Split resistant fibre

Abstract

A fibre for use in artificial turf has an elongate cross-sectional shape defining a first face and a second face that meet at side edges of the fibre. The first and second faces having respective first and second ridges that are offset with respect to each other, such that the cross-sectional shape is 2-fold rotationally symmetric with no reflectional symmetry. The fibre may be an extruded monofilament and shows improved resilience over symmetrical fibres of similar dimensions.

Claims

1. A fibre for use in artificial turf, the fibre having an elongate cross-sectional shape defining a first face and a second face that meet at side edges of the fibre, wherein a maximum thickness of the fibre is between 0.2 mm and 0.6 mm, determined based on a largest diameter circle that can fit within the cross-sectional shape and a ratio between the maximum thickness of the fibre and a length of a centre line extending between the side edges is between 0.3 and 0.6 and no part of the first and second faces crosses the centre line, wherein the largest diameter circle fits in a first position and a second position of the cross-sectional shape, wherein the first face has a first ridge which lies on a diameter of the largest diameter circle in the first position and the second face has a second ridge which lies on a diameter of the largest diameter circle in the second position, wherein the first ridge and the second ridge are offset with respect to each other and such that the cross-sectional shape is 2-fold rotationally symmetric with no reflectional symmetry.

2. The fibre according to claim 1, wherein the first and second faces have concave portions.

3. The fibre according to claim 1, wherein the first and second faces have corrugations.

4. The fibre according to claim 1, wherein the centre line has a length of between 0.5 mm and 2 mm.

5. The fibre according to claim 1, wherein the fibre has a dtex value of between 1500 and 3000.

6. The fibre according to claim 1, wherein the side edges are rounded and have a radius of curvature of at least 0.05 mm.

7. The fibre according to claim 1, wherein the first and second ridges are rounded and have a radius of curvature of at least 0.1 mm.

8. The fibre according to claim 1, wherein the first and second ridges are offset from each other along the centre line by a distance that is greater than 0.05?the centre line length but less than 0.4?the centre line length.

9. The fibre according to claim 1, wherein the fibre is an extruded monofilament.

10. The fibre according to claim 1, wherein the fibre consists of a polymer selected from the group consisting of: polyamides; polyesters; polypropylene; polyethylene; polyolefin block copolymers and blends and co-extrusions thereof.

11. The fibre according to claim 1, wherein the maximum thickness of the fibre lies between 0.2 mm and 0.6 mm.

12. Artificial turf comprising upstanding pile fibres according to claim 1, retained in a backing.

13. Artificial turf according to claim 12, wherein the pile fibres are tufted to the backing.

14. Artificial turf according to claim 12, wherein the pile fibres are woven together with the backing.

15. Artificial turf according to claim 12, wherein the pile fibres are mixed with further pile fibres having different cross-sectional shapes.

16. Artificial turf according to claim 15, wherein the further pile fibres comprise fill fibres being shorter than the pile fibres and serving to support the pile fibres in an upright position.

17. Artificial turf according to claim 12, wherein the pile fibres have a pile height of more than 4 cm.

18. Artificial turf according to claim 12, wherein the pile fibres extend in a plane of the backing over a fibre length of more than 10 mm.

19. A sports field comprising artificial turf according to claim 12.

20. A fibre for use in artificial turf, the fibre having an elongate cross-sectional shape defining a first face and a second face that meet at side edges of the fibre, the first and second faces having respective first and second ridges that are offset with respect to each other, wherein extremities of the side edges and extremities of the first and second ridges form a parallelogram and the first and second faces have concave portions such that surfaces of the fibre are displaced inwardly with respect to the surface of the parallelogram but no part of the first and second faces crosses a centre line extending between the side edges; and wherein a maximum thickness of the fibre is determined based on the largest diameter circle that can fit within the cross-sectional shape and a ratio between the maximum thickness of the fibre and a length of the centre line is between 0.25 and 0.6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

(2) FIG. 1 depicts a perspective view of a fibre according to the present invention;

(3) FIG. 2 depicts a cross-sectional view through the fibre of FIG. 1;

(4) FIG. 3 depicts artificial turf incorporating the fibres of FIG. 1; and

(5) FIG. 4 depicts a cross-sectional view of a fibre according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(6) FIG. 1 shows a magnified perspective view of a fibre 1 according to the present invention. The fibre 1 is elongate and may be attached to a backing (not shown in this view), to maintain it in an upright position. The fibre 1 has a first face 2 and a second face 4, with a first ridge 6 extending down the first face 2 and a second ridge 8 extending down the second face 4. The faces 2, 4 are also provided with corrugations 10, of which the corrugations 10 extending down the second face 4 can be seen in this view.

(7) The fibre 1 is an extrusion of metallocene ethylene-hexane copolymer having secant modulus MD (1% secant) of 111 MPa according to ASTM D882 and subjected to a draw ratio of 4.

(8) FIG. 2 shows the fibre 1 of FIG. 1 in cross-sectional view. It will be understood that due to the manner of manufacture by extrusion, the fibre is substantially identical at every cross section along the fibre length.

(9) According to FIG. 2, the first and second faces 2, 4 extend between left and right side edges 12, 14. A centre line CL is shown joining the left and right side edges 12, 14. The centre line CL has a mid-point M. According to the invention, the first ridge 6 is offset from the second ridge 8 along the centre line CL away from the mid-point M. In other words, the first ridge 6 is closer to the left side edge 12 and the second ridge 8 is closer to the right side edge 14. The portion of the first face 2 between the first ridge 6 and the right side edge 14 is identified as the major face 20 and the portion of the first face 2 between the first ridge 6 and the left side edge 12 is identified as the minor face 22. Both the major face 20 and the minor face 22 are generally concave, while the first ridge 6 is convex.

(10) The cross-section of the fibre 1 is such that it has 2-fold rotational symmetry. This means that the first face 2, when rotated through 180? about the mid-point M will coincide directly with the second face 4. Due to the offset between the first and second ridges 6, 8, there is no reflectional symmetry about the centre line CL or even about any other line.

(11) In the illustrated embodiment, the centre line CL has a length L of 1.2 mm and the offset OS between the first and second ridges 6, 8 is 0.1 mm. A thickness T of the fibre 1 measured transverse to the centre line at the widest point is around 0.38 mm.

(12) In addition to the first and second ridges 6, 8, the corrugations 10 on the first and second faces 2, 4 of the fibre 1 can also be seen in this view. There are a total of four corrugations 10 on the major face 20 and three corrugations 10 on the minor face 22. Additionally, the left side edge 12 and the right side edge 14 are both rounded. In order to avoid difficulties with splitting, the corrugations 10 are smoothly rounded in a continuous curve with no abrupt changes in contour.

(13) FIG. 3 shows a plurality of fibres 1 tufted into a backing 24 to form artificial turf 26. The turf was used in comparative testing as described below.

EXAMPLES

Example 1

(14) A sample of artificial turf measuring 1 metre?3.70 metres according to FIG. 3 was prepared using bundles of six fibres having a bundle dtex of 12000. The pile height was 60 mm and the backing was double 100% PP Thiobac, black, U.V.-stabilized, weight ca. 222 gr/m.sup.2 from Royal Ten Cate. The tufts were at ? gauge (15 mm) with a spacing of 13.5 tufts per 10 cm in the length direction. The sample was installed on a concrete base and filled with a first stabilising layer of 5 mm sand infill followed by a 35 mm layer of performance infill comprising Genan fine SBR of particle size 0.7-2.0 mm, leaving a free pile height of 20 mm.

Example 2

(15) A turf sample of Slide MAX XQ 60 from Royal Ten Cate measuring 1 metre?3.70 metres was installed on a similar basis to Example 1, using identical infill. The turf had the same dtex, tuft spacing and pile height as Example 1.

Example 3

(16) A turf sample was prepared using Evolution? fibres from Royal Ten Cate having dtex, tuft spacing and pile height as in Example 1 and measuring 1 metre?3.70 metres. The sample was installed on a similar basis to Example 1, using identical infill.

(17) The artificial turf samples of Examples 1 to 3 were subject to repetitive testing using a Lisport XL testing machine. The Lisport? XL is a new generation of wear simulation machines that realistically replicate wear simulation of sport fields after years of usage. The wear pattern is characterised by the compressive stress of football studs (cleats) and the abrasive wear caused by flat-soled sports shoes. It has been widely adopted by the industry as a means of producing realistic simulated patterns.

(18) The test samples were tested through a total of 12000 cycles with intermittent checks every 3000 cycles. Cracking, splitting and resilience of the fibres were measured and documented at each check. The protocol for the checks were as follows.

(19) Cracking

(20) A crack is defined as an opening in the fibre, either at the top of the fibre or within its length. Ten fibres were selected at random from the test area. A mark was given for each fibre that did not exhibit a crack.
Splitting A split is defined as a crack that extends from the top of the fibre to the infill layer. Ten fibres were selected at random from the test area. A mark was given for each fibre that did not exhibit a split.
Resilience the position of the top of 90% of the fibres as a percentage of the initial pile height is measured. 10 points given for 100% of the initial pile height. 9 points given for 90% etc.
Results

(21) Based on a quantitative review of the test samples as described above, and after 12000 cycles, the fibres of the Examples scored as follows: The fibres according to Example 1 scored values of 8 for cracking, 10 for splitting and 7 for resilience. The fibres of Example 2 scored values of 10 for cracking, 10 for splitting and 4 for resilience. The fibres of Example 3 scored values of 4 for cracking, 1 for splitting and 1 for resilience.

(22) The samples were also visually inspected and it was apparent that the turf of Example 1 remained more upright than the other samples. The turf of Example 3 was particularly flattened.

(23) FIG. 4 shows a second embodiment of a fibre 101 according to the invention in which like elements to the first embodiment have similar reference numerals preceded by 100.

(24) The fibre 101 of the second embodiment is substantially identical to that of the first embodiment but for the curvature of the major face 120 and minor face 122. According to this embodiment, the major face 120 is substantially concave, while the minor face 122 is more or less straight. The resulting fibre 101 has greater asymmetry than the fibre 1 of the first embodiment.

(25) Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, the fibres of FIGS. 1 and 4 may be provided without corrugations and the positions and sizes of the ridges may be adjusted accordingly. Furthermore, although straight fibres have been described, the fibres may be formed as twisted or helical fibres by adjusting the post extrusion processing accordingly.

(26) Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.