Abstract:
Vertical to horizontal draining system and a synthetic turf having such a system. The draining system of the present invention prevents water from accumulating on the turf surface, which could cause the top-dressing layer to “float” and be moved by water inundation. The draining system of the present invention also obviates the need for extensive excavation, underdrain systems and free-draining replacement materials. The draining system of the present invention incorporates a dynamic drainage blanket, preferably sandwiched between two permeable porous geosynthetic or non-woven materials. The synthetic turf system of the present invention allows the use of an infilled synthetic turf over impermeable or semi-permeable surfaces, including impermeable soils, asphalt and concrete without having to remove such surfaces.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Artificial turf has long been used in athletic venues. It is a general object of such surfaces to mimic natural grass turfs while eliminating the high maintenance required and poor durability of natural surfaces. Artificial turf filled with a mixture of sand and rubber has been shown to reduce the potential for certain turf-induced injuries by greatly reducing abrasion. For example, U.S. Pat. No. 4,337,283 discloses an artificial turf comprising a subsurface, a pile fabric having a flexible backing on the subsurface, and a compacted top-dressing layer comprising a mixture of from 25 to 95 volume percent resilient particles such as rubber, and from 5 to 75 volume percent fine sand. The top-dressing layer is interspersed among the pile elements of the pile fabric and on the backing. The purpose of the top-dressing layer is to stabilize the pile elements, prevent graininess (i.e., prevent the tendency of the pile fabric to lay in a given direction), absorb shock, and improve the footing of a player running or walking across the surface. Although the use of fine sand in the top-dressing layer adds weight and reduces sponginess to the pile fabric layer and is less abrasive than “large” sand, it still suffers from undesirable abrasiveness. Moreover, the sand has a much higher specific gravity than the rubber, and thus the two materials tend to separate and cannot be kept in a uniform mix or be spread uniformly over the area of a field. After installation, the lighter rubber material rises to the top.  
           [0002]    One problem encountered with the use of synthetic turfs is adequate water drainage. Conventional turf systems rely on gravity and the slope of the sub-base for water drainage. Playing surface flooding can not only render the surface non-functional, but also can cause dislodgement and movement of the infill materials. U.S. Pat. No. 5,976,645 discloses methods for installing vertically draining infilled synthetic turf systems which rely on extensive sub-surface construction to protect the playing surface and infill from water inundation. Previous systems relied on the installation of 6 to 18 inch open graded, free draining stone base in conjunction with an underdrain conduit system. Because of the excavation required, the removal of materials and the placement of new materials, such stone base systems significantly add to the cost of installing the synthetic turf.  
           [0003]    It therefore would be desirable to provide a synthetic turf that exhibits excellent water drainage without requiring the excavation, material removal, free-draining replacement materials and complex underdrain system previously thought necessary.  
           [0004]    It also would be desirable to provide a drainage system for a synthetic turf that can be installed faster and more economically than previous vertically draining systems.  
         SUMMARY OF THE INVENTION  
         [0005]    The problems of the prior art have been overcome by the present invention, which marries a vertically draining synthetic turf system to a horizontal underdrain system. The draining system of the present invention prevents water from accumulating on the turf surface, which could cause the top-dressing layer to “float” and be moved by water inundation. The draining system of the present invention also obviates the need for extensive excavation, underdrain conduit and free-draining replacement materials. The draining system of the present invention incorporates a drainage blanket, preferably sandwiched between two permeable porous geosynthetic or non-woven materials.  
           [0006]    The synthetic turf system of the present invention allows the use of an infilled synthetic turf over impermeable or semi-permeable surfaces, including impermeable soils, asphalt and concrete without having to remove such surfaces. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]    [0007]FIG. 1 is a cross-sectional view of the artificial turf in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    Turning now to FIG. 1, there is shown generally at  10  a synthetic turf having a sloped sub-surface base  2  layer. The subsurface base  2  is pre-existing; no excavation need be performed unless a proper grade (to a tolerance of about ½″ per 10 feet) must be established. Preferably the slope of the sub-surface base  2  is 0.5% to about 1% from the field centerline in order to facilitate drainage, and the sub-base is compacted to the maximum practical density of the existing soils to form a firm and stable surface. Conventionally, the sub-surface layer had to be excavated and made permeable by the introduction of gravel or the like, which required materials and labor. The present invention obviates this need.  
         [0009]    Positioned over the sub-base layer  10  is a dynamic drainage blanket  12 . The drainage blanket  12  is composed of a stiff, non-degradable, non-obstructive (to the flow of water) material. The blanket should be capable of evacuating at least 2 inches per hour of rainfall from the entire playing area of the turf, even with the minimum gradient (slope) of 0.5%. One preferred material is Enkadrain®, such as Enkadrain® 9812, commercially available from Colbond, Inc., which is a high density polyethylene core of fused, entangled filaments and a geotextile fabric bonded to two sides. The tangled filaments are molded into an elliptical pattern while maintaining a flexible design. The thickness of the material is about 0.4 inches. The blanket  12  should be supplied in minimum two hundred foot lengths or such length as necessary to allow the blanket widths to be installed across the full width of the playing field, from one side to the other, in the direction of slope, with no seams or breaks to inhibit the flow of water. The widths of the drainage blankets  12  are then bonded together by any suitable means, preferably using a weather-proof cold adhesive, by heat-welding, or with a hot-melt adhesive.  
         [0010]    Preferably the blanket  12  is sandwiched between two permeable geosynthetic or non-woven materials, which allows some of the rainfall to percolate into the sub-soil. The commercially available Enkadrain® material includes the geotextile fabric sandwich layers. The sandwiching layers are preferably made of a needle punched polypropylene, and are permeable to water. Each layer is about {fraction (1/16)}″ thick and surrounds a core that is about 0.4″ thick, although these dimensions are not critical. Other commercially available products include HYDRAWAY WD-100 manufactured by Monsanto. This product incorporates a rigid interior core composed of round plastic studs sandwiched between two permeable geosynthetic fabrics.  
         [0011]    The drainage blanket  12  should be used in the widest widths possible to reduce the number of seams. It is attached to the top perimeter anchor installed for the synthetic grass and is extended beyond, into an abutting or near-by trench drain  30  with a direct or an indirect connection through the drainage stone  32  to an outflow pipe  35 . More specifically, a trench is formed at the edge of the field and filled with concrete  14 . Although FIG. 1 shows formed concrete, the particular configuration of the trench need not be so formed, as long as sufficient concrete is poured to properly function as an anchor. A length of material, preferably pressure treated (P.T.) wood, is coupled to the concrete by any suitable means, such as by nailing. The drainage blanket  12  is then secured to the pressure treated wood, and extends beyond the same. A second, preferably deeper trench is formed at or near the concrete anchor, and a perforated drainage outflow pipe  35  is positioned in the trench. Preferably the perforations in pipe  35  are at or near the bottom of the pipe as the pipe lies in the trench. The drainage blanket  12  is positioned in the trench to direct the flow of water towards the pipe  35 . The drainage blanket  12  can be in direct communication with the pipe  35 , but this is not absolutely necessary. The trench is then filled with drainage stone  32  or the like to allow water to permeate towards the drainage pipe  35 . Water accumulating in the drainage pipe  35  flows out of the (sloped) pipe and into a further drainage facility as is conventional in the art.  
         [0012]    One embodiment of the playing surface  1  includes a pile fabric  9  of individual tufted yarn or yarn-like filaments. The material used for the yarn filaments is not particularly limited, and can include polypropylene or polyethylene, or a polyethylene/polypropylene blend yarn, or other suitable yarn material. A 100% polyethylene yarn is preferred due to its low abrasiveness and its grass-like appearance. Tufting through the backing at a yarn density of about 10 to 60 oz/yd 2 , preferably about 35-45 oz/yd 2 , so that the yarn is upstanding and substantially uniform in height, can be carried out to provide a higher weight playing surface.  
         [0013]    Conventional artificial turfs have used partially non-woven backings. However, the characteristics of the non-woven layer are such that in the tufting and coating process, the non-woven layer tends to stretch as it is being pulled by the rollers and/or tenner chain. While the material usually returns to its original dimensions, this distortion during the manufacturing process renders the process more difficult and costly to control. In addition, the physical structure of the non-woven material makes it difficult to penetrate with sewing needles, both during the tufting process and also during the seaming process at the job site installation. This difficulty in penetrating the non-woven material also limits the weight of the non-woven material that may be used, which in turn limits the functional ability of the non-woven layer to impart the desired dimensional stability and weight to the primary backing of the artificial turf.  
         [0014]    In accordance with one embodiment of the present invention, this problem is overcome by using a three-layer sandwich construction for the backing that incorporates only woven fabrics. The outside layers of the sandwich are a woven polyolefin with a scarified or fibrillated (“fuzzy”) side, commonly referred to in the industry as “FLW”. The fibrillated side is oriented to the outside of both of the outside layers. The interior layer of the sandwich is an open weave, isotropic, polymeric material with excellent dimensional stability (less than 0.2% in any direction), as manufactured by Amaco Fabrics and Fibers Co. Having the dimensional stable layer sandwiched bewteen equal fabric layers, with identical coefficients of expansion, balances the stresses produced between the stable and unstable layers, eliminating the tendency for the backing to bend during temperature change as it does when the stabilizing layer is asymmetrically situated.  
         [0015]    It is also important to orient the scarifed, fibrillated side of the outside layers (FLW) to the outside of the sandwich, i.e., so that the fuzzy sides oppose one another. By constructing the sandwich so that both sides expose the “fuzzy” material is a significant aid in the field installation of the synthetic turf. The fibrillated surfaces provide a superior substrate for the application and bonding of adhesives used in the seaming process, especially in the incorporation of permanent “inlaid” lines and markings. The extended fibers provide much greater bonding surface area and minimize or prevent the adhesives from leaking through the backing material. Because the fibrillated fabric is on both sides of the backing, the adhesive can bond one fibrillated side to another in the installation process. This produces a bond strength that is more than twice that attainable with prior backing constructions.  
         [0016]    The top-coating or infill layer  6  is preferably devoid of sand and its concomitant abrasiveness. It is preferably composed entirely of resilient material, preferably rubber, including natural rubber, synthetic rubber such as styrene butadiene (ground tire rubber), butyl rubber, neoprene, urethane rubber, nitrile rubber, etc. Preferably a blend of ground tire rubber and high density rubber is used, with the preferred amount of high density rubber being about 0-25% of the mix. The incorporation of round, coated, hydrophobic non-resilient particles, constituting about 2 to 5% by weight of the total infill mix, also can benefit the turf in several ways. They can reduce the resilience of the infill to a small degree but enough to “deaden” the feel of the turf. This produces a feel under the foot that is more like natural grass and less “spongy”. The feel can be specifically adjusted for individual taste by varying the non-resilient component. In addition, the incorporation of these particles inhibits the development of static electricity in the infill matrix, which is a common problem with a 100% ground rubber infill. Because these particles are round, coated and hydrophobic, they cannot compact (like sand) and therefore do not inhibit water drainage or reduce the G-max performance of the system over time.  
         [0017]    The depth of the infill should be substantially uniform and between about 0.5 inches and 1.75 inches, and is preferably about 1.25 inches in the case where the pile height is 2″. Typically the infill should be between ¾″ and 1″ below the full pile height.  
         [0018]    Other conventional infills, including sand and a combination of sand and resilient material, also can be used.  
         [0019]    To install synthetic turf in accordance with the present invention, the vegetative layer (grass and loam), if any, is removed, and the existing base materials are contoured, graded and compacted. A minimum 0.5% gradient on the sub-base materials is necessary, with a slope up to 2% being acceptable. Once the sub-base materials are fine graded, the dynamic drainage blanket is placed over the entire area. Preferably the dynamic drainage blanket is placed in the widest widths possible (most preferably widths of at least six feet) to reduce the number of seams. The widths of drainage blanket are then bonded together with an adhesive, such as a weather-proof cold adhesive, by heat-welding or with a hot-melt adhesive. The dynamic drainage blanket extends beyond the playing field to overlap an abutting trench filled with drainage stone leading to an outflow pipe or conduit. It is secured to the top of a perimeter anchor installed for the synthetic grass. Where natural or exiting drainage conditions and contours allow, the dynamic drainage blanket may be allowed to outflow freely onto adjacent ground.  
         [0020]    The infilled vertically draining synthetic grass is then placed over the blanket and installed in its usual manner. The dynamic drainage blanket has the substantial advantage of enhancing the system with additional shock attenuation, thus reducing G-max readings, while not affecting the natural feel of the turf. Expensive dynamic bases (“E-layers”) are not necessary to enhance G-max.  
         [0021]    The particular Enkadrain product chosen is preferred because it maximizes the G-max capabilities of the surface without significantly changing the natural “feel” and playability of the surface.  
         [0022]    There are three different methods that have been used to incorporate game lines into an infilled artificial turf surface. The first involves actually tufting the line directly in the surface using a different color yarn during the manufacturing (tufting) process. A second method involves installation of the lines by cutting and removing the turf from the area that the line will occupy and then inserting the line material and bonding it to the abutting turf. The third method is to simply paint the lines. The present invention utilizes a new method for in situ installation of game lines. Common line material consists simply of the same backing material as used for the turf proper, tufted with the same yarn color as the desired line, where this roll of turf is then cut into strips of line material of the desired width. In accordance with the present invention, the backing of the turf is tufted in specific width lines (usually four inches) with intervals of untufted backing (usually a minimum of 12 inches between the lines. After the roll is tufted and coated, it is then cut in the untufted portion midway between each sewn line segment. This yields line material with a tufted line having a left and right untufted flange of at backing material, with each flange having a width of at least 6 inches each. Adhesive is then applied to the top of the flange of the line material and the bottom of the abutting turf of the playing field, and the flanges are inserted under the abutting turf. The tuft and line are then pressed together by application of weight such as with a roller. Less time and less adhesive are required than with conventional methods, and the level of skill and precision necessary to successfully carry out the seaming process is reduced. Preferably the line material backing is an FLW backing layer with the fleeced side facing up, which results in more surface area for bonding to the turf.