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This is a continuation application of U.S. application Ser. No. 10/769,364, filed Jan. 30, 2004, now U.S. Pat. No. 7,340,865 the entirety of which being incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to adhesive-free, interlocking tiles and, more specifically, to an improved interlock structure for interlocking an assemblage of contiguous floor tiles with uniformly straight edges. 
   2. Background Discussion 
   Adhesive-free, interlocking floor tiles are typically molded of substantially resilient, plastic material and utilize interlock elements formed in the tile edges for effecting connections with adjacent, similar tiles. Typically, the interlock elements are pairs of substantially identical alternating projections and slots of substantially dovetail shapes. The projections and slots are supported by the tile edges to effect mating interlocks with inverted, substantially identical slots and projections, respectively, on other tiles to effect a mating interference fit between contiguous tiles of an assemblage, such as, an assemblage of floor tiles. 
   The projections serve as the male interlock elements and are typically dovetailed shaped; that is, shaped as truncated triangles with rounded corners in plan view and disposed in alignment along each tile. The male projections are alternately spaced by contiguous slots of substantially the same size and shape as the male projections, but inverted to form the female interlocking elements. Typically therefore, the slots are of identical dovetail shape and those on at least two exposed elements support edges of the tile are joined at right angles. The slots extend completely through these edges to provide female counterparts to the male elements. Interlocking of contiguous floor tiles on-site is effected by vertically aligning the male and female interlock elements of one tile with respective inverted female and male interlock elements of contiguous tiles and then driving the interlocks into resilient interference engagements by means of, for example, a mallet. The integrated installation, when thusly installed over flooring substrates, such as concrete or plywood, requires no adhesives or fasteners, and is therefore often referred to as “adhesive-free.” The male-female element pairs form one set each of the interlock structures disposed along the tile edges so that there is a series of contiguous pairs of projections and slots joined by a common dovetail-shaped sidewall. 
   For certain floor tile applications it is preferred that the tiles have four edges with one pair thereof joining at right angles to provide one corner of the tile and two uniformly solid, straight edges which define two of the four or more square or rectangular side edges of a multi-sided tile, depending on the particular overall tile shape. The pair of solid edge portions serves as straight, overlying support edges for downwardly facing interlock elements when the tile is installed horizontally. The edges have top surfaces as flush extensions of the top surface of the tile body and provide flat, top surfaces with a pair of solid, straight top edges, thereby simulating a conventional ceramic tile assemblage with linear grout lines or wood flooring with grooves and flush, coplanar top surfaces. An oppositely disposed, and second, pair of edges intersect at right angles to form a second opposite corner of the tile. The second pair of edges are likewise provided with a sequence of male-female interlocks defined by sidewalls which extend completely through the tile edges perpendicular to the plane of the tile to mate with the downwardly-projecting respective female and male interlocks of contiguous, substantially identical tiles. Examples of tiles having such interlock arrangements are disclosed by U.S. Pat. No. 4,287,693 issued on Sep. 8, 1981 to R. E. Collette; U.S. Pat. No. 6,526,705, issued on Mar. 4, 2003 to K. M. MacDonald; and, U.S. patent application Ser. No. 09/884,638, filed Jun. 19, 2001 by T. E. Ricciardelli and assigned to the same assignee as the present invention; all of the references referred to above being incorporated by reference herein and made part hereof. 
   The extent to which each essentially identical pair of interlock elements can effectively function to prevent tile separations during usage is a function of tile composition and the design of the interlocks with various considerations as to tile resilience and the extent of surface area available for inter-mating surface-to-surface engagement between interlocks, and other relevant factors known to those in the art. Thus, with certain of the prior art interlock structures, the two sides of the tile opposite those with solid edge portions utilize the full tile edge thickness for at least the female cavity sidewalls by molding dovetail slots as through-slots into the tile edges. The resulting tile has a pair of top linear edge portions and a pair of opposite or bottom edge portions with alternating non-linear or undulating edges. Advantageously, the latter may be hidden from view after tile assemblage by the overlying straight and solid top edge portions of contiguous tiles, and therefore, the top surfaces of the final tile assemblages have the desired uniformly straight edge lines and flush, top edge surfaces. 
   For a given thickness of tile, the pair of flush solid support edges forming the periphery of the top surface account for a portion of the overall tile thickness and consequently reduce the surface areas available for mating engagements between the identical pairs of interlock elements. This is because the female cavities have a reduced depth as a result of being dead-ended on-their underlying solid support edges. The male projections are also limited in height because they cannot extend beyond the planes of the top or bottom surfaces of the tile. As a result, the surface areas available to effect inter-element mating engagements is reduced, which is disadvantageous from a connective integrity standpoint. Conversely, this advantageously results in a reduction in the impact forces required to drive the downwardly-facing interlocks on the top tile edges into mating engagements with upwardly-facing interlocks of adjoining tiles, and consequently reduces the effort required for on-site tile installation. 
   It would be advantageous to provide a generally planar tile with multiple sides and a top surface having an underlying interlock structure that is adapted to facilitate on-site assemblage and removal of individual tiles with matable interlock structures on contiguous tiles, and yet is resistant to separation of the assemblage during usage. 
   An embodiment of this invention is to provide an interlocking tile with planar top and bottom surfaces and at least two linear edges extending at right angles to one another having different sets of interlock elements underlying the top edge surfaces which are specifically designed to facilitate on-site installation and removal and replacement, if required, of individual tiles without significantly degrading the resistance to tile edge separations during usage. 
   Yet another embodiment is to provide an adhesive-free tile assemblage with an interlock structure comprised of multiple pairs of differently constructed interlocks providing acceptable connective interlock integrity while facilitating the ease by which on-site installation assemblage and replacement of individual tiles can be effected with mating tiles having substantially identical, inverted interlock structures thereon. 
   Yet another embodiment is to provide an edge interlock system for a resilient tile that facilitates the initial connections and aligned orientations between the interlocks of that tile and the interlocks of similarly constructed contiguous tiles. 
   SUMMARY OF THE INVENTION 
   These embodiments are achieved by the instant invention which provides a multi-sided, interlocking tile with a corresponding multi-sided, substantially planar central portion with first, second, third and fourth elongated interlock element support edges disposed in end-wise relationship and cantilevered from different sides of the central portion. The inner edge portions of the support edges are formed integral with the central portion and extend laterally outwardly therefrom with the free, outer edge portions thereof defining the tile periphery. The first and second interlock support edges have longitudinal axes intersecting at substantially right angles to provide a first pair of adjoining interlock support edges on two sides of the central portion having interlock support surfaces that face toward the plane of the top tile surface or “upwardly.” Similarly, the third and fourth interlock support edges intersect at right angles to provide a second pair of adjoining interlock support edges on another two sides of the central tile portion having interlock support surfaces that face toward the plane of the bottom tile surface or “downwardly.” With this inverted arrangement of interlock support edges, a flat, uniformly solid, top tile, surface is available for the application of a square cornered laminate decorative and/or wear resistant layer applied during or after the tile molding process. 
   There are series of two sets each of different, male-female interlock elements on each support edge and the two sets are disposed in longitudinal alignment and project from one surface of each support edge. The two sets of interlock elements are joined by a common sidewall that traverses the surface of the underlying support edge from substantially one end to the other. The sidewalls on the first pair of support edges project upwardly and the sidewalls on the second pair of support edges project downwardly. Both sets of the interlock elements are comprised of male walled structures; one of the structures being a lug-like element and the other being a section of a rib-like element with substantially parallel inner and outer spaced-apart sidewalls. The lug and laterally opposite outer sidewall of a rib section are laterally spaced to form an essentially U-shaped channel therebetween that bottoms on its respective support edge surface. The channel forms a female interlock portion for the first of the two interlock sets, whereas the adjacent lug forms the male interlock portion of that first interlock set. 
   The inner sidewall of the rib section forms an open-ended cavity also bottoming on its enclosed support edge surface and this cavity forms the female interlock element for the second interlock set. Each of the rib sections projecting from its respective support surface is shaped to form the male interlock element for the second interlock set. The male and female elements of the two sets are shaped and sized as identical inverted counterparts of one another, so that adjacent tiles having substantially identical inverted first and second interlock sets can mesh and be matingly secured together without use of adhesives. The open-ended design of the interlocks and the tile resilience enables an installer to more readily replace individual tiles of the assembly by simply picking up one corner of the tile to effect initial separation between the interlocks. Additionally, the interlock sets on the corner ends of support edges are designed to mesh with less applied pressure and greater tolerances to initial misalignment than that required for other prior art sets of interlocks, thereby facilitating the initial interconnecting and alignments with similar interlocks of contiguous tiles and any subsequent removal of individual tiles. 
   The invention will now be described in more detail with reference to the accompanying drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a tile with edge interlocks constructed in accordance with the instant invention; 
       FIG. 2  is a bottom plan view of the tile shown in  FIG. 1 ; 
       FIG. 3  is an isometric perspective of the left-hand corner of the tile shown in  FIG. 1 ; 
       FIG. 3A  is an enlargement of the right-hand corner of  FIG. 3 , delineated by dash lines in  FIG. 3 ; 
       FIG. 4  is an isometric perspective of the right-hand corner of the tile shown in  FIG. 2 ; and, 
       FIG. 4A  is an enlargement of the right-hand corner of  FIG. 4 , delineated by dash lines in  FIG. 4  and, 
       FIG. 5  is side view of a portion of the edge of an embodiment of the tile with a decorative and/or wear-resistant top surface thereon. 
   

   DETAILED DESCRIPTION 
   With reference to the drawings,  FIG. 1  shows a top plan view of a tile  10 , constructed in accordance with this invention. The tile  10  is illustrated as having a substantially squared-shaped upper or top planar surface  13  and a lower or bottom planar surface  14  of substantially the same dimensions, the planes of the two surfaces  13  and  14  being essentially parallel and defining therebetween the “vertical” or perpendicular thickness of the tile  10 . The surfaces  13  and  14  are shown to be essentially of square shape, but may have other geometric shapes as well, for example rectangular, as disclosed in co-pending U.S. patent application Ser. No. 09/884,638, referred to hereinabove. Preferably, the top edges of the tile are uniformly solid and linear so that the tiles provide straight, solid edges with right-angled corners. The surfaces of the bottom  14  may be embossed or otherwise patterned (not shown) for slip-resistance enhancement. 
   The tile  10  is preferably composed of substantially resilient materials, such as; polyvinyl chloride (PVC), polypropylene, polyethylene, and natural or synthetic rubber or mixtures thereof that provide the molded products with a somewhat cushiony surface desirable for floor coverings and the substantially resilient interlock structures desirable for tight-fitting, essentially resilient interlocks. Advantageously, the tile  10  may be composed of recycled waste carpet scraps, as disclosed in U.S. Pat. No. 6,306,318 issued on Oct. 23, 2001, and assigned to the same assignee as the instant invention. As disclosed therein, a matrix of granulated waste polymeric carpet backing and carpet fibers and a suitable plasticizer, after being subjected to high heat and compressive forces in an injection molding machine, will produce a molded tile of PVC with embedded carpet fibers. As illustrated in  FIG. 5 , to enhance the aesthetic appearance of a floor tile assemblage, a variety of decorative polymeric-based sheets, such as decorative vinyl sheets, may be laminated to the top surface of the tile  10  to provide a decorative top layer  11  to the tile  10 . The layer  11  may be covered by transparent wear-resistant layer, not shown, if required. 
   The tile  10  is shown in plan view in  FIGS. 1 and 2  with a generally square-shaped central portion  12  of basic tile body thickness with two pairs of interlock edges; a first one of said pairs designated by numerals  14 A and  14 B in  FIGS. 1 and 3  is comprised of two substantially identical elongated edge strips  19 A and  19 B, respectively, having substantially rectangular cross-sectional shapes. The strips  19 A,  19 B have respective flat top surfaces  20 A,  20 B,  FIGS. 3 and 3A , that support interlock elements and face upwardly in the direction of a plane containing the top tile surface  13 . A pair of opposite bottom surfaces  14 A,  14 B, respectively,  FIGS. 2 and 4 , extend as flush border edge continuations of the central region  12  of the bottom tile surface  14 . The longitudinal axes of the strips  19 A,  19 B,  FIG. 3 , intersect at right angles to define one of the right-angled corners  24  of the tile  10 , and the strip surfaces  20 A,  20 B typically face upwardly when the tile is mounted with its bottom surface  14  against a floor substrate. The outermost first pair of tile  10  edges,  FIG. 3 , is uniformly solid and substantially straight edges  22 A and  22 B, respectively, simulating linear grout or groove lines which typically result when conventional ceramic tiles or wood flooring planks are assembled in abutting relationships. 
   As best seen in  FIGS. 3 and 3A , the strips  19 A and  19 B have a vertical thickness of approximately one-quarter the corresponding total thickness dimension of the tile  10 , including any additional decorative or wear layers  11  applied thereto. Typically, the portion  12  is about 15-20 inches and more specifically, about 17 inches on each side and the tile thickness with a decorative layer  11  is about 0.125-0.5 inch and more specifically, about 0.25 inch; although such dimension will vary depending upon the particular installation for weights, flexibility, and wear resistant requirements, as apparent. Flexibly cantilevered from their corresponding outer edges  21 A,  21 B of the central tile portion  12  the strips  19 A,  19 B intersect at right angles with those edges to form downwardly stepped corner edges at  21 A and  21 B, respectively, that extend parallel to support edges  20 A and  20 B, respectively, and intersect at right angles to one another at the left-hand corner of tile  10 ,  FIG. 3 . Typically, the strips  19 A and  19 B have exemplary width dimensions of about 0.5 inch to 1.0 inch and more specifically, about 0.75 inch. The dimensions of the strips are a function of the overall dimensions of the tile  10  and the size of the interlock elements molded into the strips. With the exemplary dimensions disclosed above, the top surface  13  has approximately a 15-20 inch border and more specifically about a 17.75 inch border edge. The depth or thickness of the edges  21 A,  21 B of the strips  19 A,  19 B respectively contiguous to and abutting the interlocks is determined by the vertical spacing required between the plane of top surface  13  and the interlock engaging surfaces of the interlock structures to provide flush edges with those of similar adjoining tiles. As will be apparent from  FIG. 5 , for a predetermined height of interlock projections and depth of adjacent cavities described in greater detail hereinafter, this vertical spacing will be incrementally increased in the event additional single or composite material compatible and flexible layers  11  are applied by heat bonding or adhesives to the top tile surface by the amount that such layer or layers incrementally increase the thickness of the tile. To maintain a predetermined maximum tile thickness for desired flexibility, the thickness of the strips  19 A,  19 B may be reduced by an increment substantially equal to the height increase attributable to the addition of the layers  11 . Typically the layers  11  will have a thickness ranging from 0.002 inch to 0.004 inch in total thickness. Typically, the top layer  11  comprises a layer of 0.004 to 0.020 inch of flexible PVC to which may be applied a clear coating of 0.004 to 0.007 inch of either polyurethane, melamine or melamine in mixture with aluminum oxide (Al.sub.2O.sub.3) or similar material. 
   The second pair of interlock support edges, designated  30 A and  30 B in  FIGS. 2 ,  4  and  4 A, are also comprised of elongated strips  31 A,  31 B of rectangular cross-section and of substantially identical size and shape as the strips  19 A,  19 B. Strips  31 A and  31 B, intersect at right angles to form a second tile corner  34  opposite the corner  24 . The strips  31 A,  31 B extend from, and as continuations of the central portion  12  of top tile surface  13  to provide top border edges coplanar with the plane of the top surface  13  of the central region  10 A. The strips  31 A,  31 B are also cantilevered from edge portions of their respective outer adjoining edges of the bottom central portion  10 A and when installed on a substrate are stepped downwardly at right angles thereto to provide the perpendicular or vertical spacing for flush abutments with similar adjoining tiles with their inverted interlocks facing upwardly and their interlock support edges underlying the strips  31 A,  31 B for mating connections therebetween. The strips  31 A,  31 B, respectively, have flat, interlock elements support surfaces  40 A and  40 B,  FIGS. 4 and 4A , facing the plane containing the bottom tile surface  14 , and hence, are downwardly facing when tile  10  is installed as a floor covering with the bottom surface  14  overlying the substrate. The width of the strips  31 A,  31 B is substantially the same throughout and substantially the same as that of the strips  19 A,  19 B. The ends of the strips  31 A,  31 B opposite the corner  34 ,  FIGS. 1 and 2 , may be spaced from the adjacent ends of the strips  19 A,  19 B, respectively, typically by the width of a strip to provide greater flexibility to both adjacent ends as indicated by numerals  35 A and  35 B in  FIG. 2 . As seen in  FIGS. 3A and 4A  the strips  19 A and  19 B are substantially mirror images of those on the strips  31 A and  31 B, respectively, with a pair of interlocks at each end of the strips being especially designed to provide greater mating capability between superimposed interlocks than the intermediate sets of interlocks, as discussed hereinafter. 
   With reference to  FIGS. 1 ,  3  and  3 A, projecting upwardly from each of the surfaces  20 A,  20 B of their respective strips  19 A,  19 B are a series of longitudinally-aligned first and second sets of interlock elements molded into the tile, each set being comprised essentially of a differently designed pair of male and female structural types of interlock elements. 
   The first interlock set of the series,  FIG. 3A , disposed along the mid-section of their supporting strip is comprised of a projecting male lug  40  and an adjacent female channel  42 ; the lug  40 , as viewed in plan, being shaped substantially as an equilateral triangle formed of adjoining sidewalls  40 - 1 ,  40 - 2  and  40 - 3  with rounded corners and a flat upper end surface  40 - 4 . The lugs  40  typically project from their respective strip surfaces  20 A and  20 B a distance approximately equal to one-half the total thickness of the tile  10 , leaving a vertical space between their free end surfaces  40 - 4  and the top surface of the tile  10  substantially the vertical thickness of their respective corner edges  21 A and  21 B. The vertical spacing is substantially equal to the support edge thickness of other contiguous tiles substantially identical to the tile  10  with substantially identical interlocks plus any decorative and/or wear resistant layers  11  thereon. Thus, abutting tiles will meet with flush top surfaces and joint lines when edge-connected together by their respective mating interlocks. The end surfaces  40 - 4 ,  FIG. 3A , of at least one set of lugs  40  may have longitudinal, air venting slots  40 - 5  therein to facilitate the mold release of the tile  10  from, for example, an injection molding machine. 
   The sidewalls  40 - 1 ,  40 - 2  and  40 - 3  of the lugs  40  and adjoining portions of their respective strip surfaces  20 A,  20 B,  FIG. 3A , from one-half of the right-angled wall structure for a channel  40 ; the other half being formed by the surfaces  20 A,  20 B and the laterally opposed sidewalls of tandem connected rib sections  50 - 1  of a continuous male rib wall  50  which traverses the width and extends longitudinally for the major intermediate portion of the length of their respective tile support edges  21 A,  21 B,  30 A and  30 B. Each of the male rib sidewall sections  50 - 1  projects from its respective support edge surface  20 A,  20 B,  FIGS. 3 and 3A , the same amount as the lug  40  and has an inner sidewall section  50 - 2  spaced laterally from and extending substantially parallel to an opposite one of the outer sidewall sections  50 - 1 . Thus, each traversing section of the wall  50  has a substantially rectangular cross-sectional shape for mating with U-shaped channels such as channels  42 . The two rib sections  50 - 1  define the two legs of each triangular locking structure and depend from a basewall section  50 - 3 , at approximately a 60-degree interior angle. The basewall sections  50 - 3  is molded flush with the corner edges  21 A,  21 B of the central region  10 A, thereby completing the cavity  60  enclosure. 
   Each male lug  40 ,  FIG. 3A , is disposed substantially equal distances from its laterally opposed outer sidewalls of sections  50 - 1  and substantially the same distances from their respective tile edges  22 A,  22 B. Thus, each male lug  40  is surrounded on three sides by a corresponding female channel  42  of slightly greater width than the width of laterally opposed rib wall sections  50 - 1  so as to tightly mate with similar but inverted rib wall sections of a contiguous tile. The inner sidewalls  50 - 2  of each rib  50  are also shaped in plan view as an equilateral triangle having rounded interior corners so as to have a substantially identical size and shape as a corresponding inverted lug  40 . The resulting open-ended cavities  60 ,  FIG. 3A , bottoming on their respective enclosed areas of the surfaces,  20 A,  20 B, have just slightly larger mating interiors than the lug  40  so as to receive inverted lug projections of adjoining tiles with an essentially interference fit. 
   The outer sidewalls of sections  50 - 1  of the ribs  50 ,  FIGS. 3 and 3A , are rounded adjacent the tile edges  22 A,  22 B and otherwise substantially follow the curvature of the lug  40  sidewalls  40 - 2 ,  40 - 3  to facilitate mating therebetween. The spacing between the edges  22 A,  22 B and their laterally adjacent sidewalls  40 - 1  of lugs  40  is substantially the width of the channel  42 . Thus, each inverted one of the ribs  50  can be accommodated in a corresponding female channel  42  and since each inverted lug  40  can be accommodated in a rib cavity  60 , the second set of male-female interlocks is formed by a male rib section  50 - 1  and its adjoining female cavity  60 . As will be apparent, the rib  50  follows a substantially semisoidal course a substantial length of each support strip  19 A,  19 B. The rib merges into the central portion  10  adjacent the tile corners, and thus the two endmost lugs  40 A,  40 B do not have an intervening rib section. 
   The lugs  40 A and  40 B are inverted relative to one another and are laterally spaced by a channel section  42 A. The sections  42 A are typically designed to be somewhat wider than the intermediate channels  42  to correspond with the greater width of their respective vertically aligned inverted male rib sections  50 A,  50 B of greater width. This is done to assist an installer in making alignments and the initial engagements between the corners of contiguous tiles by providing wider interlocks for initial meshing. Typically, the end rib sections  50 A and  50 B encircling a respective one of the endmost cavities  61  and  62  are typically about twice as wide as the intermediate ribs  50 . Because the rib sections  50 A and  50 B are about twice as wide as the intervening rib sections  50  readily mesh with the correspondingly wider channels  42 A and  42 B by the installer aligning and then simply pressing and corner  24  or  34  of tile  10  with its rib sections  50 A and  50 B and cavities  61  and  62  facing downwards into the upwardly facing lugs  40 A,  40 B and wider channels  42 A,  42 B, respectively, of the inverted corresponding corner of a second and substantially identical tile. Once these initial engagements are made at the superimposed tile corners the remaining, intermediate interlocks of the overlapping tiles will be drawn into generally aligned in proper meshing relationships and their relatively tighter intermediate interlock engagements requiring greater forces may be affected by the installer with the use of a tool, such as a mallet. The wider and open-ended design of this initial pair of interlocks facilitates the ease by which individual tiles may be removed from the assemblage by the installer simply raising one corner of the tile to be removed to initiate separation of the contiguous interlocks. 
   The particular tile described herein is the preferred embodiment of the instant invention but it should be understood that modifications may be made therein without departing from the scope of the invention as defined in the following appended claims. This specification has disclosed all foreseeable equivalents. Terms such as “generally” and “substantially” and the like, as used herein, are to be accorded their ordinary and customary meaning.

Summary:
A polymeric interlocking tile for an adhesive-free assemblage with adjacent tiles having substantially similar, but inverted, edge interlocks thereon. The interlocks on each edge of a tile include a row of first and second sets of male-female types of alternating interlocks. The first interlock set includes a male lug projection having sidewalls forming one sidewall of a channel of U-shaped cross-section. The channel forms a female interlock cavity for the first set. The second interlock set is contiguous to the first set and includes a male projecting rib having two parallel sidewalls, one sidewall faces the edge and forms an opposite sidewall of the channel and an opposite, inwardly facing sidewall forms an enclosure for a second female cavity of the next set. At the opposite ends of each interlock row, the U-shaped channel sidewalls are wider to facilitate an initial interlock meshing between contiguous tiles of the assemblage.