HK1058383B - Synthetic grass assembly with resilient granular top surface layer - Google Patents

Description

Artificial turf assembly with resilient granular top surface layer

Technical Field

The invention relates to an artificial turf (synthetic grass) having grass-like strips of granular infill forming an infill (enmesh) grid with a bottom layer of equal-sized sand and rubber granules and a top layer of only rubber granules.

Background

Maintenance of natural turf on sports events or scenic spots is expensive, natural turf does not grow well in dark enclosed sports stadiums, and continuously busy traffic can wear out areas in the natural turf surface. The natural turf surface deteriorates with frequent use and the exposed soil causes unwanted accumulation of water and mud. Artificial turf has therefore been developed to reduce the cost of maintaining a frequently used sports playing field, thereby making the playing surface more uniform and improving the durability of the turf surface, particularly those involving professional competition.

Artificial turf is fitted with a carpet-like pile fabric having a flexible backing laid over a well-drained compacted base such as crushed stone or other stable base material. The pile fabric has a plurality of rows of upstanding synthetic ribbons representing grass blades extending upwardly from the top surface of the substrate.

Of particular interest to the present invention are the various components for the granular infill which are disposed between upstanding strips on the upper surface of the substrate to simulate the presence of soil. Most prior art systems involve some hard particles such as sand or crushed slag particles used with resilient particles such as crushed rubber particles or foam backing to provide resiliency. The particle size, particle shape, particle composition and optimal choice of mounting in multiple layers or rows are features of the invention.

US4337283 to Haas, jr discloses a homogeneous filler mixture for simulating soil made from fine hard sand particles mixed with 25 to 95% by volume of resilient particles, thereby providing a filler with improved resilience and less friction. Such resilient particulate material may include a mixture of particulate rubber particles, cork polymer crumb, foamed rubber particles, vermiculite, and the like.

US4396653 to Tomarin discloses a heterogeneous infill with rubber particles forming a base layer and sand particles forming a top layer. The rubber particles provide the surface with inherent elasticity. The sand surface is exposed and forms a stable cover layer for the underlying layer of rubber particles.

There are a number of disadvantages to using a uniformly mixed granular infill, as in the Haas system where the hard sand particles and the elastomeric rubber particles are mixed and intermingled together in a uniform ratio throughout the depth of the infill. For example, the artificial turf infill may comprise a mixture of 60% sand and 40% granulated rubber particles by weight, mixed uniformly and laid between the erected artificial turf strips to a depth of 2.54 mm to 76.2 mm (1 to 3 inches).

A high percentage of sand is preferred to reduce the cost of such a system because rubber particles are relatively expensive compared to sand. These sand particles also improve the degree of drainage, which is necessary, for example, in closed stadiums where there is no artificial turf surface. Rubber particles tend to impede the free flow of water, while the capillary action of sand draws surface moisture down through the difference in surface tension properties between rubber and silica sand.

However, in the Haas and Tomarin systems, the abrasive hard sand particles in the top layer of the infill can cause problems in the field where soccer, rugby, soccer, hockey, softball games are played because players often fall or hit the playing surface. In these applications, it is necessary to prevent the athlete from being subjected to skin abrasion caused by the hard sand in the granular infill and to prevent the sand from splashing into the athlete's eyes, ears, and mouth.

A conventional filler is a mixture of sand and rubber particles. The rubber particles are compressed and relaxed when the ball strikes the surface or the player walks over the surface. In traditional soils, soil and humus particles provide some natural elasticity, but the bounce is more gradual due to the small moisture, particle size and relatively low natural elasticity. In the case of synthetic fillers, these particles are relatively dry and do not stick together. The rubber particles have a spring-like rapid elastic rebound which tends to throw the adjacent sand particles and rubber upward under force.

The synthetic wad is continuously subjected to water currents and impact forces, such as impacts from rain, water flooding, bouncing balls, and shocks and impacts from the contact of the athlete's feet and body with the top surface of the wad, which tend to dislodge or separate the particles. A top layer with a high proportion of sand may cause sand particles to splash when a ball or player strikes the infill surface. When the soccer ball rolls on the filler surface, sand particles, if present at the top surface, are lifted by the suction of the air flow around the spinning ball and by the electrostatic attraction. Thus, smaller sand particles are lifted on the top surface of the infill and sprayed in a "crow's foot" pattern behind the rolling ball. Over time, the area of continuous sand blast or ball impact will result in visible sand appearing on the playing surface. It is considered objectionable to see light colored sand in the artificial turf surface and especially when clouds of sand are visible on these impacts. In addition, exposed sand particles can cause significant abrasion to the skin when athletes fall or slip on the top surface and can irritate the eyes, ears, and mouth when exhaling, inhaling, or swallowing.

Another disadvantage of conventional infill is that abrasive sand particles remain on the top surface of the artificial turf, so that athletes in contact with the sand particles on this surface can suffer skin abrasion. Over time, smaller sand particles will tend to settle toward the bottom of the packed bed due to the dynamic nature of water, vibration, and shock, and will tend to rise to the top surface more easily the larger the friction sand particles. The small sand particles tumble downward under the action of vibration, water and gravity in the interstices between the larger particles. Smaller particles accumulate at the lower portion of the granular infill layer and tend to pack together. Larger sand particles remain at the top of the granular layer and these larger sand particles cause more severe abrasion to the human skin than smaller particles.

Thus, over time, the frictional characteristics of the artificial system increase and may result in certain areas of the playing surface being more abrasive than others. Commonly used hard particles and elastomer particles have angular surfaces. It has been found that angular particles are more easily packed together than spherical or round particles due to the greater friction between the sharp angular surfaces. In addition, where a wide range of particle sizes are used, smaller particles will fill in the interstices between the larger particles and increase solidity.

When using shredded rubber or ordinary floor rubber, these rubber particles have a regular surface and usually have fibrous protrusions that collect air and hold water by surface tension. When rain falls or water is injected onto the filler, the air collected by the light rubber particles causes these rubber particles to float. This is undesirable because the rubber can flow with the surface water flow to the gutters and the floating rubber separates from the heavy sand in the pack mixture, resulting in particle separation, sand compaction and loss of pack elasticity.

In the use of sand for construction purposes such as road construction or for concrete mixes, it is desirable to have a wide range of particle sizes, since the mixing of large and small particles will result in the small particles filling the gaps between the large particles, thereby increasing the contact between the particles, increasing the degree of compaction and thus the load capacity. In the case of sand or granular aggregates used in construction applications, a vibratory compactor is employed and the water content is controlled to achieve maximum soil compaction and density.

However, when sand is used as a component of the resilient infill between the voids of the artificial turf, excessive compaction is highly undesirable. Since there is a significant difference in the artificial turf surface from frequently used areas to less frequently used areas, the high compaction of the sand and the contamination of the infill by dirt and dust in the air can lead to unwanted changes in the resilience of the infill over time due to use. Uniform and consistent elasticity, maintenance free, and predictable filler performance are goals other than high load bearing strength.

The traditional solution to compaction and separation of filler particles is to periodically brush the artificial turf. Brushing can break up the compacted material and remix the top surface to recover as much of the original composition of the filler mixture as possible. Brushing adds to maintenance costs, subjects the hand-made strip to significant wear and is at best a temporary solution, since eventually traditional fillings will re-compact and must be brushed periodically.

The correct choice of spacing between the rows of sod strips has proven to be a difficult problem. A major complaint of typical professional athletes is that spikes on shoes do not consistently disengage from dense, tangled, tightly woven or knitted synthetic sports turf surfaces, causing knee and ankle injuries. Previous artificial turf surfaces were constructed more like carpeted indoor surfaces, having very closely spaced upstanding fibers extending from a woven substrate having an elastomeric backing. These fiber surfaces are designed to remain upright and avoid entanglement when trampled by a person. Thus to achieve this result, the fibers are very closely spaced. However, spikes on athletic shoes do not properly disengage, particularly when the foot is rotated on the surface, resulting in knee and ankle injuries.

On the other hand, in the case of using pure sand as a surface, for example in a horseback surface, the surface is relatively unstable and the sand particles are easily displaced. To stabilize these surfaces, US patent 4819933 to armond (fibresand limited) provides a sand mixture with relatively small weight percentages of straight man-made fibres randomly distributed and cross-linked in a loose alternative network. These fibers serve to distribute the concentrated load holding the sand together under the weight of the hooves, athletes' feet, wheeled vehicles or facilities. US5326192 of free Industries, Inc also provides a method of improving the appearance and performance characteristics of a turf surface by implanting discrete artificial fibre bundles into the soil surface.

Granular infill combined with artificial strips like standing grass solves to some extent the disadvantages of the above system by providing a granular artificial surface intermingled with standing fibres extending from the fabric substrate to simulate natural soil, embedded roots and grass. When the spikes of a player's shoe are embedded in the granular filling, the loose particles move and displace somewhat like soil. At the same time, the standing artificial grass strips become entangled with loose particles and spikes to reduce or prevent slippage. Without the artificial straps, loose particles would be very difficult to flow much like the natural beach surface of dry sand, and a dense mat of fibers would catch these spikes to prevent disengagement, potentially causing injury to the individual.

Thus, the combined structure of the upstanding strips and the loose particulate filler must be balanced or optimized to provide the desired playing surface. When these strips are packed close together, the studs do not disengage correctly, but when the strips are too far apart, sufficient adhesion and stability are not obtained. Due to the high cost of artificial turf placement and the risk of injury that can occur to highly skilled and expensive players, a predictable and reproducible artificial turf performance is desired.

Artificial turf surfaces have also been constructed with infill made of essentially only rubber. The rubber particles are relatively light and the shredded particles have a fibrous surface that collects air bubbles. Thus, when water is injected, some of the commonly laid rubber particles have floated on the water surface and thus have drained away from the artificial turf surface. The rubber particles are dislodged or displaced, resulting in areas of the artificial turf that have greatly diminished infill thickness. The lack of uniform filler thickness and elasticity over the entire surface can lead to injuries and liability for the player of the sports field.

Despite the several different rubber and sand pack compositions and fiber structures in the prior art, there are still several significant disadvantages described above.

Disclosure of Invention

It is an object of the present invention to provide a filling which will retain its properties throughout use and which will not exhibit significant separation or compaction of the filling and which reduces the need for periodic brushing of the surface.

Another object of the invention is to improve the elasticity and reduce the friction characteristics of the common granular infill that fills the gaps of the artificial grass strip and to enable the spikes of the player's shoes to disengage correctly without the risk of serious injury.

It is another object of the present invention to eliminate the splashing of sand particles and unwanted and visible sand on the fill surface.

The present invention provides a novel artificial turf assembly for laying on a supporting soil substrate to provide a surface that combines the look and feel of natural turf with the abrasion resistance of artificial turf. Although this description uses a sports arena as an example, the invention is equally applicable to any area suitable for turf coverage, such as scenic spots with heavy traffic, the middle of roads and highways, indoor gardens or golf greens and horse-riding surfaces.

The grass assembly includes a pile fabric having a flexible sheet backing (backing) and an array of upstanding synthetic ribbons representing grass blades extending upwardly from an upper surface of the backing. The distinct filler layer of the two graded layers of particulate material is disposed in the gap between the upstanding strips above the upper surface of the substrate and at a depth less than the length of the strips.

The strips are tufted through a water-permeable fabric backing and have intermittent longitudinal slits in a predetermined pattern. During the laying of the filling, the strips are lightly brushed to restore them from the initial tangled attitude to the upright attitude, which is caused by the compression of the strips as the tufted fabric tumbles after manufacture during transport and storage. These strips may be about 25.4 millimeters (1 inch) wide and have several rows of slits across their width. The light brushing easily opens the lower part of the strip, extending the slit openings forming the transverse connecting bundles arranged in a lattice structure which traps the surrounding particle filling therein. Once all the filler is installed, the upper portion of the strip extending above the filler layer is actively brushed. The strips are separated longitudinally along the slit by a brushing action into several individual free-standing, narrower width, grass-like bundles.

The present invention recognizes that granular infill is a dynamic system of continuously moving hard and elastic particles of varying sizes and having different physical characteristics under the influence of shock and vibration from athletic activities, surface maintenance and rainy weather. The present invention accommodates this dynamic activity in a number of ways.

The top surface is kept substantially free of sand by using a top layer of pure rubber particles with relatively large particles, preferably larger than those in the bottom layer. Any smaller sand particles that migrate up to the top surface under the action of the movement of the studs will be able to seep back down to the bottom layer through the pores between the larger top surface particles under the action of water, vibration and gravity. A bottom layer of sand and rubber mixed together is provided under the top layer of pure rubber to have additional elasticity, drainage and as a ballast for stabilizing the fabric substrate.

The particles are substantially spherical in shape, thereby reducing interparticle contact friction, improving drainage and preventing densification. The spherical shape reduces the resistance to particle displacement and therefore reduces the degree of compaction compared to normal angular particles. In terms of the Krumbein sphere principle, it is well known to those skilled in the art that the particle shape is in the range of 0.5 to 0.99 in a broad sense and preferably in the range of 0.6 and 0.9, so as to be perfectly round or substantially spherical.

The particle size distribution of the hard sand and the elastomeric rubber particles in the bottom layer are selected to be substantially equal to each other and the particle size is preferably limited to a range of 14 to 30 mesh size standards for racing or athletic activity surfaces. To suit other uses of the surface of the artificial turf, the particle size may range from 12.7 millimeters (0.5 inches) to 50 mesh size standards. Larger particles up to about 0.05715 meters (0.25 inches) can be used for riding purposes, but these large particles are too abrasive for contact with human skin. Particles smaller than the 50 mesh standard tend to dust and can result in unwanted compaction, reducing water permeability and particle separation. Naturally occurring soil particles of this size range are divided into medium sand, coarse sand and fine gravel size particles.

By "substantially the same" size distribution is meant that when the underfill layer is analyzed by ordinary soil laboratory screening analysis and is illustrated on a standard sieve analysis semi-logarithmic graph (the y-axis shows 0-100 percent by sieve size or weight smaller, while the x-axis shows sieve size/particle size logarithmically), the straight line for the hard particles and the straight line for the elastic particles ideally overlap each other to a considerable extent. The hard and elastic particles thus have substantially equal particle sizes and the distribution of sizes is substantially the same.

The standard sieve analysis chart itself is an inaccurate "rough and ready" method because natural soils vary greatly, for example, from building site to building site. The sieve analysis plot typically does not show a maximum of 10% and a minimum of 10% of the particle size, since these limits are considered statistically insignificant due to natural variations in soil particle size. Thus, in general, only the middle 80% of the particles are considered when examining the soil particle size in the sieve analysis.

This practice is applied to the present invention and is defined numerically or scientifically in that the particle size distribution of 80% by weight of the hard and elastic particles in the bottom layer is within a range of numerical differences across the 40 mesh standard, which particle size distribution is considered to be substantially the same or very well classified. Since sand and rubber can be divided into any desired specific specifications, it is preferred that the numerical difference can be even smaller, for example, by a 20 mesh standard to form a more uniform pack. For example, perfectly spherical manufactured glass beads have a numerical difference close to zero. However, since sand is a naturally occurring material produced by rock washing, the particle size distribution and sphericity varies greatly. A numerical difference of the 20 mesh standard would result in a particle size distribution of between 10 and 30 for a riding (equestrian) surface or between 20 and 40 for a sports playing surface.

In fact, the cheapest hard particles are typically sand, which is found to be a naturally isolated sediment and/or has been mechanically graded to suit various common construction uses, such as in concrete blenders and road bed construction. The requirements for sand for artificial turf equipment are relatively low and therefore the cost of such materials is somewhat increased if a solution requires a specially separated or graded sand particle size distribution.

When deciding the specific material to be used anywhere, it is preferred to use any acceptable sand that is readily available near the laying site. This is a relatively simple matter when purchasing resilient particles to determine that the particle size distribution is within the ranges discussed above and overlaps in the measured sand particle size distribution. Regardless of where the paving site is located, the elastomer particles must be processed, ground and transported from the manufacturing facility. The marginal cost of manufacturing elastic particles having a particle size distribution matching the particle size distribution of sand particles is relatively low compared to grading the size distribution of sand particles to match elastic particles.

By making the resilient particles match the size distribution of sand readily available at the laying site, a formation having a pack of mixed sand and rubber particles of equal size distribution will result in the benefit of significantly reducing settling and separation of the mixture of particles in use.

In contrast, conventional elastomeric particle mixtures typically have significantly larger particles than available graded sand. As a result, lighter, larger elastic particles migrate upward while heavier, smaller hard sand particles migrate downward under the combined action of gravity, shock, rain, and downward-leaking water. The separation of particles of different sizes results in a loss of optimum compactness and in uneven adhesion in the conventionally mixed filler layer.

The inventors have found that the separation of hard and elastic particles in a mixed bottom layer can be prevented or substantially reduced by: (1) selecting hard and elastic particles having equal or substantially equal size distributions; (2) a relatively narrow range of particle sizes is selected and (3) a generally spherical particle shape is selected for the hard and elastic particles. The minimal change in particle size inhibits compaction because none of the relatively smaller particles fill the pores between the larger particles when all of the particles are of substantially equal size. The spherical shape reduces the resistance to particle-to-particle displacement and reduces the tendency of adjacent particles to lock together. The fibrous grass-like artificial strips at the top surface tend to hold the relatively large top rubber particles in a loose net-like flexible structure. The loose cruciform network of filamentary fibers also allows the migrating rubber particles to return to the underlying top rubber layer as one walks over these particles and the hand strap. The combination of the net top rubber layer and the network of filamentary strips gives the natural turf surface the look and feel.

The artificial strips between the fabric substrate and the top layer provide a degree of resistance to particle displacement in the hybrid bottom layer by forming an open mesh or grid structure of vertically oriented bundles that are cross-linked together in the cross-machine direction. The mixed sand and rubber bottom layer provides a firm resilient support for the relatively thin rubber top layer. The sand content of the mixing layer provides, inter alia, the necessary ballast weight and, due to the capillary action of the sand, a better drainage.

The relatively thin top layer, which is in direct contact with the body of the athlete, has a high elasticity where body contact occurs and results in less friction against the skin due to the use of only rubber. The sand content in the mixed bottom layer provides a ballast weight to keep the turf immobile and quickly drain the surface. Drainage is particularly necessary where there is a risk of icing and in cold climates it is desirable to select a coarser mixture to improve drainage. In addition to the top surface elasticity provided by the top layer, the elastic particles in the hybrid layer also provide subsurface elasticity.

Selecting hard and elastomeric particles having substantially equal size distributions substantially reduces compaction and reduces maintenance requirements. Due to the choice of particle size, the top pure rubber top layer always remains substantially free of sand. Due to the agitation caused by contact with the player's spikes during the game, sand may move from the mixed bottom layer to the top layer surface or interfere with the actual game by this action in the same way as ordinary soil. However, the size of the sand particles is chosen to be smaller than the size of the resilient particles in the top layer. Displaced sand particles are washed down by rain water draining past the top resilient surface or smaller sand particles are returned to the bottom layer they originally were in due to the shaking and stirring of the walk.

This double layer laying method with only rubber in the top layer and mixed sand and rubber in the lower layer forms the resilient surface at lower cost and with lower thickness than the conventional methods described in, for example, US4337283 to Haas and US4396653 to Tomarin. Prior art infill layers with larger and smaller particles are easily compacted or consolidated into a more robust compacted surface. Since the top layer is pure rubber particles and the mixed lower layer is not easily separated or compacted, the present invention maintains its elasticity even when used in a thin layer. Thus creating a more predictable long term resiliency.

Artificial strips can be made and tufted on a textile substrate. Preferably, the strips are slit with relatively short longitudinal slits spaced across the width of the strips. The upper part of the artificial strip is then fibrillated, detached or abraded in situ by brushing the laid surface with a brush after the filling has been laid. The strips are manufactured with a longitudinally oriented structure so that a positive brushing action on the top surface tends to tear or break the strips into thinner grass-like strands by extending the slits longitudinally to form densely packed individual grass-like strands.

In the case of brushing the strips and splitting them in situ, the upper part of the strips wears or splits into thin grass-like strands, while the lower part remains intact and is merely stretched to a greater extent than when the fibre mat is initially formed into a substrate, leading to an expanded mesh, net or grid structure. The immediate benefit of such a grid is to stabilize the particulate infill by inter-bonding (inter-washing) the particles between the fibrillated grass-like strands and within the expanded reticulated fibrous structure. The lower mesh portion stabilizes the filling and the upper grass portion enables the spike to penetrate and loosen, rain penetrate, and drain; the slight surface elasticity is increased by the curved grass-like strands and the large elastic particles of the top layer are trapped in the grass-like network structure.

In situ fibrillation of the fibers also allows for denser top surface coverage of the grass-like strands. The relatively wide strips with short slit perforations when initially laid may be spaced apart a sufficient distance to enable the granular infill to fit between the strips. When the infill has been fully installed, brushing of the widely spaced strips causes them to break into thinner grass-like bundles which fill in the gaps between the strips and better cover the top surface of the granular infill. The dense web of cruciform fibrillated strands contains larger top layer rubber particles while allowing spikes to penetrate and water to drain. The split strips provide better coverage of the visible surface by the grass-like strands at a lower cost. In applications not intended for sports use, such as landscaping or decorative use, a less dense fiber distribution can be employed, resulting in a cost reduction for visual appearance coverage as common closely spaced artificial turf.

Other details of the invention and its advantages will be apparent from the detailed description and drawings.

Drawings

In order to facilitate an understanding of the invention, a preferred embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a natural turf assembly with infill installed showing a flexible sheet substrate with vertical strips and an infill layer composed of a top layer of relatively large resilient rubber particles and a bottom layer of mixed hard sand and resilient rubber particles with the same smaller particle size distribution;

FIG. 2 is a similar cross-sectional view showing the final structure of the grass-like strands slightly bent due to the active surface brushing to further fibrillate the ends of the ribbons;

FIG. 3 is a side view of a manufactured artificial band having a series of short longitudinal slit perforations;

FIG. 4 is a side view of an artificial band twisted at its lower end prior to tufting into a fabric substrate and expanded transversely at its upper end to reveal a net grass blade structure resulting from the transverse expansion and longitudinal extension of the slits;

FIG. 5 is a graph showing a graphical illustration of the particle size distribution resulting from standard sieve analysis of a packed bed; and is

The graph of fig. 6 shows a visual representation of particles graded on the Krumbein sphere scale (sphere scale).

Detailed Description

Referring to fig. 1, the present invention relates to a synthetic turf assembly comprised of a pile fabric having a particulate matter loading layer mounted on a supporting soil substrate to provide a sports playing surface.

The pile fabric comprises a flexible sheet substrate 1 which may comprise two or more layers of open weave fabric, one of which may be a dimensionally stable mesh to prevent stretching during installation and use. Extending upwardly from the upper surface of the substrate 1 are a plurality of upstanding composite strips 2. As shown in fig. 1, the strips 2 are tufted through the substrate 1 in rows spaced apart by a width W and have a length L. The length 'L' of the fibres is selected according to the total depth of the infill (5 plus 6) and the desired resilience of the finished synthetic turf assembly.

Disposed in the gaps between the upstanding strips 2 on the upper surface of the substrate 1 is a packed layer 3 of particulate material. The particulate material may be selected from any number of commonly available hard particles, for example: sand; hard aggregate; silicon sand; gravel; slag; granular plastic; and polymer particles. The elastomeric particles are selected from: low temperature ground rubber; rubber; cork wood; polymer particles; a synthetic polymer foam; styrene; perlite; polychloroprene rubber; ground tires and EPDM rubber.

The filling layer 3 is made of a top layer 6 and a bottom mixed layer 5. The mixed bottom layer 5 is made of hard sand particles and elastic rubber particles mixed with each other. The mixture is selected according to the volume distribution of the hard and elastomer particles of different sizes, which are substantially the same and are between 12.7 mm (0.5 inch) and 50 mesh size standards. It is preferred to limit the range of particle sizes to avoid smaller or fine particles filling the pores between larger particles and to facilitate compaction. The preferred range is between 14 and 30 mesh size standards. Depending on the application, the particle size range in the blend layer may be selected to be limited between 10 to 30, 15 to 30, or 20 to 40 mesh size standards to meet design parameters. The hard and elastic particles are substantially spherical in shape rather than angular as in the prior art to further impede compaction and settling.

As shown in the graph of fig. 5, a standard mesh (screen size) analysis is described using a vertical axis linear scale of "weight percent through mesh size" or "smaller percentage" and a horizontal axis showing a logarithmic scale of particle and/or mesh size. The exemplary straight line shown in fig. 5 represents a relatively uniform mixture of particles having a narrow range of particle sizes. Ideally, the straight line for the sand particle size distribution and the straight line for the rubber particle size distribution are the same on fig. 5 and appear to overlap each other. However, as an example, the above-mentioned range of 10 to 30 is shown in the figure as a shaded area within which any straight line will meet the requirements of such a particle size limitation.

The top layer 6 is substantially only provided with elastomeric rubber particles. The upper portion 7 of the composite strip 2 extends upwardly from the top surface 8 of the top layer 6. The resulting artificial turf surface can be used for several indoor and outdoor applications, for example: a sports playing field; a horse racing field; a sports field; scenic areas and rest areas.

To provide the double layer, the brush is passed a number of times over the substrate with the mixed sand and rubber material to ensure that the strips are upright when embedded in the infill and not buried in the infill, and further to spread the strips slightly to open the slits and form a grid structure which stabilizes the infill preventing excessive displacement of infill particles after laying. After the mixed underfill layer is applied, a substantially pure rubber particulate material is provided as the elastomeric top layer.

To lay the bottom layer, a spreader may be used and the surface then brushed to raise the nap of the pile fabric and position the strip 2 in a substantially vertical position before laying the top surface 6. After each layer is spread, the surface must be brushed and the strip raised to the upright position as shown in these figures.

Preferably, the upper part 7 of the artificial band 2 is further fibrillated by actively brushing the surface with a brush after the top layer 6 has been laid. This action separates the upper part 7 and distributes the strands evenly over the top surface 8. The strips 2 are manufactured in a relatively wide width of, for example, 1 inch, and the in situ brushing action causes the strips to further split, causing the slits to open longitudinally and form a thin grass-like bundle of narrower width as shown. The upper end of the strip 2 is brushed more vigorously to achieve the following advantages over prior art methods. The fibrillated upper part 7 is laid on top with the ends of the strips connected in a loose network which more realistically simulates the appearance of natural turf. These fibrillated ends have a slight elasticity, as they rise or fuzz slightly and more accurately simulate the elasticity of natural turf when the ball bounces off the finished surface during play. The curved end portions also visually conceal the rubber powder of the top layer 6, keeping these powder particles stationary and allowing the displaced powder to move back and forth between the top layer 6 and the upper side of the fibrillated strip 2. By splitting or fibrillating the ends of the strip 2, less surface tension is created and water more readily penetrates through the top surface 8 and drains through the bottom layer 5.

The strip 2 comprises a top structure of a plurality of grass-like strands fibrillated in situ and an expanded reticular under-structure that remains substantially in their original state but mechanically expands into a reticular grid as a result of interaction with the filler when laid. The tape may be selected from fibers such as polypropylene, polyethylene, nylon, and plastic. The combination of thick and thin widths of the fibrillated strands creates a more natural appearance and enables the ball to roll in a more predictable manner during play, relying on resistance between the fibers and the ball. Improvements in the width and density of the strips in the turf will also change the ball rolling characteristics.

The strips may be 1 to 3 inches wide when initially tufted into a fabric substrate, and the individual grass-like strands may be 1mm to 15mm wide (approximately 1/8 inches to 1/2 inches) when fiberized. Expressed in terms of art, these bundles are in the range of 800 to 5000 denier, and the thickness of the ribbons and bundles is preferably 45 to 200 micrometers (μ) (0.001771 to 0.007874 inches).

It has been found through experimentation and experience that the size and shape of the hard and resilient particles significantly affects the turf performance characteristics. It has also been found that differences in the spacing of the strips and the depth of the infill can have a significant effect on the performance of the artificial turf assembly.

The hard and elastic particle size should be in the range of 12.7 mm (0.5 inch) and 50 U.S. sieve size, but preferably in the narrower range of 14 to 30 to avoid the risk of compaction. Hard particles larger than 14 mesh size may feel somewhat abrasive to users of moving surfaces in direct contact. However, since the fibers above the top surface are easily bent thereon and prevent the user from coming into direct contact with the arched mat of elastic fibers of synthetic fibers, somewhat larger particles can be used without feeling that the particles will cause friction. Particles smaller than 50 mesh size tend to impede water penetration and adversely affect the drainage characteristics of the infill layer 3 in relatively humid climates. In dry climates, it is desirable to use smaller particles to maintain optimum moisture content and thus optimum compaction and elasticity levels. Larger elastic particles (e.g., 14 mesh size) may be used where the skin is in direct contact with the surface and potential friction from the motion itself is desired. Preferably, the sand is washed and screened to remove substantially all fine particles below 50 mesh size.

By using particles of equal size, the natural tendency of larger, relatively lighter rubber particles to migrate to the top and the secondary (complementary) tendency of smaller, heavier sand particles to migrate to the bottom of the infill layer 3 can be reduced. Particle migration is also reduced by interaction with the artificial reticular strip structure and by using spherical particle shapes. The bottom layer of the infill will retain its original mixture of sand and resilient particles of the same size due to the selection of substantially the same particle size and the interference (interference) with the particle movement caused by the network of the strips in contact with the underfill layer. These characteristics of the filling tend to inhibit compaction and maintain a uniform, predictable resiliency of the filling.

By means of the purely rubber-elastic top layer 6, elasticity is provided at the contact surface where an elastic feel is actually required. Preferably, the particle size of the rubber particles in the top layer 6 of the infill is larger than the size of the sand and the resilient particles in the bottom layer 5. The larger particles of the top layer enable the smaller particles of the bottom layer to fall back down through the gaps between the larger particles, and therefore the particle size composition of the layers remains different. The elasticity of the final layer of the filler can be finely adjusted by testing the elasticity at the surface and gradually dispersing the rubber particles to more or less increase the thickness of the top layer 6 and achieve the desired elasticity of the final top layer.

The artificial stripes are preferably arranged in spaced rows of a selected minimum spacing "W". The spacing "W" may thus vary between 57.15 millimeters (2.25 inches) and 15.875 millimeters (0.625 inches), such as 25.4 millimeters (1 inch), or less, depending on the desired firmness and the degree of freedom required for the rotation of the stud for various movements. The tighter spacing provides more firm support for the infill layer 3, while the wider spacing allows the embedded studs to rotate more easily.

The proportion of the depth of the infill layer 3 relative to the length "L" of the artificial strip may be 90% to 40%, but for most applications a preferred range is 85% to 55% or 80% to 70%. For example, in the case where the length of the strip L is 2 inches, the depth of the filler equal to 75% is 38.1 millimeters (1.5 inches) (2.0 × 0.75 ═ 1.5), and the remaining 12.7 millimeters (0.5 inches) of the strip extends above the top surface of the filler.

Although the foregoing description and drawings refer to a specific preferred embodiment as presently contemplated by the inventors, it is to be understood that the invention in its broader aspects is also intended to cover mechanical and functional equivalents of the elements described and illustrated.

Claims (21)

1. An artificial turf assembly for laying on a supporting substrate, the assembly comprising:

a pile fabric having a flexible sheet substrate and a plurality of upstanding artificial strips of selected length extending upwardly from an upper surface of said substrate;

a packed layer of particulate material disposed in the gaps between upstanding strips on said upper surface of said substrate and having a depth less than the length of the strips, said particulate material being selected from the group consisting of: hard and elastic particles; the filling layer includes:

a bottom layer having hard and elastic particles of substantially the same size distribution intermixed with each other and disposed on the top surface of the substrate; and

a top layer having resilient particles disposed on a bottom layer, an upper portion of the artificial band extending upwardly from a top surface of the top layer.

2. A synthetic grass assembly according to claim 1 wherein the resilient particles in the top layer are larger than the resilient particles in the bottom layer.

3. A synthetic grass assembly according to claim 1 or 2 wherein the hard and resilient particles in the base layer have a shape defined in the range of 0.5 to 0.99 on the Krumbein scale of sphericity.

4. A synthetic grass assembly according to claim 3 wherein the hard and resilient particles in the base layer are in the range of 0.6 to 0.9Krumbein scale.

5. A synthetic grass assembly according to claim 1 wherein the resilient particles are selected from the following materials: low temperature ground rubber; rubber; cork wood; polymer particles; a synthetic polymer foam; styrene; perlite; neoprene and EPDM rubbers.

6. A synthetic turf assembly according to claim 1 wherein the hard particles are selected from the following materials: sand; hard aggregate; silicon sand; gravel; slag; a granular plastic; and polymer particles.

7. A synthetic grass assembly according to claim 1, 2, 4, 5 or 6 wherein the particulate material of the infill comprises particles having a size between a maximum nominal diameter of 12.7 mm and a 50 U.S. sieve size specification.

8. A synthetic grass assembly according to claim 7 wherein the difference between the particle sizes of 80% by weight of the hard and resilient particles in the base layer is distributed in the range of 40 U.S. sieve size.

9. A synthetic grass assembly according to claim 7 wherein the difference between the particle sizes of 80% by weight of the hard and resilient particles in the base layer is distributed in the range of 20 U.S. sieve size.

10. A synthetic grass assembly according to claim 1,

characterized in that the artificial strip:

being intermittently cut longitudinally in a predetermined pattern of slits;

the upper portions of the strips extending over the infill layer and being split longitudinally into individual free-standing bundles of selected width to represent grass blades; and is

The lower portion of these strips has the slits extending open to form transverse cross-linked bundles within the lattice structure entrapping the surrounding particulate filler material in the web.

11. A synthetic grass assembly according to claim 1 wherein the synthetic ribbons are arranged in a selected minimum spaced apart arrangement.

12. A synthetic grass assembly according to claim 11 wherein the maximum spacing between rows of synthetic ribbons tufted in the fabric backing is 0.05715 meters.

13. A synthetic grass assembly according to claim 12 wherein the maximum spacing between rows of synthetic ribbons tufted in the textile substrate is 0.0254 meters.

14. A synthetic grass assembly according to claim 13 wherein the maximum spacing between rows of synthetic ribbons tufted in the fabric substrate is 0.015875 meters.

15. A synthetic grass assembly according to claim 1 wherein the depth of the infill layer is in the range between 90% and 40% of the length of the synthetic ribbons.

16. A synthetic grass assembly according to claim 15 wherein the infill layer has a depth in the range between 85% and 55% of the length of the synthetic ribbons.

17. A synthetic grass assembly according to claim 16 wherein the infill layer has a depth in the range between 80% and 70% of the length of the synthetic ribbons.

18. A synthetic grass assembly according to claim 1 wherein the synthetic ribbons are fibers selected from the group consisting of: polypropylene; polyethylene; nylon; and plastic.

19. A synthetic grass assembly according to claim 1 wherein the upper portion of the synthetic ribbons are fibrillated into individual strands having a width in the range between 1.0 and 15.0 mm.

20. A synthetic grass assembly according to claim 1 wherein the synthetic ribbons have a thickness in the range of between 45 and 200 microns.

21. A synthetic grass assembly according to claim 1 wherein:

said substrate and pile fabric being adapted to contain a particulate material filler filled into a portion of said selected length of said strip;

wherein the artificial strip:

being intermittently cut longitudinally in a predetermined pattern of slits;

the upper portion of the strips are longitudinally split into individual free-standing bundles of selected width to represent grass blades; and is

The lower portion of these strips has transversely cross-linked bundles formed by extending open the slits provided in a lattice structure suitable for entrapping the surrounding filler particulate material in the web.