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The present application derives priority from U.S. provisional application Ser. No. 60/860,313 filed 21 Nov. 2006.
1. Field of the Invention
The present invention relates to synthetic sport surfaces for tennis courts and, more specifically, to a two-layer padded surface for tennis courts comprising a top wear layer applied over a soft poured-in-place polyurethane elastomer (cushion) layer to provide a combination of good wear-resistance and texture for tennis.
2. Description of the Background
A wide array of natural and artificial surfaces are currently used in basketball and tennis courts, soccer and football fields, and racing tracks. In each case it is necessary to finely tune the surfacing to obtain particular surface characteristics such as cushion or rebound, wear-resistance, or low construction and maintenance costs.
Most conventional outdoor tennis courts are comprised of asphalt pavement or concrete, but both materials are subject to the development of cracks and degradation from weather, aging, and normal wear and tear. Moreover, asphalt and concrete are unyielding surfaces that frequently cause injuries.
There are also grass and synthetic grass tennis surfaces, but in both cases the surfaces require significant maintenance and fair poorly in cold climates.
Clay tennis surfaces use natural clay (i.e., naturally occurring hydrated silicate materials). These are soft and easy to play on, but expensive to install, difficult to maintain, and are not useable at all in colder climates.
There are also a variety of Acrylic™ surfaces for both indoor and outdoor tennis courts. For example, attempts have been made to laminate foam with acrylic coatings. However, normal seasonal, daily and hourly temperature changes cause undue tension on seams and multiple wrinkles from contraction and expansion of the foam. For example, TenniSphere, Inc. in Rome, Ga. sells a surface comprising a polyethylene foam with an SBR (styrene butadiene rubber) latex coating that is air dried in place, and topped by multiple layers of a conventional acrylic latex mixture (with or without sand and paint) to give the surface of the material the feel and touch of a tennis court. This surface is also subject to shrinkage when exposed to temperatures above about 50-60 degrees F. which results in cracks in the base around the outside of the tennis court. Moreover, this and other Acrylic surfaces are mainly used by large indoor and outdoor tennis installations and clubs due to the high cost.
Polyurethanes are well known for their ability to maintain physical properties over a wider range of temperatures. “Full pour” polyurethane systems are known in the running world and there are tracks that incorporate multiple layers of polyurethane coating and rubber granules. Running tracks require shock absorption rates of from 35-50%, and to achieve this in a “full pour” polyurethane system the substrate must be foamed as it is poured (e.g., air is incorporated in a polyurethane substrate either by chemical or mechanical methods). One of the issues with an air entrapped system is producing a uniform foam surface. Any irregularities in the substrate surface are multiplied by the foam system, and this causes surface irregularities. The foam system may also be susceptible to adhesion problems to the substrate (typically asphalt or concrete), because of the air entrapment. Conventional polyurethane surfacing systems cannot compensate for irregularities in the substrate surface, and such irregularities are unacceptable in the tennis world. Moreover, the conventional surfaces cannot be modified, adjusted or “tailored” to meet various performance standards or customer needs.
The International Tennis Federation (ITF) prefers shock absorption rates of 13-20%. It would be greatly advantageous to provide a two-layer padded surface for tennis courts comprising a urethane-based top wear layer applied over a soft poured-in-place polyurethane elastomer (cushion) layer, the wear layer being tunable for surface (friction) characteristics and the cushion layer being adjustable to vary the shock absorption values within the ITF range simply by adjusting the thickness.
It is therefore an object of the present invention to provide a two-layer padded surface for tennis courts comprising a urethane-based top wear layer applied over a soft poured-in-place polyurethane elastomer (cushion) layer.
It is another object to provide a tennis court surface as described above in which the wear layer is tunable for surface (friction) characteristics and the padding layer is tunable in thickness to vary the shock absorption values, thereby providing a long term durable tennis surface that meets ITF performance standards.
It is another object to provide an indoor/outdoor tennis court surface that is soft enough to absorb the impact of a foot strike, hard enough for competition, durable enough for prolonged use, and weather-resistant with good drainage properties.
In accordance with the foregoing object, the present invention is an improved padded surface for tennis courts that may be overlayed a surface foundation such as asphalt or concrete. The improved surface generally comprises a soft elastomer padding layer applied over the surface foundation, the padding layer including granulated SBR rubber added to a polyurethane elastomer. The polyurethane elastomer is formed by mixing a first component of polypropylene glycol, castor oil, silica, iron oxide pigment, a molecular sieve, a UV stabilizer, and a catalyst, with a second component formed of polypropylene glycol and methylene diphenyl diisocyanate. The soft elastomer padding layer is applied by squeegee and is set. Next, a top wear layer is applied over the soft elastomer padding layer. The top wear layer comprises any one from among a group consisting of a water-based urethane, acrylic, or urethane-acrylic hybrid intermixed with sand in a dispersion. The improved tennis surface provides an optimum balance of physical properties needed for the performance of the surface, despite a wide range of temperatures, and the thickness can be varied as desired to comply with ITF shock absorption rates of 13-20% and to suit customer preferences.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which:
FIG. 1 is a front perspective view of a section of the two-layer padded surface 1 for tennis courts comprising a top wear layer 2 applied over a soft poured-in-place polyurethane elastomer padding layer 4 according to the present invention.
The present invention is a two-layer padded surface for tennis courts comprising a urethane-based top wear layer applied over a soft poured-in-place polyurethane elastomer padding layer, the two-layer padded surface being applied over a concrete or asphalt surface foundation.
FIG. 1 is a front perspective view of a section of the two-layer padded surface 1 for tennis courts comprising a top wear layer 2 applied over a soft poured-in-place polyurethane elastomer base or cushion layer 4 according to the present invention.
The Base (Cushion) Layer 4 comprises a specially formulated two-component polyurethane elastomer, mixed with finely ground SBR rubber (from recycled tires). The Base (Cushion) Layer 4 preferably formulated as a solid polyurethane elastomer that is relatively soft (50-60 shore A).
The relative mix of polyurethane elastomer and SBR rubber is as follows:
|Component||Amt (Wt %)||Range (Wt %)|
|SBR rubber (recycled tires):||17.0%||0%-35%|
The polyurethane elastomer comprises a specially formulated two-component self-leveling polyurethane intermixed with the finely ground SBR rubber granules.
An example of the two-component polyurethane elastomer used for the Base Layer 4 follows:
|Amt (Wt. %)||(Wt %)|
|(Part A) Components|
|Polypropylene glycol (polyether) 2000 MW:||40.8%||20-60%|
|Iron oxide pigments:||3.6%||1-6%|
|(Part B) Components|
|Polypropylene glycol (polyether) 2000 MW:||35.0%||25-45%|
|Methylene Diphenyl Diisocyanate:||65.0%||50-80%|
Above two-component polyurethane is mixed at an NCO index of 1.15. The optimum-range has been found to be (1.00-1.25). Thus, for example, Part A may be mixed with Part B at an 8(A) to 1(B) volume ratio, which gives and NCO/OH index of 1.20. The finely ground SBR rubber is added to the two-component polyurethane and intermixed with a commercial mixing.
The overall shock absorption of the polyurethane elastomer can be adjusted by changing the thickness of the Base (Cushion) Layer 4. This allows the manufacturer to offer a series of shock absorbency to customers.
The top layer is comprised of a specially formulated water-based urethane coating intermixed with sand. The coating may also utilize an acrylic based or urethane-acrylic hybrid based dispersion. The sand must be comprised of high-grade uniform cylindrical sand although the mesh size used will be dependent on the texture desired. Below is a suitable mix ratio for the wear layer 2.
|Waterbased urethane or acrylic coating:||1 gallon||½-2||gal|
The following is a suitable example of a Waterbased urethane coating for the top wear layer 2:
|(Part A) Components||Amt (Wt. %)||(Wt %)|
|Bayhydrol 110 (from Bayer Corporation)||91.2%||60-98%|
|Iron Oxide Pigment||7.0%||2-12%|
Note that Bayhydrol 110 is a waterbased urethane dispersion. Other commercially available products can be used in its place. Bayhyrdrol 110 is based on an aliphatic polycarbonate dispersion. Acrylic dispersions are also suitable for this application.
Method of Application
The polyurethane elastomer and SBR rubber for the base layer 4 mixed on site and applied with trowels to ensure that proper thickness of 4-6 mm is achieved. The material is self-leveling in nature and allows for ease of installation.
Depending on the substrate a primer may be required prior to application of base layer 4 to the asphalt or concrete substrate.
The finely ground SBR rubber is added to the two-component polyurethane and intermixed with a commercial mixing machine pursuant to the above-referenced weight ratios.
Next, the wear layer 2 is similarly mixed, and this mixture is squeegee, raked, or spray applied to the cushion base layer 4.
Once the tennis surface 1 is fully set the result will be will be a seamless court surface with no chances of separation of seams which may be found in other conventional products. The use of a polyurethane poured-in-place cushion layer 4 provides an optimum balance of physical properties needed for the performance of the surface, despite a wide range of temperatures, and the thickness can be varied as desired to comply with ITF shock absorption rates of 13-20% and to suit customer preferences. Moreover, the surface characteristics can be varied by the mesh of sand in the wear layer 2 to make sure they are in line with the ITF recommendations.
For present purposes the above-described Base (Cushion) Layer 4 provides an acceptable range of softness, despite being a solid elastomer, since it is formulated on the softer side (50-60 shore A). If greater softness, or a greater range of softness is desired, it is also possible to use a poured-in-place micro-cellular polyurethane foam layer as the Base (Cushion) Layer 4. One skilled in should understand that additional layers such a poured-in-place micro cellular foam layer as the Base (Cushion) Layer 4 are within the scope and spirit of the present invention.
Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications thereto may obviously occur to those skilled in the art upon becoming familiar with the underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth herein.