Synthetic grass with resilient granular top surface layer

Details Synthetic grass with resilient granular top surface layer Synthetic grass with resilient granular top surface layer

2000-06-21

2003-04-22

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S147000, C428S150000, C428S149000, C428S017000, C428S087000, C428S092000, C428S402000

Reexamination Certificate

active

06551689

ABSTRACT:

TECHNICAL FIELD
The invention is directed to a synthetic grass with grass-like ribbons forming a lattice enmeshing a particulate infill having a bottom layer of equally sized sand and rubber granules, and a top layer of rubber granules only.
BACKGROUND OF THE ART
Maintenance of natural grass turf on athletic playing or landscaped areas is expensive, natural grass does not grow well within shaded enclosed stadiums and continuous heavy traffic wears out areas in the natural turf surface. Natural turf surfaces deteriorate under heavy use and exposed soil creates an undesirable accumulation of water and mud. Synthetic grasses therefore have been developed in order to reduce the expenses of maintaining heavily used athletic playing areas, to render playing surfaces more uniform, and increase the durability of the grass surface, especially where professional sports are involved.
Synthetic grass 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.
Of particular interest to the present invention are the various formulations for granular resilient fill that are placed between the upstanding ribbons on the upper surface of the backing to simulate the presence of soil. Most prior art systems involve some use of hard particles such as sand or crushed slag particles, together with resilient particles such as crumb rubber particles or foam backing to provide resilience. The optimal choice of particle sizes, particle shape, particle composition and installation in multiple layers or courses is a feature of the present invention.
U.S. Pat. No. 4,337,283 to Haas, Jr. discloses a homogeneous infill mixture to imitate soil that is made of fine hard sand particles mixed with 25% to 95% by volume resilient particles to provide an improved resilient and less abrasive infill. Such resilient granular material may include mixtures of granulated rubber particles, cork polymer beads, foam rubber particles, vermiculite, and the like.
U.S. Pat. No. 4,396,653 to Tomarin discloses a non-homogeneous infill with rubber particles forming a base layer and sand particles forming a top layer. The rubber particles provide inner resiliency to the surface. The sand layer is exposed and forms a stabilizing cover layer for the underlying rubber particle layer.
A number of disadvantages result from the use of a uniformly mixed granular infill as in the Haas system where hard sand particles and resilient rubber particles are mixed and blended in a uniform proportion throughout the depth of the infill. Synthetic grass infill, for example, may comprise a mixture of 60% by weight of sand and 40% granulated 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 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. 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 rubber and silica sand.
However, in both the Haas and Tomarin systems, abrasive hard sand particles present in the top surface layer of infill causes problems where such as games of football, rugby, soccer, field hockey, baseball are played since players repeatedly fall down or are knocked down on the playing surface. In such applications, there is a need to protect players from skin abrasion caused by the hard sand in the granular infill and from sand spraying into the players eyes, ears and mouth.
The conventional infill is a mixture of sand and rubber particles. The rubber particles are compressed and released when a ball hits the surface or an athlete steps on the surface. In the case of conventional soil, the soil and humus particles provide some natural resilience but the rebound is more gradual due to moisture, small particle size and relatively low natural resilience. In the case of synthetic infills, the particles are relatively dry and do not bond together. The rubber particles have a spring-like rapid resilient rebound that tends to hurl adjacent sand particles and rubber upwardly under force.
The synthetic infill is continuously subjected to water flow and impact forces that tend to dislodge or segregate the particles, such as from rainfall, flooding, the impact of bouncing balls, vibration and impact from the feet and bodies of players in contact with the top surface of the infill. A top layer with a high proportion of sand will result in spraying of sand particles when a ball or player impacts with the top surface of the infill. When soccer balls roll on the infill surface, if any sand particles are present at the top surface, sand particles are lifted by the rolling ball by the suction force of air flowing around the spinning ball and by static electric attraction. As a result the smaller sand particles on the top surface of the infill are lifted and sprayed in a “rooster tail” pattern behind the rolling ball. Over time, areas of continuous sand spray or ball impact will result in visible sand on the playing surface. It is considered undesirable to have light colored sand visible in the synthetic grass surface and, especially when clouds of sand are visible on such impacts. In addition, exposed sand granules are highly abrasive to the skin when players fall or slide on the top surface, and could irritate eyes, ears, nose and mouth when sprayed, inhaled or ingested.
A further disadvantage of conventional infills is that abrasive sand particles remain on the top surface of the synthetic grass and players on the surface who come in contact with the sand particles experience skin abrasion. Over time, due to the dynamics of water, vibration and impact, the smaller sand particles will tend to settle toward the bottom of the infill layer and larger more abrasive sand particles will rise to the top surface. The small sand particles tumble downward in the voids between larger particles under the influence of vibration, water and gravity. Smaller particles accumulate at the lower portion of a granular infill layer and tend to compact together. The larger sand particles remain at the top of the granular layer and large particles are highly abrasive to human skin relative to the smaller particles.
As a result, over time the abrasive nature of the synthetic system is increased and may result in particular areas of the playing surface which experience heavy traffic being more abrasive than other areas. Conventionally used hard particles and resilient particles have angular surfaces. It has been found however that angular particles tend to compact together more than spherical or rounded particles since the friction between sharp angular surfaces is greater. In addition, where a wide range of particle sizes is used, the smaller particles fill in the interstices between the larger particles and increase the degree of compaction.
When shredded rubber, or conventional ground rubber are used the rubber particles have irregular surfaces often with fibrous protrusions that trap air and hold water with surface tension. When the infill is rained on or flooded, the air trapped by the lightweight rubber particles causes the rubber particles to float. This is undesirable since the rubber may wash down a drain with the surface water flow, and the floating rubber separates from the heavier sand in the infill mixture thereby leading to particle segregation, sand compaction and loss of the resilience of the infill.
Where sand is used for construction purposes such as road building or in concrete mixes, it is highly desirable to have a wide range of particle sizes spec

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