Abstract:
A composite wood flooring system for a vehicular trailer floor comprising: a plurality of wood boards, each wood board comprising a top surface and a bottom surface opposite the top surface; and a filled thermoplastic composite layer comprising a thermoplastic polymer and a discontinuous filler, the thermoplastic layer being substantially bonded to the top surface of each wood board.

Description:
1. FIELD OF THE INVENTION  
       [0001]     This invention relates to improved laminated wood flooring suited for both covered and exposed floors of vehicular trailers. In particular, the invention provides for flooring that allows the use of wood species of low hardness to produce moisture and scuff resistant floor boards.  
       2. DISCUSSION OF THE BACKGROUND ART  
       [0002]     Conventional wood flooring for over-the-road closed van trailers, truck bodies and containers is normally manufactured with hardwoods, such as oak, hard maple, birch, beech, ash, etc. Lower grades of green lumber at the thickness of 4/4 (nominal 1 inch) or 5/4 (nominal 1¼ inch) are used as the starting material. This lumber has a large amount of defects, which are not allowed in the flooring product. An average of more than 50% of the lumber is either discarded or lost in the flooring manufacturing process. The lumber is suitably dried in special drying chambers under controlled conditions to moisture content of about 8%. The dried lumber is then sawed into strips of rectangular cross-section and defective portions are eliminated by cross cutting the strips. These strips or components are about 1 inch wide and 1 to 6 feet long. During the cross-cutting process, “hooks” are formed at the ends of the lumber strips. Alternatively, other shapes such as fingers, bevel, etc., may be incorporated at the ends of strips or components. These shapes are primarily designed to form a mechanical connection or joint between the ends of strips. The joint thus formed can be a hook, finger, butt, scarf or some other joint. The dimensional design of each shape can vary from one manufacturer to another. For example, thicker and shorter fingers can be used to prevent breakage of tips of finger during manual assembly.  
         [0003]     The relatively defect-free lumber strips are coated on their vertical sides or edges with an adhesive such as urea-melamine formaldehyde, polyvinyl acetate, isocyanate, or another such wood adhesive. The glue coated lumber strips are then manually assembled on a conveyor by placing them side to side and behind other strips, which were previously assembled. The adhesive is cured in a press by applying heat and pressure to large sections of the assembled lumber strips thus forming a unitary panel. Pressure is mainly applied to the components from the lateral side in the horizontal plane. The lateral pressure is responsible for the straightening of any crooked wood components, squeezing out of excess adhesive, and bonding of components. This process is known in the art as edge-gluing. A restraining pressure is applied on the top side of the wood components by a large plate. The vertical force helps to prevent buckling of the assembled components from the lateral side pressure. Longitudinal pressure can be applied on the components to close the joints at the ends of components, but it is difficult to obtain consistent pressure at all of the end-joints. Part of the reason is the need to handle about 50 rows and about 400 individual components during each curing cycle. There may be as many as 400 end-joints per press charge depending on the press size. During the assembly of the lumber strips, mechanical joints are formed at each end of every strip. Irrespective of the type of joint at the ends of components, these end-joints are structurally weak mechanical couplings without significant adhesive bonding.  
         [0004]     An adhesive can be used to impart significant amount of strength to the end-joints of wood strips. Adhesive bonding requires the application of very high and consistent longitudinal pressure. In the absence of such consistent pressure, the glue develops porosity upon heating leading to little or no strength of end-joint. Since adhesive joints are normally not used to join the ends of a large number of components during edge-gluing of trailer flooring panel, it has been critical to manually control the placement of components during assembly. For example, the industry specification does not allow an end-joint in one row of components to be placed next to another end-joint of an adjacent row of components. A solid wood component from a middle row of components needs to separate the two side-by-side end-joints. Further, the specification details the allowed distribution of the end-joints and so forth. Manual assembly and control of the end joint distribution is a labor intensive part of manufacturing laminated trailer flooring.  
         [0005]     The glue laminated wood panel is cut to a desired length (up to about 60 feet) and width (about 6 to 18 inches) to form floorboards. Most boards are 10 to 13 inches wide, and about 43 to 53 feet in length. The boards are then planed to a desired thickness and shiplaps and crusher beads are machined at the longitudinal edges. A shiplap is a rectangular projecting lip running along the length at an edge of a floorboard. Typically, the lip extends along the width of a board by about ⅜ inch to ½ inch and has about half the thickness of the board. A “top shiplap” has the lip extending from the top half thickness of the board. Similarly, a “bottom shiplap” has the lip at the bottom half of the board. The crusher bead is a small semi-circular projection running along the length on each edge of a board and placed over or below a lip. When the floorboards are assembled in a trailer such that the side edges of corresponding boards are squeezed together, the top and bottom shiplaps of adjacent boards overlap to form a seam at a board or shiplap joint. The shiplap joint between adjacent boards helps to transfer some of the applied load from one board to its adjacent board. The shiplap joint also helps to prevent the entry of road debris and water into the trailer. The crusher beads provide spacing between adjacent boards and help in preventing buckling of the boards due to expansion on absorption of moisture. Wood putty is applied at the end-joints of components on the top and bottom surfaces of the boards to fill any resident gaps. Finally, the underside and lateral sides of the floor boards are coated with a polymeric coating, which is generally referred to as “undercoating” or “board coating” to provide moisture protection. The coating is usually applied by spraying. The finished floorboards are packaged as kits, by stacking one board on top of another, with about eight boards per kit for installation in trailers. Normally, a kit consists of two boards with special edge profiles so that they will fit along the road and curb sides of a trailer. The other boards may be identical in design and they are placed between the road and curb side boards. All the boards are supported by thin-walled cross-members of I, C or hat sections, each having an upper flange, which span the width of the trailer and are regularly spaced along the length of the trailer. Each floor board is secured to the cross-members by screws extending through the thicknesses of the board and the upper flanges of the cross-members. In some cases, laminated wood boards may be affixed to the bottom part of the side walls of the trailer and used as scuff boards to prevent damage to the sidewalls.  
         [0006]     Hardwood based laminated wood flooring is popularly used in covered van trailers, truck bodies and containers since it offers many advantages. The surface characteristics of hardwoods such as hardness, wear resistance and traction are most desirable. The strength and stiffness of the flooring is important for efficient and safe transfer of the applied loads to the cross-members of the trailer. The impact resistance of wood is useful to withstand any sudden dropping of heavy cargo on the floor. Nail holding capability and ability to absorb small amounts of water, oil or grease without significantly affecting traction are yet additional favorable properties of hardwood flooring.  
         [0007]     One significant draw back to laminated hardwood flooring in general is their inability to perform in an exposed environment as in a flat-bed trailer floor. When the laminated floor gets wet and wood absorbs moisture, the wood components of the boards swell. Upon drying of the wood components in a dry environment, the wood components shrink. Multiple cycles of wetting and drying of flooring in service causes cycles of expansion and shrinkage and leads to delamination of the floorboard. Therefore, it is not possible to wash a laminated wood floor for cleaning even though it is desirable to do so after hauling certain products like nursery plants, food products or to clean up spills of chemicals, etc. While, laminated oak flooring can last 10 or more years in a van trailer, it may not last even a few months in a flat-bed trailer. Some hardwoods such as maple, beech, birch and ash are significantly less resistant to decay compared to oak in above-ground use. Therefore, laminated flooring made from these hardwoods with low resistance to decay can undergo both delamination and decay when subjected to wetting and drying.  
         [0008]     Further, even in a closed van trailer, it is possible for flooring to get wet and absorb a significant amount of moisture at the top side of flooring. It is somewhat common for truckers to leave the doors of the trailers open at the dock, parking lot or yard for loading, unloading, maintenance or due to simple neglect. An open door in times of rain means flooring will get wet at the top side for a few feet from the door. It is also possible for the body or roof of the trailer to have a leak. Any water accumulation on the top side of the trailer flooring will cause damage to the flooring over time.  
         [0009]     Typically, a 1 to 2 feet long steel plate is laid on top of the flooring near the door of the trailer. This plate, called threshold plate covers the wood and protects it from impact of heavy lift trucks coming off the trailer loading dock. However, if water gets trapped below the plate, wood flooring made of non-resistant wood species can decay in as little as 2 years of service. It is not unusual for truckers to replace a section of the floor board underneath the threshold plate during the life service of trailers.  
         [0010]     For reasons stated above, laminated wood flooring cannot be installed on the fifth-wheel plate at the front end of the van trailer. Sometimes water can get trapped between the bottom side of board and the top side of plate. Typically, oak flooring will warp under these conditions. Non-resistant wood flooring can not only warp, but also decay much earlier under the same conditions.  
         [0011]     A significant improvement to conventional laminated wood flooring is provided by continuous fiber reinforced composite wood flooring (U.S. Pat. Nos. 5,928,735; 6,183,824; and 6,179,942). This composite wood flooring consists of conventional laminated wood floorboards with an underlay of continuous glass fiber reinforced polymer. The reinforcing layer is continuously bonded to the underside of each floorboard. The top surface of the composite wood flooring is exposed wood, which is the same as that of the conventional wood flooring. Since the reinforcing layer is impervious to the passage of water, it seals the bottom of the floorboards. The fiber reinforcement improves the mechanical properties of the flooring and therefore the thickness of laminated wood can be reduced. However, this approach leads to a product that is approximately about 40% to 50% more expensive than conventional hardwood flooring. Further, the top side of flooring, which is exposed wood, can be subject to weathering in exposed environments and the effects of moisture just as a conventional wood floor. This flooring is also not suitable for washing with water at the top side of flooring.  
         [0012]     U.S. Pat. No. 6,601,357 describes conventional laminated wood flooring with a layer of un-reinforced polymer sheet bonded to the bottom side of floor boards to provide moisture protection to the flooring at the bottom side. This flooring has an exposed wood surface at the top side of boards and therefore it is subject to the same limitations as mentioned before.  
         [0013]     U.S. Pat. No. 5,509,715 describes conventional laminated wood flooring with a layer of plastic film or fabric discontinuously bonded to the bottom side of floor boards to provide moisture protection to the flooring at the bottom side. This flooring has an exposed wood surface at the top side of boards and therefore it is subject to the same limitations as mentioned before.  
         [0014]     U.S. Pat. No. 6,318,794 describes a composite wood floor similar to that described in U.S. Pat. No. 5,928,735. In addition to a reinforced composite layer of glass, carbon or polymer fibers bonded to the bottom side of conventional laminated floor board, the composite floorboard is further coated with a polymeric coating of polyurethane having a granular constituent to provide anti-slip surface. The polyurethane coating is used to prevent absorption of water by the wood. To improve wear resistance, a second reinforced composite layer is proposed for the top side with anti-slip coating.  
         [0015]     A major drawback of using continuous fiber reinforced composite layer containing glass, carbon, Kevlar or other polymer fibers is the high cost of these continuous fibers and fabrics made from these materials. Furthermore, these materials are more slippery than wood. Therefore, when they are used on the top side of a floor board, they require an anti-slip coating, which further increases the cost of the product. It is already know in the industry that high strength glass fiber reinforcement at one side of a floorboard approximately adds about 40% to 50% more to the cost of conventional hardwood flooring.  
         [0016]     U.S. Pat. No. 6,318,794 also describes laminated wood flooring with a polymeric polyurethane coating with anti-slip granular constituent covering the top surface to inhibit water penetration. However, these coatings are normally too thin (about 0.001″ to 0.01″) and they can be worn out by dragging pallets and by scraping the surface of floor with forks of lift trucks. Gouging of hardwood flooring is somewhat common in trailers. Part of the reason for gouging of wood flooring is the directional properties of wood. For example, it is easy to split wood along the grain compared to its transverse direction. For similar reasons, longitudinal gouges along the length of flooring/grain of wood caused by impacting or scraping forks can be quite long and sometimes about half the thickness of the floor in depth. In practice, a polyurethane or epoxy coating called floor restorer is sometimes applied to laminated wood flooring to fix a delaminating floor in service. This practice has been well known in the industry over the decades. The advantage of this coating is that it penetrates and seals any delamination and crack in the flooring.  
         [0017]     U.S. Pat. No. 5,143,418 describes the use of composite plywood panels as flooring in open platform trailers. The plywood is composed of veneers of wood with a majority of the veneers oriented with the wood grain along the longitudinal direction while the remaining veneers are oriented with the wood grain along the perpendicular direction. The top and bottom surfaces of the plywood panels are overlaid with cured resin impregnated cellulose sheets for providing moisture and slip resistance. Since plywood based flooring is relatively weak, the veneer panels cannot be used in van trailers due to severe structural load conditions arising from the use of lift trucks when moving cargo in and out of van trailers. Plywood is generally not available in lengths up to 53 feet, which is preferred for efficient installation of trailer flooring. Further, curing of thermosetting resin of the cellulose sheet in a hotpress is a cumbersome process for floor boards of long lengths.  
         [0018]     U.S. Pat. No. 5,679,191 describes a method of fabricating trailer length flooring for flat-bed trailers using defect-free hardwoods such as oak, hickory and imported keruing. Essentially, shorter planks of wood are finger-jointed at their ends across the width of board to increase the length of the jointed board to suitably match the length of the trailer. The planks are not edge-glued, which makes these boards narrower compared to laminated trailer floor. Further, having a finger joint across the full width of the board leads to a large weaker spot with lower fatigue strength compared to the strength of solid wood.  
         [0019]     Flooring for North American trailers (vans and flat-beds) has been traditionally made out of hardwoods for several decades. The manufacturing process for laminated hardwood flooring for van trailers is labor intensive due to the steps of manual defect removal of lumber, manual assembly and manual control of assembly of lumber strips for lamination. The lumber used is of lower grades that are not suitable for higher value products like furniture and veneer. The labor cost component of the laminated flooring product is quite significant. Further, quality of product depends on a well trained labor force. Laminated hardwood flooring is almost never used for open platform or flat-bed trailers due to the inadequacy of this flooring in exposed environments.  
         [0020]     On the contrary, finger jointed hardwood flooring used for flatbed trailers, which is composed of solid wood planks is not suitable for van trailers due to narrower widths of natural hardwood planks compared to laminated trailer floor board. A finger joint across the full width of the plank leads to a large weaker spot with lower fatigue strength compared to the strength of solid wood. It should be noted that the mechanical hook joint or finger joint of laminated flooring for van trailers is about one tenth the width of the floor board. Even though five joints may occur per square foot of flooring, the controlled joint spacing provides more uniform strength to the floor board. Plywood panels with overlay of cured resin impregnated cellulose sheets are relatively inferior in strength and they are not available in the preferred long lengths of 40 to 50 feet for trailer flooring. Due to all of the factors discussed above, flooring for flatbed and van trailers have been non-interchangeable and mutually exclusive in use.  
         [0021]     Prior art of wood flooring for van and flat-bed trailers includes the technologies of edge-gluing of small width hardwood strips, finger jointing of hardwood planks, use of high strength continuous fiber (glass, carbon, Kevlar) reinforced composites and use of un-reinforced polymer sheets at the bottom sides of floor boards, water based undercoating and polyurethane coating with slip-resistant granules. The available technologies have led to two types of flooring, one for closed van trailers and another for exposed flat-bed trailers. There is no cost-effective flooring ever designed that would be suitable for both interior and exterior use. In practice, almost all of the North American van and flatbed trailer flooring with solid wood are made from three hardwoods, namely oak, hard maple and imported keruing. Many other commercially available lower cost woods can meet the strength requirements of trailer flooring, but not the wear resistance and hardness of the above mentioned woods.  
         [0022]     Therefore, it is an objective of this invention to provide a way to use any strong wood for trailer flooring by overcoming any issue of the lack of hardness.  
       SUMMARY OF THE INVENTION  
       [0023]     One aspect of this invention is to provide wood flooring with all of the attributes of conventional laminated hardwood flooring and improvements in the areas of moisture resistance, durability, surface characteristics, manufacturability and cost. Such improvements allow the floor board of this invention to be for use in all types of vehicular trailers, including vans, flatbeds, containers, truck bodies, horse trailers, etc., and also for other applications such as decks. Specifically, the floor board of this invention relies on the strength of conventional laminated wood flooring. To improve the manufacturing process, certain relatively lower cost wood species such as southern yellow pine, Douglas fir, spruce, western larch and yellow poplar are preferred. These woods are typically about 50% to 60% of the cost of oak for the same or similar grade. At the price of lower grade oak, it is possible to purchase the above mentioned woods in a high strength grade (such as MSR or machine stress rated) with little or no structural defect. This allows tremendous cost savings over conventional oak and maple hardwoods. However, these woods have much lower surface hardness compared to oak and maple. Hardness is important to prevent wear at the top side of flooring. To solve this issue, a low-cost filled plastic layer is bonded to the top side at a minimum and further to the other sides of floor board depending on the application or end-use environment of flooring. The plastic can be a thermosetting or a thermoplastic polymer, but thermoplastic polymer is preferred for lower cost and ease of manufacturing. Fillers can be flour, chips, flakes, strands, dust, shavings and particles of wood, lignocellulosics, natural plant fibers, minerals, dis-continuous synthetic fibers and milled fibers. Natural plant fibers include such materials as wood fiber, coconut coir, hemp, sisal, jute, bamboo, kenaf, wheat straw, corn stalk, and bagasse. Synthetic short fibers can be glass, carbon, and Kevlar, but short glass fiber is preferred for lower cost. Minerals can be clay, wollastonite, calcium carbonate, limestone, barytes, alumina, talc and other such materials. One or more fillers are combined with thermoplastics polymer such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile copolymer (SAN), low density polyethylene (LDPE), high density polyethylene (HDPE), high impact polystyrene (HIPS), ethylene-vinyl-acetate (EVA), polyamide, recycled plastics, or other suitable thermoplastics to make filled plastic composite (FPC). While the FPCs are weaker than many solid woods and common laminated floor boards of oak and maple, they are durable in exposed environments, resistant to moisture and weathering, harder than many available wood species and provide a high coefficient of friction in dry and wet conditions. Further, FPC provides significant improvement in the surface gouging characteristics compared to solid wood and virgin or unfilled plastics. Even though unfilled plastics can be used in some applications where hardness is not an issue, FPC is preferred for most applications. The surface coefficient of friction of wood particulate filled FPC is higher under wet condition compared to dry condition. This provides improved traction when wet. By incorporating a durable wear and protective layer of FPC with laminated wood floor board, superior and low cost flooring is provided.  
         [0024]     A composite wood flooring system for a vehicular trailer floor comprises: a plurality of wood boards, each wood board comprising a top surface and a bottom surface opposite the top surface; and a filled thermoplastic composite layer comprising a thermoplastic polymer and a discontinuous filler, the thermoplastic layer being substantially bonded to the top surface of each wood board.  
         [0025]     The wood is preferably selected from the group consisting of a hardwood or softwood.  
         [0026]     The wood boards preferably extend longitudinally along the length of the vehicular trailer floor, each the wood board comprising a top surface, a bottom surface opposite the top surface, and a first side surface and second side surface extending between the top surface and the bottom surface, and a board width that is less than the lateral width of the vehicular trailer floor, each the wood board being formed of a plurality of solid wood segments joined to one another by coupling portions.  
         [0027]     The filler is at least one selected from the group consisting of: lignocellulosics, natural plant fibers, milled fibers, short fibers, and minerals.  
         [0028]     The thermoplastic polymer comprises at least one polymer selected from the group consisting of: polypropylene, polyethylene, polystyrene, poly-vinyl-chloride, acrylonitrile-butadiene-styrene, styrene-acrylonitrile, low density polyethylene, high density polyethylene and high impact polystyrene.  
         [0029]     The lignocellulosic is at least one selected from the group consisting of: flour, fiber, chips, flakes, dust, particles, shavings, slivers, and strands.  
         [0030]     The thermoplastic layer is additionally bonded to at least one surface selected from the group consisting of: the first side surface, the second side surface, and the bottom surface of the floor boards.  
         [0031]     The thermoplastic layer, when bonded to the first side surface or the second side surface of the wood boards, is shaped to form shiplaps of the wood boards.  
         [0032]     The plurality of wood boards are arranged such that at least one of the first side surface and the second side surface of each of the wood boards approximates one of the first side surface and the second side surface of adjacent boards or a mating portion of a metallic component of the vehicular trailer to form a continuous trailer floor having an upper thermoplastic surface and a bottom surface for extending for the lateral width of the vehicular trailer floor, a joint region being formed at locations at which the first side surface or the second side surface of adjacent wood boards approximate one another.  
         [0033]     The flooring system further comprises an undercoating disposed about the bottom surface of each of the wood boards for moisture protection.  
         [0034]     A composite board for a load carrying floor comprises a lignocellulosic particulate filled thermoplastic polymer composite layer bonded to a non-veneer wood layer, wherein the lignocellulosic particulate is discontinuous.  
         [0035]     A composite wood flooring system for a vehicular trailer floor comprises: a plurality of wood boards, each wood board comprising an unexposed top surface and a bottom surface opposite the top surface; and a thermoplastic layer comprising an exposed first surface and an unexposed second surface, wherein the unexposed second surface of the thermoplastic layer is substantially bonded to the unexposed top surface of each wood board and the exposed first surface of the thermoplastic layer comprises a rough texture. Preferably, the thermoplastic layer comprises: a thermoplastic polymer and a discontinuous filler. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]     The invention is illustrated by, but not limited to, the embodiment shown in the accompanying drawings in which:  
         [0037]      FIG. 1  is a schematic view, partially cut away, of a dry van trailer with laminated hardwood flooring;  
         [0038]      FIG. 2  is a perspective view of a conventional laminated wood panel with narrow width wood components;  
         [0039]      FIG. 3  is a perspective view of a conventional undercoated laminated floor board for a dry van trailer;  
         [0040]      FIG. 4  is a sectional view of two adjacent floor boards on a cross-member of a dry van trailer;  
         [0041]      FIG. 5  is a sectional view of a conventional laminated wood floor board for a dry van trailer.  
         [0042]      FIG. 6  is a perspective view of a laminated wood panel made of broad width wood components;  
         [0043]      FIG. 7  is a perspective view of an undercoated laminated wood floor board with broad width wood components;  
         [0044]      FIG. 8   a  is a sectional view of an extruded FPC panel;  
         [0045]      FIG. 8   b  is a sectional view of an extruded FPC profile;  
         [0046]      FIG. 9   a  is a sectional view of a laminated wood floor board with FPC layer at the top side;  
         [0047]      FIG. 9   b  is a sectional view of a laminated wood floor board with FPC layer on three sides;  
         [0048]      FIG. 9   c  is a sectional view of a laminated wood floor board with FPC layer on three sides and with FPC shiplaps;  
         [0049]      FIG. 9   d  is a sectional view of a laminated wood floor board with FPC layer on four sides and with FPC shiplaps; and  
         [0050]      FIG. 10  is a cross-sectional representation of a sandwich FPC layer with a higher toughness thermoplastic core. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]     Conventional laminated wood floor board  11  for over-the-road van trailers  12  such as that shown in  FIG. 1  is normally manufactured with hardwoods such as oak, hard maple, birch, beech, ash and the like. Any wood can be used for this purpose. However, in commercial practice, laminated wood flooring for van trailers and containers are made from oak and hard maple. These woods are preferred for their availability, strength, and hardness. Many other available woods are not used due to their lack of strength and/or hardness. Examples of strong woods that are not used due to low hardness are southern yellow pines, yellow-poplar, western larch, Douglas-fir, etc.  
         [0052]     Lower grade lumber (such as No. 2 Common and No. 3A Common for hardwoods) of oak and hard maple (sugar maple) are the most common hardwoods used for laminated wood flooring. The lumber used is 4/4 (1 inch nominal) or 5/4 (1¼ inch nominal) in thickness with varying widths of boards that are allowed in the selected grades. The green lumber is suitably dried in kilns under controlled conditions. In preparation of lumber for lamination to produce a floor board, the dried lumber is sawed into strips or components  13  ( FIG. 2 ) of rectangular cross-section and defective portions are eliminated by cross cutting the strips. The cross-section of sawed lumber strips uniformly measures less than about 1½inch in sawed width and roughly approximates the thickness of the lumber in height or thickness. The strips are turned about their longitudinal axis by 90 degrees for side-by-side lamination or edge-gluing to produce a panel. Due to the 90 degree turning of the strips, sawed width of the lumber strip becomes the thickness of the laminated panel. Typically, 1½ inch sawed width of strip is useful to make a floor board with a finished thickness of 1⅜inch. The sawed width of the strips is varied depending on the finished thickness of the floor boards made. 1 5/16 inch and 1⅜ inch thick boards are most commonly used for van trailer floors. 1⅛ inch thick floor boards are commonly used for container floors. The thickness of lumber is reflected in the finished width of strips in the laminated panel and floor boards. Finished width of the strips in the panel is uniformly about ⅞ or 1⅛inches depending on the thickness of the lumber ( 4/4 or 5/4) used. Length of the strips varies from about 1 to 6 feet after removal of defects by cross-cutting of strips. As many as 11 to 14 strips are needed side-by-side to make a common 12 inch wide floor board  11 . In summary, the thickness of lumber ( 4/4 or 5/4) has no consequence on the thickness of the flooring in the conventional flooring production process.  
         [0053]     During the cross-cutting process, “hooks” are formed at the ends of the lumber strips. Alternatively, laps, fingers, bevel or other shapes can be formed at the ends of the strips. The relatively defect-free lumber strips are coated on their vertical sides or edges (which were originally the faces of lumber boards) with an adhesive such as urea-melamine formaldehyde or polyvinyl acetate. The uncured glue coated lumber strips are then manually assembled on a conveyor by placing them side to side and behind other strips, which were previously assembled, thus forming glue lines  14  between adjacent strips  13 . The adhesive is cured by applying heat and pressure along 2 or 3 axes to large sections of the assembled lumber strips thus forming a unitary panel of laminated wood  15 . The panel may have as many as 50 or more strips of lumber side-by-side to provide a required panel width, which can be used to make about four floor boards. The relatively small sized strips of wood used in the conventional process are herein referred to as “narrow width” wood strips or components.  
         [0054]     During the assembly of the lumber strips, mechanical joints  16  such as hook, lap, finger, butt or scarf joints are formed at each end of every strip. These end-joints of strips are simple mechanical couplings with no significant adhesive bonding. Therefore, they have no significant strength compared to the strength of solid wood, irrespective of the type and quality of the joint. Often times, due to imperfect assembly, a readily visible gap  17  is formed at the end-joints of strips, which can be seen from the top and bottom sides of the laminated wood floor board. Certain rules are followed during the assembly of lumber strips to ensure proper distribution of end-joints of strips in the floor boards. One such rule involves the discarding of strips with a length less than 12 inches. Another rule does not allow the side-by-side assembly of two end-joints of adjacent strips. A solid wood strip needs to separate such inline placement of joints or the joints should be away from each other by at least a specified distance. The application of these rules in manual assembly of a very large number of narrow width strips to produce a laminated panel results in a labor intensive and time-consuming process.  
         [0055]     The cured laminated wood panel is sawed to a desired length (up to about 60 feet) and width (about 6 to 18 inches) and then machined to form several laminated wood boards. Each laminated wood board is planed to a desired thickness and shiplaps  18  and crusher beads  19  (FIGS.  3  to  5 ) are machined on its sides. When the floor boards are assembled in a trailer such that the side edges of corresponding boards are squeezed together, the shiplaps  18  of adjacent boards overlap to form a seam. The bead  19  provides spacing between adjacent boards and helps in preventing crushing and warping of the boards when they expand upon absorbing moisture. Wood putty is applied at the end-joints  16  on the top and bottom surfaces of the boards to fill any resident gaps. Finally, the underside and lateral sides including the shiplaps of the floor boards are coated by spraying a polymeric coating termed as “undercoating” or “board coating”  20  to provide moisture protection. The top side of each board is normally uncoated or exposed wood. Sometimes a thin coating of polyurethane or epoxy is applied to the top surface of flooring. This improves aesthetics and helps to slide household items in a moving van trailer at the time of loading the trailer. The finished floor boards are assembled into a kit of about eight boards for installation in trailers. Normally, a kit consists of two boards with special edge profiles so that they will fit along the road and curb sides, which are usually metallic components of the trailer  12 . The other boards may be identical in design and they are placed between the road and curb side boards. All the boards are supported by thin-walled cross-members  21  ( FIG. 1 ) of I, C or hat sections, each having an upper flange, which span the width of the trailer and are spaced along the length of the trailer. Each floor board is secured to the cross-members by screws  22  extending through the thickness of the board and the flanges of the cross-members.  
         [0056]     Irrespective of the specie of wood used to make the trailer flooring, the above described process can be used with little change. However, the efficiency of this process does not significantly improve when using small sized and narrow width strips of wood and manual assembly techniques. For example, a common floor board measuring 48 feet by 12 inches has about 240 end-joints of strips. It also has about 200 to 250 strips of wood of varying lengths that are bonded together. Manual assembly of a large number of strips is a tedious process. It is an objective of this invention to significantly improve the efficiency and productivity of the floor manufacturing process. Accordingly, in one embodiment, the invented product is made using lumber, which is thicker than 4/4 and 5/4 lumber or by using a suitable specified dimension of lumber based on the required finished thickness of floor board. As an example, lumber can be 6/4 with a nominal thickness of 1½ inch. The reason for using thicker lumber is explained in the following paragraph. Further, to significantly improve the manufacturing efficiency, higher grade lumber of certain low cost wood species is used. This type of lumber is significantly free of structural defects like loose knots, splits, wanes, etc., which helps to reduce or eliminate labor necessary for removal of these defects.  
         [0057]     High grade dimension lumber of oak and hard maple is cost prohibitive for trailer flooring. Lumber of softwoods such as southern yellow pine, fir, larch, spruce and certain hardwoods such as yellow-poplar are available at specified uniform dimensions in large volumes necessary to produce trailer flooring. By specifying a grade such as MSR (machine stress rated), structural grade lumber of softwood species can be obtained at a cost comparable to or below the cost of lower grade oak and hard maple. For example, MSR grade southern yellow pine lumber (2×4) is almost fully usable. However, an average of less than 50% of the board cuttings of No. 2 and No. 3A common oak lumber is good for structural use. Further, the strength and modulus of elasticity of MSR grade lumber is high and consistent. As an illustration, typical properties of various relevant hardwoods and softwoods are listed below at 12% moisture content (Reference: Wood Handbook: Wood as an Engineering Material, Published by Forest Products Society, 1999).  
                                                           Wood Species   Bending   Bending               Currently Used   Strength   Modulus   Hardness           for Trailer Flooring   (psi)   (million psi)   (lb)                           Chestnut Oak   13,300   1.59   1130           White Oak   15,200   1.78   1360           Sugar Maple   15,800   1.83   1450                      
 
         [0058]    
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Wood Species 
                 Bending 
                 Bending 
                   
               
               
                   
                 Unused or disallowed 
                 Strength 
                 Modulus 
                 Hardness 
               
               
                   
                 for Trailer Flooring 
                 (psi) 
                 (million psi) 
                 (lb) 
               
               
                   
                   
               
             
             
               
                   
                 Longleaf Pine 
                 14,500 
                 1.98 
                 870 
               
               
                   
                 Slash Pine 
                 16,300 
                 1.98 
                 — 
               
               
                   
                 Douglas- Fir 
                 12,400 
                 1.95 
                 710 
               
               
                   
                 Western Larch 
                 13,000 
                 1.87 
                 830 
               
               
                   
                 Yellow-Poplar 
                 10,100 
                 1.58 
                 540 
               
               
                   
                 Sweetgum 
                 12,500 
                 1.64 
                 850 
               
               
                   
                 Red Maple 
                 13,400 
                 1.64 
                 950 
               
               
                   
                   
               
             
          
         
       
     
         [0059]     The wood species in the above second table have high modulus of elasticity or bending modulus and strength, but suffer from low hardness, which makes them less resistant to abrasion, scuffing, and gouging. Forklift trucks used to load and unload trailers can easily damage the surface of wood floors made with these wood species. Several other woods with high strength and low hardness are listed in the Wood Handbook such as black ash, paper birch, red spruce, tamarack, western hemlock, etc. Many of these softer woods have high strength and are available at low cost. They also offer significant advantages in the production of trailer flooring.  
         [0060]     For example, the advantages of using 2×4 lumber of longleaf and slash pine is described below. Other dimensions of lumber such as 2×6, 2×8, 2×12 can also be used with equal or better efficiency. The 2×4 lumber is nominally 1½ inches thick and 3½ inches wide. The boards of lumber can be readily obtained at a uniform length of 8, 12, 16 or 20 feet. The conventional process of production for making laminated floor boards can be employed with this lumber. However, much higher efficiency and productivity is obtained by using the 2×4 boards of lumber as individual strip or component of laminated wood panel  23  ( FIG. 6 ). Each component is about 3½ inches wide with average length exceeding 8 feet. These components of large size and wider width are herein referred to as “broad width” components. By using long boards of broad width components of uniform dimensions, the number of end-joints of components needed to make the panel is significantly reduced. The end-joints of the components can be of any suitable kind such as conventional finger, modified spaced apart finger, lap, hook, scarf or butt joints. The larger cross-section of each component  24  helps to adhesively join the ends of the components by stronger conventional finger joints  25 . This improves the strength of the board. By using the thickness of the lumber to reflect in the thickness of the laminated panel and width of the lumber to reflect in the width of the component  24  of laminated panel  23 , the number of components needed to produce a panel is greatly reduced. This leads to significantly reduced assembly time and also much lower curing time due to fewer gluelines to make a panel of laminated wood. For example, 50 strips of 4/4 lumber can be replaced by 14 strips of 2×4 broad width components. The cure time to make the laminated panel with 2×4 pine is reduced by about 70% compared to 4/4 oak. The strength and stiffness of the resulting laminated floor board  26  ( FIG. 7 ) of broad width components of pine is sufficient to qualify for trailer flooring. Even though many low-cost woods allow the dramatic improvement of production efficiency, these woods such as southern yellow pine, Douglas-fir, yellow-poplar, etc., do not have sufficient hardness needed for trailer flooring. Therefore, it is the first objective of this invention to provide sufficient hardness to the surface of a trailer floor made with woods of low hardness.  
         [0061]     One significant draw back to laminated hardwood flooring in general is their inability to perform in an exposed environment as in a flat-bed trailer floor. Multiple cycles of wetting and drying of laminated flooring in service leads to delamination of the floorboard. Therefore, it is not possible to wash and clean a laminated wood floor in van trailers even though it is desirable to do so after hauling certain products like nursery plants, food products or to clean up spills of chemicals, etc. While, laminated oak flooring can last for 10 or more years in a van trailer, it may not last even a few months in a flat-bed trailer. Some hardwoods such as maple, beech, birch and ash are significantly less resistant to decay compared to oak in above-ground use. Therefore, laminated flooring made from these hardwoods with low decay resistance can prematurely undergo both delamination and decay when subjected to wetting and drying. Other aspects related to construction of floor system in trailers combined with the use of woods that are non-resistant to decay can also affect performance. For example, a 1 to 2 feet long steel plate is laid on top of the flooring near the door of the trailer. This plate, called threshold plate covers the wood and protects it from impact of heavy lift trucks entering the trailer at the loading dock. It has been found that when water gets trapped below the threshold plate, wood flooring made of non-resistant wood species can decay in as little as 2 years of service. Laminated wood flooring is typically not installed over the fifth-wheel plate at the front end of the van trailer. In past experience, water has been found to be trapped between the bottom side of floor boards and the top side of plate. Hardwood floor boards were found to expand at the bottom side and warp under these conditions, thus causing the floor screws to break. Non-resistant wood flooring can not only warp, but also decay much earlier under the same conditions. Therefore, it is the second objective of this invention to provide for water resistant flooring. In one embodiment, the invented flooring is suitable for van trailers and containers, wherein resistance to weathering at the rear section near the doors of trailer and resistance to moisture effects on wood flooring below the threshold plate are needed. In another embodiment of this invention the invented flooring is suitable for periodic washing and for both interior and exterior use.  
         [0062]     Ideal flat-bed trailer flooring should have resistance to decay, resistance to UV, resistance to moisture, light weight, resistance to scuffing, consistent strength, high coefficient of friction in dry and wet conditions and a length of floor board equal to the length of trailer and width of floor board wider than conventional solid wood plank or as wide as necessary. Conventional flat-bed flooring made of wood does not provide all of these attributes. Therefore, the third objective of this invention is to provide more desirable flooring for flat-bed trailers.  
         [0063]     In accordance with the aforementioned objectives, a layer of a thermoplastic panel  27  ( FIG. 8   a ) or a thermoplastic profile  28  ( FIG. 8   b ) is adhesively bonded to the top side of edge-glued laminated floor board. The thermoplastic panel and profile can be a filled, un-filled or a reinforced polymer composite. In a preferred embodiment, the thermoplastic panel is made of a Filled Plastic Composite or FPC without any synthetic continuous fiber reinforcement. In the simplest form, the filler is a discontinuous material of low cost, which is compounded with a thermoplastic polymer along with other additives for extruding a panel or a profile of FPC. Panel thickness is about 0.02 inch to 0.25 inch. Wall thickness of profile is about 0.02 inch to 0.75 inch. Examples of fillers are wood articulates, natural plant fiber, lignocellulosics, minerals, metal particulates, synthetic short fibers and milled fibers. The wood particulate can be in one or more forms of flour, dust, fiber, particles, chips, flakes, strands and slivers. Natural plant fibers can be materials such as wood fiber, coconut coir, hemp, sisal, jute, bamboo, kenaf, wheat straw, corn stalk and bagasse. Minerals can be in the form of powder, particles, or short fibers such as barytes, limestone, clay, wollastonite and talc. Metal particulates can be powders, filings, and short fibers. Synthetic short fibers can be chopped glass strands and milled glass fibers. The thermoplastic polymer can be any suitable polymer such as PP (polypropylene), PE (polyethylene), PS (polystyrene), PVC (polyvinyl chloride), LDPE, HDPE, ABS, SAN, HIPS, EVA, polyamide, recycled plastics, regrinds, and their mixture. Addition of fillers to plastic makes a filled plastic composite or FPC with superior hardness compared to virgin plastics. (For example, commercially available Trex wood polymer® lumber, which is made of recycled plastic and wood particulates, has a hardness of 1124 lbs. Reference: Trex Product Information, www.trex.com.) Wood particulate filled plastic is harder than many of the solid woods. Addition of a second filler such as milled glass fiber or minerals helps to further increase hardness. Filled plastic composite is known in the art to be compounded with suitable colorants, impact modifiers, adhesion promoters to bond the filler to the plastic, UV inhibitors, plasticizer, impact modifiers, and lubricants. Filled plastics can also be foamed to lower cost of materials. In a preferred embodiment, wood particulates are compounded with a thermoplastic polymer, wherein the wood content of the resulting composite is between 5% to 60%. In another preferred embodiment, the plastic is a PVC or ABS with a lignocellulosic filler. In a yet another preferred embodiment, the FPC has multiple types of filler, including wood particulates to enhance a desirable property such as hardness and fracture toughness.  
         [0064]     FPC differs from Fiber Reinforced Plastic or FRP, which is used to make high strength and light weight composite wood flooring for trailers. FRP is made with continuous fibers of glass, carbon, steel and Kevlar embedded in a polymer, wherein the fibers are aligned for high strength along a specified axis. FRP is primarily used for reinforcing a weaker structure and it is about 3 or 4 times more expensive than FPC. Further, any surface damage from gouging or scuffing of aligned FRP causes a very long sliver of the composite to peel off like banana skin or bamboo sliver. Woven fabric or chopped strand mat of synthetic fibers can improve the abrasion resistance of FRP, but it adds even more cost compared to continuous rovings of fibers. Therefore, a low cost filled plastic composite panel for this invention is made of discontinuous particulates and short fibers that can be compounded with thermoplastics.  
         [0065]     FRP is several times stronger than solid wood. FPC is a low cost extruded thermoplastic composite that has much lower strength compared to FRP. At best, the strength of FPC compares with the strength of solid wood such as oak, but most commercial compositions of FPC are about 50% weaker than solid wood. (For example, a 40% wood filled HIPS composite has a flexural strength of 8170 psi. Source: North Wood Plastics, Inc., Sheboygan, Wis.). For this reason, the flooring of this invention is not entirely composed of FPC even though it is possible to do so. On the contrary, the strength of laminated wood is combined with the durability, resistance to moisture and wear of FPC. It is possible to use high-strength continuous fibers of synthetic materials with floor boards of this invention to further increase the strength of the boards and/or provide weight savings, if necessary. Continuous fibers can be incorporated into the FPC or used separately as an under layer for floorboards.  
         [0066]     In one embodiment of this invention, a panel of FPC is adhesively bonded to the top side of a laminated wood floor board composed of broad width components of softer woods such as pine and Douglas-fir. The resulting composite floor board  29 , such as shown in  FIG. 9   a , is a representative example of this embodiment, which fulfills the first objective stated before. This invention makes it possible to use a strong yet softer wood for van trailer and container flooring. It also helps to enhance the manufacturing efficiency in the production of laminated wood panel  23  ( FIG. 6 ) and floor boards  26  ( FIG. 7 ). Further, it helps overcome the effects of weathering at the rear section of flooring near the doors of trailers. The FPC also protects the top surface of wood flooring from any trapped moisture under the threshold plate of trailers. In some cases, where moisture protection at the top side of flooring is a low priority than resistance to gouging and abrasion such as in locations of the drier southwest regions of the United States, not all of the floorboards need a top layer of FPC. Typically, the outer boards along the sidewall of trailer are not subjected to much wear and tear in service since fork lift trucks stay closer to the center of trailer. In such cases some floor boards of the flooring may not need the FPC top layer.  
         [0067]     In another embodiment of this invention, a profile  28  of FPC is adhesively bonded to a laminated wood floor board at the top side and the lateral sides of the board. The bottom side of the board is undercoated with a polymeric coating. The resulting composite floor boards  30  and  31  ( FIGS. 9   b  and  9   c ) are representative examples of this embodiment, which fulfills the second objective stated before. The laminated wood board can be composed of broad width or narrow width components. The shiplaps of boards are formed of FPC or they are made of wood and covered by FPC. FPC shiplaps can be solid or hollow. In addition to providing hardness to the top surface of a softer wood, a higher degree of moisture protection is provided to the flooring at the top side and at the shiplaps. Flooring composed of these floor boards are suited for periodic washing and cleaning in van trailers without causing delamination of the laminated wood board. Other advantages as stated before apply here as well.  
         [0068]     In a yet another embodiment of this invention, one or more profiles of FPC or a combination of a panel  27  and profile  28  are adhesively bonded to a laminated wood floor board at the top side, bottom side and the lateral sides of the board. The resulting composite floor board  32  ( FIG. 9   d ) is a representative example of this embodiment fulfilling the third objective stated before. The laminated wood board can be composed of broad width or narrow width wood components. The shiplaps of boards are formed of FPC or they are made of wood and covered by FPC. FPC shiplaps can be solid or hollow. In addition to providing hardness to the top surface of a softer wood, a higher degree of moisture protection is provided to the flooring at all four sides. Flooring composed of these floor boards are suited for frequent washing and cleaning in van trailers without causing delamination of the laminated wood board. Further, this flooring is also suitable for any exposed floor such as in flat-bed trailers and decks. To further improve the performance of the flooring, the lumber used to make this flooring can be suitably treated with fungicides and preservatives or the lumber can be selected from a list of naturally decay resistant woods.  
         [0069]     Due to their chemical nature in general, some thermoplastics such as PP and PE are very difficult to bond to wood with adhesives. Other thermoplastics like PVC and ABS are less difficult to bond. However, it has been found that FPCs in general are easier to bond with common adhesives. A bonding surface of FPC is sanded, scuffed or abraded to expose some of the embedded fillers such as wood particulates, plant fibers, lignocellulosics, etc. Common adhesives such as epoxy, polyurethane, isocyanate, PF, PRF, UF, MUF, PVA, hotmelt, EVA, polyamide, reactive hotmelt, pressure sensitive hotmelt, thermoplastic tie layer, film adhesive and the like can be used for bonding. In a preferred embodiment a reactive hotmelt is used to provide durable bonds.  
         [0070]     FPC provides high coefficient of friction or COF under wet condition. (For example, commercially available Trex wood polymer® lumber, which is made of recycled plastic and wood particulates has a dry COF of 0.59 to 0.7 and wet COF of 0.7 to 0.75. Reference: Trex Product Information, www.trex.com.) The high COF of FPC is beneficial in trailer flooring in wet conditions when washing the floor in a van trailer or when loading on a rainy day. In a preferred embodiment, the FPC layer at the top side of floor boards is lightly sanded to expose the lignocellulosic filler. The exposed lignocellulosic filler tends to swell up in wet condition resulting in a high COF for the surface. The FPC layer with some of the wood particulates exposed at the surface has a rough texture. This provides a significant advantage over polyurethane, epoxy, or other polymer coatings, which tend to have a smooth texture and low friction under wet conditions.  
         [0071]     As an alternative, thermoplastic panel or profile can be made of an unfilled thermoplastic polymer such as PVC and ABS. These plastics can be adhesively bonded to the top side of laminated wood boards. However, it is necessary to roughen the exposed surface of the panel or profile to ensure a high COF. Roughness can be imparted to the surface of the panel or profile by forming a textured surface at the time of extrusion of the panel or profile. A secondary operation such as rough sanding with a 40 grit belt can also be employed. However, many of the unfilled thermoplastics lack hardness and resistance to abrasion. Even then this type of flooring is suitable for a small minority of trailers that are not loaded with forklift trucks, but rather by hand trucks. Slip and moisture resistance are needed for these applications as well. For example, dedicated trailers used by some grocery retailers, postal service, and parcel service are in this category.  
         [0072]     A short coming of FPC is their relatively lower elongation to failure compared to unfilled plastics, which makes them more brittle with reduced toughness. By layering unfilled plastic  33  and FPC to produce a sandwich FPC panel  34  ( FIG. 10 ), the resulting panel has improved toughness, while preserving the surface hardness. Such a panel or profile is produced by co-extruding filled and unfilled thermoplastics. Sanding the surfaces of the sandwich panel provides improved adhesive bonding to wood floor boards and high wet friction due to the exposed lignocellulosics.  
         [0073]     Experiments were carried out to determine the bonding characteristics of a wood particle filled polypropylene FPC panel (NWP-431-A-1, supplied by Northwood Plastics, Inc., Sheboygan, Wis.). A reactive hotmelt adhesive (PUR-FECT LOK® 34-9029, supplied by National Starch and Chemical Company, Bridgewater, N.J.) was used as the adhesive. The wood filled PP composite panel was bonded to a pine board of size 36 inch by 12 inch. Both as-received panels and panels with two lightly sanded opposing surfaces were used. The as-received wood filled PP panel did not have exposed wood particles and this panel showed very poor bonding to pine. It also had a slick polymer rich surface. This panel could be peeled off from the pine board completely intact and with ease. On the contrary, light sanding of the panel exposed some of the wood particles in the FPC. Upon attempting to peel this FPC panel, the panel fractured and failed indicating good bonding of the substrates. The sanded surface with exposed wood filler was not slick upon wetting with water. The experiments showed that even a difficult to bond thermoplastic such as PP can provide significantly improved bonding when used in a wood filled thermoplastic composite. Other FPCs having thermoplastics such as PVC and ABS provide even more durable bonds to wood.  
         [0074]     While the invention has been described herein with reference to the specific embodiments thereof, it will be appreciated that changes, modification and variations can be made without departing from the spirit and scope of the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modification and variations that fall with the spirit and scope of the appended claims.