Abstract:
A tile having a support layer and a wearing layer. The wearing layer and the support layer are polygonal. The edge regions of the support layer have projections and cutouts, the projections being intended to engage in a positively locking manner in the cutouts in the support layer of adjacent tiles. The tiles may also have an intermediate layer which is electrically conductive. After the tiles have been laid, neither cutouts nor projections are visible from above, since the tiles are mechanically secured by the support layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to a hard tile having a support layer and a wearing layer and to a covering surface comprising such tiles. Nowadays, very high demands in terms of mechanical strength, resistance to wear and resistance to chemicals are imposed on covering surfaces made from plastics. Moreover, such coverings should not undergo any electrostatic charging or should at most undergo extremely slight electrostatic charging.  
           [0003]    2. Description of Related Art  
           [0004]    European Patent EP-A 1 128 713 discloses tiles made from highly compressed thermoplastic with a nonconductive support layer and a conductive wearing layer. A wearing surface of the wearing layer is provided with a securely adhering conductive substance. The tiles described in that document have connecting elements in tongue-and-groove form. Only specialist workers can lay tiles of this type. The tongue-and-groove connection often tears, and in addition the tiles are complicated and expensive to produce.  
           [0005]    Tiles for floor coverings are generally secured to one another by means of plug connections. The joints which are present between the individual tiles are susceptible to dust and dirt. This can lead to the projections curving upward over the course of time. This makes the floor covering more difficult to drive on and reduces its service life, which is undesirable for economic and ecological reasons.  
           [0006]    Therefore, it is an object of the present invention to provide a hard tile which is configured in such a way that it is easy to lay.  
           [0007]    A further object of the present invention is to provide a covering surface which is produced using tiles which are easy to lay and which has a long service life.  
         SUMMARY OF THE INVENTION  
         [0008]    The wearing layer of the tile according to the invention is polygonal in shape and is preferably square or hexagonal. The wearing layer does not have either cutouts or projections. After the tiles according to the invention have been laid, neither cutouts nor projections are visible from above, since the tiles are mechanically secured by the support layer. The floor covering has narrow joints between the individual tiles. The regular, preferably square pattern of these joints also allows simple welding, so that it is impossible for any dirt to adversely affect the floor covering. The wearing layer is preferably electrically conductive.  
           [0009]    The support layer of the tile according to the invention is of substantially the same size as the wearing layer and is preferably likewise polygonal. In its edge regions, the support layer has projections and mating cutouts. The edge region of the support layer has a width which corresponds to the length of the cutouts and projections. The projections are intended to engage in a positively locking manner in the cutouts in adjacent tiles.  
           [0010]    In one embodiment, the intermediate layer extends over at least two adjacent edge regions of the support layer and at least two further edge regions of the support layer are free of the intermediate layer. When the tiles according to the invention are being laid, this leads to those projections on the edge regions of the support layer over which the intermediate layer extends engaging in those cutouts in the edge regions of the support layer which are free of the intermediate layer. As a result, a covering which is produced using the tiles according to the invention has a continuous intermediate layer, ensuring electrical conductivity over the entire area. Since the location of the mechanical connection is not at precisely the same point as the electrical connection, this means that slight local shifts in adjacent tiles do not lead to an interruption in the conductivity, and therefore there is a high degree of reliability with regard to the electrical conductivity.  
           [0011]    In a further embodiment, the intermediate layer extends over at least two adjacent edge regions of the support layer and over the projections of the support layer of two further adjacent edge regions. The result of this is that the intermediate layer is doubled up in those regions in which the tiles are secured to one another. Therefore, a floor covering produced in this way satisfies the high demands imposed with regard to the electrical conductivity.  
           [0012]    The tiles according to the invention can even be laid on uneven subfloors without the dissipation of the electrostatic charges being adversely affected. The tiles according to the invention are laid without a fixed joint to the subfloor.  
           [0013]    Production of the tiles according to the invention is very advantageous, since only the wearing layer has to satisfy the particular demands with regard to the electrical conductivity, the resistance to wear and the resistance to aggressive chemicals. The intermediate layer has to be electrically conductive.  
           [0014]    Depending on requirements, inexpensive materials, such as for example reclaimed materials, can be used for the support layer.  
           [0015]    The wearing layer of the tile according to the invention is preferably made from thermoplastic particles, generally chips, which are provided with a conductive coating before being pressed. During the pressing at elevated temperature, the plastic particles are subjected to considerable deformation together with the conductive coating, resulting in a homogeneous block which has uniformly distributed, thin conductive layers passing through it. In a particularly preferred embodiment, the wearing layer has a grid printed on its underside, increasing the conductivity between wearing layer and intermediate layer (cf. also EP 0 869 217).  
           [0016]    It is particularly advantageous for the projections to have a dovetail-like shape, since this makes the laying of the tiles to form a covering surface and also dismantling of such a covering surface particularly simple without the electrical conductivity between the tiles being adversely affected. The dovetail-like cutouts may be either polygonal or undercut. In one embodiment, narrow and wide projections and undercuts alternate at regular intervals. The shape and width of the dovetails can be matched to the demands of the particular application; in particular, appropriate attention must be paid to the radii.  
           [0017]    The electrical charging is preferably dissipated via the edges of the covering surface produced using the tiles according to the invention.  
           [0018]    The intermediate layer of the tiles according to the invention is an electrically conductive sheet-like structure. This may, for example, be a metal grid, a pattern of conductive fabric or copper strips, but may also be a conductive film or a conductive coating layer. Polystyrene films with added carbon black and soft polyvinyl chloride films with added carbon black are particularly preferred.  
           [0019]    In a further embodiment, the load-bearing capacity of the support layer is increased if the support layer has compression elasticity properties. By way of example, the support layer may be at least half made up of a polygonal structure, such as a honeycomb structure. The recesses in the edge regions of the polygonal structures improve the ventilation of the subfloor, which is preferable in particular in moist environments. The tile according to the invention is preferably produced in such a way that the intermediate layer is applied to the wearing layer which has been laid down. This can be effected either by applying the film or by applying a coating. In a final step, the support layer is applied, preferably by means of injection molding, to the intermediate layer which has been applied to the wearing layer.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The subject matter of the invention is explained below by way of example with reference to FIGS.  1 - 9 , wherein:  
         [0021]    [0021]FIG. 1 illustrates an overall view of the tile according to the invention from below;  
         [0022]    [0022]FIGS. 2 a  and  2   b , each illustrate diagrammatically an exploded view of the support layer, intermediate layer and wearing layer of the tile;  
         [0023]    [0023]FIG. 3 illustrates an overall view of the tile according to the invention from above;  
         [0024]    [0024]FIG. 4 illustrates part of the tile, including the cutouts and projections, from below;  
         [0025]    [0025]FIG. 5 diagrammatically illustrates the support layer and the intermediate layer;  
         [0026]    [0026]FIGS. 6 a  and  6   b  diagrammatically illustrates the support layer from above and from the side, respectively;  
         [0027]    [0027]FIG. 7 diagrammatically illustrates the support layer from above;  
         [0028]    [0028]FIGS. 8 and 9, each illustrate an overall view of a preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]    [0029]FIG. 1 illustrates the tile  1  from below, having an insulating support layer  2 , an electrically conductive intermediate layer  3 , and an electrically conductive wearing layer  4 . The wearing layer  4 , is made from a highly compressed thermoplastic. Of course, the wearing layer may also be made from other materials. The intermediate layer  3  which lies between the support layer  2  and the wearing layer  4  is fixedly joined to both. At its edge region  9   a ,  9   b ,  9   c  and  9   d , the support layer  2  has integrally formed projections  6   a ,  6   b ,  6   c  and  6   d  and cutouts  7   a ,  7   b ,  7   c  and  7   d . The projections  6   a ,  6   b ,  6   c  and  6   d  are intended to engage in a positively locking manner in the cutouts  7   c ,  7   d ,  7   a  and  7   b  of adjacent tiles.  
         [0030]    In the present embodiment, the projections  6   a  and  6   c  are narrower than the projections  6   b  and  6   d . However, any desired width of the projections and cutouts is possible. By way of example, variants in which the projections and cutouts have the same width or the projections alternately have different widths are preferred.  
         [0031]    The intermediate layer  3  extends over two adjacent edge regions  9   a  and  9   b  of the support layer. The two further edge regions  9   c  and  9   d  of the support layer  2 , which lie opposite the edge regions  9   a  and  9   b  and are likewise adjacent, are free of the intermediate layer.  
         [0032]    The tile according to the invention is therefore configured in such a way that the projections  6   a  and  6   b  located in the edge regions  9   a  and  9   b  are intended to engage in the cutouts  7   c  and  7   d  of adjacent tiles, so that the intermediate layer extends continuously over the entire covering. The mechanical connection between two tiles is not at the same location as the electrical connection. Therefore, slight shifts in tiles within the area of the covering do not lead to an interruption in the electrical conductivity.  
         [0033]    [0033]FIG. 2 a  diagrammatically illustrates the support layer  2 , the intermediate layer  3  and the wearing layer  4  which are intended to be fixedly joined to one another. In an embodiment illustrated here, the intermediate layer  3  and the wearing layer  4  are of the same size and are applied one above the other over the entire surface.  
         [0034]    [0034]FIG. 2 b  diagrammatically illustrates the support layer  2 , the intermediate layer  3  and the wearing layer  4  which are intended to be fixedly joined to one another. In an embodiment shown here, the intermediate layer  3   a  has, in the edge regions  9   c ′ and  9   d ′, projections  6   c ′ and  6   d ′ which are intended to cover the projections  6   c  and  6   d  of the support layer  2 . The wearing layer  4 , the intermediate layer  3   a  and the support layer  2  are of substantially the same size.  
         [0035]    [0035]FIG. 3 illustrates the tile  1  from above, with an insulating support layer  2 , an electrically conductive intermediate layer  3  and an electrically conductive wearing layer  4 . The edge regions  9   c  and  9   d  are free of the intermediate layer.  
         [0036]    [0036]FIG. 4 shows part of the tile according to the invention. The intermediate layer  3  which has been applied to the wearing layer  4  extends over the edge region  9   a  of the support layer  2 , while the edge region  9   c  of the support layer  2  remains free of the intermediate layer.  
         [0037]    The intermediate layer of the tiles according to the invention is an electrically conductive sheet-like structure. This may, for example, be a metal grid, a pattern of conductive fabric or copper strips, but may also be a conductive film or a conductive coating layer. Polystyrene films with added carbon black and soft polyvinyl chloride films with added carbon black are particularly preferred.  
         [0038]    Polystyrene films can be made conductive by adding carbon black. These films preferably have a carbon black content of from 15 to 25%, preferably 18 to 22%. It is preferable to use polystyrene film or a PVC film with a thickness of 150 to 250 μm, preferably 200 to 250 μm. To produce these films, it is possible to use compounds in granule form, such as for example CABELEC 3896 produced by Cabot. Granules of this type have, inter alia, the following properties:  
                                                       Density   1098 kg/l           Shore D hardness   75           VICAT softening point (10 N)   118° C.           Melt flow index (200° C./10 kg)   2.5 g/10 min           Volume resistivity   10 2  Ω/cm           Flexural modulus   1800 MPa                      
 
         [0039]    The film produced therefrom, with a thickness of 200 μm, has a volume resistance determined in accordance with DIN 51953 of approx. 10 4  Ω.  
         [0040]    The coating can be applied to the wearing layer over the entire surface or in defined patterns. This makes it possible to provide the intermediate layer with a defined volume resistance. A coating of this type may, for example, have the following compositions:  
         [0041]    a) 18% of binder based on vinyl acetate/vinyl chloride,  
         [0042]    21% of graphite,  
         [0043]    1% of NH 3 ,  
         [0044]    60% of water  
         [0045]    b) 27% of graphite,  
         [0046]    73% of water  
         [0047]    c) 25% of graphite,  
         [0048]    5% of swelling wheat starch,  
         [0049]    70% of water  
         [0050]    d) 3% of carbon black,  
         [0051]    75% of vinyl acetate/vinyl chloride binder,  
         [0052]    16% of water,  
         [0053]    6% of film-forming and adhesion-promoting solvents  
         [0054]    e) 36% of PU dispersion,  
         [0055]    4% of acrylic dispersion, 6% of glycols,  
         [0056]    1% of additives,  
         [0057]    4% of a conductive substance, such as for example carbon black,  
         [0058]    49% of water.  
         [0059]    The graphite particles in the graphite suspensions have a grain size of between 1 μm and 100 μm, preferably from 1 μm to 30 μm. Suspensions incorporating graphite particles with a size of from 3 μm to 10 μm have proven particularly advantageous. For suspensions which contain carbon black, carbon black particles of large active surface area, preferably between 500 m 2 /g and 1500 m 2 /g, have proven advantageous. The coating has to be applied to the wearing layer in such a way that it forms a cohesive layer with a thickness of a few micrometers.  
         [0060]    [0060]FIG. 5 shows a diagrammatic view of the support layer  2  and the intermediate layer  3 . The intermediate layer extends over the edge regions  9   a  and  9   b  of the support layer  2 , while the edge regions  9   c  and  9   d  of the support layer  2  remain free of the intermediate layer.  
         [0061]    In a further embodiment, the load-bearing capacity of the support layer is increased if the support layer has compression elasticity properties. By way of example, the support layer may be at least half made up of a polygonal structure, such as a honeycomb structure. The recesses in the edge regions of the polygonal structures improve the ventilation of the subfloor, which is preferable in particular in moist environments.  
         [0062]    The support layer is preferably made from a reclaimed product, for example having the following composition:  
                                                       PVC (suspension quality)   38-42%           Plasticizer (phthalic acid ester)   12-14%           Inert substances (chalk, pigments)   40-44%           Heat stabilizer   2.5 to 3.5%           Processing auxiliary    0 to 1%.                      
 
         [0063]    This formulation results in Shore D hardnesses of 65 to 70. The support layer preferably has a thickness of 5 to 7 mm, particularly preferably of 6 mm.  
         [0064]    A floor covering produced using the tiles according to the invention can also be subjected to load from, and driven on by, high weights.  
         [0065]    The configuration of the tiles can be calculated using the finite element method.  
         [0066]    A tile over which a fork-lift truck drives should, for example, satisfy the following demands:  
                                                       Weight    10 t           Speed    25 km/h           Braking distance    15 m           Bearing surface area   600 cm 2             Modulus of elasticity   500 MPa           resulting in a required force of 16,000 N.                      
 
         [0067]    With a coefficient of friction of 0.5 and a symmetrical distribution of forces, the force per bearing surface area is 2000 N.  
                                                                             Number of   Modulus of               Tensile       connections   elasticity   Force   Deformation   Stress   strength       per side   (MPa)   (N)   (mm)   (N/mm)   (MPa)                                4   500   2000   3.7   37   18       8   500   2000   2.2   20   18       16   500   2000   1.4   15.3   18                  
 
         [0068]    If the floor covering is to be able to withstand a load of this level, 16 connections should be used on each side, meaning a combination of 8 projections and 8 cutouts on each side of the support layer of the tile according to the invention. If there is a smaller number of connections, the maximum load-bearing capacity is reduced accordingly.  
         [0069]    [0069]FIG. 6 a  shows part of a support layer  2   a . The support layer  2   a  is hexagonal in shape, i.e. has a honeycomb structure. The hexagon is delimited by narrow joints  12 . The projections directly adjoin the hexagon structure. The honeycomb structure increases the load-bearing capacity of the support layer, making it particularly suitable for use for industrial floors.  
         [0070]    [0070]FIG. 6 b  shows the side view of a support layer  2   a  which is shown below  6   a , from the side. The support layer may have recesses  15 . These recesses improve the ventilation of the subfloor. The recesses  15  may be distributed regularly or irregularly over the entire support layer.  
         [0071]    [0071]FIG. 7 shows a support layer  2  from above. The adjacent support layer  2   c  is arranged aligned with the support layer  2 , while the support layer  2   d  is connected to half the support layer  2 . This style of laying makes it possible to improve the load distribution.  
         [0072]    [0072]FIG. 8 shows an embodiment of the tiles according to the invention from above. In this embodiment, the electrically conductive wearing layer  4 , in addition to the defined electrical and mechanical properties, also has a pattern which is caused by carbon black or graphite inclusions and which at the same time serves as a decorative layer.  
         [0073]    [0073]FIG. 9 shows the embodiment shown in FIG. 7 from below. An additional grid-like printed pattern of a conductive substance, which has been applied to the wearing layer  3 , is able to further increase the electrical conductivity of the tile according to the invention.