ARTIFICIAL TURF FIBER AND METHOD OF MANUFACTURING THEREOF

Abstract

A method of manufacturing an artificial turf fiber includes extruding a polymer mixture through at least one fiber profile opening of an extrusion plate to form an artificial turf fiber, where the fiber profile opening includes first and second end portion openings and a curved middle portion opening has at least one spine opening proximate to at least one end portion opening, allowing the extruded polymer mixture to travel along a distance between the fiber profile opening to a quenching unit, where the at least one spine opening is sized and positioned such that a net polymer mass flow in the extruded polymer mixture from a position of the spine opening to the at least one end portion of the fiber proximate the spine opening occurs before the fiber is quenched, and quenching the extruded polymer mixture in the quenching unit to form the artificial turf fiber.

Claims

1. A method of manufacturing an artificial turf fiber, comprising: extruding a polymer mixture through at least one fiber profile opening of an extrusion plate to form an artificial turf fiber, the fiber profile opening including: first and second end portion openings, and a curved middle portion opening connected with the first and second end portion openings, the curved middle portion having at least a first spine opening proximate to the first end portion opening and a second spine opening proximate to the second end portion opening; allowing the extruded polymer mixture to travel along a distance between the at least one fiber profile opening of the extrusion plate to a quenching unit, wherein the first and second spine openings are sized and positioned such that a net polymer mass flow in the extruded polymer mixture from a position of the first spine opening to a first end portion of the fiber and from a position of the second spine opening to a second end portion of the fiber occurs before the fiber is quenched; and quenching the extruded polymer mixture in the quenching unit to form the artificial turf fiber.

2. The method of claim 1, wherein the first spine opening is positioned in the middle portion opening on a first arc length defined by a first angle of less than or equal to 60, or between 35-55, or between 40-50, or at 45, wherein the first arc length is measured along the curved middle portion opening from the first end portion opening, wherein the second spine opening is positioned in the middle portion opening on a second arc length defined by a second angle of less than or equal to 60, or between 35-55, or between 40-50, or at 45, wherein the second arc length is measured along curved middle portion opening from the second end portion opening.

3. The method of claim 1, wherein the net polymer mass flow mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of an end of the quenched fiber.

4. The method of claim 1, wherein the fiber comprises a first spine created by extruding the polymer mass through the first spine opening and comprises a second spine created by extruding the polymer mass through the second spine opening.

5. The method of claim 4, wherein the ratio of an area of the first spine opening to an area of the first end portion opening is larger than the ratio of a cross-sectional area of the first spine of the fiber to a cross-sectional area of the first end portion of the quenched fiber, the first end portion of the fiber being created by extruding the polymer mass through the first end portion opening; and wherein the ratio of an area of the second spine opening to an area of the second end portion opening is larger than the ratio of a cross-sectional area of the second spine of the fiber to a cross-sectional area of the second end portion of the quenched fiber, the second end portion of the fiber being created by extruding the polymer mass through the second end portion opening.

6. The method of claim 4, wherein an amplitude of the first spine of the fiber is less than an amplitude of the first spine opening, and wherein an amplitude of the second spine of the quenched fiber is less than an amplitude of the second spine opening.

7. The method of claim 1, wherein the width of the first end portion opening is larger than the width of the first end portion of the extruded fiber, and wherein the width of the second end portion opening is larger than the width of the second end portion of the extruded fiber.

8. The method of claim 1, wherein the quenched fiber comprises no spines at positions of the first and second spine openings.

9. The method of claim 1, wherein the curved middle portion opening has two opposing longitudinal contours, wherein at least one of the contours comprises or consists of uninterrupted undulations.

10. The method of claim 1, wherein the curved middle portion opening has a shape of one or more sinusoidal waves.

11. The method of claim 1, wherein the curved middle portion opening has a shape of an arc, wherein in particular the shape of the middle portion opening comprises one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of a segment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a .

12. The method of claim 11, wherein a radius of curvature of the middle portion opening decreases from a center of the middle portion opening towards the end portion openings.

13. The method of claim 1, wherein the polymer mixture comprises a polyethylene or a polyethylene-polyamide blend, wherein the quenching unit is a water bath, wherein the distance between the extrusion plate openings and the quenching unit is 3.0-5.0 cm, and wherein a temperature of the water bath is 28 C.-34 C.; or, wherein the polymer mixture comprises polyamide as a main polymer component or consists of polyamide, wherein the quenching unit is a water bath, wherein the distance between the extrusion plate openings and the quenching unit is 2.0-4.0 cm, and wherein a temperature of the water bath is 18 C.-20 C.

14. The method of claim 1, wherein the polymer mixture is at least a two-phase polymer mixture, wherein a first phase of the polymer mixture comprises a first polymer and a first dye and a second phase of the polymer mixture comprises a second polymer and a second dye, wherein a color of the second dye is different than a color of the first dye, wherein the second polymer is of a same or of a different type as the first polymer, wherein the first and the second phases are immiscible, and wherein the extruded fiber has a marbled appearance.

15. An extrusion plate for artificial turf fibers, the extrusion plate comprising: at least one fiber profile opening, the fiber profile opening including: first and second end portion openings, and a curved middle portion opening connected with the first and second end portion openings, having at least a first spine opening proximate to the first end portion opening and a second spine opening proximate to the second end portion opening.

16. Use of the extrusion plate of claim 15 for mitigating or preventing a reduction in width of end portions of a fiber, thereby increasing dimensional stability and/or for mitigating or preventing curling of an end of the fiber after the fiber is formed upon extruding a polymer mixture through the openings of the extrusion plate.

17. A system comprising: the extrusion plate of claim 15; at least one fiber formed by extruding a polymer mass through the at least one fiber profile opening, in particular one of the fibers of claims 18-19; and optionally a quenching unit.

18. An extruded artificial turf fiber having a cross-sectional profile comprising first and second end portions connected via a curved middle portion, wherein the middle portion comprises at least a first spine proximate to the first end portion and comprises at least a second spine proximate to the second end portion.

19. The artificial turf fiber of claim 18, wherein a width of the curved middle portion as measured between first and second boundary lines of the curved middle portion, excluding a center of the middle portion, is: constant along a longitudinal direction of the curved middle portion, or monotonically increasing along the longitudinal direction of the curved middle portion from either or both end portions towards the center of the middle portion.

20. An artificial turf comprising: a carrier; and a plurality of artificial turf fibers of claim 18 integrated into the carrier and protruding therefrom to form the artificial turf.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In the following, examples are described in greater detail making reference to the drawings in which:

[0049] FIG. 1 is a perspective 3D view of the inside of a section of the fiber;

[0050] FIG. 2 is a perspective 3D view of the outside of a section of the fiber;

[0051] FIG. 3 shows the cross-section of a fiber;

[0052] FIG. 4 shows the fiber cross-section of FIG. 3 with height and width annotated

[0053] FIG. 5 shows the fiber cross-section of FIG. 3 with the circles defining the curvature of the corrugations and the ends annotated;

[0054] FIG. 6 shows the fiber cross-section, where the fiber thicknesses at different cross-sectional areas are annotated;

[0055] FIGS. 7A and B show an example of a fiber cross-section annotated with concrete dimensions;

[0056] FIG. 8 shows an example of a cross-section of a further fiber having more undulations;

[0057] FIG. 9 shows an example of a cross-section of a further fiber having more undulations and an extended curvature;

[0058] FIG. 10 shows an example of a cross-section of a further fiber having a central thickening which leads to a visible bulge on both the outer and inner surface of the fiber;

[0059] FIG. 11 shows an example of a cross-section of a further fiber, the cross section having the shape of a catenary;

[0060] FIG. 12 shows a cross-section of an extruded artificial turf fiber, according to an embodiment;

[0061] FIG. 13 shows the cross-section of an extruded artificial turf fiber according to yet another embodiment;

[0062] FIG. 14 shows the cross-section of an extruded artificial turf fiber according to another embodiment;

[0063] FIG. 15 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to an embodiment;

[0064] FIG. 16 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to another embodiment;

[0065] FIG. 17 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to yet another embodiment;

[0066] FIG. 18 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of a horseshoe, according to an embodiment;

[0067] FIG. 19 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of the Greek letter Q, according to an embodiment;

[0068] FIG. 20 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of the letter U, according to an embodiment;

[0069] FIG. 21 shows a photograph of an extruded artificial turf fiber having an approximate sinusoidal shape, according to an embodiment;

[0070] FIG. 22 shows a photograph of an extruded artificial turf fiber having an approximate sinusoidal shape, according to another embodiment;

[0071] FIG. 23 shows a photograph of an extruded artificial turf fiber having an approximate shape of the letter U, according to an embodiment;

[0072] FIG. 24 shows a photograph of an extruded artificial turf fiber having an approximate shape of a horseshoe, according to an embodiment; and

[0073] FIG. 25 shows a photograph of an extruded artificial turf fiber having an approximate shape of a segment of a circle, according to an embodiment.

[0074] FIG. 26 shows three plots illustrating the flow path expansion induced by the spine openings and by a thickening of the end portion openings.

DETAILED DESCRIPTION

[0075] In the following, similar elements may be denoted by the same reference numerals.

[0076] FIG. 1 is a perspective 3D view of the inside of a section of an artificial turf fiber 100. For example, the fiber may be made of polyethylene or polypropylene or polyamide or a mixture of two or more of these polymers. The fiber may be generated in an extrusion process and the cross-sectional area 102 of the fiber may have essentially the same shape along the entire length of the fiber. FIG. 1 shows the inner surface 104 of the fiber defined by the concave part of the boundary line of the shape of the fiber profile. Depending on the type of artificial turf, the length of the fiber (measured from the upper surface of a carrier to the free ends of the fibers) may be different. For example, the fiber length may be in the range of e.g., 2.0 cm to 9.0 cm, preferably 3.0 cm to 7.0 cm.

[0077] FIG. 2 is a perspective 3D view of the outside of a section of the fiber 100 shown already in FIG. 1. FIG. 2 shows the outer surface 202 of the fiber defined by the outer, convex part of the boundary line of the shape of the fiber profile.

[0078] FIG. 3 shows the cross-section of the fiber 100 depicted already in FIGS. 1 and 2. The fiber comprises a first end 302 connected to the center 306 of the fiber via a first fiber arm and comprises a second end 304 connected to the center of the fiber via a second arm.

[0079] As can be inferred from FIGS. 1-3, the fiber has an arced cross-sectional shape, in this case the shape of a circle segment arc. The arced cross-sectional shape is defined by a boundary line consisting of uninterrupted undulations. This means that there are therefore no tapering elevations or recesses and no planar surface areas. In more mathematical terms, the boundary profile may be described as a curve being free of spinodes or cusps, i.e., a point on a curve where a moving point must reverse direction, or as a curve having no discontinuities in slope (i.e., having continuous values of slope) as measured at points along the curve, where slope may be defined as dy/dx at each point (x,y) on the curve, where points (x,y) that define the curve are points defined with respect to a cartesian coordinate system x-y that may be placed anywhere in the plane of FIG. 3, for example. The particular form of the boundary line consisting of uninterrupted undulations may imply that-apart from the cross-sectional area of the fiber at the upper and lower fiber ends where the fiber is cut during or after integration into a carrierthe fiber surface is basically free of any planar areas. This may be highly beneficial, because planar areas reflect the incident light directionally, not diffusely, so that the artificial turf is at least partially highly reflective and can even dazzle the observer. This creates a visual impression that is clearly different from that of a natural lawn, which is undesirable.

[0080] In the example shown, the undulations comprise alternating depressions 308 and elevations 312 on the outer fiber surface and alternating depressions 310 and elevations 314 on the inner fiber surface.

[0081] The thickness of the fiber at the thickenings 318 at the two ends is slightly greater than the thickness of the thickest portions of the fiber arms connecting the ends 302, 304 with the center 306. Moreover, there is a further thickening at the center of the fiber resulting in a protrusion/undulation 316 from the outer surface 312. In the depicted example, the central thickening does not result in a protrusion from the inner surface 102 of the fiber.

[0082] FIG. 4 shows the fiber cross-section of FIG. 3 with height h and width w annotated. For example, the width w can be measured as straight line indicating the distance of the most outer points of the two fiber ends. The height h of the fiber may be measured as the distance of the lowest points of the fiber ends to the highest point at the fiber center. As can be inferred from FIG. 4, the height h may be significantly smaller than the radius defining the curvature of the arced shape of the fiber profile, meaning that in case the arced shape is defined by a circle, the fiber profile may cover a segment that is significantly smaller than the 180 segment. In other words, the radius of this circle may be significantly longer than h.

[0083] FIG. 5 shows the fiber cross-section of FIG. 3 with the circles defining the curvature of the corrugations and the ends annotated. As illustrated in FIG. 5, the undulations of the boundary line defining the shape of the outer surface of the fiber are defined by multiple circles 508 sharing the same radius/diameter D3. The undulations of the boundary line defining the shape of the inner surface of the fiber are defined by multiple circles 510 sharing the same radius/diameter D4. The fiber has thickenings at the center and at the two ends to increase the mechanical stability. The curvature of the ends is defined by the radius/diameter D1 of the circles 502. The curvature of the protrusion 316 induced by the thickening at the center is defined by the radius/diameter D2 of circle 506. As can be inferred from FIGS. 5, D1 and D2 are significantly larger than D3 and D4. D3 and D4 are identical. D1 is slightly larger than D2.

[0084] In other embodiments (not shown), D3 and D4 may be similar, but not identical.

[0085] In addition, or alternatively, D1 and D2 may be identical. For example, both D1 and D2 may represent a diameter which is chosen such that the ratio of D1 (or D2) to D3 (or D4) approximately is the golden ratio,

[0086] FIG. 6 shows the fiber cross-section, where the fiber thicknesses at different cross-sectional areas are annotated. As can be inferred from FIG. 6, the thickness of the fiber cross section is not constant but varies only slightly: the thickness w1 602 is slightly greater than the thickness w2 604 at the two points in the fiber arms equidistant from the ends, because in the depicted example, the fiber ends comprise a thickening. The thickness w3 606 at two other points in the fiber arms equidistant from the ends is slightly greater than the thickness w2. The fiber center represents the thickest and hence stiffest portion of the fiber having a thickness w4 608 being greater than w1, w2 and w3.

[0087] In the depicted example, w2 is the smallest with in the fiber arm and w3 is the largest width of the fiber arm.

[0088] In other examples, w1 and w2 may be identical, but preferably w1 is greater than the smallest width w2 of the fiber arms, and preferably also greater than the largest width w3 of the fiber arm.

[0089] According to some examples, the fiber profile is axisymmetric with respect to a vertical axis through the center of the fiber profile as shown in FIGS. 3-6. According to other embodiments, the undulations may be shifted such that the fiber profile is not axisymmetric with respect to the vertical axis.

[0090] FIGS. 7A and 78 show an example of a fiber cross-section annotated with concrete dimensions. The fiber cross section corresponds to the cross section of the fibers depicted in FIGS. 1-6. The dimensions of the fiber 100 shown in FIGS. 7A and 7B correspond to a 1100 dtex fiber. The numbers are given in cm. For example, the width of the fiber profile measured from the outermost points of the two ends is 1.0 cm, or 0.9 cm if the distance between the centers of the two fiber ends is measured.

[0091] The fiber profile can be scaled to provide fibers of different fiber weights. For example, by scaling the outer width of the fiber profile from 1.0 cm to 1.351 cm, and scaling all other dimensions given in FIG. 7 proportionally, a fiber of 2000 dtex can be obtained. By using a different scaling factor, many different versions of the artificial turf fiber having different fiber weights can be obtained.

[0092] As can be inferred from FIGS. 7A and B, the cross-section of the fiber is shaped like the arc of a segment of a circle having a radius referred to as fiber profile circle radius.

[0093] According to FIG. 7A, the radius to the topmost point of the outer surface is 0.59 cm. The width of the fiber profile when the outmost points of the fiber ends are considered is 1.0 cm. Hence, the ratio of the width of the fiber profile and the fiber profile radius is 1.0/0.59, i.e., 1.694. This value is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, and hence approximately the golden ratio.

[0094] According to FIG. 7B, the radius of the circle 506 defining the undulation at the center of the fiber is 0.081 cm. The shared radius of the multiple smaller circles defining the undulation at the outer surface of the fiber 100 is 0.05 cm. In the depicted example, the shared radius of the multiple smaller circles defining the undulation at the inner surface of the fiber 100 is also 0.05 cm. Hence, the ratio of the radius defining the curvature of the protrusion 316 at the fiber center to the radius of the circles defining the undulations at the outer (and/or inner) surface of the fiber is 0.081/0.05, i.e., 1.62. This value is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, and hence approximately the golden ratio.

[0095] FIG. 8 shows an example of a cross-section of a further fiber 800 having more undulations than the fiber cross section depicted in FIGS. 1-7. The curvature of the whole fiber profile is the same as the profile curvature of the fibers depicted in FIGS. 1-7.

[0096] FIG. 9 shows an example of a cross-section of a further fiber 900 having more undulations than the fiber cross section depicted in FIGS. 1-7 and having an extended curvature compared to the fiber cross sections depicted in FIGS. 1-7. Extended curvature means that the fiber profile corresponds to the arc of a circular segment having a larger angle than the circular segment whose arc corresponds to the fiber profile curvature of the fibers shown in FIGS. 1-7.

[0097] FIG. 10 shows the cross-section of an example of a further fiber 1000. The depicted fiber has a thickening at its center which leads to a bulge on both the outer and inner surface of the fiber.

[0098] FIG. 11 shows the cross-section of an example of a further fiber 1100. The cross-section of the depicted fiber has the shape of a catenary.

[0099] FIG. 12 shows the cross-sectional profile of an extruded artificial turf fiber 1200, according to another embodiment. The artificial turf fiber is similar to artificial turf fiber 100 of FIGS. 1-3, and reference numbers that are the same as those in FIGS. 1-3 reference identical elements. The cross-sectional profile of the fiber 1200 includes a first end 302 (also defined as a first end portion 302), a second end 304 (also defined as a second end portion 304), a curved middle portion 1202, and a center 306 of the middle portion 1202.

[0100] As illustrated by FIG. 12, and as seen in FIGS. 1-3, the middle portion 1202 has a curved cross-sectional shape, and the first and second end portions are connected via the curved middle portion. In some embodiments, the curved cross-sectional shape is formed from one or more arced-cross sectional shapes. In the FIG. 12 embodiment, the curved cross-sectional shape is the arc of a segment of a circle. The curved cross-sectional shape of the middle portion 1202 is defined by a first boundary line 1206 and a second boundary line 1208 opposite the first boundary line. The first boundary line 1206 is a line on the outer surface 202 (FIG. 2) of the fiber 1200, and the second boundary line 1208 is a line on the inner surface 104 (FIG. 1) of the fiber 1200. The first boundary line 1206 includes or includes exclusively of first uninterrupted undulations represented collectively by the indentations 308 and protrusions 312, and the second boundary line 1208 includes or include exclusively of second uninterrupted undulations represented collectively by the indentations 310 and protrusions 314. In addition, the curved cross-sectional shape of the fiber 1200 has a longitudinal direction 1210 (also referred to as a longitudinal dimension), along which a length of the cross-sectional shape lies. The curved cross-sectional shape of the fiber 1200 also has a transverse direction that is defined by a direction that Is perpendicular to the longitudinal direction.

[0101] In one embodiment, a thickness w (also referred to as a width, a transverse width or an amplitude) of the curved cross-sectional shape of the middle portion 1202, as measured between corresponding points on first and second boundary lines 1206, 1208, where corresponding points are the two points that lie on a line that is transverse to the longitudinal direction and that also lie on the first and second boundary lines, respectively, is constant or substantially constant along the longitudinal direction 1210 of the curved cross-sectional shape. For example, thicknesses (i.e., widths) w1, w2 and w3 are equal to one another, and moreover, a thickness w of the curved cross-sectional shape of the middle portion 1202 measured at all positions along the longitudinal direction is constant or substantially constant.

[0102] In one embodiment, the first uninterrupted undulations 308, 312 have a first wavelength 1212 and the second uninterrupted undulations 310, 314 have a second wavelength 1214, where the first and second wavelengths are selected such that the thickness w of the curved cross-sectional shape of the middle portion 1202 is constant or substantially constant along the longitudinal direction 1210. The length of the second boundary line 1208 (i.e., as measured from either the first or second end portion to a position on the second boundary line 1208 opposite the center 306 along the inner surface 104 of the fiber) is shorter than the length of the first boundary line 1206 (i.e., as measured from either the first or second end portion to a position on the first boundary line 1206 opposite the center 306 along the outer surface 202 of the fiber), and the difference between the lengths depend upon the extent of the curvatures of the inner and outer surfaces of the fiber 1200. In the exemplary embodiment of FIG. 12, the radius of curvature of the inner surface 104 (and the second boundary line 1208) is smaller than the radius of curvature of the outer surface 202 (and the first boundary line 1206), and thus the length of the second boundary line 1208 is shorter than the length of the first boundary line 1206. Thus, in order to provide a substantially constant thickness w of the curved cross-sectional shape of the middle portion 1202 at all positions along the longitudinal direction 1210 of the middle portion 1202, the wavelength (also referred to as the spatial frequency, which is the inverse of the wavelength) of the second uninterrupted undulations 310, 314 is selected to be smaller than the wavelength (i.e., spatial frequency) of the first uninterrupted undulations 308, 312.

[0103] In another embodiment, thicknesses 318 of the first and second end portions 302, 304 of the fiber are greater than the constant thickness w of the curved cross-sectional shape of the middle portion 1202.

[0104] FIG. 13 shows the cross-section of an extruded artificial turf fiber 1300 according to yet another embodiment. The artificial turf fiber 1300 is similar to artificial turf fiber 1200 of FIG. 12, and reference numbers that are the same as those in FIG. 12 reference identical elements.

[0105] The difference between fiber 1200 of the FIG. 12 embodiment and fiber 1300 of the FIG. 13 embodiment is that in the FIG. 13 embodiment, a thickness w of the curved cross-sectional shape of the middle portion 1202, as measured between corresponding points on the first and second boundary lines 1206, 1208, is not constant along the longitudinal direction 1210 of the curved cross-sectional shape. That is, in contrast to the FIG. 12 embodiment, the first uninterrupted undulations 308, 312 of the first boundary line 1206 of the curved cross-sectional shape of the middle portion 1202 may have a phase offset 1216 from the second uninterrupted undulations 310, 314 of the second boundary line 1208 of the curved cross-sectional shape of the middle portion 1202. Thus, as illustrated, a phase offset, such as phase offset 1216, will result in the middle portion 1202 having a variable thickness, independent of whether the wavelengths 1212 and 1214 (i.e., spatial frequencies) are equal or not (i.e., the thickness w of the curved cross-sectional shape of the middle portion 1202 at positions along the longitudinal direction 1210 is not constant (i.e., it is variable, or non-constant)). In one embodiment, a thickness w of the curved cross-sectional shape of the middle portion 1202 is not constant along the longitudinal direction 1210 of the curved cross-sectional shape when the width varies by more the 5%.

[0106] Alternatively, or in addition to a phase offset, the first and second uninterrupted undulations may have the same (or substantially the same) wavelength (i.e., spatial frequency). For example, the first uninterrupted undulations 308, 312 have a first wavelength 1218 (also referred to as a first spatial frequency) and the second uninterrupted undulations 310, 314 have a second wavelength 1220 (also referred to as a second spatial frequency), where the first and second wavelengths (spatial frequencies) are selected to be approximately equal to one another. When the wavelengths 1218, 1220 are approximately equal to one another, the thickness w of the curved cross-sectional shape of the middle portion 1202 is variable (i.e., non-constant) along the longitudinal direction 1210, independent on whether or not there is a phase offset.

[0107] In another embodiment of FIG. 13, the thicknesses 318 of the first and second end portions 302, 304 of the fiber 1300 are greater than a maximum thickness of the variable thickness w of the curved cross-sectional shape of the middle portion 1202. For example, if w5 is the maximum thickness of the variable thickness of the curved cross-sectional shape of the middle portion 1202, then the thicknesses 318 of the first and second end portions 302, 304 of the fiber 1300 are greater than w5.

[0108] Referring to FIG. 12, and according to another embodiment, the curved cross-sectional shape of each of the first and second end portions 302, 304 are defined by boundary lines 1222, 1224, respectively. Although the boundary lines 1222, 1224 are curved, they do not include undulations. However, in an alternate embodiment, the curved cross-sectional shapes of each of the first and second end portions 302, 304 are defined by boundary lines 1226, 1228, respectively, that consist of third uninterrupted undulations. In yet another embodiment, wavelengths (i.e., spatial frequencies) of the third uninterrupted undulations of boundary lines 1226, 1228 are greater than or equal to the wavelengths (i.e. spatial frequencies) of the first and second undulations of the first and second boundary lines 1206, 1208. Although not illustrated, the curved cross-sectional shapes of each of the first and second end portions 302, 304 of fiber 1300 (FIG. 13) may also be defined by boundary lines consisting of third uninterrupted undulations as described with respect to the fiber 1200 (FIG. 12).

[0109] According to other embodiments of FIGS. 12 and 13, the curved cross-sectional shape of the extruded artificial turf fiber 1200, 1300 comprises one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of at least a segment of a horseshoe, an arc of at least a segment of a U, or an arc of at least a segment of a . Each point on an arc of an ellipse has a different radius from neighboring points. The scope of the disclosed embodiments of the curved cross-sectional shapes of the extruded artificial turf fibers include arcs defined by boundary lines that have a varying radius of curvature along the longitudinal direction of the cross-sectional shapes.

[0110] According to yet other embodiments of FIGS. 12 and 13, and with reference to FIG. 5, the first boundary line 1206 is an outer, convex boundary line (i.e., a line on the outer surface 202 (FIG. 2) of the fiber) and the second boundary line 1208 is an inner, concave boundary line (i.e., line on the inner surface 104 of the fiber), where at least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line 1206 are defined by first circles having a same first diameter D3, and where at least 70%, in particular at least 80%, e.g., 100% of the undulations of the inner boundary line 1208 are defined by second circles having a same second diameter D4.

[0111] In another embodiment, the center 306 of the middle portion 1202 of the fiber 1200, 1300 comprises a thickening that forms a rounded protrusion 316 to at least one side of the fiber. Although the embodiments of FIGS. 12 and 13 illustrate a thickening at the center 306 of the middle portion 1202 of the fiber resulting in a protrusion 316 from an outer surface, such as outer surface 202 (FIG. 2), in other embodiments the central thickening may result in a protrusion only from the inner surface, such as inner surface 104 (FIG. 1), or a first protrusion from the outer surface 202 and a second protrusion from the inner surface 104, where the protrusions are formed opposite one another on the two surfaces. In additional embodiments, the center 306 does not have any thickening or bulge. In one embodiment, the bulge has a thickness that is 10-20% thicker than a maximum thickness of the other portions of the middle portion.

[0112] FIG. 14 shows the cross-section of an extruded artificial turf fiber 1400 according to another embodiment. Reference numbers that are the same as those in FIGS. 12 and 13 reference identical elements. As illustrated in the FIG. 14 embodiment, an average thickness (also referred to as an average width) of the curved cross-sectional shape of the middle portion 1202 is not constant along the longitudinal direction 1210, but increases as the longitudinal distance from the center 306 decreases.

[0113] In one embodiment, the average thickness of the middle portion, as also illustrated in FIGS. 15, 16 and 17, and which hereinafter applies to all disclosed embodiments, is the transverse distance between a first base line 1518 and a second baseline 1520, where the first and second baselines are lines that pass through, e.g., all the peaks of the protrusions of the undulations on both the first and second boundary lines 1508, 1510, respectively. However, the baselines may be defined to be any line that passes through points on the boundary lines that have the same amplitude values (e.g., see baselines 1618, 1620 of FIG. 16 and baselines 1718, 1720 of FIG. 17). As illustrated in FIG. 14, the average thickness w3 is larger than the average thickness w2, which is larger than the average thickness w1.

[0114] Furthermore, in another embodiment, the middle portion 1202 has at least one spine proximate to respective end portions 302 and/or 304. For example, and as illustrated by FIG. 14, the middle portion 1202 includes at least a first spine 1402 proximate to the first end portion 302 and at least a second spine 1404 proximate to the second end portion 304. As illustrated by FIG. 14, the first boundary line 1206 of the middle portion 1202 has the first spine 1402 and the second spine 1404. In one embodiment, a spine is defined as a protrusion that is slightly larger in amplitude than neighboring protrusions, and in other embodiments, as a protrusion that is slightly larger in amplitude that all other protrusions on both the first and second boundary lines of the cross-sectional shape of the middle portion 1202. A slightly larger amplitude is defined to be an amplitude that is about 2-5% larger than amplitudes of neighboring protrusions, or alternatively may be defined to represent a thickness of the middle portion (corresponding to a spine) that is less than about 10% larger than an average thickness of the middle portion, or less than about 5% larger than the average thickness of the middle portion, or between about 2-5% larger than the average thickness of the middle portion.

[0115] In yet other embodiments, a width (i.e., thickness or amplitude) of the first spine 1402 is less than 125%, in particular less than 115%, in particular 101% to 115% of an average width (i.e., thickness or amplitude) of the middle portion 1202, and/or a width of the second spine 1404 is less than 125%, in particular less than 115%, in particular 101% to 115% of the average width of the middle portion 1202, where the average width of the middle portion 1202 is determined without considering (i.e., to the exclusion of) the width of an optional central bulge (e.g., the optional bulge 316 at the center 306 of the middle portion 1202).

[0116] In some embodiments, the first boundary line 1206 of the middle portion 1202 includes at least one spine (e.g., spines 1402 and 1404) that is continuous with neighboring first uninterrupted undulations.

[0117] In other embodiments, the at least one spine (e.g., spines 1402 and 1404) are positioned on an outer half, or on an outer third, of the middle portion 1202, as measured from the center 306 of the middle portion to the respective end portions 302, 304. Other embodiments of the positioning of the spine(s) will be discussed further below in conjunction with FIG. 17, applicable to the FIG. 14 embodiment as well.

[0118] Advantageously, and as will be described further below with respect to FIG. 17, a gradual monotonical increase of average thickness of the middle portion 1202 of the fiber as the longitudinal distance from the center 306 of the fiber decreases, in combination with one or more spines (e.g., an even number of spines), preferable positioned on an outer half, or outer third, of the middle portion 1202, tend to add more mechanical stability to the curvature of the fiber.

[0119] In further embodiments, and as illustrated in FIG. 14, the thicknesses w4, w5 of the middle portion corresponding to the location of the spines 1402, 1404, respectively, represent the maximum thickness of the middle portion 1202, excluding the thickness of the middle portion 1202 at the center 306 that corresponds to the bulge 316, for those embodiments that include a thickening at the center 306.

[0120] Although FIG. 14 illustrates an embodiment in which the average thickness of the curved cross-sectional shape of the middle portion 1202 (excluding regions that contain the spines) is not constant along the longitudinal direction 1210 (i.e., it increases as the longitudinal distance from the center 306 decreases), the scope of the invention includes other embodiments in which the thickness of the curved cross-sectional shape of the middle portion 1202, including the central portion and including the regions containing the spines, is constant along the longitudinal direction. According to further embodiments, the thickness of the curved cross-sectional shape of the middle portion 1202, excluding the regions containing the spines and/or excluding the center 306 of the middle portion 1202, is either constant along the longitudinal direction or monotonically increasing along the longitudinal direction from either or both end portions 302, 304 towards the center 306 of the middle portion 1202.

[0121] FIGS. 15, 16 and 17 illustrate, in respective lower panels, a cross-section of an extrusion dye (also referred to as an extrusion plate) though which a polymer mixture is extruded as part of the process of forming an extruded artificial turf fiber, and in respective upper panels, a photo of the artificial turf fiber (i.e., the product) extruded through the dye.

[0122] FIG. 15 illustrates a cross-section of an extrusion dye 1502 and a photo of an artificial turf fiber 1504 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1502. An outline 1506 of the extrusion dye 1502 is superimposed on the artificial turf fiber 1504 for purposes of comparing the shape of the final product 1504 with the desired shape 1506. In the FIG. 15 embodiment, the average width wd of the extrusion dye 1502 is constant along a longitudinal length of the dye, where the average width wd is defined as a transverse distance between corresponding pairs of points, where first points of pairs of corresponding points are located on a first baseline 1518 that passes through the peaks of the protrusions of the undulations on an outer boundary line 1508 (on an outer surface of the dye) and second points of the pairs of corresponding points are located on a second baseline 1520 that passes through the peaks of the protrusions of the undulations on an inner boundary line 1510 (on an inner surface of the dye). Although the cross-sectional shape of the extrusion dye 1502 has uninterrupted undulations, the cross-sectional shape of the extrusion dye 1502 does not include any spines.

[0123] A comparison of the photo of the artificial turf fiber 1504 with the desired shape 1506 (i.e., the cross-sectional shape of the extrusion dye) shows a reduction in curvature of the artificial turf fiber 1504, and a thinning of the thickness of at least one end portion 1512 of the fiber.

[0124] FIG. 16 illustrates a cross-section of an extrusion dye 1602 and a photo of an artificial turf fiber 1604 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1602. In the FIG. 16 embodiment, the average width wd of the extrusion dye 1602 monotonically increases along a longitudinal length of the dye from the end portions 1605 to a center 1606, where the average width wd at the center 1606 is a maximum width of the dye and the average width wd adjacent the end portions 1605 is a minimum width of the dye. As in the FIG. 15 embodiment, the cross-sectional shape of the extrusion dye 1602 has uninterrupted undulations, but does not include any spines.

[0125] A comparison of the photo of the artificial turf fiber 1604 with the desired shape (i.e., the shape of the extrusion dye 1602) shows a reduction in curvature of the artificial turf fiber 1604. In addition, the thicknesses of the end portions 1608 of the fiber appear to show a thinning when compared to the thickness of the end portions 1605 of the dye 1602. However, when compared to FIG. 15, the end portions 1608 of the FIG. 16 embodiment appear to be better defined with respect to the adjacent uninterrupted undulations.

[0126] FIG. 17 illustrates a cross-section of an extrusion dye 1702 and a photo of an artificial turf fiber 1704 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1702. Although extrusion dye 1702 includes one fiber profile opening (i.e., first and second end portion openings 1703 and 1705, a curved middle portion opening 1707 connected with the first and second end portion openings, and at least a first spine opening 1710 proximate to the first end portion opening 1703 and a second spine opening 1712 proximate to the second end portion opening 1705), other extrusion dye embodiments (not shown) include two or more fiber profile openings. In the FIG. 17 embodiment, the average width wd of the extrusion dye 1702 monotonically increases along a longitudinal length of the dye from the end portion openings 1703, 1705 to a center 1706 of the curved middle portion opening 1707, where the average width wd1 in the center 1706 is a maximum width of the dye and the average width wd2 adjacent the end portion openings 1703, 1705 is a minimum width of the dye. However, the rate of increase in the average width with respect to longitudinal distance is less than the rate of increase in average width as illustrated by the FIG. 16 embodiment. As in the FIGS. 15 and 16 embodiments, the cross-sectional shape of the extrusion dye has uninterrupted undulations, however unlike FIGS. 15 and 16, the cross-sectional shape of the extrusion dye of the FIG. 17 embodiment includes the spine openings 1710 and 1712. The cross-sectional shape of the extrusion dye 1702 also has an optional rounded bulge opening 1714 at the center 1706.

[0127] A comparison of the photo of the artificial turf fiber 1704 with the desired shape (i.e., the shape of the extrusion dye 1702) shows a better retention of curvature of the artificial turf fiber 1704 in comparison to FIGS. 15 and 16. In addition, the end portions (i.e., first and second end portions 1715, 1717) of the fiber appear to show a better retention of the thickness in comparison to FIGS. 15 and 16.

[0128] In other embodiments (not shown), the average width wd of the extrusion dye 1702 is constant (or substantially constant) along a longitudinal length of the dye from the end portion openings 1703, 1705 to the center 1706, the cross-sectional shape of the extrusion dye 1702 still includes spine openings, for example spine openings 1710 and 1712, and the curved middle portion opening 1707 is not bulged at the center 1706 (i.e., the cross-sectional shape of the extrusion dye 1702 does not have the optional rounded bulge opening 1714 at the center 1706).

[0129] In one embodiment, a maximum width of the first spine opening wmax.sub.1 is larger than 110%, in particular larger than 115%, in particular 110% to 160%, in particular 115% to 135% of an average width wd of the middle portion opening, where the average width of the middle portion opening is determined without considering (i.e., exclusive of) a width (wo+wd1) of the optional central bulge opening 1714, if any, and where a maximum width of the second spine opening wmax.sub.2 is larger than 110%, in particular larger than 115%, in particular 110% to 160%, in particular 115% to 135% of the average width wd of the middle portion opening, where the average width of the middle portion opening is determined without considering the width of the optional central bulge opening, if any.

[0130] FIG. 17 further illustrates positioning of the spine openings 1710, 1712 of the middle portion opening 1707, according to embodiments of the present invention. In some embodiments, the first spine opening 1710 is positioned in the middle portion opening 1707 on a first arc length AL1 subtended by a first angle 1 of less than or equal to 60, or between 35-55, or between 40-50, or at 45. As illustrated, the first arc length AL1 is measured along the curved middle portion opening 1707 from the first end portion opening 1703. Furthermore, the second spine opening 1712 is positioned in the middle portion opening 1707 on a second arc length AL2 subtended by a second angle 2 of less than or equal to 60, or between 35-55, or between 40-50, or at 45. The second arc length AL2 is measured along curved middle portion opening 1707 from the second end portion opening 1705. .sub.1 is subtended by a first straight line drawn between a first distal end point 1709 of the first end portion opening 1703 and a center point 1713, and a second straight line drawn between a peak of the first spine 1710 and the center point 1713. .sub.2 is subtended by a third straight line drawn between a second distal end point 1711 of the second end portion opening 1705 and the center point 1713, and a fourth straight line drawn between a peak of the second spine 1712 and the center point 1713. For curved middle portion openings having a shape of an arc, such as an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of a segment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a , the center point 1713 is defined as a midpoint on the straight line drawn between the first distal end point 1709 and the second distal end point 1711.

[0131] For a curved middle portion opening having a shape of one or more sinusoidal waves, such as a middle portion opening of an extrusion plate (not shown) corresponding to the middle portion of the fibers extruded from such extrusion plate (e.g., see FIG. 22), a first center point is defined as a point on a first straight line wavelength from a first distal end point of a first end portion opening and a second center point is defined as a point on a second straight line wavelength from a second distal end point of a second end portion opening. A first spine opening is positioned in the middle portion opening on a first arc length subtended by a first angle .sub.1 of less than or equal to 60, or between 35-55, or between 40-50, or at 45. The first arc length is measured along a curved middle portion opening from the first end portion opening. Furthermore, the second spine opening is positioned in the middle portion opening on a second arc length subtended by a second angle .sub.2 of less than or equal to 60, or between 35-55, or between 40-50, or at 45. The second arc length is measured along the curved middle portion opening from the second end portion opening. .sub.1 is subtended by the first straight line and a third straight line drawn between a peak of the first spine and the first center point. .sub.2 is subtended by the second straight line and a fourth straight line drawn between a peak of the second spine and the second center point.

[0132] Advantageously, positioning of at least one spine opening, preferentially in the middle portion opening 1707 on a first arc length AL1 defined by a first angle .sub.1 of less than or equal to 60, or between 35-55, or between 40-50, or at 45, provides a fiber that has reinforced mechanical stability and/or strength (i.e., retains its shape and maintains its structural integrity (less prone to splitting) after repeated loading by external forces, such as forces applied to the fibers from people, animals and/or weather events when the fibers are incorporated into carriers of artificial turfs.

[0133] That is, positioning at least one spine according to the embodiments described above and/or sizing the width (also referred to as the amplitude) of the spine openings relative to the average width of the middle portion opening, where the average width of the middle portion opening is determined without considering the width (wo+wd1) of the optional central bulge opening, advantageously enables a net polymer mass flow in the polymer mixture of the extruded fiber, which occurs between the time that the polymer mixture exists the extrusion plate (in the form of an unquenched extruded fiber) and time that the extruder fiber is quenched via, for example, a quenching unit such as a water bath. The spines according to embodiments of the present invention enable a net polymer mass flow (that occurs in the unquenched fiber as the fiber travels between the extrusion plate and the quenching unit), where the net polymer mass flow is in a direction from a position of the first spine opening (i.e., from a position on the extruded fiber that coincides with the position of the first spine opening of the extrusion plate) to the first end portion of the fiber, and in a direction from a position of the second spine opening (i.e., from a position on the extruded fiber that coincides with the position of the second spine opening of the extrusion plate) to the second end portion of the fiber.

[0134] The net polymer mass flow in the extruded polymer fiber, which occurs between extrusion and quenching, and which is caused by the extrusion plate having one or more spine openings, mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of the end of the quenched fiber.

[0135] In addition, extrusion of an artificial turf fiber through an extrusion plate having a combination of one or more spine openings with one or more of: (1) an average cross-sectional width of a middle portion opening that increases (preferably monotonically) from the end portion openings to the center of the middle portion opening; (2) thickened end portion openings (preferably having a thickness (i.e., width) that is greater than a thickness (i.e., width) of the middle portion opening, excluding the thickness of the center of the middle portion opening when the center includes a rounded bulge opening; and (3) a thickened center opening (i.e., a bulge opening), where the thickness is preferably thicker that the thicknesses of the end portion openings, synergistically results in a fiber that has even more reinforced mechanical stability and/or strength.

[0136] According to another embodiment, an artificial turf fiber includes a first spine created by extruding a polymer mass through a first spine opening of an extrusion plate and includes a second spine created by extruding the polymer mass through a second spine opening of the extrusion plate. By way of an exemplary embodiment, the artificial turf fiber 1704 extruded through extrusion dye 1702 has barely visible spines 1722, 1724, however other embodiments of extruded artificial turf fibers have more prominent spines. By way of further exemplary embodiments, artificial turf fibers 1800, 1900, 2000, 2200, 2300 and 2400 of FIGS. 18, 19, 20, 22, 23 and 24, respectively, extruded through respective extrusion dyes (not shown) having differently-shaped fiber profile openings, include spines 1802, 1804, spines 1902, 1904, spines 2002, 2004, spines 2202, 2204, spines 2302, 2304, and spines 2402, 2404, respectively. Shapes of the fiber profile openings of the extrusion dyes corresponding to FIGS. 18-25 will be discussed further below.

[0137] In another embodiment, and referring back to FIG. 17 as one exemplary illustration, the ratio of an area of the first spine opening 1710 to an area of the first end portion opening 1703 is larger than the ratio of a cross-sectional area of the first spine 1722 of the fiber 1704 to a cross-sectional area of the first end portion 1715 of the fiber, and the ratio of an area of the second spine opening 1712 to an area of the second end portion opening 1705 is larger than the ratio of a cross-sectional area of the second spine 1724 of the fiber 1704 to a cross-sectional area of the second end portion 1717 of the fiber. The second end portion 1717 of the fiber is formed by extruding a polymer mass through the second end portion opening 1705 and the first end portion 1715 of the fiber is formed by extruding the polymer mass through the first end portion opening 1703.

[0138] According to yet another embodiment, an amplitude (also referred to as width) of the first spine 1722 of the fiber 1704 is less than an amplitude wmax.sub.1 (also referred to as width) of the first spine opening 1710, and an amplitude of the second spine 1724 of the fiber 1704 is less than an amplitude wmax.sub.2 of the second spine opening 1712.

[0139] In one embodiment, a width wep1 of the first end portion opening 1703 is larger than a width wd2 of a first section 1726 of the middle portion opening 1707 adjacent to the first end portion opening 1703, a width wep2 of the second end portion opening 1705 is larger than a width wd2 of a second section 1728 of the middle portion opening 1707 adjacent to the second end portion opening 1705, a width wf1 of the first end portion 1715 of the fiber 1704 is larger than a width wfa1 of a first section 1730 of a middle portion 1732 of the fiber 1704 adjacent to the first end portion of the fiber, and a width wf2 of a second end portion 1717 of the fiber 1704 is larger than a width wfa2 of a second section 1734 of the middle portion of the fiber adjacent to the second end portion of the fiber.

[0140] According to other embodiments, the width of the first and second end portion openings wep1, wep2 are respectively larger than a maximum width of the middle portion opening 1707, and the width of the first and second end portions wf1, wf2 are respectively larger than a maximum width of a middle portion 1732 of the fiber.

[0141] In another embodiment, a center 1706 of the curved middle portion opening 1707 includes a bulge opening 1714, and a maximum width of the middle portion opening 1707 including the bulge opening 1714 is greater than a maximum width of the first and second end portion openings 1703, 1705.

[0142] In one embodiment, the fiber 1704 includes either no spines or no spines visible to the human eye at positions (i.e., corresponding to positions) of the first and second spine openings 1710, 1712.

[0143] In another embodiment, the curved middle portion opening 1707 has two opposing longitudinal contours 1206, 1208 (also referred to as boundary lines), where at least one of the contours includes or includes exclusively of uninterrupted undulations.

[0144] Although the curved middle portion opening 1707 as illustrated by the FIG. 17 embodiment has the shape of an arc, in other embodiments, the curved middle portion opening 1707 has a shape of one or more sinusoidal waves. For those embodiments in which the curved middle portion opening has the shape of an arc, the radius of curvature of the middle portion opening 1707 may decrease from a location at the center 1706 of the middle portion opening towards locations near or at the end portion openings 1703, 1705, and/or where the arc may include one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of a segment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a .

[0145] FIGS. 18, 19 and 20 illustrate cross-sections of extruded artificial turf fibers according to other embodiments. Fibers 1800, 1900, and 2000 are similar to fibers 1400 and 1704, however the extruded artificial turf fiber 1800 includes a curved middle portion 1801 having a shape of an arc of a horseshoe, the extruded artificial turf fiber 1900 includes a curved middle portion 1901 having a shape of an arc of an Q, and the extruded artificial turf fiber 2000 includes a curved middle portion 2001 having a shape of an arc of a U. The curved middle portion 1801 of fiber 1800 is connected with first and second end portions 1806, 1808, and includes at least a first spine 1802 proximate to the first end portion 1806 and a second spine 1804 proximate to the second end portion 1808. The curved middle portion 1901 of fiber 1900 is connected with first and second end portions 1906, 1908, and includes at least a first spine 1902 proximate to the first end portion 1906 and a second spine 1904 proximate to the second end portion 1908. The curved middle portion 2001 of fiber 2000 is connected with first and second end portions 2006, 2008, and includes at least a first spine 2002 proximate to the first end portion 2006 and a second spine 2004 proximate to the second end portion 2008.

[0146] Each of fibers 1800, 1900, and 2000 are manufactured by extrusion of a polymer mass through corresponding extrusion plates (not shown) having fiber profile openings including middle portion openings in the shape of an arc of a horseshoe, an arc of an Q, and an arc of a U, respectively, including respective spine openings coinciding with the spines of fibers 1800, 1900 and 2000. Although the fibers 1800, 1900 and 2000 have visible spines, in other embodiments of the present invention, the spines are either not visible via a visual inspection or are not present, although the effects produced by the spine openings of the corresponding extrusion plates, when a polymer mass is extruded through the fiber profile openings, still occur (i.e., mitigation of a thinning of the fiber end portions relative to the thickness of the end portion openings of the extrusion plates)

[0147] In some embodiments, an average thickness of the curved cross-sectional shapes of each middle portion of the fibers 1800, 1900 and 2000, excluding the regions containing the spines, may either be constant along the longitudinal direction, or increasing in the longitudinal direction as the center is approached (i.e., increasing as the distance from the center decreases).

[0148] FIGS. 21 and 22 show photographs of extruded artificial turf fibers according to other exemplary embodiments. As illustrated, fibers 2100 and 2200 have shapes (i.e., cross-sectional shapes when viewed in a longitudinal plane of the fiber) that approximate sinusoids, where the fibers include middle portions having undulations and thickened end portions. In some embodiments, the middle portions of the fibers 2100 and 2200 include two approximately circular arcs (e.g., similar to the shapes of the approximately circular arcs of the middle portions of fibers 1200, 1300, 1400, or the shape of the approximately circular arc of a middle portion of the extrusion dye 1702, with or without: a rounded bulge at the center, non-constant average thickness and/or spines) that form a middle portion that approximates the shape of a sinusoid.

[0149] An average width of the curved cross-sectional shape of the middle portions 2102, 2104 of fiber 2100 increases at a greater rate (along a longitudinal distance of the fiber from either of the end portions 2106, 2108 to the respective center 2110, 2112 closest to the respective end portion) than the average width of the curved cross-section of corresponding middle portions of fiber 2200, and the fiber 2100 is extruded from an extrusion dye that does not include spine openings. The fiber 2200, however, is extruded from an extrusion dye that include spine openings, which are slightly visible as spines 2202 and 2204. As illustrated, fiber 2200 has less thinning of the thicknesses of the end portions 2206, 2208.

[0150] FIGS. 23, 24 and 25 show photographs of extruded artificial turf fibers according to yet other exemplary embodiments. As illustrated, fibers 2300, 2400 and 2500 have shapes (i.e., cross-sectional shapes when viewed in a longitudinal plane of the fiber) that approximate an arc of the letter U, an arc of a horseshoe, and an arc of a segment of a circle, respectively.

[0151] The average widths of the curved cross-section shapes of the middle portions of each of fibers 2300, 2400 and 2500 increase along a longitudinal distance of the fiber from either end portion to a center of the middle portion, and spines (2302,2304), (2402, 2404) and (2502, 2504) are visible on each of the fibers 2300, 2400 and 2500, respectively. As illustrated, each of the fibers 2300, 2400 and 2500 have end portions without any reduction (or only slight reduction) in thickness (as compared to the thickness of the end portions of the respective extrusion dyes (not shown)), and without any flattening (or only slight flattening) or distortion to the curvatures of the fibers when compared to the curvatures of the respective extrusion dyes (not shown).

[0152] According to another embodiment, the extruded artificial turf fiber 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400 and/or 2500 is formed from a polymer mixture, where the polymer mixture is at least a two-phase polymer mixture, where a first phase of the polymer mixture includes a first polymer and a first dye and a second phase of the polymer mixture includes a second polymer and a second dye, where a color of the second dye is different than a color of the first dye, where the second polymer is of a same or of a different type as the first polymer, where the first and the second phases are immiscible, and where the extruded artificial turf fiber has a marbled appearance.

[0153] In one embodiment, upon creation of the liquid polymer mixture, the two different dyes are separated in two different phases wherein one of the phases is emulsified in the second phase in the form of beads. This is advantageous as it is not necessary to use or create customized extruders which mechanically prevent a premature intermixing of the two dyes, thereby ensuring that a monofilament with a marbled pattern rather than a monofilament with a color being the intermediate of the first and second color is created. The polymer mixture is extruded into a monofilament including a marbled pattern of the first and second color. The monofilament is then heated, and then stretched to deform the polymer beads (containing one of the dyes) into threadlike regions and to form the monofilament into an artificial turf fiber.

[0154] In another embodiment, the polymer mixture further includes a compatibilizer. According to some embodiments, the compatibilizer (which may be considered a third phase of the polymer mixture) is added to the polymer mixture and interfaces the first and second polymers, thereby further preventing the delamination of the two different types of polymers. Preferably, the compatibilizer is added to the polymer mixture whose phase separation is caused by a polarity difference between a polar and an apolar polymer. The first phase forms polymer beads surrounded by the third phase within the second phase.

[0155] According to another embodiment, the first polymer is any one of the following: polyamide, polyethylene terephthalate, and polybutylene terephthalate, and the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof. Using a mixture of polymers of different types, e.g. the apolar polyethylene and the polar polyamide, with the above-described dyes, has the advantage that an artificial turf fiber is created that shows a marbled color pattern and that has increased durability against wear and tear due to the more rigid PA and at the same time a smoother surface and increased elasticity compared to pure PA based monofilaments.

[0156] Furthermore, an artificial turf fiber having a marbled color pattern in combination with a middle portion having a curved cross-sectional shape with uninterrupted undulations and/or with the curved-cross sectional shape having constant width along a length of the curved-cross sectional shape, or the uninterrupted undulations (on opposite boundary lines defining the curved cross-sectional shape) being offset in phase from one another, or the uninterrupted undulations (on opposite boundary lines defining the curved cross-sectional shape) having equal spatial frequencies, advantageously results in a fiber that is not only more mechanically stable (e.g., better elasticity) with increased strength (less susceptible to splitting), but also more natural looking (due to the increased diffusion of light upon scattering from the undulated surfaces combined with the marbled pattern).

[0157] In yet another embodiment, a method of a method of manufacturing an artificial turf fiber includes extruding a polymer mixture through at least one fiber profile opening of an extrusion plate (e.g., 1702) allowing the extruded polymer mixture to travel along a distance between the at least one fiber profile opening of the extrusion plate to a quenching unit, and quenching the extruded polymer mixture in the quenching unit to form the artificial turf fiber. The fiber profile opening includes first and second end portion openings 1703, 1705, and a curved middle portion opening 1707 connected with the first and second end portion openings. The curved middle portion opening has at least a first spine opening 1710 proximate to the first end portion opening and a second spine opening 1712 proximate to the second spine opening. The first and second spine openings are sized and positioned such that the extruded polymer mixture, when traveling along the distance between the at least one fiber profile opening of the extrusion plate to the quenching unit, incurs a net polymer mass flow from a position on the middle portion of the fiber corresponding to the first spine opening to a first end portion of the fiber and from a position on the middle position of the fiber corresponding to the second spine opening to a second end portion of the fiber. Quenching of the fiber halts any further movement (i.e. flow) of the polymer mass in the fiber.

[0158] Advantageously, the net polymer mass flow mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of the end of the quenched fiber.

[0159] In one embodiment, the quenched fiber includes a first spine created by extruding the polymer mass through the first spine opening and a second spine created by extruding the polymer mass through the second spine opening. In other embodiments, the quenched fiber includes no spines at positions (i.e., corresponding to positions) of the first and second spine openings, or alternatively, no visible (to the human eye without magnification) spines at positions (i.e., corresponding to positions) of the first and second spine openings.

[0160] In other embodiments, the ratio of an area of the first spine opening to an area of the first end portion opening is larger than the ratio of a cross-sectional area of the first spine of the quenched fiber to a cross-sectional area of the first end portion of the quenched fiber, where the first end portion of the fiber is created by extruding the polymer mass through the first end portion opening, and/or the ratio of an area of the second spine opening to an area of the second end portion opening is larger than the ratio of a cross-sectional area of the second spine of the quenched fiber to a cross-sectional area of the second end portion of the quenched fiber, where the second end portion of the fiber is created by extruding the polymer mass through the second end portion opening.

[0161] In another embodiment, an amplitude (also referred to as width) of the first spine of the quenched fiber is less than an amplitude (also referred to as width) of the first spine opening, and/or an amplitude of the second spine of the quenched fiber is less than an amplitude of the second spine opening.

[0162] Yet in another embodiment, a width of the first end portion opening is larger than a width of a first section of the middle portion opening adjacent to the first end portion opening, and a width of the second end portion opening is larger than a width of a second section of the middle portion opening adjacent to the second end portion opening, and/or a width of the first end portion of the quenched fiber is larger than a width of a first section of a middle portion of the quenched fiber adjacent to the first end portion of the quenched fiber and a width of the second end portion of the quenched fiber is larger than a width of a second section of the middle portion of the quenched fiber adjacent to the second end portion of the quenched fiber.

[0163] In one embodiment, widths of first and second end portion openings are respectively larger than a maximum width of the middle portion opening, and widths of first and second end portions are respectively larger than a maximum width of a middle portion of the quenched fiber.

[0164] In another embodiment, a center of the curved middle portion opening includes a bulge opening, and a maximum width of the middle portion opening including the bulge opening is greater than a maximum width of the first and second end portion openings.

[0165] In some embodiments, the curved middle portion opening has two opposing longitudinal contours, where at least one of the contours includes (or includes entirely of) uninterrupted undulations.

[0166] In one embodiment, the curved middle portion opening has a shape of one or more sinusoidal waves. In other embodiments, the curved middle portion opening has a shape of an arc, and optionally a radius of curvature of the middle portion opening decreases from a center of the middle portion opening towards the end portion openings. In some embodiments, a shape of the middle portion opening comprises one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of a segment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a .

[0167] In other embodiments, the polymer mixture includes a polyethylene or a polyethylene-polyamide blend, where the quenching unit is a water bath, where the distance between the extrusion plate openings and the quenching unit is 3.0-5.0 cm, and wherein a temperature of the water bath is 28 C.-34 C.

[0168] In some embodiments, the polymer mixture includes a polyamide as a main polymer component or includes exclusively of the polyamide, where the quenching unit is a water bath, where the distance between the extrusion plate openings and the quenching unit is 2.0-4.0 cm, and wherein a temperature of the water bath is 18 C.-20 C.

[0169] In embodiments, the polymer mixture is at least a two-phase polymer mixture, where a first phase of the polymer mixture includes a first polymer and a first dye and a second phase of the polymer mixture includes a second polymer and a second dye, where a color of the second dye is different than a color of the first dye, where the second polymer is of a same or of a different type as the first polymer, where the first and the second phases are immiscible, and where the extruded fiber has a marbled appearance. In some embodiments, the first phase forms polymer beads within the second phase, and the polymer mixture further includes a nucleating agent and/or a compatibilizer.

[0170] Yet in other embodiments, the first polymer is any one of the following: polyamide, polyethylene terephthalate, and polybutylene terephthalate, and wherein the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof.

[0171] FIG. 26 shows three plots 2602, 2604, 2606 illustrating the mass flow u of the polymer mixture in the fiber profile opening of the extrusion plate at the moment when the polymer mass is pressed through the fiber profile opening, whereby the mass flow depends on the shape of the fiber profile opening. The grey areas illustrate the walls of the extrusion plate defining extrusion openings. The y coordinate of each plot indicates the dotted line (neutral line) within the fiber profile opening depicted in the middle portion of each plot. The lower portion of each plot illustrates the polymer mass flow u at various positions along the neutral line and hence depicts a mass flow profile u (y) along the neutral line. The top-view cross-section of the fiber profile opening is indicated in the middle of each plot and a photo of the real, extruded and processed fibers is shown at the top of each plot.

[0172] Plot 2602 illustrates the polymer mass flow in a fiber profile opening having a middle portion opening between the first and second end portion opening with approximately constant width. The polymer mass flow profile 2608 depends on the distance from the walls of the extrusion plate. As can be seen from the lower part of plot 2602, the mass flow is approximately homogeneous across the whole distance y. However, the curvature of the resulting fiber depicted in the upper part of the plot is quite flat and hence the fiber may be flattened easily when it is transported, processed and used. Furthermore, the fiber ends are thinned as a result of an undesired mass flow from the fiber ends towards the center of the fiber.

[0173] The plot 2604 shows the mass flow profile observed in a different fiber profile opening. This fiber profile opening was designed with an attempt to improve the mechanical stability of the fiber by increasing the width of the middle portion of the fiber. As a consequence, the polymer mass flow was observed to significantly change and to be much higher in the middle portion than at the fiber ends (see high peak of the mass flow profile 2610). As a consequence, the thinning of the ends was observed to have increased. The thinning of the fiber ends is undesirable, as this results in a reduced robustness of the ends of the artificial turf fiber against curling.

[0174] The plot 2606 shows a polymer mass flow profile obtained for a still different fiber profile opening according to an embodiment of the invention. This embodiment was able to overcome both disadvantages of the fiber profiles depicted in plots 2602 and 2604: thanks to the spine openings and thanks to the increased size of the first and second end portion openings in the fiber profile opening of the extrusion plate, the polymer flow is basically constant over most of the neutral line (dotted midline between the first and second boundary lines, represented by coordinate y), even though the central part of the middle portion opening has a greater width than the fiber end portion openings. The introduction of the spine openings and also the increasing of the width/cross-sectional area of the fiber end portion opening results in a more homogeneous distribution of the polymer flux along the midline (compared to a fiber profile shown in plot 2604 lacking spine openings and having smaller end portion openings. The introduction of the spine openings induces a net polymer flow from the position of the spine openings to the end portions in the extruded fiber. Thus, a thinning of the fiber ends is prevented and the resulting, extruded fiber has an arc-shaped (and hence mechanically stable) cross section and has ends which are approximately as thick as the middle portion of the fiber profile, resulting in an increased robustness against the curling of the fiber ends. This desirable effect has been observed to be enhanced by increasing the width of the fiber end portion openings.

[0175] Hence, introducing the spines, and the optional increasing of the width (and hence, also the area) of the end portion openings, result in a flow path expansion, and in a net polymer flow from the spines to the end portions. Thereby the robustness of the fiber against being flattened and against the curling of fiber ends is increased.

[0176] According to some embodiments, the width of the first and second fiber end portions of the extruded fiber is approximately identical to the average width of the middle portion of the extruded fiber. For example, the average width may be the width between a first baseline of the undulations of the first boundary line and a second baseline of the undulations of the second boundary line. A with being approximately identically to another width can be a width that differs less than 15%, in particular less than 10%, in particular less than 5% from the width of said other width.

[0177] According to some embodiments, the width of the first end portion opening is larger than the width of the first end portion of the extruded fiber, and the width of the second end portion opening is larger than the width of the second end portion of the extruded fiber.

[0178] According to some embodiments, the area of the first end portion opening is larger than the area of the first end portion of the extruded fiber, and the area of the second end portion opening is larger than the area of the second end portion of the extruded fiber. The area in this context may mean cross-sectional area.

[0179] The width is measured along a dimension that is basically orthogonal to the curvature of the fiber profile. For example, the width of the three fiber profile openings depicted in the middle portion of the three plots 2602, 2604 and 2608 is indicated in the form of arrows which are oriented basically orthogonally to the dotted neutral line and basically orthogonally to a first and a second boundary line. The first and second boundary lines of a fiber profile may represent, for example, the lines connecting the maxima peaks (outward directed peaks) of the undulations in one fiber side in the middle portion of the fiber, or lines connecting the minima of the peaks (inward directed peaks) of the undulations in one fiber side in the middle portion of the fiber, or lines connecting the base line of the peaks (average of the peaks) of the undulations in one fiber side in the middle portion of the fiber.

[0180] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0181] Embodiments of the invention may be described by the following clauses: [0182] 1. A method of manufacturing an artificial turf fiber, comprising: [0183] extruding a polymer mixture through at least one fiber profile opening of an extrusion plate (1702) to form an artificial turf fiber (1704), the fiber profile opening including: [0184] first and second end portion openings (1703, 1705), and [0185] a curved middle portion opening (1707) connected with the first and second end portion openings, the curved middle portion having at least a first spine opening (1710) proximate to the first end portion opening and a second spine opening (1712) proximate to the second end portion opening; [0186] allowing the extruded polymer mixture to travel along a distance between the at least one fiber profile opening of the extrusion plate to a quenching unit, wherein the first and second spine openings are sized and positioned such that a net polymer mass flow in the extruded polymer mixture from a position of the first spine opening to a first end portion (1715) of the fiber and from a position of the second spine opening to a second end portion (1717) of the fiber occurs before the fiber is quenched; and [0187] quenching the extruded polymer mixture in the quenching unit to form the artificial turf fiber. [0188] 2. The method of clause 1, [0189] wherein the first spine opening is positioned in the middle portion opening on a first arc length defined by a first angle of less than or equal to 60, or between 35-55, or between 40-50, or at 45, wherein the first arc length is measured along the curved middle portion opening from the first end portion opening, [0190] wherein the second spine opening is positioned in the middle portion opening on a second arc length defined by a second angle of less than or equal to 60, or between 35-55, or between 40-50, or at 45, wherein the second arc length is measured along curved middle portion opening from the second end portion opening. [0191] 3. The method of clauses 1 or 2, wherein the net polymer mass flow mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of an end of the quenched fiber. [0192] 4. The method of any one of the preceding clauses, [0193] wherein the fiber comprises a first spine (1722) created by extruding the polymer mass through the first spine opening and comprises a second spine (1724) created by extruding the polymer mass through the second spine opening. [0194] 5. The method of clause 4, [0195] wherein the ratio of a cross-sectional area of the first spine opening to a cross-sectional area of the first end portion opening is larger than the ratio of a cross-sectional area of the first spine of the fiber to a cross-sectional area of the first end portion of the quenched fiber, the first end portion of the fiber being created by extruding the polymer mass through the first end portion opening; and [0196] wherein the ratio of a cross-sectional area of the second spine opening to a cross-sectional area of the second end portion opening is larger than the ratio of a cross-sectional area of the second spine of the fiber to a cross-sectional area of the second end portion of the quenched fiber, the second end portion of the fiber being created by extruding the polymer mass through the second end portion opening. [0197] 6. The method of clauses 4 or 5, wherein an amplitude of the first spine of the fiber is less than an amplitude of the first spine opening, and wherein an amplitude of the second spine of the quenched fiber is less than an amplitude of the second spine opening. [0198] 7. The method of any one of the preceding clauses, [0199] wherein a width of the first end portion opening is larger than a width of a first section of the middle portion opening (1726) adjacent to the first end portion opening, and wherein a width of the second end portion opening is larger than a width of a second section of the middle portion opening (1728) adjacent to the second end portion opening; and [0200] wherein a width of the first end portion of the fiber is larger than a width of a first section of a middle portion (1730) of the fiber adjacent to the first end portion of the fiber, and wherein a width of the second end portion of the fiber is larger than a width of a second section of the middle portion (1734) of the quenched fiber adjacent to the second end portion of the quenched fiber. [0201] 8. The method of any one of the preceding clauses, wherein the width of the first and second end portion openings are respectively larger than a maximum width of the middle portion opening, and wherein the width of the first and second end portions are respectively larger than a maximum width of a middle portion of the quenched fiber. [0202] 9. The method of any one of the preceding clauses, wherein a center of the curved middle portion opening includes a bulge opening (1714), and wherein a maximum width of the middle portion opening including the bulge opening is greater than a maximum width of the first and second end portion openings. [0203] 10. The method of any one of clauses 1-3, wherein the quenched fiber comprises no spines at positions of the first and second spine openings. [0204] 11. The method of any one of the preceding clauses, wherein the curved middle portion opening has two opposing longitudinal contours (1206, 1208), wherein at least one of the contours comprises or consists of uninterrupted undulations. [0205] 12. The method of any one of the preceding clauses, wherein the curved middle portion opening has a shape of one or more sinusoidal waves. [0206] 13. The method of any one of clauses 1-11, wherein the curved middle portion opening has a shape of an arc. [0207] 14. The method of clause 13, wherein a radius of curvature of the middle portion opening decreases from a center (1706) of the middle portion opening towards the end portion openings. [0208] 15. The method of clause 13, wherein a shape of the middle portion opening comprises one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of a segment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a . [0209] 16. The method of any one of the preceding clauses, wherein the polymer mixture comprises a polyethylene or a polyethylene-polyamide blend, wherein the quenching unit is a water bath, wherein the distance between the extrusion plate openings and the quenching unit is 3.0-5.0 cm, and wherein a temperature of the water bath is 28 C.-34 C. [0210] 17. The method of any one of clauses 1-15, wherein the polymer mixture comprises polyamide as a main polymer component or consists of polyamide, wherein the quenching unit is a water bath, wherein the distance between the extrusion plate openings and the quenching unit is 2.0-4.0 cm, and wherein a temperature of the water bath is 18 C.-20 C. [0211] 18. The method of any one of the preceding clauses, wherein the polymer mixture is at least a two-phase polymer mixture, wherein a first phase of the polymer mixture comprises a first polymer and a first dye and a second phase of the polymer mixture comprises a second polymer and a second dye, wherein a color of the second dye is different than a color of the first dye, wherein the second polymer is of a same or of a different type as the first polymer, wherein the first and the second phases are immiscible, and wherein the extruded fiber has a marbled appearance. [0212] 19. The method of clause 18, wherein the first phase forms polymer beads within the second phase, and wherein the polymer mixture further comprises a nucleating agent and/or a compatibilizer. [0213] 20. The method of clauses 18 or 19, wherein the first polymer is any one of the following: polyamide, polyethylene terephthalate, and polybutylene terephthalate, and wherein the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof. [0214] 21. An extrusion plate (1702) for artificial turf fibers, the extrusion plate comprising: [0215] at least one fiber profile opening, the fiber profile opening including: [0216] first and second end portion openings (1703, 1705), and [0217] a curved middle portion opening (1707) connected with the first and second end portion openings, having at least a first spine opening (1710) proximate to the first end portion opening and a second spine opening (1712) proximate to the second end portion opening. [0218] 22. The extrusion plate of clause 21, [0219] wherein a maximum width of the first spine opening is larger than 110%, in particular larger than 115%, in particular 110% to 160%, in particular 115% to 135% of an average width of the middle portion opening, wherein the average width of the middle portion opening is determined without considering a width of an optional central bulge opening, if any, and [0220] wherein a maximum width of the second spine opening is larger than 110%, in particular larger than 115%, in particular 110% to 160%, in particular 115% to 135% of the average width of the middle portion opening, wherein the average width of the middle portion opening is determined without considering the width of the optional central bulge opening, if any. [0221] 23. Use of the extrusion plate of clause 21 or 22 for mitigating or preventing a reduction in width of end portions (1715, 1717) of a fiber (1704), thereby increasing dimensional stability and/or for mitigating or preventing curling of an end of the fiber after the fiber is formed upon extruding a polymer mixture through the openings of the extrusion plate. [0222] 24. A system comprising: [0223] the extrusion plate of clause 21; [0224] at least one fiber formed by extruding a polymer mass through the at least one fiber profile opening, in particular one of the fibers of clauses 25-29; and [0225] optionally a quenching unit. [0226] 25. An extruded artificial turf fiber (1400, 1704, 1800, 1900, 2000, 2200, 2300, 2400, 2500) having a cross-sectional profile comprising first and second end portions connected via a curved middle portion, wherein the middle portion comprises at least a first spine proximate to the first end portion and comprises at least a second spine proximate to the second end portion. [0227] 26. The artificial turf fiber of clause 25, [0228] wherein a width of the first spine is less than 125%, in particular less than 115%, in particular 101% to 115% of an average width of the middle portion, wherein the average width of the middle portion is determined without considering a width of an optional central bulge, if any, and [0229] wherein a width of the second spine is less than 125%, in particular less than 115%, in particular 101% to 115% of the average width of the middle portion, wherein the average width of the middle portion is determined without considering the width of the optional central bulge, if any. [0230] 27. The artificial turf fiber of clauses 25 or 26, [0231] wherein a center of the middle portion of the fiber comprises a thickening that forms a bulge to at least one side of the fiber. [0232] 28. The artificial turf fiber of any one of clauses 25-27, wherein a width of the curved middle portion as measured between first and second boundary lines of the curved middle portion, excluding a center of the middle portion, is: [0233] constant along a longitudinal direction of the curved middle portion, or [0234] monotonically increasing along the longitudinal direction of the curved middle portion from either or both end portions towards the center of the middle portion. [0235] 29. The artificial turf fiber of any one of clauses 25-28, wherein the cross-sectional profile of the fiber comprises a first and a second boundary line, the first and second boundary lines comprising or consisting of uninterrupted undulations. [0236] 30. The artificial turf fiber of clause 29, wherein the first boundary line is an outer, convex boundary line and the second boundary line is an inner, concave boundary line. [0237] 31. An artificial turf comprising: [0238] a carrier; and [0239] a plurality of artificial turf fibers of any one of clauses 25-30 integrated into the carrier and protruding therefrom to form the artificial turf. [0240] 32. The artificial turf of clause 31, the artificial turf being configured for use as a hockey field artificial turf.

REFERENCE SIGNS LIST

[0241] 100 artificial turf fiber [0242] 102 cross section area [0243] 104 inner surface [0244] 202 outer surface [0245] 302 first fiber end [0246] 304 second fiber end [0247] 306 center of the fiber [0248] 308 undulation of outer surface in the form of an indentation [0249] 310 undulation of inner surface in the form of an indentation [0250] 312 undulation of outer surface in the form of an protrusion [0251] 314 undulation of the inner surface in the form of a protrusion [0252] 316 protrusion caused by a central thickening [0253] 318 thickenings at the fiber ends [0254] 502 circle defining the curvature of an undulation of the first fiber end [0255] 504 circle defining the curvature of an undulation of the second fiber end [0256] 506 circle defining the curvature of an undulation at the thickened fiber center [0257] 508 circles defining the curvature of undulations at the outer surface [0258] 510 circles defining the curvature of undulations at the inner surface [0259] 602 fiber width at the fiber ends [0260] 604 fiber width at one position of the fiber arms [0261] 606 fiber width at another position of the fiber arms [0262] 608 fiber width at the fiber center [0263] 800 artificial turf fiber [0264] 900 artificial turf fiber [0265] 1000 artificial turf fiber [0266] 1100 artificial turf fiber [0267] 1200 artificial turf fiber [0268] 1202 middle portion [0269] 1206 first boundary line [0270] 1208 second boundary line [0271] 1210 longitudinal direction [0272] 1212 first wavelength [0273] 1214 second wavelength [0274] 1216 phase offset [0275] 1218 first wavelength in another embodiment [0276] 1220 second wavelength in another embodiment [0277] 1222 boundary line of first end portion 302 [0278] 1224 boundary line of second end portion 304 [0279] 1226 boundary line of first end portion 302 in another embodiment [0280] 1228 boundary line of second end portion 304 in another embodiment [0281] 1300 artificial turf fiber [0282] 1400 artificial turf fiber [0283] 1402 first spine [0284] 1404 second spine [0285] 1500 artificial turf fiber [0286] 1502 extrusion dye [0287] 1504 photo of artificial turf fiber [0288] 1506 outline (i.e., shape) of extrusion dye 1502 [0289] 1508 outer boundary line [0290] 1510 inner boundary line [0291] 1512 end portion [0292] 1518 first baseline [0293] 1520 second baseline [0294] 1600 artificial turf fiber [0295] 1602 extrusion dye [0296] 1604 photo of artificial turf fiber [0297] 1605 end portions [0298] 1606 center [0299] 1608 end portions of photo 1604 [0300] 1618 first baseline [0301] 1620 second baseline [0302] 1700 artificial turf fiber [0303] 1702 extrusion dye [0304] 1703 first end portion opening [0305] 1704 photo of artificial turf fiber [0306] 1705 second end portion opening [0307] 1706 center [0308] 1707 middle portion opening [0309] 1709 first distal end [0310] 1710 first spine opening [0311] 1711 second distal end [0312] 1712 second spine opening [0313] 1713 center point [0314] 1714 bulge [0315] 1715 first end portion [0316] 1716 end portions of photo 1704 [0317] 1717 second end portion [0318] 1718 first baseline [0319] 1720 second baseline [0320] 1722 first spine [0321] 1724 second spine [0322] 1726 first section of middle portion opening [0323] 1728 second section of middle portion opening [0324] 1730 first section of middle portion [0325] 1732 middle portion [0326] 1734 second section of middle portion [0327] 1800 artificial turf fiber [0328] 1801 middle portion [0329] 1802 first spine [0330] 1804 second spine [0331] 1806 first end portion [0332] 1808 second end portion [0333] 1900 artificial turf fiber [0334] 1901 middle portion [0335] 1902 first spine [0336] 1904 second spine [0337] 1906 first end portion [0338] 1908 second end portion [0339] 2000 artificial turf fiber [0340] 2001 middle portion [0341] 2002 first spine [0342] 2004 second spine [0343] 2006 first end portion [0344] 2008 second end portion [0345] 2100 artificial turf fiber [0346] 2102 first middle portion [0347] 2104 second middle portion [0348] 2106 first end portion [0349] 2108 second end portion [0350] 2110 center of first middle portion [0351] 2112 center of second middle portion [0352] 2200 artificial turf fiber [0353] 2202 first spine [0354] 2204 second spine [0355] 2206 first end portion [0356] 2208 second end portion [0357] 2300 artificial turf fiber [0358] 2302 first spine [0359] 2304 second spine [0360] 2400 artificial turf fiber [0361] 2402 first spine [0362] 2404 second spine [0363] 2500 artificial turf fiber [0364] 2502 first spine [0365] 2504 second spine [0366] 2602 plot [0367] 2604 plot [0368] 2606 plot [0369] 2608 polymer mass flow profile [0370] 2610 polymer mass flow profile [0371] 2612 polymer mass flow profile