EP2726674B1

EP2726674B1 - Synthetic fibre and an artificial lawn comprising such a fibre

Info

Publication number: EP2726674B1
Application number: EP12733231.0A
Authority: EP
Inventors: Jean-Claude Auguste; Harry R. Ma
Original assignee: Ten Cate Thiolon BV
Current assignee: Ten Cate Thiolon BV
Priority date: 2011-07-01
Filing date: 2012-06-27
Publication date: 2019-04-10
Anticipated expiration: 2032-06-27
Also published as: KR20140071325A; TR201910153T4; KR102373501B1; EP2726674A1; WO2013006042A1; KR20210005736A; AU2012278394A1; CN103764915A; AU2012278394B2; RU2637261C2; ES2734059T3; RU2014101667A; ZA201400486B; CN103764915B; PL2726674T3

Description

FIELD OF THE INVENTION

The present invention relates to synthetic fibers and artificial lawn comprising such a fibre. More particularly, the invention relates to grass-like monofilament type fibers having a curved cross section and an artificial grass lawn, especially an artificial grass sports field, comprising such a fibre.

DESCRIPTION OF THE PRIOR ART

Natural grass is often used intensively and as a result thereof and as a result of others such as varying weather influences, sustain a great deal of damage. A number of artificial lawns have been introduced to provide an alternative for natural grass. These artificial lawns are used both indoors as well as outdoors. A well known example of such an outdoor artificial lawn is an artificial grass sport field, for example, for playing soccer, field hockey, tennis, American football and the like. For example in WO 2010/082816 A1 in the name of the same applicant such an artificial lawn is disclosed.
Artificial lawns, like artificial grass sport fields, require less maintenance and can be used/played-on much more intensively than lawns of natural grass. Artificial lawns, however, must have specific properties in order to be able to withstand the loads to which they are subjected as a result of intensive use. Furthermore they must exhibit a natural look.
A drawback of synthetic fibres used for artificial lawns is that they tend to assume a flat orientation relative to the ground surface during use. This can result in so-called "bare patches" in the lawn and can thus increase the risk of injuries, decrease the playing characteristics and/or give a less natural look, etc.
In order to, at least partially, overcome this drawback, a thick layer of infill can be provided on the artificial lawn. Such a thick layer of infill is for example disclosed in EP 1158099 A2 . Installing this thick layer of infill is, however, more labor intensive than installation of a natural lawn. Furthermore substantially more maintenance is required as the infill, over time, gets a less uniform distribution due to non-uniform use of the lawn.
An alternative for the thick layer of infill is to provide an artificial lawn having synthetic fibres which have an increased stiffness and resilience. This result can be achieved by changing the chemical composition and/or the processing method. This, however, is undesirable because it will lead to a more complex production process and/or abrasive artificial lawn with an increased risk of injuries.
Another solution for the problem as described above is to adapt the geometry of the synthetic fibre, for example as disclosed in WO 2010/082816 A1 . The fibre disclosed herein has such a geometry that it has an increased resistance to the loads applied thereon when playing a sport on the field. The surface of the fibre however is smooth and in combination with used chemical compositions result in a shiny, non natural, synthetic look. In WO 2005/005730 A1 a fibre is disclosed comprising stiffness-enhancing agents. These agents, i.e. protrusion ribs, increase the fibre's stiffness/resilience and because of the non-smooth surface exhibits a light scattering effect, decreasing the synthetic fibre's shiny look.
Due to the presence of thickened or narrowed parts, i.e. so called "spines" or "buckles", in the fibres discloses in both documents WO 2010/082816 A1 and WO 2005/005730 , a concentration of material stresses will inevitably take place when loads are exerted thereon, which may lead to fracture or splitting of the fibre.
It is an object of the present invention to provide an improved synthetic fibre for use in an artificial lawn. More specific, it is also an object of the present invention to provide a synthetic fibre with a decreased risk of worn flat due to splitting of the fibre and an improved natural-like look.

SUMMARY

According to a first aspect of the invention, a synthetic fibre of the monofilament type for use in an artificial lawn is provided in accordance with the features of claim 1, in particular for use in an artificial sports lawn, which synthetic fibre has a curved cross section, wherein the synthetic fibre has a centre line arc length (L) to maximum thickness (T) ratio (L/T) of between 4.5 and 3.8, and more preferably between 4.4 and 4.0.
In a further embodiment the synthetic fibre has a convex surface radius (R1) to concave surface radius (R2) ratio (R1/R2) of less than 0.9. More particularly the convex surface radius (R1) to concave surface radius (R2) ratio (R1/R2) is between 0.6 and 0 and even more particular between 0.35 and 0.
In yet a further embodiment the synthetic fibre has a linear mass density between 1000 dtex and 2500 dtex.
From WO 2005/005730 A1 a synthetic fibre having stiffness-enhancing agents is known. These agents, arranged as protrusion ribs, increase the stiffness of the fibre. The stiffness-enhancing agents are provided at a central axis of the fibre or at both ends of the wings of the fibre. These stiffness-enhancing agents do on the one hand increase the stiffness of the fibre but do on the other hand increase the risk of fracture or splitting of the fibre. This however is a unwanted side-effect of such a design. During play the fibre is exposed to a large load applied thereon. As a result of such a large load the fibre exhibits material stress, which stress is concentrated on weak points of the fibre. These weak points are points where due to a non-smooth surface of the fibre the stress is concentrated. As added ribs on a fibre exhibit a non-smooth transition at the point where the rib shape protrudes, a concentration of stress at this point will directly during use of the field, or inevitably after time, cause the fibre to fracture or split.
Known prior art fibres, such as the fibre known from WO 2005/005730 A1 , have a certain thickness to centre line arc length ratio, which ratio, amongst others, determine properties/characteristics of the fibre such as flexibility, resilience and flexural strength. For curved cross section fibres, this thickness is the maximum thickness, and is located at the central portion of the fibre (see reference "T" in figure 1a for example). The centre line arc length is the length of the centre line (see reference "L" in figure 1a for example). As the centre line of curved fibres having a certain curvature or radius, the length of this centre line arc is larger than the over all width (W) of the fibre. The ratio of a fibre according to the invention is determined not by the width of the fibre but by the length of the centre arc line.
Study showed that such a synthetic fibre according to a first aspect or to the first and more of the above stated aspects of the invention, has improved aesthetics (e.g., appearance) and mechanical properties and closely simulates natural turf. Whereas prior art synthetic fibres show a non optimal stiffness upon a load applied thereon, a synthetic fibre according to an aspect of the invention, having a L/T, R1/R2 ratio within the range of linear mass density as described above, has an increased optimal stiffness upon a load applied thereon. The fibre exhibits increased and more optimal combination of resilience, flexibility, strength and stiffness.
In a further embodiment the curved cross section has a central portion having a maximum thickness and tapered edges having a minimum thickness. The fibre geometry of such a fibre thickness combination provides desirable balance of stiffness and flexibility, as well as of bending resilience of the fibre, preventing a flat orientation in the artificial lawn.
In a further embodiment the cross sectional shape has a circular segment shaped cross section, and in yet another embodiment the synthetic fibre has a convex side which is curved and a side formed by a straight line. A synthetic fibre according to an aspect of the invention can be provided with a convex side and on the other side a line which is anywhere between a straight line and a strong concave line.
A synthetic fibre that is provided with a wave shaped pattern around the circumferential surface has, with respect to prior art fibres such as for example the fibre known from WO 2005/005730 , an increased stiffness, because all waves of the pattern do function as stiffness enhancements. A further advantage lies in the smooth transitions of the surface contour having a multiple wave shaped pattern. This wave shaped pattern exhibits an increased stiffness without an increased risk of fracture or splitting of the fibre. All load applied on the fibre during use is divided along the whole surface of the fibre by the multiple waves. Because of this enhanced stress distribution, no stress concentration point exist on the surface of the fibre. It is therefore for a fibre having such a wave shaped pattern less likely to split or fracture. In a further embodiment the wave shaped pattern can also be arranged and extended continuously in the longitudinal direction.
For production of synthetic fibres, the choice of the chemical composition is limited. Several polymers can be used for the production of the fibres. For example polyethylene, polypropylene, polyamide or a combination thereof can be used. When a fibre is produced from such a compositions it has a shiny effect over its surface. This shiny effect gives the fibre a non natural look. As adding certain chemical additives to the composition for reducing this effect, it also changes the intrinsic characteristics of the fibre to unwanted effect. A fibre having a wave shaped patterned surface however does provide a solution to this problem. No change in chemical composition or use of additives is needed. The wave shapes on the fibre surface have a significant light scattering effect, and therefore the fibre has a more "dull" look. The wave patterned surface reflects light in different directions resulting in the light scattering effect. The synthetic fibre can be provided with either a circular segment shaped cross section or a cross section having a convex side and a side formed by a straight line.
Fibre characteristics of an artificial fibre according to an aspect of the invention, having a curved cross section with a maximum thickness central portion and tapered edges with a wave shaped pattern around its circumference can be further optimized by changing the amount of and/or adjusting its size/dimension of the wave shapes. Increasing the amount of wave shapes will increase the light scattering effect, making the fibre more dull, and therefore more natural like. Increase the size/dimension of the wave shapes will lead to an increased stiffness of the fibre, because the waves function as stiffness-enhancing means. Larger waves will exhibit a larger stiffness-enhancing effect.According to the invention, the wave shaped pattern is a sine wave shaped pattern. The advantage of a sine wave shaped pattern is that it has an even smoother wave transition in between the antinodes of the pattern. Therefore the fibre can resist an even greater load without losing stiffness and without an increased risk of splitting/fracture.
In yet another embodiment the wave shaped pattern on a convex side of the curved synthetic fibre has an equal, number of antinodes as that, on a concave side of the curved synthetic fibre. In addition, the antinodes of the wave shaped pattern on the convex side of the curved synthetic fibre can be positioned opposite to the nodes of the wave shaped pattern on the concave side of the curved synthetic fibre.
In a different embodiment the wave shaped pattern on the convex side of the curved synthetic fibre has a larger number of antinodes than that on the concave side of the curved synthetic fibre.
In another embodiment the number of antinodes on either the convex side or the concave side is at least 4 but not more than 30.
In yet another embodiment at least some waves of the wave pattern have different dimensions.
With changing the dimensions of the wave shapes the characteristics of the fibre can be changed. By combining different sizes, protrusions, dimensions or the like a combination of effects can be achieved. For example large waves can be alternated with small ones combining different effects like stiffness, light scattering effect, fibre resilience, and the like.
In another embodiment of the invention, the synthetic fibre of the monofilament type for use in an artificial lawn is provided, in particular for use in an artificial sports lawn, which synthetic fibre has a curved cross section, wherein the circumferential surface of the synthetic fibre is provided with a wave shaped pattern. In addition, the wave shaped pattern is arranged in the longitudinal direction of the fibre.
The invention also provides in an embodiment an artificial lawn, in particular an artificial sports lawn, comprising a substrate having artificial fibres according to any of the features described above attached thereto.
The above-mentioned and other features and advantages of the invention are illustrated in the following description with reference to the enclosed drawings which are provided by way of illustration only and which are not limitative to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1a-1b show a synthetic fibre having a centre line arc length to maximum thickness ratio according to the invention but without a wave-shaped pattern;
Figs 2 and 3 show a synthetic fibre according to the invention wherein the fibre has different cross sectional shapes and the fibre is provided with different shapes around the circumferential surface;
Figs. 4 and 5 schematically show a few embodiments of an artificial lawn comprising a synthetic fibre according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, like elements will be indicated by the same reference numbers in the description of the figures below.
Fig. 1a shows in a cross sectional view a fibre not falling under the scope of the invention wherein with reference number 10a a synthetic/artificial fibre, for example a synthetic grass sports fibre is illustrated, which is preferably of a monofilament type obtained by an extrusion process.
The bending radius 10a6 or amount of curvature of the fibre 10a shown in figure 1a has an effect on the characteristics of the artificial lawn in which it is provided. Increasing the curvature will increase the flexural stiffness of the fibre, which as a result thereto will not unnecessarily assume a flat orientation in the artificial lawn of which the fibre 10a forms part. Increasing the stiffness, however, can decrease the playing characteristics of the artificial lawn because when played on, it can lead to an increased risk of injuries and in particular when sliding tackles are made thereon.
Decreasing the stiffness however, will tend the fibre to assume a more flat orientation during play on the artificial lawn. As a result the fibre's functionality as regards to the playing characteristics of the artificial lawn will be lost. "Bare" patches on the field will appear and the risk of injury is increased there.
An optimal stiffness is therefore required to on the one hand prevent a flat orientation and on the other hand still provide a relative soft player friendly artificial lawn with low risk of injuries..
Figure 1a shows that the fibre 10a has a curved shape, which curve radius 10a6 shown in figure 1a is only indicative.
The ratio between the concave surface radius 10a7 (R2) and the convex surface radius 10a8 (R1) is in this embodiment less than 0.9, and preferably between 0.6 and 0, and even more preferably between 0.35 and 0. The fibre shown in figure 1b has a flat surface at its concave side R2.
Besides the stiffness other characteristics of a fibre influence the playability of an artificial grass sports field. In order to provide a natural like artificial grass sports field the fibres used therein, should also have an optimal flexibility and resilience. Flexibility can prevent the fibre from splitting or fracture when undergoing high material stress when being played on. Resilience is needed for the fibre to re-assume an erect orientation after impact of forces applied thereon during play.
The fibre 10a shown in figure 1a is tapered near the edges 10a1a, 10a1b and reaches its maximum thickness at the centre portion 10a1c. The fibre 10a shown here has relative thin edges 10a1a, 10a1b. Increasing this thickness will increase the stiffness of the fibre. The edges 10a1a and 10a1b are preferably round. The fibre 10 does therefore not only have non-sharp edges, which have a positive effect on the playing characteristics, it also decreases the risk of injuries when for example making a sliding or tackle.
The centre line arc length 10a6 of the fibre 10a disclosed in figure 1a is clearly larger than the thickness T 10a3, measured at the middle, central part 10a1c of the fibre. The centre line arc length 10a6 is determined by, and defined as, the length of dotted line Rc 10a6 from one end of the fibre 10a1a to the other 10a1b. According to the invention the ratio (L/T) between the centre line arc length 10a6 and the maximum thickness 10a3 is between 4.5 and 3.8, and preferably between 4.4 and 4.0.
The linear mass density of a fibre according to an aspect of the invention, is in the range between 1000 dtex and 2500 dtex. As the centre arc line length to thickness ratio is dependent upon the fibre's dtex, the centre arc line length or thickness of a fibre according to an aspect of the invention can be calculated when the dtex and one of the centre arc line length and thickness is given.
The above stated characteristics can be changed, and an optimum combination of stiffness, flexibility and resilience can be achieved according to an aspect of the invention wherein the fibre is a fibre 10a having a L/T ratio as it is described above, the fibre 10a exhibits improved characteristics. Study shows that especially the stiffness of a fibre 10a according to this aspects has substantially increased with respect to prior art fibres. The fibre 10a characteristics are such that not only a sufficient resilience and flexibility is achieved, but also that it exhibits a flexural stiffness such that it will not unnecessarily assume a flat orientation in the artificial lawn, or the artificial grass sports field in case of a synthetic grass sports fibre of which the fibre 10a forms part of.
Such a fibre according to an aspect of the invention and according to figures 1a-1b, are preferably made of polypropylene, polyethylene, polyamide, a copolymer, or a blend of one or more of the these polymers. In possible embodiments of the synthetic fibre, the fibre may therefore be made of rubber, which is permanently elastic synthetic polymer, or of a synthetic (co)polymer which will remain within the elastic range upon being subjected to a load.
The fibre 20 as shown in figure 2, being provided with a sine wave shaped pattern around the circumferential surface. The sine wave shaped pattern is provided with nodes 21c and antinodes 21a, 21b. The nodes 21c of the fibre function as stiffness-enhancing means and the size, amount and position can be changed to influence the stiffness needed for a particular artificial lawn.
The way the fibre 20 is provided with a sine wave shaped surface increases it's natural look. Light rays striking the surface of the fibre 20 are directed in a different direction than the direction they originated from. Parallel rays of light striking a fibre 20 according to the invention having a wave shaped surface will be directed to different directions. The amount of waves/antinodes and nodes and the size/dimension of the waves influence this light scattering effect. Study showed that a fibre 20 according to the invention which is provided with a wave shaped pattern as indicated in figure 2 has an increased light scattering effect and therefore such a natural look that it closely resembles real grass.
In figure 2, the smooth transition between the antinodes (positive 21a, and negative 21b) prevent the fibre from splitting or fracture, and an increased lifetime is herewith achieved.
The fibre 20 shown in figure 2 has relative small and sharp edges 20a and 20b and an optimal L/T ratio of 3.8. The concave side of the fibre 20 is provided with eight nodes 21c and seven antinodes 21a, 21b. The other side which in this figure lies below the central portion 20c of the fibre 20, being the convex side of the fibre 20, is provided with ten nodes 21c and 9 antinodes 21a, 21b.
In figure 3a different embodiment of the invention is disclosed wherein a fibre 70 has a curved cross section with a wave shaped pattern around the circumferential, however the fibre is, seen in cross sectional view, flat at one side. The wave shaped pattern, which in this embodiment is a sine shaped pattern, consists of nodes 71c and both negative antinodes 71b as well as positive antinodes 71a. Such a sine shaped pattern will decrease the risk of splitting or fracture due to the smooth transitions at the nodes. The flat side of an embodiment of the fibre 70 shown in figure 3 is provided with seven (both positive and negative) antinodes 71a, 71b and eight nodes 71c and on its convex side, the fibre 70 is provided with nine (both positive and negative) antinodes 71a, 71b and ten nodes 71c.
Figures 4 and 5 show a few embodiments of an artificial lawn such as an artificial grass sports field in which a synthetic fibre according to the invention can be used. In both figures the artificial lawn comprises a backing 1, to which the several synthetic fibres 2 (corresponding to the fibres 20 and 70 shown in figures 2 and 3) are attached at the locations indicated by reference numeral 3, for example by tufting or weaving. The extruded synthetic fibre 2 may be individually attached to the backing 1 or in a bundle of, for example twined, fibres 2a-2c. The backing member in figure 4 has an open structure and is composed of a grid of supporting yarns 1a-1b, to which the synthetic fibres 2 are attached.

Claims

A synthetic fibre (20, 70) of the monofilament type for use in an artificial lawn, in particular an artificial sports lawn, which synthetic fibre has a curved cross section, wherein the synthetic fibre has a centre line arc length (L) to maximum thickness (T) ratio between 4.5 and 3.8 and wherein the circumferential surface of the synthetic fibre is provided with a sine wave shaped pattern.
The synthetic fibre (20, 70) according to claim 1, wherein the synthetic fibre has a centre line arc length (L) to maximum thickness (T) ratio between 4.4 and 4.0.
The synthetic fibre (20, 70) according to any of the previous claims, wherein the synthetic fibre has a convex surface radius (R1) to concave surface radius (R2) ratio of less than 0.9, and in particular between 0.6 and 0, more in particular between 0.35 and 0.
The synthetic fibre (20, 70) according to any of the previous claims, wherein the synthetic fibre has a linear mass density between 1000 dtex and 2500 dtex.
The synthetic fibre (20, 70) according to any of the previous claims, wherein the curved cross section has a central portion having a maximum thickness (T) and tapered edges (20a, 20b, 70a, 70b) having a minimum thickness.
The synthetic fibre (20, 70) according to any of the previous claims, wherein the synthetic fibre has a circular segment shaped cross section.
The synthetic fibre (20, 70) according to any of the previous claims, wherein the cross sectional shape has a convex side and a side formed by a straight line.
The synthetic fibre (20, 70) according to claim 1, wherein the wave shaped pattern is arranged in the longitudinal direction of the fibre.
The synthetic fibre (20, 70) according to claim 1, wherein the wave shaped pattern on a convex side of the curved synthetic fibre has an equal number of antinodes as the wave shaped pattern on the other, concave side of the curved synthetic fibre.
The synthetic fibre (20, 70) according to claim 1, wherein at least some waves of the wave shaped pattern have different dimensions seen in the same circumference of the cross section of the fibre.
The synthetic fibre (20, 70) according to claim 1, wherein the wave shaped pattern on a convex side of the curved synthetic fibre has a larger number of antinodes than the wave shaped pattern on the other, concave side of the curved synthetic fibre.
The synthetic fibre (20, 70) according to claim 1, wherein the antinodes of the wave shaped pattern on a convex side are positioned opposite to the nodes of the wave shaped pattern on the other, concave side of the curved synthetic fibre.
An artificial lawn, in particular an artificial sports lawn, comprising a substrate having artificial fibres according to any of the previous claims attached thereto.