Patent Application
20060269757
This invention relates, generally, to multi-layered systems for protection for humans and even animals from injury from falling on hard, unforgiving surfaces, and more particularly, to systems which have a special purpose of protection for children falling out of playground equipment onto compacted dirt, cement or the like, and, even grass, which would otherwise cause serious, even fatal injuries to such children; and also relates to methods for manufacturing and installing such systems on the surface below where such playground equipment will be used.
The following description delineates the vastly improved aspects of the present invention, when compared to the prior art:
The present invention is a wheel chair accessible, seamless, unitary, poured in place rubber safety surface for playgrounds that has the structural integrity to be formed, poured, and troweled directly on the ground (over dirt, clay, sand, gravel, etc.). The hard, shock reducing, and expensive sub-bases that are required for other poured in place playground surfaces are completely unnecessary for the present invention.
Predominate Elements at Issue:
Much Stronger and More Durable: By optimizing the size and shape of the rubber pieces used in the shock absorbent underlayment I have been able to dramatically increase the polymer binder content without compromising shock absorbency. By changing the shape of the rubber pieces in the wear layer and by applying a liquid polymer which fills the wear layer's pores and voids with a strong UV stable rubber compound, I have increased the elongation and flexibility of the wear layer making it much less likely to crack or crumble. The UV stable liquid rubber polymer also protects the underlying binder from UV ray degradation.
More Shock Absorbent and Less Expensive: By eliminating the need for a hard sub-base, cost is dramatically reduced while shock absorbency is dramatically increased (making child safety more affordable). And because the present invention is so strong, it can be installed over inexpensive rubber gravel making it far more shock absorbent than any other unitary playground surface. The present invention dramatically exceeds the Federal fall height shock absorbency standards established by the U.S. Consumer Product Safety Commission. Compliance is documented by the ASTM Test F-1292.
Easier to Install and Repair: By changing the size and shape of the rubber pieces in the wear layer I have made it possible to feather the material which virtually eliminates weak seams. A low viscosity binder penetrates through the pores of the two overlapping feathered layers which permanently binds them into one. Eliminating the weak seam problem makes for easy and strong repairs. It also allows the laborers to patiently focus on workmanship, instead of working rapidly to avoid seams.
No Precise Mixing Ratio's: With the prior art products, the margin for error is extremely small. If too much poly is used, the prior art product will be too hard to provide children protection from serious head injury. If too little poly is used the product will fail very quickly. This compromise between strength and shock absorbency has resulted in many law suits. But with the present invention this liability has been almost eliminated. Both strength and shock absorbency can be maintained with a wide margin for error.
Referring now to the drawings in more detail, FIG's 1A-1F illustrate a multi-layer system according to the invention, having a shock-absorbing layer 12, a wear-layer 14 and a coating 16, illustrated as over-laying three types of typical base layers 10S (soft base, such as dirt or grass), 10L (loose-fill base, such as mulch, pea gravel, sand and rubber gravel) and 10H (hard base, such as concrete, asphalt and compacted rock).
The shock-absorbing layer 12 is applied first over whichever base is present, whether soft, loose-fill, hard, or combinations there. The layer 12 comprises a rubbery aggregate used with a binder, wherein the binder is 13-19% of the total weight of said shock-absorbing layer and the remainder of said shock-absorbing layer is the first rubbery aggregate. The aggregate preferably comprises elongated pieces of rubber that pass through a conventional vibrating sieve system of screens. The elongated pieces of rubber are preferably 3-10 times longer than their width. The screens are sized to accommodate their width. The pieces used in the aggregate pass through an ASTM 0.265 screen but are retained by an ASTM #8 screen. An ASTM 0.265 screen is a 3-mesh screen (9 holes per square inch). An ASTM #8 screen is an 8-mesh screen (64 holes per square inch).
After the elongated rubbery polymeric pieces have been selected for size by the vibrating sieve system, the aggregate is then mixed with a liquid, low viscosity polyurethane binder, preferably comprising either pure Methyl Diphenyl Isocyanate, or polymeric Methyl Diphenyl Isocyanate, or combinations thereof.
The preferred elongated rubber pieces for the aggregate are longer than the width of the screen holes in the sieves through which they must pass to be accepted for the various layers in the system. Such rubber pieces generally pass through the screen only because of the vibration of the screens. Thus, the number passing through the screen is a function of the duration of the vibration process. However, the elongation of the pieces is a valuable feature of the invention with respect to the shock absorbency of the layers.
Although such elongated rubber pieces could come from various sources, one such source is the so-called “buffing” pieces used in removing rubber, typically Styrene Butadiene rubber, from truck tires prior to their being recapped.
After the binder and the aggregate have been mixed, the resulting mixture is laid down in place over the base to form the shock-absorbing layer 12, illustrated in
After the layer 12 has been cured, a wear-layer 14 is applied over the top of the layer 12. The wear-layer 14 also comprises a rubbery aggregate mixed with a low viscosity liquid polyurethane binder, preferably the low viscosity binder used in layer 12, but the pieces of elongated rubber used in the wear-layer 14 are sized smaller than those used in layer 12. The layer 14 comprises a rubbery aggregate used with a binder, wherein the binder is 19-23% of the total weight of the wear-layer 14, and the remainder of said wear layer is the rubbery aggregate. For example, the elongated rubber pieces in layer 14 are pieces that pass through an ASTM #8 screen but are retained by an ASTM #16 screen. An ASTM #8 screen is a 8 mesh screen (64 holes per sq/in). An ASTM #16 screen is a 14 mesh (196 holes per sq/in).
Although different sizes of rubber particles can be used in practicing the invention, it is an important feature of the invention that the length and width of the rubber pieces used in the shock-absorber layer 12 are sized larger than the length and width of the rubber pieces used in the wear-layer 14, to thereby improve the overall performance of the system in passing various fall tests, oftentimes required for use under children's playground equipment, such as, for example, the ASTM-F 1292-04 and F-355-01 tests.
As an additional feature, the multi-layer system illustrated in
After the wear-layer 14 has been laid over the top of the shock-absorber layer 12, and has been allowed to cure by ambient air-drying, typically for 12-36 hours, a coating 16, preferably an acrylic polymer, is applied over the top of the porous wear layer 14, and is allowed to percolate into the layer 14, thus filling some of the voids in the wear-layer 14. Because the acrylic coating 16 is water-based, heated air can be used to cure the coating. As an alternative, the coating 16 can also be polyurethane.
Although the system according to the invention can be used with various dimensions, a typical such system will be made to result in a total thickness of 4 inches (layers 12 and 14 and coating 16 together being 2 inches), installed over a 2-inch thickness of rubber gravel. The preferred makeup of the layers 12 and 14 typically being 1.5 inches thick (layer 12) and 0.5 inch thick (layer 14).
The acrylic polymer coating 16 reflects the UV rays from the sun, thus keeping the surface temperature of the system to a minimum (protecting bare feet of children) and also protects the polyurethane binder from UV degradation.
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It is fairly common for jobs to be interrupted due to the weather, darkness, equipment failure, shortage of materials, etc. In any of such events, workers oftentimes have had to leave the job and return 6-8 hours later. When the job is resumed, weak seams and the inevitable repair of such weak seams are often the results. This problem has been resolved because, by using the properly sized and shaped rubber pieces according to the invention, coupled with a low viscosity binder in the wear-layer, the workers can return to the unfinished job, and by feathering the otherwise present weak seams, the low viscosity binder penetrates through the pores of the two overlapping feathered layers which permanently binds them into a single layer, no weak seam. This eliminates the weak seam problem, making for easy and strong repairs, and also allows the workers to patiently focus on workmanship instead of hurriedly working to avoid seams.
