WO2000010804A1

WO2000010804A1 - Plastic reinforced wood flooring for trailers and method and apparatus for manufacturing same

Info

Publication number: WO2000010804A1
Application number: PCT/US1999/019270
Authority: WO
Inventors: Rodney P. Ehrlich; Karthik Ramani; Michael J. Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-24
Filing date: 1999-08-23
Publication date: 2000-03-02
Anticipated expiration: 2001-02-24
Also published as: AU5783599A; CA2339832A1

Abstract

The present invention provides a novel structure for forming a reinforced wood composite panel (20), and the method and apparatus for forming the same. The reinforced wood composite panel is preferably used to form a floor (22) of a trailer (24). The reinforced wood composite panel is formed of a wood board (28) having a plastic layer (32) bonded thereto. The plastic layer is formed from thermoplastic material having an adhesion bonding properties therein which allows the plastic layer to be bonded to the wood, or is formed from a polymer which de-polymerizes on melting, forming a low viscosity polymer, and solidifies upon cooling. The adhesion properties cause the plastic layer to mechanically and chemically bond to the wood. A second plastic layer may be bonded to the first plastic layer. The plastic layer can be fiber reinforced, such as glass fibers. A commingled glass-fiber polypropylene can be used for the plastic layer.

Description

PLASTIC REINFORCED WOOD FLOORING FOR TRAILERS AND METHOD AND APPARATUS FOR MANUFACTURING SAME

This application claims the priority of provisional application Serial No.

60/097,656, filed August 24, 1998 and entitled "Plastic Reinforced Wood Flooring for Trailers and Method and Apparatus for Manufacturing Same".

BACKGROUND OF THE INVENTION

This invention is generally directed to a novel plastic reinforced wood flooring for a trailer or the like and the method and apparatus for manufacturing same.

Through history materials have limited design. Even the ages in which humans have lived — stone, bronze, and iron — are named after materials. Today is an age where new products and evolutions of existing ones are determined by the novel combinations of materials and with new nanostructures, microstructures, and macrostructures. Bonding of dissimilar materials in ways to provide significant benefits, while keeping the manufacturing processes economical, is of paramount importance in meeting the demanding requirements of industry. Judicious combinations of different materials can help achieve high load bearing capability, good environmental resistance, durability under dynamic loading conditions, high specific strength, insulation and acoustic properties, and lower weights, while reducing costs.

Composite materials using high strength fibers to reinforce a matrix provide numerous advantages to designs. The fiber type, content, and orientation provide means for the designer to alter properties, in addition to altering the matrix that holds them together. Fibers are typically small, ten's of micro meters in diameter, and a tow of fibers consists of a bundle with thousands of fibers. To make use of the fibers effectively, the bundle is to be penetrated with the matrix, fully coated, and adhered with the polymer matrix.

Polymers used as matrices in composites can in general be classified into thermosets and thermoplastics. During processing, thermosets are of much lower viscosity than thermoplastics. Therefore, the impregnation of fibers with thermosets is not difficult. With thermoplastics, however, the penetration of the fiber bundles with the polymer is very difficult due to the higher melt viscosity of thermoplastic polymers. This invention concerns the use of fibers in a thermoplastic polymeric matrix. Polymeric fiber-reinforced composite materials can be broadly classified as thermoplastic composites and thermoset composites, based on the matrix material. Thermoplastics offer several potential advantages over thermosets, such as impact resistance, reprocessability, repairability, environmental resistance and recyclability. Thermoplastics can be heated and shaped to complex shapes and cooled to solidify, resulting in a short cycle time of the order of minutes. Thermoset composites in general have lengthy cycle times due to the cure of the resin. Wood has been used in many applications as a primary structural material including trailer floors, the primary field-of-use in this application. Wood in trailer floors absorbs moisture preventing the floor from becoming slippery, absorbs dirt to keep the floor clean, acts as a natural insulator preventing condensation, is easily nailed through, and acts as an even-wear surface while resisting abuse of the floor. Therefore, wood is a preferred material for the inside surface in a trailer floor. The lack of uniformity of physical properties of wood, however, has lead to uncertainty in engineering design of the trailer floor, resulting in high thickness and weight. The floors to-date are made of oak wood. The floor underside that is exposed to the roadside is subject to water from beneath that degrades the wood. The floors are also subject to significant bending loads, for example forklifts move on it, and typically fail in the joint areas.

Reinforcing the wood floor on the tension side ~ the underside ~ with a fiber reinforced composite material provides several advantages. These advantages include protection of the wood from moisture and the resulting rotting conditions, removal of the peak stresses in the tension side of wood especially in the joint areas, improved durability, reduction of the utilization of wood and weight, and reduction of cost compared to non-reinforced flooring. The properties of the reinforced wood in bending are predictable. A reduction in variability in properties allows significant design improvement over today's floors. With as little as five percent by cross-section area reinforced with an uni-directional high-tensile capability material, the load carrying capacity of the wood can increase by as much as forty percent.

A conventional trailer floor is composed of individual wood boards joined together, each wood board being approximately one inch thick. A single board does not run the length of the floor, rather, there are lap joints along the length of the floor between the boards. When subjected to bending, the lap joints can fail. This failure results in the boards on either side thereof not being able to carry any bending load. Failure of the whole floor follows shortly.

The prior art has considered reinforcing wood with thermoset composite materials. A key to the success of the wood reinforced composite is the adhesion of the thermoset composite to the wood for transfer of stresses. The thermoset resin used in the composite penetrates the pores in wood easily and forms a good bond. Thermoset reinforced wood, however, has not been made commercially feasible in high volumes. Thermoset based technology, which is fairly well developed, does not provide a cost-effective process for bonding to wood, although the resulting wood-thermoset composite shows properties sufficient for application. Several problems are associated with processing wood reinforced with thermoset composites. The thermoset resin cannot be controlled as a liquid on top of the wood surface, the thermoset resin leaks on the sides while forming a composite under heat and pressure, and the process tends to be very messy. In addition, controlling heat, glass, fibers, and liquid on the wood is very difficult. When heat is applied to the thermoset resin, the thermoset resin acts as a hydraulic liquid. That is, when heat is applied to a fiber- reinforced thermoset composite, the thermoset becomes much thinner and has a higher viscosity before hardening. When this occurs, the fibers in the composite tend to move around.

Applicant has found in the present invention that thermoplastic or thermoplastic composite processing is very clean, but can be difficult. First of all, a good method for impregnation of thermoplastic polymers into fibers has not been accessible to industry, the only options being expensive or not proven in an industrial scale. Secondly, wood is very sensitive to heating; bonding wood to thermoplastic composites that process at higher temperatures than thermosets is a challenge. Thirdly, bonding of the thermoplastic to wood is not easy because of the divergent chemical nature of the thermoplastic and wood, and the high melt viscosity of the thermoplastic that makes the thermoplastic difficult to penetrate wood pores.

Applicant has found in the present invention that bonding temperature-sensitive wood to higher temperature thermoplastic materials requires new processes very different from those used with thermosets. The present invention is intended to present such a process. Although thermoplastic composites have potential benefits compared to thermosetting composites, the difficult impregnation of thermoplastic polymers into continuous fibers for structural applications poses an economical barrier. Several process approaches have been explored for impregnation in the past such as solvent- based and melt-based processes. Solvent-based processes are not environmentally friendly, and many thermoplastics do not have solvents. Melt-based impregnation has difficulty in wetting the fibers thoroughly and the resulting composite has poor properties. Pre-impregnated fiber materials can be purchased from certain suppliers, but these materials tend to be expensive. The material economics of high volume transportation applications do not justify the purchase of such materials. The disadvantages of solvent-based and melt-based processes led to the development of powder and co-mingled techniques, such as the commingled technique developed by Certainty Glass Corporation. These techniques are based on the concept of intimately placing the polymer within the fibers without using a melt-based impregnation. Powder based processes include those developed by Purdue University. In co-mingled thermoplastics, wet-out of the fibers and consolidation is made possible at lower pressures without long exposures to melt temperatures.

The present invention provides a novel plastic reinforced wood flooring for a trailer and the method and apparatus for manufacturing same which overcomes the problems found in the prior art.

SUMMARY OF THE INVENTION

The present invention discloses a novel structure for forming a reinforced wood composite panel, and the method and apparatus for forming same. The reinforced wood composite panel is preferably used to form a floor of a trailer, but may be used in other applications. The reinforced wood composite panel is formed of a wood board having a plastic layer bonded thereto. The plastic layer is formed from thermoplastic material having adhesion bonding properties therein which allows the plastic layer to be bonded to the wood, or is formed from a polymer which de-polymerizes on melting, forming a low viscosity polymer, and solidifies upon cooling. The adhesion bonding properties of the plastic layer causes the plastic layer to mechanically and chemically bond to the wood. A second plastic layer may be bonded to the first plastic layer. The plastic layer can be fiber reinforced, such as with glass fibers. A commingled glass-fiber polypropylene can be used for the plastic layer. BRIEF DESCRIPTION OF THE DRAWINGS

The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which:

FIGURE 1 is a partial perspective view of a trailer with outer walls thereof being broken away to show a floor of the trailer which incorporates the features of the invention;

FIGURE 2 is a partial perspective view of a trailer floor which incorporates the features of the invention;

FIGURES 3 A-3D are elevational view of a press showing the steps in a surface heating process of bonding a plastic layer in the form of a pre-consolidated sheet of laminate to one side of a piece of wood in a batch process for forming a panel in accordance with the present invention; FIGURE 4 is a side elevational view, shown partially in cross-section, of an assembly for effecting a combined surface heating and through heating process to bond a plastic layer in the form of a pre-consolidated laminate and a tie-layer to one side of a piece of wood in a continuous process for continuously forming a panel in accordance with the present invention; FIGURE 5 is a side elevational view, shown partially in cross-section, of a first embodiment of an assembly for effecting a combined formation of plastic fiber reinforced rovings into a laminate and bonding a tie-layer and the laminate to one side of a piece of wood in one integrated step in and a continuous process for continuously forming a panel in accordance with the present invention; FIGURE 6 is a side elevational view, shown partially in cross-section, of a second embodiment of an assembly for effecting a combined formation of plastic fiber reinforced rovings into a laminate and bonding a tie-layer and the laminate to one side of a piece of wood in one integrated step in and a continuous process for continuously forming a panel in accordance with the present invention; FIGURE 7 is a side elevational view, shown partially in cross-section, of a third embodiment of an assembly for effecting a combined formation of plastic fiber reinforced rovings into a laminate and bonding a tie-layer and the laminate to one side of a piece of wood in one integrated step in and a continuous process for continuously forming a panel in accordance with the present invention;

FIGURE 8 is a side elevational view, shown partially in cross-section, of a fourth embodiment of an assembly for effecting a combined formation of plastic fiber reinforced rovings into a laminate and bonding a tie-layer and the laminate to one side of a piece of wood in one integrated step in and a continuous process for continuously forming a panel in accordance with the present invention;

FIGURE 9 is a side elevational view, shown partially in cross-section, of a fifth embodiment of an assembly for effecting a combined formation of plastic fiber reinforced rovings into a laminate and bonding a tie-layer and the laminate to one side of a piece of wood in one integrated step in and a continuous process for continuously forming a panel in accordance with the present invention;

FIGURE 10 is a graph showing time versus temperature for the process of FIGURE 4;

FIGURE 11 is a graph showing time versus temperature for the embodiments of the process shown in FIGURES 5-9; FIGURES 12A and 12B are cross-sectional views of a novel structure for containing plastic material on wood using the assembly shown in FIGURES 3A-3D;

FIGURES 13A and 13B are cross-sectional views of a novel structure for containing plastic material on wood using the assembly shown in FIGURES 4-9;

FIGURE 14A is a magnified image of the cross-section of the pre-consolidated fiber reinforced laminate and the wood interface using the process of

FIGURE 4 magnified one hundred times after bonding;

FIGURE 14B is an enlargement of a portion of FIGURE 14A with the contrast between the polypropylene and the tie-layer enhanced;

FIGURE 15A is a magnified image of the cross sections of the bond line at the plastic layer/tie-layer/wood interface using the combined consolidation and bonding process of FIGURES 5-9;

FIGURE 15B is an enlargement of a portion of FIGURE 15A;

FIGURE 16A is a perspective view of a link in an endless chains used in the embodiments of the process shown in FIGURES 4-9;

FIGURES 16B is an exploded perspective view of a link in the endless chains used in the embodiments of the process shown in FIGURES 4-9; and

FIGURE 17 is a cross-sectional view of an assembly for forming the composite plastic layer while bonding the composite plastic layer to the wood using an extruder to generate a molten plastic layer and bonding in a continuous process to one side of the wood.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, specific embodiments with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.

The present invention provides a novel structure for forming a reinforced wood composite panel 20, and the method and apparatus for forming same. The reinforced wood composite panel 20 is preferably used to form a floor 22 of a trailer

24. As shown in FIGURES 1 and 2, the floor 22 of the trailer 24 has a plurality of panels 20 joined together at lap joints 26. When the novel reinforced wood composite panel 20 of the present invention is used in the floor 22, the floor 22 is capable of longer wear and is less susceptible to damage from the environment. The reinforced wood composite panel 20 is formed of wood board 28, which is preferably oak, but may be hickory, beech or the like, having a thin tie-layer 30 provided between the wood 28 and a plastic layer 32. The tie-layer 30 is very thin, approximately 250-500 μm. The tie-layer 30 has adhesion bonding properties therein which allows the plastic layer 32 to be bonded to the tie-layer 30 and allows the wood 28 to be bonded to the tie-layer 30. The adhesion bonding properties causes the tie- layer 30 to mechanically and chemically bond to the wood 28. The tie-layer 30 and the plastic layer 32 are bonded to one side of the wood 28 to form the reinforced wood composite panel 20. When used in the trailer floor 22, the tie-layer 30 and the plastic layer 32 are bonded to the underside of the trailer floor 22, i.e. the side of the floor 22 which faces the roadway, and overlays the lap joints 26 between the wood boards 28. Thus, the lap joints 26 are reinforced. The tie-layer 30 is formed from thermoplastic and is formulated using a blend of polymers (or their co-polymer equivalents) incorporating elements compatible with the plastic layer 32 and the wood 28. Examples of such blends include polypropylene and ethylene-propylene copolymer; polyethylene and polyisobutylene; propylene acrylic acid co-polymer and ethylene acrylic acid copolymer or maleic anhydride modified polypropylene. These blends may comprise these polymers in the form of ter-polymers and co-polymers, such as ethylene-propylene co-polymer. The bonding characteristics of the tie-layer 30 is obtained by specific interactions: 1) hydrogen bonding exhibited by hydroxyl containing polymers, either as terminal groups, or pendant groups, 2) ionic bonding observed in ionomers, and 3) polar functional groups in polymer backbone chain (ester, ether, amide group or urethane group).

Polar groups can also form on the surface of the tie-layer 30 during heating and processing. In addition to chemical interactions, the tie-layer 30 mechanically interlocks with the pores in the wood 28 as described herein. The adhesion bonding properties in the tie-layer 30 are formed by virtue of the material choice provided in the present invention to allow the plastic layer 32 to be bonded to the tie-layer 30 and allows the wood 28 to be bonded to the tie-layer 30. There are many variations of the material choice for the tie-layer 30 which may be used in the present invention so long as the tie-layer 30 allow the plastic layer 32 to be bonded to the tie-layer 30 and allows the wood 28 to be bonded to the tie-layer 30. Preferably, the tie-layer 30 of the present invention is formed for bonding oak wood with polypropylene composite skin. Two types of tie-layers 20 are preferably used. The first type is a blend of polyolefin plastics component (low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene-propylene copolymer, or polypropylene) and elastomer component (polyisobutylene, polybutylene). The required tie-layer 30 material composition has 5%-50% by weight of elastomer, the remaining being polyolefin plastics component. The two components are thoroughly blended using a twin screw extruder and then pelletized. The pellets thus obtained are made into film form by a single screw extruder fitted with a film die. The second type of tie-layer 30 film has non-polar polyolefin component (low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene-propylene copolymer, or polypropylene) and polar component (ethylene-acrylic acid copolymer, propylene acrylic acid copolymer, maleic anhydride modified polypropylene). The tie layer 30 formulation has polar component from 10%-80% by weight. The corresponding resins in pellet forms are dry blended, extruded using a twin screw extruder or a single screw extruder with a special mixing head at the end, and pelletized to obtain homogenous mixture. Then the resultant pellets are extruded again fitted with a film die to produce tie-layer 30 film (cast film process). By adjusting the take-off speed of the film casting unit, the thickness of cast films was controlled to 100 +/- 20 micron.

The plastic layer 32 is also formed from a thermoplastic material 34 made from a low-cost polymer. A variety of thermoplastic polymers may be used for the thermoplastic material 34, such as polypropylene (PP), PBT, thermoplastic urethane (TPU), nylon, polyethyleneterephthalate (PET), polyethylene (PE), polyacetal, as well as blends of these polymers. Polypropylene is preferred because it has good engineering properties, and is a low-cost, high-volume engineering polymer.

The thermoplastic material 34 can be fiber reinforced, such as with glass fibers 36. The glass fibers 36 support the wood board 28 while reducing the stress on the lap joints 26 by directing the stress around each lap joint 26. This further resists the failure of the floor 22, especially at the lap joints 26.

In addition, a commingled glass-fiber polypropylene can be used to economically form a continuous-glass-fiber-reinforced-polypropylene ("CGFRPP") for the plastic layer 32. The commingling is performed in the glass manufacturing operation at very high speeds of over fifty feet per second, wherein the polymer is drawn along with the glass fibers. Therefore, for an end user, the material form does not involve any intermediate suppliers and consolidation does not involve high pressures and temperatures characteristic of melt-based processes. CGFRPP can be consolidated at low pressures (approximately 100-150 psi), and high speeds (approximately 25 in sec), reducing costs and satisfying high volume needs. It is to be understood that there are multiple processes to make CGFRPP: a powder process, multi-layering, a polypropylene bath, a depolymerized polymer and commingling. If CGFRPP is used, a plurality of rovings 38 are laid side-by-side to form a mat and are heated to commingle the thermoplastic material 34 and the glass fibers 36. The glass fibers 36 are continuous along generally the length of the floor 22 to provide for additional reinforcement of the floor 22. That is to say, the continuous fibers 36 may extend over the length of one of more panels 20 depending on the length of the floor 22 and how many panels 20 are used to form the length of the floor 22. Because the hydrophilic nature of cellulose fiber in the wood 28 resists interaction with a hydrophobic thermoplastic material 34, the adhesion bonding properties within the tie-layer 30 is used to overcome this problem. Elastomeric components can be added to the tie-layer 30, such as ethylene-propylene, to provide additional strength at the interface between the tie-layer 30 and the wood 28 because the polymer has to stretch before the interface fractures.

Instead of providing a separate tie-layer 30 having the adhesion bonding properties therein, the materials which are used to form the tie-layer 30 can be added to the plastic layer 32, thereby eliminating the tie-layer 30 as shown in FIGURE 2. That is, the blend of polymers (or their co-polymer equivalents) incorporating elements compatible with the wood 28 can be added to the plastic layer 32. Again, examples of such blends include polypropylene and ethylene-propylene copolymer; polyethylene and polyisobutylene; propylene acrylic acid co-polymer and ethylene acrylic acid copolymer or maleic anhydride modified polypropylene. These blends may comprise these polymers in the form of ter-polymers and co-polymers, such as ethylene-propylene co-polymer. The bonding characteristics of the plastic layer 32 having these materials therein is obtained by specific interactions: 1) hydrogen bonding exhibited by hydroxyl containing polymers, either as terminal groups, or pendant groups, 2) ionic bonding observed in ionomers, and 3) polar functional groups in polymer backbone chain (ester, ether, amide group or urethane group).

Polar groups can also form on the surface of the plastic layer 32 during heating and processing. In addition to chemical interactions, the plastic layer 32 with these materials therein mechanically interlocks with the pores in the wood 28. The adhesion bonding properties by virtue of the material choice causes the plastic layer 32 to mechanically and chemically bond to the wood 28 when the tie-layer 30 is eliminated. The plastic layer 32 is then bonded directly to the one side of the wood 28.

When the wood 28 is laminated with the tie-layer 30 and the plastic layer 32, or with solely the plastic layer 32 having the adhesion bonding properties therein, in accordance with the present invention, the laminate formed by the tie-layer 30/plastic layer 32 or the plastic layer 32 takes up the tension load in addition to the wood 28 taking up the tension load. The wood 28 with the laminate thereon acts as a compressive member. The laminated side provides the tension side and the wood side provides the compressive side. In addition, when the wood 28 is laminated in accordance with the present invention, moisture does not get into the lap joints 26 because the laminate covers the lap joints 26. Moreover, when a forklift is driven over the wood floor 22 laminated in accordance with the present invention, wood fiber breakage does not occur because of the laminate. Now the different embodiments of the process for forming the novel reinforced wood composite panel 20 is described.

Attention is now directed to FIGURES 3A-3D, which illustrates a surface heating process of bonding the plastic layer 32 in the form of a pre-consolidated sheet of laminate 40 to one side of the wood 28 in a batch process to form the reinforced wood composite panel 20. The laminate 40 is laminated onto the surface of the wood 28. As shown in the drawings, the tie-layer 30 has been eliminated and the materials providing the adhesion bonding properties are provided directly in the plastic layer 32.

A consolidation press 42 is provided which has an upper platen 44 and a lower platen 46. A movable infrared (IR) heater 48 is provided and is movable to a first position between the platens 44, 46 and to a second position outwardly from between the platens 44, 46. The heater 48 is moved by suitable moving means (not shown).

When the platens 44, 46 are moved apart from each other such that the consolidation press 42 is in an open position, the wood 28 at room temperature and the laminate 40 formed from the plastic layer 32 at room temperature are placed on the platens 44, 46 and are secured thereto by suitable means. As shown in the drawings, the wood 28 is secured to the upper platen 44 by suitable means, and the laminate 40 sits on the bottom platen 46. When the consolidation press 42 is open, the wood 28 and the laminate 40 are spaced apart from each other a predetermined distance.

Again, with the consolidation press 42 still in the open position, the heater 48 is placed between the wood 28 and the laminate 40 and heats the surfaces of the wood 28 and the laminate 40 which face each other for a predetermined time such that surfaces are heated to a temperature which is above the temperature required to bond the laminate 40 to the wood 28. The heater 48 is then removed from between the wood 28 and the laminate 40 by the moving means, and the wood 28 and the laminate 40 are quickly pressed together by moving the platens 44, 46 towards each other using suitable known moving means to close the consolidation press 42 such that the heated surfaces are placed into contact with each other. The press 42 is closed quickly after removal of the heater 48 to prevent significant cooling of the surfaces. The consolidation press 42 applies pressure to the wood 28 and the laminate 40, thereby squeezing the wood 28 and the laminate 40, while the wood 28 and the laminate 40 cools. This bonds the laminate 40 formed from the plastic layer 32 to the one side of the wood 28 to form the reinforced wood composite panel 20 such that the laminate

40 is laminated onto the wood 28. After a predetermined time, the platens 44, 46 are moved apart from each other to the open position by the moving means and the reinforced wood composite panel 20 is removed from the consolidation press 42. If an entire floor 22 comprised of a plurality of wood boards 28 joined together by lap joints 26 is to be laminated, the entire floor 22 is placed on the upper platen 44 and the laminate 40 which is sufficient to cover the entire floor 22 is placed on the bottom platen 46.

In order to minimize the time between heating and bonding, the surface of the wood 28 and the surface of the laminate 40 are heated after they are loaded into the consolidation press 42. Applicant has found that a very short cycle time can be obtained on the order of two minutes for the entire cycle. An advantage of this surface heated batch process is that no conductive through heating is involved, the consolidation press 42 does not have to heat the wood 28 and the laminate 40 (that is a cold press is used), the cycle is short such that it can be implemented for high volumes. This surface heating process is fast and efficient because only a small amount of material needs to be heated to the process temperature. This process does require a sheet of laminate 40, such as a pre-consolidated fiber-reinforced panel. In addition, this process requires that the consolidation press 42 be as long and as wide as the floor 22 (approximately fifty feet for trailers). Applicant has found that the surface heating process takes about one hundred and fifteen seconds. During the first seventy seconds, the surface of the wood 28 and the surface of the laminate 40 are heated from room temperature to the bonding or process temperature. If polypropylene is used, the temperature must exceed the melting temperature of 165 °C. The wood 28 must be above that temperature, but below approximately 200 °C at which the wood 28 degrades. In the next five seconds the heater 48 is withdrawn and the consolidation press 42 is closed. The surfaces of the wood 28 and the laminate 40 will cool to less than 170°C in a few seconds, requiring that the consolidation press 42 be rapidly closed after the heater 48 is removed to place the heated surfaces of wood 28 and the laminate 40 into contact with each other. The consolidation press 42 is then held closed under pressure for thirty seconds, while the bond line cools and solidifies.

In this process as described, the tie-layer 30 is not used and therefore, the materials providing the adhesion bonding properties are in the laminate 40 formed from the plastic layer 32. If the tie-layer 30 is used, the tie-layer 30 may be placed between the wood 28 and the plastic layer 32 while the heater 48 is being removed. Alternatively, the tie-layer 30 may be bonded to the surface of the wood 28 which faces the plastic layer 32 or to the surface of the plastic layer 32 which faces the wood 28 before the wood 28 or the plastic layer 32 is placed in the consolidation press 42. To bond the tie-layer 30 to the surface of the wood 28, the surface of the wood

28 is heated using a heater 48 until the surface temperature is above the temperature at which the tie-layer 30 melts. This typically takes one hundred to one hundred and twenty seconds. The tie-layer 30 is then placed on the surface of the wood 28. The heater 48 is then used to heat the tie-layer 30 until fully melted. Typically, this requires seven to fifteen seconds of heating. The tie-layer 30 is then pressed onto the wood 28 with approximately fifty psi. The pressure applied to the tie-layer 30 is not critical as long as good surface wetting of the wood 28 is achieved. During surface heating experiments, using a polyethylene based tie-layer 30, it was found that the polyethylene tie-layer has a lower melting temperature and is not as strong as a polypropylene tie-layer.

Attention is now directed to FIGURE 4, which illustrates a combined surface heating and through heating process to bond a plastic layer 32 in the form of a pre-consolidated laminate 40 and a tie-layer 30 to one side of the wood 28 in a continuous process. The continuous process is not as laborious as the batch process as shown in FIGURES 3A-3D and is better controlled.

In this process a continuous press 50 is provided. A first upper section 52 of the press 50 has a plurality of platens 54 mounted on an endless chain 56 and is herein called the "consolidation section." The endless chain 56 is mounted around pair of spaced apart, toothed wheels 58, 60. Between the toothed wheels 58, 60, a support beam 62 is provided within the endless chain 56. A second upper section 64 of the press 50 has a plurality of platens 66 mounted on an endless chain 68 and is herein called the "cooling section." The endless chain 68 is mounted around a pair of spaced apart, toothed wheels 70, 72. A support beam 74 is provided within the endless chain 68 and is mounted between the toothed wheels 70, 72. The consolidation section and the cooling sections 52, 64 of the press 50 are in-line with each other. The cooling section 64 may be shorter in length than the consolidation section 52. In addition, an endless release belt 76, which may be made of out TEFLON® impregnated cloth or stainless steel, encircles the consolidation and cooling sections 52, 64 of the press. The release belt 76 is supported on a plurality of rollers 78. A bottom section 80 of the press 50 has a plurality of platens 82 mounted on an endless chain 84. The endless chain 84 is mounted around a pair of spaced apart, toothed wheels 86, 88. The bottom section 80 is slightly longer in length than the combined length of the consolidation and cooling sections 52, 64. A support beam 90 is provided within the endless chain 84 and is mounted between the toothed wheels 86, 88. Each support beam 62, 74, 90 is supported on one side by a rigid frame (not shown) and on the other by adjustable hydraulic supports (not shown).

The wood 28, the tie-layer 30 and the laminate 40 start out on different conveying lines. A length of wood 28 is surface heated using suitable means, such as an IR heater 92, as the wood 28 is moved past the heater 92 by rollers 94. That is, one surface of the wood 28 is heated by the heater 92. A supply of the tie-layer 30 at room temperature is then laid down on the heated surface of the wood 28. Thereafter, a supply of the laminate 40 at room temperature is laid down on the tie-layer 30 such that the tie-layer 30 is sandwiched between the laminate 40 and the wood 28. As the laminate 40 is being laid onto the tie-layer 30, the laminate 40 is bent by roller 96. Roller 96 also ensures contact of the laminate 40 and the tie-layer 30 as the laminate 40 and the tie-layer 30 pass through the nip formed by the roller 96 and the wood 28. The laminate 40 and the tie-layer 30 are then through heated by a heater 98 by heating the surface of the laminate 40 opposite to that which is in contact with the tie- layer 30 until an acceptable processing temperature is reached and the laminate 40 and tie-layer 30 melt. It has been found that if polypropylene is used in the laminate 40, a homogeneous bond is not formed unless the polypropylene is through-heated before being bonded to the wood 28 because the polypropylene does not remain above the melt temperature for a long period of time.

After the through-heating step, the wood 28, the molten laminate 40 and the molten tie-layer 30 are conveyed together by rollers 94 into and through the press 50 by passing between the consolidation section 52 and the bottom section 80, and then through the cooling section 64 and the bottom section 80. The platens 54, 66 in the consolidation and cooling sections 52, 64 are prevented from touching the sticky, melted laminate 40 by the endless release belt 76, thereby preventing the laminate 40 from adhering to the platens 54, 66. The platens 82 in the bottom section 80 engage against the exposed surface of the wood 28. The continuous press 50 compresses the wood 28, the tie-layer 30 and the laminate 40 together as it passes therethrough to form a bond therebetween and is thereafter cooled. Because of pressure applied by the consolidation, cooling and bottom sections 52, 64, 80, the surface of the wood 28 is compressed. As the finished reinforced wood composite panel 20 passes outwardly from between the cooling section 64 and the bottom section 80, the release film 76 is peeled away from the laminate 40 by means of the roller 78. This process does not require that the continuous press 50 be heated.

Surface heating of the wood 28 increases the speed of the continuous process. It has been found that overheating of the laminate 40 and bending causes fiber waviness on the inside surface of the resulting reinforced wood composite panel 20 when fiber-reinforced plastic is used as the laminate 40. In this embodiment, the heat can be delivered by contact heating by a hot press or with non-contact heating such as IR heaters. An example of a test using a hot press to heat the materials is that the materials were heated with a 250 °C platen under 25 psi for one hundred and twenty seconds, followed by ninety seconds at 100 psi for bonding. The platen was then removed and replaced with a room temperature platen at only 3 psi for cooling. The graph shown in FIGURE 10 shows processing temperatures and pressures from the test. In this test, polypropylene was used for the laminate 40. The top temperature trace shows the temperature of the polypropylene at the face of the platen. The lower temperature trace shows the temperature at the wood surface. The heating and bonding times could have been shortened, but were kept long to provide a comparison with a test of the combined consolidation and bonding method described below and shown in the graph of FIGURE 11.

FIGURES 5-9 illustrate combined formation of plastic fiber reinforced rovings 38 into a laminate 40 and bonding the tie-layer 30 and the laminate 40 to one side of the wood 28 in one integrated step in and a continuous process. The continuous process is not as laborious as the batch process as shown in FIGURES 3 A-3D and is better controlled.

Attention is now directed to FIGURE 5 which illustrates the preferred embodiment of the process. In this process a continuous press 50 identical to the continuous press 50 shown in FIGURE 4 except that a heater 100 is provided between the consolidation section 52 and the release film 76 is provided to heat an outer surface of the platens 54 of the consolidation section 52 as the platens 54 pass thereby. Therefore, like reference numerals are used for like elements.

The wood 28, the tie-layer 30 and the fiber reinforced plastic rovings 38 start out on different conveying lines. A length of wood 28 at room temperature is advanced by rollers 94. A supply of the tie-layer 30 at room temperature is thereafter laid down on one surface of the wood 28 by rollers 102.

A plurality of the rovings 38 having unconsolidated fiber and polymer (such as commingled glass polypropylene) are supplied. The rovings 38 are fed through guiding means 104 for fiber placement, shown as rollers in the drawings, and are placed on the tie-layer 30 to form a mat which covers the tie-layer 30.

The rovings 38, the tie-layer 30 and the wood 28 are advanced through and between the consolidation section 52 and the bottom platen 80 by the rollers 94. The platens 54 in the consolidation section 52 are heated when they pass along the top of their track by the heater 100 which may take a variety of forms, including, but not limited to, a burner box, hot gas vent, contact heating shoe, and the like. The platens 54 on the consolidation section 52 are kept from coming into contact with the sticky, melted plastic in the commingled fibers formed by heating the rovings 38 because the platens 54 in the consolidation section 52 contact the release belt 76. The platens 82 on the bottom section 80 contact the exposed surface of the wood 28. The commingled fibers in the rovings 38 are heated from the side away from the tie-layer 30 and the wood 28 by the platens 54 in the consolidation section 52 of the press 50. The heated commingled fibers, the tie-layer 30 and the wood 28 are held under heat and pressure from the press 50 while the plastic material, such as polypropylene, impregnates the glass fibers and consolidates to form the laminate 40. Simultaneously, the laminate 40 also bonds to the tie-layer 30, while the tie-layer 30 bonds with the wood 28 to form a layered or sandwich-type structure. Therefore, formation of the laminate 40, and the bonding of the laminate 40, the tie-layer 30 and the wood 28 are effected together all in one integrated combined process.

Thereafter, the sandwich-type structure is cooled by contact with platens 66 in the cooling section 64 that are not heated. The commingled fibers are solidified and cooled in the cooling section 64. The sandwich-type structure passes through and between the cooling section 64 and the bottom platen 80 by the rollers 94. The platens 66 in the cooling section 64 are kept from touching the commingled fibers by the endless release belt 76. As the finished reinforced wood composite panel 20 passes outwardly from between the cooling section 64 and the bottom section 80, the release belt 76 is peeled away from the laminate 40 (formed by the melted rovings 38) by means of the roller 78. The finished reinforced wood composite panel 20 exits the continuous press 50 at a low enough temperature that the reinforced wood composite panel 20 can be handled and stacked without damage.

Because of pressure applied by the platens 54, 66, 82, the surface of the wood 28 is compressed. The heating step can be shortened by preheating the wood surface before the tie-layer 30 and the rovings 38 are placed thereon. Consolidation of the laminate 40, bonding of the laminate 40 to the tie-layer 30, and bonding of the tie- layer 30 to the wood 28 have a plurality of ranges of feasible temperatures, pressures and times.

Formation of the reinforced wood composite panel 20 using this process provides a unique interface character in contrast to that formed by the through heating process. The interface between the tie-layer 30 and the laminate 40 also has mechanically interlocked sites and has high shear strengths. In addition, the fibers are close to the surface of wood 28. FIGURES 14A and 14B show the microstructures of the interface formed in the through heating and combined consolidation process, respectively.

It has been found that the specifics of temperature, time, and pressure during processing can cover a wide range. They are interdependent variables. Higher platen temperatures allow lower heating times. Longer times allow lower consolidation pressure. Higher consolidation pressures increase heat transfer through the commingled fibers and allows for lower platen temperatures.

An example of test performed for the process shown in FIGURE 5 is as follows. The consolidation section 54 was operated at 250 °C and pressure was applied at under twenty-five psi pressure for one hundred and twenty seconds. Pressure was then increased to one hundred psi and held for another ninety seconds. Thereafter, pressure of three psi was applied to the sandwich-type structure. The graph in FIGURE 11 shows temperatures and pressures during the test. The top temperature trace shows the temperature of the plastic layer, polypropylene in this case, at the face of the platens. The lower temperature trace shows the temperature at the tie-layer 30 and wood 28 interface. Attention is now directed to the embodiment of the process shown in FIGURE 6 which is identical to the embodiment shown in FIGURE 5 except in the process shown in FIGURE 6, the bottom section of the continuous press 50 is replaced by a plurality of hydraulically supported rollers 106. The force exerted by each roller 106 can be controlled independently of the rest, allowing separation of the continuous press 50 into distinct preheating and consolidation zones. For example, working from left to right in the drawing, the first three rollers 106 can be operated at low pressure, the middle six rollers 106 can be operated at high pressure and the last three rollers 106 can be operated at low pressure. Attention is now directed to the embodiment of the process shown in FIGURE

7. The embodiment in FIGURE 7 is identical to the embodiment shown in FIGURE 5 except that the surface of the wood 28 is pre-heated using a heater 108 before the tie- layer 30 is laid thereon, the surface of the tie-layer 30 is pre-heated after it is laid on the heated surface of the wood 28 using a heater 110, and the rovings 38 are pre- heated by heaters 112 prior to being laid onto the heated surface of the tie-layer 30. In addition, the consolidation section 52 of the continuous press 50 is shorter because the wood 28, the tie-layer 30 and the rovings 38 are pre-heated before they enter into the continuous press 50. As shown in FIGURE 7, the rovings 38 are heated while suspended away from the tie-layer 30 and the wood 28, thereby allowing fast heating of the rovings 38 from all sides. The rovings 38 could also be heated while held in place on top of the tie-layer 30, similar to FIGURE 4.

The embodiment of the process illustrated in FIGURES 8 and 9 are identical to the embodiment shown in FIGURE 5 except that the endless release belt of FIGURE 5 is replaced with a thin plastic film 114. This film 114 serves the same function as the release belt 76, that is, to prevent the sticky, melted plastic layer 32 from adhering to the platens 54, 66 in the consolidation and cooling sections 52, 64.

In FIGURE 8, the film 114 is supplied by a supply roll 116 and laid on the rovings 38 prior to entry of the wood 28, the tie-layer 30 and the rovings 38 into the continuous press 50. The film 114 is collected on a take-up roll 118 after the finished sandwich-type structure exits the continuous press 50. A roller 120 is used to peel the film 114 away from the finished sandwich-type structure. The used film 114 can be recycled or discarded.

In FIGURE 9, the film 114 is supplied by the supply roll 116 and laid on the rovings 38 prior to entry of the wood 28, the tie-layer 30 and the rovings 38 into the continuous press 50 and is left on the finished sandwich-type structure as a permanent addition to the surface of the finished sandwich-type structure. During the consolidation section 52, the film 114 is bonded to the laminates 40, but maintains the prevention of the platens 54, 66 from coming into contact with the sticky, melted plastic layer 32.

The chains 56, 68, 84 used in the present invention are similar in design to a bicycle chain, see the links 113 of the chains 56, 68, 84 shown in FIGURES 16A and 16B. The individual links 113 are about four inches in length. Roller bushings span the middle of the respective chains 56, 68, 84. The chains 56, 68, 84 roll along the respective support beams 62, 74, 90. The support beams 62, 74, 90 are just narrow enough to fit between the walls of the respective chains 56, 68, 84 and contact the rollers. The respective platens 54, 66, 82 are mounted thereon.

FIGURES 14A and 14B are magnified images of cross sections of the plastic layer/tie-layer/wood interface after bonding. FIGURE 14A shows the bond line between the pre-consolidated fiber reinforced laminate 40 and the wood 28 using the process of FIGURE 4 magnified one hundred times. The top portion of the image is the wood surface. The large hole in the left side of the wood 28 is a natural capillary in the wood 28. The lower portion of the image shows glass fibers 36 viewed end on. Between the glass 36 fibers and the wood surface is a dark band. This band is composed of polypropylene 34 in the lower half and the tie-layer 30 in the upper half.

The border between the polypropylene 34 and the tie-layer 30 has been highlighted by a blue line for clarity. FIGURE 14B is an enlargement of a portion of FIGURE 14A with the contrast between the polypropylene 34 and the tie-layer 30 enhanced. The band at the bond line exists because the manufacturer of the pre-consolidated fiber reinforced laminate 40 adds a thin film of pure polypropylene to the fiber reinforced laminate surface. This "polypropylene enrichment" completely covers any exposed glass fibers.

FIGURE 15 A shows the bond line, magnified, between the commingled fibers formed out of the rovings 38, the tie-layer 30 and the wood 28 using the combined consolidation and bonding process of FIGURES 5-9. The top portion of the image is the wood surface. Several capillaries in the wood 28 are visible. The lower portion shows the glass fibers 36. The tie-layer 30 invades the glass fiber matrix during consolidation. Because of this, the glass fibers 36 from the combined processing sample lie much closer to the surface of the wood 28 than the glass fibers 36 in the pre-consolidated fiber reinforced laminate 40.

FIGURES 12A, 12B, 13A and 13B illustrate a novel structure for preventing the melted plastic layer 32 from overflowing the edge of the wood 28 during consolidation. This may be used during any of the embodiments of the process shown in FIGURES 4 and 5-9. Plastic tends to flow when heated, and commingled fibers especially tend to flow during consolidation. The mass of unconsolidated commingled fibers has a larger volume than the final composite. The fiber mat reduces in thickness by more than 50% during processing. Unless contained, the plastic material will flow out from between the platen(s) 54, 66 and the wood 28, carrying the glass fibers 36 with it if glass fibers 36 are provided. If uncontained, the excess material forms a bead at the edge of the wood 28. This bead must be cut away and discarded. Furthermore, when the plastic flows, it disturbs the alignment of the glass fibers 36, thus reducing the effectiveness of the reinforcement provided by the glass fibers 36. In the embodiment of FIGURE 4, as shown in FIGURES 12 A and 12B, a pair of elongated blocks 122 of silicone rubber-like material are mounted on the upper platen 44 and spans the length thereof. The elongated blocks 122 are spaced apart from each other. In the embodiments of FIGURES 5-9, as shown in FIGURES 13 A and 13B, a pair of endless blocks 124 of silicone rubber-like material are mounted on the exterior of the platens 82 of the bottom endless chain 84. The elongated blocks 124 are spaced apart from each other on the chain 84. When the wood 28 is placed on the upper platen 44 as shown in FIGURES 12A and 12B or engages against the platens 82 on the bottom endless chain 84 as shown in FIGURES 13 A and 13B, the respective blocks 122, 124 seat tightly against the opposite edges of the wood 28. The blocks 122, 124 have a height which is greater than the height of the wood 28 and preferably extends beyond the surface of the wood 28 approximately one quarter of an inch. The material of which the blocks 122, 124 are formed must withstand repeated cycling at process temperatures. In the embodiment of the process shown in FIGURE 4, the laminate 40 is placed on the platen 46 with a small gap between the laminate 40 and each block 122. As the platens 44, 46 come together, the upper platen 33 closes on the blocks 122, locking the blocks 122 in place by friction. That is, friction with the platens 44, 46 keeps the blocks 122 from being pushed sideways by the plastic material as it flows. The sides of the blocks 122 bulge outward at 126 making a tight seal with the edge of the wood 28. The press 42 closes further until the laminate 40 is compressed and consolidated. The melted plastic flows up to the blocks 122 but is prevented from flowing down the edges of the wood 28 by the tight seal the blocks 122 form with the wood 28 and the platen 46. In the embodiment of the process shown in FIGURES 5-9, the laminate 40, formed by melted rovings 38, is placed on top of the wood 28 with a small gap between the laminate and each block 124. As the materials move into the continuous belt 50, the platens 54, 66 on the endless chains 56, 68 close on the blocks 124, locking the blocks 124 in place by friction. That is, friction with the platens 82; 54, 66 keeps the blocks 124 from being pushed sideways by the plastic material as it flows. The sides of the blocks 124 bulge outward at 128 making a tight seal with the edge of the wood 28. The melted plastic material flows up to the blocks 124 but is prevented from flowing down the edges of the wood 28 by the tight seal the blocks 124 make with the wood 28 and the platens 82; 54, 66. The overall height of the blocks 122, 124 is large compared to its change in height during processing. This reduces the wear and tear on the blocks 122, 124 thus increasing reusability.

Attention is now directed to FIGURE 17, which illustrates forming the composite plastic layer 32 while bonding the composite plastic layer 32 to the wood

28 using an extruder 130 to generate a molten plastic layer 134 and bonding in a continuous process to one side of the wood 28.

A length of wood 28, which can be preheated, is drawn into and through a Pultrusion die 134 along with raw glass fibers 36 which are supplied from a source. Prior to entering into the Pultrusion die 134, a plurality of the glass fibers 36 are laid on top of the wood 28 using rollers 136.

The molten plastic material 132, which is a polymer melt, is generated in a extrusion process and injected under pressure into the Pultrusion die 134 through the extruder 130. Preferably, a polymer is used that de-polymerizes on melting, forming a low viscosity polymer, such as rigid thermoplastic urethane (TPU) which is a variation of a typical thermoplastic polymer. The low viscosity polymer penetrates and wets the glass fibers 36, which may be formed in bundles, on top of the wood 28 with relative ease, and invades the wood surface thereby bonding it to the wood 28. The polymer re-polymerizes and forms a higher molecular weight polymer on cooling. After cooling the wood/fiber reinforced composite panel 20 is formed.

Adhesion of the glass reinforced plastic layer 132 to the wood 28 can be enhanced, if necessary, by a tie-layer 30 (not shown) or additives to the molten plastic 132.

Applicant conducted a variety of experiments to test bond shear strength using a variety of different parameters under each embodiment of the process described, using the tie-layer 30 to bond the wood 28 to a thermoplastic material 34. The surface heating results represent a range of process parameters with over fifty different samples. Process Average Shear Number of

Strength Samples Averaged

Surface Heating, 900 to 1200 PE tie-layer

Through Heat, 1467 psi, PE tie-layer sigma 365 psi

Through Heat, 1990 psi, PP tie-layer sigma 193 psi

Combined 2010 psi, Consolidation sigma 250 psi

It is to be understood that a variety of heating means can be provided. For example, conduction, such as contact heating, or, convection or radiation, such as infrared heating, can be used to heat the materials to their processing temperatures. During contact heating, a heater is placed in physical contact with the material to be heated and heat is transferred by conduction. Convection heating is useful because it is easy to design and requires no physical contact.

In addition, it is to be understood that different press designs can provide the pressure needed for consolidation while holding the materials in place. Further, it is to be understood that other types of wood than oak can be used, for example, beech or hickory. Also, it is to be understood that the plastic does not have to be glass- reinforced.

While preferred embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.

Claims

THE INVENTION CLAIMED IS:

1. A panel comprising: a piece of wood having a predetermined length and width, a plastic layer having adhesion bonding properties for mechanically and chemically bonding said plastic layer to said wood, said plastic layer being bonded to one side of said wood.

2. A panel as defined in claim 1 , wherein said plastic layer comprises thermoplastic material.

3. A panel as defined in claim 2, wherein said thermoplastic material has a plurality of fibers provided therein which are completely embedded within said thermoplastic material.

4. A panel as defined in claim 3, wherein said fibers are arranged longitudinally along the length of said piece of wood.

5. A panel as defined in claim 4, wherein said fibers are continuous along the length of said piece of wood.

6. A panel as defined in claim 1, wherein said plastic layer comprises continuous-glass-fiber-reinforced-polypropylene.

7. A panel as defined in claim 1, wherein said plastic layer comprises a polymer comprised of polypropylene, PBT, thermoplastic urethane, nylon, PET, polyethylene, polyacetal, or a blend of said polymers.

8. A panel as defined in claim 1 , wherein said adhesion bonding properties of said plastic layer is formed from a blend of polymers or co-polymers.

9. A panel as defined in claim 8, wherein said blend comprises polypropylene and ethylene-propylene copolymer; polyethylene and polyisobutylene; propylene acrylic acid co-polymer and ethylene acrylic acid copolymer; or maleic anhydride modified polypropylene.

10. A panel as defined in claim 8, wherein said blend is formed from said polymers in the form of ter-polymers and co-polymers.

11. A panel as defined in claim 10, wherein said ter-polymers and co-polymers is formed from ethylene-propylene co-polymer.

12. A panel as defined in claim 1, wherein said thermoplastic material includes at least one elastomer.

13. A panel as defined in claim 1, further including a second plastic layer bonded to said first-defined plastic layer.

14. A panel as defined in claim 13, wherein said second plastic layer comprises thermoplastic material.

15. A panel as defined in claim 14, wherein said thermoplastic material of which said second plastic layer has a plurality of fibers provided therein which are completely embedded within said thermoplastic material.

16. A panel as defined in claim 15, wherein said fibers are arranged longitudinally along the length of said piece of wood.

17. A panel as defined in claim 16, wherein said fibers are continuous along the length of said piece of wood.

18. A panel as defined in claim 13 , wherein said second plastic layer is formed from continuous-glass-fiber-reinforced-polypropylene.

19. A panel as defined in claim 13, wherein said second plastic layer comprises a polymer comprised of polypropylene, PBT, thermoplastic urethane, nylon, PET, polyethylene, polyacetal, or a blend of said polymers.

20. A panel as defined in claim 13, wherein said adhesion bonding properties in said first-defined plastic layer is formed from a blend of polymers or co-polymers.

21. A panel as defined in claim 20, wherein said blend comprises polypropylene and ethylene-propylene copolymer; polyethylene and polyisobutylene; propylene acrylic acid co-polymer and ethylene acrylic acid copolymer; or maleic anhydride modified polypropylene.

22. A panel as defined in claim 20, wherein said blend is formed from said polymers in the form of ter-polymers and co-polymers.

23. A panel as defined in claim 22, wherein said ter-polymers and co-polymers is formed from ethylene-propylene co-polymer.

24. A panel as defined in claim 13, wherein said first-defined plastic layer includes at least one elastomer.

25. A panel as defined in claim 13, wherein said first-defined plastic layer is approximately 250-500 μm in thickness.

26. A panel as defined in claim 13, wherein said first-defined plastic layer is formed from a thermoplastic material.

27. A trailer floor comprised of a plurality of panels as defined in claim 13, said panels being joined together by joints, said tie-layer and said plastic layer overlaying said joints for reinforcing said joints.

28. A trailer floor comprised of a plurality of panels as defined in claim 1, said panels being joined together by joints, said plastic layer overlaying said joints for reinforcing said joints.

29. A method of forming a reinforced panel comprising the steps of: providing a piece of wood having opposite sides; providing a plastic material having adhesion bonding properties therein for mechanically and chemically bonding said plastic layer to said wood; and bonding said plastic material to said one side of said wood.

30. A method as defined in claim 29, wherein said plastic material comprises thermoplastic.

31. A method as defined in claim 29, wherein the step of bonding said plastic material to said wood includes the steps of applying heat to said plastic material and applying pressure to said plastic material and said wood after said plastic material and said wood have been engaged against each other.

32. A method as defined in claim 31 , further including the steps of providing a second plastic material and bonding said second plastic material to said first-defined plastic material.

33. A method as defined in claim 31, wherein said step of applying heat to said plastic material is performed before said plastic material and said wood have been engaged against each other.

34. A method as defined in claim 33, further including the steps of providing a second plastic material and bonding said second plastic material to said first-defined plastic material.

35. A method as defined in claim 31, further including the step of applying heat to said wood before said plastic material has been engaged thereagainst.

36. A method as defined in claim 31 , wherein said step of applying heat to said plastic material is performed after said plastic material and said wood have been engaged against each other.

37. A method as defined in claim 36, wherein said plastic material comprises a sheet of thermoplastic.

38. A method as defined in claim 36, wherein said plastic material comprises a sheet of fiber reinforced thermoplastic.

39. A method as defined in claim 38, wherein said fibers are arranged longitudinally along the length of said wood.

40. A method as defined in claim 36, wherein said plastic material is a plurality of rovings which are laid on said wood, and during the step of applying heat to said plastic material, said rovings melt and form a laminate on said wood.

41. A method as defined in claim 40, wherein said rovings are formed from plastic material and glass fibers bundled together, and during the step of applying heat to said plastic material, said plastic material commingles with said glass fibers.

42. A method as defined in claim 41, wherein said fibers are arranged longitudinally along the length of said wood.

43. A method as defined in claim 36, further including the step of applying heat to said wood before said plastic material has been engaged thereagainst.

44. A method as defined in claim 31 , further including the step of providing means for containing said plastic material when heated on said wood.

45. A method as defined in claim 44, wherein said means comprises blocks of resilient material which are compressed and deformed when pressure is applied to said plastic material and said wood during said step applying pressure to said plastic material and said wood after said plastic material and said wood have been engaged against each other.

46. A method as defined in claim 29, wherein the step of applying pressure to said plastic material and said wood after said plastic material is effected by use of a continuous platen press.

47. A method as defined in claim 46, further including the step of providing blocks of resilient material which are compressed and deformed when pressure is applied to said plastic material and said wood by said continuous platen press to maintain said plastic material on said wood.

48. A method as defined in claim 46, wherein said continuous platen press includes a heating section having a heating means therein, and further including the step of applying heat to said plastic material and said wood by use of said continuous platen press as said plastic material and said wood pass therethrough.

49. A method as defined in claim 46, further including the step of supplying a release film between said continuous platen press and said plastic material such that said continuous platen press does not contact said plastic material.

50. A method as defined in claim 49, further including the steps of peeling said release film from said plastic material after exiting the continuous platen press and collecting said release film.

51. A method as defined in claim 48, wherein said continuous platen press has a cooling section through which said plastic material and said wood pass through after passing through said heating section, such that upon exiting said continuous platen press, said wood having said plastic material laminated thereon can be handled.

52. A method as defined in claim 46, wherein said plastic material is a plurality of rovings which are laid on said wood, and during the step of applying heat to said plastic material using said continuous platen press, said rovings melt and form a laminate on said wood.

53. A method as defined in claim 52, wherein said rovings are formed from plastic material and glass fibers bundled together, and during the step of applying heat to said plastic material, said plastic material commingles with said glass fibers.

54. A method as defined in claim 53, wherein said fibers are arranged longitudinally along the length of said wood.

55. A method as defined in claim 29, further including the steps of mounting said wood on a platen and mounting said plastic material on an opposed platen, and said step of bonding said plastic material to said wood includes the steps of applying heat to a surface of said plastic material and a surface of said wood, and thereafter moving said platens toward each to engage said plastic material and said wood against each other, and applying pressure to said plastic material and said wood.

56. A method as defined in claim 55, wherein said step of applying heat to a surface of said plastic material and a surface of said wood is performed by moving a heater between said plastic material and said wood and after said plastic material and said wood have been heated, removing said heater from between said plastic material and said wood prior to said step of moving said platens toward each other.

57. A method as defined in claim 55, further including the step of providing blocks of resilient material which are compressed and deformed when pressure is applied to said plastic material and said wood by said platens to maintain said plastic material on said wood.

58. A method of forming a reinforced panel comprising the steps of: providing a piece of wood having opposite sides; providing a plastic material; applying heat to said plastic material and applying pressure to said plastic material and said wood after said plastic material and said wood have been engaged against each other to bond said plastic material and said wood together.

59. A method as defined in claim 58, wherein the step of applying pressure to said plastic material and said wood after said plastic material and said wood have been engaged against each other is performed by using a die through which said wood and said plastic material travel.

60. A method as defined in claim 59, further including the steps of laying fibers on said wood and thereafter moving said wood into said die, said plastic material being injected into said die in a molten form to coat said fibers.

61. A method as defined in claim 59, wherein said plastic material is a polymer melt which de-polymerizes on melting and bonds to said wood.