FIELD OF ARTIFICIAL GRASS AND FIBRE MATERIAL INTENDED FOR SUCH A FIELD OF ARTIFICIAL GRASS

Abstract: An artificial grass field consisting of a substructure construction and a carpet of synthetic fibres provided thereon, with a layer of sand distributed between these fibres, whereby the carpet of synthetic fibres consists of frizzed fibres and the fibres are provided, at least partly and in any case their upper parts, with a coating film of an elastic material which reduces the coefficient of friction and which at the same time extends the power of recovery of the fibre.

Description: The invention relates to a field of artificial grass consisting of a substructure construction and provided thereon a carpet of synthetic fibres with a sand layer distributed between said fibres. The invention also relates to the fibrous material which obviously is intended for being processed into a mat for the field of the intended artificial grass. Such a field of artificial grass has been known for several years and is described in the British patent specification 1,528,264 published in 1978. Further improvements thereon have been disclosed in US patent specification 4,337,283 published in 1982, also in the name of F.T. Haas. That US patent mentions as background of the art that the solution for laying a field of artificial grass with a certain damping power may be found in the specific substructure. The solution that is offered according to that US patent is that in the sand filling between the fibres a granular,elastic material such as cork, rubber or a certain polymer has been incorporated. The German patent application 3,204,215 relates to a field of artificial grass whereby sand is strewn in in several layers, whereby the grain size of the sand decreases from the lower level to the upper level. The first developed fields of artificial grass were intended for tennis and golf whilst the later fields of artificial grass could be used for playing hockey. The requirements made in connection with a field of artificial grass strongly depend on the purpose aimed at or which sport is to be practised on such a field. The field must be flat, well pervious to water and resistant to moisture, to fluctuations in temperature and to ageing, it must be colour fast and resistant to ultraviolet rays. Furthermore the field of artificial grass should have a damping power which is in relation to the sport to be practised. A hockey field e.g. can thus have a smaller damping power than a soccer field, where a smaller damping power means that the field has a harder feeling. With soccer more jumps and slidings are made, whereby a field with little damping may form a load being too heavy for certain muscles. However the damping power of a field of artificial grass is mainly determined by the substructure construction. Proceeding on the proposition that by a certain substructure construction the desired damping power can be achieved for the entire construction of the field of artificial grass for practising the game of soccer thereon, the present patent application is directed to the artificial grass itself. The first fields of artificial grass which were not strewn in with sand contained more fibrous material per square metre and had the disadvantage that they were comparatively costly and that the sportsman could sustain burns when making falling or sliding movements as a result of the local high rise in temperature on those parts of the body making the sliding movement across the artificial grass. Consequently it is necessary for such fields of artificial grass to be sprayed with water regularly. This disadvantage has overcome to a large extent with the fields of artificial grass that are strewn in with sand. In this way cheaper fields of artificial grass were obtained and it was no longer necessary to spray them.Nevertheless the risk of sustaining injuries as a result of burning or grazing remained greater than with a field of natural grass, which risks however were acceptably low with hockey, because in hockey substantially fewer sliding are made than in soccer. In spite of the fact that for the soccer field more severe requirements are made for an artificial grass field than with practising the game of hockey it is to be expected that a field of artificial grass strewn in with sand can be used for 2000 hours per year, which will be a factor 8 higher than t he use of a field of natural grass. Also it will be possible to reduce the cost of maintenance by a factor 5 - 10, which can make it very attractive to install fields of artificial grass for practising the game of soccer. It will be necessary then to meet the demand that the movements which a soccer player can make on a field of natural grass are also possible on an artificial grass field without the risk of sustaining injuries increasing. This objective has now been reached with a field of artificial grass according to the invention as mentioned in the preamble and it is characterized in that the carpet of synthetic fibres consists of curled or frizzed fibres, whereby the fibres are provided, at least partially and in any case at their upper parts, with a coating film of an elastic material which reduces the coefficient of friction and at the same time extends the power of recovery of the fibre. By providing the curling in the synthetic fibre the upper surface of the mat of synthetic fibres will form a partial covering of the layer of sand as a result of which the carpet of artificial grass will get a more voluminous character. The strewn-in sand will make the mat containing synthetic fibres heavier so that the mat will remain fixed on the substructure construction and the synthetic fibres will remain upright, also when a kicking movement or sliding movement is made or when the sportsman lands after a jump. The film of the elastic solid substance ensures that the fibre will keep its elastic properties longer and is not non-slipping. The frizzing or curling can be provided in the fibre in various manners, e.g. by knitting - deknitting. The frizzing provided is such that the length of the fibre is reduced by 20 - 40 %. From the Dutch patent application 6709109 there is known a method for frizzing yarn, but said yarn is used for making carpets or clothing. No indication is given, however, for using such frizzed fibres for fields of artificial grass. The sand which grazing effect is avoided as much as possible, which can be achieved by choosing sand with a round shape of grain, is provided to such a height that the frizzed fibre protrudes to a length of 2 - 8 mm from the layer of sand, whilst the entire length of pile of the frizzed fibre is 20 - 28 mm. The sand is preferably quartz sand which particles are round and comparatively soft, for the most part having a grain size of 0.2 - 0.6 mm. The fibres are provided in a ground foil or tuft cloth pervious to water and on a soccer field about 25 - 28 kg of sand per square metre are provided. By the combination of frizzing in the fibre and the provision of a coating of an elastomeric material around the fibre a field of artificial grass has now been obtained on which the sliding during the game of soccer can be made with the same effect as on a field of natural grass. An example of a material to be used for reducing the coefficient of friction is silicone oil. Providing said silicone oil on the fibre takes place e.g. by spaying the oil, whether or not in a solvent, and then allowing it to dry, possibly while being heated, to 120 °C so that a solid elastomeric film is formed. To stimulate the formation of a solid material from silicone oil the mixture comprising silicone oil can also contain additives such as curing agents and equalizing agents. This reduces the coefficient of friction so that sliding across the surface is facilitated. On the other hand the static coefficient of friction remains sufficiently high because of the strewn-in sand, as a result of which the player maintains sufficient grip on the field. Because of said combination the risk of injury by burning or grazing is minimized. The use of a silicone oil as a lubricant in liquid condition, by providing said lubricant with water on a dry ski run, is known from the French patent applicaiton 2,238,805, but in that manner an artificial ski run is obtained. Also from the German patent application 2,553,529 the use of a sil icone oil as a lubricant is known for preparing an ice-rink. With the present method, however, a solid film of an elastomeric material is formed around the synthetic fibre which on the one hand reduces the coefficient of friction but on the other hand also makes the fibres maintaining the elastic power for a longer time. Instead of a silicone oil which is polymerized on the fibre it is possible to use other elastomeric materials such as an acrylic elastomer and a polyurethane elastomer. Such a coating on the fibres for an artificial grass field can also be successfully provided with non-frizzed fibres such as used for e.g. a hockey field, because it has become apparent that such a coating keeps the fibres in better condition, so that the change of signs of ageing is minimized. With fields of artificial grass for various purposes it may be advantageous, therefor, to provide the fibre, or at least that part which protrudes from the layer of sand, with such an elastomeric coating in order to prevent/delay the ageing process.Consequently the invention also relates to fields of artificial grass whereby a non-frizzed fibre is used,but whereby the fibre material is still provided, at least partly, with such a coating film. For practising the game of soccer on a field of artificial grass a construction has now been obtained whereby the synthetic fibres protruding from the layer of sand show a "voluminous" surface as a result of the use of comparatively long fibres which length has been reduced to 20 28 mmm by frizzing. Because of the coating provided thereon the dynamic coefficient of friction is lowered and the ageing process, which manifests itself in the extra formation of fibrils at the outer end of the fibres, is prevented as much as possible and the field of artificial grass preserves its elasticity better than with fields of artificial grass composed of fibres without the filmlike coating. According to a preferred embodiment of the method according to the invention polypropylene fibres having a pile length of about 35 mm are frizzed to a length of 22 mm, whereby approximately 16,000 piles are provided per square metre. The fibres are passed through a tuft cloth, also made of polypropylene, with a joint weight of approximately 1.2 kg/m². The fibres are provided with a thin film of silicone oil for which purpose 50 - 100 cc of oil, possibly diluted with an aqueous solution, is provided per square metre of artificial grass. Of course it will also be possible to provide the polypropylene fibres with the coating film before the fibres are passed through the tuft cloth. After the oil has been provided it becomes elastomeric by hardening the fibres under surrounding-circumstances so that an elastomeric, well-adhering film is formed around the fibres. The oil may also be provided at a later stage when the field of artificial grass has already been played on, so that this treatment can also be carried out as maintenance-treatment. On a thus obtained artificial grass field a sliding can be made in a natural manner and the risk of burning and grazing is reduced to a minium. Such a field of artificial grass meets the requirements made for a soccer field, whereby the present field of artificial grass can be used more often and at lower costs of maintenence than a natural soccer field.

Claims: 1. An artificial grass field consisting of a substructure construction and a carpet of synthetic fibres provided thereon, with a layer of sand distributed between these fibres, characterized in that the carpet of synthetic fibres consists of frizzed fibres and the fibres are provided, at least partly and in any case their upper parts, with a coating film of an elastic material which reduces the coefficient of friction and which at the same time extends the power of recovery of the fibre. 2. The artificial grass field according to claim 1, characterized in that the frizzing is such that as a result of the frizzing t he length of a fibre is reduced by 20 - 40 % relative to its extended condition. 3. The artificial grass field according to claims 1 - 2, characterized in that the frizzing is carried out by a knitting - deknitting operation. 4. The artificial grass field according to claims 1 - 3, characterized in that the length of pile of the fibre in frizzed condition amounts to 20 - 28 mm. 5. The artificial grass field according to claims 1 - 4, characterized in that the layer of sand is strewn in to such a height that the fibres protrude from the layer of sand to a length of 2 - 8 mm. 6. The artificial grass field according to claims 1 - 5, characterized in that the strewn-in sand is quartz sand which particles for the most have a grain size of 0.2 - 0.6 mm. 7. The artificial grass field consisting of a substructure construction and a carpet of synthetic fibres provided thereon, with a layer of sand distributed between said fibres, characterized in that non-frizzed fibres from which the carpet is built up are provided, at least partially and in any case their upper parts, with a coating film of an elastic material which reduces the coefficient of friction and which at the same time extends the power of recovery of the fibres. 8. The artificial grass field according to claims 1 - 7, characterized in that at least that part of the fibres which protrudes from the layer of sand is provided with a coating film. 9. The artificial grass field according to claims 1 - 8, characterized in that the film material is a silicone oil which hardens after having been applied. 10. The artificial grass field according to claims 1 - 8, characterized in that the film material has been chosen from an acrylic elastomer and a polyurethane elastomer. 11. A fibrous material obviously intended for being used for an artificial grass field, characterized in that the fibres are provided with a coating according to claims 1 and 8 - 10 and are possibly frizzed or curled as disclosed in claims 2 - 7.

Inventors: TRANOY ROLAND ACHIEL OCTAAF
Applicants: TAPIJTFABRIEK H. DESSEAUX N.V.
Application year: 1987
Main classification: E01C13
IPC codes: E01C13