Abstract:
The described method of fabricating a composite engineered wood material floor board, having a top wood layer secured to a wood material substrate layer, minimizes the effect of telegraphy in the resulting floor board. The method includes selecting a top wood layer from a top surface quality wood material having a thickness of between 1 mm and 8 mm, and selecting a substrate wood material layer having a minimum thickness of 6 mm and a thickness ratio between 1:1 and 1:10 between the top wood layer and the substrate wood material layer. A plurality of transverse rectangular spaced-apart grooves are also formed in a bottom surface of said wood substrate layer. The ratio between the depth of said grooves and the thickness of the substrate wood material has an impact on telegraphy of said grooves in said top wood layer and is therefore selected accordingly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 13/412,656 filed Mar. 6, 2012, which is a division of U.S. application Ser. No. 12/264,962 filed Nov. 5, 2008, now abandoned, the entire contents of each of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a composite engineered wood material piece and its method of fabrication. The wood material piece has a top wood layer secured to a substrate layer provided with the grooves which are sized and oriented such as to substantially eliminate the effects of telegraphy in the top finished surface of the top wood layer. 
     BACKGROUND ART 
     It is well known in the prior art to fabricate wood boards, particularly for the construction of wood floors, wherein the wood boards are formed from solid wood or laminated wood which contains grooves in the back surface thereof whereby to enhance the flexibility of the boards. It is also known to fabricate wood flooring strips having small wooden slats glued to the backside thereof at regular spaced intervals to add additional flexibility to the floor board. The desired flexibility of floor boards is that they can conform to irregularities in the subfloor to which the boards are to be secured. Generally these floor boards are of thicknesses of ½ inch up to about 1 inch and provided with tongue and grooves whereby to engage one another in a side-by-side and end-to-end relationship. Such boards and the disadvantages of the related prior art are discussed for example in U.S. Pat. No. 5,283,102 issued on Feb. 1, 1994. 
     In recent years, laminated wood boards have become thinner with the top solid wood layer also becoming thinner normally in the range of about ⅛ inch and such laminated wood boards are installed directly on a solid wood floor or on a sound absorbing material secured to the subfloor. Transverse grooves are formed in the substrate layer of these laminated boards to provide the desired flexibility of the boards to facilitate installation thereof. However, because the top wood layer is relatively thin as compared to the substrate layer to which it is secured, the grooves formed in the substrate layer become visible in the top surface of the top wood layer by the phenomenon of telegraphy. Accordingly, the grooves need to be made very shallow and the top surface of the top wood layer is preferably of light tone or provided with a non-lustre varnish in an attempt to try to conceal the appearance or reflection of these grooves in the top surface. Therefore, laminated products have been constructed with the top wood layer having a thickness ratio in the range of one-to-one with respect to the substrate and thus affecting the flexibility of the wood board and increasing the cost thereof. 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to provide a composite engineered wood material piece and method of fabrication which substantially overcomes the above-mentioned disadvantages of telegraphy. 
     According to the above feature, from a broad aspect, the present invention provides a composite engineered wood material piece which is comprised of a top wood layer secured to a substrate layer by binding means. The substrate layer has a plurality of grooves formed therein from a bottom surface thereof to enhance the flexibility of the wood material piece. The grooves are spaced from one another by one or more predetermined space distances and have one or more predetermined depth and width calculated based on parameters of the material piece to substantially eliminate the effects of telegraphy of the grooves on a top finished surface of the top wood layer. 
     According to a further broad aspect of the present invention, there is provided a method of fabricating a composite engineered wood material piece having a top wood layer secured to a substrate layer by binding means. The method comprises the steps of calculating from known parameters of the top wood layer and substrate layer, the depth, width and spacing of the grooves to be formed in a bottom surface of the substrate layer to enhance the flexibility of the wood material layer while substantially eliminating the effects of telegraphy of the grooves on a top finished surface of the top wood layer. The method further comprises forming a plurality of grooves in the bottom surface of the substrate layer having dimensions and spacing as calculated from the known parameters. 
     According to a further broad aspect, the predetermined depth and width and spacing of the grooves, in accordance with the present invention, are effected by the analysis of the following parameters: a) the type of wood of the top wood layer, b) the intrinsic properties of the substrate layer, c) the thickness ratio between the top wood layer and the substrate layer, d) the top surface texture of the top wood layer, e) the properties of the binding means, and f) the type of finish coating to be applied to a top surface of the top wood layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is a fragmented perspective view of a section of a composite engineered wood material piece constructed in accordance with the present invention; 
         FIG. 2  is a side view of an example of a composite engineered wood material piece constructed in accordance with the present invention; 
         FIG. 3A  is a perspective top view of a top wood layer to be secured to a substrate layer and formed of oak material having a clearly defined and visible grain surface texture; 
         FIG. 3B  is a perspective view similar to  FIG. 3A  but showing a top wood layer fabricated from a different type of wood, herein maple wood having a faint wood grain; and 
         FIG. 4  is a plan view of the rear surface of a composite engineered wood material piece having grooves therein formed of different spacing, size and orientation to provide a sheet adapted to be cut to a template shape to produce a contoured sheet having different flexible regional characteristics to form a top surface of a shaped member, such as an article of furniture, an irregularly shaped wall surface or a multitude of other articles. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings and more particularly to  FIG. 1 , there is shown generally at  10  a composite engineered wood material piece such as a floor board or slats constructed in accordance with the prior art and which comprises a top wood layer constructed of a superior material such as oak, pine or maple and secured by a glue layer  12  to a substrate layer  13 . Grooves  14  are formed in the substrate material  13  from a bottom surface  15  thereof and at spaced intervals whereby to provide flexibility to the floor board  10 . As previously described, such grooves  14 , through the phenomenon of telegraphy, form shaded zones  16  in the top finished surface  17  of the top wood layer  11 . 
     The present invention addresses this phenomenon of telegraphy and substantially eliminates the effects thereof on the top finished surface  17 . This is achieved by calculating the dimension of the depth and width as well as the spacing of the grooves from a set of parameters of the top wood layer and the substrate layer. These parameters include the type of wood of the top wood layer, the intrinsic properties of the substrate layer, the thickness ratio between the top wood layer and the substrate layer, the top surface texture of the top wood layer, the properties of the binding means and the type of finish coating to be applied to a top surface of the top wood layer. All of these parameters have an interrelationship with respect to one another and produce the resulting telegraphy. It has been ascertained that this telegraphy is caused by four phenomenon and namely the induced tension within the composite laminated material piece, the deformation of the composite material piece caused by deflection when it is installed on a irregular subsurface, the change in humidity in the composite material piece causing it to expand and retract, and the dispersion or conduction of humidity throughout the composite wood material piece. 
     The composite engineered wood material piece of the present invention is comprised of two distinct laminated wood materials, namely a top wood layer  11  of wood material and a substrate layer comprised of laminated or compressed inferior wood material glued together, or another suitable type of substrate. These glued materials will be subject to tension and stress which will produce the telegraphy of the grooves formed in the bottom surface thereof. The ratio between the thickness of the top wood layer  11  and the substrate layer  13  is an important factor in determining the spacing  18 , see  FIG. 1 , between the grooves  14 . If the ratio between the thickness of the top wood layer  11  and that of the substrate layer  13  is close to 1 (i.e. the top wood layer  11  has the same thickness as the substrate layer  13 ), the telegraphy of the grooves will be very weak due to the thickness of the top wood layer  11  which is less conductive. However, if the ratio between the top wood layer and the substrate layer is 1:10 (i.e. the top wood layer  11  is ten times thinner than the substrate layer  13 , or stated alternately, the substrate layer  13  is ten times thicker than the top wood layer  11 ), the telegraphy would be greatly amplified as the top wood layer is very thin compared to the substrate layer. Accordingly, the spacing  18  between the grooves will require to be reduced to thereby have the grooves  14  closer to one another, and the dimension of the depth  19  of the groove would have to be shorter (i.e. less depth). The width  20  of the grooves may also be made narrower. 
     Example 1 
     If the top wood layer  11  has a thickness of 8 mm and the substrate layer  13  has a thickness of 8 mm, the telegraphy of the grooves  14  formed in the substrate layer is nearly inexistent for the reason that the substrate layer cannot have much effect on the top wood layer which is of equal thickness. However, if the top wood layer is of 1 mm thickness and the substrate layer much thicker, say 8 mm, the telegraphy of the grooves would be very visible. Therefore, the ratio between the thickness of the top wood layer and the substrate layer is an important factor to consider in the determination of the configuration and spacing of the grooves. 
     Example 2 
     Considering now two top wood layers  11 , one of 2 mm and one of 4 mm, glued on a 6 mm thick substrate and with the grooves being spaced-apart 2 inches and having a depth of 4 mm. The groove telegraphy in the 2 mm top wood layer will be very visible. Accordingly, the spacing between the grooves will need to be reduced to 1 inch to reduce substantially the telegraphy. However, for the top wood layer of 4 mm a groove spacing of 1½ inches would be sufficient to obtain an acceptable level of reduction of the telegraphy. 
     Another important factor to consider is the binding material which is preferably a glue coating applied between the top wood layer  11  and the substrate layer  13  with further application of pressure by means of presses, as is well known in the art. The adhesive material can also be polyurethane foam or contact cement applied to opposed surfaces to be mated and let dry before the layers are contacted under pressure. The adhesive binder or glue  12  has a predetermined elastic property and thickness and such is also a factor in the determination of the predetermined spacing  18  of the grooves  14 . Glue which is very flexible will permit a spacing  18  between the grooves which is larger or permit a depth of groove which is deeper as the glue acts as a relaxation zone for the constraints of the substrate layer. The glue, or other binding agent, could also acts as vapour barrier and reduces the transmission of humidity. 
     Another important factor taken into consideration is the depth  19  of the grooves  14 . The ratio between the depth  19  of the grooves  14  and the thickness of the substrate layer  13  has an impact on the telegraphy and the flexibility of the wood material piece  10 . 
     The depth  19  of the grooves also has a negative effect in that it defuses humidity within the substrate layer and can provoke increased telegraphy on the top surface  17  of the top wood layer  11 . Although the glue layer  12  and the glue present in the substrate provide a barrier to humidity, this barrier is broken at each groove  14 . As pointed out herein above the reason for the grooves is to diminish the rigidity of the composite material piece or layer in order to facilitate installation on irregular subsurfaces. 
     Example 3 
     With reference to  FIG. 2 , there is shown a specific composite engineered wood material piece  10 ′ constructed in accordance with the present invention. The top wood layer  11  is formed of maple wood and has a thickness of 4 mm. The substrate layer  13  is formed of birch wood and has a thickness of 9 mm. If the grooves  14 ′ have a depth of 2 mm, the telegraphy in the top finished surface  17  is practically invisible. However, if the grooves  14 ″ have a depth of 8 mm, for the same groove width, the telegraphy would be very visible in the top finished surface  17 . However, the grooves  14 ′ are not deep enough to provide the desired flexibility of the composite wood material piece  10 . 
     Another important factor taken into consideration is the composition of the substrate layer  13 . The intrinsic properties of the substrate layer  13  have an important effect on telegraphy. Substrate layers of material all have a specific density and modulus of elasticity and hygroscopic properties as well as other characteristics. By the formation of grooves in the substrate layer, there is created constraints in the substrate layer which are manifest on the top finished surface of the top wood layer. A substrate material which has a high hygroscopic movement will be, affected substantially by the formation of grooves and would have a greater impact on the appearance of the grooves on the top surface of the top wood layer. Accordingly, rigidity of the substrate layer affects telegraphy. The tensions which exit in certain substrate materials due to their lamination and the orientation of wood particles and fibres, can also provoke telegraphy when grooves are formed in such material. As above-described, the humidity barrier characteristic of the substrate is also an important factor. 
     Example 4 
     We will now consider the effects of a top wood layer  11  having a thickness of 4 mm secured to two types of substrate layer  13 , namely a substrate layer constructed of MDF material and having a thickness of 8 mm as compared to a substrate layer of the same thickness but fabricated from plywood material. During humidity variations, the MDF substrate layer will have more important dimensional instability and will provoke more telegraphy when compared to the plywood sheet substrate which has a greater dimensional stability. Thus, the composite material which has a substrate layer having a greater modulus of elasticity will provoke increased telegraphy on the finished surface of the top wood layer as there will be more deformation in the surrounding area of the grooves. 
     Another factor to consider in the determination of the configuration and spacing of the grooves is the top surface texture of the top wood layer.  FIG. 3A  shows a top wood layer formed of oak material which is a very rigid wood material having a very high modulus of elasticity and such with therefore greatly reduce the telegraphy of the grooves. The oak wood has a pronounced textured grain  26  which also conceals defects in the top finished surface  17 . When the wood material pieces are used as floor boards, one or more coats of varnish are applied to the top surface  17  for shine and durability. It has been found that a glossy surface is more conductive of the telegraphy phenomenon that is a less glossy surface. Also, if a stain is applied to the top surface of the top wood layer, the darker the stain, the more visible becomes any telegraphy and this may also be taken into consideration when calculating the size and spacing of the groove. 
     Example 5 
     As described above with reference to  FIG. 3A and 3B , there is shown the oak material top layer  25  which is darker and provided with a pronounced textured grain and a maple wood top layer  27  which is lighter and contains less grain. The maple top wood layer  27  will show more telegraphy than the oak layer. Both top wood layers  25  and  27  have a thickness of 2 mm and are secured to a same substrate layer. It has been found that the maple top wood layer produces a more important telegraphy than does the oak layer  25 . Also, the textured grain  28  in the maple wood  27  is less pronounced and visible and therefore provides less camouflage to any telegraphy transmission in the wood material. 
     Example 6 
     Considering now a top wood layer of oak material having a natural colour with a mat finish on its top surface as opposed to a top wood layer of maple which is stained a dark color and provided with a high lustred finish on its top surface. Both top wood layers are 4 mm in thickness and are glued onto a substrate layer formed of birch and having a thickness of 9 mm and grooves having a depth of 6 mm and a width of 2 mm. The grooves are also spaced apart 1½ inch. When comparing both products it has been found that the oak material top layer provides an adequate reduction of the telegraphy of the grooves on its top surface. Accordingly, it would be possible to utilize a glue which is less flexible or to have the grooves spaced a greater distance apart, about 1½ inches. However, with the dark stain maple wood top layer, the telegraphy was slightly apparent. Therefore, a reduction in the spacing between the grooves would be necessary to greatly reduce this telegraphy, a spacing of 1⅛ inch. 
     In conclusion, the finish coating applied to the top surface of the top wood layer  11  has an impact on telegraphy. A finished coating which has less lustre will produce less telegraphy than does a high lustre surface as above-mentioned. However, high lustre surfaces are the preferred surfaces of floor wood board, furniture, wall decorations, etc., and accordingly, it is important to therefore configure the grooves such as to substantially eliminate or greatly reduce the telegraphy phenomenon. 
     A further factor for consideration is the determination of the width  20  of the grooves  14 . A very narrow groove width produces very little telegraphy. For the laminated wood boards as above-described, it has been found that a width of 1 to 2 mm provokes an average telegraphy whereas a width which is greater than 3 mm or more than 4 mm will enhance telegraphy. There is therefore a proportional relationship between the transmission of telegraphy and the groove width. 
     As mentioned, another consideration in reducing telegraphy is the spacing  18  between the grooves. Generally speaking, a spacing of more than 2 inches greatly increases telegraphy depending of course on the depth and width of the grooves. A spacing of 1¼ inches or less will improve the reduction of telegraphy and it has been found that a spacing of about one inch is more desirable as it further reduces telegraphy. However, the amount of grooves should be limited not to greatly affect the modulus of elasticity of the substrate material. 
     Example 7 
     For a composite material piece having a substrate layer formed of birch material and of a thickness of 9 mm, and a top surface layer of maple having a thickness of 4 mm with a glossy surface coating, grooves having a width of 2 mm and a depth of 6 mm would be desirable. However, with such a product specification, the risk of telegraphy is highly present as we have a ratio of thickness between the top wood layer and the substrate layer of 4:9, a ratio of groove depth of 6:9, a rigid modulus of elasticity of the substrate, and a glossy top surface finish on the maple top wood surface. Also, any humidity will provoke deformation in the wood material. Therefore, a spacing between the grooves of 2 inches will make the grooves very visible on the top surface by telegraphy. By decreasing the spacing to about 1⅛ inch, the telegraphy is practically non-visible and the grain in the top maple wood layer becomes more visible due to the practically non-existing phenomenon of the telegraphy. By reducing the spacing between the grooves to about 1 inch, the grain becomes more visible and the surface is almost unaffected by telegraphy. 
     Referring now to  FIG. 4 , there is shown a composite engineered wood material piece, herein a sheet of material, formed in accordance with the present invention. As hereinshown, the rear surface  31  of the substrate layer  32  is provided with grooves oriented in groups, namely groups  33  and and wherein the orientation of the grooves  33 ′ of group  33  and grooves  34 ′ of Group  34  extend at different angles whereby to provide different zones and orientation of flexibility to the layer. Also, the grooves  34 ″ in group  34  are more closely spaced in a section of the group  34  to provide added flexibility in that section. Such an engineered composite layer may be formed for specific applications and wherein the layer may be cut to the shape of a template, such as indicated by phantom line  35 , to form an overlay sheet for a repetitive product, such as an article of furniture wherein the sheet is to be bent to conform to a certain shape. The spacing and dimension of the grooves is also calculated to substantially eliminate or greatly reduce the phenomenon of telegraphy. It is pointed out that the grooves can be formed by various means, such as by the use of a saw, a router bit, a slitting blade, or by spaces between glued material strips. 
     It is within the ambit of the present invention to cover any obvious modifications of the preferred embodiment described herein, provided such modifications fall within the scope of the appended claims.