottom deck structure having a test board made from OPC material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 13, a top deck of the pallet has separated from the spacer blocks.
  • FIG. 14 is a photograph illustrating pallet failure mode 2 for a bottom deck sub-assembly using a welded shiplap joint and having a test board made from an OPC material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 14, several of the nails coupling the test board to the spacer block have been pulled out of the spacer blocks, but the shiplap joint between the bottom deck boards is of sufficient strength to inhibit removal of the test board from the pallet by hand or with the use of hand tools.
  • FIG. 15 is a photograph illustrating pallet failure mode 2 for a bottom deck sub-assembly using a mechanical joint and having a test board made from an OPC material in which the test board is coupled with a spacer block by a plurality of nails. In FIG. 15, several of the nails coupling the test board to the spacer block have been pulled out of the spacer blocks, but the mechanical joint between the bottom deck boards is of sufficient strength to inhibit removal of the test board from the pallet by hand or with the use of hand tools.
  • DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION Terms
  • “Solid state” refers to a polymer (or polymer composition) that is below the softening temperature of the polymer (or polymer composition). Hence, “solid state drawing” refers to drawing a polymer or polymer composition that is below the softening temperature of the polymer (or polymer composition). “Solid state die drawing” refers to drawing a polymer or polymer composition that is below its softening temperature through a shaping die.
  • “Polymer composition” comprises at least one polymer component and can contain non-polymeric components. A “filled” polymer composition includes discontinuous additives, such as inorganic or organic fillers.
  • An “orientable polymer” is a polymer that can undergo induced molecular orientation by solid state deformation (for example, solid state drawing). An orientable polymer can be amorphous or semi-crystalline (semi-crystalline polymers have a melt temperature (Tm) and include those polymers known as “crystalline”). Desirable orientable polymers include semi-crystalline polymers, and in particular, linear polymers (polymers in which chain branching occurs in less than 1 of 1,000 polymer units). Semi-crystalline polymers can be particularly desirable because they can result in greater increase in strength and flexural modulus than amorphous polymer compositions. Semi-crystalline polymer compositions can result in 4-10 times greater increase in strength and flexural modulus upon orientation over amorphous polymer compositions.
  • An “orientable polymer phase” is a polymer phase that can undergo induced molecular orientation by solid state deformation (for example, solid state drawing). Typically, 75 wt % or more, even 90 wt % or more or 95 wt % or more of the polymers in the orientable polymer phase are orientable polymers based on total orientable polymer phase weight. All of the polymers in an orientable polymer phase can be orientable polymers. An orientable polymer phase may comprise one or more than one type of polymer and one or more than one type of orientable polymer.
  • “Oriented polymer composition article”, “OPC” and “oriented polymer composition” are interchangeable and refer to an article made by orienting the polymers of a polymer composition. An oriented polymer composition comprises polymer molecules that have a higher degree of molecular orientation than that of a polymer composition extruded from a mixer.
  • “Weight-percent” and “wt %” are interchangeable and are relative to total polymer weight unless otherwise stated.
  • “Softening temperature” (Ts) for a polymer or polymer composition having as polymer components only one or more than one semi-crystalline polymer is the melting temperature for the continuous phase polymer in the polymer composition.
  • “Melting temperature” (Tm) for a semi-crystalline polymer is the temperature half-way through a crystalline-to-melt phase change as determined by differential scanning calorimetry (DSC) upon heating a crystallized polymer at a specific heating rate. Tm for a semi-crystalline polymer can be determined according to the DSC procedure in ASTM method E794-06. Tm for a combination of polymers, and for a filled polymer composition, can also be determined by DSC using the same test conditions in ASTM method E794-06. If the combination of polymers or filled polymer composition only contains miscible polymers and only one crystalline-to-melt phase change is evident in the a DSC curve, then Tm for the polymer combination or filled polymer composition is the temperature half-way through the phase change. If multiple crystalline-to-melt phase changes are evident in a DSC curve due to the presence of immiscible polymers, then Tm for the polymer combination or filled polymer composition is the Tm of the continuous phase polymer. If more than one polymer is continuous and they are not miscible, then the Tm for the polymer combination or filled polymer composition is the highest Tm of the continuous phase polymers.
  • “Softening temperature” (Ts) for a polymer or polymer composition having as polymer components only one or more than one amorphous polymer is the glass transition temperature for the continuous phase of the polymer composition.
  • If the semi-crystalline and amorphous polymer phases are co-continuous, then the softening temperature of the combination is the lower softening temperature of the two phases. If the polymer composition contains a combination of semi-crystalline and amorphous polymers, the softening temperature of the polymer composition is the softening temperature of the continuous phase polymer of the polymer composition.
  • “Glass transition temperature” (Tg) for a polymer or polymer composition is the temperature half-way through a glass transition phase change as determined by DSC according to the procedure in ASTM method D3418-03. Tg for a combination of polymers and for a filled polymer composition can also be determined by DSC under the same test conditions in D3418-03. If the combination of polymer or filled polymer composition only contains miscible polymers and only one glass transition phase change is evident in the DSC curve, then Tg of the polymer combination or filled polymer composition is the temperature half-way through the phase change. If multiple glass transition phase changes are evident in a DSC curve due to the presence of immiscible amorphous polymers, then Tg for the polymer combination or filled polymer composition is the Tg of the continuous phase polymer. If more than one amorphous polymer is continuous and they are not miscible, then the Tg for the polymer composition or filled polymer composition is the highest Tg of the continuous phase polymers.
  • If the polymer composition contains a combination of semi-crystalline and amorphous polymers, the softening temperature of the polymer composition is the softening temperature of the continuous phase polymer or polymer composition.
  • “Drawing temperature” refers to the temperature of the polymer composition as it begins to undergo drawing in a solid state drawing die.
  • “Linear Draw Ratio” is a measure of how much a polymer composition elongates in a drawing direction (direction the composition is drawn) during a drawing process. Linear draw ratio can be determined while processing by marking two points on a polymer composition spaced apart by a pre-orientated composition spacing and measuring how far apart those two points are after drawing to get an oriented composition spacing. The ratio of final spacing to initial spacing identifies the linear draw ratio.
  • “Nominal draw ratio” is the cross sectional surface area of a polymer composition as it enters a drawing die divided by the polymer cross sectional area as it exits the drawing die.
  • An OPC is “similar” to another OPC if its composition is substantially the same as the other OPC in all respects except those noted in the context where the similar OPC is referenced. Compositions are substantially the same if they are the same within reasonable ranges of process reproducibility.
  • “ASTM” refers to ASTM International, formerly American Society for Testing and Materials; the year of the method is either designated by a hyphenated suffix in the method number or, in the absence of such a designation, is the most current year prior to the filing date of this application.
  • “Multiple” means at least two.
  • “And/or” means “and, or as an alternative.”
  • Ranges include endpoints unless otherwise stated.
  • Temperatures are given in degrees Celsius, abbreviated as “C” unless otherwise stated.
  • Flexural modulus (modulus of elasticity (MOE)) and flexural strength (modulus of rupture (MOR)) are measured according to ASTM method ASTM D-6109-05, “Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastic Lumber and Related Products.” Per ASTM D-6109-05, a force versus displacement under a four point bending load is measured. The force versus displacement curve is converted to a stress versus strain curve and the MOE and MOR are subsequently determined from the curve according to the methods set forth in ASTM D-6109-05.
  • Density is measured according to ASTM method ASTM D-792-00.
  • “Block”, “spacer”, and “spacer block” are used herein interchangeably. A block is a rectangular, square, multisided, or cylindrical deck spacer, often identified by its location within the pallet as corner block, end block, edge block, inner block, or center or middle block.
  • A “deck board” is a pallet element or component of a pallet top or bottom, perpendicular to stringers or stringer boards.
  • “Stringer and “stringer board” are used interchangeably herein. A stringer is a continuous, longitudinal, solid, built up, or notched beam component of a pallet, supporting and spacing deck components, often identified by its location as edge (side) or interior (center) stringer.
  • “Spacer member” refers to the pallet member which directly or indirectly couples the top deck boards to the bottom deck boards. In some cases, the spacer member may be in the form of a stringer board which couples the top deck boards together and through which the bottom deck boards are coupled with the top deck to form the assembled pallet. The stringer boards may also reinforce the pallet structure. A stringer pallet is an example of such a configuration. Alternatively, the spacer member may be in the form of blocks which are used to couple the top deck and the bottom deck together. An example of this type of configuration is a block pallet. It is also within the scope of the invention for a combination of stringer boards and blocks to be used to form the pallet. An example of this type of configuration is also sometimes referred to as a block pallet in which one or more stringer boards are used to couple the top deck boards together and a plurality of blocks are coupled with the stringer boards and the bottom deck boards to form the assembled pallet. The spacer members can also provide space between a top deck and a bottom deck of a pallet to allow entry of the forks of a forklift to lift and move the pallet.
  • “Gang nail”, “gang nail plate”, “gang nail connector plate”, “mending plate” and “truss plate” are used interchangeably and refer to a sheet of galvanized steel, with pointed prongs that are cut and bent perpendicular to a plate face of the gang nail, allowing it to be hammered or pressed into a number of surfaces simultaneously. The prongs are often of triangular shape and the gang nail typically has several prongs or teeth per square inch of plate.
  • A “corrugated fastener” is a thin strip of sheet metal that has a pattern of alternating grooves and is typically made from 18 to 22 gauge sheets of stainless or cold-rolled steel. Typically, increased joint strength is observed as the number of corrugated fasteners used to fasten a joint is increased. Also, typically, if two or more corrugated fasteners are used in a given joint, improved joint strength is observed when they are placed so that they are not parallel to one another.
  • “Readily deconstructed” in the context of a pallet assembly means that a worker using his hands and/or unpowered hand tools, e.g., a claw hammer, can remove a pallet board that has been damaged in less than 5 minutes, and still continue to use the pallet assembly without the damaged, removed portion. Damage can include damage to the board itself or damage to the connection between the board and one or more parts of the pallet assembly, such as damage to one or more fasteners, pull through of a fastener, and/or pull out of a fastener. Removal of the damaged portion of the pallet assembly may include removal of adjacent portions that were not damaged.
  • A wood pallet can be any of those described as wood pallets in Uniform Standard for Wood Pallets”, Copyright 2012, National Wooden Pallet and Container Association (referred to herein as the “NWPCA bulletin”), Alexandria, Va. 22314-2805, but is not limited to these pallet designs, especially when pallets are designed for geographies other than North America. A top deck of a pallet can consist of one or more than one deck board transverse to the length direction of the pallet. A bottom deck can be a single board with wheel openings or, preferably, can have 3 or more often up to 5 boards, while still leaving space for a pallet jack to enter and lift a pallet. Between the top deck and the bottom deck are spacers that may be stringers, as is common in two-way entry pallets, or spacer blocks as is typical in four way entry pallets, or a combination of stringers and spacer blocks. A non-limiting list of suitable natural wood species can be found in Annex B, Wood Species Classes, “Uniform Standard for Wood Pallets”, Copyright 2012, NWPCA.
  • Four-way entry pallets include a top deck, a bottom deck and spacer members. The top deck of a pallet, in some instances may be constructed of a single deck board, but more typically consists of two or three or more deck boards and in some cases can consist of as many as nine or more deck boards. The top deck typically includes a pair of end boards (also referred to as lead boards) and a plurality of intermediate load supporting deck boards. The bottom deck is provided with a relatively large surface area, but with openings to accommodate the wheels of a transport apparatus (e.g. pallet jack).
  • In a conventional block pallet, the top and bottom decks are separated by means of spacer members which can include longitudinally extending stringers and/or mounted spacer blocks, often of wood, laminated wood layers (plywood) or a wood composite material. The spacer blocks can be square in horizontal cross-section, but are more typically rectangular so that the bottom perimeter deck board can be attached to the blocks. Typically, nine blocks are installed at the corners of the pallet and intermediately of the end and side members to provide access to all four sides of the pallet by the forks of a forklift or hand transport (pallet jack). The spacer bocks need not be all of the same size, although the blocks are usually the full width of the members that overlay them.
  • FIGS. 1-2 illustrate the construction of a conventional four-way entry pallet 10. The block pallet 10 includes a top deck 12 which is adapted to support the articles which are placed on the pallet 10 and a bottom deck 14. The top deck 12 includes a plurality of deck boards 20 a-g supported by a plurality of stringer boards 18, which are supported by a plurality of spacer members in the form of end blocks 16 and intermediate blocks 17. The block pallet 10 has a length 21 and a width 22 which may be the same or different. Preferably the stringer boards 18 have a width 23 that is the same as a width 24 of the blocks 16, with the stringer boards 18 extending across the full width 22 of the pallet 10. The end blocks 16 and the intermediate blocks 17 can have the same or different dimensions. In the pallet 10 of FIG. 1, the end blocks 16 and intermediate blocks 17 are illustrated as having the same width 24 with the end blocks 16 having a length 25 that is greater than the width 24. The length 26 of the intermediate blocks 17 can be the same as the width 24 or any other suitable length smaller or greater than the width 24.
  • The deck boards 20 a-g are provided at right angles to the stringer boards 18 and extend for the full length 21 of the pallet 10. The two deck boards 20 a and 20 g located at the outside opposite edges of the pallet 10 are commonly referred to as lead boards or end boards. The top deck 12 can include any number of deck boards 20 a-g that are all the same width or of different widths. As illustrated in FIG. 1, a center deck board 20 d can have the same or a different width than the lead boards 20 a and 20 g. The center deck board 20 d may correspond to the deck board provided in the middle of an equal number of deck boards on either side and/or may correspond to the deck board which is aligned with the intermediate blocks 17. The intermediate deck boards 20 b-c and 20 e-f can be of the same or different widths and the number and width of the deck boards 20 a-g can be selected so as to provide a desired gap or space 27, or lack thereof, between adjacent deck boards 20 a-g. As illustrated in FIG. 1, in some cases the deck boards 20 b, 20 f adjacent to the lead boards 20 a, 20 g typically abut the lead boards 20 a, 20 g such that little to no space is provided between deck boards 20 b, 20 f and lead boards 20 a, 20 g, respectively.
  • The pallet 10 can be constructed manually or can be constructed using machines built for that purpose. In one illustrative method of constructing a pallet, the top deck 12 of FIG. 1 can be assembled by laying out the nine blocks 16 and 17 so that the length dimension 25 is aligned lengthwise with the stringer boards 18. Then the stringer boards 18 are placed on the blocks 16, 17 at the correct positions followed by deck boards 20 a-g in the arrangement shown in FIG. 1. The lead boards 20 a, 20 g can be attached to the corner end blocks 16 with fasteners 32 through the stringer boards 18. Next, the center deck board 20 d is attached to the three intermediate blocks 17 with fasteners 32 through the stringer boards 18 to provide a top deck 12 and spacer pallet assembly 33. The top deck 12 includes the lead boards 20 a, 20 g, the center deck board 20 d, and the intermediate boards 20 b-c, e-f, while the spacer pallet assembly 33 includes the end blocks 16, the intermediate blocks 17, and the stringer boards 18. The fasteners 32 used to fasten the top deck boards 20 a-g to the blocks 16, 17 are typically longer than those used to fasten the top deck boards 20 a-g at positions at which there are no spacer blocks 16, 17. The most common prior art block pallets constructed for use as returnable pallets comprise wooden boards and all wood or wood-composite blocks and use nails or screws as fasteners. Typical fasteners are nails of the types described in the NWPCA bulletin and include nails and wire staples. However, screws can be used to give added strength. Nails are typically driven using a nail gun of any of the types known in the art. A portion or all of the assembly process can be automated to facilitate uniform placement of the fasteners and to reduce labor costs. The type and number of fasteners used can affect the strength of the pallet assembly. However, using more fasteners can also make the pallet more costly for little additional benefit in use.
  • FIG. 2 illustrates the bottom deck 14 of the conventional wooden block pallet 10 of FIG. 1. The bottom deck 14 comprises a pair of bottom deck edge boards 34 which extend along the width 22 of the pallet 10, and are typically of the same width as the width 24 of the end blocks 16, and a pair of bottom deck lead boards 29. The bottom deck lead boards 29 typically have a width 30 that is less than the length dimension 25 of the end blocks 16 to provide enough surface on the end block 16 to also fasten the bottom deck edge boards 34 to the end block 16 adjacent the bottom deck lead boards 29. The bottom deck 14 also includes a bottom center deck board 31 which is typically of the same width as the intermediate block 17 and is parallel to the bottom deck edge boards 34 and spans a gap between the bottom deck lead boards 29. In some pallet constructions, an additional board (not shown in the figure) can be fastened to the intermediate blocks 17 between the bottom deck edge boards 34 and midway between the bottom deck lead boards 29.
  • In one illustrative method of fastening the bottom deck 14 to the top deck 12 and spacer pallet assembly 33, the top deck 12 and spacer pallet assembly 33 are positioned so that the top deck 12 is facing toward a floor or work table surface with the spacer pallet assembly 33 facing upward. The bottom deck boards 34, 29, 31 are laid out on the top deck 12 and spacer pallet assembly 33 with the bottom deck lead boards 29 positioned above the top deck lead boards 20 a, 20 g and the edge boards 34 and bottom center deck board 31 positioned above the stringer boards 18. The bottom deck boards 34, 29, 31 can be fastened using fasteners 42 to the top deck 12 and spacer assembly 33. In this construction, a thickness of the bottom deck 14 is typically as thick as a single bottom deck board 34, 29, 31.
  • A source of damage to pallets can arise when, in certain instances, the forks of a forklift truck or pallet jack make contact with the lead boards 20 a, 20 g or 29 of the top deck 12 or bottom deck 14, respectively, and/or block members 16 or 17 during insertion of the forklift into the pallet 10 for lifting. If the force is significant, the lead boards 20 a, 20 g, 29 and/or block members 16, 17 can be damaged. A number of suggestions have been made to reduce damage to lead boards for upper decks, including end-caps or protective parts for the access end of the pallet, multi-ply laminated boards (e.g. U.S. Publication No. 2011/0005435 to Renck et al.), pultruded boards (e.g. U.S. Publication No. 2006/0081158 to Ingham), and energy absorbing structures for the lead boards (U.S. Pat. No. 8,261,673 to Ingham).
  • Because a pallet jack operates differently than does a forklift, a pallet jack, unlike a forklift, has forks that serve as a base and also includes wheels. Thus, an additional opportunity for pallet damage is possible when a pallet jack is used to transport a pallet. In order to lift a pallet with a pallet jack the fork is wheeled into the inner space of the pallet and then lifted, typically, hydraulically. FIG. 3 illustrates the correct positioning of a pallet jack 50 with wheels 51 aligned in the spaces of the bottom deck 14 between the edge boards 34 and the bottom center deck board 31. Hitting or running into the bottom deck lead boards 29 can damage the bottom deck lead boards 29 in a manner similar to that described above for the top deck lead boards 20 a, 20 g of the pallet 10.
  • Referring now to FIG. 4, damage can also occur on the bottom deck 14 of the pallet 10 when the pallet jack 50 is inserted into the pallet 10 incorrectly. If the wheels 51 of the pallet jack 50 are sitting on one of the bottom deck lead boards 29 when the pallet jack 50 is activated to raise the forks 52 against the top deck lead board 20 a, the action of the hydraulic pallet jack 50 can force the top deck lead board 20 a away from the bottom deck lead board 29, potentially pulling the top deck lead board 20 a away from the blocks 16, 17. Alternatively, this action of the pallet jack 50 can result in splitting or cracking of the bottom deck lead boards 29 and/or the top deck lead boards 20 a, 20 g. Both of these damage mechanisms can lead to loss of the entire bottom deck lead board 29 and/or the top deck lead boards 20 a, 20 g.
  • When the pallet 10 is entirely constructed of relatively cheap materials, for example, boards from wood species such as pine or oak, damage can be cost effectively managed by deconstructing the damaged portion of the pallet 10 and replacing the damaged or lost board with another board of the same relatively cheap material. However, when pallets 10 are constructed of more expensive materials, deconstructing the damaged portion of the pallet 10 and replacing the damaged or lost board with another board of the same, more expensive material, may not be cost effective. For example, in order to mitigate lead board damage, more expensive materials, such as a laminated board or a pultruded composite board, can be used to form the lead board. However, when this more expensive lead board does get damaged and needs replacement or becomes lost, the replacement costs compared to more economic wood boards of oak or pine can become economically unfeasible and thus can make these more expensive materials undesirable for use, even though the more expensive materials can make the lead board more resistant to damage.
  • The embodiments of the invention described herein provide a bottom deck sub-assembly in which each bottom deck board is coupled to an adjacent bottom deck board and wherein at least the bottom deck lead boards are made from a fiber filled thermoplastic or oriented plastic composite material. The fiber filled thermoplastic or oriented plastic composite provides an increase in impact strength of the deck boards as determined by the constrained impact test described herein compared to conventional deck board materials made of wood or wood plastic composite materials. The deck boards of the sub-assembly can also be coupled with one another to provide a predetermined joint strength to inhibit separation of a bottom deck board from the sub-assembly. The joint strength can be selected such that a joint strength of the bottom deck board joints is greater than a joint strength between the bottom deck sub-assembly and the spacer members. Alternatively, or additionally, the bottom deck board joint strength can be selected to prevent or minimize the likelihood that a damaged bottom deck board is readily deconstructed and separated from the adjacent bottom deck boards by hand and/or using unpowered hand tools, or even using some predetermined powered tools. The bottom deck sub-assembly described herein can minimize problems associated with bottom deck lead board damage, subsequent loss of that board, and the need to replace the expensive lead board when damaged, as described above for the conventional pallet 10. The bottom deck sub-assembly can also, with some types of pallet manufacturing equipment, simplify the overall pallet assembly process.
  • As used herein, the bottom deck sub-assembly refers to a pair of bottom deck lead boards coupled to one another through at least one additional board. In an exemplary embodiment, the bottom deck sub-assembly includes a pair of bottom deck lead boards coupled with a pair of bottom deck edge boards and/or a center board. It is also within the scope of the invention for the sub-assembly to optionally include additional boards coupled with the lead boards and/or the edge or center boards. It is also within the scope of the invention for the bottom deck sub-assembly to be provided as a unitary sub-assembly in which each bottom deck board is coupled with the adjacent bottom deck board independent of the coupling of the bottom deck with the top deck. When provided as a unitary sub-assembly, the bottom deck sub-assembly can be pre-assembled and then coupled to a top deck of a pallet as a single unit. While the bottom deck sub-assembly is described in the context of the conventional pallet 10 having a top deck 12 and spacer blocks 16, 17, the bottom deck sub-assembly described herein can be used with any type of pallet having a top deck and spacer members in the form of blocks and/or stringers, or any other type of spacer member, and may be configured for use with any type of pallet, non-limiting examples of which include two-way, four-way, or euro pallets. While the four-way entry pallet 10 is illustrated as a block pallet in which the spacer members include a combination of stringers and spacer blocks, it is also within the scope of the invention for the four-way entry pallet 10 to be in the form of a stringer pallet in which the spacer members are in the form of stringers and which may also include openings for side entry of a pallet transportation device. It is also within the scope of the invention for the pallet 10 to be a two-way block or two-way stringer pallet.
  • Referring now to FIG. 5, a bottom deck sub-assembly 100 includes a pair of bottom deck lead boards 102 coupled with a pair of bottom deck edge boards 104 and a bottom deck intermediate board 106, in this case a single center board, by fasteners 108. The bottom deck sub-assembly 100 may optionally include additional intermediate deck boards (not shown) positioned between the bottom deck edge boards 104 and spanning the distance between the bottom deck lead boards 102, depending on the intended use of the bottom deck sub-assembly 100.
  • The fastener 108 may be any type of mechanical fastener, non-limiting examples of which include corrugated fasteners, truss plates, connector plates, particularly truss plates of the gang nail type, or any other type of fastening or fasteners know in the art to give strength to a joint between two adjacent boards. The fasteners 108 may be applied in any orientation with respect to the direction of orientation, grain or fiber direction of the deck boards 102, 104, and 106. A desired joint strength may be engineered by using gang nails and by choosing the number of prongs per unit area, the total area of the gang nail, the type of metal used, and the size of the prong. These fasteners 108 provide great joint strength and are not readily removed so that the bottom deck sub-assembly 100 cannot be readily deconstructed when gang nail-type fasteners are used. As illustrated in FIG. 5, the fasteners 108 can be in the form of truss plates, preferably made from galvanized steel, which bridge the joint between the bottom deck edge boards 104 and the bottom deck center board 106 at each end with the bottom deck lead boards 102. The fastener 108 can be applied to the joint between deck boards on a bottom face of the deck board, i.e. the face adjacent the surface upon which the assembled pallet 100 rests, and/or on an upper face of the deck board, opposite the bottom face, which is adjacent an interior of the assembled pallet.
  • The dimensions of the bottom deck sub-assembly 100 can be selected based on the dimensions of the top deck to which the bottom deck sub-assembly 100 is to be coupled. For example, as illustrated in FIG. 6, the dimensions of the bottom deck sub-assembly 100 can be configured to correspond to the top deck 12 and spacer blocks 16, 17 of the conventional pallet 10 of FIG. 1. The bottom deck sub-assembly 100 can be secured to the top deck 12 through the spacer blocks 16, 17 using any suitable fastening system, such as screws or nails, to form a hybrid pallet 110.
  • The bottom deck sub-assembly 100 can be used with any type of pallet, such as a two-way or four-way block pallet (see for example block pallet 10 of FIG. 1) or stringer pallet. The bottom deck sub-assembly 100 can be coupled with top deck boards through a spacer member, such as one or more blocks and/or stringers to form the assembled hybrid pallet. The spacer members can be made of any material known in the pallet art, including wood composite materials, plywood and wood of various species. Preferred spacer members comprise wood, particularly pine or oak, for pallets in which the bottom deck sub-assembly 100 is mechanically fastened to the spacer members using nails or screws. The material and dimensions for the spacer members and the size, type, and number of fasteners can be selected to provide the desired joint strength between the bottom deck sub-assembly 100 and the spacer members.
  • The top deck boards of the hybrid pallet 110 which may be used with the bottom deck sub-assembly 100 may be any known in the art, such as the top deck boards 20 a-g of the block pallet 10 of FIG. 1, and can include one or more boards spanning the area of the top deck. Where multiple boards span the top deck, it is preferred that the lead board be of a damage resistant construction. A particularly preferred lead board is a fiber filled thermoplastic or OPC lead board, similar to that used for the bottom deck sub-assembly 100, as is described in more detail below. The remaining boards of the top deck may be any known in the art, especially any species of wood or wood plastic composite suitable for pallets.
  • FIGS. 7A-7B illustrate a second embodiment of the invention comprising a bottom deck sub-assembly 200 that is similar to the bottom deck sub-assembly 100, except for the manner in which the sub-assembly 200 is assembled. Therefore, elements in the bottom deck sub-assembly 200 similar to those of the bottom deck sub-assembly 100 are numbered with the prefix 200. As illustrated in FIG. 7A, the bottom deck edge boards 204 and the bottom deck center board 206 are coupled at each end with the bottom deck lead boards 102 through a shiplap joint 220, also sometimes referred to as a rabbet joint.
  • Referring now to FIG. 7B, the shiplap joints 220 are formed by machining a surface of the bottom deck lead boards 202 to form lead board joint portions 222 in which a thickness of the bottom deck lead boards 202 is reduced. Corresponding joint portions 224 can be machined into the bottom deck edge boards 204 and the bottom deck center board 206 and the lead board joint portions 222 can be overlapped with the joint portions 224 to form the shiplap joints 220. In a preferred embodiment the joint portions 222 and 224 are machined into the respective boards 202, 204, and 206, to decrease a thickness of the boards 202, 204, and 206 by one-half. In this manner a total thickness of the shiplap joints 220 is the same as a thickness of the adjacent deck boards 202, 204, and 206 forming the shiplap joint 220. Alternatively, rather than reducing a thickness of each of the deck boards 202, 204, and 206 forming the shiplap joint 220 equally, the deck boards 202, 204, and 206 forming each shiplap joint 220 can be reduced in thickness unequally. For example, the thickness of the bottom deck lead board 202 can be reduced by one-third to form the lead board joint portion 222 while the thickness of the bottom deck edge boards 204 and the bottom deck center board 206 can be reduced by two-thirds to form the corresponding joint portions 224. The thus formed shiplap joint 220 will still have a total thickness equal to the thickness of the adjacent deck boards 202, 204, and 206 forming the shiplap joint 220.
  • The bottom deck lead board 202 can be coupled with the bottom deck edge boards 204 and the bottom deck center board 206 at the shiplap joint 220 by causing the joint portions 222 and 224 to adhere to one another using any suitable non-mechanical fastener. Non-limiting examples of non-mechanical fastener joining include solvent welding, solvent based adhesives and thermal welding. A particularly preferred adhesive joint is an overlapping joint of the shiplap type where the overlapping faces are thermally welded. For example, the joint portion 222 and/or the joint portion 224 can be heated to melt the surface of the joint portion 222 and/or the joint portion 224 and the joint portions 222 and 224 can be overlapped and pressure applied to form the joint 220. In another example, the joint portion 222 and/or the joint portion 224 can be provided with an adhesive, such as a solvent-based adhesive, to adhere the joint portion 222 to the joint portion 224. In yet another example, the joint portions 222 and 224 can be adhered using an ultrasonic weld.
  • It is also within the scope of the invention for the bottom deck lead board 202 to be coupled with the bottom deck edge boards 204 and the bottom deck center board 206 by a butt weld, which can include solvent welding, solvent based adhesives, or thermal welding, for example.
  • Similar to the bottom deck sub-assembly 100, the dimensions of the bottom deck sub-assembly 200 can be selected based on the dimensions of the top deck to which the bottom deck sub-assembly 200 is to be coupled with. For example, as illustrated in FIG. 8, the dimensions of the bottom deck sub-assembly 200 can be configured to correspond to the top deck 12 and spacer blocks 16, 17 of the conventional pallet 10 of FIG. 1. The bottom deck sub-assembly 200 can be secured to the top deck 12 through the spacer blocks 16, 17 using any suitable fastening system, such as screws or nails, to form a hybrid pallet 210. Alternatively, as described above with respect to the bottom deck sub-assembly 100, the bottom deck sub-assembly 200 can be used with any suitable top deck and spacer members, such as blocks and/or stringers, to form a hybrid pallet 210.
  • It is also within the scope of the invention for the bottom deck sub-assembly to be assembled using a combination of the fastener 108 of the bottom deck sub-assembly 100 of FIG. 5 and the shiplap type joint 220 of the bottom deck sub-assembly 200 of FIG. 7A to provide the desired joint strength between the boards of the bottom deck sub-assembly.
  • The bottom deck sub-assembly 100, 200 consists of fiber filled thermoplastic or oriented plastic composite boards in at least the lead board position 102, 202 and is assembled with mechanical fasteners (bottom deck sub-assembly 100) or adhesive fastening (bottom deck sub-assembly 200) to provide the bottom deck subassembly 100, 200. The bottom deck edge boards 104, 204 and bottom deck center board 106, 206 can be made of the same or different material than the bottom deck lead boards 102, 202. In one example, the bottom deck edge boards 104, 204 and/or the center board 106, 206 can also be made from a fiber filled thermoplastic or oriented plastic composite material to provide these boards with protection against damage from a forklift or pallet jack. Alternatively, the bottom deck edge boards 104, 204 and/or the center board 106, 206 can be of wood of any suitable species, such as pine or oak, or a wood composite material.
  • The bottom deck sub-assembly 100, 200 can be entirely or partially made from fiber filled thermoplastic boards or OPC boards. The fibrous filler in the fiber filled thermoplastic is believed to improve the impact resistance and break strength of such boards making them suitable in the lead board position. Any fiber filler known in the art is useful, including but not limited to naturally occurring fibers, such as flax or bamboo, glass fiber, carbon fiber, polyester fiber, aramid fiber and the like. In general, longer fibers provide a greater impact resistance than shorter fibers.
  • OPC refers to an article made by orienting the polymers of a polymer composition and comprises polymer molecules that have a higher degree of orientation than that of a polymer composition extruded from a mixer. OPC boards are OPC articles in the shape of boards with a length, a thickness, and a width wherein the cross-sectional shape is substantially rectangular. OPC boards can be produced using a solid state die drawing process which elements are described in U.S. Pat. No. 8,142,697 to Nichols et al. and in U.S. Pat. No. 8,871,130 to Nichols et al., the contents of which are incorporated herein by reference in their entirety. For use in pallets, the length, width and thickness can be any dimensions suitable for the desired pallet design. Standard pallets dimensions depend on the geography, and industry of use. For example, the length can vary from 600 mm to 1200 mm and the width can vary from 400 mm to 1200 mm. European pallets typically require deck boards of 1000 mm length, but may be as short as 600 mm.
  • Suitable oriented plastic composite (OPC) boards may be made by the following process. Selected plastics materials and additives are introduced to an extruder and, after processing in the extruder, are extruded through a die and calibrator to produce a hot billet (extrudate) of the extruded material which is moved by a puller to a temperature conditioning stage, where the material is cooled below its softening temperature Ts. The cooled extrudate is then drawn, using a puller, in a solid state die draw stage through a solid state drawing die at a drawing temperature that aligns the long chains of the polymer in the lengthwise direction of drawing and then cooled with a cooling tank to a cutting temperature to form a continuous OPC drawn piece. The OPC drawn piece is subsequently fed using pullers or other means to a saw, to cut the OPC drawn piece to a desired length to produce an OPC board. The OPC board may be later cut to a shorter length if desired.
  • As described above, an orientable polymer is a polymer that can undergo polymer alignment. Orientable polymers can be amorphous or semi-crystalline. Herein, “semi-crystalline” and “crystalline” polymers interchangeably refer to polymers having a melt temperature (Tm). While not meaning to be limited by any theory, polyolefins are believed to undergo cavitation in combination with filler particles, because polyolefins are relatively non-polar and as such adhere poorly to filler particles. Linear polymers (that is, polymers in which chain branching occurs in less than 1 of 1,000 monomer units such as linear low density polyethylene) are even more desirable.
  • Non limiting examples of suitable orientable polymers include polymers and copolymers based on polystyrene, polycarbonate, polypropylene, polyethylene (for example, high density, very high density and ultra-high density polyethylene), polyvinyl chloride, polymethylpentane, polyamides, polyesters (for example, polyethylene terephthalate) and polyester-based polymers, polycarbonates, polyethylene oxide, polyoxymethylene, and combinations thereof. A first polymer is “based on” a second polymer if the first polymer comprises the second polymer. For example, a block copolymer is based on the polymers comprising the blocks. Preferred orientable polymers include polymers based on polyethylene and polypropylene, examples of which include linear polyethylene having a weight average (Mw) or number average (Mn) from 50,000 to 3,000,000 g/mol; preferably from 100,000 to 1,500,000 g/mol; more preferably from 750,000 to 1,500,000 g/mol.
  • Polypropylene (PP)-based polymers (that is, polymers based on PP) are one example of a particularly preferred orientable polymer for use in the present invention. PP-based polymers generally have a lower density than other orientable polyolefin polymers and, therefore, facilitate lighter articles than other orientable polyolefin polymers. PP-based polymers also offer greater thermal stability than other orientable polyolefin polymers. Therefore, PP-based polymers, made by any of the means known in the art may also form oriented articles having higher thermal stability than oriented articles of other polyolefin polymers. Suitable PP-based polymers include PP homopolymer; PP random copolymer (with ethylene or other alpha-olefin present from 0.1 to 15 percent by weight of monomers); or PP impact copolymers. It is preferred to use a PP-based polymer that has a melt flow rate of greater than 0.3 g/10 min., preferably greater than 1 g/10 min., more preferably greater than 1.5 g/10 min., and even more preferably greater than 2 g/10 min., while at the same time having a melt flow rate of less than 8 g/10 min., preferably less then 6 g/10 min., more preferably less than 4 g/10 min., and even more preferably less than 3 g/10 min. It is also preferred to use a PP-based polymer that has 55% to 70%, preferably 55% to 65% crystallinity.
  • PP obtained from either industrial or commercial recycle streams, including filled or reinforced recycled PP, may be used. The recycled PP may range from 0 to 100% of the orientable polymer used in the orientable polymer composition.
  • PP can be ultra-violet (UV) stabilized, and desirably can also be impact modified. Particularly desirable PP can be stabilized with organic stabilizers. The PP can comprise titanium dioxide or be free of titanium dioxide pigment.
  • The oriented polymer composition can further comprise fillers, including organic fillers and inorganic fillers. OPC articles can have filler levels from 10 wt % up to 60 wt %. Organic fillers, because they are less dense than inorganic fillers can often be as low as 10 wt % and as high as 35 wt %, 40 wt % or even higher. Organic fillers can be cellulosic or synthetic polymers. Cellulosic fillers include cellulosic materials such as wood fiber, wood powder and wood flour and are susceptible, even within a polymer composition, to decomposition, mold and mildew when exposed to humidity. Furthermore, cellulosic fillers can harbor pests that can be problematic for use of a pallet in international use.
  • Fillers are preferably, inert inorganic fillers. Inorganic materials do not suffer from some of the challenges of organic fillers. Inorganic fillers are either reactive or inert. Inert fillers can be more preferred than reactive fillers in order to achieve a stable polymer composition density. However, inorganic fillers are generally denser than organic fillers. For example, inert inorganic fillers for use in the present invention typically have a density of at least two grams per cubic centimeter. Therefore, polymer compositions comprising inorganic fillers typically can contain more void volume than a polymer composition comprising the same volume of organic fillers in order to reach the same polymer composition density.
  • Non-limiting examples of inert inorganic fillers include talc, clay (for example, kaolin), magnesium hydroxides, aluminum hydroxides, dolomite, titanium dioxide, glass beads, silica, mica, metal fillers, feldspar, Wollastonite, glass fibers, metal fibers, boron fibers, carbon black, nano-fillers, calcium carbonate, and fly ash. Particularly desirable inert inorganic fillers include talc, calcium carbonate, magnesium hydroxide, or clay. The inorganic filler can comprise one, or a combination of more than one inorganic filler. More particularly, the inert inorganic filler can be any one inert inorganic filler or any combination of more than one inert inorganic filler. Embodiments of the invention can have 20 wt % or more, 25 wt %, 35 wt %, 45 wt %, 50 wt %, 55 wt % or more, or even 60 wt % filler. Embodiments in which the inorganic filler level is between about 40 wt % and 55 wt % are preferred because cavitation can increase and density decrease (void volume increases) as filler level increases in this range.
  • Solid state die drawing is different from extrusion, in which the material is pushed through a die in a hot, flowable state above the glass transition temperature Tg of the material, and pultrusion, where the material is both pushed and pulled. Solid state die drawing involves pulling the material having a softening temperature Ts at a temperature below its melt temperature Tm through a drawing die using drive rollers or drive tracks or belts (caterpillars) so that the material is under a state of tension and the die drawing occurs at a drawing temperature Td below the polymer composition softening temperature Ts. The drawing temperature Td is ten or more degrees below the polymer softening temperature, including, 15, 20, or even 30 degrees below Ts. Generally, the drawing temperature Td range is 40° C. or less below the polymer composition's Ts in order to achieve a linear draw ratio using economically reasonable draw rates. (Higher rates are preferred on economic grounds.) It is preferred to maintain the temperature of the polymer composition at a temperature within a range between the polymer composition's Ts and 50° C. below Ts inclusive of endpoints, while the polymer composition is drawn. Preferably, the polymer composition is cooled after exiting the drawing die prior to cutting to length. Subsequently, the board can be treated to provide a length dimension stable board.
  • Drawing causes the long polymer chains of the material to elongate (or straighten) and generally align in the direction of drawing. The individual polymer chains or groups of polymer chains can be somewhat entangled and also mechanically bonded to one another, giving the material great strength and toughness that can be greater than that of typical un-oriented plastic material or even some types of woods used to fabricate wood articles.
  • Fillers and additives can be incorporated with the orientable polymer to make an orientable polymer composition. Such fillers function as impediments to polymer chain alignment during solid state drawing and have the effect of introducing cavitation into the material as the polymer chains are forced to slide past and detach from the particles during their elongation. Such cavitation reduces the density of the composite polymer material. The filler particles can vary in size, shape and selection (blends). Other additives may include pigments, fire retardants, and other additives known in the art. Some of these fillers, such as fire retardants, may comprise hard particles and may have a beneficial dual purpose as both a fire retardant and as a portion of, or all, the filler constituent of the polymer composition if cavitation of the material is desired.
  • Generally, the extent of cavitation (that is, amount of void volume introduced due to cavity formation during orientation) is directly proportional to filler concentration. Increasing the concentration of inorganic filler, since it is typically of higher density than the matrix thermoplastic, increases the density of a polymer composition, but also tends to increase the amount of void volume resulting from cavitation in the oriented polymer composition. Particularly desirable embodiments of the present filled oriented polymer composition article have 25 volume-percent (vol %) or more, preferably 35 vol % or more, more preferably 45 vol % or more void volume and even 55 vol % or more based on total polymer composition volume.
  • Additional void volume may be created by the use of foaming agents, either exothermic or endothermic. Herein, “foaming agent” includes chemical blowing agents and decomposition products therefrom. Foaming agents include, but are not limited to moisture introduced as part of a filler, for example wood flour or clay, or by chemicals that decompose under the heating conditions of the billet extrusion process, Chemical blowing agents include the so-called “azo” expanding agents, certain hydrazide, semi-carbazide, and nitroso compounds, sodium hydrogen carbonate, sodium carbonate, ammonium hydrogen carbonate and ammonium carbonate, as well as mixtures of one or more of these with citric acid or a similar acid or acid derivative. Another suitable type of expanding agent is encapsulated within a polymeric shell. Blowing agent may be used up to at least 1.5 wt % blowing agent to achieve density reductions compared to an un-foamed billet of up to 20% or even more. Measure weight percent blowing agent relative to total oriented polymer composition weight.
  • Examples
  • The following examples illustrate embodiments of the present invention and not necessarily the full scope of the present invention. While the exemplary embodiments are described in the context of OPC materials, it will be understood that the scope of the invention is not limited to such materials, but may also include fiber filled thermoplastics. Fiber filled thermoplastics, particularly those that include longer fibers, such as long glass fibers, generally have high impact performance.
  • Description of Pallet Construction
  • Pallets were constructed similar to the conventional pallet 10 of FIGS. 1 and 2 and compared below with the hybrid pallets 110 and 210 constructed using the bottom deck sub-assembly 100 and 200 of FIGS. 5 and 7A, respectively, as described in more detail below. The exemplary hybrid pallets 110 and 210 described below include the bottom deck sub-assembly 100 and 200, respectively, coupled with the top deck 12 and spacer pallet assembly 33 of the conventional pallet 10 of FIGS. 1 and 2.
  • Test Top Deck Construction
  • The top deck 12 used in the comparisons was similar to that shown in FIGS. 1 and 2 except that five intermediate oak boards of thickness 0.688 inch (17.48 mm), width 3.5 inch (89 mm) and length 40 inch (1016 mm) were used between the lead boards, and four oak boards of thickness 0.688 inch (17.48 mm), width 5.5 inch (140 mm) and length 40 inch (1016 mm) oak boards were provided at the lead board positions 20 a, 20 g and adjacent to the lead board positions 20 b, 20 f. Three oak stringer boards 18 of thickness 0.688 inch (17.48 mm) width 5.5 inch (140 mm) and length 48 inch (1219 mm) were also used. At each corner and at the midpoint between the corners along the length 21 of the pallet were six spacer blocks 16 of height 3.5 inch (89 mm) width 5.5 inch (140 mm) and length 7.5 inch (190.5 mm) of either oak or treated pine as indicated in Table 3. At the midpoint between the blocks described above, in the width direction 22 of the pallet, are three spacer blocks 17 of height 3.5 inch (89 nm) width 5.5 inch (140 mm) and length 3.75 inch (95.25 mm) of either oak or treated pine as indicated in Table 3.
  • The top deck is assembled by laying the nine blocks 16, 17 on a fabrication surface so that the length dimension 25 of the larger blocks 16 lies in the direction of the width dimension 22 of the pallet. Then the stringer boards 18 are placed on the blocks 16, 17 at the correct positions followed by the lead boards 20 a, 20 g and the intermediate deck boards.
  • The top deck lead boards 20 a, 20 g are attached (fasteners 32) to each of the end blocks 16 with six 3 inch (75 mm) long, 0.120 inch (3.05 mm) diameter Grip Rite brand ring shank nails from Prime Source Building Products Inc. installed with a Hitachi NR90AE 3.5 inch strip nailer. The top deck center board 20 d is attached to each of the three interior smaller blocks 17 with three of these same type of nails. Two of these nails are also used wherever intermediate deck boards 20 b, 20 f overlapped the spacer blocks 16. The remaining nails 32 in the intermediate deck boards are 1.25 inch (31.8 mm) long, 0.090 inch (2.29 mm) diameter hot dipped galvanized ring nails purchased from CLS Metal Fasteners, Grand Rapids Mich., and were installed with a Bostich Model N66 Industrial siding nailer.
  • The conventional comparative bottom deck and the exemplary bottom deck sub-assemblies were created from several different materials and using several different assembly methods and coupled with the above described test top deck 12 through the stringer boards 18 and spacer members 16, 17 for comparison as described below.
  • Determination of Joint Strength of Mechanical Fasteners
  • Table 1 illustrates the joint strength in tension for exemplary fastening methods for the bottom deck sub-assemblies 100, 200. To determine the joint strength in tension, two OPC boards were joined using the mechanical fasteners as noted in Table 1. The boards were then placed in a mechanical testing device of the constant-rate-of-crosshead-movement type with one fixed member carrying a grip and one movable member carrying a second grip in a position such that the joint could be tested in tension. The grip area is 4.9 inches (12.45 cm) in length and the full width of the board being tested and has four beads of approximate height 0.0625 inches (1.58) running across the board in the board width direction. Each end of the boards making up the joint to be tested are secured in the grips by tightening eight bolts on each of the top and bottom grips, four on each of the grip plate edges. The boards were then pulled in tension at a rate of 1 inch/minute (2.54 cm/min.). The joint break force is determined at failure of the fastener, including pull-out or breakage of the fastener and is reported in Newtons. The results of that testing are shown in Table 1. When more than one joint of the same type is tested, the results are an average of the strength of the joints tested.
  • TABLE 1
    Methods for fastening bottom deck sub-assembly boards to one another
    Strength of Joint
    Method Short Form in Tension
    No. Description Description (Newtons)
    1 No attachment of one bottom deck board to another. Nailed only
    2 Attachment by truss plate* on the bottom face of the bottom Gang nail 11,180
    deck (as illustrated in FIG. 5) of the pallet at each joint bottom
    between bottom deck boards.
    3 Same as Method No. 2, except the side on which the truss Gang nail 11,180
    plates were attached differed in orientation with respect to the top
    top deck. The truss plates were facing the pallet interior.
    3a Same as Method No. 3, except the truss plates were smaller at Gang nail 3240
    each joint of the bottom deck sub-assembly.** top (A)
    4 Attachment by truss plates on both the top face and bottom face Gang nail 19460
    of the bottom deck boards of the pallet at each joint between Both
    bottom deck boards.
    5 Corrugated fasteners, 2 per joint, driven between the bottom Corrugated 600
    deck boards and aligned with the direction of orientation of the fastener
    bottom deck boards edge and center boards. The corrugated
    fasteners were ⅝ inch high 20 gauge corrugated steel.
    6 Lead, edge, and center deck boards of the bottom deck were Welded Not
    routed so as to provide an overlap for the full width of each determined
    board at the joint between the lead board and the bottom deck
    edge and center boards. The routed area on each board was
    heated to melt the polymer surface, and then the routed areas
    were pressed together to provide a welded joint. The joint area
    so welded was nominally 140 mm by 140 mm.
    *20 gauge galvanized steel truss plates produced by Mitek Building Products were used as follows: connecting the lead boards to the center board are 2 inch (5 cm) by 5 inch (12.5 cm) plates and connecting the lead boards to the edge boards are 3 inch (7.5 cm) by 4 inch (10 cm) plates; the truss plates were placed so that plate slots were aligned with the direction of orientation of the bottom deck edge and center boards.
    **20 gauge galvanized steel truss plates one inch (2.5 cm) by four inch (10 cm) at each joint.
  • The bottom deck lead boards for the conventional, comparative pallets, and the exemplary bottom deck sub-assembly were the same dimensions as the top deck lead boards and for each of the examples and the comparative examples was as indicated in Table 3. The bottom deck edge and center boards were of the material indicated in Table 3 of thickness 0.688 inch (17.48 mm) and width 5.5 inch (140 mm) and length 37 inch (940 mm). For the exemplary bottom deck sub-assemblies, the boards of the bottom deck were joined into a sub-assembly as described in Table 1, depending on the type of joint specified in Table 1.
  • The exemplary bottom deck sub-assembly was attached with fasteners to the top deck 12 through the spacer blocks 16, 17 with the Grip Rite 3 inch (76.2 mm) long, 0.120 inch (3.05 mm) diameter ring shank nails using the nail pattern shown in FIG. 2 for fasteners 42 to form the exemplary hybrid pallets. Specifically, the bottom deck lead boards had four nails in a square pattern in to each of the corner and mid-point larger spacer blocks 16. The bottom edge and center boards had four nails in a linear pattern in the larger end blocks 16 and three nails in a triangular pattern in to the smaller middle blocks 17 as shown in FIG. 2. The bottom deck lead boards for the conventional, comparative pallets were fastened to the spacer blocks 16, 17 using the same pattern illustrated in FIG. 2 to form the conventional, comparative pallets.
  • The conventional, comparative pallets and the exemplary hybrid pallets were tested using the pallet jack test procedure described below. Because each pallet consists of two bottom deck lead boards, two tests were performed on each pallet, one on each of the two bottom lead deck boards. The pallet jack was positioned and the hydraulic system was used to lift the top deck upward and away from the bottom deck. The pressure gauge on the pallet jack was monitored and the gauge reading was noted when failures occurred. During and after the test, the pallets were examined to determine which of the failure modes of Table 2 had occurred during the test. Results were recorded and are compiled in Table 3.
  • Pallet Jack Lift Test
  • The pallet jack lift test was performed on the comparative and exemplary hybrid pallets of Table 3 as follows. Place a pallet on the warehouse floor so that a pallet jack can be inserted in the entry position beneath one set of top and bottom deck lead boards. Place a second pallet, upon which a 1200 pound (545 kilogram) weight is loaded, on the top deck of the test pallet so that a front edge of the weighted pallet is aligned vertically with a front edge of the test pallet (i.e. the front edges of the lead boards of the weighted pallet are aligned with the front edge of the lead board to be tested). A pallet lift jack, equipped with a pressure gauge capable of measuring the pressure of the hydraulic system of the pallet jack is inserted into the test pallet so that the lead wheels of the pallet jack are centered on the bottom deck lead board to be tested, similar to the scenario illustrated in FIG. 4. When the forks are raised by the hydraulic system, the forks are aligned so that the top deck of the test pallet may be lifted away from the bottom deck of the test pallet. The forks are raised and the pressure gauge monitored until a bottom face of the center spacer block of the test pallet at the lead board test position is from 8 to 11.7 cm (3.2 to 4.7 inches off the floor). During the raising of the forks of the pallet jack, the pressure gauge reading is noted and the type of failure mode is recorded when any failure of the pallet is observed. During the test, as pallet failure occurs, the spacer blocks are lifted away from the floor and any portions of the top deck attached to the spacer blocks are also lifted from the floor. Because the wheels are resting on the lead board, as the forks lift the top dock, the lead board may flex and/or separate from the spacer blocks and eventually break or splinter in some cases. The break force is recorded as the breakage pressure based on the pressure gauge reading as shown in Equation 1:

  • Breakage Pressure (psi)=1072*Gauge reading (psi)−229.4  (Equation 1)
  • Equation 1 was determined by applying known weights to a pallet deck and recording the gauge reading required to lift the loaded pallet, fitting the resulting graph of actual load weight versus gauge reading to a straight line equation using a linear regression software program. The breakage pressure, i.e. the break force, can be converted from pounds per square inch (psi) to megapascals (Mpa).
  • Subsequent to the test, the bottom deck lead board which was tested was examined and the observations were recorded in Tables 3A and 3B according to the failure modes described in Table 2.
  • TABLE 2
    Pallet failure types - description of failure.
    Pallet
    Failure
    Mode Description
    1 Fastener head pulled through bottom deck board. In this
    failure mode at least one of the fasteners used to couple
    the lead board to the spacer blocks is at least partially
    pulled into or through the lead board. An example of
    this type of failure mode is illustrated in FIG. 9.
    2 Pull out of bottom deck board nails from the spacer
    blocks. In this failure mode at least one of the
    fasteners used to couple the lead board to the spacer
    blocks is fully or partially pulled out of the spacer
    block through the lead board. An example of this type
    of failure mode is illustrated in FIG. 10.
    3 Failure of deck board by breakage in the direction of the
    board length. If the board is made of wood or OPC, this
    corresponds to the wood or OPC grain direction; WPC does not
    have a grain. An example of this type of failure mode is
    illustrated in FIG. 11.
    4 Failure of deck board by breakage in the direction of
    board width. If the board is made of wood or OPC, this
    corresponds to the wood or OPC cross grain direction; WPC
    does not have a grain. An example of this type of failure
    mode is illustrated in FIG. 12.
    5 Failure of top deck board fastening. This failure mode
    is not a failure mode of the test lead board but of
    the top deck of the pallet. An example of this type of
    failure mode is illustrated in FIG. 13.
    6 This failure mode corresponds to the test lead board
    being damaged or loosened such that the test board
    separates from the spacer blocks or partially separates
    from the spacer blocks such that the test board is readily
    deconstructed (i.e. removed from the pallet by hand and/or
    unpowered hand tools). Test boards which failed according
    to failure modes 3 and 4 in which the integrity of the test
    board itself was damaged to such an extent that the test
    board would have to be removed in order to have an operable
    pallet are also considered to have failed according to
    failure mode 6.
  • Tables 3A and 3B illustrate the lift jack test breakage pressure and pallet failure mode results for pallets having a conventional or non-bottom deck sub-assembly structure and pallets having a bottom deck sub-assembly structure, respectively.
  • TABLE 3A
    Results of pallet jack lift test for conventional/non-
    bottom deck sub-assembly
    Assembly Lift Jack
    Exam- Spacer Bottom Method - Test Breakage Pallet
    ple block lead Short Pressure Failure
    No. material boards form* (MPa) Modes
    Wood Pine1 Pine1 Nailed only 16.9 3, 6
    Exam-
    ple 1
    WPC Oak2 WPC13 Nailed only 22.8 4, 6
    Exa-
    mple 1
    WPC Pine1 WPC13 Nailed only 22.5 4, 6
    Exam-
    ple 2
    WPC Oak2 WPC24 Nailed only 23.6 4, 6
    Exam-
    ple 3
    OPC Oak2 OPC15 Nailed only 35.4 2, 6
    Exam-
    ple 1
    OPC Oak2 OPC15 Nailed only 35.4 6
    Exam-
    ple 2
    OPC Oak2 OPC15 Nailed only 35.4 1, 2, 6
    Exam-
    ple 3
  • TABLE 3B
    Results of pallet jack lift test for exemplary
    bottom deck sub-assembly structure
    Assembly Lift Jack
    Exam- Spacer Bottom deck Method - Test Breakage Pallet
    ple block sub-assembly Short Pressure Failure
    No. material boards form* (MPa) Modes
    WPC Oak2 WPC13 Gang nail 28 2, 4, 6
    Exam- both
    ple 4
    WPC Oak2 WPC24 Gang nail 22.5/31.7 4, 6
    Exam- both
    ple 5
    WPC Pine1 WPC24 Gang nail 22.5 4, 6
    Exam- both
    ple 6
    Hybrid Pine1 OPC25 Gang nail 28.0 2
    Exam- bottom
    ple 1
    Hybrid Pine1 OPC25 Gang nail 28.0 2
    Exam- both
    ple 2
    Hybrid Pine1 OPC25 Gang nail 28.0 2
    Exam- top
    ple 3
    Hybrid Pine1 OPC15 Welded 34.3 1
    Exam-
    ple 4
    Hybrid Oak2 OPC15 Welded 38 2
    Exam-
    ple 5
    Hybrid Oak2 OPC15 Welded 28.7 2
    Exam-
    ple 6
    Hybrid Oak2 OPC25 Gang nail 35.4 1
    Exam- top (A)
    ple 7
    Hybrid Pine2 OPC25 Gang nail 28.0 2
    Exam- top (A)
    ple 8
    1Yellow pine is No 2 pine board, nominal 1 inch by 6 inch, purchased from Sequin Lumber, Bay City MI, and machined to the required dimensions for use in pallets.
    2Oak is pallet grade oak purchased from Hugo Brothers Pallet Manufacturing, Kawkawlin, MI
    3WPC1 is Veranda brand decking, a wood plastic composite manufactured by Fiberon from Home Depot. It was planed to a thickness of 0.688 inch (17.48 mm) specified for pallet boards and used at the purchased width of 5.375 inches (13.65 cm).
    4WPC2 is Azek brand decking, a cellular PVC/wood composite produced by Azek Building Products, a Division of CPG International, Scranton PA, USA. It was planed to a thickness of 0.688 inch (17.48 mm) specified for pallet boards and used at the purchased width of 5.375 inches (13.65 cm).
    5OPC1 and OPC2 are oriented plastic composite boards and are produced at the required thickness and width. The orientable composition base polymer is polypropylene Inspire 404 from Braskem, Philadelphia, PA and is filled with 48 wt % calcium carbonate No. 10 white.
    *Short form assembly method is defined in Table 1.
  • Table 3A compares the effect of different bottom deck board materials on the lift jack test breakage pressure and the pallet failure modes for conventional/non-bottom deck structures. Pallets having a conventional bottom deck structure made from wood or a wood plastic composite (WPC) material exhibited lower lift jack test breakage pressures than similar pallets made using an oriented polymer composition (OPC) material. As can be seen in Table 3A, all of the pallets having a conventional bottom deck structure in which the bottom decks boards are nailed to the spacer blocks and are not coupled with adjacent deck boards exhibited failure mode 6. In some cases, bottom decks boards can be damaged to such an extent, such as by breakage of the board itself, that the board needs to be removed and/or replaced in order for the pallet to remain operable.
  • In some failure modes, a board can be separated or loosened from the pallet, but the board itself is still usable. In these cases, and particularly when the boards are made of more expensive materials, it is more cost effective to reuse the separated or loosened board. In a pool pallet system, when a board becomes separated from the pallet or is damaged such that separation can be achieved without special tools (e.g. a hammer or crowbar) and/or by hand with little effort, the damaged board is removed and typically discarded or lost, even when it is feasible to reuse the same board. When the damaged board is made of a relatively inexpensive material, such as wood, removal of the board can be cost effectively addressed by replacing the missing board. However, when more expensive materials, such as the WPC and OPC materials of WPC Examples 1-3 and OPC Examples 1-3, replacement of the damaged board can become cost prohibitive, especially in a large pool pallet system where boards may be damaged over and over again. Table 3A demonstrates that while exhibiting some increase in robustness compared to wood, the WPC Examples 1-3 and OPC Examples 1-3 all still exhibited failure mode 6, requiring replacement of the damaged or discarded board(s) and are thus not a cost effective solution for maintaining pallets.
  • Table 3B compares the effect of different bottom deck board materials on the lift jack test breakage pressure and the pallet failure modes for pallets assembled using the bottom deck sub-assembly. Table 3B demonstrates that the exemplary bottom deck sub-assembly structure described herein in combination with the use of OPC material for forming the deck boards addresses the problem of failure mode 6 in which the damaged lead board is discarded or lost. Decreasing the likelihood that the expensive lead board is discarded or lost can provide substantial cost savings in maintaining pallets. The bottom deck sub-assembly structure couples the lead board with the other boards of the sub-assembly and thus, even when the lead board is damaged and becomes separated or partially separated from the spacer blocks, the damaged lead board is still connected with the remaining sub-assembly boards and thus cannot be readily deconstructed. This can facilitate maintaining the damaged lead board with the sub-assembly, such as for example by re-fastening or fixing damaged fastening, rather than removing the damaged lead board
  • WPC Examples 4-6 of Table 3B, exhibited failure modes, such as failure mode 4 in which the lead board breaks in the direction of board width, which would result in a need for the damaged board to be removed and replaced. While WPC Examples 4-6 were not readily deconstructed as a result of the joint strength between the bottom deck boards of the sub-assembly, because the damaged board is connected with the other boards in the sub-assembly, removal of the damaged board can become time consuming and may require special tools. In some cases, the entire sub-assembly may need to be removed to replace the damaged board and/or the replace the entire sub-assembly. Thus, even the combination of the more expensive WPC material and the bottom deck sub-assembly may not provide the desired cost effective solution for maintaining pallets.
  • In contrast, when OPC materials are used to form the bottom deck sub-assembly and assembled with a top deck to form a hybrid pallet (Hybrid Examples 1-8), none of the hybrid pallets demonstrate failure modes 3 or 4, which would require removal and replacement of the broken board, and further, none of the hybrid pallets demonstrated pallet failure mode 6. FIG. 14 illustrates pallet failure mode 2 for a bottom deck sub-assembly using a welded shiplap joint similar to Hybrid Examples 4-6 in which several of the nails coupling the test board to the spacer block have been pulled out of the spacer blocks, but the shiplap joint between the bottom deck boards is of sufficient strength to inhibit removal of the test board from the pallet by hand or with the use of hand tools. FIG. 15 illustrates pallet failure mode 2 for a bottom deck sub-assembly using a mechanical joint similar to Hybrid Examples 1-3 in which several of the nails coupling the test board to the spacer block have been pulled out of the spacer block, but the mechanical joint between the bottom deck boards is of sufficient strength to inhibit removal of the test board from the pallet by hand or with the use of hand tools. Hybrid Examples 1-8 also demonstrate a bottom deck sub-assembly in which the joint strength between the bottom deck boards is stronger than the joint strength between the bottom deck boards and the spacer members, and thus the connection between the bottom deck boards and the spacer members is lost or weakened before the connection between the bottom deck boards is lost.
  • Tables 3A and 3B further illustrate examples that used OPC boards (OPC Examples 1-5 and Hybrid Examples 1-8) and demonstrate that OPC boards did not split or crack when acted upon by a pallet jack in this test procedure. As demonstrated in Table 3B, the only failure modes for the Hybrid Examples 1-8 related to the fastener coupling the test board to the spacers. This type of damage can be easily repaired by simply re-fastening the lead board to the spacer blocks, either with the existing fasteners or with new fasteners. Thus, it is preferred that the materials and the structure of the bottom deck sub-assembly be selected such that the boards of the sub-assembly do not break, split, or crack before the connection between the spacer members and the bottom deck boards is broken or weakened.
  • When the OPC deck boards are joined together using gang nails or by thermal welding (Hybrid Examples 1-8), while the joint between the bottom deck boards and the spacer members may be broken or weakened, the bottom deck boards are still joined with the adjacent bottom deck boards, decreasing the likelihood that a damaged bottom deck board is removed and discarded or lost. Tables 3A and 3B demonstrate that it is the combination of the OPC materials and the bottom deck sub-assembly structure that provides a bottom deck structure that is sufficiently robust to resist board breakage during the pallet jack lift test and which further inhibits removal of a damaged or loosened bottom deck board and in this manner the hybrid pallet can provide a solution for pallet management having an increase in cost effectiveness.
  • Determination of Lead Board Constrained Impact Strength
  • The lead board constrained impact strength test was performed on boards made of traditional wood or wood plastic composite materials and exemplary OPC materials. Place a pallet upside down on the warehouse floor so that a section of the bottom deck lead board nailed to a spacer block is centered so that a dart can be dropped on the bottom deck lead board. The dart has a weight of 6.29 kg (13.85 pounds) and the dart face which impacts the bottom deck lead board is a short section of standard nominal 2 inch×4 inch lumber (3.8 cm by 8.9 cm) affixed to weights to provide the dart weight. The dart is raised sequentially from the lowest test height for the test apparatus to the lowest test height at which bottom deck lead board failure is observed. Failure is defined as splitting according to any one of the definitions of pallet damage set forth in sections 7.1.3 through 7.1.5 or missing board as set forth in sections 7.1.6 through 7.1.12 of the NWPCA bulletin. The impact strength is reported in units of energy (Joules) and is the dart mass multiplied by the drop height and the acceleration of gravity.
  • TABLE 4
    Deck board materials and test results*
    Constrained
    Impact Strength
    Avg. Highest Pass
    Density/ Energy/Lowest
    Board MOE MOR Ranges Fail Energy
    Material (GPa) (MPa) (g/cc) (Joules)
    Oak 9.8 64 0.48 131/187
    Yellow 13.2 80 0.47  94/113
    Pine
    WPC1 4.47 20 1.1 47/56
    WPC2** 1.46 Bent, did 0.58 56/66
    not break
    OPC1*** 3.55 ± 10% Bent, did 0.77/0.75-0.78 >263/did not
    notbreak fail under
    test
    conditions
    OPC2*** 4.45 ± 10% Bent, did 0.76 Test not run
    not break
    *Results for MOE, MOR and density are the average of three measurements. The MOR was obtained using a span of 21 inches instead of the normal test conditions for MOR of 16 inch span.
    **Technical Data Sheet for Azek Deck Board shows MOR of 3600 psi. http://www.azek.com/files/files/technical-center/techincal-docs/Deck,Porch/AZEK%20Deck%20Tech%20Data%20Arbor%20Terra.pdf
    ***MOE, MOR and Density data was obtained on multiple samples during the production of the boards actually used in the testing.
  • One common source of damage to lead boards is from the forklift or pallet jack running into the lead boards during alignment of the forks. A preferred material will be tough enough to withstand contact with the forklift or pallet jack without suffering damage that requires the board to be replaced. As described above, replacement of a damaged board forming part of the bottom deck sub-assembly can decrease the cost effectiveness of the hybrid pallet and thus should be minimized. The constrained impact strength in Joules is determined as described for the Determination of Lead Board Constrained Impact Strength and is representative of the toughness of the board, i.e. the ability of the board to withstand damage from contact with the forklift or pallet jack. As demonstrated in Table 4, oak is tougher than pine, which are both tougher than WPC1 and WPC2, as illustrated by the constrained impact test. OPC1 is significantly tougher than both the wood species, oak and pine, and the WPC materials, as demonstrated by the constrained impact test. In order for the hybrid pallet to be cost effective, the lead board needs to be at least as tough as the wood species to withstand impact from the forklift or pallet jack and minimize the number of times the bottom deck boards of the sub-assembly need to be replaced. The OPC 1 material has significantly higher constrained impact strength and did not fail under the test conditions, which indicates that the OPC lead board is more resistant to impact damage than the wood species or the WPC material, and thus less likely to require replacement due to impact forces. In a preferred embodiment, the constrained impact strength of the material used in the lead boards of the bottom deck sub-assembly is at least comparable to that of the wood species typically used in pallets and thus the preferred constrained impact strength of the bottom deck lead boards is not less than 95 Joules, preferably not less than 113 Joules, more preferably not less than 131 Joules, and still more preferably not less than 190 Joules.
  • As discussed above, one of the challenges of using more robust, and thus typically more expensive materials to form the pallets, is that when pallet boards are damaged in a way such that they could be re-used, they are typically discarded or lost, rather than re-used, which can significantly increase the overall cost of maintaining the pallet. This can negatively impact the benefits of using a material that is more resistant to damage, such as an OPC material. In order to address this challenge, Applicants have found that when the bottom deck is made from OPC boards, it is desirable to provide the bottom deck as a sub-assembly in which the bottom deck boards are connected to adjacent bottom deck boards to inhibit removal of a damaged or loosened bottom deck board from the pallet. In one embodiment, the joint strength between adjacent bottom deck boards is greater than a joint strength between the bottom deck boards and the spacer members. In this manner, when a bottom deck board is damaged such that it is loosened or disconnected from the spacer members, the damaged bottom deck board is still connected with at least one adjacent bottom deck board, thus minimizing the likelihood that the damaged board will be separated from the pallet and lost or discarded. Alternatively, or additionally, the joint strength between adjacent bottom deck boards can be selected such that if the bottom deck board is damaged it is not readily deconstructed from the remainder of the sub-assembly.
  • The joint strength may be provided by a number of methods of adhering the side boards to the lead boards, including but not limited to nailing or gang-nailing, corrugated fasteners, thermal welding or solvent based welding or adhesives, or a combination of one or more of these methods. In one example, the number and type of fasteners joining the boards of the bottom deck sub-assembly can be selected to provide the desired joint strength based on the desired decrease in the incidence of discarded or lost boards. In an exemplary embodiment, any joints between the edge and lead boards have a joint strength greater than that of the pull out strength of the fasteners joining the bottom deck sub-assembly to the spacer blocks so that the joints between the bottom deck boards remains relatively undamaged in the pallet jack lift test. Therefore, according to one embodiment of the invention, it is desirable that the joint strength be two times, three times or even more than the strength of the joint between the spacer blocks and the bottom deck sub-assembly to minimize the damage during the pallet jack lift test.
  • One challenge in pallet management, particularly in pallet pool systems, is the incidence of discarded or lost boards as a result of users removing damaged boards rather than repairing them. Typically, users will remove damaged boards using their hands or unpowered tools, such as a hammer or crowbar, which may be available on site. As has been discussed, replacement of the discarded or lost boards can become cost prohibitive as the cost of the board increases and thus decreasing the incidence of discarded or lost boards that could otherwise be re-used can provide significant cost savings. The number and type of fasteners joining the boards of the bottom deck sub-assembly can be selected to provide the desired joint strength based on the desired decrease in the incidence of discarded or lost boards. Thus, the joint strength can be selected to resist separation of a board from the sub-assembly by hand, such as a joint strength when pulled in tension of at least 450 Newtons. In another example, the joint strength can be selected to be higher to resist both separation by hand and separation by unpowered hand tools, such as a claw tooth hammer, such as a joint strength when pulled in tension of at least 1200 Newtons and preferably at least 5000 Newtons. The joint strength can further be selected to resist separation by certain powered tools to further decrease the rate of incidence of discarded or lost boards, depending on the particular pallet management system. It will be understood that a joint strength that resists separation can vary depending on the strength of an individual and the type of tools available to the individual, the joint strength can be selected to provide the desired decrease in the incidence of discarded or lost boards. As demonstrated by methods 2, 3, and 4 in Table 1, several exemplary bottom deck sub-assemblies have a joint strength of greater than 10,000 Newtons, making it extremely difficult for a user to separate a board from the sub-assembly and thus decreasing the likelihood that a damaged board is discarded or lost. The joint strength can be selected based on the desired resistance to removal as well as taking into consideration additional factors related to the sub-assembly and hybrid pallet, such as manufacturing costs, type of materials, assembly method, intended use, etc. and can be at least 450 Newtons, preferably at least 1200 Newtons, more preferably at least 5000 Newtons, and even 10,000 Newtons or greater.
  • In warehouse storage racks, loaded pallets are typically only supported by the edges of the pallet. Thus, pallets, particularly the bottom deck of a pallet, must resist excessive deflection when loaded pallets are stored in a rack. The materials used to form the pallet bottom deck boards are selected to provide the resistance to deflection based on the intended use of the pallet. In the exemplary embodiment shown in Table 4 the OPC material has a flexural modulus of at least 3.55±10% GPa. The boards may be selected to provide a lower or higher flexural modulus and may be selected to have a flexural modulus greater than 2.75 GPa (400M psi), more preferably greater than 3.25 GPa, even more preferably greater than 3.75 GPa, still more preferably greater than 4.25 GPa and even still more preferably greater than 4.75 GPa, for example, depending on the intended use of the pallet. OPC boards are particularly desirable because they do not fail in a flexural modulus test and can be bent a full 180 degrees, while having a significant elastic modulus.
  • The embodiments of the invention provide for a pallet having a bottom deck sub-assembly in which at least the bottom deck lead boards are made from a material that is resistant to impact damage and damage as a result of an improperly aligned pallet jack or forklift and further provides a bottom deck sub-assembly which inhibits separation of a damaged, but re-usable board from the pallet, thus decreasing the likelihood that a damaged or loose lead board is discarded rather than repaired.
  • Additional non-limiting embodiments contemplated by the present invention include:
  • A method of forming a pallet comprising the following steps: coupling a plurality of top deck boards comprising at least a first and second top deck lead board and at least one intermediate board positioned between the first and second top deck lead boards, with a plurality of spacer members; forming a bottom deck sub-assembly by coupling a first bottom deck lead board at a first end of the bottom deck sub-assembly and a second bottom deck lead board at a second end of the bottom deck sub-assembly, opposite the first, with at least one intermediate board extending between the first and second bottom deck lead boards to form a joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards, wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead board has a joint strength in tension of 450 Newtons or greater; and coupling the bottom deck sub-assembly with the top deck through the plurality of spacer members to form the pallet, wherein the first bottom deck lead board or the second bottom deck lead board comprises an oriented plastic composite or fiber filled thermoplastic material.
  • According to one embodiment, a pallet has a top deck coupled with a bottom deck through a plurality of spacer members. A plurality of fasteners join the top and bottom decks with the spacer members to couple the top deck, bottom deck, and spacer members into an assembled pallet. The bottom deck is provided as a sub-assembly comprising at least two lead bottom deck boards and at least one additional bottom deck board, each bottom deck board coupled with at least one other bottom deck board by a bottom deck joint, and wherein each board of the bottom deck sub-assembly is further coupled with at least one of the plurality of spacer members to couple the bottom deck sub-assembly with the top deck. The bottom deck joints can be configured to have a predetermined joint strength. In one embodiment, the predetermined joint strength corresponds to a strength such that the bottom deck boards of the bottom deck assembly are not readily deconstructed by hand and/or with unpowered hand tools. Alternatively, or additionally, the deck boards of the bottom deck assembly are configured such that the predetermined joint strength of the bottom deck joint is greater than a joint strength between the bottom deck sub-assembly and the spacer members.
  • To the extent not already described, the different features and structures of the various embodiments of the invention may be used in combination with each other as desired. For example, one or more of the features illustrated and/or described with respect to one of the bottom deck sub-assemblies 100 or 200 can be used with or combined with one or more features illustrated and/or described with respect to the other of the bottom deck sub-assemblies 100 or 200. That one feature may not be illustrated in all of the embodiments is not meant to be construed that it cannot be, but is done for brevity of description. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described.
  • While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention defined in the appended claims.

Claims (17)

What is claimed is:
1. A pallet having a top deck comprising a first top deck lead board at a first end of the top deck and a second top deck lead board at a second end of the top deck, opposite the first, at least one intermediate board positioned between the first and second top deck lead boards, and a plurality of spacer members coupled with the top deck, the pallet comprising:
a bottom deck sub-assembly comprising:
a first bottom deck lead board at a first end of the bottom deck sub-assembly and a second bottom deck lead board at a second end of the bottom deck sub-assembly, opposite the first; and
at least one intermediate board extending between the first and second bottom deck lead boards and fastened to an adjacent first and second bottom deck lead board to form a joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards;
wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead board has a joint strength in tension of 450 Newtons or greater;
wherein the bottom deck sub-assembly is coupled with the top deck through the plurality of spacer members to form the pallet; and
wherein the first bottom deck lead board or the second bottom deck lead board comprises an oriented plastic composite or fiber filled thermoplastic material.
2. The pallet of claim 1 wherein a constrained impact strength of the first bottom deck lead board, the second bottom deck lead board, or both is greater than 95 Joules.
3. The pallet of claim 2 wherein a constrained impact strength of the first bottom deck lead board, the second bottom deck lead board, or both is greater than 235 Joules.
4. The pallet of claim 1 wherein the pallet further comprises at least two longitudinally extending stringers coupled with at least a portion of the plurality of spacer members and wherein the top deck is coupled with the spacer members through the stringers.
5. The pallet of claim 1 wherein at least the first and second top deck lead boards of the top deck comprise an oriented plastic composite or fiber filled thermoplastic material.
6. The pallet of claim 1 wherein at least a portion of the top deck, plurality of spacer members, bottom deck sub-assembly, or combinations thereof comprise a natural wood material and a portion of the top deck, plurality of spacer members, bottom deck sub-assembly, or combinations thereof comprise an oriented plastic composite or fiber filled thermoplastic material.
7. The pallet of claim 1 wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards has a joint strength in tension of at least 1200 Newtons.
8. The pallet of claim 7 wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards has a joint strength in tension of at least 5000 Newtons.
9. The pallet of claim 1 wherein the at least one intermediate board is fastened to the adjacent first and second bottom deck lead boards by at least one mechanical fastener.
10. The pallet of claim 9 wherein the at least one mechanical fastener comprises a gang nail, a nail, a screw, a truss plate, a connector plate, a corrugated fastener, or combinations thereof.
11. The pallet of claim 1 wherein the at least one intermediate board is fastened to the adjacent first and second bottom deck lead boards by at least one non-mechanical fastener.
12. The pallet of claim 11 wherein the at least one non-mechanical fastener comprises solvent welding, solvent based adhesives, thermal welding, or combinations thereof.
13. The pallet of claim 1 wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards comprises a shiplap joint.
14. The pallet of claim 13 wherein the joint further comprises at least one mechanical or non-mechanical fastener.
15. The pallet of claim 1 wherein the first bottom deck lead board, the second bottom deck lead board, or both have a flexural modulus of at least 2.75 GPa.
16. The pallet of claim 1 wherein the first bottom deck lead board and the second bottom deck lead board comprises an oriented plastic composite or fiber filled thermoplastic material.
17. The pallet of claim 16 wherein the at least one intermediate board also comprises an oriented plastic composite or fiber filled thermoplastic material.
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