Artificial turf fiber with undulated boundary lines

Abstract

The invention relates to an extruded artificial turf fiber (100; 800-1200; 2100-2500) having a cross-sectional shape. The cross-sectional shape of the fiber comprises: - first and second end portions (1605, 1608); and - a middle portion (1202, 2001, 1901) having a curved cross-sectional shape, o wherein the curved cross-sectional shape of the middle portion is defined by a first boundary line (1206, 1222) and a second boundary line (1208, 1226) opposite the first boundary line, o wherein the first boundary line consists of first uninterrupted undulations and the second boundary consists of second uninterrupted undulations, and o wherein either:  the width of the curved cross-sectional shape as measured between the first and second boundary lines is constant along the length of the curved cross-sectional shape, or  the first uninterrupted undulations have a phase offset from the second uninterrupted undulations and / or the first and second uninterrupted undulations have different, equal or modulated spatial frequencies

Description

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -ARTIFICIAL TURF FIBER WITH UNDULATED BOUNDARY LINES -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -FIELD OF THE INVENTION

[0001] The invention relates to the field of artificial turf, and more particular to artificialturf fibers. 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 associated with 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 section witha series of flat, planar sections which may lead to decreased mechanical stiffness andother 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 artificial turf fiber and artificial turfcomprising the same. The objectives underlying the invention are solved by the featuresof the independent claims.SUMMARY

[0010] In one aspect, an extruded artificial turf fiber has a cross-sectional shape thatincludes first and second end portions, and a middle portion having a curved cross-sectional shape. The curved cross-sectional shape of the middle portion is defined by afirst boundary line and a second boundary line opposite the first boundary line, where the first boundary line consists of first uninterrupted undulations and the secondboundary consists of second uninterrupted undulations, and where either the width ofthe curved cross-sectional shape of the middle portion as measured between the firstand second boundary lines is constant along the length of the curved cross-sectionalshape of the middle portion, or the first uninterrupted undulations have a phase offsetfrom the second uninterrupted undulations and / or the first and second uninterrupted undulations have different, equal or modulated spatial frequencies.

[0011] A modulated frequency of an undulation as used herein is a frequency that hasbeen altered in accordance with a modulating function or scheme. The modulation maybe described as a variation of the amplitude, frequency, and / or phase in accordance witha function or schema. The modulation may, for example, result in an increase ordecrease of the undulation frequency and / or amplitude of the undulations of the first and / or second boundary line from one fiber profile end to the other.

[0012] 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.

[0013] 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.

[0014] As explained above, some prior art artificial turf fibers have a boundary linecomprising a series of elevations 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 successiveconcave depressions or multiple successive convex elevations. Such an outline hasseveral 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.

[0015] 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, the boundary lines have a continuous slope as measured at each point along the boundarylines. In other words, the boundary lines have no discontinuities in slope.

[0016] 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, also the extrusion die profile is free of such pointed protrusions or elevations. As a consequence, the formation of speed differences of theextruded polymer mass during extrusion which may result in deformed fibers may be prevented.

[0017] The width of the curved cross-sectional shape as measured between the first andsecond boundary lines being constant along the length of the curved cross-sectionalshape of the middle portion, advantageously result in an increase in mechanical stabilityof the fiber (e.g., increase the fiber’s elasticity, or in other words, its ability to stand up again and resume its original curved cross-sectional shape after the fiber is repeatedly trampled down).

[0018] The first uninterrupted undulations having a phase offset from the seconduninterrupted undulations and / or the first and second uninterrupted undulations havingequal spatial frequencies imply that the width of the fiber is not constant. For example,the fiber may be thicker at the center of the fiber than at the distal portions of the fiber close to the ends. This may provide the fiber a more natural appearance, as many natural grass species also have a thickened, comparatively stiff central portion and more flexible,thinner arms. A fiber with a curved profile, i.e., a fiber with a concave side and a convexside, will have a concave-side outline that is shorter than the outline of the convex side. Ifboth sides have equal spatial frequencies, the fiber width cannot be constant, as thecurvature will introduce an offset between the undulations on both sides.

[0019] According to other examples, the first and second uninterrupted undulationsdifferent, e.g. modulated spatial frequencies. This may more faithfully represent the natural appearance of grass fibers.

[0020] The width of the fiber may hence not be constant in some embodiments of theinvention.

[0021] According to some examples, the first and second ends of the fiber have a radiusof curvature being at least as large as (or larger as) the smallest radius defining theundulations of the boundary line of the other parts of the cross-sectional shape of themiddle portion.

[0022] For example, the ends may have a radius of curvature being at least 5% larger,e.g., at least 10% larger, e.g., at least 15% larger, e.g., 25% larger than the smallest radiusdefining the undulations of the boundary line of the other parts of the cross-sectionalshape of the middle portion.

[0023] This may be beneficial as the ends will have a curvature based on a radius which isat least as large, and possible larger, than the smallest radius defining one or more of the undulations of the boundary line of other fiber parts, e.g., the center.

[0024] This may be beneficial as it protects the fiber against abrasion and also eases themanufacturing process: filigree fiber ends may result in a strongly reduced flow rate of the polymer matrix at the respective portions of the extrusion nozzle opening, which may result in a significant deviation of the shape of the extruded fiber from the shape of the extrusion nozzle opening. A further advantage of the above-mentioned fiber endcurvature is that incident light is diffusely scattered even when it falls on the ends of thefibers. This is because a large radius of curvature at the fiber ends ensures that the incident light hits a relatively wide surface at the ends, so that the light scattering behavior of the fiber surface at its ends is similar to the scattering behavior at its wide inside and outside surfaces. With artificial turf, due to the industrial manufacturingprocess, there is always a risk that the synthetic lawn optics will depend on the viewingangle, as the fibers can have an unnatural-looking uniform orientation or distribution, for example. Because the ends have a comparatively large curvature radius, the light is scattered similarly at the ends as in the wide side and it is less noticeable if the majority of the fibers should have the same orientation.

[0025] According to some examples, the fiber has thickenings at the fiber ends. Thewidths (or in the case of circularly-shaped fiber ends, the “diameter”) of each of thethickenings is thicker than the thickest part of the middle portion of the fiber. Forexample, the middle portion of the fiber may have a width (i.e., a thickness) that isconstant along a longitudinal direction of the fiber, or a width that is variable (i.e., non- constant) along the longitudinal direction..

[0026] For example, the diameter of each of the thickenings of the end portions may beat least 5%, e.g., at least 10%, e.g., at least 15%, e.g., 25% thicker than the thickest part ofthe middle portion of the fiber. For example, the diameter of the thickening may be thewidth of the thickening measured along a line perpendicular to the curved longitudinalaxis of the fiber.

[0027] This feature may have similar beneficial effects like the use of the above-mentioned use of fiber end undulation having a radius of at least a certain size. It is possible, however, that the boundary line of the thickened ends comprises multiple undulations and hence cannot be described by the size of a single curvature radius.

[0028] Applicant has observed that thickenings at the fiber end portions may increasethe mechanical stability of the fiber and increase its ability to stand up again after thegrass was trampled down. As the thickenings are rounded, the damage caused byabrasion at the fiber end portions is reduced compared to fibers lacking a roundedthickening at the fiber arms.

[0029] According to some examples, the curved cross-sectional shape of the middleportion has an outer, convex boundary line and an inner, concave boundary line. At least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line are defined by first circles (508) having the same first diameter. At least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line are defined by second circles having the same second diameter.

[0030] For example, the first and second diameters can be identical or similar, wherein asimilar diameter lies in a range of plus or minus 10 % of the other diameter.

[0031] The largely uniform wave shape of the bounding line may have the advantagethat there are no particularly deep wave valleys where the fiber thickness is reduced tosuch an extent that weak points are created at which the fiber tears open undermechanical load. The risk of splicing is thereby further reduced. Likewise, there may notexist particularly high protrusions which may be particularly prone to wear and tear. Thismay further help to prevent the generation of microplastic waste.

[0032] According to some further examples, the fiber comprises a thickening at its centerwhich forms a rounded protrusion to at least one side of the fiber. The curvature of the protrusion is defined by a circle having a radius selected such that a ratio of the said radius to the radius of the first circles is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.

[0033] According to some further examples, the radius of curvature of the fiber ends isselected such that a ratio of the radius of curvature of the fiber ends to the radius of thefirst circle is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.

[0034] According to a further example, the cross-section of the fiber is shaped like thearc of a segment of a circle. This circle is referred herein as the “fiber profile circle” and the radius of this circle the “fiber profile circle radius”. According to some embodiments, the ratio of the width of the fiber profile and the fiber profile radius is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.

[0035] Applicant has observed that this ratio provides for a particularly “natural” look ofa synthetic yarn made of respective fibers. Without the intention to be bound by any theory, applicant believes that this effect may be the result of said ratio value rangeapproximately representing the “golden ratio”.

[0036] If one divides a stretch of an elongated object into two parts, of which the smallerpart relates to the larger part as the larger part relates to the whole, then one speaks of the so-called 'golden ratio’. In this case, the relationship of the larger part to the smaller part is: 1.618[…] and also the ratio of the whole to the larger part is 1.618[…]. In a circle, this "golden ratio" corresponds to an angle of 137.5 degrees. And this is exactly the most common arrangement of leaves and flowers around a plant stem in nature. For example,the golden ratio can be found in the arrangement of leaves and inflorescences of manyplants. In these plants, the angle of two successive leaves divides the full circle in the ratio of the golden section. For example, the petals of the rose are arranged according to the golden ratio.

[0037] According to some examples, the fiber comprises a nucleating agent.

[0038] 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.

[0039] 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.

[0040] 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 agentat the surface and within a fiber may increase the brittleness of the fiber, thereby increasing the tendency to break or splice.

[0041] According to some examples, the cross-section of the fiber and / or the cross-sectional shape of the middle portion is shaped like the arc of a segment of a circle, or anarc of segment of an ellipse, or an arc of a segment of a horseshoe, or an arc of a segmentof a U, or an arc of a segment of a Ω. Applicant has observed that a cross-section of thefiber being shaped like an arc of a segment of an ellipse, an arc of a segment of ahorseshoe, an arc of a segment of a U, or an arc of a segment of a Ω may have theadvantage 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 asobserved in a segment of a horseshoe, a segment of a U, or a segment of a Ω, provides anintrinsic 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 too uniform orientation of the fibers due to the manufacturing process does not have any artificial dependence of the optical impression on the viewing angle.

[0042] According to some other examples, the cross-section of the fiber is shaped like acatenary. The catenary is a particular type of arced curve which is particularly robustagainst mechanical stress.

[0043] Using an artificial turf fiber having a cross-section shaped like a catenary maystrengthen the ability of a downed fiber to straighten up quickly. With artificial turf, the problem exists that synthetic fibers that have been depressed by the ball or the players need several minutes or even hours to straighten up again. In some cases, the fibers do not straighten at all. This has the disadvantage that the footprints of the players arevisible on the turf for a longer period of time, because the bent-down, essentially horizontally oriented fibers reflect the light differently. The footprints in artificial turf are therefore visible for a certain time as highly reflective, bright, shiny areas. This not only looks unnatural and unattractive; it can even lead to spectators and players being dazzled in strong sunlight. By using a fiber profile having a cross-section shaped like a catenary, the fiber becomes particularly mechanically stable. The tendency of the fiber to buckle under low loads is reduced, and the ability of the fiber to quickly straighten up again after a temporary load-induced buckling increases. Thus, this special shape not only supports the mechanical robustness of the fibers, but also has the particular effect of giving the turf a more natural-looking overall appearance, as footprints are no longer as strong or visible for as long.

[0044] According to some examples, the fiber comprises a thickening at its center (i.e., ata center of the middle portion of the fiber).

[0045] This may help increasing the mechanical strength of the fiber and to increase theability of the fiber to quickly straighten up again after a temporary load-induced buckling.

[0046] For example, the thickening at its center can be formed such that a round bulge(or protrusion) is formed towards the outer surface of the fiber, wherein the thickening does not lead to a bulge (or protrusion) towards the inner surface of the fiber.

[0047] According to some examples, the fiber has a width (w) measured as a straight lineconnecting the first and second ends of 0.7 to 2.5 mm, in particular of 0.9 to 1.5 mm.

[0048] According to some examples, the undulations are formed such that the fiber hasat least 6, in particular at least 7, in particular 7-11, e.g., 9 round bulges on its outersurface, and / or such that the fiber has at least 6, in particular 6-10, e.g., 8 round bulgeson its inner surface.

[0049] According to some examples, the majority of undulations form consecutive pairsof a round bulge and a round indentation, wherein each pair has a length of 0.10 mm to 0.30 mm, e.g.0.10 to 0.20 mm.

[0050] According to some examples, at least 70% of the undulations of the inner surfaceand at least 70% of the outer surface have the same or a similar undulation length, wherein an undulation length is similar to a given length if it differs no more than plus orminus 10% from said given length.

[0051] The above-mentioned dimension and ranges have been observed to provide forartificial turf fibers capable to form a synthetic lawn that faithfully reproduces the look of natural grass.

[0052] According to some further examples, the first boundary line comprises at leastone spine that is continuous with neighboring first uninterrupted undulations, where the at least one spine is positioned on an outer half, or in another embodiment and outerthird, of the middle portion of the fiber, and wherein the amplitude of the spine is largerthan the amplitudes of the neighboring first uninterrupted undulations. Advantageously,an artificial turf fiber having at least one spine results in a fiber that has more mechanicalstability and / or strength. Furthermore, an artificial turf fiber having at least one spine incombination with one or more of: (1) an average cross-sectional width of a middle portion that increases (preferably monotonically) from the end portions to the center; (2)thickened end portions (preferably having a thickness that is greater than the maximumthickness of the middle portion (between the two end portions), excluding the thickness of the center of the middle portion when the center may include a rounded bulge; and (3) a thickened center (of the middle portion), where the thickness is preferably thicker that the thicknesses of the end portions, results in a synergistic effect that provides afiber that has even more reinforced mechanical stability and / or strength. Furthermore,extrusion profiles having a thickening at the position of the spine for producing the spine have been observed to have the benefit of preventing a thinning of the fiber ends.

[0053] In a further aspect, disclosed herein is an artificial turf comprising: a carrier; and aplurality of the artificial turf fibers described herein in various embodiments andexamples integrated into the carrier and protruding therefrom to form an artificial turf.

[0054] In a further aspect, disclosed herein is the use of artificial turf fibers describedherein in various embodiments and examples for providing artificial grass that looks like natural grass.

[0055] 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.

[0056] 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

[0057] In the following, examples are described in greater detail making reference to thedrawings in which:

[0058] Fig. 1 is a perspective 3D view of the inside of a section of the fiber;

[0059] Fig. 2 is a perspective 3D view of the outside of a section of the fiber;

[0060] Fig. 3 shows the cross-section of a fiber;

[0061] Fig. 4 shows the fiber cross-section of Fig.3 with height and width annotated

[0062] Fig. 5 shows the fiber cross-section of Fig. 3 with the circles defining thecurvature of the corrugations and the ends annotated;

[0063] Fig. 6 shows the fiber cross-section, where the fiber thicknesses at differentcross-sectional areas are annotated;

[0064] Figs. 7A and B show an example of a fiber cross-section annotated with concretedimensions;

[0065] Fig. 8 shows an example of a cross-section of a further fiber having moreundulations;

[0066] Fig. 9 shows an example of a cross-section of a further fiber having moreundulations and an extended curvature;

[0067] 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;

[0068] Fig. 11 shows an example of a cross-section of a further fiber, the cross sectionhaving the shape of a catenary;

[0069] Fig. 12 shows a cross-section of an extruded artificial turf fiber, according to anembodiment;

[0070] Fig. 13 shows the cross-section of an extruded artificial turf fiber according to yetanother embodiment;

[0071] Fig. 14 shows the cross-section of an extruded artificial turf fiber according toanother embodiment;

[0072] 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;

[0073] 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;

[0074] 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;

[0075] Fig. 18 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of a horseshoe, according to an embodiment;

[0076] Fig. 19 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of the Greek letter Ω , according to an embodiment;

[0077] Fig. 20 illustrates a curved cross-section of an extruded artificial turf fiber havingthe shape of the letter U , according to an embodiment;

[0078] Fig. 21 shows a photograph of an extruded artificial turf fiber having anapproximate sinusoidal shape, according to an embodiment;

[0079] Fig. 22 shows a photograph of an extruded artificial turf fiber having anapproximate sinusoidal shape, according to another embodiment;

[0080] Fig. 23 shows a photograph of an extruded artificial turf fiber having anapproximate shape of the letter “U,” according to an embodiment;

[0081] Fig. 24 shows a photograph of an extruded artificial turf fiber having anapproximate shape of a horseshoe, according to an embodiment; and

[0082] Fig. 25 shows a photograph of an extruded artificial turf fiber having anapproximate shape of a segment of a circle, according to an embodiment. DETAILED DESCRIPTION

[0083] In the following, similar elements may be denoted by the same referencenumerals. 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 ofthe fiber defined by the concave part of the boundary line of the shape of the fiberprofile. 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. Forexample, 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.

[0085] 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.

[0086] 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 first fiber arm and comprises a second end 304 connected to the center of the fiber via a second arm.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] Figure 4 shows the fiber cross-section of Fig. 3 with height h and width wannotated. For example, the width w can be measured as straight line indicating the distance of the most outer points of the two fiber ends. The height h of the fiber may be measured as the distance of the “lowest” points of the fiber ends to the “highest” point at the fiber center. As can be inferred from figure 4, the height h may be significantly smaller than the radius defining the curvature of the arced shape of the fiber profile, meaning that in case the arced shape is defined by a circle, the fiber profile may cover a segment that is significantly smaller than the 180° segment. In other words, the radius of this circle may be significantly longer than h.

[0091] 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.

[0092] In other embodiments (not shown), D3 and D4 may be similar, but not identical.

[0093] 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.

[0094] 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 hence stiffest portion of the fiber having a thickness w4608 being greater than w1, w2 and w3.

[0095] In the depicted example, w2 is the smallest with in the fiber arm and w3 is thelargest width of the fiber arm.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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 circle radius”.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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 extendedcurvature 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.

[0105] 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.

[0106] 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.

[0107] Figure 12 shows the cross-section 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 fiber 1200 includes a first end 302 (also defined as a first endportion 302), a second end 304 (also defined as a second end portion 304), a middleportion 1202, and a center 306 of the middle portion 1202.

[0108] As illustrated by Fig. 12, and as seen in Figs. 1-3, the middle portion 1202 has acurved cross-sectional shape. 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 consists of first uninterrupted undulations represented collectively by theindentations 308 and protrusions 312, and the second boundary line 1208 consists ofsecond uninterrupted undulations represented collectively by the indentations 310 andprotrusions 314. In addition, the curved cross-sectional shape of the fiber 1200 has alongitudinal direction 1210 (also referred to as a longitudinal dimension), along which alength of the cross-sectional shape lies. The curved cross-sectional shape of the fiber1200 also has a transverse direction that is defined by a direction that Is perpendicular to the longitudinal direction.

[0109] In one embodiment, a thickness w (also referred to as a width or transversewidth) of the curved cross-sectional shape of the middle portion 1202, as measuredbetween 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.

[0110] 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 toas 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.

[0111] 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.

[0112] 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.

[0113] 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%.

[0114] 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.

[0115] In another embodiment of Fig. 13, the thicknesses 318 of the first and second endportions 302, 304 of the fiber 1300 are greater than the maximum thickness of thevariable thickness w of the curved cross-sectional shape of the middle portion 1202. Forexample, if w5 is the maximum thickness of the variable thickness of the curved cross-sectional shape of the middle portion 1202, then the thicknesses 318 of the first andsecond end portions 302, 304 of the fiber 1300 are greater than w5.

[0116] 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).

[0117] According to embodiments, the entire boundary line of the fiber, which may alsobe referred to as “contour line”, is free of planar areas, pointed elevations and pointeddepressions. For example, the contour line of the cross-sectional shape of the artificialturf fiber may consist of uninterrupted undulations. For example, the first, second andthird undulations may form an uninterrupted series of undulations, whereby the first, second and / or third undulations may have the same or different amplitudes, and / or may have the same or different frequencies.

[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 artificial turf fibers include arcs defined by boundary lines that have a varying radius of curvature along the longitudinal direction of the cross-sectional shapes.

[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 the 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 illustrated inFigs.15, 16 and 17, and which hereinafter applies to all disclosed embodiments, is thetransverse distance between a first base line 1518 and a second baseline 1520, wherethe 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 baselines1618, 1620 of Fig. 16 and baselines 1718, 1720 of Fig. 17).As illustrated in Fig. 14, theaverage 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. In yet another embodiment, and as illustrated by Fig. 14, the first boundary line1206 of the middle portion 1202 has a first spine 1402 and a 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 ofthe 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 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 withneighboring first uninterrupted undulations. In another embodiment, the at least onespine (e.g., spines 1402 and 1404) are positioned on an outer half, or on an outer third,of the middle portion 1202.

[0125] 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.

[0126] 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.

[0127] 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, is constant along the longitudinal direction.

[0128] Figs. 15, 16 and 17 illustrate, in a lower panel, a cross-section of an extrusion diethough which a polymer mixture is extruded as part of the process of forming anextruded artificial turf fiber, and in an upper panel, a photo of the artificial turf fiber (i.e.,the product) extruded through the die.

[0129] 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 a longitudinal length of the die, where the average width wd isdefined 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 pointsare 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.

[0130] 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.

[0131] 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 disclosed according 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 a longitudinal length of the die from the end portions1605 to a center 1606, where the average width wd at the center 1606 is the 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.

[0132] 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.

[0133] 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. In the Fig. 17 embodiment, the average width wd of the extrusion die 1702monotonically increases along a longitudinal length of the die from the end portions1708 to a center 1706, where the average width wd1 in the center 1706 is the maximumwidth of the die and the average width wd2 adjacent the end portions 1708 is aminimum width of the die. However, the rate of increase in the average width withrespect to longitudinal distance is less than the rate of increase in average width asillustrated by the Fig. 16 embodiment. As in the Fig. 15 and 16 embodiments, the cross-sectional shape of the extrusion die has uninterrupted undulations, however unlike Figs.15 and 16, the cross-sectional shape of the extrusion die of the Fig. 17 embodimentincludes spines, for example spines 1710 and 1712. The cross-sectional shape of theextrusion die 1702 also has a rounded bulge 1714 (or rounded thickening) at the center1706.

[0134] 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 portions1716 of the fiber appear to show a better retention of the thickness in comparison toFigs.15 and 16.

[0135] In another embodiment, the average width wd of the extrusion die 1702 isconstant (or substantially constant) along a longitudinal length of the die from the endportions 1708 to the center 1706 , the cross-sectional shape of the extrusion die 1702includes spines, for example spines 1710 and 1712, and the cross-sectional shape of theextrusion die 1702 does not have the rounded bulge 1714 (or rounded thickening) at thecenter 1706.

[0136] Advantageously, one of the boundary lines, in particular the convex boundaryline, may include at least one spine preferentially located on an outer half, or outer third,of the length of the cross-sectional profile of the fiber, and hence located on an outerhalf, or outer third, of the boundary line. This may provide a fiber that has reinforced mechanical stability and / or strength (i.e., retains its shape and maintains its structural integrity (less prone to splitting) after repeated loading by external forces, such as forces applied to the fibers from people, animals and / or weather events when the fibers areincorporated into carriers of artificial turfs. In addition, an artificial turf fiber having acombination of one or more spines with one or more of: (1) an average cross-sectionalwidth that increases (preferably monotonically) from the end portions to the center; (2)thickened end portions (preferably having a thickness that is greater than a thickness ofthe middle portion (between the two end portions), excluding the thickness of the center of the middle portion when the center includes a rounded bulge; and (3) a thickened center (of the middle portion), where the thickness is preferably thicker that the thicknesses of the end portions, results in a fiber that has even more reinforced mechanical stability and / or strength.

[0137] Figs. 18, 19 and 20 illustrate cross-sections of extruded artificial turf fibersaccording to other embodiments. Fibers 1800, 1900, and 2000 are similar to fiber 1400,however the curved cross-sectional shape of the extruded artificial turf fiber 1800 is anarc of a horseshoe, the curved cross-sectional shape of the extruded artificial turf fiber1900 is an arc of an Ω , and the curved cross-sectional shape of the extruded artificial turffiber 2000 is an arc of a U. Fiber 1800 has at least one spine per middle portion (e.g., seespines 1802, 1804), fiber 1900 has at least one spine per middle portion (e.g., see spines1902, 1904), and fiber 2000 has at least one spine per middle portion (e.g., see spines2002, 2004). The average thickness of the curved cross-sectional shapes of each middleportion of the fibers 1800, 1900 and 2000, excluding the regions containing the spines, may either be constant along the longitudinal direction, or increasing in the longitudinal direction as the center is approached (i.e., increasing as the distance from the center decreases).

[0138] 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 ourwithout: 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.

[0139] An average width of the curved cross-sectional shape of the middle portion offiber 2100 increases at a greater rate (along a longitudinal distance of the fiber from either of the end portions to the center closest to the end portion) than the average width of the curved cross-section of the middle portion of fiber 2200, the fiber 2100 doesnot include spines, and the fiber 2200 include spines. As illustrated, fiber 2200 has lessthinning of the thicknesses of the end portions.

[0140] 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. The fiber depicted in Fig. 25 is another example of the fiber 1704 ofFig. 17 and includes a (hardly visible) spine on outer halves of the middle portion of thefiber.

[0141] The average widths of the curved cross-section shapes of the middle portions ofeach of fibers 2300, 2400 and 2500 increase along a longitudinal distance of the fiber from either end portion to the center, and each of the fibers 2300, 2400 and 2500include spines. As illustrated, each of the fibers 2300, 2400 and 2500 have end portionswithout any reduction (or only slight reduction) in thickness (as compared to thethickness of the end portions of the respective extrusion dies (not shown)), and withoutany flattening (or only slight flattening) or distortion to the curvatures of the fibers whencompared to the curvatures of the respective extrusion dies (not shown).

[0142] According to another embodiment, the extruded artificial turf fiber 1200, 1300,1400, 1500, 1600 and / or 1700 is formed from a polymer mixture, where the polymermixture is at least a two-phase polymer mixture, where a first phase of the polymermixture includes a first polymer and a first dye and a second phase of the polymermixture includes a second polymer and a second dye, where a color of the second dye isdifferent than a color of the first dye, where the second polymer is of a same or of adifferent type as the first polymer, where the first and the second phases are immiscible, and where the extruded artificial turf fiber has a marbled appearance.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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) having a varyingwidth 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).

[0147] 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.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 portion1206 first boundary line 1208 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 line1224 boundary line 1226 boundary line1228 boundary line1300 artificial turf fiber1400 artificial turf fiber 1402 first spine 1404 second spine1500 artificial turf fiber1502 extrusion die1504 photo of artificial turf fiber1506 outline (i.e., shape) of extrusion die 1508 outer boundary line 1510 inner boundary line 1512 end portion 1518 first baseline 1520 second baseline 1600 artificial turf fiber 1602 extrusion die 1604 photo of artificial turf fiber 1605 end potions 1606 center 1608 end portions 1618 first baseline 1620 second baseline1700 artificial turf fiber1702 extrusion die1703 first end portion opening1704 photo of artificial turf fiber 1706 center 1710 first spine 1712 second spine 1714 bulge 1716 end portions of photo 1704 1718 first baseline 1720 second baseline 1800 artificial turf fiber1801 middle portion1802 first spine 1804 second spine 1900 artificial turf fiber1901 middle portion1902 first spine 1904 second spine 2000 artificial turf fiber2001 middle portion2002 first spine2004 second spine 2100 artificial turf fiber 2200 artificial turf fiber 2300 artificial turf fiber 2400 artificial turf fiber 2500 artificial turf fiber

Claims

CLAIMS1. An extruded artificial turf fiber (100; 800-1200; 2100-2500) having a cross-sectionalshape comprising:- first and second end portions (1605, 1608); and- a middle portion (1202, 2001, 1901) having a curved cross-sectional shape,o wherein the curved cross-sectional shape of the middle portion isdefined by a first boundary line (1206, 1222) and a second boundary line(1208, 1226) opposite the first boundary line, owherein the first boundary line consists of first uninterruptedundulations and the second boundary consists of second uninterrupted undulations, and owherein either:^ the width of the curved cross-sectional shape of the middle portionas measured between the first and second boundary lines is constant along the length of the curved cross-sectional shape ofthe middle portion, or ^the first uninterrupted undulations have a phase offset from thesecond uninterrupted undulations and / or the first and second uninterrupted undulations have different, equal or modulatedspatial frequencies.

2. The extruded artificial turf fiber of claim 1, wherein the first and second endportions are thicker than the middle portion.

3. The extruded artificial turf fiber of claims 1 or 2, wherein the fiber curved cross-sectional shape of the middle portion as measured between the first and second boundary lines along the length of the curved cross-sectional shape of the middleportion has a non-constant width.

4. The extruded artificial turf fiber of claim 3, wherein the widths of the first andsecond end portions of the fiber are greater than the maximum of the non-constant width of the curved cross-sectional shape of the middle portion.

5. The extruded artificial turf fiber of any one of the previous claims, wherein the firstand second end portions have curved cross-sectional shapes, and wherein the curved cross-sectional shapes of the first and second end portions are defined by respective boundary lines consisting of third uninterrupted undulations.

6. The extruded artificial turf fiber of claim 5, wherein the third uninterruptedundulations comprise a spatial frequency that is different than the spatial frequencies of the first and / or second uninterrupted undulations.

7. The extruded artificial turf fiber of any one of the previous claims, wherein thecurved cross-sectional shape of the middle portion 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.

8. The extruded artificial turf fiber of any one of the claims 1-6,- wherein the first boundary line is an outer, convex boundary line and the secondboundary line is an inner, concave boundary line, -wherein at least 70%, in particular at least 80%, e.g., 100% of the undulations ofthe outer boundary line are defined by first circles having a same first diameter, and -wherein at least 70%, in particular at least 80%, e.g., 100% of the undulations ofthe inner boundary line are defined by second circles having a same second diameter.

9. The extruded artificial turf fiber of any one of the previous claims, wherein thecenter of the middle portion of the fiber comprises a thickening that forms a rounded protrusion to at least one side of the fiber.

10. The extruded artificial turf fiber of any one of the previous claims, wherein the firstboundary line comprises at least one spine that is continuous with neighboring first uninterrupted undulations, wherein the at least one spine is positioned on an outer half of the middle portion of the fiber, and wherein the amplitude of the spine islarger than the amplitudes of the neighboring first uninterrupted undulations.

11. The extruded artificial turf fiber of any one of the previous claims, wherein the fiberis formed from a polymer mixture, wherein the polymer mixture is at least a two- phase polymer mixture, wherein a first phase of the polymer mixture comprises a first polymer and a first dye and a second phase of the polymer mixture comprises a second polymer and a second dye, wherein a color of the second dye is different than a color of the first dye, wherein the second polymer is of a same or of a different type as the first polymer, wherein the first and the second phases are immiscible, and wherein the extruded artificial turf fiber has a marbled appearance.

12. The extruded artificial turf fiber of claim 11, wherein the first phase forms polymerbeads within the second phase.

13. The extruded artificial turf fiber of claims 11 or 12, wherein the polymer mixturefurther comprises a nucleating agent and / or a compatibilizer.

14. The extruded artificial turf fiber of any one of claims 11-13, wherein the firstpolymer 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.

15. An artificial turf comprising:- a carrier; and- a plurality of artificial turf fibers, each artificial turf fiber comprising theextruded artificial turf fiber of any one of the previous claims integrated into the carrier and protruding therefrom to form the artificial turf.

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