AU2001277392A1 - A synthetic grass surface - Google Patents

Description

A SYNTHETIC GRASS SURFACE

FIELD OF THE INVENTION The present invention relates to an underlay for a synthetic grass layer. The present invention also relates to a synthetic grass surface formed from the underlay and the synthetic grass layer. In particular the present invention relates to a synthetic golf green.

The present invention will be described with particular reference to a synthetic grass surface for playing the game of golf. However, it will be appreciated that the surface may be used for playing of other sports or games and no limitation is intended thereby.

BACKGROUND ART Natural grass surfaces are traditionally used for playing a wide variety of sports. Strains of grasses and techniques for planting, growing and maintaining grass surfaces have been developed to provide surfaces which match the particular requirements of a specific sport. For example, surfaces upon which contact sports are played must provide a certain degree of impact resistance as opposed to a harder surface such as cricket pitches or tennis courts where ball bounce is important.

A disadvantage of a natural grass surface is the level of maintenance required to keep the surface at an optimum playing condition. Maintenance includes regular watering, fertilizing, applying pest control formulations such as insecticides, applying herbicides, top dressing and in some cases rolling. Providing sufficient water to maintain the grass in an optimum healthy condition may be a particular problem in arid areas where water supply is limited. Still further, natural grass cannot tolerate low light levels, frost and overuse.

In an attempt to overcome the above difficulties and to provide a low maintenance and cost effective option to natural grass, synthetic grass surfaces have been proposed. Synthetic grass surfaces are essentially a carpet like material in which imitation grass pile is stitched onto a backing layer. In order for a synthetic grass surface to be acceptable it is desirable that the surface not only looks like grass but also simulates other properties of a natural grass surface. Such properties include ball bounce, impact absorbance (essential for contact sports and/or when players run on the surface), ball holding ability (which determines the speed at which a ball travels over the surface). These properties can vary considerably between different sports.

This desire to provide a synthetic grass surface which can imitate a natural grass surface has led to much research and experimentation. One proposal has been to provide a compacting infill or topdressing material which is spread over the surface of the synthetic grass. Typical infill materials are sand or silica. Typically a number of different grades of particle size are used. This enables the infill to compact. The infill provides support for the grass and holds it in an upright condition (in a similar manner to soil in natural grass). The compacting nature of the infill also hardens the surface and may be used to modify ball bounce and ball rolling characteristics of the synthetic surface. However, it is believed that improvements may still be made to develop a surface which is sufficiently similar to natural grass.

It has been particularly difficult to develop a surface which is suitable for use as a golf green. This is because a golf green must posses the dual properties of being sufficiently resilient such that a ball bounces in a controlled manner but being sufficiently hard to provide an acceptable putting surface. Ball bounce is important as on a golf range balls are generally chipped onto the green. It is desirable that the ball bounces two or three times in a controlled manner before coming to rest. If the ball bounces too much and in an uncontrolled manner it is not possible for the golfer to control the approach shot.

Further, golfers typically apply backspin to a golf ball when chipping onto a natural grass green to avoid the ball rolling too far. It is desirable that synthetic grass greens are able to "hold" onto a back-spinning ball. In order to achieve the desired impact properties it has been proposed to incorporate an elastomeric underlay to the synthetic grass. This underlay is similar to this underlays used with conventional carpets. However, in practice such underlays result in the grass surface being too soft for applications such as golf greens. This has an adverse effect on performance by slowing down the rolling speed of a putted ball. Conversely, a harder surface with an acceptable ball speed may have an unacceptable bounce. In view of these difficulties, the use of synthetic greens on golfing ranges has not been widely adopted. Current synthetic golf greens are generally limited to use as practice putting greens upon which the ball is not chipped onto the green.

OBJECT OF THE INVENTION It is therefore an object of the present invention to provide an underlay for a synthetic grass which may at least partially overcome the above disadvantage or provide the public with a useful choice.

According to a first broad form of the invention there is provided an underlay for a synthetic grass layer, the underlay including a layer of a resilient material having an upper surface with a plurality of indentations, wherein the indentations are at least partially filled with a particulate filler.

The resilient material may be any suitable material and is typically an elastomeric plastics material such as natural rubber, synthetic rubbers including styrene butadiene rubbers, neoprene rubbers, polyurethane, ethylene vinyl acetate copolymers, polyesters, polyethers and poly vinylchloride. A particularly preferred material is a poly-ether urethane foam.

It will be appreciated that the thickness and density of the foam may be varied if desired so as to modify the resilient properties of the synthetic grass surface including the underlay. The desirable resilient properties may vary with the types of sport to be played thereon. For use in a golf green, the resilient material typically has a density of between about 10 to about 40KgM³ and typically between about 27 to about 33KgM³. The thickness of the foam is typically between about 10 to about 50mm, preferably between about 20 to about 30mm. The resilient layer is typically a convoluted foam. The dimensions of the convolutions may be varied according to the desired properties of the final surface. When used in the construction of a golf green it is preferred that the convolutions have a diameter less than the diameter of a golf ball. Typically the diameter of the convolutions is between about 20 to about 37mm. A preferred convoluted foam for use in a synthetic golf green would have convolutions of this diameter and a peak to valley depth of between about 5 to about 20, preferably between about 7 to about 13mm.

The indentations are at least partially filled, preferably completely filled with a particulate filler. The filler is typically inorganic filler such as sand, or silica. The average particle size may be varied depending upon the degree of bounce desired for the surface. This will of course depend upon the sport to be played on that surface. For a golf green, a preferred particle size range is between about 0.47 to about 0.81mm, preferably between about 0.56 to about 0.70mm. It is preferred that only a single size fraction of a particulate filler is used. The use of multiple size fractions or aggregates can lead to compaction of the filler. This can result in an unacceptable hardening of the surface.

Typically, the resilient layer is coated with a sealant. The sealant may also protect the layer from any abrasion by the sand. Any suitable coating layer may be used which is compatible with the material from which the resilient layer is formed. Typically, the sealant is water resistant. The underlay is typically placed on a base formed from known base materials such as crusher dust, road base or sand blended with cement. The typical minimum depth of the base layer is about 75mm. The base need not be flat and may be shaped to any shape or contour which may be desired for example in the construction of a golf green. An artificial grass layer may then be laid over the resilient layer.

According to a further broad from of the invention there is provided a synthetic grass surface comprising an underlay of the first broad from and an upper layer of a synthetic grass.

The synthetic grass layer may be a conventional type of synthetic grass carpet. Typical synthetic grasses for use on golf greens, have a pile height of about 12-13mm and a machine gauge (distance between rows of about 3/16" (5mm). It is conventional practice to topdress synthetic grass surfaces for use in applications such as golf, bowling greens and tennis courts with a compacting particulate filler. The topdressing supports the synthetic fibers and maintains them in an upright manner. Topdressing also counteracts the tendency of conventional synthetic grasses to lay in a particular direction. (This can adversely affect the run of a ball). The pile elements typically have a characteristic bias or tendency to lie in a particular direction which is related to the direction the material passed through the production machinery. Topdressing also imparts a degree of hardness to the surface which is desirable for ball bounce. Conventional practice has been to use a sand or silica infill of different size fractions. The purpose of using the different size fractions is that this allows compaction of the particles and hardening of the surface.

The present inventors have also surprisingly and unexpectedly found that a novel synthetic grass having improved performance may be constructed by providing a synthetic grass with an increased pile height in combination with an infill material having a single size fraction. Whilst not wishing to be bound by theory it is believed that by providing an increased amount of a noncompacting infill material that an improved surface may be obtained. The increased pile height allows the synthetic grass of the present invention to hold a larger amount of infill material than conventional grass surfaces.

According to a further broad from of the invention there is provided a synthetic grass comprising a pile fabric having a backing layer and normally upstanding pile elements, the pile elements having a height of between about 13 to about 30mm and a top dressing layer of a particulate filler having a particle size of between about 0.81 to about 0.47mm.

The pile height is preferably about 25mm. Typically the pile is tufted. Where the pile is crimped or of the knit de knit type, a pile height of 25 mm would normally relax to about 20mm. Tufting of the piles may assists in stabilizing the top dressing against shifting and may also assist in rolling of a golf ball across the surface. Typically, the pile is crimped and in a particularly preferred from of the invention, the yarn is of the knit de knit type. In the knit de knit process a yarn end is tightly knit into a tubular prefabric, the stitch is heat set, and the prefabric is then unraveled (deknit) and taken up onto a yarn carrier. Treated in this manner the resulting yarn has a characteristic texture and bulk, or "crinkle". It has been observed that a knit de knit type yarn can provide a non-directional pile surface as opposed to the inherent bias in conventional type yarns as referred to above. This lack of bias assists in the golf ball maintaining a correct line when putted. Preferably the synthetic grass has a gauge of up to about 3/8"

(5mm), although gauges of down to about 5/32" (1.25mm) may also be suitable. For a faster green surface, the 3/8" (5mm) gauge is preferred. It has been observed that the presence of an increasing number of pile tufts results in a slower green surface. The synthetic grass layer of the present invention has been observed to be particularly suitable for use with the underlay of the first broad from of the invention. When used with the underlay, it is preferred that the infill has substantially the same particle size as the particulate filler which at least partially fills the indentations in the upper surface of the underlay. According to a further broad form of the invention there is provided a synthetic grass surface comprising the underlay of the first broad form and the synthetic grass of the further broad from.

According to a further broad from of the invention there is provided a method of constructing a synthetic grass surface, comprising the steps of: providing a base layer, forming an underlay of a resilient material having an upper surface with a plurality of indentations, at least partially filling the indentations with a particulate filler and laying the underlay over the base, laying a top layer of a synthetic grass over the underlay and placing a particulate infill material on the grass layer. BRIEF DESCRIPTION OF THE DRAWING Figure 1. Illustrates a section view of an embodiment of the invention

BEST MODE By way of example only, the present invention is now described with reference to figure 1.

The figure illustrates a preferred synthetic surface 11 of the present invention in the form of a golf green. The surface 11 includes a preferred underlay 12 of the present invention in association with a preferred synthetic grass 13 of a further form of the invention. The surface 11 has a base 14 formed from a layer of about 75mm compacted crusher dust.

The underlay 12 is formed from a convoluted foam material having a series of convolutions 15 on the upper surface thereof. The foam is a semi-closed cell polyether-urethane foam material having a density of about 29KgM³. The foam has a depth of 25mm and the height of the convolutions (peak to valley height) is about 10mm. The convolutions 15 have a diameter of between about 37 and about 28mm.

The foam is coated with a sealant material comprising an aqueous polymer consisting of a carboxylated styrene/butadiene and poly- isoprene formulated with calcium carbonate and special ceramic fillers. The convolutions 15 are filled with pure graded silica 20 which has been kiln dried and washed. The silica has an effective size of between about 0.76 to about 0.70mm and a uniform co-efficient of less than 1.5mm, a specific gravity of about 2.6 and a bulk density of about 1.5M³.

The grass layer 13 has a backing layer 16 comprising a primary polypropylene backing layer and a secondary layer formed from a carboxylated self curing styrene butadiene rubber latex. The grass surface has synthetic grass piles 17 stitched into the backing 16. The pile has a tufted height of about 25mm and due to relaxation of the yarn the finished height is 20mm. The yarn is a knit de knit style yarn. The stitch rate is 190 per meter and the machine gauge is 3/8" (5mm) and the lineal density is 840 Tex (7600 denier). The pile 17 is filled to a depth of about 17 to about 18mm with the same filler 20a is used to fill the convolutions in the underlay. The top 5mm is filled with a layer of green sand, for aesthetic reasons.

The procedure for laying the golf green is as follows: The base is formed from crusher dust, watered and compacted. The base may be formed on a ground surface having any desirable contour suitable for a golf green. The coated underlay is then laid over the base and conforms to the contour of the base. The underlay is then filled with the infill to the top of the peaks of the convolutions and leveled. The synthetic grass layer is then laid over the underlay and joined with tape at the seams, anchored and buried into the ground around the perimeter. The synthetic grass is then filled with infill to about 17 to about 18mm, then topped with green sand fill to the desired level. (When filled to a high level, there is less pile protruding above the infill. In this case the speed of the green is faster than when the tips of the pile are protruding a greater amount).

The golf green laid according to the above procedure has been observed to provide a surface which can emulate a natural grass green both when a ball is chipped onto the green and during putting. The ball typically bounces two or three time in a controlled manner and then rolls on in a similar manner to a natural golf green before stopping. Whilst not wishing to be bound by theory, it is believed that the presence of the particulate filler in the convolutions in the foam layer provides a dampening effect between the grass and the underlay, whilst providing sufficient rigidity for the ball to roll on in a natural manner after the final bounce. The result is a surface with desirable energy absorbing properties. During putting, the surface is sufficiently hard and the synthetic grass pile is non-biased such that the ball can maintain a correct line once putted and will not roll too far.

Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising" or the term "includes" or variations thereof, will be understood to imply the inclusion of any other element or integer or group of elements or integers, but not the exclusion of any element or integers.

It will be appreciated that various changes and modifications may be made to the embodiments as described herein without departing from the spirit and scope of the invention.

Claims (17)

CLAIMS:

1. An underlay for a synthetic grass layer, the underlay comprising a layer of a resilient material which has an upper surface formed with a plurality of indentations, and a particulate filler which at least partially fills said indentations.

2. The underlay of claim 1 , wherein the resilient material is selected from the group consisting of elastomeric plastics material including natural rubber, synthetic rubbers including styrene butadiene rubbers, neoprene rubbers, polyurethane, ethylene vinyl acetate copolymers, polyesters, polyethers ,poly vinylchloride, and poly-ether urethane foam.

3. The underlay of claim 2, wherein the resilient material has a density of between about 10 to about 40KgM³ .

4. The underlay of claim 3, wherein the resilient material has a thickness of between about 10 to about 50mm.

5. The underlay of claim 4, wherein the resilient material is a convoluted foam.

6. The underlay of claim 5, wherein the convolutions in the foam have a diameter of between about 20 to about 37 mm.

7. The underlay of claim 6, wherein the convolutions have a peak to valley depth of between about 5 mm to about 20 mm.

8. The underlay of claim 7, wherein the particulate filler comprises a silica.

9. The underlay of claim 8, wherein the particulate filler has a particle size range of between about 0.47 to about 0.81 mm.

10. The underlay of claim 9, including a water resistant sealant which coats the resilient layer.

11. A synthetic playing surface comprising the underlay of claim 1 and an upper layer of a synthetic grass.

12. The synthetic playing surface of claim 11, wherein synthetic grass has a backing layer, and a multiplicity of upstanding pile elements attached to the backing layer, the pile elements having a height of between about 13 to about 30mm and a top dressing layer of a particulate filler having a particle size of between about 0.81 to about 0.47mm.

13. The synthetic playing surface of claim 12, wherein the synthetic grass has a pile height of about 12-13mm and a machine gauge of about 5 mm.

14. A method of constructing a synthetic playing surface, comprising the steps of: providing a base layer, forming an underlay of a resilient material having an upper surface with a plurality of indentations, at least partially filling the indentations with a particulate filler and laying the underlay over the base, laying a top layer of a synthetic grass over the underlay and placing a particulate infill material on the grass layer.

15. A synthetic grass surface which has a backing layer, and a multiplicity of upstanding pile elements attached to the backing layer, the pile elements having a height of between about 13 to about 30mm and a top dressing layer of a particulate filler having a particle size of between about 0.81 to about 0.47mm.

16. The grass of claim 15, wherein the particulate filler is a silica.

17. The grass of claim 16, wherein the pile elements have a length of approximately 25 mm, and the pile elements are crimped.