HK1038950C - Device for synthetic grass - Google Patents

Description

Artificial turf device

Technical Field

The present invention relates to an artificial turf having a unique multi-layer resilient particulate infill that combines the look and feel of natural turf with the wear resistance of artificial turf.

Background

Natural turf has traditionally been grown on athletic surfaces for sporting events and sporting activities. Natural turf is generally preferred over hard surfaces, for example, because natural turf provides some resilience and cushioning to foot impacts and games in which players often fall on sports surfaces, such as soccer and soccer. Natural turf stabilizes the underlying soil to minimize soil and dust problems and provides a beautiful appearance.

The maintenance of natural turf on sports arenas is expensive, natural turf does not grow well in shaded enclosed sports fields, and the continual heavy commute wears some of the ground in the turf surface, making it very difficult to prevent the accumulation of water and dirt.

Accordingly, artificial turf has been developed in the past to reduce the cost of maintaining athletic fields and to increase the durability of turf surfaces, particularly those involved in professional sports.

Artificial turf typically comprises a carpet-like pile fabric having a flexible backing laid over a compacted substrate such as crushed stone or other stable base material. The pile fabric has a plurality of rows of upstanding, artificial strips representing grass blades extending upwardly from the top surface of the substrate. Of particular interest to the present invention are various formulations of granular elastomeric fillers that are laid between upstanding strips on the upper surface of the substrate to simulate the presence of soil. Most of the prior art involves the use of some sand or grit particles in conjunction with a resilient foam backing or crumb rubber particles to provide resiliency.

For example, U.S. patent 3,995,079 to Haas, jr discloses the use of a pile fabric to cover a golf green. The filler is selected from the group consisting of granulated coal slag, ground flint or ground granite. The resilient foam underlay provides some resilience, however the angular particles of the filling are relatively abrasive. Where abrasion is a problem, such as in football, rugby, soccer, hockey, softball games and other games where players fall or are knocked down on playing surfaces, it is desirable to lay an elastomeric material on the granular infill that has no abrasive effect. For example, U.S. patent 4,337,283 to Haas, jr discloses mixing fine, hard sand particles with 25 to 95% by volume of elastomeric particles to provide an improved resilient and non-abrasive simulated soil filling. Such elastomeric materials may include a mixture of particulate rubber particles, cork polymer beads, foam rubber particles, vermiculite, and the like.

The use of a uniformly mixed granular infill results in a number of disadvantages, for example in prior art systems where the hard sand particles and the elastomeric rubber particles are mixed in a uniform manner throughout the thickness of the infill. The artificial turf infill may for example comprise a mixture of 60% sand and 40% granular rubber particles by weight uniformly mixed together and disposed between upright strips of artificial grass and having a thickness of 1 inch (25.40mm) to 3 inches (76.20 mm). Since rubber particles are expensive compared to sand, a high percentage of sand is preferred to minimize the cost of such a system. The sand particles also improve the drainage level, which is necessary for example in the case of artificial grass surfaces not located in a closed stadium. Rubber particles tend to impede the free flow of water, while the capillary action of sand particles tends to draw surface water down due to the difference in surface tension properties between rubber and silica sand.

The prior art filling systems fail to recognize that the filling is a dynamic system that continues to be in motion under the influence of vibrations and impacts of the bouncing ball, player's feet and body in contact with the top surface of the filling. For example, a uniformly mixed pack with a high proportion of sand results in sand particles being splashed when a ball or player impacts the top surface of the pack. Over time, the areas of successive impacts will separate and sand will be seen. It is considered undesirable to see a light colored sand in the surface of artificial grass, and particularly undesirable to see a cloud of sand when subjected to such an impact. In addition, exposed sand particles can scratch the skin when the player falls onto or slides over the top surface.

Especially in the case of relatively thin infill layers, infill layers of sand and rubber tend to sort themselves and tightly bond to a relatively solid surface. Thus, the uniformly mixed packing layer provides a sufficient degree of elasticity when initially installed, but over time, the elasticity decreases for hard and tight surfaces. To avoid this problem, a thicker filling layer may be installed, however the resulting surface is too elastic and may cause injury to the player. Professional athletes often complain that cleats on shoes do not consistently release from a tightly woven or knitted synthetic sports turf surface, causing injury to the knees and ankles, and that the synthetic surface is hard and abrasive, causing skin burns or abrasions. Granular infill has these disadvantages by creating an artificial surface that better mimics natural soil and turf.

A further disadvantage of the homogeneously mixed infill is that abraded sand particles remain on the top surface of the artificial turf, where the skin of the athlete in contact with these sand particles is scratched. Over time, smaller sand particles tend to settle toward the bottom of the packed bed, while larger, coarser sand particles rise to the top surface due to the dynamic effects of vibration and shock. As a result, the abrasive nature of the artificial system increases over time and may cause certain areas of the surface subject to heavy traffic to be more abrasive than others.

Disclosure of Invention

It is an object of the present invention to provide a filling which maintains its properties throughout its use. It is also an object of the present invention to reduce the abrasive properties of the artificial turf infill. It is also an object of the invention to stabilize the top surface of the infill to maintain a resilient grass-like surface that does not become firm or deteriorate in quality over extended periods of use.

The present invention provides a novel artificial turf assembly for installation on a supporting soil substrate to provide a playing surface that combines the abrasion resistance of artificial turf with the look and feel of natural turf.

The turf assembly includes a pile fabric having a flexible sheet substrate and a plurality of upstanding artificial strips extending upwardly from an upper surface of the substrate to represent grass blades. A distinct fill layer of layers of different grades of particulate material is laid in the gaps between the upstanding strips on the upper surface of the substrate and is of a depth less than the length of the strips.

The prior art uses a filler consisting of sand and rubber particles which are mixed homogeneously. The filler has not heretofore been recognized as a dynamic system when impacted and vibrated by the physical activity on the top surface. When a ball or player strikes the top surface of the packed bed, sand particles migrate upward under the impact. Dust and hard sand particles can scratch the skin and splash into the eyes or ears of the athlete. The appearance of the light colored sand in the green artificial grass fiber is poor, while the dark colored rubber particles are more like a natural soil surface.

Thus, the obvious disadvantage of having sand particles at the top surface of the pack is: can cause chafing and sand splash to athletes. However, the use of rubber particles alone as a filler is expensive and can result in a highly elastic unnatural playing surface. Fillers consisting of rubber particles alone have poor capillary drainage characteristics relative to sand. Sand has traditionally been mixed with rubber particles to provide drainage properties, reduce the cost of the filler, reduce elasticity, and provide sufficient weight to hold the fabric in place. Water penetration through the pack tends to move the sand particles downward, however, because the sand and rubber mix throughout the pack, there is a significant volume of sand near the moving surface.

The invention recognizes that the filling is a dynamic system of particles that continuously move under the influence of shock and vibration from racing activity, surface maintenance and precipitation. The present invention regulates this dynamic activity in a number of ways. The top surface is kept substantially sand-free by providing a top layer of pure rubber particles. A layer of pure sand is used as a bottom layer to regulate water penetration and drainage. The dynamic interaction between the pure sand and the pure rubber layer is cushioned by the selected proportions of the intermediate mixed layer, for example: three parts of sand and one part of rubber by weight. The filamentary tips of the grass-like artificial strips hold the relatively large top rubber particles in a loose net-like flexible structure. The loose crisscross network of fibrils of fibers also allows displaced rubber particles to return to the underlying top rubber layer as the foot passes over these particles and the artificial band. The combination of the top layer of pure rubber and the network of strips with filaments produces the look and feel of a natural turf surface. The sand and rubber mixed intermediate layer forms a firm and resilient support and the entire high content of sand component provides weight and better drainage through the capillary action of the sand.

A bottom layer is first placed on the top surface of the substrate and consists essentially of hard sand particles. A small amount of rubber particles may be mixed with the sand without significantly affecting the function of the sand layer. The sand is washed to remove fine sand below 70 mesh (212 μm) to improve surface drainage. The maximum particle size can be varied significantly depending on the application. For athletic activity fields, the sand has a particle size below 20 mesh (850 μm) to avoid frictional contact with the user of the playing surface. The size of the sand particles used for racing purposes is preferably between 30 and 50 U.S. sieve size (600 μm to 300 μm). For application on a racetrack surface, friction is not an issue, and larger particle sizes below 14 mesh (1.4mm) may be used.

Then, a middle layer of hard sand and elastomeric rubber particles mixed with each other in a selected weight ratio (e.g., 3: 1) is laid on the bottom layer. Finally, a top layer consisting exclusively of elastomer particles is laid on the intermediate layer. The size of the rubber particles is between 10 and 30 mesh size (2mm to 600 μm).

The thinner top layer, which comes into contact with the user, has a high elasticity where the contact occurs and, due to the special use of rubber, the friction is low. The bottom layer of sand provides weight to hold the turf still and quickly drain the water from the surface. Good drainage is particularly necessary where ice formation is likely.

The middle layer of mixed sand and rubber particles acts as a buffer layer to keep the bottom sand and top rubber separated. The intermediate mixing layer prevents excessive migration of the abrasive sand towards the top surface layer. The light colored sand at the top surface is unsightly and creates dust when in contact with bouncing balls and can scratch the eyes and body. The intermediate mixed sand and rubber layer prevents the sand from migrating substantially upwards to the top layer due to vibrations from surface game activities. The lighter weight and larger particle rubber will rest on the smaller and heavier sand particles. Due to the smaller size and denser density of sand particles compared to rubber particles, sand particles fall downward in the interstices between the larger rubber particles under the influence of gravity and when carried along by the downward penetrating water. Local shocks and vibrations caused by surface activities such as impacts from bouncing balls and players' feet may cause some sand particles to move up in the intermediate mixing layer and into the top layer. The top layer of pure rubber will however remain substantially free of sand particles, since the sand particles are washed down by the action of the water draining through the top surface, which will return the sand particles to the middle layer. The relatively large voids between the large rubber particles allow smaller sand particles to fall downward under the influence of gravity and vibration.

The combined layers produce a resilient surface at lower cost and thinner thickness than prior methods. In contrast, a uniformly mixed infill layer tends to consolidate into a firm compact surface and if applied in a thick layer, it is highly elastic and costly. The present invention maintains its elasticity even when applied in the form of a thin layer because the top layer thereof is composed of pure rubber particles and the respective layers are not easily separated or tightly combined.

Depending on the sport or other desired use of the surface, the upper portion of the artificial band may extend upwardly from the top surface of the top layer by 0.25 inches (635mm) to 1 inch (25.40mm) to provide the appearance of grass blades and control the rolling of the ball during sports. The rolling characteristics of the ball during play can also be varied by varying the thickness and density of the grass blades strips extending across the top surface. Or by passing over the mounting surface with a rigid wire brush or other brush-like device to fiberize, separate, or fray the upper portion of these man-made strips in the field. Alternatively, the tape may be fiberized into several fiber tapes that are spread apart to produce a similar result, rather than a single tape that is fiberized in situ. Fiberization and multiple fibers have several advantages. The fibrillated surface has a slight elasticity similar to real turf and looks more like natural turf. The cruciform fiberized fibers contain the top layer of rubber particles while allowing the displaced rubber particles to return to their original position and allow water to pass therethrough for drainage.

Drawings

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

In order that the invention may be readily understood, 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 an installed artificial turf assembly showing a flexible sheet substrate with upstanding strips and a infill layer of multiple layers of hard sand and resilient rubber granules;

fig. 2 is a similar cross-sectional view showing the upper portion of the artificial band after brushing through a rigid wire brush to fibrillate the top of the band.

Detailed Description

Referring to fig. 1, the present invention relates to an artificial turf assembly comprising a pile fabric with an infill layer of particulate material laid on a supporting soil substrate to provide a playing surface. The fleece comprises a flexible sheet substrate 1, the substrate 1 being shown in this embodiment as a double layer scrim. A number of upstanding artificial strips 2 extend upwardly from the upper surface of the substrate 1. As shown in fig. 1, the strips 2 are tufted through the substrate 1, spaced row-to-row by a spacing W, and having a length L. The length is selected according to the depth of the infill and the desired resilience of the finished artificial turf assembly. A packed layer 3 of granular material fills the gaps between the upstanding strips 2 on the upper surface of the substrate 1. The particulate material may be selected from commonly available hard particles such as sand, small stones or other grades of particulate material and resilient particles such as crumb rubber.

The filling layer 3 is composed of a bottom layer 4, an intermediate layer 5 and a top layer 6. The bottom layer 4 is essentially composed of only hard sand particles laid directly on the top surface of the substrate 1. The intermediate layer 5 is composed of hard sand particles and elastic rubber particles mixed with each other. The mixture is selected on the basis that the weight ratio of hard and elastic particles is greater than 2: 1. The top layer 6 consists essentially only of elastic rubber particles. The upper portion 7 of the artificial band 2 extends upwardly from the top surface 8 of the top layer 6. The resulting artificial turf surface can be adapted for a variety of indoor and outdoor uses, such as: sports fields, horse races and casinos.

In order to lay a number of different layers, it is necessary to pass several times over the same area, first laying substantially pure sand and then laying a mixture of sand and rubber over the same area. After which it must pass through the area again and be laid with substantially pure rubber material. Known methods may be employed. For example, for sanding the sub-layer, a sand spreader may be used, after which the surface is brushed with a brush to lift the pile of the pile fabric and place the strip 2 in a substantially upright position before laying the second layer 5. After each layer is laid, the surface must be brushed with a brush and the strip raised into an upright position as shown in the figure.

A significant difference between the method of the present invention and the prior art is the laying of a plurality of individual layers, each layer having different characteristics. Of course, laying multiple courses involves more skill and time than laying a single thick course, however the advantage is significant and can be adjusted as explained above.

As shown in fig. 2, the upper part 7 of the artificial band 2 is preferably fibrillated after the third top layer 6 has been mounted, by brushing the surface, for example with a wire brush or other brush-like device. This operation bends the upper section 7 over the top surface 8, as can be seen by comparing fig. 1 and 2. The ends of the strip 2 are split, frayed or fibrillated to obtain the following advantages over the prior art. The covering of the fibrillated upper part 7 interweaves the ends into a loose network, which more realistically imitates the appearance of natural turf. The fibrillated curved ends are somewhat resilient due to their slight rise or looseness and more accurately mimic the resilience of natural turf as the ball bounces on the finished surface during play. The curved end portions simultaneously visually cover the rubber particles of the top layer 6, hold these rubber particles still and allow the displaced rubber particles to move back and forth between the top layer 6 and the upper side of the fiberising strip 2. By splitting or fiberizing the ends of the strip 2, water more readily penetrates the top surface 8 and drains through the bottom layer 4.

It will be appreciated that although the embodiments described herein relate to the use of hard sand particles and elastomeric rubber particles, other suitable materials may be used. All materials must be graded in size and elasticity to ensure that the different layers remain substantially distinct and separate. For example, the hard particles may be synthetic plastic particles, crushed slag, or any other hard particles that provide the desired drainage function. Water that seeps from the surface must rapidly flow through the top layer 6 and the middle layer 5 to the bottom layer 4. The substrate 1 may be a loose fabric or porous to allow water to pass rapidly between the top surface 8 and the underlying basal soil 9. Likewise, suitable resilient particles include rubber, vermiculite, cork, foam, black or colored EPDM rubber, and other relatively stable materials that do not degrade over time. The larger sized light colored rubber particles will remain on top of the filler layer and will reduce the warmth of the filler layer.

The tapes may comprise a mixture of multiple fibers and single tapes that are fiberized or left undisturbed in situ. Fine fibers cannot be laid on site because they are more easily damaged and sag more easily than coarse fibers, especially in high temperature environments. The combination of coarse and fine fibers or ribbons causes the ball to roll in a more predictable manner during play, depending on the resistance of the fibers to the ball. Varying the width and density of the strips in the turf also changes the rolling characteristics of the ball.

It has been found experimentally and empirically that the desired size of the hard particles is between 14 and 70 U.S. sieve size (1.4mm to 212 μm). For hard particles larger than 20 mesh size (850 μm), the user of the playing surface feels abrasive, while particles smaller than 70 mesh size (212 μm) tend to impede water penetration and adversely affect the drainage characteristics of the packed layer 3. Where the skin does not contact the surface and abrasion does not occur, larger size particles such as 14 mesh size (14mm) may be used. The sand is preferably washed to remove substantially all fines below the size of 70 mesh (212 μm). The cost of obtaining such sand can be higher than sand that has not been washed, however improved drainage characteristics and elimination of dust during drying are highly desirable. It is believed that the preferred size of the sand particles is between 20 and 50(850 μm to 300 μm) to avoid the risk of scratching and to provide excellent drainage characteristics.

The mixed intermediate layer has a specific weight ratio determined by the intended use. For example, in the case of sports fields, the preferred ratio of sand to rubber particles is greater than 2: 1, and, to reduce costs, this ratio may be increased to about 3: 1. Thus, the cost of the intermediate layer is reduced, since sand is generally much cheaper than rubber particles. Where higher or lower elasticity is required, the ratio may be varied as desired.

The elastomeric particles are preferably crumb rubber particles which are cryogenically ground to a size of between 10 and 30 U.S. sieve size (2mm to 600 μm). This selection of the relative sizes of the sand and rubber particles creates a gradual grading of the material between the bottom layer of pure sand 4 and the top layer of pure rubber 6.

These sand particles tend to remain in the lower region even under the action of shock and vibration because they are smaller in size and higher in density. The larger and less dense rubber particles will migrate towards the top of the filling layer 3.

The present invention thus recognizes that: there is a certain degree of movement in the dynamic system when the particles of the strip 2 and the infill layer 3 are disturbed by foot traffic and impacts acting on the surface during play. The top layer 6 of substantially pure rubber provides elasticity where elasticity is primarily required, where impact of the athlete's foot and falling objects can occur. Poor drainage occurs if the top layer 6 is too thick or lacks minimal sand mixed with rubber particles. Periodic brushing will remix enough sand with the rubber particles to continue capillary drainage. The substantially pure sand bottom layer 4 remains at the bottom of the infill layer due to its higher density and smaller size to provide the weight required to hold the pile fabric in place and to provide the necessary drainage capacity. The intermediate layer 5 of mixed sand and rubber particles acts as a buffer zone to keep the top layer 6 of pure sand and the bottom layer 4 of pure sand separated and to add a controlled degree of elasticity depending on the size and relative mixing ratio of the particle components.

As mentioned above, there is a significant disadvantage to having sand particles close to the top surface 8 for filling. Sand rubs more against the skin than rubber particles. If sand accumulates on the top surface 8, it is unsightly and dust or particle splash can be generated, which not only is unsightly, but can also contact and cause injury to the athlete's eyes. In the event that the surface is subjected to precipitation, the penetration of water down through the top layer 6 will tend to carry the sand particles with it, thereby washing the top surface 6 and causing the sand particles to relocate in the bottom layer 4 and the intermediate layer 5.

As shown in fig. 2, the fibrosis and flexing of the top 7 of the strip 2 will tend to retain or restrain the rubber particles of the top layer 6. As mentioned above, the present invention contemplates that some movement of the strip 2 and particles may occur due to the motion and movement of the foot.

The natural tendency of larger and relatively lighter rubber particles to migrate to the top and the complementary tendency of smaller and heavier sand particles to migrate to the bottom of the infill layer 3 are beneficial. By providing a pure rubber elastic top layer 6, the actually required elasticity is provided. Periodically brushing the top layer 6 will mix enough sand into the top layer 6 to maintain the drainage characteristics. Additional flexibility may be provided by varying the thickness or mixing ratio of the layers, if desired. In contrast, the prior art provides an overall homogeneous mixture, and the elastomeric particles located near the bottom of the layer provide a poorer elastomeric effect at the top of the surface.

The sand particles packed at the top surface, as mentioned above, create significant disadvantages including friction, dust and an unsightly appearance. In contrast, the present invention uses sand for the bottom layer to provide drainage and weight. When mixed homogeneously, elasticity is provided throughout where needed. When the different layers are filled, a better elasticity is felt at the top surface. When the rubber is mixed evenly throughout, more rubber is needed to achieve the same elastic feel at the top surface for filling the same thickness. The reduction in the amount of rubber reduces costs. Moreover, the overall thickness of the filling layer 3 can be reduced. The cost of the material is significantly less than the cost of a system that also provides the same degree of flexibility. For example, the top layer 6 may be fitted with a top surface area having a basis weight of 0.5-0.6 pounds per square foot or less, which has been found to be entirely sufficient for these applications. The upper portion 7 of the composite strip 2 may extend anywhere from 0.25 inches (6.35mm) to 1 inch (25.40mm) up from the top surface 8 of the top layer 6. It has been found that this length of the upper portion 6 provides a convincing, realistic turf-like appearance at a reasonable cost.

Claims (11)

1. An artificial turf assembly for mounting on a support substrate to provide a playing surface, the turf assembly comprising:

a pile fabric having a flexible sheet substrate (1) and a plurality of upstanding artificial strips (2) of selected length representing grass blades, the strips extending upwardly from the upper surface of the substrate; and

a packed layer (3) of granular material disposed in the interstices between the upstanding strips (2) on the upper surface of the substrate (1) and having a depth less than the length of the strips (2), the granular material being selected from the group consisting of: hard and elastic particles, characterized in that the filling layer comprises:

a bottom layer (4) consisting only of hard particles disposed on the top surface of the substrate;

an intermediate layer (5) consisting of hard and elastic particles mixed together in a selected relative weight ratio, which is arranged on the bottom layer (4); and

a top layer (6) consisting only of resilient particles arranged on the intermediate layer (5), the upper part (7) of the artificial band extending upwards from the top surface of the top layer.

2. A synthetic turf assembly according to claim 1 wherein the relative weight ratio of hard to resilient granules is greater than 2: 1.

3. A synthetic turf assembly according to claim 1 wherein the hard particles are sand particles having a size of between 1.4mm and 212 μm.

4. A synthetic turf assembly according to claim 3 wherein the sand particle size is between 850 μm and 300 μm.

5. A synthetic grass turf assembly according to claim 3 or claim 4 wherein the sand is washed to remove all fines below 212 μm in size.

6. A synthetic turf assembly according to claim 1 wherein the resilient granules are crumb rubber granules having a size of between 2mm and 600 μm.

7. A synthetic turf assembly according to claim 2, characterised in that the weight ratio of hard particles to resilient particles in the intermediate layer (5) is 3: 1.

8. A synthetic turf assembly according to claim 1, characterised in that the top layer (6) has a top surface area mounted with a unit weight of up to 2.93kg per square metre.

9. A synthetic grass turf assembly according to any one of claims 1 to 4, characterised in that the upper part of the synthetic ribbons (2) is fiberised in situ.

10. A synthetic grass turf assembly according to any one of claims 1 to 4, characterised in that each synthetic strip (2) comprises a plurality of fibres having an upper portion which is curved downwards.

11. A synthetic grass turf assembly according to claim 1, characterised in that the upper part of the synthetic ribbons (2) extends upwards from the top surface of the top layer (6) by 6.35mm to 25.40 mm.