For years natural turf surfaces were used for most outdoor sports: for example, soccer, football, field hockey, cricket, rugby, etc. Natural turf surfaces are surfaces constructed with a grass grown in soil, or some other surface layer of growth medium (e.g., sand and organic mixes, etc.), that is constructed upon a suitable foundation. A natural turf surface is generally preferred for its comfort, feel, grip, and appearance.
However, under heavy use and/or poor weather conditions, natural turf surfaces deteriorate rapidly and maintenance is costly. Intense activity on the turf destroys the grass and its root system, leaving mud and/or dirt on the playing surface. Prior to re-establishment of the turf, the surface is unsightly and often pockmarked, uneven, and possibly hazardous to use. Another problem associated with natural turf surfaces is the use of painted-on yardage and boundary lines. Typically, such boundary lines are formed by painting the playing surface. For aesthetic reasons, such lines are generally painted just prior to each official game played on the playing surface. The repeated application of paint to the surface of the playing surface tends to kill the grass that is located under the painted surface. In addition, over time the multiple layers of paint build up, forming a surface that is substantially harder than the surrounding natural grass playing surface.
Due to the needs of sports programs, even after destruction of portions of the turf, play usually continues on the playing surface, even when the surface is badly damaged, until the sport's season is over, when the turf can be re-established. Thus, the playing conditions on the playing surface continually decline over the season. At the end of the season, the natural turf surfaces are reseeded, the divots leveled and filled, etc. The natural turf surfaces are not usable during this re-establishment period. The re-establishment period typically takes at least four months, or longer, under ideal weather conditions, during which the natural turf surface should not be used.
Synthetic surfaces provide an alternative to natural turf surfaces. Synthetic surfaces generally come in three types, i.e., conventional, cryogenic rubber filled, and sand-filled or a combination of sand and cryogenic rubber. Conventional synthetic surfaces are a dense synthetic material that has the appearance of grass blades. Sand-filled and cryogenic rubber filled synthetic are synthetic materials that are similar to conventional synthetic turf, but with greater spacing between the blades, to accommodate a sand and/or cryogenic rubber filling.
Synthetic turf is installed with a carpet-like pile fabric having a flexible backing laid on a well drained compacted substrate, such as crushed stone or other stabilized base material. The pile fabric has rows of upstanding synthetic ribbons representing grass blades extending upwardly from the top surface of the backing.
Synthetic grass infill, for example, may comprise a mixture of 60% by weight of sand and 40% granulated cryogenic rubber particles uniformly mixed and deposited between the upstanding synthetic grass ribbons to a depth of 1 to 3 inches.
A high percentage of sand is preferred to minimize the cost of such systems, since cryogenic rubber particles are relatively expensive compared to sand. The sand particles also provide an improved degree of drainage that is needed where the synthetic grass surface is not in an enclosed stadium for example. Cryogenic rubber particles tend to impede the free flow of water, whereas the capillary action of the sand particles draws surface moisture downwardly due to the differences in surface tension characteristics between cryogenic rubber and silica sand.
Both the conventional and sand-filled synthetics are placed indoors or outdoors, upon a foundation that may include asphalt, concrete, wood, or other supporting subsurface along with cushioning mats, water drainage, and water irrigation. Although synthetic turf surfaces are more durable than well-established natural turf surfaces, they are only moderately successful for sports and other uses. The most notable disadvantages of synthetic turf surfaces are the discomfort for the players and an increased number of injuries. Yet, another concern with current synthetic grass systems is that there is a tendency of the filling (sand or cryogenic rubber) to compact over time. Thus, these surfaces are not satisfactory for many sports because the compaction of the top dressing limits the shock absorbing ability of the surface, and because “fill” top dressing is abrasive. Further, compacting of the fill eventually blocks the drainage holes of a synthetic turf system, thereby inhibiting proper drainage of moisture.
As can be seen from the above discussion, there exists a need for an improved surface for sports and other uses, and a method of making the improved surface, wherein the surface provides improved comfort and fewer injuries to the users, while being durable under heavy use and in poor weather conditions. The present invention is directed to fulfilling this need.