EP1853765A1

EP1853765A1 - Artificial turf structure with granular infill

Info

Publication number: EP1853765A1
Application number: EP06723263A
Authority: EP
Inventors: Albertus Otto Dozeman; Mario Martinus Johanna Smit; Bart Gerardus Christiaan Johannes Wijers
Original assignee: DSM IP Assets BV
Current assignee: SoFTer SpA
Priority date: 2005-03-01
Filing date: 2006-03-01
Publication date: 2007-11-14
Also published as: WO2006092337A1

Abstract

The present invention relates to an artificial turf structure comprising a backing sheet provided with fibres of a selected length, the fibres extending upwardly from the upper surface of the backing sheet and an infill layer of a particulate material disposed between the upstanding fibres upon the upper surface of the backing sheet characterized in that the particulate material comprises a granulate having a cylindrical shape with a length/diameter (UD) ratio between 0.8-1.2 and having a substantial uniform particle size.

Description

ARTIFICIAL TURF STRUCTURE WITH GRANULAR INFILL

The present invention relates to an artificial turf structure comprising a backing sheet with an upper surface provided with synthetic fibres of a selected length, the fibres extending upwardly from the upper surface and an infill layer of a particulate material disposed between the fibres The present invention further relates to the use of a granulate having a defined shape as infill material in an artificial turf structure. Artificial turf structures made of synthetic fibres connected to a backing sheet and infill material dispersed between the fibres is for example known from EP-A-1389649. As infill layer a granular material is disclosed with a grain size smaller than 5 mm. A disadvantage of this turf structure is that the granules compact together and are sticking together after several months. Other prior art artificial turf structures comprising e.g. rubber and sand infill also are not able to provide permanent good long term properties because of compaction of undefined shaped rubber particles and sand infill material, which results in a decrease of shock absorption and vertical deformation and an increase of the traction and vertical ball bounce. The problem of compaction is for example disclosed in WO-A-0198589, which describes an artificial turf structure based on a multilayer infill composition comprising a base layer of a mixture of hard and resilient granules and a top layer of exclusively resilient granules. The resilient granules are preferably crumb rubber particles having several grain sizes between 0.5-2.00 mm. The granules are substantially spherical and defined in terms of the Krumbein standard with a sphericity in the range of 0.5-0.99 to prevent compaction and to improve drainage. This multilayer infill has the disadvantage that it comprises at least two layers thereby making the construction of the artificial turf structure uneconomical. Despite the construction a further disadvantage is that the desired level of properties as for example shock absorption, vertical deformation, traction and vertical ball rebound is not reached and that the artificial turf structure still not provides the performance of natural turf.

The object of the present invention is to overcome the above stated drawbacks and to provide an artificial turf structure, which reproduces the characteristics of a natural turf system for football or rugby, as required in respectively the FIFA 2 star (1 July 2004) and IRB regulations (April 2004) on artificial turf and which provides permanent good long term properties.

The object of the present invention is achieved in that the artificial turf structure comprises as particulate material a granulate having a cylindrical shape with a length/diameter (UD) ratio between 0.8-1.2 and having a substantially uniform particle size.

In the present invention it has been found that the uniform size and shape of the infill granules significantly affect the turf performance characteristics such as shock absorption, vertical deformation, vertical ball bounce and traction.

Surprisingly an artificial turf structure has been found comprising a granulate with a specified particle shape and size as infill material, that reproduces as faithfully as possible the characteristics of a natural turf system as applied for football or rugby. Even on the long term these characteristics are still fulfilling the FIFA two star requirements on shock absorption, vertical deformation, vertical ball bounce and traction.

The artificial turf structure of the present invention fulfils the FIFA two star requirements and IRB requirements on shock absorption, vertical deformation, vertical ball bounce and traction imposed for an artificial turf system. These standards reproduce the characteristics of natural turf football or rugby. In particular, the artificial turf structure according to the present invention complies with the required specifications for shock absorption, vertical deformation, traction and vertical ball bounce. Moreover these properties still comply with the required specifications on the long term, which is proved by testing the turf system after 5000 cycles on a lisport test. The Lisport test is a standard procedure within the requirements of FIFA and the IRB.

Good long term properties may be further supported by ageing tests of the infill granulates itself, which show no change in intrinsic material properties after oxidation and UV-resistance tests.

A further advantage of the artificial turf structure according to the present invention is that no other infill or shock-absorbing layer such as an e-layer or lava-rubber mixture is required as a sub-base.

Still another advantage of the present invention is that the specific choice of particulate infill granulates include an excellent behaviour in an artificial turf structure when slidings are performed during a football game. Another advantage of the present invention is that the particulate infill granules do not form dust after 5000 cycles on a Lisport test.

A packed structure is reached directly after installation and is stable during the service life of the artificial turf. However, the particles are loose enough to move under influence of a force. This results in a constant open structure of the infill layer, which is responsible for the natural turf character. In the top layer of the infill, the granules are still free to move, which means that the studs of the player shoes can penetrate into the turf system, even after years. This is a very important advantage, because it contributes to the grip of the football shoe and therefore provides a natural turf feeling. The granules have a length/diameter (L/D) ratio between 0.8-1.2, preferably a L/D ratio between 0.9-1.1 and more preferably a L/D ratio about equal to 1. This ratio leads to the most stable performance during time. L/D ratio's below 0.8 or above 1.2 lead to more open structures directly after installation, which may on the longer term lead to compaction. Compaction results in a significant decreasing shock absorption and vertical deformation and in an increasing vertical ball bounce and traction.

The L/D ratio is a typical indication for cylindrical shaped particles. The length and the diameter are defined as can be seen in figure 1.

The unique characteristic of the shape and the uniform size of the granules of the present invention is that the granules are immediately searching for a packed structure. This packed structure is reached directly after installation and is stable during time because it cannot compact more than this. However, the particles are loose enough to move under influence of force. This results in a structure of the infill layer, which is responsible for a natural turf character. The extend to which a structure is packed can be expressed in terms of its relative density PR, being defined as the ratio of the bulk density (pβ) of the granulate and the specific density of the granulate (p_s). Preferably the relative density of the granulate is at least 0.5, more preferably at least 0.55 and most preferably at least 0.60. The bulk density of the granules measured in accordance with NEN-ISO 60 (1978) is generally between 0.5 and 1 , for materials with specific gravities of betweeni and 1.5 kg/dm³.

The particle size of the granules is for example between 1 and 4 mm. Preferably betweeni and 2.5 mm. More preferably between 1.2 and 2.2 mm. Even more preferably the particle size is between 1.5 and 2.1 mm. Most preferably the particle size is between 1.6 and 2.1 mm. It has been found that the particle size below 1mm has a negative influence on the drainage. A particle size above4 mm has a negative influence on the homogeneous distribution of the granules between the fibers.

The particle size of the granules is substantial uniform. A substantial uniform particle size is understood to be a particle length L having a relative standard deviation (ΔL/L) of less than 0.5, preferably less than 0.3, more preferably less than 0.15, wherein ΔL is the standard deviation of the length L. The more uniform the particle size is, the better the shock absorption, vertical deformation and vertical ball bounce and traction. The granules are for example manufactured of plastomers, vinyl based polymers, polyolefin based polymers, reactor TPO's, thermoplastic elastomers or dynamically vulcanised thermoplastic elastomers. Preferably the granules are manufactured from a vinyl based polymer, a thermoplastic elastomer or a plastomer or mixtures thereof.

Examples of plastomers are ethylene/alpha-olefin copolymers with a density of less than about 0.93 g/cm³ at a molecular weight (Mw) greater than about 20.000. Examples of ethylene/alpha-olefin copolymers include ethylene/1 -butene, ethylene/1 -pentene, ethylene/1 -hexene, ethylene/1 -octene, and ethylene/2- norbornene. Commercially available copolymers are for example EXACT™ or ENGAGE™. Examples of vinyl-based polymers are styrene-isobutylene-styrene (SIBS), styrene-isobutylene (SIB), styrene-ethylene-butylenes-styrene polymers (SEBS) or styrene-butadiene-styrene polymers abbreviated as (SBS) or ethylene vinyl acetate (EVA). Preferably SEBS is used as vinyl based polymer. Examples of polyolefin-based polymers are polyethylene, polypropylene or metallocene polymerised polyolefinics. Reactor TPO's are commercially available for example under the trade name Hifax®. Examples of thermoplastic elastomers are polyurethanes or polyethersters or polymers comprising a thermoplastic and a rubber. The thermoplastic may be chosen from polyethylene or polypropylene homo-or copolymers and polyisobutylene. The rubber may be chosen from ethylene-propylene copolymers, hereinafter called EPM, ethylene-propylene-diene terpolymers, hereinafter called EPDM, natural rubbers, styrene-butadiene rubber (SBR), nitrile-butadiene rubbers (NBR), polyisoprene, butyl rubber or halogenated butyl rubber. The rubber may be dynamically vulcanised by the use of a cross linking agent such as sulphur, sulphurous compounds, metal oxides, maleimides, siloxane compounds for example hydrosilane or vinylalkoxysilane, phenol resins or peroxides. In case of dynamic vulcanisation the thermoplastic and the rubber are subjected to kneading or to other shear forces in the presence of the cross linking agent at temperatures between for example 140 and 300° C until the rubber is at least partially vulcanised.

Preferably the granules are made of a thermoplastic elastomer for example Terra XPS™ which is commercially available by DSM DTE. Most preferably the granules are made of a dynamically vulcanised thermoplastic elastomer or a vinyl- based polymer. The above polymers may be mixed with each other as long as the shore A hardness of the mixture is between 45-90.

Depending on the polymers used for the manufacturing of the granules, the granules according to the present invention may also comprise for example reinforcing and non-reinforcing fillers, plasticizers, antioxidants, UV-stabilizers, antistatic agents, waxes, foaming agents, lubricants or flame retardants as described in for example the Rubber World Magazine Blue Book. The granulate may include a suitable pigment and can be provided in any colour. Preferred is a lighter colour for example a brown, green, or beige colour because if a lighter colour is used sun light is more reflected which results in a lower temperature of the pitch.

Examples of fillers are clay, talc, CaCO3. Examples of plasticizers are aromatic, naphtalenic or paraffinic oil, preferably oil with a low aromatic and sulphur content. An example of an UV stabiliser is a HALS compound. The granules according to the present invention may be manufactured by microgranulation of the extruded melt through a die plate with a diameter of holes in the range of 0.8 to 2.5 mm. For example the micro granulation can be conducted with commercial available underwater pelletizers.

The thickness of the infill layer comprising the particulate material is for example between 10-30 mm, preferably between 20 and 25 mm. Not necessary but possible a layer of sand may be used having a thickness up to 15 mm.

The backing sheet may consist of a sheet of plastic material such as, for example, a non-woven fabric, which is impregnated with for instance latex, such as for example SBR latex. Extending upwardly from the upper surface of the backing sheet a large number of upstanding fibres is present. The length of the fibres is selected depending upon the depth of the infill material and the desired resilience of the completed artificial turf structure. The depth of the infill layer is less than the length of the fibres. The length of the fibres is for example below 50 mm. Preferably the length of the fibres is below 45 mm.

The fibres are preferably synthetic fibres composed of polyethylene, polypropylene or nylon. The fibres are for example single fibres or multiple fibres but also a mixture of multiple fibres and single fibres may be used. The thickness of the fibres may vary. However also a mix of thick and thin fibres is possible. This causes a ball to roll in a more predictable manner depending on the resistance of the fibres to the ball during play. However the general criteria for making the backing sheet and the fibres are known in the art, and hence do not require a detailed description. During its lifecycle the artificial turf structure must stand extremely high forces and pressures. As the infill material takes care of the most of these forces, it must be of enough strength to prevent permanent deformation and/or "melting" of the granules together. ISA Sport has developed a special test in which an amount of infill is pressurized at 2 N/mm2 for 72 hrs. After this time, the pressure is released and it is checked if the infill granules are still loose from each other and return back in their original shape.

Because most of the artificial turf structures are in direct contact with raining water and the ground, all materials or components, which are applied for the construction of an artificial turf structure, must be absolute safe towards the environment. Therefore the artificial turf industry has a big responsibility to use or apply only materials which contain no hazardous ingredients or, at least, no hazardous materials are leaching during time. Only this way, problems of pollution of ground, ground water of surface water can be avoided. In this test the material is brought into contact water, to simulate the leaching of material as a results of raining water. At the end of the test the water is analysed and checked on heavy metals and toxic materials. If these materials are found and exceed maximum concentration, it means that pollution of the ground and/or groundwater can be expected which can cause problems on short or long term. This test is also subscribed by UEFA and DIN 18035-7. The present invention further relates to the use of a granulate with binder systems, such as polyurethane, as anti-slip floorings for example in boats or swimming pools, floorings for housing and commercial area's, as shock absorbing material in running tracks for horses, for tennis courts, for football or rugby turf pitches, for recreation and playing area's or for athletics tracks. The present invention further relates to the use of a granulate having a defined shape as infill material in artificial turf structures. The description of the granulate is given above. The added value of the shape of the granules is further supported by an experiment in which an infill layer of specific infill material is installed without an artificial pitch. The granulate according to the present invention may be used in e- layers or shock pad's, safety tiles for recreation and playing area's but may also be used as infill material in artificial turf pitches for American football, artificial turf pitches for korfball, artificial turf for landscaping, artificial turf golf courses, artificial turf pitches for hockey. Moreover it can be used in safety artificial turf as infill between the of artificial turf system and recreation and playing area's or in artificial turf tennis courts as infill material between the artificial turf fibres.

Recently the FIFA has issued the FIFA Artificial turf regulations, which describe test methods for assessing an artificial turf structure or the infill material for artificial turf structures. The test methods are limited to those that are relevant for football and for example include shock absorption of the surface, vertical deformation of the surface under load, rotational resistance, ball rebound and ball roll. FIFA's accredited test institutes are published on www.fifa.com.

Force reduction is a measure for the shock absorbency of a field. The force reduction is measured in accordance with the Football-Related Technical

Requirements of the UEFA, by dropping a falling weight of 20 kg with a hard striking surface on a concrete surface and on a test piece of an artificial turf surface, whereby the forces measured between the ball and the concrete (F_max (co_nc_rete) ), respectively the artificial turf surface (F_masX(testpiece)) are measured. The Force reduction is then calculated from the expression:

FR= (1 - Fmasxftestpiecs/ F_max (concrete))- 100%

The test method is referred to in the FIFA test manual and the specification is between 60 and 70%. According to the present invention the shock absorption of the artificial turf structure is at least 60%.

Vertical deformation is determined by allowing a mass to fall onto a spring that rests, via a load cell and test food, on to a test specimen and the deformation of the surface under standard force is measured. The test method is referred to in the FIFA test manual and the specification is between 4 and 8 mm. The vertical deformation of the artificial turf according to the present invention is found to be between 4-8 mm.

Rotational friction is determined by measuring the torque that is required to rotate a loaded studded disk in contact with the top surface of the specimen. The test method is referred to in the FIFA test manual and the specification is 30-45Nm. The rotational friction of the artificial turf structure according to the present invention is found to be between 30-45 Nm.

Ball rebound is determined as follows: a FIFA test ball is released from 2 m above the surface of the specimen and the height of the rebound from the top surface is calculated. The specification is 60-90 cm. The ball rebound of the artificial turf structure according to the present invention is between 60-90 cm.

A Lisport test stands for two cylinders with described positioned studs, which are moving with friction over a test piece of the turf system. One of the two cylinders is running with the same speed as the driving speed and the other cylinder is moving faster or slower, therefore causing a certain friction. After 5000 cycles (one way and back) the turf system is abraded to an equivalent of more then 5 years. With this test the abrasion resistance of the fibres and infill material can be checked, but also the amount of compaction of the infill material (see figure 2). The invention will be illustrated by the following examples without being restricted thereto.

Example 1

An artificial turf structure was construed as follows, a carpet like pile fabric provided with upstanding artificial fibres representing turf blades (number of fibres per square meter was 8820). The length of the fibres was 45 mm. Then a layer of

Terra XPS 1001 01 as infill material was applied (weight per unit area 10 kg/m²). The average diameter of the granules was 2 mm and the length was 2 mm (L/D=1).

The thickness of the infill layer of the particulate material was 12.5 mm. Also a sand layer of 12.5 mm was applied as infill material. The distance between the top surface of the infill layer and the top surface of the turf blades was 20 mm.

The results are presented in table 2, wherein FFD denotes the Force reduction measured with the Flat Food of the Berlin Athlete Test under Dry circumstances. The support for carpet and infill system was either a concrete floor (indicated with concrete) or a sub-base of 20 cm sand + 10 cm stabilised lava stones of

0 - 16 mm (indicated with lava. The FIFA one and two star requirement are indicated with FIFA^* and FIFA^** respectively.

As is clear from the results in table 2, the artificial turf structure complied with all the requirements of the FIFA one star, on shock absorption, vertical deformation, traction and vertical ball bounce as set out in the FIFA test manual.

Example 2

An artificial turf structure was construed as explained in example 1 with the difference that no sand infill layer was used. A layer of Terra XPS 1001 01 infill material was applied (weight per unit area 15 kg/m²). The average diameter of the granules was 2 mm and the length was 2 mm (L/D=1). The thickness of the infill layer of the particulate material was 22.5 mm.

As is clear from the results in table 2, the artificial turf structure complied with all the requirements of the FIFA two star on shock absorption, vertical deformation, traction and vertical ball bounce as set out in the FIFA test manual.

Example 3 An artificial turf structure was construed as explained in example 2. A layer of Terra XPS 1001 01 infill material was applied (weight per unit area 20 kg/m²). The average diameter of the granules was 2 mm and the length was 2 mm (L/D=1). The thickness of the infill layer of the particulate material was 30 mm. As is clear from the results in table 2, the artificial turf structure complied with all the requirements of the FIFA two star on shock absorption, vertical deformation, traction and vertical ball bounce as set out in the FIFA test manual.

Comparative Experiment I

An artificial turf structure was construed as explained in example 4. A layer of Terra XPS infill material was applied (weight per unit area 20 kg/m³' ). The average diameter of the granules was 2 mm and the length was 4 mm (L/D=2). The thickness of the infill layer of the particulate material was 30 mm.

As is clear from the results in table 2, the turf system characteristics are decreased significantly after 5000 cycles at the lisport test due to compaction of the infill material, which is proved by the lower shock absorption and vertical deformation.

FIBRE SYSTEM: Monofilament

FIBRE HEIGHT: 45 mm.

STITCHES/WEIGHT: 8820/m² 1540 gr./m²

SAND INFILL 0 mm

ELASTOMER INFILL TYPE Terra XPS L/D = 2

ELASTOMER INFILL (kg/m2) 20

ELASTOMER INFILL (mm.) Measured: 30 mm.

SHOCK PAD No Comparative Experiment Il

An artificial turf structure was construed as explained in example 4. A layer of Terra XPS infill material was applied (weight per unit area 20 kg/m² ). The average diameter of the granules was 2 mm and the length was 1 mm (UD=O.5). The thickness of the infill layer of the particulate material was 30 mm.

Example 4

The shock absorption was measured in accordance with the UEFA standard for the Force Reduction on in an artificial turf system as described in Example 2 comprising Terra XPS granules with different L/D ratio's and compared with EPDM and grounded rubber of car tires.

The results in table 1 show that Terra XPS with an L/D ratio between 0.8 and 1.2 resulted in the highest Force Reduction.

Table 1

Table 2

Claims

CLAlMS

I . Artificial turf structure comprising a. a backing sheet with an upper surface provided with fibres of a selected length, the fibres extending upwardly from the upper surface and b. an infill layer of a particulate material disposed between the fibres, characterized in that the particulate material comprises a granulate having a cylindrical shape with a length/diameter (UD) ratio between 0.8-1.2 and having a substantial uniform particle size.

2. Artificial turf structure according to claim 1 characterised in that the relative standard deviation of the length of the granulate is less than 0.15.

3. Artificial turf structure according to any one of claims 1-2 characterised in that the granules have a particle size between 1 and 2.5 mm.

4. Artificial turf structure according to any one of claims 1-3 characterised in that the granules have a relative density of at least 0.5.

5. Artificial turf structure according any of the claims 1-4 characterised in that the granulate is manufactured from a vinyl based polymer, a thermoplastic elastomer or a plastomer.

6. Artificial turf structure according to claim 3 characterised in that the thermoplastic elastomer is dynamically vulcanised.

7. Use of a granulate having a cylindrical shape with a length/diameter (L/D) ratio between 0.8-1.2 and having a substantial uniform particle size as infill material in an artificial turf structure.

8. Use of a granulate according to claim 7 characterized in that the granules have a relative density of at least 0.5.

9. Use of a granulate according to any one of claims 7-8 characterised in that the granules have a particle size between 1.5 and 2.1 mm

10. Use of a granulate according to any one of the claims 7-9 characterized in that the granulate is manufactured from a vinyl based polymer, a thermoplastic elastomer or a plastomer.

I 1. Use of a granulate according to claim 10 characterized in that the thermoplastic elastomer is dynamically vulcanised.