NO321879B1 - Synthetic turf. - Google Patents

Description

TECHNICAL AREA

The invention relates to a synthetic turf with a unique multi-layer elastic particle infill layer that combines the look and feel of natural turf with the durability of synthetic turf.

BACKGROUND TECHNOLOGY

Maintenance of natural grass turf on playground or park and sports areas is

expensive, as natural grass does not grow well inside enclosed stadiums and continuous heavy traffic wears out areas of the natural turf surface. Natural turf surfaces are destroyed under heavy use and exposed soil creates an unwanted accumulation of water and sludge. Synthetic grass has therefore been developed to reduce the maintenance costs of heavily used sports or play areas, to make the playing surfaces more uniform, and to increase the durability of the grass surface, especially where professional sports are involved.

Synthetic grass is installed with a carpet-like pile-woven fabric with a flexible support plate laid on a well-drained compacted substrate, such as crushed stone or other stabilized base material. The upholstery has rows of raised synthetic bands representing blades of grass extending upwards from the top of the support plate.

Of particular interest for the present invention are the different compositions for granular elastic full material which are placed between the raised bands on the upper side of the support layer to simulate the presence of soil. Most prior art systems involve some kind of use of hard particles such as sand or crushed slag particles, together with elastic particles such as a crust of rubber particles or foam rubber backing plate to provide elasticity. The optimal choice of particle dust Izer, particle shape, particle composition and installation in several layers or paths is a feature of the present invention.

US Patent 4,337,283 (Haas, Jr.) discloses a homogeneous fill mixture for imitating soil that is prepared from fine hard sand particles mixed with 25 to 95 volume percent elastic particles to provide an improved elastic and less abrasive fill. Such elastic granular material may include mixtures of granulated rubber particles, cork polymer beads, foam rubber particles, vermiculite, and the like.

US patent 4,396,653 (Tomarin) shows a non-homogeneous filling with rubber particles forming a base layer and sand particles forming a top layer. The rubber particles provide internal elasticity to the surface. The sand layer is uncovered 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 fill such as in the above mentioned Haas system where hard sand particles and elastic rubber particles are mixed and compounded in a uniform proportion throughout the depth of the fill. Synthetic grass infill can, for example, comprise a mixture of 60% by weight sand particles and 40% granulated rubber particles uniformly mixed and deposited between the raised synthetic grass strips to a depth of from 2.5 to 7.5 cm.

A high percentage of sand is preferred to minimize the cost of such systems, as rubber particles are relatively expensive compared to sand. The sand particles also provide an improved degree of drainage which is needed where the synthetic grass surface is not an enclosed stadium for example. Rubber particles will tend to impede the free flow of water, while the capillary action of the sand particles pulls surface moisture downwards due to the differences in surface tension characteristics between rubber and quartz sand.

However, in both the above Haas and Tomarin systems, abrasive hard sand particles present in the top surface layer of the infill will cause problems where such games as football, rugby, soccer, field hockey, baseball are played where players repeatedly fall or are caused to fall on the playing surface. By such

applications there is a need to protect the players against skin abrasion caused by the hard sand in the granulated filling and protection against sand entering the players' eyes, ears or mouth.

The conventional filling is a mixture of sand particles and rubber particles. The rubber particles are compressed and released when a ball seals the surface or an athlete steps on the surface. In the case of conventional soil, soil and jumus particles provide some natural elasticity but the springback is more gradual due to moisture, small particle size and relatively low natural elasticity. In the case of synthetic fillings, the particles are relatively dry and are not firmly bound together. The rubber particles have a spring-like fast elastic rebound which will tend to throw adjacent sand particles and rubber particles upwards.

The synthetic infill is continuously exposed to water flow and impact forces which will tend to displace or segregate the particles, for example due to rain, flooding, the impact of bouncing balls, vibration and impact from the feet and bodies of players in contact with the top surface of the filling. A top layer with a high proportion of sand will result in dispersion of sand particles when a ball or player collides with the top surface of the infill. When soccer balls roll on the infill surface, if any sand particles are present on the top surface, these are lifted by the rolling ball by the suction effect of the air flowing around the rotating ball and by static electrical attraction. As a result, smaller sand particles on the top surface of the fill are lifted up and dispersed in a "rooster tail-like" pattern behind the rolling ball. Over time, areas with continuous sand spreading 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 appear after such impacts. in addition, uncovered grains of sand are highly abrasive to the skin when players fall or slip on the top surface and this could irritate the eyes, ears, nose and mouth when spread, inhaled or swallowed.

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 into contact with the sand particles are exposed to skin abrasion. Over time, due to the dynamic effects of water, vibration and impact, the smaller sand particles will tend to settle towards the bottom of the fill layer and larger, more abrasive sand particles will rise to the top surface. The smaller sand particles tumble down into the cavities between larger particles under the influence of vibration, water and gravity. Smaller particles collect at the lower part of a granular filling layer and will tend to be compacted together. The larger sand particles remain on top of the granulated layer and large particles are highly abrasive to human skin compared to the smaller particles.

As a result, over time the abrasive nature of the synthetic system will. increase and may result in particular areas of the playing surface exposed to heavy traffic becoming more abrasive than other areas. Conventionally used hard particles and elastic particles have angled surfaces. However, it has been found that angled particles tend to compact together more strongly than spherical or rounded particles as the friction between sharp angled surfaces is greater. In addition, where a wide range of particle sizes is used, the smaller particles will fill in the spaces between the large particles and increase the degree of compaction.

When shredded rubber or conventionally ground rubber is used, the rubber particles have irregular surfaces, often with fibrous protrusions that hold air and retain water with surface tension. When it rains on the fill or it floods, the air held by the light rubber particles causes the rubber particles to float up. This is undesirable as the rubber can run down a drain together with the surface water flow and the floating rubber particles are separated from the heavier sand in the filling mixture so that it leads to particle segregation, sand compaction and loss of elasticity in the filling.

Where sand is used for construction purposes such as road construction or in concrete mixtures, it is highly desirable to have a wide range of particle sizes specifically because a mixture of small and large particles will result in small particles filling the spaces between the large particles, increased inter-particle contact, superior compaction and therefore a higher load-carrying capacity. Where sand or granulated aggregates are used in construction applications, vibrating compactors are used and the moisture content is controlled to produce maximum soil compaction and density.

However, where sand is used as a component of an elastic filling in the cavities of synthetic grass, strong compaction is highly undesirable. A high

degree of compaction of sand and contamination of the infill from airborne dirt and dust leads to undesirable changes in the elasticity of the infill over time as a result of use which can vary considerably across the synthetic grass surface from areas of high intensity of use to areas of low intensity of use. Uniform consistent elasticity, elimination of maintenance and predictable performance of the filling are the goals rather than the high load-bearing strength.

The conventional solution to the compaction and separation of infill particles is to periodically brush the synthetic grass. Brushing serves to break up compacted material and re-mix the top surface while restoring the original composition of the fill mixture to the greatest extent possible. Brushing increases the cost of maintenance, exposes synthetic bands to significant wear and is at best a temporary solution after which eventually the conventional filling compacts and needs to be brushed regularly.

The correct choice of spacing between the rows of grass strips has also proven to be problematic. Quite often, the major complaint from professional athletes is that studs on shoes do not consistently release from tightly packed matted, tightly woven or meshed synthetic sports turf surfaces and cause damage to knees and ankles. Older artificial grass surfaces were built very similar to indoor carpet surfaces with very closely spaced upright fibers extending from a woven base with elastic backing. These fiber surfaces were designed to remain upright and avoid tangling when stepped on. To achieve this result, the fibers were arranged with an extremely small distance from each other. However, the knobs on sports shoes often did not loosen properly, especially when the foot was rotated on the surface, and this resulted in damage to the knees and ankles.

On the other hand, where a sand is used as a surface, for example on pedestrian surfaces, the surface is relatively unstable and sand particles are easily displaced. To stabilize such surfaces, US patent 4,819,933 (Armond) Fibersand Ltd.) provides a mixture of sand with a relatively low weight percentage of straight synthetic fibers randomly distributed and cross-linked in a loosely displaceable network. The fibers serve to distribute concentrated loads, hold the sand together under the weight of horses' hooves, athletes' feet, wheeled vehicles or implements. US Patent 5,326,192 (Freed) Synthetic Ind., Inc) also provides a method of improving the appearance and performance characteristics of a turf surface by incorporating separate bundles of synthetic fibers into the soil surface.

Granular infill combined with raised grass-like synthetic ribbons aims to remedy the disadvantages of the above systems to some extent by providing a granular synthetic surface entangled with the raised fibers extending from a backing sheet textile to better imitate a natural soil subsoil, with embedded roots and grass. When the studs of an athlete's shoes are embedded in the granular fill, the loose particles will shift and shift to some extent as in natural soil. At the same time, the raised synthetic grass strips will become entangled with the loose particles and the knobs to reduce or prevent slips. Without the synthetic bands, the loose particles would be very difficult to run on, quite similar to a natural beach surface of dry sand, while, on the other hand, a compact fiber mat would hold the knobs and prevent release and possibly cause personal injury.

The combined structure with raised bands and loose particulate filling must therefore be balanced or optimized to provide a desirable playing surface. When the bands are tightly packed, the knobs cannot be released properly, but when the bands are arranged too far apart, adequate drive and stability are not available. Due to the high cost of artificial grass installations and the risk of injury to highly skilled and highly paid athletes, a predictable and reproducible artificial grass performance is required.

Synthetic grass surfaces have been built up with infilling mainly of rubber alone. Rubber particles are relatively light, and torn particles have fibrous surfaces that trap air bubbles. As a result, when flooded, the rubber particles in some conventional installations have floated to the surface of the water and washed away from the synthetic grass surface. Rubber particles are drained away or replaced resulting in areas of the synthetic grass that have depleted infill thickness. A lack of uniform fill thickness and elasticity over the surface can result in damage and liability for the owner of the sports ground.

Despite several different filling compositions of rubber and sand and fiber structures according to the prior art, several significant disadvantages remain as stated above.

DESCRIPTION OF THE INVENTION

It is an aim of the present invention to provide a filling which will retain its properties during long-term use without significant segregation or compaction of the filling and with a reduced requirement for periodic brushing of the surface.

It is a further object of the invention to improve the elasticity and reduce the abrasive nature of the conventional granular infills which fill the spaces between the synthetic grass strips while enabling the studs in sports shoes to be properly released without serious risk of injury.

It is a further object of the invention to eliminate the spreading of sand particles and unwanted visible sand on the fill surface.

The objectives of the present invention are achieved by a synthetic turf assembly for installation on a supporting substrate, to provide a sports playing surface, ton/assembly includes: a pole textile with a flexible backing plate and a plurality of upright synthetic ribbons of a selected length, representing blades of grass, extending upwardly from an upper surface of the support plate; and

a filling layer of particulate material arranged in the spaces between the raised bands on the upper side of the support plate and with a depth

less than the length of the bands, the particulate material being selected from the group consisting of hard and elastic grains,

characterized by the filling layer comprising:

a bottom layer consisting mainly of only hard combs placed on the upper side of the support plate;

a middle layer of intermixing hard and elastic grains of a selected relative weight ratio, disposed on the bottom layer; and

a top layer which mainly consists only of elastic bands arranged on the middle layer, an upper part of the synthetic bands extending upwards from an upper side of the top layer.

Preferred embodiments of the synthetic grass turf assembly are further elaborated in claims 2 to 11 inclusive.

The invention is based on the fact that the granulated filling is a dynamic system of continuously moving hard and elastic particles of different sizes and with different physical properties under the influence of shock and vibration from player activity, surface maintenance and weathering. The invention is adapted to such dynamic activity in a number of different ways.

The top surface is kept mainly free of sand by using a clean rubber particle top layer 6 of relatively large particles, preferably significantly larger than the particles in the bottom layer. Any smaller sand particles that could migrate up to the surface from the displacement action of knobs will then be able to percolate through the voids between the large surface particles and back down to the bottom layer under the action of water, vibration and gravity. A bottom layer of sand and rubber mixed together is arranged between the pure rubber top layer for additional elasticity, moisture drainage and as a ballast to stabilize the textile backing plates.

The particle shapes are mainly spherical to reduce contact friction between the particles, improve drainage and prevent compaction. The spherical shape reduces resistance to particle displacement and therefore reduces the degree of compaction compared to conventional angular surface particles. On the basis of Krumbein's spherical shape standard, known to those skilled in the art, the particle shapes are broadly in the range from 0.5 to 0.99 but preferably in the range between 0.6 and 0.9, being well rounded or mainly spherical.

The particle size distribution for particles of hard sand and elastic rubber in the bottom layer is chosen to be substantially equal to each other and the particle sizes are preferably limited for sports or sports field surfaces to the range of 14-30 standard mesh size. To adapt to other applications of the synthetic grass surfaces, the particle size can be in the range from 12.7 mm to 50 standard sieve mesh size. Larger particles can be used for pedestrian applications up to approximately 6.3 mm but these large grains are too abrasive for contact with human skin. Particles smaller than the 50 sieve mesh standard will tend to create dust and can lead to unwanted compaction, a reduced rate of water percolation and particle segregation. Naturally occurring soil particles in this size range are classified as particles corresponding to medium sand, coarse sand and fine gravel.

By substantially identical "size distribution" is meant that when the bottom fill layer is analyzed by conventional soil laboratory sieve analysis and plotted on a semi-logarithmic graph for standard sieve analysis (the y-axis shows 0-100 weight percent passing the sieve size or less and the x-axis shows sieve/particle size logarithmically ) the line for hard particles and the line for elastic particles ideally lie above each other to a significant extent. The hard and elastic particles therefore have mainly the same particle sizes and the size distribution is essentially the same.

The graphs for the standard sieve analyzes are in themselves an inaccurate "provisional" as natural soils vary considerably over, for example, the surface of a construction site. The graphs for sieve analysis generally do not show the largest 10% and smallest 10% of the particle sizes after which these extremes are considered statistically insignificant due to the natural variation in the soil's particle size. Conventionally, therefore, only the average 80% of the particles are considered when examining soil particle sizes in a sieve analysis.

By applying this practice for the invention, defined numerically or scientifically, where the particle sizes of 80 percent by weight of hard and elastic grains in the bottom layer are distributed in an area that spans a numerical difference of 40 standard sieve mesh widths, the particle size distribution is considered essentially identical or very well sorted out. As sand and rubber can be graded to any desired specification, it is preferred that the numerical difference be even smaller such as 20 standard sieve mesh widths to produce a more uniform fill. For example, perfectly spherically produced glass beads would have a numerical difference approaching zero. However, since sand is a naturally occurring substance created from the erosion of rock, the particle size distribution and the degree of sphericity vary considerably. A numerical difference of, for example, 20 standard sieve mesh widths can result in a particle size distribution between 10 and 30 for pedestrian surfaces or between 20 and 40 for sports field surfaces.

In practice, the cheapest hard particulate material is usually sand that is found in naturally segregated deposits and/or has been mechanically graded to suit various common construction purposes, such as use in concrete mixes and road surface construction. The demand for sand for use in artificial grass installations is relatively low and if a composition requires a particularly segregated or graded sand particle size distribution, the price for such material would increase somewhat.

When deciding on the specific materials to be used at a selected location, it is preferred to use any acceptable sand that is readily available near the installation site. It is a relatively simple task when purchasing elastic particles to specify the elastic particle size distribution so that this is within the ranges discussed above and which can be superimposed on the measured sand particle size distribution. Elastic particles must be processed, painted and transported from a production facility regardless of where the installation site is located. The marginal cost of producing elastic particles with a particle size distribution corresponding to the particle size distribution of the sand particles is relatively low compared to the alternative of grading the size distribution of the sand particles to correspond to the elastic particles.

By producing the elastic particles so that they correspond to the size distribution of the readily available sand at the installation site, the bottom layer of the filling with mixed particles of sand and rubber with equally distributed sizes will result in the advantage of significantly reduced deposition and separation of the particle mixture in use.

In contrast, conventional mixtures of elastic particles generally have significantly larger particles than the available graded sand. As a result, the light larger elastic articles escape upwards and the heavier less hard sand particles escape downwards under the combined action of gravity, vibration, rain and downward percolating water. Segregation of differently sized particles leads to loss of optimal compactness and uneven grip in conventional mixed infill layers.

The inventor has found that the separation of hard and elastic particles in the mixed bottom layer can be prevented or substantially reduced by 1 selecting hard and elastic particles with equal or substantially identical size distribution 2, selection of a relatively narrow range of particle size, and 3 selection of generally spherical particle shapes for both hard and elastic particles. The minimal variation in particle size counteracts compaction as there are no relatively smaller particles to fill the spaces between the large particles when all particles are essentially the same size. The spherical shapes reduce the resistance to inter-particle displacement and reduce the tendency for adjacent particles to lock together.

The fibrillated grass-like synthetic bands at the surface will hide and retain the relatively large top rubber particles in a loose net-like flexible structure. The loose mesh of fibril wood fibers criss-crossing also allows displaced rubber particles to work their way back into the underlying top rubber layer when foot traffic passes over the particles and the synthetic bands. The combination of pure top rubber layer and network of fibrillated bands gives the look and feel of a natural grass turf surface.

The synthetic bonds between the textile backing layer and the top layer provide a degree of resistance to particle displacement in the mixed base layer by forming an open mesh or network structure of vertically oriented bundles which are laterally cross-linked. The mixed bottom layer of sand and rubber provides firm elastic support for the relatively thin rubber top layer. The sand content in the mixed layer in particular provides the necessary weight for ballast and better drainage due to the capillary action of the sand.

The relatively thin top layer which is in immediate contact with the athletes' body has high elasticity where physical contact occurs and results in low skin abrasion due to the exclusive use of rubber. The sand content of the mixed subsoil provides ballast weight to hold the grass in place and quickly drain the surface. Drainage is particularly necessary where there is a risk of freezing and selection of a coarser mixture for improved drainage may be necessary in cold climates. The elastic particles in the mixed layer also provide subsurface elasticity in addition to the top surface elasticity provided by the top layer.

The choice of hard and elastic particles with essentially the same size distribution significantly reduces compaction and reduces the requirements for maintenance. The top clean rubber top layer will always remain essentially free of sand due to the choice of particle size. Sand can be displaced from the mixed base layer to the surface of the top layer by agitation caused by contact with the players' shoe cleats during a game or practice session much in the same way that conventional soil is disturbed by this action. However, the size of sand particles is chosen to be smaller than the size of elastic particles in the top layer. The downwash of the displaced sand particles due to rainwater draining through the upper elastic surface or from vibration and shaking due to foot traffic returns the smaller sand particles to the bedrock from which they came.

The two-layer installation with only rubber in the top layer and mixed sand rubber in the bottom layer produces an elastic surface at a lower cost and with a lower thickness than conventional methods such as those described in US patent 4,337,283 (Haas) and US 4,396,653 (Tomarin); The previously known filling layers with large and small particles would like to compact or consolidate into a more firmly compacted surface. The invention retains its elasticity even when used in thin layers since the top layer is of only rubber granules and the mixed bottom layer does not tend to separate or compact. A more predictable long-term elasticity is thus created.

The synthetic tapes can be produced and tufted to the textile support layer. It is preferred to slit the bands with relatively short longitudinal slits separated over the width of the bands. After installation of the filling, the upper one of the synthetic tapes is then fibrillated, slit or unraveled vertically in place by passing a brush over the installed surface. The strips have a longitudinally oriented structure when manufactured and therefore aggressive brushing action on the upper side will tend to tear up or split the strips into thinner grass-like threads by extending the slits in the longitudinal direction to form closely packed individual grass-like threads.

When ribbons are brushed and split in place by brushing, the upper portions of the ribbons are unraveled or split into thin grass-like strands while the lower portions remain intact and are merely stretched open into an expanded web, net or network structure, to a greater extent than when the fibers was initially tufted into the support plate. A direct advantage of this network structure is the stabilization of the particulate filling by entanglement of the particles between the fibrillated grass-like threads and within the expanded lattice-like structure. The lower grid-like part stabilizes the fill and the upper grass-like part allows knob penetration and knob release, rainwater penetration and drainage, allows a small surface elasticity due to the curved grass-like threads, and holds the large elastic particles in the top layer in a grass-like mesh structure.

Local fibrillation of the fibers also allows a more dense top surface coating of grass-like threads. The relatively wide bands with short slot perforations initially installed can be spaced sufficiently apart to allow granular fill to be installed between the bands. When the infill has been fully installed, the brushing of the widely spaced bands will break them up into thinner grass-like strands which fill the gap between the bands and better cover the top surface of the granular infill. The dense network of fibrillated threads criss-crossing contains the large rubber domes in the top layer which allow knob penetration and water to drain through. The split bands add better grass-like wire coverage to the visible surface at a lower cost. In applications that are not oriented towards sports use, such as for example when used in landscaping or for decorative purposes, less dense fiber distributions can be used, which results in a lower price for the same visually visible coverage as conventional densely packed synthetic grass.

Further details of the invention and its advantages will be apparent from the following description and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order for the invention to be more easily understood, a preferred embodiment of the invention shall be described as an example, with reference to the attached drawings in which: Fig. 1 is a cross-section through a synthetic grass assembly with infill installed and shows the flexible support plate with raised bands and the infill layer constructed in the form of a top layer of relatively large elastic rubber grains and a bottom layer of mixed grains of hard sand and elastic rubber with an identical smaller particle size distribution; Fig. 2 is a similar cross-section showing the final configuration of the grass-like strands slightly curved as a result of aggressive surface brushing to further fibrillate the ends of the ribbons; Fig. 3 is a side view of a synthetic tape as made with a series of short longitudinal slit perforations; Fig. 4 is a side view of a synthetic ribbon at the lower end twisted before tufting into the textile backing plate and at the upper end stretched laterally to show the lattice-like structure of grass that results from the lateral stretching and longitudinal extension of the slits; Fig. 5 is a table showing the graphical representation of the particle size distribution resulting from standard sieve analysis of the fill layers; and Fig. 6 is a table showing a visual representation of particles graded according to Krumbein's spheroid scale.

EMBODIMENT OF THE INVENTION

With reference to fig. 1 the invention relates to a synthetic grass assembly consisting of a pole textile with an infill layer of particulate substance installed on a supporting soil substrate to provide a sports or playground surface.

The Pol textile includes an elastic support plate 1 which may include two or more layers of open woven textile, one of which may be dimensionally stable netting to prevent stretching during installation and use. A number of upright synthetic bands 2 extend upwards from the upper side of the support plate 1. As shown in fig. 1, the bands 2 are tufted through the support plate 1 separated in rows spaced " apart and with a length L. The length "L" of fibers is chosen depending on the total depth (5 plus 6) of the filling and the desired elasticity of the completed synthetic grass assembly.

Arranged in the spaces between the upright bands 2 on the upper side of the support plate 1 is a filling layer 3 of particulate substance. The particulate matter may be selected from any number of commonly available hard grains such as: sand; hard aggregate; quartz sand; gravel; slag; granulated plastic material and polymer beads. The elastic grains may be selected from: cryogenically ground rubber; rubber; cork; polymer beads; synthetic polymer foam; styrene; per-lit, neoprene, painted car tires and EPDM rubber.

The filling layer 3 consists of a bottom layer 4, a middle layer 5 and a top layer 6.

The bottom layer 4 mainly consists only of hard sand grains which are placed immediately on the upper surface of the support plate 1. The middle layer 5 is made of intermingling hard sand grains and elastic rubber grains. The bottom layer's mixture is chosen on the basis of a weight ratio greater than 2:1 of hard and elastic com. The top layer 6 is mainly made of elastic rubber granules only. An upper part of the synthetic bands 2 extends upwards from an upper surface 8 of the top layer 6. The resulting artificial tone/surface can be adapted for various indoor and outdoor applications, such as: sports playing fields; horse racing and recreational areas.

The mixture is selected on the basis of the volume distribution of different sizes of hard grains and elastic grains which are essentially identical and range in size between 12.7 mm and 50 standard sieve mesh. Preferably, the range of particle sizes is limited to avoid small or fine particles that fill the spaces between larger particles and promote compaction. The preferred range between 15 and 30 standard sieve mesh size. Depending on the application, the range of particle sizes in the mixed layer can be limited to 10-30, 15-30 or 20-40 standard sieve mesh size as chosen to fit design parameters. The shape of hard and elastic grains is mainly spherical and not angled as in prior art to further inhibit compaction and deposition.

As shown in the graph in fig. 5, a standard mesh size sieve analysis is depicted with a vertical axis with a linear scale of "weight percent passing sieve size" or alternatively "percent less" and the horizontal axis as a logarithmic scale showing particle and/or sieve size. The example line shown in fig. 5 shows relatively uniform mixtures of particles with a narrow range of particle sizes. Ideally, the line in fig. 5 for the sand particle size distribution and the rubber particle size distribution line identical and would be shown superimposed. As an example, however, the 10-30 range mentioned above is graphically illustrated as a shaded zone within which any line will satisfy the requirements of this particle size limitation.

The top layer 6 mainly consists of elastic rubber grains alone. An upper part 7 of the synthetic bands 2 extends upwards from an upper side 8 of the top layer 6.

The resulting artificial grass surface can be adapted for many indoor and outdoor applications, such as sports fields; horse racing tracks, playgrounds, landscaped areas and recreational areas.

To deposit multiple layers, brushes pass over the backing plate with a mixed material of sand and rubber several times to ensure that the bands stand up when embedded in the fill and not be submerged during the fill, and further to expand the bands to some extent to open the slots and produce a network structure which stabilizes the filling and prevents excessive displacement of the filling particles after installation. After the mixed bottom filling layer has been laid down, a mainly pure rubber particle-shaped material is applied as an elastic top layer.

To deposit the bottom layer, a spreader can be used and then the surface is brushed to raise the threads of the pole textile and position the bands 2 in a generally upright position before the top layer 6 is deposited. After the repair of each layer, it is necessary to brush the surface and to raise the bands to an upright position as shown in the drawings.

It may be preferred that after installation of the top layer 6, the upper part 7 of the synthetic band 2 is further fibrillated by aggressively running a brush over the surface. This operation splits the upper parts 7 and spreads the threads evenly over the upper side 8. The produced width of the bands 2 is relatively large such as 2.5 cm and the brushing operation carried out on the spot further splits the bands and opens the slits in the longitudinal direction and forms thinner grass-like threads of a smaller width as illustrated. The other ends of the bands 2 are brushed more vigorously to achieve the following advantages over previously known methods. The welting of the fibrillated upper parts 7 mutually interlocks the band ends into a loose network that more realistically stimulates the appearance of natural grass: The fibrillated ends impart a slight elasticity after which they are slightly erect or down and more accurately simulate the elasticity of natural grass grass when balls during play bounce on the completed surface. The raised ends also hide loose rubber from the top layer 6 from view, hold the loose particles in place and allow a movement of loose particles back and forth between the top layer 6 and the upper side of the fibrillated bands 2. When splitting or fibrillating the ends of the band 2 , less surface tension is created and water penetrates more easily through the top surface 8 and drains away through the bottom layer 4.

The ribbons 2 include a top structure of many grass-like strands fibrillated in place and an expanded lattice-like lower structure which is left essentially in its original state but mechanically expanded into a lattice structure due to interaction with the fill as it is deposited. Bands can be chosen from fibers such as polypropylene, polyethylene, nylon and other plastic materials. A mixture of large and small width fibrillated threads produces a more natural appearance and causes a ball to roll in a more predictable manner depending on the resistance of the fibers to the ball during play. Modifying the width and density of the grass will also modify the ball's rolling properties.

The ribbons when initially tufted to the textile backing sheet can have a width in the range of about 2.5 to 7.5 cm and when fibrillated the individual grass-like strands can be in the range of 1 mm to 15 mm in width. Expressed in terms applied to the range, the threads range from 800 to 5,000 denier and the thickness of the tapes and threads is in the preferred range from 45 to 200 micrometers

It has been found through trial and experience that the size and shape of hard granules and elastic granules significantly affect the turf performance characteristics. It has also been found that the distance between the bands and the variation in the depth of the infill can have a strong influence on the performance of the synthetic grass assembly.

The hard and elastic particle sizes should be in the range between 12.7 mm and 50 US standard sieve mesh, but preferably a narrower range of 14 to 30 avoids the danger of compaction. Hard granules larger than 14 standard mesh size can be perceived as somewhat abrasive by users of the sports surface if direct contact is established. As the fibers above the top surface would like to bend over and protect the user from direct contact with a curved elastic fibrous entanglement of synthetic fibres, somewhat larger particles can however be used without the particles being perceived as abrasive. Particles smaller than 50 standard mesh size will hide, prevent the penetration of water and adversely affect the drainage properties of the filling layer 3 in relatively humid climates. In dry climates, the use of smaller particles may be desirable to maintain an optimum moisture content for optimum levels of compaction and elasticity. Larger elastic particles (such as 14 standard mesh size) can be used where skin contact with the surface and possible abrasion based on the nature of the sport is expected. Preferably, the sand is washed and graded to mainly remove all the fine particles with a size smaller than the corresponding 50 standard sieve mesh size.

The natural tendency of the large relatively light rubber particles to migrate to the top and the complementary tendency of smaller, heavier sand particles to migrate to the bottom of the filling layer 3 can be reduced by using particles of the same size. Particle migration is also reduced by the interaction with the synthetic lattice-like band structure and by the use of spherical particle shape. The bottom layer of the fill maintains its initial mixture of sand and elastic particles of equal size due to the selection of substantially identical particle sizes and interference with particle movement resulting from the lattice-like structure of the bands in contact with the bottom fill layer. These characteristics of the fill layer would like to inhibit compaction and maintain the uniform predictable . elasticity of the filling.

With an elastic top layer 6 of pure rubber, elasticity is provided at the contact surface where the perception of elasticity is really needed. Preferably, the particle size of rubber particles in the top layer 6 of the filling is larger than the particles of sand and elastic particles in the bottom layer 4. The larger particles in the top layer allow smaller particles in the bottom layer to fall back down through the gaps between the large particles and as a result remain the particle size composition of the layers distinct. The elasticity of the final layer of the filling can be fine-tuned by testing the elasticity at the surface and gradually spreading the rubber particles until marginally increasing the thickness of the top layer 6 and achieving the desired elasticity of the final top layer.

The synthetic bands are preferably arranged in rows at a distance from each other corresponding to a selected minimum distance "W". Depending on the firmness desired and the degree of freedom required for the knobs to rotate for different sports, the distance "W" can vary between 57 mm and 15.9 mm or less. A smaller distance provides firmer support for the filling 3, while a larger distance allows easier rotation of embedded knobs.

The depth of the filling layer 3 in relation to the length "L" of the synthetic tapes can be in the range from 90% to 40% but the preferred range for most applications will be from 85% to 55% or from 80% to 70%. Where, for example, the length of the bands L is 51 mm, a depth of the filling corresponding to 75% would be a depth of 38.1 mm (51 x 0.75 = 38.1) (51 x 0.75 « 38.1) with the remaining 12.7mm of ribbon sticking up over the top of the filling.

Although the preceding description and attached drawings relate to a specific preferred embodiment which has hitherto been considered included by the inventor, it should be understood that the invention in its broad aspect includes mechanical and functional equivalents of the described and illustrated elements.

Claims (11)

1. Synthetic turf assembly for installation on a supporting substrate, to provide a sports playing surface, the ton/assembly comprising: a pole textile with a flexible support plate (1) and a plurality of upright synthetic ribbons (2) of a selected length, which represents blades of grass extending upwards from an upper surface of the support plate; and a filling layer (3) of particulate material arranged in the spaces between the upright bands (2) on the upper side of the support plate (1) and with a depth less than the length of the bands (2), the particulate material being selected from the group consisting of hard and elastic grains, characterized in that the filling layer comprises: a bottom layer (4) which mainly consists only of hard balls placed on the upper side of the support plate; a middle layer (5) of intermingling hard and elastic came with a selected relative weight fomold, placed on the bottom layer (4); and a top layer (6) which mainly consists only of elastic bands arranged on the middle layer (5), an upper part (7) of the synthetic bands extending upwards from an upper side of the top layer. 2. Synthetic turf composition according to claim 1, characterized in that the relative weight ratio between hard and elastic fibers is greater than 2 to 1. 3. Synthetic grass turf composition according to claim 1, characterized in that the hard grains are sand particles with a size that is in the range between 14 to 70 US standard sieve mesh size. 4. Synthetic grass turf assembly according to claim 3, characterized in that the size of the sand particles is in the range between 20 and 50 mesh size. 5. Synthetic grass turf assembly according to claim 3 or 4, characterized in that the sand has been washed to remove mainly all fine particles below mesh size 70. 6. Synthetic grass turf assembly according to claim 1, characterized in that the elastic grains are torn rubber particles with a size in the range from 10 to 30 US standard sieve mesh size. 7. Synthetic grass turf composition according to claim 2, characterized in that the weight ratio of the middle layer (5) is of the order of magnitude 3 to 8. Synthetic grass turf assembly according to claim 1, characterized in that the top layer (6) has an installed unit weight of up to 2.9 kg/m<2> of the upper surface area. 9. Synthetic turf assembly according to claims 1 to 8, characterized in that the upper part of the synthetic bands (2) is fibrillated on the spot. 10. Synthetic grass turf assembly according to claims 1 to 8, characterized in that the synthetic bands (2) each comprise several fibers with a downwardly curved upper part. 11. Synthetic grass turf assembly according to claims 1 to 10, characterized in that the upper part of the synthetic bands (2) extends extending upwards 6.35 mm to 25.40 mm from the upper surface of the upper layer (6).