EP1837423A1

EP1837423A1 - Synthetic turf resembling a grass field

Info

Publication number: EP1837423A1
Application number: EP06447040A
Authority: EP
Inventors: Jan De Clerck
Original assignee: DOMO Zele NV
Current assignee: DOMO Zele NV
Priority date: 2006-03-21
Filing date: 2006-03-21
Publication date: 2007-09-26
Also published as: EP2004885A2; WO2007107307A2; WO2007107307A3

Abstract

The present invention provides a new type of synthetic turf resembling grass fields. The synthetic turf comprises a tuftcloth and tufts projecting thereof whereby at least a number of the yarns making up the tufts consist essentially of a mixture of high density polyethylene and low density linear polyethylene, providing the turf with improved resilience and sliding-friendliness. The invention further encloses yarns with different cross-section profiles resulting in a better resilience. The synthetic turf comprising these yarns has a much better resilience as well as a more natural look. To even further enhance the natural look of the synthetic turf and to prevent a rather artificial look, the present invention also discloses the use of at least two different colors and preferably three or more different colors for the yarns, such as yellow-green, bright green and dark green.

Description

FIELD OF THE INVENTION

The present invention relates to artificial grass fields and more specific to a synthetic turf having yarns with a specific chemical composition. The invention further relates to the cross-section profile and/or color of yarns comprised by a synthetic turf.

BACKGROUND OF THE INVENTION

Synthetic or artificial turf is used more and more to replace natural grass turf on playing surfaces, in particular on sport fields like fields for playing football, rugby, tennis, golf, hockey, baseball, etc. In order to provide a somewhat resilient surface, a top-dressing can be applied onto the backing layer. The thickness of this top-dressing is smaller than the height of the tufts so that the grass-like filaments project above the top-dressing. A top-dressed synthetic turf is disclosed for example in US-A-4 337 283 and WO 2004/077914 .
In practice, the top-dressing of so-called third generation synthetic grass fields usually consists of a hard layer and on top a layer of resilient granules, as for instance disclosed in WO 01/98589 . This document discloses a synthetic grass assembly for installation on a supporting substrate comprising a pile fabric with a flexible sheet backing and a plurality of upstanding synthetic ribbons of a selected length. An infill layer of particulate material, selected from the group consisting of hard and resilient granules, is disposed interstitially between the upstanding ribbons upon the upper surface of the backing with a depth less than the length of the ribbons. The infill layer in particular comprises a bottom course of hard granules, disposed upon the top surface of the backing and a top course substantially exclusively of resilient granules disposed upon the bottom course.
Frequently applied resilient granular materials that may be used as infill materials may include mixtures of granulated rubber particles like SBR (styrene butadiene rubber) recycled from car tires, EPDM (ethylene-propylene-diene monomer), other vulcanised rubbers or rubber recycled from belts. However, these rubbers have several important disadvantages. In particular, they can not be re-used and have a limited life span since they loose there properties throughout use. Furthermore, the use of this type of rubbers in a top-dressing layer of a synthetic turf does not provide sufficient resilience or shock absorption.
Most of the synthetic turf for football fields consists nowadays of pile fabric made of fibrillated yarn. This fibrillated yarn is usually made of polyethylene or of a mixture of polyethylene and polypropylene and is tufted on a machine with a needle distance of between 5/8" (≈15.8 mm) and 3/16" (≈4.7 mm). A drawback of the used fibrillated yarns is that they have a relatively low wear resistance and that a post-fibrillation with a rigid (steel) brush is required after having laid the synthetic turf. The post-fibrillation is required to separate the different filaments of the fibrillated yarn from one another in order to hide the top-dressing better from view and in order to achieve the look of natural grass. A drawback of such a post-fibrillation however is that the pile yarn is damaged.
In addition to synthetic turf made of fibrillated yarn, there is also synthetic turf made of so-called monotape or monofilament yarn. The difference between monotape and monofilament yarn is that, for the production of monotape yarn, a film is extruded which is cut into small bands whilst for the production of monofilament yarn the bands forming the monofilaments are separately extruded. A drawback of synthetic turf made of monotape or monofilaments is that the top-dressing is less stabilised against shifting and/or erosion and that the rubber granules are less hampered from jumping up. Furthermore in practice, most of the monotape or monofilament yarns used to make artificial turf consist of polypropylene, which offers better resilience properties than polyethylene, but which has a higher coefficient of friction so that burning wounds occur much quicker, for example when falling or making a sliding on the synthetic turf surface.
Synthetic turfs formed by yarns made of polyamide have been reported in the art, and are for instance disclosed in US 3,940,522 and WO 99/04074 . In US 3,940,522 synthetic turfs are described comprising grass-like synthetic fibers and crimped fibers. One or more of the grass-like fibers are combined with an appropriate multi-fiber strand of crimped and/or latently crimpable fibers. The fibers are made of polyamides such as nylon 6, nylon 6,6, nylon 6,10, nylon 6,12, and copolymers and blends of these. WO 99/04074 discloses yarns containing polyamide in combination with a polyolefin compound for producing artificial grass. A major disadvantage of synthetic turfs formed by yarns made of polyamide is that the turfs show high sliding resistance and a high coefficient of friction, so burning wounds occur much quicker, for example when falling or making a sliding on the synthetic turf surface.
In practice there is also a synthetic turf on the market comprising alternating rows of tufts made of fibrillated yarn and rows of tufts made of monofilament yarns. An advantage of such a combination is that the turf has an appearance which immediately resembles more natural grass. However, a post-fibrillation or several months of wear is still required to make the synthetic turf look like natural grass. A further drawback of this combination is that, due to the fact that the fibrillated yarn wears more quickly than the monofilament yarns, the difference in wear pattern between the fibrillated yarn and the monofilament yarns can clearly be seen after a more prolonged time of use.
WO 2004/077914 provides a synthetic turf overcoming some of these problems. Instead of alternating fibrillated and monofilament yarns, the turf is made by combining fibrillated and monofilament yarns into the tufts. A tuft is made of a composite yarn, which is composed of a fibrillated yarn twined around several monofilament yarns, thereby avoiding differences in wear patterns to become visible. Also, because of the more homogeneously mixing of both types of yarn, the turf immediately resembles better natural grass, so no post-fibrillation is needed. Furthermore, by using yarns made of polyethylene the synthetic turf is rendered more sliding-friendly, due to the lower coefficient of friction of polyethylene than that of polypropylene. A disadvantage however is that by gaining sliding-friendliness the turf also loses in resilience.
Another drawback of the synthetic turfs known nowadays is that, despite all the efforts made to create a synthetic grass field with a more natural look, the turfs still display a rather artificial look.
Therefore, it is an object of the present invention to provide a new type of synthetic turf displaying UV-stability and wear resistance, while combining resilience with sliding-friendliness. Furthermore, the invention aims to provide this turf with a better resemblance to natural grass and to prevent the artificial look of synthetic turfs presently known in the

prior art.

SUMMARY OF THE INVENTION

The present invention relates to a synthetic turf, according to claim 1, whereby at least a number of the yarns making up the tufts (2) consist essentially of a mixture of high density polyethylene (HDPE) and low density linear polyethylene (LLDPE). This mixture comprises between 20 to 80% HDPE and 80 to 20% LLDPE, preferably 40 to 60% HDPE and 60 to 40% LLDPE and even more preferably is the amount of HDPE approximately the same as that of LLDPE. The effect obtained by using a combination of both raw materials is that the yarns combine the stiffness, resilience, UV-stability and wear resistance of HDPE with the softness and sliding-friendliness of LLDPE.
In an embodiment at least a number of the tufts (2) of the turf, according to the present invention, are made of a composite yarn, twining fibrillated (6) and filament (7) yarns of HDPE and LLDPE together. The more homogeneously mixing of both yarn types results in an improved resemblance to natural grass, without the need for post-fibrillation or subjecting to wear for some time, and prevents that a difference in wear pattern can be seen without a close inspection of the tufts.
In a further embodiment the fibrillated yarn (6) is twined around the individual filament yarns (7) so that the composite yarn has an outer surface which is mainly formed by the fibrillated yarn (6). Composed in this way the composite yarns are fed to the tufting machine more easily and with a higher efficiency.
To increase the appearance of natural grass even further, the choice of the yarn number of the composite yarn is very important. Therefore the yarn number of the composite yarn is chosen between 5000 and 30000 dtex, preferably between 9000 and 20000 dtex and more preferably about 16000 dtex. This is done by carefully selecting the yarn numbers of the fibrillated (6) and filament (7) yarns, making up said composite yarn. For this purpose also the number of different yarns making up the composite yarn is chosen carefully. According to the present invention, the best results are achieved by twining 1 to 3 fibrillated yarns (6), and preferably 1, together with 3 to 9 individual filament yarns (7), and preferably 6.
Fibrillated yarns (6) are comprised in the tufts (2) because, compared to individual filament yarns (7), they are more resilient and provide a better stabilization of the top-dressing of the finished turf. The fibrillated yarn (6) is produced by making longitudinal slits in a tape, preferably of LLDPE, thereby forming laterally interconnected filaments. The slits are made in such that the yarns achieve the natural look of grass immediately after tufting.
The present invention also relates to an individual filament yarn (7), according to claim 9, comprising a convex or curved cross-section. The cross-section of the yarn can further have rounded edges and/or an S or slightly curved profile. The yarn can also exhibit point symmetry. These enclosed features result in an improved resilience of the individual filament yarn (7) and provide the turf made out of such yarns with a more natural look.
According to claim 13, the present invention also relates to a synthetic turf comprising tufts (2) made of a composite yarn, composed of at least one fibrillated yarn (6) twined together with individual filament yarns (7) having the previously discussed features or any combination thereof. These composite yarns can also comprise individual filament yarns (7) with a flat profile. A turf comprising composite yarns composed in this way has the benefit of being more resilient and looking more like natural grass. Furthermore, by making a number of these yarns, and preferably all of them, in the mixture of HDPE and LLDPE, as described in claim 1, the turf will also exhibit the stiffness, resilience, UV-stability and wear resistance of HDPE and the softness and sliding-friendliness of LLDPE.
The synthetic turf of the present invention is given a more natural look to resemble grass by using yarns in at least two different colors and preferably in three or more different colors, such as yellow-green, bright green and dark green, to compose the tufts (2). This way the artificial appearance of uni-colored turfs is prevented.

BRIEF DESCRIPTION OF THE FIGURES

Fig.1 is a schematic picture comparing the resilience (A), the temperature stability (B) and the wear resistance (C) of a monofilament yarn (7), a fibrillated yarn (6) and the composite yarn according to the present invention.
Fig. 2 demonstrates the composition of a tuft (2), originated from a composite yarn, consisting of one fibrillated yarn (6) twined around six individual filament yarns (7).
Fig. 3 is a cross-sectional view, according to A-A of Fig. 2, of a possible embodiment of an individual filament yarn (7) having a propeller profile.
Fig. 4 is a cross-sectional view, according to A-A of Fig. 2, of a possible embodiment of an individual filament yarn (7) having a biconvex profile.
Fig. 5 is a cross-sectional view, according to A-A of Fig. 2, of a possible embodiment of an individual filament yarn (7) having a S-like profile.
Fig. 6 is a cross-sectional view, according to A-A of Fig. 2, of a possible embodiment of an individual filament yarn (7) having a waving profile.
Fig. 7 is a cross-sectional view through a finished synthetic grass field, comprising a tuftcloth (1) and tufts (2) made from a composite yarn and the turf filled further with a two layered top-dressing (4 and 5).

DETAILED DESCRIPTION OF THE INVENTION

The synthetic turf illustrated in Fig. 7 comprises a flexible tuftcloth (1) provided with rows of tufts (2) made of a composite or combined yarn. The tufts (2) shown in this figure are actually cross-sections displaying only one half of the tufts in the synthetic turf of the invention, whereas the front view of the tuft (2) in Fig. 2 displays both halfs but shows only the upper part of the tuft (2). Such a turf may be defined by 5000 to 10000 tufts (2) per m² of tuftcloth (1), preferably between 6124 and 8250, and more preferably 6929 tufts/m². To finish the artificial grass field the synthetic turf is filled with a top-dressing, for example comprising a layer of sand (4) and a layer of rubber granules (5). The thickness of this top-dressing is smaller than the height of the tufts so that the tufts project above the top-dressing. Preferably the thickness of this top-dressing comprises between 0.5 and 5.0 cm and more preferably between 2.0 and 3.0 cm. The weight of the top-dressing is between 5000 and 40000 g/m², preferably, of between 21000 and 32000 g/m² The layer of sand (4) allows a good water permeability and ensures stability, whereas the rubber infill (5) is spread on top of the sand to prevent burnings and to obtain an excellent shock absorption.
The synthetic turf, comprising a tuftcloth (1) and tufts (2), is produced by feeding the composite or combined yarn through the needles of a tufting machine and inserting them through the tuftcloth (1). The tufts (2) are made up by both ends of the composite or combined yarn projecting from the tuftcloth (1) and are secured by stitching said yarn to the tuftcloth (1). The height of the tufts (2) is between 1.5 to 30 cm, preferably of between 3 and 15 cm and more preferably of between 5 to 8 cm. The tuftcloth (1) may consist for example of a woven HO6 sheet and a glass fibre netting fixed to each other by means of an adhesive material, such as latex or foam. Since the tuftcloth (1) is no essential feature of the present invention, no further details will be described thereof.
In order to enable the presence of a top-dressing, the tufts (2) of the synthetic turf have preferably an average height larger than 30 mm and more preferably an average height larger than 40 mm. In this way, the tufts (2) of the pile layer still project over a sufficient distance above the top-dressing. The average height of the tufts (2) is usually smaller than 75 mm and is preferably comprised between 50 and 60 mm. The average height of the tufts (2) is to be determined by measuring and totalling the height of the different filaments and dividing the achieved number by the number of filaments.
In Fig. 7 a schematic cross-sectional view of some tufts (2) according to the present invention is displayed. Fig. 2 provides a front view of the upper part of a preferred embodiment of a tuft (2). The tufts (2) comprise individual filament yarns (7) and at least one fibrillated yarn (6). Combining these two yarn types prevents differences in wear pattern, illustrated in Fig. 1C, to become visible without the need for a close examination of the tufts. According to claim 1, at least a number of these yarns consist essentially of a mixture of high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). The composition of this mixture comprises 20 to 80% HDPE and 80 to 20% LLDPE, preferably 40 to 60% HDPE and 60 to 40% LLDPE, and more preferably about 50% HDPE and about 50% LLDPE. LLDPE has the advantage that it is resistant to very low temperatures, has a small coefficient of friction, thereby rendering the turf soft and sliding-friendly, and has a higher wear resistance than for example polypropylene. HDPE, on the contrary, is more rigid and has a higher resilience, a better UV-stability and an even better wear resistance. A turf, made up of yarns comprising a mixture of these both raw materials, displays a better resilience, UV-stability and wear resistance and combines the stiffness of HDPE with the softness, and resulting sliding-friendliness, of LLDPE. For a skilled person it is clear that the polyethylene contains certain additives such as UV and heat stabilisers, colour pigments and/or colorants. Optionally, it may even contain small amounts of one or more other polymers, more particularly in an amount of less than 10 % by weight, preferably less than 5 % by weight.
Fig. 1 illustrates the comparison of three features, i.e. resilience (A), temperature stability (B) and wear resistance (C), of individual filament yarns (7), fibrillated yarns (6) and the tufts made of the composite yarn. Clearly shown in Fig. 1A the fibrillated yarns (6) are the most resilient yarns and contribute the most to the high resilience of the tufts (2). Furthermore, Fig. 1 B displays the temperature stability of the yarns (6, 7) and tuft (2). Also, the wear resistance of the different yarns is demonstrated in Fig. 1C. The individual filament yarns (7) are much more resistant than fibrillated yarns (6) and the same wear pattern is found in the yarns of the composite yarn. However, because of the more homogeneous mixing of the yarns (6, 7) in the composite yarn, the difference in wear pattern between the fibrillated (6) and the individual filament (7) yarns isn't visible without close examination of the turf.
in an embodiment of the present invention the tufts (2) are derived from composite yarns, formed of fibrillated (6) and filament (7) yarns of the previously described mixture of HDPE and LLDPE. In order to make the composite yarn, the individual filament yarns (7) and the fibrillated yarn (6) are twined together. The word "twined" here has to be understood in its broadest meaning and includes for example also a simple twisting of the yarns. The composite yarn may further be twined into the S or Z direction. The number of windings (per meter) during the twining process must be limited in such a manner that the filaments will spread themselves again after the tufting process. This can be determined experimentally. When twining the composite yarn, the fibrillated yarn (6) is preferably twined around the individual filament yarns (7) so that the composite yarn has an outer surface which is mainly formed by the fibrillated yarn (6). Twining the yarns in such a way has the advantage that the composite yarn can be fed to the tufting machine and tufted more easily and efficiently.
By making the tufts of the present synthetic turf by means of a composite yarn, the number and yarn number of the fibrillated (6) and individual filament (7) yarns can be easily selected in such a manner that, without post-fibrillation, the turf immediately resembles grass. The composite yarn will usually comprise 3 to 9, and preferably 6 individual filament yarns (7). It may comprise up to three fibrillated yarns (6) but preference is given to the presence of only one. In this case, i.e. when only one fibrillated yarn (6) is present, it may have a larger yarn number so that the filaments are better connected with one another. The yarn number of the composite yarn is indeed preferably formed for at least 40%, more preferably for at least 50%, by the individual filament yarns (7) in order to resemble immediately as much as possible natural grass. On the other hand, in order to improve stabilisation of the top-dressing, preferably at least 30%, and more preferably at least 35% of the yarn number of the composite yarn is formed by the fibrillated yarn or yarns (6). In order to be able to provide, on the one hand, a fibrillated yarn (6) with a relatively high yarn number and, on the other hand, a relatively large yarn number of individual filament yarns (7) and due to the limitations of the tufting machine, the yarn number of the composite yarn will usually be between 5000 and 30000 dtex, preferably between 9000 and 20000 dtex and even more preferably about 16000 dtex.
In view of the relatively high yarn number of the composite yarns according to the present invention, the distances between the rows of tufts may be larger. Usually, the mutual distances between the rows will be comprised between 8 and 24 mm, preferably between 10 and 20 mm, and more preferably between 12 and 18 mm. A mutual distance of 16 mm or larger is most preferred.
A fibrillated yarn (6) is produced starting from an extruded film which is first cut into bands. In these bands longitudinal slits are made so that laterally interconnected filaments are formed. These slits can be made for example by means of a drum provided with needles (and rotated at a speed different from the speed of the film led over this drum) or teeth as disclosed in US-A-3 496 259 . The fibrillated yarn (6) has for example a total width of 9 mm, the slits being arranged so that the interconnected filaments have a width which is preferably somewhat smaller than the width of the individual filament yarns. Moreover, the slits are preferably not provided on the same mutual distances so that broader filaments are separated by narrower filaments which provide for a looser connection between the broader filaments. By selecting a smaller width of the filaments and/or a looser connection between the filaments, the filaments become immediately spread in a random manner after the tufting operation thus contributing to achieving immediately the natural look of grass. The yarn number of the fibrillated yarn (6) will normally be comprised between 2000 and 11000 dtex, preferably between 5000 and 8500 dtex, and more preferably 6800 dtex. When using a fibrillated yarn (6) with a smaller yarn number, the composite yarn may contain more individual filament yarns (7) since the maximum yarn number of the composite yarn is limited by the tufting technique. The composite yarn can for example be made with three fibrillated yarns (6), having each a yarn number of 2000 dtex. These fibrillated yarns (6) can first be twined together and can subsequently, in a second twining operation, be twined together with the individual filament yarns (7). The thickness of the fibrillated yarn (6) is preferably comprised between 60 and 100 µm, and more preferably between 70 and 90 µm. Since the filaments of the fibrillated yarn (6) are interconnected, the thickness thereof may be smaller than the thickness of the individual filament yarns (7). A predetermined minimum thickness is however preferred because of the higher wear resistance (mechanical wear and/or heat and UV degradation) and the increased resiliency obtained by a larger thickness.
The individual filament yarns (7) are produced in such a way that they resemble grass. Therefore, the yarn number will usually be comprised between 1000 and 3000 dtex, and preferably between 1100 and 1700 dtex. The composite yarn may combine for example two individual filament yarns (7) of 1500 dtex and four such yarns (7) of 1550 dtex. Furthermore the width of the yarns (7) is preferably smaller than 7 mm, more preferably smaller than 4 mm, and most preferably smaller than 2 mm, but larger than 0.8 mm, and preferably larger than 1 mm. A fine, natural grass look is for example obtained when the width of the filament yarns (7) comprises about 1.4 mm. The thickness of the individual filament yarns (7) is not only important to achieve the look of natural grass, but also to achieve the required resilience properties. The individual filament yarns (7) will usually have a thickness of between 100 and 400 µm. Good results have for example been obtained when the thickness of the individual filament yarns (7) comprises about 160 µm.
According to the present invention also the shape of the yarn can make a contribution to its resilience. The best results were achieved by using individual filament yarns (7) having a convex or curved cross-section. The cross-section of the yarn could further be provided with rounded edges and/or an S or slightly curved profile. The yarns obtaining the best results also exhibit point symmetry. Four different embodiments, meeting one or more of these requirements, are illustrated in Figs. 3 to 6 and demonstrate four different cross-sectional profiles responsible for the much better resilience of the individual filament yarn (7). As is clear to a person skilled in the art, these embodiments are only exemplifying and aren't limitative to the scope of the invention.
In the first embodiment, illustrated in Fig. 3, the yarn (7) has a cross-section of a propeller profile, displaying a node and two arms. The node, in the centre of the yarn (7), comprises the thickness previously described. The arms, starting from the node and separated from each other over 180°, have, at the node, a thickness of 50 to 100 µm, which gradually decreases towards the ends of the arms to a thickness in between 1 and 50 µm. Also, the propeller shape of the yarn is characterized in that the ends of the arms are curved in opposite direction over a distance of between 20 and 200 µm and over an angle of between 20° and 70°, and preferably over an angle of 45°.
The second embodiment, illustrated in Fig. 4, describes an individual filament yarn (7) with a cross-section of a biconvex profile. The centre of the yarn displays the same thickness as previously described, and this thickness gradually decreases in a convex way towards the sides of the yarn, preferably to a point.
In the third embodiment, illustrated in Fig. 5, an individual filament yarn (7) is described with a cross-section of a S-like profile. The thickness in the centre of the yarn is the same as previously described, but decreases gradually in a convex manner until a thickness of between 1 and 50 µm. The ends of the yarn are curved in opposite direction over a distance of between 20 and 200 µm and over an angle of between 20° and 70°, and preferably over an angle of 45°.
A fourth embodiment, illustrated in Fig. 6, relates to a yarn (7) displaying the cross-section of a waving profile. The yarn has a thickness as mentioned before, which remains substantially the same over its entire width, and comprises two curves bent in opposite direction. The ends of the yarn are rounded.
The present invention also relates to a synthetic turf comprising tufts (2) made of a composite yarn, composed of at least one fibrillated yarn (6) twined together with individual filament yarns (7), having a convex, curved, S, slightly curved profile, rounded edges and/or point symmetry, or any combination thereof. These composite yarns, with at least one fibrillated yarn and one of said individual filament yarns (7), can also comprise individual filament yarns (7) with a flat profile. A turf comprising composite yarns composed in this way has the benefit of being more resilient and looking more like natural grass. Furthermore, by making a number of these yarns, and preferably all of them, in the mixture of HDPE and LLDPE, as described before, the turf will also exhibit the stiffness, resilience, UV-stability and wear resistance of HDPE and the softness and sliding-friendliness of LLDPE.
Also, the synthetic turf of the present invention is given a more natural look to resemble grass by using yarns in at least two different colors and preferably in three or more different colors, such as yellow-green, bright green and dark green, to compose the tufts (2). This way the artificial appearance of uni-colored turfs is prevented.

EXAMPLES

Example 1

A composite yarn was made by twining one fibrillated yarn (6) around six individual monofilament yarns (7). The composite yarn had a yarn number of 16000 dtex and was composed of one fibrillated yarn (6) having a yarn number of 6800 dtex, four individual monofilament yarns (7), having a propeller profile and a yarn number of 1550 dtex, and two flat shaped yarns of 1500 dtex. The individual monofilament yarns (7) were all made of a mixture of 50% HDPE and 50% LLDPE, containing UV and heat stabilizers. To some of the yarns a yellow-green pigment was added, to others a bright green pigment and to the remaining yarns a dark green pigment. A tuft (2) was made by combining the different colored yarns in such a way that the resulting turf had a more natural look of grass. The composite yarn was tufted on a tuftcloth (1) consisting of a woven HO6 layer and a glass fiber netting. The needle distance of the tufting machine was set at 5/8" and an average of 6929 tufts (2) was placed every m² of the tuftcloth (1). The tufts (2) had an average height (h) of 50 mm and an average weight of 1330 g/m². Fixation of the tufts (2) to the tuftcloth (1) was achieved by stitching, in particular 11 stitches per 10 cm. The resulting synthetic grass is illustrated in Fig. 7. In this figure, each tuft (2) shows only one portion of the composite yarn. In practice, each tuft (2) comprises, due to the tufting technique, two portions of the composite yarn, the filaments of both portions being intermixed with one another. To finish to synthetic turf, it was filled with a top-dressing comprising a layer of sand (4) and subsequently a layer of rubber granules (5). The resulting weight of the entire composition was 2624 g/m². The synthetic turf immediately resembled natural grass, i.e. no post-fibrillation or wear was necessary to achieve this look.

Example 2

A composite yarn was made by twining one fibrillated yarn (6) around six individual monofilament yarns (7). The composite yarn had a yarn number of 16000 dtex and was composed of one fibrillated yarn (6) having a yarn number of 6800 dtex, four individual propeller shaped monofilament yarns with a yarn number of 1550 dtex and two flat shaped yarns of 1500 dtex. The individual monofilament yarns were all made of a mixture of 50% HDPE and 50% LLDPE, containing UV and heat stabilizers. To some of the yarns a yellow-green pigment was added, to others a bright green pigment and to the remaining yarns a dark green pigment. A tuft (2) was made by combining the different colored yarns in such a way that the resulting turf had a more natural look of grass. The composite yarn was tufted on a tuftcloth (1) consisting of a woven HO6 layer and a glass fiber netting. The needle distance of the tufting machine was set at 5/8" and an average of 6929 tufts (2) was placed every m² of the tuftcloth (1). The tufts (2) had an average height (h) of 60 mm and an average weight of 1575 g/m². Fixation of the tufts (2) to the tuftcloth (1) was achieved by stitching, in particular 11 stitches per 10 cm. The resulting synthetic grass is illustrated in Fig. 7. In this figure, each tuft (2) shows only one portion of the composite yarn. In practice, each tuft (2) comprises, due to the tufting technique, two portions of the composite yarn, the filaments of both portions being intermixed with one another. To finish to synthetic turf, it was filled with a top-dressing comprising a layer of sand (4) and subsequently a layer of rubber granules (5). The resulting weight of the entire composition was 2869 g/m². The synthetic turf immediately resembled natural grass, i.e. no post-fibrillation or wear was necessary to achieve this look.

Example 3

A composite yarn was made by twining eight individual monofilament yarns (7) together. The composite yarn had a yarn number of 12200 dtex and was composed of four individual waving shaped monofilament yarns with a yarn number of 1550 dtex and four flat shaped yarns of 1500 dtex. The yarns with the cross-section of a waving profile have a total width of L₁, being 6.38 cm. Over a width L₂ of 6 cm, the thickness d remains 0.38 cm while the rounded ends have a radius R₃ of 0.19 cm. The outer diameter R₁ and inner diameter R₂ of the curves comprise respectively 6.38 and 6 cm. The individual monofilament yarns (7) were all made of a mixture of 50% HDPE and 50% LLDPE, containing UV and heat stabilizers. To some of the yarns a yellow-green pigment was added, to others a bright green pigment and to the remaining yarns a dark green pigment. A tuft (2) was made by combining the different colored yarns in such a way that the resulting turf had a more natural look of grass. The composite yarn was tufted on a tuftcloth (1) consisting of a woven HO6 layer and a glass fiber netting. The needle distance of the tufting machine was set at 5/8" and an average of 6929 tufts (2) was placed every m² of the tuftcloth (1). Fixation of the tufts (2) to the tuftcloth (1) was achieved by stitching, in particular 11 stitches per 10 cm. The resulting synthetic grass is illustrated in Fig. 7. In this figure, each tuft (2) shows only one portion of the composite yarn. In practice, each tuft (2) comprises, due to the tufting technique, two portions of the composite yarn, the filaments of both portions being intermixed with one another. To finish to synthetic turf, it was filled with a top-dressing comprising a layer of sand (4) and subsequently a layer of rubber granules (5). The resulting weight of the entire composition was 2869 g/m². The synthetic turf immediately resembled natural grass, i.e. no post-fibrillation or wear was necessary to achieve this look.

Claims

A synthetic turf comprising a tuftcloth (1) and tufts (2) projecting thereof, the tufts comprising individual filament yarns (7) and at least one fibrillated yarn (6), characterized in that at least a number of said yarns consist essentially of a mixture of high density polyethylene (HDPE) and low density linear polyethylene (LLDPE).
A synthetic turf according to claim 1, characterized in that the composition of said mixture comprises 20 to 80% HDPE and 80 to 20% LLDPE, preferably 40 to 60% HDPE and 60 to 40% LLDPE, and more preferably approximately 50% HDPE and 50% LLDPE.
A synthetic turf according to claim 1 or 2, characterized in that at least a number of said tufts (2) consist of a composite yarn formed by said fibrillated yarn or yarns (6) twined together with a number of said individual filament yarns (7).
A synthetic turf according to any of the claims 1 to 3, characterized in that said composite yarn consists of a fibrillated yarn (6) twined around the individual filament yarns (7) so that the composite yarn has an outer surface which is mainly formed by the fibrillated yarn (6).
A synthetic turf according to any of the claims 1 to 4 characterized in that said composite yarn has a yarn number between 5000 and 30000 dtex, preferably between 9000 and 20000 and more preferably around 16000 dtex.
A synthetic turf according to any of the claims 1 to 5, characterized in that said composite yarn comprises between 3 to 9 said individual filament yarns (7), and preferably 6.
A synthetic turf according to any of the claims 1 to 6, characterized in that said composite yarn comprises between 1 to 3 said fibrillated yarns (6) and preferably 1.
A synthetic turf according to any of the claims 1 to 7, characterized in that said fibrillated yarn (6) is comprised of a tape having longitudinal slits forming laterally interconnected filaments.
An individual filament yarn suitable for use in the synthetic turf according to any of the preceding claims 1 to 8, comprising a convex or curved cross-section.
A yarn according to claim 9, characterized in that the edges of the cross-section of the yarn are rounded.
A yarn according to claim 9 or 10, characterized in that the cross-section of the yarn comprises an S-profile or a slightly curved profile.
A yarn according to any of the claims 9 to 11, comprising point symmetry.
A synthetic turf comprising a tuftcloth (1) and tufts (2) projecting thereof, characterized in that at least a number of said tufts (2) consist of a composite yarn formed by fibrillated yarn or yarns (6), twined together with individual filament yarns (7) according to any of the claims 9 to 12 or any combination thereof and preferably further combined with individual filament yarns (7) with a flat profile.
A synthetic turf according to claim 13, characterized in that at least one of said individual filament yarns (7), preferably all of them, and preferably also the fibrillated yarn or yarns (6), consist essentially of a mixture of high density polyethylene (HDPE) and low density linear polyethylene (LLDPE).
A synthetic turf according to any of the claims 1 to 8 or 13 or 14, characterized in that said tufts (2) consist of said yarns colored yellow-green, bright green or dark green, whereby the tufts comprise a composition of colored yarns in such that they have a more natural look and resemble grass.