A composite panel for constructing an interior real wood finished floor comprising a rectangular planar unit having top, middle and bottom layers, the top layer being solid wood with a unidirectional grain parallel to opposite edges of the panel, the bottom layer being constructed of wood and having at least portions of its thickness with a grain running perpendicular to the unidirectional grain, the middle layer being an elastomeric material bonded to the top and bottom layers.

BACKGROUND OF THE INVENTION 
     The invention relates to flooring and, in particular, to wood-based flooring tiles or planks. 
     PRIOR ART 
     The natural beauty and durability of real wood flooring are qualities that explain its continued use and popularity in interior construction. Traditionally, wood floors have been constructed with planks or parquet tiles. Various wood-based composite constructions have been commercially sold or proposed. These have taken the form, for example, of plywood, chipboard and particle board. It has also been proposed to assemble layers of wood or wood-based material and a layer of elastomeric material. 
     There remains a need for a natural wood look in a premium floor product that improves the sound-deadening capacity, comfort level of a person standing or ambulating on the floor and durability from impacts or concentrated loads over what can be obtained from traditional solid wood flooring. 
     SUMMARY OF THE INVENTION 
     The invention relates to a premium wood-based flooring tile or plank (collectively a panel) that affords the natural beauty and richness of real wood with improved performance qualities. The panel of the invention is a multilayer composite comprising wood top and bottom layers separated by an intermediate elastomeric layer. Preferably, the intermediate layer is a relatively compressible natural or synthetic foamed material adhered to both the top and bottom wood layers. More specifically, the top layer is preferably a solid high density wood that serves to give the panel its appearance and its wear surface. The bottom layer, ideally, is a low grade, low density, or soft wood-based plywood with the majority of its plies having their grain arranged to run crosswise to the grain direction of the top layer. The intermediate foam layer has negligible strength compared to the wood top and bottom layers, but is protected by such layers during shipping, handling, installation and service. Notably, the intermediate elastomeric layer requires no extra labor in the installation of the panel product. The intermediate foam layer, which can be relatively thin compared to the top and bottom layers, serves a plurality of functions. The intermediate layer acts as a cushion so that a person standing, walking, or even running on the panel is more comfortable compared to what would be experienced on conventional floor board construction. The intermediate layer serves to dampen noise and reduce sound transmission. Additionally, the intermediate layer absorbs impact loads and distributes concentrated loads imposed on the top layer. Still further, the intermediate layer isolates the top and bottom layer from shear loads so that differential expansion or contraction of the top and bottom layers does not result in delamination and/or cupping of the layers. This can be particularly beneficial when the bottom layer is adhered to a sub-floor or concrete slab. As still another attribute, the intermediate layer serves as a thermal break between the top and bottom layers. 
     In its preferred form, the panel has a tongue and groove geometry machined in and confined to the top layer. This arrangement takes full advantage of the inherent integrity and toughness of the dense top layer. By eliminating contributions to the tongue and groove joint from the intermediate and bottom layers, a tight gap-free joint at the visible surface is more readily obtained. Additionally, the tongue and groove feature of the panel enables abutting panels to transfer compressive loads from one panel to the adjacent panel thereby lessening peak stresses on a particular panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a panel constructed in accordance with the invention with portions broken away to reveal details of its construction; 
         FIG. 2  is an end view, partially broken away, of the floor panel of  FIG. 1  on an enlarged scale; and 
         FIG. 3  is a graph of load vs. deflection of a sample of one example of a panel constructed in accordance with the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A floor panel  10  constructed in accordance with the invention can take the form of a rectangular tile or a plank, it being understood that square is included in the term rectangular. The illustrated panel  10  is a tile having, by way of example but not limitation, nominal thickness of 15.2 mm and planar face dimensions of 150 mm in width and 300 mm in length. The panel  10  comprises top, intermediate and bottom layers  11 ,  12  and  13 , respectively. The top layer  11  comprises solid wood with its grain running in a direction parallel to the length of the panel, assuming it is rectangular. The top layer  11  can be built-up of a plurality of bar-like strips  14  glued together at their abutting edges  16  in parallel vertical planes. Ideally, the wood forming the top layer  11  is a premium grade of high density or hard wood such as oak or maple. An upper surface  17  of the top layer  11 , desirably, is prefinished with a stain or colorant and/or protective coating such as polyurethane or acrylic lacquer or the like. Two intersecting edges  18 ,  19  of the top layer  11  are formed or machined with tongues  21  and the remaining two edges  22 ,  23  are formed with grooves  24  complementary to the tongues, as is customary. 
     The top or upper layer  11 , disregarding the extension of the tongues  21  determines the nominal face size of the panel  10 . Inspection of  FIG. 2  shows that the intermediate and bottom layers  12 ,  13  are slightly smaller, in plan view, than the top layer  11  so that the top layer projects slightly beyond the intermediate and bottom layers around the full periphery of the panel  10  to assure that the panel will mate with identical panels and form tight joints at the top layer  11 . 
     The lower layer  13  is a plywood construction of low density soft wood such as, for example, lauan mahogany. In the illustrated example, the lower layer  13  comprises three wood plies  26 - 28  adhered uniformly across their abutting surfaces with a suitable glue or adhesive. As is customary, the grains of abutting plies  26 ,  27  and  27 ,  28  are arranged perpendicularly to one another. The wood grain direction of the outer plies  26 ,  28  (the upper and lower plies) largely determines the bending stiffness of the lower layer  13  and are arranged perpendicularly to the grain of the upper layer  11 . This enables the lower or bottom layer  13  to reinforce and stiffen the upper layer  11  against any bending about an axis parallel to the grain direction of the upper layer  11 . 
     The intermediate layer  12  is preferably foamed elastomeric material either of natural or synthetic origin such as natural rubber or a polymeric resin material such as polyvinylchloride, polyethylene, urethane, or the like. The elastomeric material of the intermediate layer  12  is ideally relatively soft and characterized with low stiffness, elasticity, and moderate to high damping capacity. The intermediate layer  12  is permanently uniformly bonded to the top and bottom layers  11 ,  13 . The elastomeric material is preferably made with a foaming ratio of about at least 2 up to about 4.5. If desired, the intermediate layer  12  can be discontinuous or patterned such that there are areas between the upper and lower layers  11 ,  13  devoid of the intermediate layer material. 
     The panel  10  can be bonded to a sub-floor with a suitable adhesive applied first to the subfloor on site or to the lower face of the bottom layer  13  during manufacture or on site. A plurality of panels  10  are assembled together to make up the total floor surface with the top layer  11  constituting the appearance and wear surface. The tongue and grooves  21 ,  24  assure a smooth floor surface will be produced across joints of abutting panels. The intermediate layer  12  and bottom layer  13 , as mentioned, are spaced slightly inward of the perimeter of the top layer  11  (apart from the tongues  21 ) to assure that the joint between the butting panels  10  is formed by the top or upper layer and is tight. The tongue and groove joint between the panels  10  beneficially allows compressive loads on one panel to be partially transferred and, therefore, shared by an abutting panel. The compressibility of the foamed intermediate layer  12  cushions a person's footsteps on a floor surface made up of the panels  10  making it more comfortable than a solid wood floor without the intermediate layer. 
     A sample of the flooring panel  10  was cut into 1 inch×1 inch squares and loaded in a compression testing machine. A typical force vs. deflection curve is shown in  FIG. 3 . The initial portion of the curve of  FIG. 3  (deflections from 0 to 0.04 inches) is dominated by the compression of the soft central layer  12 . The central region of the curve (deflections from 0.04 to 0.1 inches) is associated with the elastic compression of the compacted intermediate layer  12  as well as the wood layers  11 ,  13 . Over 0.1 inch deflections, non-linear deformation in the wood  11 ,  13  occurs. The curve of  FIG. 3  illustrates the desirable relatively soft, compliant nature of the intermediate layer  12 . While the intermediate layer  12  is desirably relatively soft, it is protected from physical damage by the top and bottom layers  11  and  13 . 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.