FIELD OF THE INVENTION

The invention relates to an artificial turf suitable for use as a sports surface. The invention further relates to a method for manufacturing an artificial turf.

BACKGROUND OF THE INVENTION

Artificial turf systems generally consist of a backing, a large number of artificial grass fibers attached to the back ^¬ ing, and a thick infill layer distributed on the backing between the grass fibers. The artificial grass fibers, which can be tufted or knitted to the backing or co-woven therewith, protrude substantially perpendicularly to the backing. These artificial grass systems generally have a granular infill layer of rubber granules, sand, or both. Sand is used for stabilization of the turf and elastic material is used to endow the turf with elas ^¬ ticity.

Depending on the circumstances of use, an artificial turf sports field can be exposed to moisture and temperature variations, UV light and abrasion due to the use of the field. Problems associated with known artificial turfs include wear and fibrillation of the grass, as well as low elasticity of the turf. The use of granular infill in an artificial turf system has a number of drawbacks. Not only is the installation of such an artificial turf sports field more labour-intensive, but an artificial turf system comprising granular infill material requires regular maintenance also after it has been installed.

In the past years a number of non-granular infill sys- terns have been introduced as alternatives to artificial turf systems comprising granular infill material.

US 6753049 B2 discloses an artificial turf having fi ^¬ brous, inherently damping material arranged between artificial grass blades and connected to the backing or the blades. The fi- brous material can be arranged in the form of blades connected to the backing, or it can also take the form of a knit through which the artificial grass blades protrude and which can be formed integrally with the backing. US 6955841 B2 discloses an artificial grass lawn with a base layer comprising a material having damping properties. The damping material can be in the form of a damping mat which is fixed to the base layer by means of artificial grass fibers. The damping material can be made of rubber or a synthetic foam prod ^¬ uct can be used.

US 8557363 B2 discloses an artificial grass turf carpet having a base layer comprising a plurality of synthetic base layer fibers attached to the ground structure and positioned be- tween upstanding synthetic grass fibers. The base layer fibers are positioned so tight against one another and against adjacent grass fibers to provide a tightly packed base layer above which the grass fibers extend.

Drawbacks of the prior art are that the known damping materials are not sufficiently wear-resistant. As a consequence, the turf may have to be fixed or replaced after a relatively short time. Also, the elasticity of known damping base layers is reduced quite rapidly.

The normally used pile yarns are relatively thin and therefore the base fibers have to be tightly packed in order to allow the layer to withstand the weight of the players and to sufficiently stabilize the turf. This is because the current production methods for artificial turfs are not readily suitable for tufting or weaving yarns above certain thickness. Tightly packed base layer fibers do not allow the studs of a football shoe to penetrate into the base layer. Instead, the grip of the football shoes on the turf is poor thus causing a danger of injury to the players.

The inventors have therefore recognized the need for a new type of artificial turf comprising non-granular damping material having improved elasticity, stability and wear- resistance .

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new type of artificial turf that can be used without granular infill or can be used with reduced granular infill. Specifically, the pur- pose of the invention is to provide an artificial turf with im ^¬ proved properties, e.g. improved elasticity and wear-resistance.

SUMMARY

The present invention relates to an artificial turf comprising a backing of open net structure, a plurality of arti ^¬ ficial grass fibers and a plurality of artificial base fibers. The grass and base fibers are attached to the backing and extend upwardly from the backing when in use. The base and grass fibers are reinforced by non-granular infill material applied as a coating on each fiber and covering part of the length of the grass fibers and at least part of the length of the base fibers. The reinforced parts of the base and grass fibers form a resili ^¬ ent and water-permeable layer which is attached to the backing and over which the grass fibers extend, and the layer is able to maintain the grass fibers in an approximately vertical orienta ^¬ tion in use without requiring the provision of a granular infill .

The present invention relates to an artificial turf comprising a backing of open net structure, a plurality of arti ^¬ ficial grass fibers and a plurality of artificial base fibers. The grass and base fibers are attached to the backing and extend upwardly from the backing when in use. The backing comprises a second side opposite the grass and base fibers. The base and grass fibers are reinforced by non-granular infill material com ^¬ prising elastomer applied as a coating on each fiber and covering part of the length of the grass fibers and at least part of the length of the base fibers. The non-granular infill material is extruded from the second side of the backing. The reinforced parts of the base and grass fibers form a resilient and water- permeable layer which is attached to the backing and over which the grass fibers extend, and the layer is able to maintain the grass fibers in an approximately vertical orientation in use without requiring the provision of a granular infill.

The present invention further relates to a method for manufacturing an artificial turf comprising the steps of:

- providing a backing of open net structure comprising a first side, a second side and a plurality of holes, - attaching pile yarn at spaced intervals to the first side of the backing to provide artificial grass fibers extending upwardly from the backing when in use,

- attaching pile yarn at spaced intervals to the first side of the backing to provide artificial base fibers extending upwardly from the backing when in use,

- extruding non-granular infill material from the second side of the backing through the holes in the backing into the spaces between the grass fibers and base fibers so that the non-granular infill material is applied as a coating on each fiber in such a way that it covers part of the length of the grass fibers and at least part of the length of the base fibers and thereby reinforces said fibers. The reinforced parts of the base and grass fibers form a resilient and water-permeable layer which is attached to the backing and over which the grass fibers extend, and the layer is able to maintain the grass fibers in an approximately vertical orientation in use without requiring the provision of a granular infill.

The present invention further relates to a method for manufacturing an artificial turf comprising the steps of:

- providing a backing of open net structure comprising a first side, a second side and a plurality of holes,

- attaching pile yarn at spaced intervals to the first side of the backing to provide artificial grass fibers extending upwardly from the backing when in use,

- attaching pile yarn at spaced intervals to the first side of the backing to provide artificial base fibers extending upwardly from the backing when in use,

extruding non-granular infill material comprising elastomer from the second side of the backing through the holes in the backing into the spaces between the grass fibers and base fibers so that the non-granular infill material is applied as a coating on each fiber in such a way that it covers part of the length of the grass fibers and at least part of the length of the base fibers and thereby reinforces said fibers. The rein ^¬ forced parts of the base and grass fibers form a resilient and water-permeable layer which is attached to the backing and over which the grass fibers extend, and the layer is able to maintain the grass fibers in an approximately vertical orientation in use without requiring the provision of a granular infill.

The base and grass fibers of the artificial turf are reinforced by non-granular infill material applied as a coating on individual fibers. In one embodiment the base and grass fi ^¬ bers have mutual points of contact and the coating binds the re ^¬ inforced parts of the base and grass fibers together at the points of contact. As a result, a resilient layer is formed at the foot of the grass fibers, comprising the reinforced parts of the base and grass fibers including the coating of infill mate ^¬ rial applied on the surface of the fibers. In one embodiment non-reinforced parts of the base fibers extend above the resili ^¬ ent layer.

The resilient layer is porous and contains spaces be- tween the fibers. In addition, the reinforced fibers are bound together at their points of contact. This kind of structure gives the layer good elasticity and improves the layer' s ability to return to its original shape after applied physical stress.

The resilient layer is water-permeable and allows water to penetrate through the layer. In known artificial turfs, the attachment of the fibers is normally improved by applying adhe ^¬ sive as a non-permeable layer on the second side of the backing. This adhesive layer contains holes at certain intervals to allow water to penetrate the adhesive layer. Said holes are easily clogged up, thereby reducing water-permeability over time. The resilient layer according to the present invention improves at ^¬ tachment of the fibers into the backing. It is therefore not necessary to apply a separate non-permeable adhesive layer on the second side of the backing. Thus, the artificial turf ac- cording to the present invention is water-permeable throughout the turf, which reduces risk of clogging. Also, the water is able to quickly penetrate the turf.

The structure of the resilient layer allows the layer to maintain its elasticity for a long period of time. The dura- bility of the reinforced base fibers is better than the durabil ^¬ ity of corresponding non-reinforced base fibers, making the turf wear-resistant. The damping effect caused by the layer of rein ^¬ forced fibers is uniform over the entire turf. Also, the behav- ior of the ball on the surface is similar to the behavior of the ball on natural grass.

The thickness of the coating applied on the surface of the fibers depends on the application and the infill material used. In one embodiment the coating is not uniform over the sur ^¬ face of the fibers. In the final product, part of the length of the grass fibers and at least part of the length of the base fi ^¬ bers is covered by the coating. In one embodiment part of the length of the grass fibers and at least most of the length of the base fibers is covered by the coating. In one embodiment, the whole length of the base fibers is covered by the coating.

In one embodiment, the shock absorption of the artifi ^¬ cial turf is from 30% to 70%, as measured according to standard EN 14808 (Surfaces for sports areas. Determination of shock ab- sorption) using the Artificial Athlete 2A equipment. Shock ab ^¬ sorption is a measure of resiliency of the layer. In one embodi ^¬ ment, the deformation of the artificial turf according to the present invention is from 4 to 12 millimeters, as measured ac ^¬ cording to standard EN 14809 (Surfaces for sports areas. Deter- mination of vertical deformation) using the Artificial Athlete 2A equipment. Deformation is a measure of surface stability. The shock absorption and the deformation are measured for the turf comprising no granular infill material and placed on concrete base. In other words, good shock absorption and deformation val- ues are achieved without the use of granular infill. In addi ^¬ tion, the turf according to the present invention maintains good shock absorption and good deformation values for many years.

The layer of reinforced fibers is able to maintain the grass fibers in an approximately vertical orientation in use without requiring the provision of a granular infill. Hence, the layer of reinforced base fibers is capable of totally replacing granular infill which is traditionally used in artificial turf systems. However, depending on the application, the turf may also be supplied with granular infill. Granular infill may assist e.g. in stabilizing turfs that have to withstand the weight of heavy vehicles. In one embodiment the artificial turf according to the present invention comprises an infill layer of rubber granules, sand, or both. In one embodiment of the present invention the artifi ^¬ cial turf is installed on a firm surface. In one embodiment the artificial turf is installed on a separate resilient base layer. The resilient base layer can be of any elastic material.

In one embodiment the base fibers are reinforced by heating them to a temperature near to or equal to the melting point of the raw material of the fibers, followed by rapid cool ^¬ ing. The heating causes the surface of the fibers to melt there ^¬ by reinforcing the structure of the fibers. The temperature and duration of the heat treatment is determined by the material of the fibers. In one embodiment the grass fibers are attached to the backing before the heat treatment so that the grass fibers are exposed to the heat treatment simultaneously with the base fibers. In one embodiment the grass fibers are attached to the backing after the heat treatment of the base fibers so that the grass fibers are not exposed to the heat treatment.

The backing can consist of one or more layers of woven or non-woven fabric each having a relatively open net structure. The open net structure of the backing comprises holes. In one embodiment the mesh of the fabric used as a backing is from 1 to 15 millimeters. The open net structure can be inherent to the fabric wherein pile yarns forming the grass and base fibers are attached by tufting. The open net structure of the fabric may also be formed by weaving while simultaneously co-weaving the pile yarns into the fabric. The backing comprises a first side and a second side. The pile yarns forming artificial grass and base fibers are attached to the backing so that they protrude from the backing to the direction of the first side. The second side is the side opposite to the first side.

In one embodiment, synthetic pile yarns forming the ar ^¬ tificial grass and base fibers are attached to the backing by weaving or tufting. In one embodiment pile yarn is attached to the backing by traditional weaving or tufting techniques. Tradi ^¬ tional weaving or tufting results in a turf wherein the distance between successive pile yarns in a row is constant. In one em ^¬ bodiment, pile yarns are attached to the backing by Matrix weav ^¬ ing technique or Matrix tufting technique. In Matrix technique, the distance between successive pile yarns in a row is not con ^¬ stant. For instance, four short stitches are followed by one longer stitch in a row. The number of successive short and long stitches may vary. In one embodiment, three short stiches are followed by one longer stitch in a row. As a consequence, the pile yarns are not uniformly distributed over the surface of the turf but the turf comprises discrete dense groups of pile yarns called bundles. The distance between pile yarn bundles is longer that the distance between successive pile yarns in a row. As a result, the turf is resilient and behavior of the ball on the surface is closer to natural grass.

In one embodiment the pile yarns are fixed to the back ^¬ ing by means of an adhesive, such as polyurethane or latex. In one embodiment the pile yarns are not fixed to the backing by means of an adhesive. In one embodiment the pile yarns are fixed to the backing by a water-permeable layer of adhesive.

In one embodiment, the pile yarns are attached by tuft ^¬ ing. In one embodiment, the gauge of the tufting machine is 3/16'' (4.67 mm) and the number of stiches in a row is from 15 to 30 per 10 centimeters. In one embodiment, the gauge of the tufting machine is 5/32'' (3.97 mm) and the number of stiches in a row is from 15 to 30 per 10 centimeters. In one embodiment, the gauge of the tufting machine is 5/16'' (7.9 mm) and the num ^¬ ber of stiches in a row is from 10 to 30 per 10 centimeters. In one embodiment, the gauge of the tufting machine is 5/8'' (15.8 mm) and the number of stiches in a row is from 10 to 30 per 10 centimeters. In one embodiment, the gauge of the tufting machine is 3/8'' (9.53 mm) and the number of stiches in a row is from 10 to 30 per 10 centimeters. In one embodiment, the gauge of the tufting machine is 3/4'' (19.6 mm) and the number of stiches in a row is from 10 to 30 per 10 centimeters. The gauge of the tufting machine refers to the number of needles per inch and corresponds to the number of stitches per inch in a direction perpendicular to rows. The number of stitches in a row is af ^¬ fected by the size of the needles in the tufting machine and the thickness of the yarn. In one embodiment, the pile yarns are attached by weaving and the distance between successive pile yarns in a row is from 1 to 10 millimeters and the distance be ^¬ tween adjacent rows is from 1 to 10 millimeters. In one embodi ^¬ ment, the pile yarns are attached by Matrix weaving and the gap between successive pile yarn bundles in the direction of rows is from 5 to 20 millimeters and the gap between adjacent pile yarn bundles in the direction perpendicular to rows is from 5 to 20 millimeters. In one embodiment, the pile yarns are attached by tufting and the distance between successive pile yarns in a row is from 3 to 15 millimeters and the distance between adjacent rows is from 3 to 25 millimeters. In one embodiment, the pile yarns are attached by Matrix tufting and the gap between succes ^¬ sive pile yarn bundles in the direction of rows is from 5 to 15 millimeters and the interval between adjacent pile yarn bundles in the direction perpendicular to rows is from 5 to 20 millimeters .

Both the grass and base fibers can comprise straight or crimped yarns or a combination of straight and crimped yarns. The yarn may also be made of a raw material that is crimped un- der certain reaction conditions, e.g. when the yarn is exposed to heat. The raw material of pile yarn can be, for instance, polyethylene, polypropylene, nylon, or any other suitable plas ^¬ tic material. Both the grass and base fibers may comprise fibers made of different materials. In one embodiment the height of grass fibers is from 30 to 75 millimeters and preferably from 30 to 40 millimeters. In one embodiment the height of straight base fibers is from 20 to 75 millimeters and preferably from 20 to 30 millimeters. In one embodiment the height of crimped base yarns is from 20 to 75 millimeters and preferably from 20 to 30 milli- meters. In one embodiment, the height of the base fibers is low ^¬ er than the height of the grass fibers. In one embodiment, the height of the base fibers is equal to the height of the grass fibers .

In one embodiment of the present invention the artifi- cial grass fibers comprise monofilament pile yarn. In one embod ^¬ iment of the present invention the artificial base fibers com ^¬ prise monofilament pile yarn. In one embodiment of the present invention the artificial grass fibers comprise multifilament pile yarn. In one embodiment of the present invention the arti- ficial base fibers comprise multifilament pile yarn. In one em ^¬ bodiment pile yarn is produced from single filaments by winding from 1 to 40, preferably from 1 to 20, and most preferably from 6 to 10 filaments together. In one embodiment the dtex of the individual filament ranges between 500 and 4000 dtex, and pref- erably between 800 and 3000 dtex. Dtex is a measure of linear mass density of fibers and is defined as the mass in grams per 10000 meters.

In one embodiment the artificial grass fibers comprise fibrillated pile yarn. In one embodiment the artificial base fi ^¬ bers comprise fibrillated pile yarn. Fibrillated pile yarn is produced in the form of a band having a width of 10-15 mm, fol ^¬ lowed by incision thereof (fibrillation) . In one embodiment the dtex of fibrillated pile yarn ranges between 1500 and 17000 dtex, and preferably between 6000 and 12000 dtex. The artificial grass fibers or artificial base fibers may also comprise both monofilament or multifilament pile yarn and fibrillated pile yarn .

In one embodiment the turf is further processed after the formation of the resilient layer of reinforced base fibers by using different downstream processes. For example, the turf may be immersed in water or a suitable chemical. Alternatively, water or a suitable chemical may be sprayed on the turf. The turf may also be exposed to heat treatment. The purpose of the further processing steps may be to detach loose infill material from certain parts of the turf or to improve the adhesion of the infill material to the base fibers.

The non-granular infill material is extruded from the second side of the backing, i.e. from the side opposite the grass and base fibers. The extrusion from the rear side of the backing allows applying the infill material only to the base fi ^¬ bers and the lower parts of the grass fibers, thereby leaving the upper parts of the grass fibers, and optionally the upper parts of the base fibers, untreated.

In one embodiment, the non-granular infill material is applied on the rear side of the backing and pressed through the holes in the backing so as to form a porous layer of non ^¬ granular infill material at the foot of the grass fibers. In one embodiment the non-granular infill material is pressed by a press roll through the holes in the backing into the spaces be ^¬ tween grass fibers. The mixing of the infill material with the base fibers and porosity of the resulting resilient layer can be improved by application of pressurized air after the application or extrusion of the non-granular infill material. In one embodiment of the present invention, the non ^¬ granular infill material comprises elastomer. In this specifica ^¬ tion, the expression "elastomer" should be understood as a poly ^¬ mer having both viscosity and elasticity. In one embodiment the elastomer is thermoset elastomer. In one embodiment the elasto ^¬ mer is thermoplastic elastomer. In one embodiment the elastomer is fluent. In one embodiment the fluent elastomer is in liquid form. In one embodiment the fluent elastomer is in a form of a gel. In one embodiment of the present invention fluent elastomer is extruded from the second side of the backing through the holes in the backing into the spaces between the grass fibers and base fibers, and the elastomer is cured or vulcanized to form a resilient and water-permeable layer of reinforced fibers. The curing or vulcanization can be achieved e.g. by heat, chemi- cal additives or electron beams or by exposure to air or water. In one embodiment, curing or vulcanization is performed at room temperature .

In one embodiment of the present invention, the non ^¬ granular infill material consists of elastomer.

In one embodiment the elastomer is silicone, styrene- butadiene rubber (latex), polyacrylic rubber or polyurethane . In one embodiment the elastomer is silyl modified polymer. In this specification, the expression silicone should be understood as a polymer that includes silicon, carbon, hydrogen, oxygen and op- tionally other elements. In one embodiment, silicone is silicone oil, silicone grease, silicone rubber, silicone resin or sili ^¬ cone caulk. In one embodiment the silicone is polysiloxane or polydimethylsiloxane. In one embodiment the silicone is polyx- ane . In one embodiment the elastomer is an adhesive. The choice of the elastomer is determined by the raw material and the prop ^¬ erties of the fibers.

In one embodiment of the present invention the fluent elastomer is allowed to penetrate in between the base fibers from the rear side of the backing by immersing the artificial turf in a container containing liquid elastomer of low viscosity. The elastomer is thus absorbed into artificial turf from the rear side. The height of the forming resilient layer depends on the viscosity of the elastomer and the time of the procedure. In one embodiment additives may be added to the elasto ^¬ mer before applying the elastomer on the surface of the fibers. The additives may be used to improve the properties of the arti ^¬ ficial turf e.g. by improving resistance to UV light, by reduc- ing friction or by adding scent of natural grass.

In one embodiment the height of the resilient and wa ^¬ ter-permeable layer is from 2 to 50 millimeters, preferably from 5 to 30 millimeters, and most preferably from 10 to 30 millime ^¬ ters .

In one embodiment the grass fibers extend from 5 to 25 millimeters above the resilient and water-permeable layer. In one embodiment the top parts of the base fibers extend above the resilient layer. The height of grass fibers, base fibers and re ^¬ silient layer is determined by the application of the turf, i.e. whether the turf is used as a sports field, in landscape use or for children's playground.

In one embodiment the fibers consist of filaments and the number of filaments per square meter is from 90000 to 350000. In order to achieve adequate resiliency of the turf, the number of reinforced fibers per square meter does not need to be as high as the number of corresponding fibers that are not reinforced. In other words, the number of filaments per square meter does not need to be as high in the turf according to the present invention as the number of filaments that are not reinforced. The number of filaments in a turf without granular infill is typically from 300000 to 600000 per square meter. Because the number of filaments per square meter is lower in the present in ^¬ vention than with non-reinforced fibers, the resulting layer permits the studs of football shoes to penetrate into said layer thereby improving the grip of the football shoes on the turf. The layer of reinforced base fibers thus resembles natural soil.

The embodiments of the invention described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodi- ment of the invention. An artificial turf or a method for manu ^¬ facturing an artificial turf, to which the invention is related, may comprise at least one of the embodiments of the invention described hereinbefore. The turf according to the present invention allows omitting the use of granular infill which is easily displaced during use and maintenance and causes non-uniform damping over the turf. An advantage of the present invention is that the dampening effect is uniform over the whole surface of the turf. The turf is extremely wear-resistant because the resilient layer comprises reinforced base fibers. The resilient layer improves attachment of the fibers to the backing. Further, the elasticity of the elastomeric layer is maintained remarkably long. The po- rous structure of the turf allows good water-permeability which is maintained for years. The artificial turf according to the present invention therefore requires little maintenance, result ^¬ ing in reduced costs. The performance of the turf is not depend ^¬ ent on regular maintenance, but stays constant over the years. In addition, recycling of the material of the artificial turf according to the present invention is easy.

An advantage is that the individual base fibers are re ^¬ inforced by a coating of non-granular infill material surround ^¬ ing the fibers. As a consequence, the base fibers need not be as tightly packed as without the reinforcing coating in order to achieve the same resiliency. The structure of the base layer thus allows the studs of football shoes to penetrate into the resilient layer in a similar manner as they would penetrate into natural soil. This brings about a good grip on the artificial turf. Also, the behaviour of the ball on the surface resembles the behavior of the ball on natural grass. This kind of struc ^¬ ture is also able to efficiently dampen shocks during the game. An advantage is that the artificial turf is not heated in the sunshine to the same extent that an artificial turf containing granular infill.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro ^¬ vide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the inven ^¬ tion and together with the description help to explain the principles of the invention. In the drawings: Fig. 1 is a cross-sectional view of an artificial turf according to one embodiment of the present invention,

Fig. 2 is a cross-sectional view of an artificial turf according to a second embodiment of the present invention,

Fig. 3 is a cross-sectional view of a reinforced grass fiber of the turf according to Figures 1 and 2 (III-III),

Fig. 4 is a cross-sectional view of a reinforced base fiber of the turf according to Figures 1 and 2 (IV-IV),

Fig. 5 is a top view of an artificial turf according to a third embodiment of the present invention, and

Fig. 6 is a top view of an artificial turf according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings .

The description below discloses some embodiments of the invention in such a detail that a person skilled in the art is able to utilize the invention based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious for the person skilled in the art based on this specification.

For reasons of simplicity, item numbers will be main- tained in the following exemplary embodiments in the case of re ^¬ peating components.

Figures 1 and 2 are cross-sectional views of artificial turfs according to one and second embodiment of the present in ^¬ vention. The turf comprises a backing 1 having an open net structure. The backing 1 comprises a first side 11 and a second side 12. Pile yarn 14 simulating grass fibers 2 and base fibers 3 are attached to the backing 1 by tufting of weaving. In Figure 1, both the grass 2 and base fibers 3 are made of straight pile yarn 14 producing straight fibers. In figure 2, the grass fibers 2 are made of straight pile yarn 14 and the base fibers 3 are made of crimped pile yarn 14. The height 4 of the base fibers 3 is about half of the height 17 of the grass fibers 2. The height 4,17 of the base 3 and grass fibers 2 may vary depending on the embodiment and also the mutual relationship of their height can vary. For reasons of clarity, the distance between individual fibers 2,3 in the figure is relatively long. In practice, the fibers 2,3 can be attached to the backing 1 more densely. The fibers 2,3 extend upwardly from the backing 1 on the first side 11 of the backing 1. The grass 2 and base fibers 3 touch each other at mutual points of contact 9.

In Figures 1 and 2 parts 7 of the grass 2 and base fi ^¬ bers 3 have been reinforced by application of a coating 6 com- prising non-granular infill material 5 on the surface of the fi ^¬ bers 2,3. The coating 6 has been applied by extruding non ^¬ granular infill material 5 from the second side 12 of the back ^¬ ing 1 so that the infill material forms a layer 8 of certain height 10. The height 10 of the layer 8 has been marked in the figure by a straight line. However, in practice the height 10 of the layer 8 is not constant throughout the layer 8 but varies from one position to another. For reasons of simplicity, the coating 6 has not been marked in the figure. The fibers 2,3 are reinforced by the coating 6 within the layer 8. The coating 6 makes the fibers 2,3 stronger and improves their elasticity. The coating 6 also binds the fibers 2,3 together at the points of contact 9 where the individual fibers 2,3 touch each other. The reinforced parts 7 of the grass 2 and base fibers 3 thereby form a resilient and water-permeable layer 8. The layer 8 comprises spaces 16 to allow water to penetrate the layer.

Figure 3 is a cross-sectional view of a reinforced grass fiber 2 of the turf according to Figures 1 and 2 (III- III) . In other words, Figure 3 shows the horizontal cross- section of the grass fiber 2 within the resilient and water- permeable layer 8. The non-particular infill material 5 forms a coating 6 on the surface of the grass fiber 2. The thickness of the coating 6 material is not uniform over the surface of each individual fiber 2 but is varying. The thickness of the coating 6 depends on the orientation of the neighboring fibers 2,3. The coatings 6 of the neighboring fibers 2,3 may be combined togeth ^¬ er. The thickness of the coating 6 also depends on the thickness of the infill material 5 applied on the surface of the fibers 2. In Figure 3, the cross-section of the grass fiber 2 has a coni- cally tapering and distorted shape. The grass fiber 2 can, how- ever, have a cross-section of any other shape, e.g. rectangular, V shaped or rhombus shaped.

Figure 4 is a cross-sectional view of a reinforced base fiber 3 of the turf according to Figures 1 and 2 (IV-IV) . In other words, Figure 4 shows the horizontal cross-section of the base fiber 3 within the resilient and water-permeable layer 8. The non-particular infill material 5 forms a coating 6 on the surface of the base fiber 3. The thickness of the coating 6 ma ^¬ terial is not uniform over the surface of each individual fiber 3 but is varying. The thickness of the coating 6 depends on the orientation of the neighboring fibers 3,2. The coatings 6 of the neighboring fibers 3,2 may be combined together. The thickness of the coating 6 also depends on the thickness of the infill ma ^¬ terial 5 applied on the surface of the fibers 3. In Figure 4, the cross-section of the base fiber 3 has a conically tapering and distorted shape. The base fiber 3 can however have a cross- section of any other shape, e.g. rectangular, V shaped or rhombus shaped.

Figure 5 is a top view of an artificial turf according to a third embodiment of the present invention. The turf has been manufactured by Matrix weaving technique. The backing 1 comprises an open net structure comprising holes 13. Only part of the net structure is shown in the figure. The pile yarn form ^¬ ing grass fibers 2 are attached to the backing 1 in rows 18 and at spaced intervals 15. For reasons of simplicity, base fibers 3 are not shown in the figure. The distance between successive grass fibers 2 in a row 18 is not constant. Four short stitches are followed by a longer one, thereby forming a larger gap 19 between successive grass fibers 2 in a row. The mutual distance between four adjacent rows 18 is constant, followed by a longer gap 19 between two adjacent rows 18. The grass fibers 2 located at an equal distance from adjacent grass fibers 2 form bundles 20 of grass fibers 2. One bundle 20 contains sixteen pile yarns forming grass fibers 2. These grass fiber 2 bundles 20 are sepa- rated from each other by a gap 19 of a longer distance than the distance of adjacent grass fibers 2 within a bundle 20.

Figure 6 is a top view of an artificial turf according to a fourth embodiment of the present invention. The turf has been manufactured by Matrix tufting technique. The backing 1 comprises an open net structure comprising holes 13. Only part of the net structure is shown in the figure. The pile yarn form ^¬ ing grass fibers 2 are attached to the backing 1 in rows 18 and at spaced intervals 15. For reasons of simplicity, base fibers 3 are not shown in the figure. The distance between successive grass fibers 2 in a row 18 is not constant. Four short stitches are followed by a longer one, thereby forming a larger gap 19 between successive grass fibers 2 in a row. The mutual distance between rows 18 of grass fibers 2 is constant. The grass fibers 2 in a row located at an equal distance from successive grass fibers 2 form bundles 20 of grass fibers 2. One bundle 20 con ^¬ tains four successive pile yarns in a row forming grass fibers 2. These grass fiber 2 bundles 20 are separated from each other by a gap 19 of a longer distance than the distance of adjacent grass fibers 2 within a bundle 20.

EXAMPLES EXAMPLE 1 - Manufacturing artificial turf according to the present invention by Matrix tufting

An artificial turf was manufactured on a polypropene backing having an open net structure. The mesh of the backing was 3 millimeters. The dtex value of the pile yarn used in the current example was 2000. Straight pile yarn made of polyeth ^¬ ylene was attached by tufting at spaced intervals to one side of the backing to provide artificial grass fibers. Four successive pile yarns in a row forming grass fibers were attached at inter- vals of 5 millimeters, followed by a longer gap of 10 millime ^¬ ters. In addition, crimped pile yarn made of polyamide was at ^¬ tached by tufting at spaced intervals to the same side of the backing to provide artificial base fibers. Four successive pile yarns in a row forming base fibers were attached at intervals of 5 millimeters, followed by a longer gap of 10 millimeters. The height of the grass fibers, as measured from the backing, was 40 millimeters and the height of the base fibers was 30 millime ^¬ ters. The fibers were attached so that they extend upwardly from the backing when the turf is in use. After tufting the yarns were fixed to the backing by adding a permeable layer of polyu ^¬ rethane adhesive on the second side of the backing. The amount of polyurethane per square meter was from 250 to 500 grams.

5000 grams per square meter silicone (polyoxane) was then applied on the rear side of the backing, i.e. the side op ^¬ posite to the grass and base fibers. Silicone was extruded from the rear side of the backing through the holes in the backing into the spaces between the grass fibers and base fibers in or ^¬ der to mix the silicone with the fibers. The silicone thus formed a reinforcing coating on individual fibers. The length of the base and grass fibers was partly covered with the coating. The silicone coating extended from 25 to 30 millimeters upwards from the fabric. The reinforced base fibers thereby formed a re ^¬ silient layer comprising holes and allowing water to penetrate through. The shock absorption of the turf was 50%, as measured according to standard EN 14808 using the Artificial Athlete 2A equipment. The deformation of the turf was 5.8 millimeters, as measured according to standard EN 14809 using the Artificial Athlete 2A equipment. The grass fibers of the turf manufactured according to this example extend over the resilient layer, and the layer is able to keep the grass fibers in an approximately vertical orientation in use without the provision of sand or rubber granules. EXAMPLE 2 - Manufacturing artificial turf according to the present invention by Matrix weaving

An artificial turf was manufactured by Matrix weaving, and the pile yarn forming the grass and base fibers were simul- taneously attached. The resulting turf had a backing having an open net structure and the mesh of the backing was 1 millimeter. The dtex value of pile yarn used in the current example was 2500. Straight pile yarn made of polypropylene was attached by weaving at intervals of 9 millimeters to one side of the backing to provide artificial grass fibers. In addition, straight pile yarn made of polypropylene was attached by weaving at intervals of 9 millimeters to the same side of the backing to provide ar ^¬ tificial base fibers. The height of the grass fibers, as meas ^¬ ured from the backing, was 30 millimeters and the height of the base fibers was 20 millimeters. The fibers were attached so that they extend upwardly from the backing when the turf is in use. After weaving the yarns were fixed to the backing by adding a permeable layer of adhesive, i.e. 600 grams per square meter polypropylene dispersion.

800 grams per square meter polyurethane was then ap ^¬ plied on the rear side of the backing, i.e. the side opposite to the grass and base fibers. Polyurethane was then extruded from the rear side of the backing through the holes in the backing into the spaces between the grass fibers and base fibers in or ^¬ der to mix the polyurethane with the fibers. The polyurethane thus formed a reinforcing coating on individual fibers. The length of the base and grass fibers was partly covered with the coating. The polyurethane coating extended approximately 20 mil- limeters upwards from the backing. The reinforced base fibers thereby formed a resilient layer comprising holes and allowing water to penetrate through. The shock absorption of the turf was 43%, as measured according to standard EN 14808 using the Arti ^¬ ficial Athlete 2A equipment. The deformation of the turf was 4.2 millimeters, as measured according to standard EN 14809 using the Artificial Athlete 2A equipment. The grass fibers of the turf manufactured according to this example extend over the re ^¬ silient layer, and the layer is able to keep the grass fibers in an approximately vertical orientation in use without the provi- sion of sand or rubber granules.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embod- iments are thus not limited to the examples described above; in ^¬ stead they may vary within the scope of the claims.