An 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.

Description

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -AN ARTIFICIAL TURF FIBER AND METHOD OF MANUFACTURING THEREOF -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -FIELD OF THE INVENTION

[0001] The invention relates to the field of artificial turf, and more particular to artificialturf fibers and the manufacture thereof. BACKGROUND

[0002] Synthetic grass fields (or artificial turf) have been used for years to provide asurface that simulates natural grass. These synthetic grass fields have many benefits over natural grass and, in addition, can be installed and used in places that do not allow for natural grass fields, for example, in regions where it is particularly hot and dry.

[0003] Artificial lawns, like artificial grass sport fields, require less maintenance and canbe used more intensively than lawns of natural grass. Although attempts are made tomake the synthetic fibers used for the production of artificial turf look as natural as possible, for example by adding green pigments to the fibers or selecting the fiber cross- section to resemble the cross-section of certain grasses (as described e.g., in EP000003480344A1), in certain situations the artificial turf can still leave a visual impression that is clearly different from that of natural grass and appear "artificial" or "unnatural".

[0004] In addition, an exact reproduction of certain types of grass can lead to the fibersbeing mechanically unstable or not being able to be produced in the desired form. Thus, the production of artificial turf fibers that give an artificial turf a natural appearance for as long as possible during the entire period of use still represents a major technical challenge.

[0005] US patent US 10,793,973 B2 relates to a synthetic monofilament fiber for use inan artificial lawn which has multiple tapered elevations which are believed be associatedwith increased risk of skin abrasion, and an increased proneness to wear and tear and the associated generation of microplastic waste.

[0006] EP 1950350 A1 discloses various fibers, some of which have large bulbs at thecenter and on the ends. These fibers have stress points at the point the bulbs areconnected to the fiber. As a result, these types of fibers have a tendency to fray or split along these stress points.

[0007] A further fiber is disclosed in US006491991B2 which has a curved cross sectionwith a series of flat, planar sections which may lead to decreased mechanical stiffnessand other undesired properties.

[0008] Korean patent KR 10-1989-0002109 discloses a spinneret for manufacturingmonofilaments for artificial turf. In cross-section, the spinneret has an outer peripheryformed of continuously repeated triangles of the same size, and an inner peripheryformed of continuously repeated curved parts of the same size, for forming amonofilament that by definition has a cross-section that is the same as the cross-sectionof the spinneret. Since the triangles and the curved parts are connected to neighboringtriangles and curved parts for forming the outer periphery and inner periphery,respectively, then a slope (which may also be referred to as tangent line) isindeterminate at each connection point on each respective periphery. That is, the slopeat each connection point between neighboring triangles and curved parts on eachrespective periphery is indeterminate, or in other words, the slope as measured at eachpoint along the respective peripheries has a discontinuity at each connection point. Ifeach point on each respective periphery is defined with respect to a cartesian coordinatesystem x-y to have coordinate (x,y), then the slope at each point is dy / dx.

[0009] It is an objective to provide for an improved manufacture of artificial turf fibers,improved artificial turf fibers, and artificial turf comprising the same. The objectivesunderlying the invention are solved by the features of the independent claims.SUMMARY

[0010] In one aspect, a method of manufacturing an artificial turf fiber includes extrudinga 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 openingproximate to the second end portion opening; allowing the extruded polymer mixture totravel along a distance between the at least one fiber profile opening of the extrusion plate to a quenching unit, where 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 isquenched; and quenching the extruded polymer mixture in the quenching unit to formthe artificial turf fiber.

[0011] The first spine opening being “proximate” the first end portion opening” meansthat the first spine opening is more proximate to the first end portion opening than tothe second end portion opening. Likewise, the second spine opening is more proximateto the second end portion opening than to the first end portion opening.

[0012] Advantageously, manufacturing an artificial turf fiber by extruding a polymermixture through at least one fiber profile opening of an extrusion plate including 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 results in a fiber that has lessthinning of the fiber end portions, more resistance to curling of the end of the fiber, andhence more mechanical stability and / or strength. The fiber end portions are defined asthe end portions in a cross-section of the fiber, whereas the end of the fiber refers to theend of the length of the fiber (i.e. the tip of the fiber). The one or more spine openings ofthe extrusion plate result in a net polymer mass flow, which occurs between extrusion ofa polymer mass from the extrusion plate (in the form of an unquenched polymer fiber)and quenching of the fiber via, for example, a quenching unit. For example, the extrudedfiber may travel a specified distance before entering the quenching unit. The net polymermass flow, which is in the direction from a region of the extruded fiber (corresponding to the spine opening of the extrusion plate) to the closest end portion of the fiber, mitigates or prevents a reduction in width of the first and second end portions of the quenchedfiber in comparison to the 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. For example, the width of an end portion or end portion opening may be measured as the longest line connecting the first and the second boundary lines of the fiber, the connecting line being a) basically orthogonal to the first and the second boundary line, and b) lying within the fiber end portion / fiber end portion opening. In examples where the fiber end portion has circular shape, this distance may be the diameter of the circle.

[0013] According to some examples, the first spine opening is positioned in the middleportion 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°, where the first arc length ismeasured along the curved middle portion opening from the first end portion opening, and the second spine opening is positioned in the middle portion opening on a secondarc length defined by a second angle of less than or equal to 60°, or between 35°- 55°, orbetween 40°- 50°, or at 45°, where the second arc length is measured along curvedmiddle portion opening from the second end portion opening. For example, the first andsecond angles may be measured as illustrated in figure 4B.

[0014] These features have the benefit of optimizing the net polymer mass flow in thedirection towards the end portion of the fibers, which occurs during the time elapsed between extrusion of the polymer mass (in the form of an unquenched fiber) andquenching of the unquenched fiber. Quenching halts any polymer mass flow in the fiber.

[0015] According to other examples, the quenched fiber includes a first spine created byextruding the polymer mass through the first spine opening and a second spine createdby extruding the polymer mass through the second spine opening. However, in someexamples, the quenched fiber, even though formed by extruding a polymer mass throughan extrusion dye having one or more spine openings, has no visible spines, although thefiber retains the benefits of being extruded through an extrusion die having one or morespine openings (i.e., mitigation of thinning of the width (or no thinning of the width) ofthe end portions of the fibers in comparison to the width of the end portion openings ofthe extrusion die).

[0016] According to examples, the ratio of the area of the first spine opening to the areaof the first end portion opening is larger than the ratio of the cross-sectional area of thefirst spine of the quenched fiber to the cross-sectional area of the first end portion of thequenched fiber, the first end portion of the fiber being created by extruding the polymermass through the first end portion opening, and / or the ratio of the area of the secondspine opening to the area of the second end portion opening is larger than the ratio of across-sectional area of the second spine of the quenched fiber to the cross-sectional areaof 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.

[0017] The expression “the area of the first / second end portion opening” as used hereinrefers to the total area of the first / second end portion opening. Likewise, the expression“the cross-sectional area of the first / second end portion” as used herein refers to thetotal area of the first / second end portion of the cross-sectional profile of the extrudedartificial turf fiber.

[0018] Given that the thinning of the end portions is mitigated or even stopped, then thisfeature has the benefit that the spines on the fiber are smaller than the spine openings of the extrusion plate, meaning that the spines may in some instances be barely visible, or in some cases, even invisible.

[0019] According to other examples, an amplitude of the first spine of the quenchedfiber is less than an amplitude of the first spine opening, and an amplitude of the second spine of the quenched fiber is less than an amplitude of the second spine opening.

[0020] According to yet other examples, the width of the first end portion opening islarger than the width of a first section of the middle portion opening adjacent to the firstend portion opening, the width of the second end portion opening is larger than thewidth of a second section of the middle portion opening adjacent to the second endportion opening, and / or the width of the first end portion of the quenched fiber is largerthan the width of a first section of a middle portion of the quenched fiber adjacent to thefirst end portion of the quenched fiber, and the width of the second end portion of thequenched fiber is larger than the width of a second section of the middle portion of thequenched fiber adjacent to the second end portion of the quenched fiber.

[0021] These features advantageously result in a fiber that is more resilient to forces andless likely to fray or tear, and may further result in a fiber that is less likely to flatten through use (i.e., the fiber, including the curved middle portion, retains its curvature).

[0022] According to yet other examples, the width of the first and second end portionopenings are respectively larger than a maximum width of the middle portion opening, and the width of the first and second end portions are respectively larger than amaximum width of a middle portion of the quenched fiber. These features may alsoadvantageously result in a fiber that is more resilient to forces and less likely to fray or tear, and may further result in a fiber that is less likely to flatten through use (i.e., thefiber, including the curved middle portion, may exhibit increased elasticity, therebyretaining its curvature).

[0023] According to examples, a center of the curved middle portion opening includes abulge 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.

[0024] This feature may also advantageously result in a fiber that is more resilient toforces, and may further result in a fiber that is less likely to flatten through use (i.e., the fiber, including the curved middle portion, retains its curvature), particularly when combined with other features, such as the width of the first and second end portions being respectively larger than a maximum width of a middle portion of the quenchedfiber. The bulge opening may further provide a fiber with increased mechanical strengththat increase the ability of the fiber to quickly straighten up again after a temporary load- induced buckling.

[0025] According to examples, the curved middle portion opening has two opposinglongitudinal contours (i.e., boundary lines), where at least one of the contours includes,or includes exclusively of, uninterrupted undulations.

[0026] The effect of a boundary line consisting completely of uninterrupted undulationsmay be beneficial because the entire boundary line of the fiber is free of planar areas,pointed elevations and pointed depressions.

[0027] This can provide a highly advantageous compromise between mechanicaldurability, wear resistance and a natural look and feel: the multiple undulations cause the fiber to scatter incident light and therefore appear dull, like most natural grass fibers.

[0028] Some prior art artificial turf fibers have a boundary line comprising a series ofelevations or depressions to scatter incident light and provide a matt surface impression which is similar to the look of a natural grass fiber surface. However, some prior art fibers have fiber profile contours with multiple successive concave depressions or multiple successive convex elevations. Such an outline has several disadvantages: series of concave depressions result in thin, pointed protrusions. These can lead to a very rough surface, especially when using relatively hard, mechanically robust polymer material, which in turn can lead to skin damage. In addition, these pointed protrusions are subject to high mechanical stress, resulting in a large amount of material being abraded in a short period of time. This abrasion can end up in the environment as unwanted microplastic waste. Series of convex bumps in turn create thin, conical depressions. Dirt and unwanted germs can accumulate in these depressions and negatively affect the appearance and hygiene of the artificial turf. In addition, such conical depressions, especially if they are large, represent a mechanical weak point where the fibers can easily tear (splice) under mechanical stress.

[0029] To the contrary, a shape with a contour consisting of uninterrupted undulationsaccording to embodiments the invention has the advantage that the incident light is diffusely scattered, so that a matt, natural surface impression is created, without having to accept problems regarding the risk of injury, microplastics, hygiene or mechanicalintegrity of the fibers. In a fiber cross section of a fiber according to embodiments of theinvention, all depressions and indentations of the fiber surface are rounded, or in other words, a tangent line may be formed or defined (i.e., a tangent line is determinate) at each point on boundary lines that define the fiber in cross section, thereby minimizing the risk of splicing, the risk of skin burns, the generation of microplastic and theaccumulation of dirt and debris. That is, if each point on the boundary lines is definedwith respect to a cartesian coordinate system x-y to have coordinate (x,y), then the slopeat each point is dy / dx, and according to an embodiment of the present invention, theboundary lines have a continuous slope as measured at each point along the boundarylines. In other words, the boundary lines have no discontinuities in slope.

[0030] A further benefit may be that the extrusion process can run true to shape. Thismeans that the shape of the fiber cross section essentially matches the shape of the extrusion die profile opening. As the boundary line of the fiber profile is free of pointed protrusions or indentations, the extrusion die profile is also free of such pointed protrusions or elevations. As a consequence, the formation of speed differences of the extruded polymer mass during extrusion which may result in deformed fibers may be prevented.

[0031] According to other examples, the curved middle portion opening has a shape ofone or more sinusoidal waves, or the curved middle portion opening has 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 asegment of a horseshoe, an arc of a segment of a U, or an arc of a segment of a Ω. Insome examples, a radius of curvature of the middle portion opening decreases from acenter of the middle portion opening towards the end portion openings. These featureshave the benefit of providing a fiber of increased strength and increased resilienceagainst being trampled down (i.e., better retention of elasticity). Furthermore, Applicanthas observed that a cross-section of the fiber being shaped like 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 Ω may have the advantage of providing fibers which are particularly robust against the flattening of the fiber during production or use. It has been observed that small curvatures do not always recover their original shape (as produced during the extrusion process) after being compressed or flattened during transport through rollers and spinnerets or when subjected to a weight, e.g. the weight of a player or a ball. To the contrary, a strong curvature as observed in a segment of a horseshoe, a segment of a U, or a segment of a Ω, provides an intrinsic elasticity and ability to recover the original shape. The use of fiber profiles with a boundary line that is curved like a circular segment arc can have the advantage that light falling from different directions is scattered homogeneously because the curvature of the fiber profile is the same when viewed from all directions. This also means that the light reflected by the artificial turf looks the same when viewed from different angles. As a result, even a synthetic turf that has a toouniform orientation of the fibers due to the manufacturing process does not have any artificial dependence of the optical impression on the viewing angle.

[0032] Furthermore, an artificial turf fiber extruded from an extrusion die having at leastone spine opening in combination with one or more of: (1) an average cross-sectional width of a middle portion opening that increases (preferably monotonically) from theend portion openings to the center of the middle portion; (2) thickened end portionopenings (preferably having a thickness that is greater than a maximum thickness of themiddle portion opening (between the two end portion openings), excluding the thicknessof the center of the middle portion opening when the center may include a roundedbulge opening; and (3) a thickened center opening of the middle portion opening (i.e. arounded bulge opening), where the thickness is preferably thicker that the thicknesses ofthe end portion openings, has the synergistic effect of providing a fiber that has evenmore reinforced mechanical stability and / or strength and even less thinning of the fiberends.

[0033] According to some examples, the polymer mixture includes a polyethylene or apolyethylene-polyamide blend, where the quenching unit is a water bath, where thedistance between the extrusion plate openings (also referred to as the fiber profileopening) and the quenching unit is 3.0 – 5.0 cm, and where a temperature of the waterbath is 28°C - 34°C.

[0034] Advantageously, these features have the benefit of providing parameters thatoptimize the amount of polymer mass flow upon extrusion and before quenching for mitigating thinning of the end portions of the fiber.

[0035] In other examples, the polymer mixture includes a polyamide as a main polymercomponent or a polyamide as an exclusive polymer component, where the quenchingunit is a water bath, where the distance between the extrusion plate openings and thequenching unit is 2.0 – 4.0 cm, and where a temperature of the water bath is 18°C - 20°C.

[0036] Advantageously, these features have the benefit of providing parameters thatoptimize the amount of polymer mass flow upon extrusion and before quenching for mitigating thinning of the end portions of the fiber.

[0037] According to some examples, the polymer mixture is at least a two-phase polymermixture, where a first phase of the polymer mixture includes a first polymer and a firstdye 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.

[0038] According to other examples, the first phase forms polymer beads within thesecond phase, and wherein the polymer mixture further comprises a nucleating agentand / or a compatibilizer and / or the first polymer is any one of the following: polyamide,polyethylene terephthalate, and polybutylene terephthalate, and where the secondpolymer is any one of the following: polyethylene, polypropylene, and a mixture thereof.

[0039] This may have the advantage of further increasing the surface roughness, becausethe nucleating agent may induce or boost the formation of polymer microcrystals at the surface of the fiber during or after the extrusion process.

[0040] For example, the nucleating agent may be a substance or substance mixtureselected from a group comprising: talcum; kaolin (also known as “China clay”); calcium carbonate; magnesium carbonate; silicate: aluminum silicate and; as e.g. sodium aluminosilicate (in particular zeolites of natural and synthetic origin); amorphous and partially amorphous silica and mixed morphologies hereof, e.g. fumed silica; silicic acid and silicic acid esters; e.g. tetraalkyl orthosilicate (also known as orthosilicic acid ester)aluminum trihydrate; magnesium hydroxide; meta- and / or polyphosphates; and coal flyash (CFA); coal fly ash is a fine recovered e.g. from coal-fires of electric generation power plants; wherein the organic nucleating agent consists of one of the following items or a mixture thereof: 1,2-cyclohexane dicarbonic acid salts (also known as main component of “Hyperform®”); in particular calcium salts of the 1,2-cyclohexane dicarbonic acid; benzoic acid; benzoic acid salt; the benzoic acid salt may be, in particular, an alkaline metal salt of the benzoic acid (e.g. sodium and potassium salts of the benzoic acid); and an alkaline earth metal salt of the benzoic acid (e.g. magnesium and calcium salts of the benzoic acid); sorbic acid; and sorbic acid salt.

[0041] According to some examples, 0.01 % - 3.0 % by weight of the artificial turf fiberconsists of the nucleating agent. preferably, 0.2 %- 0.4 % by weight of the artificial turffiber consists of the nucleating agent. This is a comparatively low amount. Nevertheless,applicant has observed that this small amount is sufficient to achieve a diffuse light scattering that is almost indistinguishable from the light scattering on natural grass. It is possible to use only very small amounts of the nucleating agent, because the diffuse scattering is not only caused by the crystals on the fiber surface, but also by the undulations of the fiber profile. Using only very small amounts of the nucleating agent (or none at all) may be beneficial as the crystalline portions induced by the nucleating agent at the surface and within a fiber may increase the brittleness of the fiber, thereby increasing the tendency to break or splice.

[0042] In one aspect, an extrusion plate for artificial turf fibers includes at least one fiberprofile 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 portionopenings. The curved middle portion opening has at least a first spine opening proximateto the first end portion opening and a second spine opening proximate to the second end portion opening.

[0043] The features of the extrusion plate result in a fiber that has less thinning of thefiber end portions, more resistance to curling of the end of the fiber, and hence moremechanical stability and / or strength. The one or more spine openings of the extrusionplate result in a net polymer mass flow, which occurs between extrusion of a polymer mass from an extrusion plate (in the form of an unquenched polymer fiber) andquenching of the fiber via, for example, a quenching unit. For example, the extrudedfiber may travel a specified distance before entering the quenching unit. The net polymermass flow, which is in the direction from a region of the extruded fiber (corresponding to the spine opening of the extrusion plate) to the closest end portion of the fiber, mitigatesor prevents a reduction in width of the first and second end portions of the quenchedfiber in comparison to the 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.

[0044] In some examples, a maximum width of the first spine opening is larger than110%, in particular larger than 115%, in particular 110% to 160%, in particular 115% to 135% of an average width of the middle portion opening, where the average width of themiddle portion opening is determined without considering the width of an optionalcentral bulge opening, if any, and where 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, where the average width of the middle portion opening is determined without considering the width of the optional central bulge opening, if any.

[0045] In one aspect, an extruded artificial turf fiber has a cross-sectional profileincluding first and second end portions connected via a curved middle portion, where the middle portion includes at least a first spine proximate to the first end portion and at least a second spine proximate to the second end portion.

[0046] The features of the first and second spine indicate that that fiber has been formedby extruding a polymer mass through a die having spine openings, thereby providing afiber with end portions that are approximately to specification (i.e., end portions having dimensions that are approximately the same as the dimensions of the end portion openings of the die), resulting in a fiber with increased strength and resilience against flattening and curling.

[0047] In some examples, the width of the first spine is less than 125%, in particular lessthan 115%, in particular 101% to 115 % of an average width of the middle portion, wherethe average width of the middle portion is determined without considering the width ofan optional central bulge, if any, and where the width of the second spine is less than125%, in particular less than 115%, in particular 101% to 115 % of the average width of the middle portion, where the average width of the middle portion is determined without considering the width of the optional central bulge, if any.

[0048] An “undulation” as used herein is a curve having a continuous up and downshape. Hence, a boundary line consisting of uninterrupted undulations may be describedas a boundary line not having a vertical tangent. A boundary line consisting ofuninterrupted undulations may also be described as a mathematically differentiable curve.

[0049] It is understood that one or more of the aforementioned embodiments andexamples may be combined as long as the combined embodiments are not mutuallyexclusive.BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In the following, examples are described in greater detail making reference to thedrawings in which:

[0051] Fig. 1 is a perspective 3D view of the inside of a section of the fiber;

[0052] Fig. 2 is a perspective 3D view of the outside of a section of the fiber;

[0053] Fig. 3 shows the cross-section of a fiber;

[0054] Fig. 4A shows the fiber cross-section of Fig.3 with height and width annotated;

[0055] Fig. 4B shows how angles and arc lengths being descriptive of spine positions canbe determined;

[0056] Fig. 5 shows the fiber cross-section of Fig. 3 with the circles defining thecurvature of the corrugations and the ends annotated;

[0057] Fig. 6 shows the fiber cross-section, where the fiber thicknesses at differentcross-sectional areas are annotated;

[0058] Figs. 7A and B show an example of a fiber cross-section annotated with concretedimensions;

[0059] Fig. 8 shows an example of a cross-section of a further fiber having moreundulations;

[0060] Fig. 9 shows an example of a cross-section of a further fiber having moreundulations and an extended curvature;

[0061] Fig. 10 shows an example of a cross-section of a further fiber having a centralthickening which leads to a visible bulge on both the outer and inner surface of the fiber;

[0062] Fig. 11 shows an example of a cross-section of a further fiber, the cross sectionhaving the shape of a catenary;

[0063] Fig. 12 shows a cross-section of an extruded artificial turf fiber, according to anembodiment;

[0064] Fig. 13 shows the cross-section of an extruded artificial turf fiber according to yetanother embodiment;

[0065] Fig. 14 shows the cross-section of an extruded artificial turf fiber according toanother embodiment;

[0066] Fig. 15 illustrates a cross-section of an extrusion die and a photo of an artificialturf fiber formed in part by extruding a polymer mixture through the extrusion die, according to an embodiment;

[0067] Fig. 16 illustrates a cross-section of an extrusion die and a photo of an artificialturf fiber formed in part by extruding a polymer mixture through the extrusion die, according to another embodiment;

[0068] Fig. 17 illustrates a cross-section of an extrusion die and a photo of an artificialturf fiber formed in part by extruding a polymer mixture through the extrusion die, according to yet another embodiment;

[0069] Fig. 18 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of a horseshoe, according to an embodiment;

[0070] Fig. 19 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of the Greek letter Ω , according to an embodiment;

[0071] Fig. 20 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of the letter U , according to an embodiment;

[0072] Fig. 21 shows a photograph of an extruded artificial turf fiber having anapproximate sinusoidal shape, according to an embodiment;

[0073] Fig. 22 shows a photograph of an extruded artificial turf fiber having anapproximate sinusoidal shape, according to another embodiment;

[0074] Fig. 23 shows a photograph of an extruded artificial turf fiber having anapproximate shape of the letter “U,” according to an embodiment;

[0075] Fig. 24 shows a photograph of an extruded artificial turf fiber having anapproximate shape of a horseshoe, according to an embodiment; and

[0076] Fig. 25 shows a photograph of an extruded artificial turf fiber having anapproximate shape of a segment of a circle, according to an embodiment.

[0077] Fig. 26 shows three plots illustrating the flow path expansion induced by the spineopenings and by a thickening of the end portion openings. DETAILED DESCRIPTION

[0078] In the following, similar elements may be denoted by the same referencenumerals.

[0079] Figure 1 is a perspective 3D view of the inside of a section of an artificial turf fiber100. 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. Figure 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.

[0080] Figure 2 is a perspective 3D view of the outside of a section of the fiber 100shown already in figure 1. Figure 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.

[0081] Figure 3 shows the cross-section of the fiber 100 depicted already in figures 1 and2. The fiber comprises a first end 302 connected to the center 306 of the fiber via a firstfiber arm and comprises a second end 304 connected to the center of the fiber via a second arm.

[0082] As can be inferred from figures 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 ofuninterrupted undulations may imply that - apart from the cross-sectional area of thefiber at the upper and lower fiber ends where the fiber is cut during or after integrationinto a carrier – the fiber surface is basically free of any planar areas. This may be highlybeneficial, 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.

[0083] In the example shown, the undulations comprise alternating depressions 308 andelevations 312 on the outer fiber surface and alternating depressions 310 and elevations 314 on the inner fiber surface.

[0084] The thickness of the fiber at the thickenings 318 at the two ends is slightly greaterthan 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.

[0085] Figure 4A shows the fiber cross-section of Fig. 3 with profile height h and profilewidth w annotated. For example, the profile width w can be measured as straight lineindicating the distance of the most outer points of the two fiber ends. The profile heighth of the fiber may be measured as the distance of the “lowest” points of the fiber ends tothe “highest” point at the fiber center as illustrated in figure 4A. As can be inferred fromfigure 4A, the profile height h may be significantly smaller than the profile width w and may be significantly smaller than a radius R defining the curvature of the arced shape ofthe fiber profile, meaning that in case the arced shape is defined by a circle, or can beapproximately characterized by a circle having radius R, the fiber profile may cover asegment that is significantly smaller than the 180° segment of a circle having radius R. Inother words, the radius R of this circle may be significantly (e.g., at least 20%, e.g., atleast 30%, or even more than 40% longer than h.

[0086] According to some embodiments, the artificial turf fiber profile and / or theartificial turf fiber profile opening has a minimum curvature K. The curvature may be measured via a radius R of a circle that is fitted to the curved cross-sectional profile / profile opening, e.g., fitted to the second / outer base line of the curved cross-sectional profile / profile opening as illustrated in figure 4B. K is computed according to:K=1 / R, so a minimum curvature corresponds to a maximum radius R. According to someembodiments, the curvature K is at least 1 / 1.5 cm =0.67 / cm, which corresponds to amaximum radius of curvature R of at most 1.5 cm. According to some embodiments, thecurvature K is at least 1 / 1.12cm = 0.89 / cm, which corresponds to a maximum radius ofcurvature R of at most 1.2 cm.

[0087] Fig. 4B shows how angles and arc lengths which may be used for specifying theposition of the spines can be determined. Figure 4B shows a cross-sectional profile of anextrusion plate for extruding an artificial turf fiber. The profile comprises a first spineopening 1710 and a second spine opening 1712.

[0088] The first spine opening is positioned in the middle portion on a first arc length Al1defined by a first angle θ1 of less than or equal to 60°, or between 35°- 55°, or between40°- 50°, or at 45°. The first arc length is measured along the curved middle portionstarting from the first end portion opening

[0089] The second spine opening is positioned in the middle portion opening on a secondarc length Al2 defined by a second angle θ2 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 alongcurved middle portion opening from the second end portion opening. The angles are given in absolute degrees here, i.e., irrespective of their orientation within a 360° circle.

[0090] In embodiments in which small spines are still visible in the extruded artificial turffiber profiles, the position of these spines in the fiber profile is specified analogously.

[0091] As can be inferred from figure 4B and the other figures, a “first spine openingproximate to the first end portion opening” is a spine opening positioned in the one ofthe two arms of the profile which connects the first end portion opening 1703 with thecenter of the profile. Analogously, a “second spine opening proximate to the second endportion opening” is a spine opening positioned in the one of the two arms of the profilewhich connects the second end portion opening 1705 with the center of the profile.

[0092] Figure 5 shows the fiber cross-section of Fig. 3 with the circles defining thecurvature of the corrugations and the ends annotated. As illustrated in figure 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 figure 5, D1 and D2 are significantly larger than D3 and D4. D3 and D4 are identical. D1 is slightly larger than D2.

[0093] In other embodiments (not shown), D3 and D4 may be similar, but not identical.

[0094] In addition, or alternatively, D1 and D2 may be identical. For example, both D1and 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.

[0095] Figure 6 shows the fiber cross-section, where the fiber thicknesses at differentcross-sectional areas are annotated. As can be inferred from figure 6, the thickness of the fiber cross section is not constant but varies only slightly: the thickness w1602 is slightly greater than the thickness w2604 at the two points in the fiber arms equidistant fromthe ends, because in the depicted example, the fiber ends comprise a thickening. Thethickness w3606 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 hencestiffest portion of the fiber having a thickness w4608 being greater than w1, w2 and w3.

[0096] In the depicted example, w2 is the smallest with in the fiber arm and w3 is thelargest width of the fiber arm.

[0097] In other examples, w1 and w2 may be identical, but preferably w1 is greater thanthe smallest width w2 of the fiber arms, and preferably also greater than the largest width w3 of the fiber arm.

[0098] According to some examples, the fiber profile is axisymmetric with respect to avertical axis through the center of the fiber profile as shown in figures 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.

[0099] Figures 7A and 7B show an example of a fiber cross-section annotated withconcrete dimensions. The fiber cross section corresponds to the cross section of the fibers depicted in figures 1-6. The dimensions of the fiber 100 shown in figures 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.

[0100] The fiber profile can be scaled to provide fibers of different fiber weights. Forexample, by scaling the outer width of the fiber profile from 1.0 cm to 1.351 cm, and scaling all other dimensions given in figure 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.

[0101] As can be inferred from Figures 7A and B, the cross-section of the fiber is shapedlike the arc of a segment of a circle having a radius referred to as “fiber profile circleradius”. The fiber profile radius is illustrated with the letter R in figure 4A. The width w ofthe fiber profile when the outmost points of the fiber ends are connected is referred to as “w” in figure 4A.

[0102] According to figure 7A, the radius to the topmost point of the outer surface is0.59 cm. The width of the fiber profile when the outmost points of the fiber ends areconsidered 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.

[0103] According to figure 7B, the radius of the circle 506 defining the undulation at thecenter 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 thecurvature of the protrusion 316 at the fiber center to the radius of the circles defining theundulations 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.

[0104] Figure 8 shows an example of a cross-section of a further fiber 800 having moreundulations than the fiber cross section depicted in figures 1-7. The curvature of thewhole fiber profile is the same as the profile curvature of the fibers depicted in figures 1- 7.

[0105] Figure 9 shows an example of a cross-section of a further fiber 900 having moreundulations than the fiber cross section depicted in figures 1-7and having an extended curvature compared to the fiber cross sections depicted in figures 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 Figures 1-7.

[0106] Figure 10 shows the cross-section of an example of a further fiber 1000. Thedepicted fiber has a thickening at its center which leads to a bulge on both the outer and inner surface of the fiber.

[0107] Figure 11 shows the cross-section of an example of a further fiber 1100. Thecross-section of the depicted fiber has the shape of a catenary.

[0108] Figure 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 fiber100 of Figs.1-3, and reference numbers that are the same as those in Figs.1-3 referenceidentical 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 endportion 304), a curved middle portion 1202, and a center 306 of the middle portion 1202.

[0109] As illustrated by Fig. 12, and as seen in Figs. 1-3, the middle portion 1202 has acurved cross-sectional shape, and the first and second end portions are connected viathe curved middle portion. In some embodiments, the curved cross-sectional shape isformed from one or more arced-cross sectional shapes. In the Fig. 12 embodiment, thecurved 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 asecond boundary line 1208 opposite the first boundary line. The first boundary line 1206is a line on the outer surface 202 (Fig. 2) of the fiber 1200, and the second boundary line1208 is a line on the inner surface 104 (Fig. 1) of the fiber 1200. The first boundary line1206 includes or includes exclusively of first uninterrupted undulations representedcollectively by the indentations 308 and protrusions 312, and the second boundary line1208 includes or include exclusively of second uninterrupted undulations representedcollectively 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 alongitudinal dimension), along which a length of the cross-sectional shape lies. Thecurved 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.

[0110] In one embodiment, a thickness w (also referred to as the width, a transversewidth 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 ofthe curved cross-sectional shape. For example, thicknesses (i.e., widths) w1, w2 and w3are equal to one another, and moreover, a thickness w of the curved cross-sectionalshape of the middle portion 1202 measured at all positions along the longitudinaldirection is constant or substantially constant.

[0111] In one embodiment, the first uninterrupted undulations 308, 312 have a firstwavelength 1212 and the second uninterrupted undulations 310, 314 have a second wavelength 1214, where the first and second wavelengths are selected such that thethickness w of the curved cross-sectional shape of the middle portion 1202 is constant orsubstantially constant along the longitudinal direction 1210. The length of the secondboundary line 1208 (i.e., as measured from either the first or second end portion to aposition on the second boundary line 1208 opposite the center 306 along the innersurface 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 boundaryline 1206 opposite the center 306 along the outer surface 202 of the fiber), and thedifference between the lengths depend upon the extent of the curvatures of the innerand outer surfaces of the fiber 1200. In the exemplary embodiment of Fig. 12, the radiusof curvature of the inner surface 104 (and the second boundary line 1208) is smaller thanthe radius of curvature of the outer surface 202 (and the first boundary line 1206), andthus the length of the second boundary line 1208 is shorter than the length of the firstboundary line 1206. Thus, in order to provide a substantially constant thickness w of thecurved cross-sectional shape of the middle portion 1202 at all positions along thelongitudinal 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 seconduninterrupted undulations 310, 314 is selected to be smaller than the wavelength (i.e..spatial frequency) of the first uninterrupted undulations 308, 312.

[0112] 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-sectionalshape of the middle portion 1202.

[0113] Figure 13 shows the cross-section of an extruded artificial turf fiber 1300according to yet another embodiment. The artificial turf fiber 1300 is similar to artificialturf fiber 1200 of Fig.12, and reference numbers that are the same as those in Fig.12 reference identical elements.

[0114] The difference between fiber 1200 of the Fig. 12 embodiment and fiber 1300 ofthe 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 thelongitudinal direction 1210 of the curved cross-sectional shape. That is, in contrast to theFig.12 embodiment, the first uninterrupted undulations 308, 312 of the first boundaryline 1206 of the curved cross-sectional shape of the middle portion 1202 may have aphase offset 1216 from the second uninterrupted undulations 310, 314 of the secondboundary 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 portion1202 having a variable thickness, independent of whether the wavelengths 1212 and1214 (i.e., spatial frequencies) are equal or not (i.e., the thickness w of the curved cross-sectional shape of the middle portion 1202at positions along the longitudinal direction1210 is not constant (i.e., it is variable, or non-constant)). In one embodiment, athickness 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%.

[0115] Alternatively, or in addition to a phase offset, the first and second uninterruptedundulations may have the same (or substantially the same) wavelength (i.e., spatialfrequency). For example, the first uninterrupted undulations 308, 312 have a firstwavelength 1218 (also referred to as a first spatial frequency) and the seconduninterrupted undulations 310, 314 have a second wavelength 1220 (also referred to as asecond 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 thelongitudinal direction 1210, independent on whether or not there is a phase offset.

[0116] In another embodiment of Fig. 13, the thicknesses 318 of the first and second endportions 302, 304 of the fiber 1300 are greater than a maximum thickness of the variablethickness 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-sectionalshape of the middle portion 1202, then the thicknesses 318 of the first and second endportions 302, 304 of the fiber 1300 are greater than w5.

[0117] 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 byboundary lines 1222, 1224, respectively. Although the boundary lines 1222, 1224 arecurved, they do not include undulations. However, in an alternate embodiment, thecurved cross-sectional shapes of each of the first and second end portions 302, 304 aredefined by boundary lines 1226, 1228, respectively, that consist of third uninterruptedundulations. In yet another embodiment, wavelengths (i.e., spatial frequencies) of thethird uninterrupted undulations of boundary lines 1226, 1228 are greater than or equalto the wavelengths (i.e. spatial frequencies) of the first and second undulations of thefirst 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 undulationsas described with respect to the fiber 1200 (Fig. 12).

[0118] According to other embodiments of Figs. 12 and 13, the curved cross-sectionalshape of the extruded artificial turf fiber 1200, 1300 comprises one of: an arc of asegment of a circle, an arc of a segment of an ellipse, an arc of at least a segment of ahorseshoe, an arc of at least a segment of a U, or an arc of at least a segment of a Ω. Eachpoint on an arc of an ellipse has a different radius from neighboring points. The scope ofthe disclosed embodiments of the curved cross-sectional shapes of the extruded artificialturf fibers include arcs defined by boundary lines that have a varying radius of curvature along the longitudinal direction of the cross-sectional shapes.

[0119] 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 outersurface 202 (Fig. 2) of the fiber) and the second boundary line 1208 is an inner, concaveboundary line (i.e., line on the inner surface 104 of the fiber), where at least 70%, inparticular at least 80%, e.g., 100% of the undulations of the outer boundary line 1206 aredefined by first circles having a same first diameter D3, and where at least 70%, inparticular 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.

[0120] In another embodiment, the center 306 of the middle portion 1202 of the fiber1200, 1300 comprises a thickening that forms a rounded protrusion 316 to at least oneside of the fiber. Although the embodiments of Figs. 12 and 13 illustrate a thickening atthe center 306 of the middle portion 1202 of the fiber resulting in a protrusion 316 froman outer surface, such as outer surface 202 (Fig. 2), in other embodiments the centralthickening 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 protrusionfrom the inner surface 104, where the protrusions are formed opposite one another onthe two surfaces. In additional embodiments, the center 306 does not have anythickening or bulge. In one embodiment, the bulge has a thickness that is 10-20% thickerthan a maximum thickness of the other portions of the middle portion.

[0121] Fig. 14 shows the cross-section of an extruded artificial turf fiber 1400 accordingto another embodiment. Reference numbers that are the same as those in Figs. 12 and13 reference identical elements. As illustrated in the Fig. 14 embodiment, an averagethickness (also referred to as an average width) of the curved cross-sectional shape ofthe middle portion 1202 is not constant along the longitudinal direction 1210, butincreases as the longitudinal distance from the center 306 decreases.

[0122] In one embodiment, the average thickness of the middle portion, as alsoillustrated in Figs.15, 16 and 17, and which hereinafter applies to all disclosedembodiments, is the transverse distance between a first base line 1518 and a secondbaseline 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 inFig.14, the average thickness w3 is larger than the average thickness w2, which is larger than the average thickness w1.

[0123] Furthermore, in another embodiment, the middle portion 1202 has at least onespine proximate to respective end portions 302 and / or 304. For example, and asillustrated 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 thesecond end portion 304. As illustrated by Fig. 14, the first boundary line 1206 of themiddle portion 1202 has the first spine 1402 and the second spine 1404. In oneembodiment, a spine is defined as a protrusion that is slightly larger in amplitude thanneighboring 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 thecross-sectional shape of the middle portion 1202. A slightly larger amplitude is defined tobe 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 middleportion, or between about 2-5% larger than the average thickness of the middle portion.

[0124] In yet other embodiments, the width (i.e., thickness or amplitude) of the firstspine 1402 is less than 125%, in particular less than 115%, in particular 101% to 115 % ofan average width (i.e., thickness or amplitude) of the middle portion 1202, and / or thewidth 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 theexclusion of) the width of an optional central bulge (e.g., the optional bulge 316 at thecenter 306 of the middle portion 1202).

[0125] In some embodiments, the first boundary line 1206 of the middle portion 1202includes at least one spine (e.g., spines 1402 and 1404) that is continuous with neighboring first uninterrupted undulations.

[0126] In other embodiments, the at least one spine (e.g., spines 1402 and 1404) arepositioned on an outer half, or on an outer third, of the middle portion 1202, asmeasured 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 furtherbelow in conjunction with Fig.17, applicable to the Fig.14 embodiment as well.

[0127] Advantageously, and as will be described further below with respect to Fig. 17, agradual monotonical increase of average thickness of the middle portion 1202 of the fiberas the longitudinal distance from the center 306 of the fiber decreases, in combinationwith one or more spines (e.g., an even number of spines), preferable positioned on anouter half, or outer third, of the middle potion 1202, tend to add more mechanicalstability to the curvature of the fiber.

[0128] In further embodiments, and as illustrated in Fig. 14, the thicknesses w4, w5 ofthe middle portion corresponding to the location of the spines 1402, 1404, respectively,represent the maximum thickness of the middle portion 1202, excluding the thickness ofthe middle portion 1202 at the center 306 that corresponds to the bulge 316, for those embodiments that include a thickening at the center 306.

[0129] Although Fig. 14 illustrates an embodiment in which the average thickness of thecurved 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 includesother embodiments in which the thickness of the curved cross-sectional shape of themiddle portion 1202, including the central portion and including the regions containingthe spines, is constant along the longitudinal direction. According to furtherembodiments, the thickness of the curved cross-sectional shape of the middle portion1202, excluding the regions containing the spines and / or excluding the center 306 of themiddle portion 1202, is either constant along the longitudinal direction or monotonicallyincreasing along the longitudinal direction from either or both end portions 302, 304 towards the center 306 of the middle portion 1202.

[0130] Figs. 15, 16 and 17 illustrate, in respective lower panels, a cross-section of anextrusion die (also referred to as an extrusion plate) though which a polymer mixture isextruded as part of the process of forming an extruded artificial turf fiber, and inrespective upper panels, a photo of the artificial turf fiber (i.e., the product) extrudedthrough the die.

[0131] Fig. 15 illustrates a cross-section of an extrusion die 1502 and a photo of anartificial turf fiber 1504 formed in part by extruding a polymer mixture, as disclosedaccording to the embodiments in the present application, through the extrusion die1502. An outline 1506 of the extrusion die 1502 is superimposed on the artificial turffiber 1504 for purposes of comparing the shape of the final product 1504 with thedesired shape 1506. In the Fig. 15 embodiment, the average width wd of the extrusiondie 1502 is constant along the longitudinal length of the die, where the average width wdis defined as a transverse distance between corresponding pairs of points, where firstpoints of pairs of corresponding points are located on a first baseline 1518 that passesthrough the peaks of the protrusions of the undulations on an outer boundary line 1508(on an outer surface of the die) 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 die).Although the cross-sectional shape of the extrusion die 1502 has uninterruptedundulations, the cross-sectional shape of the extrusion die 1502 does not include anyspines.

[0132] A comparison of the photo of the artificial turf fiber 1504 with the desired shape1506 (i.e., the cross-sectional shape of the extrusion die) 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.

[0133] Fig. 16 illustrates a cross-section of an extrusion die 1602 and a photo of anartificial turf fiber 1604 formed in part by extruding a polymer mixture, as disclosedaccording to the embodiments in the present application, through the extrusion die1602. In the Fig. 16 embodiment, the average width wd of the extrusion die 1602monotonically increases along the longitudinal length of the die from the end portions1605 to a center 1606, where the average width wd at the center 1606 is a maximumwidth of the die and the average width wd adjacent the end portions 1605 is a minimumwidth of the die. As in the Fig. 15 embodiment, the cross-sectional shape of the extrusiondie 1602 has uninterrupted undulations, but does not include any spines.

[0134] A comparison of the photo of the artificial turf fiber 1604 with the desired shape(i.e., the shape of the extrusion die 1602) shows a reduction in curvature of the artificialturf fiber 1604. In addition, the thicknesses of the end portions 1608 of the fiber appearto show a thinning when compared to the thickness of the end portions 1605 of the die1602. However, when compared to Fig. 15, the end portions 1608 of the Fig. 16embodiment appear to be better defined with respect to the adjacent uninterruptedundulations.

[0135] Fig. 17 illustrates a cross-section of an extrusion die 1702 and a photo of anartificial turf fiber 1704 formed in part by extruding a polymer mixture, as disclosedaccording to the embodiments in the present application, through the extrusion die1702. Although extrusion die 1702 includes one fiber profile opening (i.e., first andsecond 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 dieembodiments (not shown) include two or more fiber profile openings. In the Fig. 17embodiment, the average width wd of the extrusion die 1702 monotonically increasesalong the longitudinal length of the die from the end portion openings 1703, 1705 to acenter 1706 of the curved middle portion opening 1707, where the average width wd1 inthe center 1706 is a maximum width of the die and the average width wd2 adjacent theend portion openings 1703, 1705 is a minimum width of the die. However, the rate ofincrease in the average width with respect to longitudinal distance is less than the rate ofincrease in average width as illustrated by the Fig. 16 embodiment. As in the Fig. 15 and16 embodiments, the cross-sectional shape of the extrusion die has uninterruptedundulations, however unlike Figs.15 and 16, the cross-sectional shape of the extrusiondie of the Fig. 17 embodiment includes the spine openings 1710 and 1712. The cross-sectional shape of the extrusion die 1702 also has an optional rounded bulge opening1714 at the center 1706.

[0136] A comparison of the photo of the artificial turf fiber 1704 with the desired shape(i.e., the shape of the extrusion die 1702) shows a better retention of curvature of theartificial 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 betterretention of the thickness in comparison to Figs.15 and 16.

[0137] In other embodiments (not shown), the average width wd of the extrusion die1702 is constant (or substantially constant) along the longitudinal length of the die fromthe end portion openings 1703, 1705 to the center 1706 , the cross-sectional shape ofthe extrusion die 1702 still includes spine openings, for example spine openings 1710 and1712, and the curved middle portion opening 1707 is not bulged at the center 1706 (i.e.,the cross-sectional shape of the extrusion die 1702 does not have the optional roundedbulge opening 1714 at the center 1706).

[0138] In one embodiment, a maximum width of the first spine opening wmax1 is largerthan 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) awidth (wo + wd1) of the optional central bulge opening 1714, if any, and where amaximum width of the second spine opening wmax2 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.

[0139] Fig. 17 further illustrates positioning of the spine openings 1710, 1712 of themiddle portion opening 1707, according to embodiments of the present invention. Insome embodiments, the first spine opening 1710 is positioned in the middle portionopening 1707 on a first arc length AL1 subtended by a first angle θ1 of less than or equalto 60°, or between 35°- 55°, or between 40°- 50°, or at 45°. As illustrated, the first arclength AL1 is measured along the curved middle portion opening 1707 from the first endportion opening 1703. Furthermore, the second spine opening 1712 is positioned in themiddle portion opening 1707 on a second arc length AL2 subtended by a second angle θ2of less than or equal to 60°, or between 35°- 55°, or between 40°- 50°, or at 45°. Thesecond arc length AL2 is measured along curved middle portion opening 1707 from thesecond end portion opening 1705. θ1 is subtended by a first straight line drawn betweena 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 thecenter point 1713. Θ2 is subtended by a third straight line drawn between a second distalend 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 point1713. For curved middle portion openings having a shape of an arc, such as an arc of asegment 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 Ω, the center point 1713 is definedas a midpoint on the straight line drawn between the first distal end point 1709 and thesecond distal end point 1711.

[0140] Preferably, the width of a fiber profile or fiber profile opening is measured bydetermining a first base line 1518, 1618, 1718 and a second baseline 1520, 1620, 1720 asillustrated e.g. in figures 15 to 17. The first and second baselines are lines that passthrough all of the protrusions of the undulations on both longitudinal sides of the profile,respectively. For example, the baselines may pass the undulations all at their peaks, or at the reference line from which the undulations (the wave-like pattern) oscillates. Preferably, the width is measured along a line connecting two points of the first and second baseline that is basically orthogonal to the first and second base line.

[0141] In embodiments where the fiber end portions and / or the fiber end portionopenings have the form of a circle or ellipse, the width of the fiber end portion and / orthe fiber end portion opening is determined at the center of the circle or the ellipse.

[0142] In embodiments where the fiber end portions and / or the fiber end portionopenings have the form of a circle, the width of the fiber end portion and / or the fiber end portion opening is the diameter of this circle.

[0143] In case the fiber end portions and / or the fiber end portion openings do not havethe form of a circle, the width of the fiber end portion and / or the fiber end portionopening is determined as the longest line connecting the first and the second boundarylines of the fiber, the connecting line being a) basically orthogonal to the first and thesecond boundary line, and b) lying within the fiber end portion / fiber end portionopening.

[0144] For a curved middle portion opening having a shape of one or more sinusoidalwaves, 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 ¼ wavelength from a firstdistal end point of a first end portion opening and a second center point is defined as a point on a second straight line ¼ wavelength from a second distal end point of a secondend portion opening. A first spine opening is positioned in the middle portion opening ona first arc length subtended by a first angle θ1 of less than or equal to 60°, or between35°- 55°, or between 40°- 50°, or at 45°. The first arc length is measured along a curvedmiddle portion opening from the first end portion opening. Furthermore, the secondspine opening is positioned in the middle portion opening on a second arc lengthsubtended by a second angle θ2 of less than or equal to 60°, or between 35°- 55°, orbetween 40°- 50°, or at 45°. The second arc length is measured along the curved middleportion opening from the second end portion opening. θ1 is subtended by the firststraight line and a third straight line drawn between a peak of the first spine and the firstcenter point. Θ2 is subtended by the second straight line and a fourth straight line drawnbetween a peak of the second spine and the second center point.

[0145] Advantageously, positioning of at least one spine opening, preferentially in themiddle portion opening 1707 on a first arc length AL1defined by a first angle θ1of lessthan or equal to 60°, or between 35°- 55°, or between 40°- 50°, or at 45°, provides a fiberthat has reinforced mechanical stability and / or strength (i.e., retains its shape andmaintains 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.

[0146] That is, positioning at least one spine according to the embodiments describedabove and / or sizing the width (also referred to as the amplitude) of the spine openingsrelative to the average width of the middle portion opening, where the average width ofthe 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 awater bath. The spines according to embodiments of the present invention enable a netpolymer mass flow (that occurs in the unquenched fiber as the fiber travels between theextrusion plate and the quenching unit), where the net polymer mass flow is in adirection 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) tothe first end portion of the fiber, and in a direction from a position of the second spineopening (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.

[0147] The net polymer mass flow in the extruded polymer fiber, which occurs betweenextrusion 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 endportions of the quenched fiber in comparison to the width of the end portion openings ofthe extrusion plate, thereby increasing dimensional stability and / or mitigating or preventing curling of the end of the quenched fiber.

[0148] In addition, extrusion of an artificial turf fiber through an extrusion plate having acombination 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) thickenedend portion openings (preferably having a thickness (i.e., width) that is greater than athickness (i.e., width) of the middle portion opening, excluding the thickness of thecenter 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 ispreferably thicker that the thicknesses of the end portion openings, synergistically resultsin a fiber that has even more reinforced mechanical stability and / or strength.

[0149] According to another embodiment, an artificial turf fiber includes a first spinecreated by extruding a polymer mass through a first spine opening of an extrusion plateand includes a second spine created by extruding the polymer mass through a secondspine opening of the extrusion plate. By way of an exemplary embodiment, the artificialturf fiber 1704 extruded through extrusion die 1702 has barely visible spines 1722, 1724,however other embodiments of extruded artificial turf fibers have more prominentspines. By way of further exemplary embodiments, artificial turf fibers 1800, 1900, 2000,2200, 2300 ad 2400 of Figs.18, 19, 20, 22, 23 and 24, respectively, extruded throughrespective extrusion dies (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 profileopenings of the extrusion dies corresponding to Figs.18-25 will be discussed further below.

[0150] In another embodiment, and referring back to Fig. 17 as one exemplaryillustration, the ratio of the area of the first spine opening 1710 to the area of the firstend portion opening 1703 is larger than the ratio of a cross-sectional area of the firstspine 1722 of the fiber 1704 to a cross-sectional area of the first end portion 1715 of thefiber, and the ratio of the area of the second spine opening 1712 to the area of thesecond end portion opening 1705 is larger than the ratio of a cross-sectional area of thesecond spine 1724 of the fiber 1704 to a cross-sectional area of the second end portion1717 of the fiber. The second end portion 1717 of the fiber is formed by extruding apolymer mass through the second end portion opening 1705 and the first end portion1715 of the fiber is formed by extruding the polymer mass through the first end portionopening 1703.

[0151] According to yet another embodiment, an amplitude (also referred to as width) ofthe first spine 1722 of the fiber 1704 is less than an amplitude wmax1 (also referred to aswidth) of the first spine opening 1710, and an amplitude of the second spine 1724 of thefiber 1704 is less than an amplitude wmax2 of the second spine opening 1712.

[0152] In one embodiment, the width wep1 of the first end portion opening 1703 islarger than the width wd2 of a first section 1726 of the middle portion opening 1707adjacent to the first end portion opening 1703, the width wep2 of the second endportion opening 1705 is larger than a width wd2 of a second section 1728 of the middleportion opening 1707 adjacent to the second end portion opening 1705, the width wf1 ofthe first end portion 1715 of the fiber 1704 is larger than a width wfa1 of a first section1730 of a middle portion 1732 of the fiber 1704 adjacent to the first end portion of thefiber, and the width wf2 of a second end portion 1717 of the fiber 1704 is larger than thewidth wfa2 of a second section 1734 of the middle portion of the fiber adjacent to thesecond end portion of the fiber.

[0153] According to other embodiments, the width of the first and second end portionopenings wep1, wep2 are respectively larger than a maximum width of the middleportion opening 1707, and the width of the first and second end portions wf1, wf2 arerespectively larger than a maximum width of a middle portion 1732 of the fiber.

[0154] In another embodiment, a center 1706 of the curved middle portion opening1707 includes a bulge opening 1714, and a maximum width of the middle portionopening 1707 including the bulge opening 1714 is greater than a maximum width of thefirst and second end portion openings 1703, 1705.

[0155] In one embodiment, the fiber 1704 includes either no spines or no spines visibleto the human eye at positions (i.e., corresponding to positions) of the first and secondspine openings 1710, 1712.

[0156] In another embodiment, the curved middle portion opening 1707 has twoopposing longitudinal contours 1206, 1208 (also referred to as boundary lines), where atleast one of the contours includes or includes exclusively of uninterrupted undulations.

[0157] Although the curved middle portion opening 1707 as illustrated by the Fig 17embodiment has the shape of an arc, in other embodiments, the curved middle portionopening 1707 has a shape of one or more sinusoidal waves. For those embodiments inwhich 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 ofthe 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 ofa 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 Ω.

[0158] Figs. 18, 19 and 20 illustrate cross-sections of extruded artificial turf fibersaccording to other embodiments. Fibers 1800, 1900, and 2000 are similar to fibers 1400and 1704, however the extruded artificial turf fiber 1800 includes a curved middleportion 1801 having a shape of an arc of a horseshoe, the extruded artificial turf fiber1900 includes a curved middle portion 1901 having a shape of an arc of an Ω , and theextruded artificial turf fiber 2000 includes a curved middle portion 2001 having a shapeof an arc of a U. The curved middle portion 1801 of fiber 1800 is connected with first andsecond 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 portion1808. The curved middle portion 1901 of fiber 1900 is connected with first and secondend 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.

[0159] Each of fibers 1800, 1900, and 2000 are manufactured by extrusion of a polymermass 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 Ω , and an arc of a U, respectively, including respective spine openings coinciding with thespines of fibers 1800, 1900 and 2000. Although the fibers 1800, 1900 and 2000 havevisible spines, in other embodiments of the present invention, the spines are either notvisible via a visual inspection or are not present, although the effects produced by thespine 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 fiberend portions relative to the thickness of the end portion openings of the extrusion plates)

[0160] In some embodiments , an average thickness of the curved cross-sectional shapesof each middle portion of the fibers 1800, 1900 and 2000, excluding the regionscontaining 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).

[0161] Figs. 21 and 22 show photographs of extruded artificial turf fibers according toother 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 approximatesinusoids, where the fibers include middle portions having undulations and thickenedend portions. In some embodiments, the middle portions of the fibers 2100 and 2200include 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 theapproximately circular arc of a middle portion of the extrusion die 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.

[0162] An average width of the curved cross-sectional shape of the middle portions2102, 2104 of fiber 2100 increases at a greater rate (along the longitudinal distance ofthe 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-sectionof corresponding middle portions of fiber 2200, and the fiber 2100 is extruded from anextrusion die that does not include spine openings. The fiber 2200, however, is extrudedfrom an extrusion die that include spine openings, which are slightly visible as spines2202 and 2204. As illustrated, fiber 2200 has less thinning of the thicknesses of the endportions 2206, 2208.

[0163] Figs. 23, 24 and 25 show photographs of extruded artificial turf fibers according toyet other exemplary embodiments. As illustrated, fibers 2300, 2400 and 2500 haveshapes (i.e., cross-sectional shapes when viewed in a longitudinal plane of the fiber) thatapproximate an arc of the letter “U,” an arc of a horseshoe, and an arc of a segment of acircle, respectively.

[0164] The average widths of the curved cross-section shapes of the middle portions ofeach of fibers 2300, 2400 and 2500 increase along the longitudinal distance of the fiberfrom 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 portionswithout any reduction (or only slight reduction) in thickness (as compared to the thickness of the end portions of the respective extrusion dies (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 dies (not shown).

[0165] 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 isformed from a polymer mixture, where the polymer mixture is at least a two-phasepolymer mixture, where a first phase of the polymer mixture includes a first polymer anda 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, wherethe first and the second phases are immiscible, and where the extruded artificial turf fiber has a marbled appearance.

[0166] In one embodiment, upon creation of the liquid polymer mixture, the twodifferent 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 notnecessary 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 thefirst and second color is created. The polymer mixture is extruded into a monofilamentincluding a marbled pattern of the first and second color. The monofilament is thenheated, 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.

[0167] In another embodiment, the polymer mixture further includes a compatibilizer.According to some embodiments, the compatibilizer (which may be considered a thirdphase of the polymer mixture) is added to the polymer mixture and interfaces the firstand 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 apolarpolymer. The first phase forms polymer beads surrounded by the third phase within thesecond phase.

[0168] 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 polarpolyamide, with the above-described dyes, has the advantage that an artificial turf fiberis 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 andincreased elasticity compared to pure PA based monofilaments.

[0169] Furthermore, an artificial turf fiber having a marbled color pattern in combinationwith 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).

[0170] In yet another embodiment, a method of a method of manufacturing an artificialturf fiber includes extruding a polymer mixture through at least one fiber profile openingof an extrusion plate (e.g., 1702) allowing the extruded polymer mixture to travel along adistance 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 toform the artificial turf fiber. The fiber profile opening includes first and second endportion openings 1703, 1705, and a curved middle portion opening 1707 connected withthe first and second end portion openings. The curved middle portion opening has atleast a first spine opening 1710 proximate to the first end portion opening and a secondspine opening 1712 proximate to the second spine opening. The first and second spineopenings are sized and positioned such that the extruded polymer mixture, whentraveling along the distance between the at least one fiber profile opening of theextrusion plate to the quenching unit, incurs a net polymer mass flow from a position onthe middle portion of the fiber corresponding to the first spine opening to a first endportion of the fiber and from a position on the middle position of the fiber correspondingto the second spine opening to a second end portion of the fiber. Quenching of the fiberhalts any further movement (i.e. flow) of the polymer mass in the fiber.

[0171] Advantageously, the net polymer mass flow mitigates or prevents a reduction inwidth of the first and second end portions of the quenched fiber in comparison to the 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.

[0172] In one embodiment, the quenched fiber includes a first spine created byextruding the polymer mass through the first spine opening and a second spine createdby extruding the polymer mass through the second spine opening. In otherembodiments, 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.

[0173] In other embodiments, the ratio of the area of the first spine opening to the areaof the first end portion opening is larger than the ratio of the cross-sectional area of thefirst spine of the quenched fiber to the cross-sectional area of the first end portion of thequenched fiber, where the first end portion of the fiber is created by extruding thepolymer mass through the first end portion opening, and / or the ratio of the area of thesecond spine opening to the area of the second end portion opening is larger than theratio of the cross-sectional area of the second spine of the quenched fiber to the cross-sectional area of the second end portion of the quenched fiber, where the second endportion of the fiber is created by extruding the polymer mass through the second endportion opening.

[0174] In another embodiment, an amplitude (also referred to as width) of the first spineof the quenched fiber is less than the amplitude (also referred to as width) of the firstspine opening, and / or an amplitude of the second spine of the quenched fiber is lessthan the amplitude of the second spine opening.

[0175] Yet in another embodiment, the width of the first end portion opening is largerthan the width of a first section of the middle portion opening adjacent to the first endportion opening, and the width of the second end portion opening is larger than thewidth of a second section of the middle portion opening adjacent to the second endportion opening, and / or the width of the first end portion of the quenched fiber is largerthan the width of a first section of a middle portion of the quenched fiber adjacent to thefirst end portion of the quenched fiber and the width of the second end portion of thequenched fiber is larger than the width of a second section of the middle portion of thequenched fiber adjacent to the second end portion of the quenched fiber.

[0176] In one embodiment, widths of first and second end portion openings arerespectively larger than a maximum width of the middle portion opening, and widths offirst and second end portions are respectively larger than a maximum width of a middle portion of the quenched fiber.

[0177] In another embodiment, a center of the curved middle portion opening includes abulge 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.

[0178] In some embodiments, the curved middle portion opening has two opposinglongitudinal contours, where at least one of the contours includes (or includes entirely of) uninterrupted undulations.

[0179] In one embodiment, the curved middle portion opening has a shape of one ormore sinusoidal waves. In other embodiments, the curved middle portion opening has ashape 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 portionopenings. In some embodiments, a shape of the middle portion opening comprises oneof: 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 Ω.

[0180] In other embodiments, the polymer mixture includes a polyethylene or apolyethylene-polyamide blend, where the quenching unit is a water bath, where thedistance 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.

[0181] In some embodiments, the polymer mixture includes a polyamide as a mainpolymer component or includes exclusively of the polyamide, where the quenching unit is a water bath, where the distance between the extrusion plate openings and thequenching unit is 2.0 – 4.0 cm, and wherein a temperature of the water bath is 18°C -20°C.

[0182] 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 asecond 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 thesecond 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 marbledappearance. In some embodiments, the first phase forms polymer beads within thesecond phase, and the polymer mixture further includes a nucleating agent and / or acompatibilizer.

[0183] 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.

[0184] Figure 26 shows three plots 2602, 2604, 2606 illustrating the mass flow u of thepolymer 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 ofthe extrusion plate defining extrusion openings. The y coordinate of each plot indicatesthe dotted line (“neutral line”) within the fiber profile opening depicted in the middleportion of each plot. The lower portion of each plot illustrates the polymer mass flow uat 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 indicatedin the middle of each plot and a photo of the real, extruded and processed fibers isshown at the top of each plot.

[0185] Plot 2602 illustrates the polymer mass flow in a fiber profile opening having amiddle portion opening between the first and second end portion opening withapproximately constant width. The polymer mass flow profile 2608 depends on thedistance from the walls of the extrusion plate. As can be seen from the lower part of plot2602, 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 isquite flat and hence the fiber may be flattened easily when it is transported, processedand used. Furthermore, the fiber ends are thinned as a result of an undesired mass flowfrom the fiber ends towards the center of the fiber.

[0186] The plot 2604 shows the mass flow profile observed in a different fiber profileopening. This fiber profile opening was designed with an attempt to improve themechanical stability of the fiber by increasing the width of the middle portion of thefiber. As a consequence, the polymer mass flow was observed to significantly change andto 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 haveincreased. The thinning of the fiber ends is undesirable, as this results in a reducedrobustness of the ends of the artificial turf fiber against curling.

[0187] The plot 2606 shows a polymer mass flow profile obtained for a still different fiberprofile opening according to an embodiment of the invention. This embodiment was ableto 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 isbasically constant over most of the neutral line (dotted midline between the first andsecond boundary lines, represented by coordinate y), even though the central part of themiddle 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 lackingspine openings and having smaller end portion openings. The introduction of the spineopenings induces a net polymer flow from the position of the spine openings to the endportions 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 desirableeffect has been observed to be enhanced by increasing the width of the fiber end portionopenings.

[0188] Hence, introducing the spines, and the optional increasing of the width (andhence, also the area) of the end portion openings, result in a flow path expansion, and ina net polymer flow from the spines to the end portions. Thereby the robustness of thefiber against being flattened and against the curling of fiber ends is increased.

[0189] According to some embodiments, the width of the first and second fiber endportions 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 widthbetween a first baseline of the undulations of the first boundary line and a secondbaseline 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.

[0190] According to some embodiments, the width of the first end portion opening islarger than the width of the first end portion of the extruded fiber, and the width of thesecond end portion opening is larger than the width of the second end portion of the extruded fiber.

[0191] According to some embodiments, the area of the first end portion opening islarger than the area of the first end portion of the extruded fiber, and the area of thesecond end portion opening is larger than the area of the second end portion of theextruded fiber. The ‘area’ in this context may mean ‘cross-sectional area’.

[0192] The width is measured along a dimension that is basically orthogonal to thecurvature of the fiber profile. For example, the width of the three fiber profile openingsdepicted in the middle portion of the three plots 2602, 2604 and 2608 is indicated in theform of arrows which are oriented basically orthogonally to the dotted neutral line andbasically orthogonally to a first and a second boundary line. The first and secondboundary lines of a fiber profile may represent, for example, the lines connecting themaxima peaks (outward directed peaks) of the undulations in one fiber side in the middleportion 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 connectingthe base line of the peaks (average of the peaks) of the undulations in one fiber side in the middle portion of the fiber.

[0193] While the invention has been illustrated and described in detail in the drawingsand 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.

[0194] Embodiments of the invention may be described by the following clauses:1. A method of manufacturing an artificial turf fiber, comprising:o extruding a polymer mixture through at least one fiber profile opening ofan extrusion plate (1702) to form an artificial turf fiber (1704), the fiber profile opening including: ^first and second end portion openings (1703, 1705), and^ a curved middle portion opening (1707) connected with the firstand second end portion openings, the curved middle portionhaving 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; oallowing the extruded polymer mixture to travel along a distance betweenthe 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 oquenching the extruded polymer mixture in the quenching unit to formthe artificial turf fiber.The method of clause 1,o wherein the first spine opening is positioned in the middle portionopening 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 thefirst arc length is measured along the curved middle portion opening from the first end portion opening, owherein the second spine opening is positioned in the middle portionopening 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°, whereinthe second arc length is measured along curved middle portion opening from the second end portion opening.The method of clauses 1 or 2, wherein the net polymer mass flow mitigates orprevents 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.The method of any one of the preceding clauses,o wherein the fiber comprises a first spine (1722) created by extruding thepolymer mass through the first spine opening and comprises a second spine (1724) created by extruding the polymer mass through the second spine opening.5. The method of clause 4,o wherein the ratio of the cross-sectional area of the first spine opening tothe cross-sectional area of the first end portion opening is larger than theratio of the cross-sectional area of the first spine of the fiber to the 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 owherein the ratio of the cross-sectional area of the second spine openingto the cross-sectional area of the second end portion opening is largerthan the ratio of the cross-sectional area of the second spine of the fiberto the cross-sectional area of the second end portion of the quenchedfiber, the second end portion of the fiber being created by extruding the polymer mass through the second end portion opening.6. The method of clauses 4 or 5, wherein an amplitude of the first spine of the fiber isless 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 any one of the preceding clauses,o wherein the width of the first end portion opening is larger than the widthof a first section of the middle portion opening (1726) adjacent to the first end portion opening, and wherein the width of the second end portionopening is larger than the width of a second section of the middle portionopening (1728) adjacent to the second end portion opening; and owherein the width of the first end portion of the fiber is larger than thewidth of a first section of a middle portion (1730) of the fiber adjacent tothe first end portion of the fiber, and wherein the width of the second endportion of the fiber is larger than the width of a second section of themiddle portion (1734) of the quenched fiber adjacent to the second end portion of the quenched fiber.8. The method of any one of the preceding clauses, wherein the width of the first andsecond 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.9. The method of any one of the preceding clauses, wherein a center of the curvedmiddle 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.10. The method of any one of clauses 1-3, wherein the quenched fiber comprises nospines at positions of the first and second spine openings.11. The method of any one of the preceding clauses, wherein the curved middleportion opening has two opposing longitudinal contours (1206, 1208), wherein atleast one of the contours comprises or consists of uninterrupted undulations.12. The method of any one of the preceding clauses, wherein the curved middleportion opening has a shape of one or more sinusoidal waves.13. The method of any one of clauses 1-11, wherein the curved middle portion openinghas a shape of an arc.14. The method of clause 13, wherein a radius of curvature of the middle portionopening decreases from a center (1706) of the middle portion opening towards the end portion openings.The method of clause 13, wherein a shape of the middle portion opening comprisesone 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 Ω.The method of any one of the preceding clauses, wherein the polymer mixturecomprises a polyethylene or a polyethylene-polyamide blend, wherein the quenching unit is a water bath, wherein the distance between the extrusion plateopenings and the quenching unit is 3.0 – 5.0 cm, and wherein a temperature of thewater bath is 28°C - 34°C.The method of any one of clauses 1-15, wherein the polymer mixture comprisespolyamide as a main polymer component or consists of polyamide, wherein the quenching unit is a water bath, wherein the distance between the extrusion plateopenings and the quenching unit is 2.0 – 4.0 cm, and wherein a temperature of thewater bath is 18°C - 20°C.The method of any one of the preceding clauses, wherein the polymer mixture is atleast 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.The method of clause 18, wherein the first phase forms polymer beads within thesecond phase, and wherein the polymer mixture further comprises a nucleating agent and / or a compatibilizer.The method of clauses 18 or 19, wherein the first polymer is any one of thefollowing: polyamide, polyethylene terephthalate, and polybutylene terephthalate,and wherein the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof.An extrusion plate (1702) for artificial turf fibers, the extrusion plate comprising:o at least one fiber profile opening, the fiber profile opening including:^ first and second end portion openings (1703, 1705), and^ a curved middle portion opening (1707) connected with the firstand 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.The extrusion plate of clause 21,o 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 the width of an optional central bulge opening, if any, ando wherein a maximum width of the second spine opening is larger than110%, 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.Use of the extrusion plate of clause 21 or 22 for mitigating or preventing areduction in width of end portions (1715, 1717) of a fiber (1704), thereby increasing dimensional stability and / or for mitigating or preventing curling of anend of the fiber after the fiber is formed upon extruding a polymer mixture throughthe openings of the extrusion plate.A system comprising:o the extrusion plate of clause 21;o at least one fiber formed by extruding a polymer mass through the at leastone fiber profile opening, in particular one of the fibers of clauses 25-29; and optionally a quenching unit.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.The artificial turf fiber of clause 25,o wherein the width of the first spine is less than 125%, in particular lessthan 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 the width of an optional central bulge, if any, ando wherein the width of the second spine is less than 125%, in particular lessthan 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.The artificial turf fiber of clauses 25 or 26,o wherein a center of the middle portion of the fiber comprises a thickeningthat forms a bulge to at least one side of the fiber.The artificial turf fiber of any one of clauses 25-27, wherein the width of the curvedmiddle portion as measured between first and second boundary lines of the curved middle portion, excluding a center of the middle portion, is: oconstant along the longitudinal direction of the curved middle portion, oro monotonically increasing along the longitudinal direction of the curvedmiddle portion from either or both end portions towards the center of the middle portion.29. The artificial turf fiber of any one of clauses 25-28, wherein the cross-sectionalprofile of the fiber comprises a first and a second boundary line, the first and second boundary lines comprising or consisting of uninterrupted undulations.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.31. An artificial turf comprising:o a carrier; ando a plurality of artificial turf fibers of any one of clauses 25-30 integratedinto the carrier and protruding therefrom to form the artificial turf.32. The artificial turf of clause 31, the artificial turf being configured for use as a hockeyfield artificial turf.REFERENCE SIGNS LIST100 artificial turf fiber102 cross section area104 inner surface202 outer surface302 first fiber end304 second fiber end306 center of the fiber308 undulation of outer surface in the form of an indentation310 undulation of inner surface in the form of an indentation312 undulation of outer surface in the form of an protrusion314 undulation of the inner surface in the form of a protrusion316 protrusion caused by a central thickening318 thickenings at the fiber ends502 circle defining the curvature of an undulation of the first fiber end504 circle defining the curvature of an undulation of the second fiber end506 circle defining the curvature of an undulation at the thickened fiber center508 circles defining the curvature of undulations at the outer surface510 circles defining the curvature of undulations at the inner surface602 fiber width at the fiber ends604 fiber width at one position of the fiber arms606 fiber width at another position of the fiber arms608 fiber width at the fiber center800 artificial turf fiber900 artificial turf fiber1000 artificial turf fiber1100 artificial turf fiber1200 artificial turf fiber 1202 middle portion 1206 first boundary line1208 second boundary line 1210 longitudinal direction 1212 first wavelength1214 second wavelength1216 phase offset 1218 first wavelength in another embodiment 1220 second wavelength in another embodiment1222 boundary line of first end portion 3021224 boundary line of second end portion 304 1226 boundary line of first end portion 302 in another embodiment1228 boundary line of second end portion 304 in another embodiment1300 artificial turf fiber1400 artificial turf fiber 1402 first spine 1404 second spine1500 artificial turf fiber1502 extrusion dye1504 photo of artificial turf fiber1506 outline (i.e., shape) of extrusion dye 1502 1508 outer boundary line 1510 inner boundary line 1512 end portion 1518 first baseline 1520 second baseline 1600 artificial turf fiber 1602 extrusion dye 1604 photo of artificial turf fiber 1605 end potions 1606 center 1608 end portions of photo 1604 1618 first baseline 1620 second baseline1700 artificial turf fiber1702 extrusion dye1703 first end portion opening1704 photo of artificial turf fiber1705 second end portion opening1706 center 1707 middle portion opening1709 first distal end1710 first spine opening1711 second distal end1712 second spine opening1713 center point1714 bulge1715 first end portion1716 end portions of photo 17041717 second end portion1718 first baseline 1720 second baseline1722 first spine1724 second spine1726 first section of middle portion opening1728 second section of middle portion opening1730 first section of middle portion1732 middle portion1734 second section of middle portion1800 artificial turf fiber1801 middle portion1802 first spine 1804 second spine1806 first end portion1808 second end portion 1900 artificial turf fiber1901 middle portion1902 first spine 1904 second spine1906 first end portion1908 second end portion 2000 artificial turf fiber2001 middle portion2002 first spine2004 second spine2006 first end portion2008 second end portion 2100 artificial turf fiber2102 first middle portion2104 second middle portion2106 first end portion 2108 second end portion2110 center of first middle portion2112 center of second middle portion2200 artificial turf fiber2202 first spine2204 second spine2206 first end portion 2208 second end portion 2300 artificial turf fiber2302 first spine2304 second spine2400 artificial turf fiber2402 first spine2404 second spine2500 artificial turf fiber2502 first spine2504 second spine2602 plot2604 plot2606 plot2608 polymer mass flow profile2610 polymer mass flow profile 2612 polymer mass flow profile

Claims

CLAIMS 1. A method of manufacturing an artificial turf fiber, comprising:o extruding a polymer mixture through at least one fiber profile opening ofan extrusion plate (1702) to form an artificial turf fiber (1704), the fiberprofile opening including: ^first and second end portion openings (1703, 1705), and^ a curved middle portion opening (1707) connected with the firstand second end portion openings, the curved middle portion having at least a first spine opening (1710) and a second spine opening (1712), the first spine opening being more proximate tothe first end portion opening than to the second end portion opening, and the second spine opening (1712) being moreproximate to the second end portion opening than to the first endportion opening; oallowing the extruded polymer mixture to travel along a distance betweenthe 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 oquenching the extruded polymer mixture in the quenching unit to formthe artificial turf fiber.

2. The method of claim 1,o wherein the first spine opening is positioned in the middle portionopening on a first arc length Al1 defined by a first angle θ1of less than or equal to 60°, or between 35°- 55°, or between 40°- 50°, or at 45°, whereinthe first arc length is measured along the curved middle portion opening from the first end portion opening,o wherein the second spine opening is positioned in the middle portionopening on a second arc length Al2 defined by a second angle θ2of 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, owherein in particular the first and second angles and arc lengths aredetermined as illustrated below: o.

3. The method of claims 1 or 2, wherein the net polymer mass flow mitigates orprevents a reduction in width (wf1, wf2) of the first and second end portions of the quenched fiber in comparison to the width (wep1, wep2) of the end portionopenings 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 any one of the preceding claims,o wherein the fiber comprises a first spine (1722) created by extruding thepolymer mass through the first spine opening and comprises a second spine (1724) created by extruding the polymer mass through the second spine opening.

5. The method of claim 4,o wherein the ratio of the area of the first spine opening to the area of thefirst end portion opening is larger than the ratio of the cross-sectional areaof the first spine of the fiber to the cross-sectional area of the first endportion 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 owherein the ratio of the area of the second spine opening to the area ofthe second end portion opening is larger than the ratio of the cross-sectional area of the second spine of the fiber to the cross-sectional areaof 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 claims 4 or 5, wherein the amplitude of the first spine of the fiber isless than the amplitude of the first spine opening, and wherein the amplitude ofthe second spine of the quenched fiber is less than the amplitude of the secondspine opening.

7. The method of any one of claims 1-4, wherein the width (wep1) of the first endportion opening is larger than the width (wf1) of the first end portion of the extruded fiber, and wherein the width (wep2) of the second end portion opening islarger than the width (wf2) of the second end portion of the extruded fiber.

8. The method of any one of claims 1-3, wherein the quenched fiber comprises nospines at positions of the first and second spine openings.

9. The method of any one of the preceding claims, wherein the curved middle portionopening has two opposing longitudinal contours (1206, 1208), wherein at least oneof the contours comprises or consists of uninterrupted undulations.

10. The method of any one of the preceding claims, wherein the curved middle portionopening has a shape of one or more sinusoidal waves.

11. The method of any one of claims 1-10, wherein the curved middle portion openinghas a shape of an arc, wherein in particular the shape of the middle portionopening 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 Ω.

12. The method of claim 11, wherein a radius of curvature of the middle portionopening decreases from a center (1706) of the middle portion opening towards the end portion openings.

13. The method of any one of the preceding claims,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, andwherein a temperature of the water bath is 28°C - 34°C; or. wherein the polymer mixture comprises polyamide as a main polymer componentor 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 – 4.0cm, and wherein a temperature of the water bath is 18°C - 20°C.

14. The method of any one of the preceding claims, wherein the polymer mixture is atleast 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 (1702) for artificial turf fibers, the extrusion plate comprising:o at least one fiber profile opening, the fiber profile opening including:^ first and second end portion openings (1703, 1705), and^ a curved middle portion opening (1707) connected with the firstand second end portion openings, having at least a first spineopening (1710) proximate to the first end portion opening and a second spine opening (1712) proximate to the second end portion opening.

16. The extrusion plate of claim 15 , wherein the fiber profile opening has a curvature Kthat is at least 0.66 / cm, in particular at least 0.89 / cm.

17. The extrusion plate of claim 15 or 16, wherein, the width of the first and secondend portion openings are respectively larger than a maximum width of the middle portion opening.

18. Use of the extrusion plate of any one of claims 15-17 for mitigating or preventing areduction in width of end portions (1715, 1717) of a fiber (1704), therebyincreasing 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.

19. A system comprising:o the extrusion plate of any one of claims 15-18;o at least one fiber formed by extruding a polymer mass through the at leastone fiber profile opening, in particular one of the fibers of claims 20-21; and optionally a quenching unit.

20. 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.

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

22. An artificial turf comprising:o a carrier; ando a plurality of artificial turf fibers of any one of claims 20 or 21 integratedinto the carrier and protruding therefrom to form the artificial turf.

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