Patent Publication Number: US-2020283965-A1

Title: Artificial turf mat and method for manufacture thereof

Description:
The invention relates to an artificial turf mat, comprising a woven backing and a number of artificial grass blades connected thereto. Such an artificial turf mat is known in different forms. 
     The known artificial turf mat is formed by a rather dense weave, from which artificial grass blades protrude on one side. These artificial grass blades are attached to the backing by means of tufting or weaving. The side of the backing remote from the protruding blades is generally stabilized by a layer of latex or by another coating. This additional layer also serves to fix the artificial grass blades firmly in the backing. 
     The known artificial turf mat has the drawback that it is fully sealed on the underside by the layer of latex or the other coating, this adversely affecting the drainage of the artificial turf field. 
     US 2016/265170 A1 describes an artificial turf mat with a flexible base layer from which long blades and shorter blades extend. The short blades serve to support the longer blades, whereby they have better shock-absorbing properties. 
     EP 3 029 198 A1 describes a hybrid grass surface with a base sheet with therein holes through which roots of grass can protrude, and with grouped filaments which are connected to the base sheet by tufting. 
     JP 2005 015 972 A describes an artificial turf mat formed by coupling a number filaments to each other in strips and weaving therefrom a mat wherein yet other filaments form pile threads. 
     The invention now has for its object to provide an artificial turf mat of the above described type wherein this drawback does not occur, or at least does so to lesser extent. According to the invention, this is achieved in such a mat in that the woven backing comprises a leno weave of warp and weft threads wherein at least some of the threads are formed by melting threads, and wherein the artificial grass blades are woven into the woven backing. By making use of a leno weave, which forms a much stronger connection than a conventional weave in that the warp threads are in a leno weave arranged twisted in pairs round the weft threads, and by here also applying melting threads for additional bonding, a woven backing is formed which has sufficient intrinsic stability to in principle be used without latex or other coating, and wherein the co-woven artificial grass blades are bonded very well. An artificial turf mat having a very open structure and good drainage properties can thus be formed. 
     Because the artificial grass fibres are woven into the backing, for instance as warp or weft threads forming pile threads, the artificial grass blades can be formed by locally cutting these fibres or pile threads. It is possible already to cut through the fibres during weaving, for instance in the manner as described in WO 2010/120174. It is possible to envisage here that the artificial grass fibres are cut through such that the artificial grass blades formed thereby have a pointed shape which approximates the shape of natural blades of grass. 
     When the artificial grass blades protrude from the backing on both sides, a two-sided artificial turf mat is obtained which can also be placed vertically in order to function for instance as screen or partition. 
     At least some of the warp threads can further be formed by melting threads, and/or at least some of the weft threads can be formed by melting threads. In order to be able to twist the warp threads properly round the weft threads so as to form the leno weave it is preferred for the warp threads and/or the weft threads to have a substantially round cross-section. 
     In order to combine a good bonding with sufficient strength it is preferred for each melting thread to comprise a temperature-resistant thread core and a meltable coating surrounding the thread core. The melting thread can here as it were be welded to nearby threads by the melting of the coating. 
     The thread core can for this purpose comprise a plastic with a relatively high melting temperature, particularly polypropylene, while the coating can comprise a plastic with a relatively low melting temperature, particularly polyethylene. 
     In order to further increase the stability of the weave at least some of the warp and/or weft threads can be formed by shrinking yarns. By shrinking the yarns after weaving, for instance by heating them, surrounding threads are fixated extra firmly. 
     At least some of the warp and/or weft threads can in addition or instead be formed by spiral yarns. The surrounding threads can thus also be additionally fixated by having the yarns curl after weaving. 
     When at least some of the warp and/or weft threads are biodegradable, open spaces can be formed in the artificial turf mat, through which natural grass can grow. A hybrid turf mat can thus be formed. 
     At least some of the artificial grass blades can be manufactured from biodegradable material. The artificial grass blades can thus in the first instance support natural grass blades growing through the artificial turf mat. By the time this support is no longer needed, the biodegradable artificial grass blades decay and only the non-degradable artificial grass blades and the natural grass remain, these together forming a hybrid field. 
     An easily manufactured artificial turf mat is obtained when only a part of the backing is woven as leno weave. For the stability it often suffices to locally fixate conventionally woven zones by means of zones with leno weave. 
     Arranged between two pairs of leno-woven warp threads can thus be a larger number of conventionally woven warp threads. 
     In order to increase the stability of the artificial turf mat it can be provided with at least one secondary backing connected to the woven backing. This secondary backing can also be a weave. 
     The at least one secondary backing can here be manufactured from a natural fibre material, particularly jute or viscose. This natural fibre material can decay once the artificial turf mat has been laid, since the stability is then provided by the ground surface. 
     The artificial turf mat can even be provided with a plurality of secondary backings, which are manufactured from different materials. The outer secondary backing can here serve mainly to protect the other layers when the artificial turf mat is heated in order to melt the melting threads. 
     The invention also relates to a method for manufacturing an artificial turf mat. A conventional method comprises the steps of weaving a backing and connecting a number of artificial grass blades thereto. 
     The method according to the invention is distinguished from the conventional method in that at least a part of the backing is woven by interweaving a number of warp and weft threads by means of leno weaving, wherein at least some of the interwoven threads are formed by melting threads and wherein the artificial grass blades are woven into the woven backing. 
     Preferably applied variants of the method according to the invention are described in the dependent claims  18 - 28 . 
    
    
     
       The invention will now be elucidated on the basis of a number of embodiments, wherein reference is made to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an artificial turf mat according to a first embodiment of the invention on a ground surface, wherein some of the artificial grass blades have been omitted, 
         FIG. 2  is a schematic top view of a leno weave as applied in the backing of the artificial turf mat according to the invention, 
         FIG. 3  is a cross-section through a melting thread for application in the artificial turf mat according to the invention, 
         FIG. 4A and 4B  are respectively a side view of and a cross-sectional view through a weft thread embodied as melting thread and two warp threads of the leno weave before and after melting of the melting thread, 
         FIG. 5A and 5B  are schematic perspective views showing the connection between a weft thread and two warp threads embodied as shrinking yarns of the leno weave, before and after heating of the shrinking yarns, 
         FIG. 6  is a schematic perspective view of a weft thread and two warp threads twisted therearound of a leno weave, wherein a number of threads is embodied as spiral yarns, 
         FIG. 7  is a flow diagram with the most important steps of the method according to the invention, and 
         FIG. 8  is a schematic bottom view of a backing of an artificial turf mat according to a second embodiment of the invention. 
     
    
    
     An artificial turf mat  1  ( FIG. 1 ) comprises a woven backing  2  and a large number of artificial grass blades  3  connected thereto and protruding from the backing  2  on one side—the side forming the upper side T in use. Backing  2  is woven from threads or yarns which, just as artificial grass blades  3 , can themselves be manufactured from plastic. In order to form a very stable backing  2  without use having to be made for this purpose of a coating or a layer of latex, at least a part of the weave of backing  2  is according to the invention a leno-weave. In such a leno-weave the warp threads  7   a,    7   b  are arranged twisted in pairs round weft threads  8  ( FIG. 2 ). Due to this pairwise twisting of warp threads  7   a,    7   b,  the weft threads  8  are gripped tightly therebetween, whereby slippage of the threads relative to each other is prevented and a stronger connection in the weave is achieved than is possible with conventional weaving techniques. 
     In order to stabilize backing  2  still further the warp threads  7   a,    7   b  and/or the weft threads  8  are in any case partially formed by melting threads. By melting these threads after the weaving the weave is in fact “welded”, whereby it is strengthened still further. Because the weave of backing  2  is thus intrinsically stable, and can be used without coating or stabilizing layer of latex, backing  2  is lighter and easier to handle than a conventional backing with coating, while the eventual artificial turf mat will in addition have an open structure owing to the absence of the coating or the layer of latex, and is thus for instance air-permeable and water-permeable. 
     Each melting thread can be formed by a temperature-resistant thread core  9  and a meltable coating  10  which encloses thread core  9  ( FIG. 3 ). This meltable coating  10  provides for the bonding, while the thread core  9  will not melt and thus guarantees the strength and stability of the weave. A plastic with relatively high melting temperature, such as polypropylene, is for instance suitable as material for the thread core  9 . A plastic with a relatively low melting temperature, such as for instance polyethylene, could be chosen for coating  10 . The difference in melting temperature between thread core  9  and coating  10  need otherwise not be exceptionally great, as long as it is sufficient to ensure that the mechanical properties of thread core  9  are not affected, or hardly so, when backing  2  is heated to a degree that coating  10  of the melting thread melts. As can be seen, the melting thread here has a round cross-section, whereby the leno weaving is simplified. In the case of other cross-sections, particularly flat cross-sections, the twisting of warp threads  7   a,    7   b  around weft thread  8  results in deformation, whereby an irregular weave is obtained. 
     For the purpose of heating the melting threads use can be made of any desired heating technique, such as for instance heating by irradiation with infrared radiation. It is also possible to envisage guiding the weave along a heated roller and thus heat the melting threads. In that case it can be advantageous to protect the backing  2  on the side facing toward the heated roller with an additional backing which is manufactured from a non-meltable material, for instance a natural fibre material or a biodegradable material. 
     As can be seen by comparing  FIG. 4A  and  FIG. 4B , when weft thread  8  is embodied as melting thread, the warp threads  7   a,    7   b  will sink slightly into coating  10  of weft thread  8 , and tightly enclose thread core  9 , when coating  10  of weft thread  8  is melted. The material of meltable coating  10  will here flow around warp threads  7   a,    7   b  so that they become wholly or partially embedded therein. When the temperature is then once again reduced and meltable coating  10 ′ solidifies again, a very strong welded connection (shown in broken lines) will be created between weft thread  8  and warp threads  7   a,    7   b.    
     Although weft thread  8  is embodied as melting thread in this example, it is of course equally possible to envisage, in addition to or instead of weft thread  8 , one of the warp threads  7   a ,  7   b  or even both of the warp threads  7   a,    7   b  being embodied as melting thread. 
     It is additionally or instead possible to achieve a particularly strong connection between the warp and weft threads  7 ,  8  when some of these threads are formed by shrinking yarns. When warp threads  7   a,    7   b  are for instance formed by shrinking yarns, they can in the first instance be interwoven in twisted manner with weft threads  8  in order to thus form a leno weave ( FIG. 5A ), after which warp threads  7   a,    7   b  can shrink by heating and are thus pulled even more tightly around weft threads  8  ( FIG. 5B ). When weft threads  8  are here once again embodied as melting threads, an even stronger connection is formed. 
     Another way of achieving an additional strengthening of the leno weave is shown in  FIG. 6 , where the weft thread  8  and warp threads  7   a,    7   b  are all embodied as spiral yarns. Owing to the spiral form of the warp and/or weft threads  7 ,  8  they engage even more tightly in each other than is the case with smooth yarns, since the spiral yarns as it were hook into each other. This counteracts slippage of the threads relative to each other still further. 
     The backing  2 , which is formed as a leno weave and the warp and/or weft threads  7 ,  8  of which are embodied as melting threads, can be applied for the purpose of forming an artificial turf mat  1 . The artificial grass blades  3  are for this purpose woven into backing  2 . Some of the warp or weft threads  7 ,  8  are brought out of a main plane of the weave of backing  2  in loops in order to there form the artificial grass blades  3 . The loops can optionally be cut through so that each loop forms two individual artificial grass blades  3 . This cutting can already take place during the weaving, as described in WO 2010/120174. Because the combination of leno weave and the use of melting threads results in a very stable backing  2  with artificial grass blades  3  co-woven therein, a relatively large mesh width of the weave can be chosen. A relatively open structure is thus formed, which is very well water-permeable and thus results in an artificial turf field with good drainage properties. The structure is also air-permeable and thereby suitable for ventilation and/or heating of the artificial turf field. 
     It can be useful to make the leno weave of backing  2  on the basis of shrinking yarns, because the artificial grass blades  3  are thereby very tightly enclosed or gripped. In that case it can further be useful to apply a secondary backing  4  ( FIG. 1 ) in order to prevent deformation of the primary backing  2  when the shrinking yarns shrink. The secondary backing  4  can ensure that primary backing  2  remains flat. Secondary backing  4  can be manufactured from a natural fibre material, such as jute or viscose. As stated, an additional secondary backing (not shown here), which serves mainly to protect primary backing  2  and secondary backing  4  from overheating during heating of the melting threads, can in addition also be provided. This additional backing can be manufactured from a biodegradable material so that it eventually decays once artificial turf mat  1  has been laid on a ground surface  5 . The secondary backing  4  and/or the additional backing can further serve to support and fixate a filler layer (to be discussed below) when an artificial turf field  11  is installed on the basis of artificial turf mat  1 . 
     Because the artificial turf mat  1  already has sufficient strength and stability even without coating, latex layer or secondary backing, it is also suitable to be suspended vertically, for instance in order to form a screen or partition. In that case the pile threads can be brought out of the main plane of the weave and cut on both sides, so that protruding artificial grass blades  3  are formed on both sides of backing  2 . A two-sided artificial turf mat  1  is then thus in fact formed. 
     As can be seen in  FIG. 8 , it is not necessary to embody the whole backing  2  as leno weave, but it is possible to suffice with several zones  12  formed by leno weaving, whereby zones  13  with conventional weave are fixated and stabilized. In the shown example the backing is formed by strips  13  of conventional weave, which are finished on both sides with one or more pairs of warp threads  7   a,    7   b  which are interwoven in twisted manner with weft threads  8  for the purpose of forming a local leno weave  12 . These local leno weaves  12  hold in place the warp threads of the conventional weave  13  arranged therebetween. Otherwise also formed between woven strips  12 ,  13  in this example are strips  14 , where no warp threads are present and the weft threads  8  thus lie loosely. A very open backing  2  is thus created. 
     The different steps of the method for manufacturing the artificial turf mat according to the invention are shown in  FIG. 7 . The method starts with providing warp threads  7  (step  100 ) and weft threads  8  (step  101 ). The warp threads ( 7 ) and/or the weft threads  8 , or at least some of these threads, can here be embodied as melting threads. The warp and weft threads  7 ,  8  or some of these threads can also be embodied as shrinking yarns and/or spiral yarns. 
     In a subsequent step  102  the warp and weft threads  7 ,  8  are interwoven by making use of a leno weaving technique, wherein the warp threads  7  are intertwined. In step  103  the artificial grass blades  3  can then be connected to the woven backing  2 . Since the artificial grass blades  3  are here connected to backing  2  by weaving, the steps  102  and  103  in fact coincide, as shown schematically by the dotted block  102   a.    
     After artificial grass blades  3  have been woven into backing  2  a secondary backing  4  can optionally be connected to the leno weave backing  2  (step  104 ). This step is optional and could be skipped. Secondary backing  4  can be glued to primary backing  2 , but it is also possible to envisage these backs  2 ,  4  being connected to each other by for instance double weaving or any other type of connecting technique. In addition to a secondary backing  4  which, as stated, could be manufactured from natural fibre material it is possible to arrange another additional backing, for instance a backing which functions as protective layer during heating and which can be manufactured from a biodegradable material. This backing can also be connected to the other backings in different ways. 
     In a subsequent step  105  the artificial turf mat  1  formed in the foregoing steps is fixated by being heated. The melting threads will here partially melt, whereby welded connections are formed with the surrounding threads, also including the pile threads forming the artificial grass blades  3 . The heating can take place by radiation, for instance infrared radiation, or by guiding artificial turf mat  1  over a heated roller. The additional backing is especially important in this latter case. 
     Finally, artificial turf mat  1  is wound onto a roll (step  106 ) and is ready to be transported to a location where an artificial turf field  11  has to be installed. 
     The artificial turf field  11  formed using the above described artificial turf mat  1  comprises in conventional manner a ground surface  5  on which the backing  2  (in the shown example with the secondary backing  4  thereunder) is placed. The artificial grass blades  3  protrude above the backing  2  on the upper side T. The space between the artificial grass blades  3  can then be filled with a filler material or “infill”  6 , which ensures on the one hand that the artificial grass blades are supported and in addition serves for resilience and damping. Rubber granules, cork and other materials, generally in combination with sand, are suitable as filler material  6 . When backing  2  and/or artificial grass blades  3  are manufactured partially from a biodegradable material, and the artificial turf mat  1  is thus intended to form a hybrid field, the ground surface  5  can be seeded with grass seed (not shown here) prior to artificial turf mat  1  being laid. It is also possible to envisage the grass seed being sown in the layer of filler material  6  when this filler layer  6  comprises a natural material in which the grass can grow. 
     The invention thus provides an artificial turf mat which is lighter and cheaper than existing artificial turf mats, and is easier to handle. The artificial turf mat according to the invention further has greatly improved mechanical properties, while in addition enabling a better drainage and ventilation than existing artificial turf mats. 
     Although the invention is described above with reference to a number of embodiments, it will be apparent that it is not limited thereto but can be varied in many ways. The warp and weft threads  7 ,  8  can thus for instance have other cross-sectional forms than shown here. It is also possible to apply materials other than those stated here, both for the synthetic fibres and for the natural fibres. The scope of the invention is therefore defined solely by the following claims.