Patent Publication Number: US-8530026-B2

Title: Artificial fiber for use in an artificial grass sports field

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 11/883,434, filed Mar. 13, 2008 as the National Stage of PCT/NL2006/000057 filed Feb. 3, 2006 claiming the priority of NL1028224, filed Feb. 8, 2005, the entire disclosures of which are incorporated herein by reference. 
    
    
     DESCRIPTION 
     The invention relates to an artificial fiber of the monofilament-type for use in an artificial grass sports field wherein, seen in a transverse sectional direction of the fiber, at least part of the fiber is provided with stiffness-enhancing portion extending in the longitudinal direction thereof. 
     The invention also relates to an artificial grass lawn suitable for sports fields, consisting at least of a substrate to which one or more artificial fibers according to the invention are attached. 
     Many sports, such as field hockey, tennis, American football, etc., are now played on artificial grass sports fields, which sports fields are composed of an artificial grass lawn on which artificial fibers are provided. Although athletes sustain fewer injuries on a natural grass sports field when falling or making a sliding tackle, on account of the softer surface thereof, such sports fields are often severely damaged when the above sports are played thereon, precisely because they are used intensively and because of the varying influence of the weather conditions. 
     A drawback of the artificial fibers that are currently known is that they attend to assume a flat orientation relative to the ground surface after being played on. This results in so-called “bare patches” in the artificial grass sports field and thus in an increased risk of injuries, etc. 
     This problem can be eliminated in part, for example, by providing a granular infill material such as sand or granules of a plastic material between the artificial fibers. The presence of these infill granules leads to a more upright orientation of the artificial grass fibers. In addition, the infilled grains provide a softer, shock-absorbing playing surface on which players are less prone to injury. Furthermore, they provide improved playing characteristics, so that the playing characteristics of artificial grass sports fields resemble those of natural grass sports fields as much as possible. 
     The use of an infill in artificial grass sports fields, however, has a number of drawbacks. Not only is the construction of such an artificial grass sports field more labor-intensive than the construction of a natural grass sports field, but an artificial grass sports field provided with an infill requires subsequent maintenance as well. The initially uniform distribution of the granular infill can be disturbed by intensive usage. As a result, areas containing hardly any infill may form in places where the field is played on very intensively, for example, in the goal area. This has an adverse effect on the quality of play, which can lead to an increased risk of injury. 
     Another solution to the problem as described above is to increase the stiffness of the monofilament by changing the chemical composition and/or the processing method thereof. This is undesirable, however, because it will lead to a more abrasive artificial grass sports field with an increased risk of injuries. 
     A further solution to the problem as described above is to adapt the geometry of the artificial fiber, for example, as proposed in U.S. 2001/033902 or in WO 2005/005730. Both patent documents disclose fibers provided with stiffness-enhancing means. However, on account of the geometry of the fiber and the location of the stiffness-enhancing means, the artificial fibers that are obtained exhibit an increased risk of splitting and/or fracture as a result of material stresses that may be set up in the fiber, for example, due to loads exerted thereon during play or temperature changes that may occur. 
     It is also noted in this connection that U.S. 2001/033902 discloses a composite filament fiber (also called multifilament) which, on account of the geometry and the orientation of the stiffness-enhancing means, specifically provides weak lines of fracture in the composite fiber. The fiber is required to split in that case to create multiple filament fibers. 
     Similar weak artificial fibers that are liable to split and/or fracture are disclosed in WO 2005/005730. That publication also discloses a fiber comprising stiffness-enhancing means, but the fiber, on account of its geometry, has undesirable points or lines of fracture at which undesirable material stresses may be set up, for example, due to loads being exerted thereon during play (sliding tackles, etc.) or temperature changes that may occur. 
     It is one object of the present invention to avoid such a weak artificial fiber that remains susceptible to splitting and fracture, and to provide an improved artificial fiber for use in an artificial grass sports field, which fiber is provided with stiffness-enhancing portion. The fiber is less flexible, on account of the geometry of the fiber, exhibits less tendency to assume a flat orientation or to split or fracture, and furthermore does not exhibit an increased risk of injuries or have an adverse effect on the playing characteristics. 
     According to the invention, the artificial fiber comprises at least two fiber flange portions, at least one fiber flange portion forming the stiffness-enhancing portion, while at least two fiber flange portions have a uniform thickness. 
     More specifically, the stiffness-enhancing portion extends the full length of the fiber. On the other hand, the stiffness-enhancing portion can extend at least partially in the transverse sectional direction. 
     In another embodiment, the stiffness-enhancing portion is configured as at least one fiber flange portion extending at an angle to the plane formed by the fiber. The at least one fiber flange portion extends at an angle of about 90 degrees or about 45 degrees to the plane formed by the fiber in that embodiment. 
     In other embodiments, the at least one fiber flange portion is straight, curved or spiral-shaped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in more detail with reference to the drawings, in which: 
         FIGS. 1-5  show various embodiments of an artificial fiber according to the invention; and 
         FIGS. 6 and 7  schematically show a few embodiments of an artificial grass sports field provided with an artificial fiber according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1-5  are cross-sectional views of artificial fibers according to the invention, in which each fiber  30 - 70  is provided with stiffness-enhancing portion  33 - 73  extending in the longitudinal direction of the fiber. 
     In the embodiment shown in  FIG. 1 , the fiber  30  is configured as an extruded band of plastic material having a longitudinal direction  32 , which artificial fiber  30  has a V-shaped transverse cross-section made up of two fiber flange portions  30   a  and  30   b,  respectively, which extend in a transverse direction on either side of the longitudinal axis  32 . The stiffness-enhancing portion is indicated at  33  in the embodiment shown in  FIG. 1  and comprises a curved or rounded portion along the longitudinal axis joining laterally opposed, directionally diverging fiber flange portions  30   a  and  30   b.  The stiffness-enhancing portion resists deformation of the fiber. 
     In the embodiment shown in  FIG. 2 , the stiffness-enhancing portion  43  is configured as at least one fiber flange portion  43  extending at an angle to the plane formed by the artificial fiber  40 . In this embodiment, the artificial fiber  40  also has a V-shaped cross-section made up of two fiber flange portions  40   a - 40   b,  which extend symmetrically in a transverse direction with respect to the longitudinal axis  42 . The stiffness-enhancing portion  43  is incorporated in the fiber at the location of the longitudinal axis  42 . 
     In the embodiment shown in  FIG. 3 , the fiber  50  includes two fiber flange portions  50   a - 50   b,  which extend symmetrically in a transverse direction with respect to the longitudinal axis  52  and which have a curved shape, which curved shape forms the stiffness-enhancing portions  53   a  and  53   b,  respectively. In this embodiment, the fiber flange portion  50   a - 50   b  is curved, with each fiber flange portion  50   a - 50   b  comprising a curve. 
       FIG. 4  shows an alternative embodiment of the artificial fiber shown in  FIG. 3 , in which the artificial fiber  60  is provided with fiber flange portions  60   a - 60   b  exhibiting multiple curves (two in this embodiment). Each fiber flange portion  60   a - 60   b  exhibits two curves  63   a - 63   a ′ and  63   b - 63   b ′, respectively, which form the stiffness-enhancing portion. 
     In the embodiment shown in  FIG. 5 , the artificial fiber  70  comprises three fiber flange portions  70   a - 70   c,  which extend in a star-shaped manner with respect to the longitudinal axis  72 . It will be apparent that more than three fiber flange portions extending symmetrically with respect to the longitudinal axis  72  may be used in this embodiment. In addition, each fiber flange portion  70   a - 70   c  in this embodiment comprises a curve, which curves form in the stiffness-enhancing portions  73   a - 73   c.    
     While the fiber flange portions  70   a - 70   c  extend in a star-shaped, albeit curved, manner with respect to the longitudinal axis  72  in  FIG. 5 , the flange portions  70   a - 70   c  of the fiber  70  of another embodiment (not shown) may be straight. The fiber flange portions  70   a - 70   c  (the legs) may be identical in length in that embodiment, while in another embodiment the legs may be different in length, similar to the embodiment shown in  FIG. 2 . 
     It is noted that the artificial fiber shown in  FIGS. 1-5  is configured as a monofilament fiber obtained by means of an extrusion process. In view of the geometries as shown in  FIGS. 1-5 , use is made of stiffness-enhancing portions, which preferably extend in the longitudinal direction of the fiber and which may optionally extend in the transverse direction of the fiber. As a result, the fiber is less flexible, and thus will exhibit less tendency to assume a flat orientation in the artificial grass sports field. 
     In spite of the use of less flexible artificial fibers that, according to the invention, include stiffness-enhancing portions incorporated in the fiber, it has become apparent that the risk of injuries does not significantly increase and furthermore that the playing characteristics of an artificial grass sports field comprising such artificial fibers  10 - 100  are not adversely affected. 
     It is also pointed out that the embodiments shown in  FIGS. 1-5  provide a possibility of absorbing or retaining water, which has a positive effect on the playing characteristics of the field. 
     In addition, the fiber flange portions  30   a - 30   b;    40   a - 40   b;    50   a - 50   b;    60   a - 60   b  and  70   a - 70   b  in  FIGS. 1-5  each have a uniform thickness. Thus, no material stresses that might lead to undesirable deformation occur in the fiber material. Moreover, the uniform thickness significantly adds to the life of the fiber, as wear is prevented. 
       FIGS. 6 and 7  show a few embodiments of an artificial grass sports field in which an artificial fiber according to the invention can be used. In both Figures, the artificial grass sports field comprises a substrate  1 , to which several artificial fibers  2  (corresponding to the fibers  30 - 70  in  FIGS. 1-5 ) are attached at the locations indicated at  3 . The extruded artificial fiber may be provided on the substrate either individually or in the form of a bundle of fibers  2   a - 2   c,  which are twined together, for example. 
     In another embodiment, as shown in  FIG. 7 , the artificial fiber according to the invention may be a monofilament. In this embodiment, several monofilaments may also be combined into bundles by twining, after which each bundle is attached to the substrate  1 . The substrate shown in  FIG. 7  has an open structure, being composed of a grid of supporting yarns  1   a - 1   b,  on which the artificial fibers  2  are provided. 
     The foregoing description and the accompanying drawings are illustrative of the present invention. Other variations and arrangements are possible without departing from the spirit and scope of the invention.