Artificial turf fiber with undulated boundary lines

Abstract

The invention relates to an extruded artificial turf fiber (100; 800-1200; 2100-2500). The fiber comprises: - first and second end portions (1605, 1608); and - a middle portion (2001, 1901) having a curved cross-sectional shape, ∘ wherein the curved cross-sectional shape is defined by a first boundary line (1222) and a second boundary line (1226) opposite the first boundary line, ∘ wherein the first boundary line consists of first uninterrupted undulations and the second boundary consists of second uninterrupted undulations, and ∘ wherein either: ▪ a width of the curved cross-sectional shape as measured between the first and second boundary lines is constant along a 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

FIELD OF THE INVENTION

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

[0002] Synthetic grass fields (or artificial turf) have been used for years to provide a surface 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 can be used more intensively than lawns of natural grass. Although attempts are made to make 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 fibers being 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 in an 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 1950 350 A1 discloses various fibers, some of which have large bulbs at the center and on the ends. These fibers have stress points at the point the bulbs are connected 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 with a series of flat, planar sections which may lead to decreased mechanical stiffness and other undesired properties.

[0008] Korean patent KR 10-1989-0002109 discloses a spinneret for manufacturing monofilaments for artificial turf. In cross-section, the spinneret has an outer periphery formed of continuously repeated triangles of the same size, and an inner periphery formed of continuously repeated curved parts of the same size, for forming a monofilament that by definition has a cross-section that is the same as the cross-section of the spinneret. Since the triangles and the curved parts are connected to neighboring triangles and curved parts for forming the outer periphery and inner periphery, respectively, then a slope (which may also be referred to as tangent line) is indeterminate at each connection point on each respective periphery. That is, the slope at each connection point between neighboring triangles and curved parts on each respective periphery is indeterminate, or in other words, the slope as measured at each point along the respective peripheries has a discontinuity at each connection point. If each point on each respective periphery is defined with respect to a cartesian coordinate system 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 turf comprising the same. The objectives underlying the invention are solved by the features of the independent claims.SUMMARY

[0010] In one aspect, an extruded artificial turf fiber includes first and second end portions, and a middle portion having a curved cross-sectional shape. The curved cross-sectional shape is defined by a first boundary line and a second boundary line opposite the first boundary line, where the first boundary line consists of first uninterrupted undulations and the second boundary consists of second uninterrupted undulations, and where either a width of the curved cross-sectional shape as measured between the first and second boundary lines is constant along a 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.

[0011] A modulated frequency of an undulation as used herein is a frequency that has been altered in accordance with a modulating function or scheme. The modulation may be described as a variation of the amplitude, frequency, and / or phase in accordance with a function or schema. The modulation may, for example, result in an increase or decrease 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 undulations may 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 mechanical durability, 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 line comprising 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 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.

[0015] To the contrary, a shape with a contour consisting of uninterrupted undulations according 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 mechanical integrity of the fibers. In a fiber cross section of a fiber according to embodiments of the invention, 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 the accumulation of dirt and debris. That is, if each point on the boundary lines is defined with respect to a cartesian coordinate system x-y to have coordinate (x,y), then the slope at 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 boundary lines. 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. This means 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 the extruded 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 and second boundary lines being constant along a length of the curved cross-sectional shape, advantageously result in an increase in mechanical stability of 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 second uninterrupted undulations and / or the first and second uninterrupted undulations having equal 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 convex side, will have a concave-side outline that is shorter than the outline of the convex side. If both sides have equal spatial frequencies, the fiber width cannot be constant, as the curvature will introduce an offset between the undulations on both sides.

[0019] According to other examples, the first and second uninterrupted undulations different, 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 the invention.

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

[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 radius defining the undulations of the boundary line of the other parts of the cross-sectional shape.

[0023] This may be beneficial as the ends will have a curvature based on a radius which is at 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 the manufacturing 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 end curvature is that incident light is diffusely scattered even when it falls on the ends of the fibers. 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 manufacturing process, there is always a risk that the synthetic lawn optics will depend on the viewing angle, 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. The widths (or in the case of circularly-shaped fiber ends, the "diameter") of each of the thickenings is thicker than the thickest part of the middle portion of the fiber. For example, the middle portion of the fiber may have a width (i.e., a thickness) that is constant 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 be at least 5%, e.g., at least 10%, e.g., at least 15%, e.g., 25% thicker than the thickest part of the middle portion of the fiber. For example, the diameter of the thickening may be the width of the thickening measured along a line perpendicular to the curved longitudinal axis 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 increase the mechanical stability of the fiber and increase its ability to stand up again after the gras was trampled down. As the thickenings are rounded, the damage caused by abrasion at the fiber end portions is reduced compared to fibers lacking a rounded thickening at the fiber arms.

[0029] According to some examples, the curved cross-sectional shape 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 a similar 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 advantage that there are no particularly deep wave valleys where the fiber thickness is reduced to such an extent that weak points are created at which the fiber tears open under mechanical load. The risk of splicing is thereby further reduced. Likewise, there may not exist particularly high protrusions which may be particularly prone to wear and tear. This may further help to prevent the generation of microplastic waste.

[0032] According to some further examples, the fiber comprises a thickening at its center which 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 is selected such that a ratio of the radius of curvature of the fiber ends to the radius of the first 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 the arc 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 of a 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 range approximately representing the "golden ratio".

[0036] If one divides a stretch of an elongated object into two parts, of which the smaller part 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 many plants. 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, because the 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 mixture selected 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 fly ash (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 fiber consists of the nucleating agent. preferably, 0.2 %- 0.4 % by weight of the artificial turf fiber 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.

[0041] According to some examples, the cross-section of the fiber is shaped like the arc of a segment of a circle, or an arc of segment of an ellipse, or an arc of a segment of a horseshoe, or an arc of a segment of a U, or an arc of a segment of a Ω. Applicant has 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 S2 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 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 a catenary. The catenary is a particular type of arced curve which is particularly robust against mechanical stress.

[0043] Using an artificial turf fiber having a cross-section shaped like a catenary may strengthen 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 are visible 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., at a center of the middle portion of the fiber).

[0045] This may help increasing the mechanical strength of the fiber and to increase the ability 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 line connecting 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 has at least 6, in particular at least 7, in particular 7-11, e.g., 9 round bulges on its outer surface, and / or such that the fiber has at least 6, in particular 6-10, e.g., 8 round bulges on its inner surface.

[0049] According to some examples, the majority of undulations form consecutive pairs of 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 surface and 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 or minus 10% from said given length.

[0051] The above-mentioned dimension and ranges have been observed to provide for artificial 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 least one 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 outer third, of the middle portion of the fiber, and wherein an amplitude of the spine is larger than amplitudes of the neighboring first uninterrupted undulations. Advantageously, an artificial turf fiber having at least one spine results in a fiber that has more mechanical stability and / or strength. Furthermore, an artificial turf fiber having at least one spine in combination 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 a maximum thickness 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 a fiber 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 a plurality of the artificial turf fibers described herein in various embodiments and examples 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 described herein 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 down shape. Hence, a boundary line consisting of uninterrupted undulations may be described as a boundary line not having a vertical tangent. A boundary line consisting of uninterrupted undulations may also be described as a mathematically differentiable curve.

[0056] It is understood that one or more of the aforementioned embodiments and examples may be combined as long as the combined embodiments are not mutually exclusive.BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following, examples are described in greater detail making reference to the drawings in which: Fig. 1 is a perspective 3D view of the inside of a section of the fiber; Fig. 2 is a perspective 3D view of the outside of a section of the fiber; Fig. 3 shows the cross-section of a fiber; Fig. 4 shows the fiber cross-section of Fig. 3 with height and width annotated Fig. 5 shows the fiber cross-section of Fig. 3 with the circles defining the curvature of the corrugations and the ends annotated; Fig. 6 shows the fiber cross-section, where the fiber thicknesses at different cross-sectional areas are annotated; Figs. 7A and B show an example of a fiber cross-section annotated with concrete dimensions; Fig. 8 shows an example of a cross-section of a further fiber having more undulations; Fig. 9 shows an example of a cross-section of a further fiber having more undulations and an extended curvature; Fig. 10 shows an example of a cross-section of a further fiber having a central thickening which leads to a visible bulge on both the outer and inner surface of the fiber; Fig. 11 shows an example of a cross-section of a further fiber, the cross section having the shape of a catenary; Fig. 12 shows a cross-section of an extruded artificial turf fiber, according to an embodiment; Fig. 13 shows the cross-section of an extruded artificial turf fiber according to yet another embodiment; Fig. 14 shows the cross-section of an extruded artificial turf fiber according to another embodiment; Fig. 15 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to an embodiment; Fig. 16 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to another embodiment; Fig. 17 illustrates a cross-section of an extrusion dye and a photo of an artificial turf fiber formed in part by extruding a polymer mixture through the extrusion dye, according to yet another embodiment; Fig. 18 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of a horseshoe, according to an embodiment; Fig. 19 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of the Greek letter Ω, according to an embodiment; Fig. 20 illustrates a curved cross-section of an extruded artificial turf fiber having the shape of the letter U , according to an embodiment; Fig. 21 shows a photograph of an extruded artificial turf fiber having an approximate sinusoidal shape, according to an embodiment; Fig. 22 shows a photograph of an extruded artificial turf fiber having an approximate sinusoidal shape, according to another embodiment; Fig. 23 shows a photograph of an extruded artificial turf fiber having an approximate shape of the letter "U," according to an embodiment; Fig. 24 shows a photograph of an extruded artificial turf fiber having an approximate shape of a horseshoe, according to an embodiment; and Fig. 25 shows a photograph of an extruded artificial turf fiber having an approximate shape of a segment of a circle, according to an embodiment. DETAILED DESCRIPTION

[0058] In the following, similar elements may be denoted by the same reference numerals.

[0059] Figure 1 is a perspective 3D view of the inside of a section of an artificial turf fiber 100. For example, the fiber may be made of polyethylene or polypropylene or polyamide or a mixture of two or more of these polymers. The fiber may be generated in an extrusion process and the cross-sectional area 102 of the fiber may have essentially the same shape along the entire length of the fiber. 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.

[0060] Figure 2 is a perspective 3D view of the outside of a section of the fiber 100 shown 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.

[0061] Figure 3 shows the cross-section of the fiber 100 depicted already in figures 1 and 2. The fiber comprises a first end 302 connected to the center 306 of the fiber via a first fiber arm and comprises a second end 304 connected to the center of the fiber via a second arm.

[0062] 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 of uninterrupted undulations may imply that - apart from the cross-sectional area of the fiber at the upper and lower fiber ends where the fiber is cut during or after integration into a carrier - the fiber surface is basically free of any planar areas. This may be highly beneficial, because planar areas reflect the incident light directionally, not diffusely, so that the artificial turf is at least partially highly reflective and can even dazzle the observer. This creates a visual impression that is clearly different from that of a natural lawn, which is undesirable.

[0063] In the example shown, the undulations comprise alternating depressions 308 and elevations 312 on the outer fiber surface and alternating depressions 310 and elevations 314 on the inner fiber surface.

[0064] The thickness of the fiber at the thickenings 318 at the two ends is slightly greater than the thickness of the thickest portions of the fiber arms connecting the ends 302, 304 with the center 306. Moreover, there is a further thickening at the center of the fiber resulting in a protrusion / undulation 316 from the outer surface 312. In the depicted example, the central thickening does not result in a protrusion from the inner surface 102 of the fiber.

[0065] Figure 4 shows the fiber cross-section of Fig. 3 with height h and width w annotated. For example, the width w can be measured as straight line indicating the distance of the most outer points of the two fiber ends. The height h of the fiber may be measured as the distance of the "lowest" points of the fiber ends to the "highest" point at the fiber center. As can be inferred from 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.

[0066] Figure 5 shows the fiber cross-section of Fig. 3 with the circles defining the curvature of the corrugations and the ends annotated. As illustrated in 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.

[0067] In other embodiments (not shown), D3 and D4 may be similar, but not identical.

[0068] In addition, or alternatively, D1 and D2 may be identical. For example, both D1 and D2 may represent a diameter which is chosen such that the ratio of D1 (or D2) to D3 (or D4) approximately is the golden ratio.

[0069] Figure 6 shows the fiber cross-section, where the fiber thicknesses at different cross-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 w1 602 is slightly greater than the thickness w2 604 at the two points in the fiber arms equidistant from the ends, because in the depicted example, the fiber ends comprise a thickening. The thickness w3 606 at two other points in the fiber arms equidistant from the ends is slightly greater than the thickness w2. The fiber center represents the thickest and hence stiffest portion of the fiber having a thickness w4 608 being greater than w1, w2 and w3.

[0070] In the depicted example, w2 is the smallest with in the fiber arm and w3 is the largest width of the fiber arm.

[0071] In other examples, w1 and w2 may be identical, but preferably w1 is greater than the smallest width w2 of the fiber arms, and preferably also greater than the largest width w3 of the fiber arm.

[0072] According to some examples, the fiber profile is axisymmetric with respect to a vertical axis through the center of the fiber profile as shown in 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.

[0073] Figures 7A and 7B show an example of a fiber cross-section annotated with concrete dimensions. The fiber cross section corresponds to the cross section of the fibers depicted in 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.

[0074] The fiber profile can be scaled to provide fibers of different fiber weights. For example, by scaling the outer width of the fiber profile from 1.0 cm to 1.351 cm, and scaling all other dimensions given in 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.

[0075] As can be inferred from Figures 7A and B, the cross-section of the fiber is shaped like the arc of a segment of a circle having a radius referred to as "fiber profile circle radius".

[0076] According to figure 7A, the radius to the topmost point of the outer surface is 0.59 cm. The width of the fiber profile when the outmost points of the fiber ends are considered is 1.0 cm. Hence, the ratio of the width of the fiber profile and the fiber profile radius is 1.0 / 0.59, i.e., 1.694. This value is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, and hence approximately the golden ratio.

[0077] According to figure 7B, the radius of the circle 506 defining the undulation at the center of the fiber is 0.081 cm. The shared radius of the multiple smaller circles defining the undulation at the outer surface of the fiber 100 is 0.05 cm. In the depicted example, the shared radius of the multiple smaller circles defining the undulation at the inner surface of the fiber 100 is also 0.05 cm. Hence, the ratio of the radius defining the curvature of the protrusion 316 at the fiber center to the radius of the circles defining the undulations at the outer (and / or inner) surface of the fiber is 0.081 / 0.05, i.e., 1.62. This value is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, and hence approximately the golden ratio.

[0078] Figure 8 shows an example of a cross-section of a further fiber 800 having more undulations than the fiber cross section depicted in figures 1-7. The curvature of the whole fiber profile is the same as the profile curvature of the fibers depicted in figures 1-7.

[0079] Figure 9 shows an example of a cross-section of a further fiber 900 having more undulations 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.

[0080] Figure 10 shows the cross-section of an example of a further fiber 1000. The depicted fiber has a thickening at its center which leads to a bulge on both the outer and inner surface of the fiber.

[0081] Figure 11 shows the cross-section of an example of a further fiber 1100. The cross-section of the depicted fiber has the shape of a catenary.

[0082] 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 fiber 100 of Figs. 1-3, and reference numbers that are the same as those in Figs. 1-3 reference identical elements. The fiber 1200 includes a first end 302 (also defined as a first end portion 302), a second end 304 (also defined as a second end portion 304), a middle portion 1202, and a center 306 of the middle portion 1202.

[0083] As illustrated by Fig. 12, and as seen in Figs. 1-3, the middle portion 1202 has a curved cross-sectional shape. In some embodiments, the curved cross-sectional shape is formed from one or more arced-cross sectional shapes. In the Fig. 12 embodiment, the curved cross-sectional shape is the arc of a segment of a circle. The curved cross-sectional shape of the middle portion 1202 is defined by a first boundary line 1206 and a second boundary line 1208 opposite the first boundary line. The first boundary line 1206 is a line on the outer surface 202 (Fig. 2) of the fiber 1200, and the second boundary line 1208 is a line on the inner surface 104 (Fig. 1) of the fiber 1200. The first boundary line 1206 consists of first uninterrupted undulations represented collectively by the indentations 308 and protrusions 312, and the second boundary line 1208 consists of second uninterrupted undulations represented collectively by the indentations 310 and protrusions 314. In addition, the curved cross-sectional shape of the fiber 1200 has a longitudinal direction 1210 (also referred to as a longitudinal dimension), along which a length of the cross-sectional shape lies. The curved cross-sectional shape of the fiber 1200 also has a transverse direction that is defined by a direction that Is perpendicular to the longitudinal direction.

[0084] In one embodiment, a thickness w (also referred to as a width or transverse width) of the curved cross-sectional shape of the middle portion 1202, as measured between corresponding points on first and second boundary lines 1206, 1208, where corresponding points are the two points that lie on a line that is transverse to the longitudinal direction and that also lie on the first and second boundary lines, respectively, is constant or substantially constant along the longitudinal direction 1210 of the curved cross-sectional shape. For example, thicknesses (i.e., widths) w1, w2 and w3 are equal to one another, and moreover, a thickness w of the curved cross-sectional shape of the middle portion 1202 measured at all positions along the longitudinal direction is constant or substantially constant.

[0085] In one embodiment, the first uninterrupted undulations 308, 312 have a first wavelength 1212 and the second uninterrupted undulations 310, 314 have a second wavelength 1214, where the first and second wavelengths are selected such that the thickness w of the curved cross-sectional shape of the middle portion 1202 is constant or substantially constant along the longitudinal direction 1210. The length of the second boundary line 1208 (i.e., as measured from either the first or second end portion to a position on the second boundary line 1208 opposite the center 306 along the inner surface 104 of the fiber) is shorter than the length of the first boundary line 1206 (i.e., as measured from either the first or second end portion to a position on the first boundary line 1206 opposite the center 306 along the outer surface 202 of the fiber), and the difference between the lengths depend upon the extent of the curvatures of the inner and outer surfaces of the fiber 1200. In the exemplary embodiment of Fig. 12, the radius of curvature of the inner surface 104 (and the second boundary line 1208) is smaller than the radius of curvature of the outer surface 202 (and the first boundary line 1206), and thus the length of the second boundary line 1208 is shorter than the length of the first boundary line 1206. Thus, in order to provide a substantially constant thickness w of the curved cross-sectional shape of the middle portion 1202 at all positions along the longitudinal direction 1210 of the middle portion 1202, the wavelength (also referred to as the spatial frequency, which is the inverse of the wavelength) of the second uninterrupted undulations 310, 314 is selected to be smaller than the wavelength (i.e.. spatial frequency) of the first uninterrupted undulations 308, 312.

[0086] In another embodiment, thicknesses 318 of the first and second end portions 302, 304 of the fiber are greater than the constant thickness w of the curved cross-sectional shape of the middle portion 1202.

[0087] Figure 13 shows the cross-section of an extruded artificial turf fiber 1300 according to yet another embodiment. The artificial turf fiber 1300 is similar to artificial turf fiber 1200 of Fig. 12, and reference numbers that are the same as those in Fig. 12 reference identical elements.

[0088] The difference between fiber 1200 of the Fig. 12 embodiment and fiber 1300 of the Fig. 13 embodiment is that in the Fig. 13 embodiment, a thickness w of the curved cross-sectional shape of the middle portion 1202, as measured between corresponding points on the first and second boundary lines 1206, 1208, is not constant along the longitudinal direction 1210 of the curved cross-sectional shape. That is, in contrast to the Fig. 12 embodiment, the first uninterrupted undulations 308, 312 of the first boundary line 1206 of the curved cross-sectional shape of the middle portion 1202 may have a phase offset 1216 from the second uninterrupted undulations 310, 314 of the second boundary line 1208 of the curved cross-sectional shape of the middle portion 1202. Thus, as illustrated, a phase offset, such as phase offset 1216, will result in the middle portion 1202 having a variable thickness, independent of whether the wavelengths 1212 and 1214 (i.e., spatial frequencies) are equal or not (i.e., the thickness w of the curved cross-sectional shape of the middle portion 1202at positions along the longitudinal direction 1210 is not constant (i.e., it is variable, or non-constant)). In one embodiment, a thickness w of the curved cross-sectional shape of the middle portion 1202 is not constant along the longitudinal direction 1210 of the curved cross-sectional shape when the width varies by more the ± 5%.

[0089] Alternatively, or in addition to a phase offset, the first and second uninterrupted undulations may have the same (or substantially the same) wavelength (i.e., spatial frequency). For example, the first uninterrupted undulations 308, 312 have a first wavelength 1218 (also referred to as a first spatial frequency) and the second uninterrupted undulations 310, 314 have a second wavelength 1220 (also referred to as a second spatial frequency), where the first and second wavelengths (spatial frequencies) are selected to be approximately equal to one another. When the wavelengths 1218, 1220 are approximately equal to one another, the thickness w of the curved cross-sectional shape of the middle portion 1202 is variable (i.e., non-constant) along the longitudinal direction 1210, independent on whether or not there is a phase offset.

[0090] In another embodiment of Fig. 13, the thicknesses 318 of the first and second end portions 302, 304 of the fiber 1300 are greater than a maximum thickness of the variable thickness w of the curved cross-sectional shape of the middle portion 1202. For example, if w5 is the maximum thickness of the variable thickness of the curved cross-sectional shape of the middle portion 1202, then the thicknesses 318 of the first and second end portions 302, 304 of the fiber 1300 are greater than w5.

[0091] Referring to Fig. 12, and according to another embodiment, the curved cross-sectional shape of each of the first and second end portions 302, 304 are defined by boundary lines 1222, 1224, respectively. Although the boundary lines 1222, 1224 are curved, they do not include undulations. However, in an alternate embodiment, the curved cross-sectional shapes of each of the first and second end portions 302, 304 are defined by boundary lines 1226, 1228, respectively, that consist of third uninterrupted undulations. In yet another embodiment, wavelengths (i.e., spatial frequencies) of the third uninterrupted undulations of boundary lines 1226, 1228 are greater than or equal to the wavelengths (i.e. spatial frequencies) of the first and second undulations of the first and second boundary lines 1206, 1208. Although not illustrated, the curved cross-sectional shapes of each of the first and second end portions 302, 304 of fiber 1300 (Fig. 13) may also be defined by boundary lines consisting of third uninterrupted undulations as described with respect to the fiber 1200 (Fig. 12).

[0092] According to other embodiments of Figs. 12 and 13, the curved cross-sectional shape of the extruded artificial turf fiber 1200, 1300 comprises one of: an arc of a segment of a circle, an arc of a segment of an ellipse, an arc of at least a segment of a horseshoe, an arc of at least a segment of a U, or an arc of at least a segment of a Ω. Each point on an arc of an ellipse has a different radius from neighboring points. The scope of the disclosed embodiments of the curved cross-sectional shapes of the extruded artificial turf fibers include arcs defined by boundary lines that have a varying radius of curvature along the longitudinal direction of the cross-sectional shapes.

[0093] According to yet other embodiments of Figs. 12 and 13, and with reference to Fig. 5, the first boundary line 1206 is an outer, convex boundary line (i.e., a line on the outer surface 202 (Fig. 2) of the fiber) and the second boundary line 1208 is an inner, concave boundary line (i.e., line on the inner surface 104 of the fiber), where at least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line 1206 are defined by first circles having a same first diameter D3, and where at least 70%, in particular at least 80%, e.g., 100% of the undulations of the inner boundary line 1208 are defined by second circles having a same second diameter D4.

[0094] In another embodiment, the center 306 of the middle portion 1202 of the fiber 1200, 1300 comprises a thickening that forms a rounded protrusion 316 to at least one side of the fiber. Although the embodiments of Figs. 12 and 13 illustrate a thickening at the center 306 of the middle portion 1202 of the fiber resulting in a protrusion 316 from an outer surface, such as outer surface 202 (Fig. 2), in other embodiments the central thickening may result in a protrusion only from the inner surface, such as inner surface 104 (Fig. 1), or a first protrusion from the outer surface 202 and a second protrusion from the inner surface 104, where the protrusions are formed opposite one another on the two surfaces. In additional embodiments, the center 306 does not have any thickening or bulge. In one embodiment, the bulge has a thickness that is 10-20% thicker than a maximum thickness of the other portions of the middle portion.

[0095] Fig. 14 shows the cross-section of an extruded artificial turf fiber 1400 according to another embodiment. Reference numbers that are the same as those in Figs. 12 and 13 reference identical elements. As illustrated in the Fig. 14 embodiment, an average thickness (also referred to as an average width) of the curved cross-sectional shape of the middle portion 1202 is not constant along the longitudinal direction 1210, but increases as the longitudinal distance from the center 306 decreases.

[0096] In one embodiment, the average thickness of the middle portion, as illustrated in Figs. 15, 16 and 17, and which hereinafter applies to all disclosed embodiments, is the transverse distance between a first base line 1518 and a second baseline 1520, where the first and second baselines are lines that pass through, e.g., all the peaks of the protrusions of the undulations on both the first and second boundary lines 1508, 1510, respectively. However, the baselines may be defined to be any line that passes through points on the boundary lines that have the same amplitude values (e.g., see baselines 1618, 1620 of Fig. 16 and baselines 1718, 1720 of Fig. 17).As illustrated in Fig. 14, the average thickness w3 is larger than the average thickness w2, which is larger than the average thickness w1.

[0097] Furthermore, in another embodiment, the middle portion 1202 has at least one spine. In yet another embodiment, and as illustrated by Fig. 14, the first boundary line 1206 of the middle portion 1202 has a first spine 1402 and a second spine 1404. In one embodiment, a spine is defined as a protrusion that is slightly larger in amplitude than neighboring protrusions, and in other embodiments, as a protrusion that is slightly larger in amplitude that all other protrusions on both the first and second boundary lines of the cross-sectional shape of the middle portion 1202. A slightly larger amplitude is defined to be an amplitude that is about 2-5% larger than amplitudes of neighboring protrusions, or alternatively may be defined to represent a thickness of the middle portion (corresponding to a spine) that is less than about 10% larger than an average thickness of the middle portion, or less than about 5% larger than the average thickness of the middle portion, or between about 2-5% larger than the average thickness of the middle portion.

[0098] In some embodiments, the first boundary line 1206 of the middle portion 1202 includes at least one spine (e.g., spines 1402 and 1404) that is continuous with neighboring first uninterrupted undulations. In another embodiment, the at least one spine (e.g., spines 1402 and 1404) are positioned on an outer half, or on an outer third, of the middle portion 1202.

[0099] Advantageously, and as will be described further below with respect to Fig. 17, a gradual monotonical increase of average thickness of the middle portion 1202 of the fiber as the longitudinal distance from the center 306 of the fiber decreases, in combination with one or more spines (e.g., an even number of spines), preferable positioned on an outer half, or outer third, of the middle potion 1202, tend to add more mechanical stability to the curvature of the fiber.

[0100] In further embodiments, and as illustrated in Fig. 14, the thicknesses w4, w5 of the middle portion corresponding to the location of the spines 1402, 1404, respectively, represent the maximum thickness of the middle portion 1202, excluding the thickness of the middle portion 1202 at the center 306 that corresponds to the bulge 316, for those embodiments that include a thickening at the center 306.

[0101] Although Fig. 14 illustrates an embodiment in which the average thickness of the curved cross-sectional shape of the middle portion 1202 (excluding regions that contain the spines) is not constant along the longitudinal direction 1210 (i.e., it increases as the longitudinal distance from the center 306 decreases), the scope of the invention includes other embodiments in which the thickness of the curved cross-sectional shape of the middle portion 1202, including the central portion and including the regions containing the spines, is constant along the longitudinal direction. According to further embodiments, the thickness of the curved cross-sectional shape of the middle portion 1202, excluding the regions containing the spines, is constant along the longitudinal direction.

[0102] Figs. 15, 16 and 17 illustrate, in a lower panel, a cross-section of an extrusion dye though which a polymer mixture is extruded as part of the process of forming an extruded artificial turf fiber, and in an upper panel, a photo of the artificial turf fiber (i.e., the product) extruded through the dye.

[0103] Fig. 15 illustrates a cross-section of an extrusion dye 1502 and a photo of an artificial turf fiber 1504 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1502. An outline 1506 of the extrusion dye 1502 is superimposed on the artificial turf fiber 1504 for purposes of comparing the shape of the final product 1504 with the desired shape 1506. In the Fig. 15 embodiment, the average width wd of the extrusion dye 1502 is constant along a longitudinal length of the dye, where the average width wd is defined as a transverse distance between corresponding pairs of points, where first points of pairs of corresponding points are located on a first baseline 1518 that passes through the peaks of the protrusions of the undulations on an outer boundary line 1508 (on an outer surface of the dye) and second points of the pairs of corresponding points are located on a second baseline 1520 that passes through the peaks of the protrusions of the undulations on an inner boundary line 1510 (on an inner surface of the dye). Although the cross-sectional shape of the extrusion dye 1502 has uninterrupted undulations, the cross-sectional shape of the extrusion dye 1502 does not include any spines.

[0104] A comparison of the photo of the artificial turf fiber 1504 with the desired shape 1506 (i.e., the cross-sectional shape of the extrusion dye) shows a reduction in curvature of the artificial turf fiber 1504, and a thinning of the thickness of at least one end portion 1512 of the fiber.

[0105] Fig. 16 illustrates a cross-section of an extrusion dye 1602 and a photo of an artificial turf fiber 1604 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1602. In the Fig. 16 embodiment, the average width wd of the extrusion dye 1602 monotonically increases along a longitudinal length of the dye from the end portions 1605 to a center 1606, where the average width wd at the center 1606 is a maximum width of the dye and the average width wd adjacent the end portions 1605 is a minimum width of the dye. As in the Fig. 15 embodiment, the cross-sectional shape of the extrusion dye 1602 has uninterrupted undulations, but does not include any spines.

[0106] A comparison of the photo of the artificial turf fiber 1604 with the desired shape (i.e., the shape of the extrusion dye 1602) shows a reduction in curvature of the artificial turf fiber 1604. In addition, the thicknesses of the end portions 1608 of the fiber appear to show a thinning when compared to the thickness of the end portions 1605 of the dye 1602. However, when compared to Fig. 15, the end portions 1608 of the Fig. 16 embodiment appear to be better defined with respect to the adjacent uninterrupted undulations.

[0107] Fig. 17 illustrates a cross-section of an extrusion dye 1702 and a photo of an artificial turf fiber 1704 formed in part by extruding a polymer mixture, as disclosed according to the embodiments in the present application, through the extrusion dye 1702. In the Fig. 17 embodiment, the average width wd of the extrusion dye 1702 monotonically increases along a longitudinal length of the dye from the end portions 1708 to a center 1706, where the average width wd1 in the center 1706 is a maximum width of the dye and the average width wd2 adjacent the end portions 1708 is a minimum width of the dye. However, the rate of increase in the average width with respect to longitudinal distance is less than the rate of increase in average width as illustrated by the Fig. 16 embodiment. As in the Fig. 15 and 16 embodiments, the cross-sectional shape of the extrusion dye has uninterrupted undulations, however unlike Figs. 15 and 16, the cross-sectional shape of the extrusion dye of the Fig. 17 embodiment includes spines, for example spines 1710 and 1712. The cross-sectional shape of the extrusion dye 1702 also has a rounded bulge 1714 (or rounded thickening) at the center 1706.

[0108] A comparison of the photo of the artificial turf fiber 1704 with the desired shape (i.e., the shape of the extrusion dye 1702) shows a better retention of curvature of the artificial turf fiber 1704 in comparison to Figs. 15 and 16. In addition, the end portions 1716 of the fiber appear to show a better retention of the thickness in comparison to Figs. 15 and 16.

[0109] In another embodiment, the average width wd of the extrusion dye 1702 is constant (or substantially constant) along a longitudinal length of the dye from the end portions 1708 to the center 1706, the cross-sectional shape of the extrusion dye 1702 includes spines, for example spines 1710 and 1712, and the cross-sectional shape of the extrusion dye 1702 does not have the rounded bulge 1714 (or rounded thickening) at the center 1706.

[0110] Advantageously, a first boundary line (i.e., an upper boundary line) defining an upper boundary of a cross-sectional shape of a fiber, that includes at least one spine preferentially located on an outer half, or outer third, of the upper boundary line, provides a fiber that has reinforced mechanical stability and / or strength (i.e., retains its shape and maintains its structural integrity (less prone to splitting) after repeated loading by external forces, such as forces applied to the fibers from people, animals and / or weather events when the fibers are incorporated into carriers of artificial turfs. In addition, an artificial turf fiber having a combination of one or more spines with one or more of: (1) an average cross-sectional width 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 of the 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.

[0111] Figs. 18, 19 and 20 illustrate cross-sections of extruded artificial turf fibers according to other embodiments. Fibers 1800, 1900, and 2000 are similar to fiber 1400, however the curved cross-sectional shape of the extruded artificial turf fiber 1800 is an arc of a horseshoe, the curved cross-sectional shape of the extruded artificial turf fiber 1900 is an arc of an Ω , and the curved cross-sectional shape of the extruded artificial turf fiber 2000 is an arc of a U. Fiber 1800 has at least one spine per middle portion (e.g., see spines 1802, 1804), fiber 1900 has at least one spine per middle portion (e.g., see spines 1902, 1904), and fiber 2000 has at least one spine per middle portion (e.g., see spines 2002, 2004). The average thickness of the curved cross-sectional shapes of each middle portion of the fibers 1800, 1900 and 2000, excluding the regions containing the spines, may either be constant along the longitudinal direction, or increasing in the longitudinal direction as the center is approached (i.e., increasing as the distance from the center decreases).

[0112] Figs. 21 and 22 show photographs of extruded artificial turf fibers according to other exemplary embodiments. As illustrated, fibers 2100 and 2200 have shapes (i.e., cross-sectional shapes when viewed in a longitudinal plane of the fiber) that approximate sinusoids, where the fibers include middle portions having undulations and thickened end portions. In some embodiments, the middle portions of the fibers 2100 and 2200 include two approximately circular arcs (e.g., similar to the shapes of the approximately circular arcs of the middle portions of fibers 1200, 1300, 1400, or the shape of the approximately circular arc of a middle portion of the extrusion dye 1702, with our 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.

[0113] An average width of the curved cross-sectional shape of the middle portion of fiber 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 does not include spines, and the fiber 2200 include spines. As illustrated, fiber 2200 has less thinning of the thicknesses of the end portions.

[0114] Figs. 23, 24 and 25 show photographs of extruded artificial turf fibers according to yet other exemplary embodiments. As illustrated, fibers 2300, 2400 and 2500 have shapes (i.e., cross-sectional shapes when viewed in a longitudinal plane of the fiber) that approximate an arc of the letter "U," an arc of a horseshoe, and an arc of a segment of a circle, respectively. The fiber depicted in Fig. 25 is another example of the fiber 1704 of Fig. 17 and includes a (hardly visible) spine on outer halves of the middle portion of the fiber.

[0115] The average widths of the curved cross-section shapes of the middle portions of each of fibers 2300, 2400 and 2500 increase along a longitudinal distance of the fiber from either end portion to the center, and each of the fibers 2300, 2400 and 2500 include spines. As illustrated, each of the fibers 2300, 2400 and 2500 have end portions without any reduction (or only slight reduction) in thickness (as compared to the thickness of the end portions of the respective extrusion dyes (not shown)), and without any flattening (or only slight flattening) or distortion to the curvatures of the fibers when compared to the curvatures of the respective extrusion dyes (not shown).

[0116] 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 polymer mixture is at least a two-phase polymer mixture, where a first phase of the polymer mixture includes a first polymer and a first dye and a second phase of the polymer mixture includes a second polymer and a second dye, where a color of the second dye is different than a color of the first dye, where the second polymer is of a same or of a different type as the first polymer, where the first and the second phases are immiscible, and where the extruded artificial turf fiber has a marbled appearance.

[0117] In one embodiment, upon creation of the liquid polymer mixture, the two different dyes are separated in two different phases wherein one of the phases is "emulsified" in the second phase in the form of beads. This is advantageous as it is not necessary to use or create customized extruders which mechanically prevent a premature intermixing of the two dyes, thereby ensuring that a monofilament with a marbled pattern rather than a monofilament with a color being the intermediate of the first and second color is created. The polymer mixture is extruded into a monofilament including a marbled pattern of the first and second color. The monofilament is then heated, and then stretched to deform the polymer beads (containing one of the dyes) into threadlike regions and to form the monofilament into an artificial turf fiber.

[0118] In another embodiment, the polymer mixture further includes a compatibilizer. According to some embodiments, the compatibilizer (which may be considered a third phase of the polymer mixture) is added to the polymer mixture and interfaces the first and second polymers, thereby further preventing the delamination of the two different types of polymers. Preferably, the compatibilizer is added to the polymer mixture whose phase separation is caused by a polarity difference between a polar and an apolar polymer. The first phase forms polymer beads surrounded by the third phase within the second phase.

[0119] According to another embodiment, the first polymer is any one of the following: polyamide, polyethylene terephthalate, and polybutylene terephthalate, and the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof. Using a mixture of polymers of different types, e.g. the apolar polyethylene and the polar polyamide, with the above-described dyes, has the advantage that an artificial turf fiber is created that shows a marbled color pattern and that has increased durability against wear and tear due to the more rigid PA and at the same time a smoother surface and increased elasticity compared to pure PA based monofilaments.

[0120] Furthermore, an artificial turf fiber having a marbled color pattern in combination with a middle portion having a curved cross-sectional shape with uninterrupted undulations and / or with the curved-cross sectional shape having constant width along a length of the curved-cross sectional shape, or the uninterrupted undulations (on opposite boundary lines defining the curved cross-sectional shape) having a varying width 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).

[0121] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.REFERENCE SIGNS LIST

[0122] 100artificial turf fiber 102cross section area 104inner surface 202outer surface 302first fiber end 304second fiber end 306center of the fiber 308undulation of outer surface in the form of an indentation 310undulation of inner surface in the form of an indentation 312undulation of outer surface in the form of an protrusion 314undulation of the inner surface in the form of a protrusion 316protrusion caused by a central thickening 318thickenings at the fiber ends 502circle defining the curvature of an undulation of the first fiber end 504circle defining the curvature of an undulation of the second fiber end 506circle defining the curvature of an undulation at the thickened fiber center 508circles defining the curvature of undulations at the outer surface 510circles defining the curvature of undulations at the inner surface 602fiber width at the fiber ends 604fiber width at one position of the fiber arms 606fiber width at another position of the fiber arms 608fiber width at the fiber center 800artificial turf fiber 900artificial turf fiber 1000artificial turf fiber 1100artificial turf fiber 1200artificial turf fiber 1202middle portion 1206first boundary line 1208second boundary line 1210longitudinal direction 1212first wavelength 1214second wavelength 1216phase offset 1218first wavelength in another embodiment 1220second wavelength in another embodiment 1222boundary line 1224boundary line 1226boundary line 1228boundary line 1300artificial turf fiber 1400artificial turf fiber 1402first spine 1404second spine 1500artificial turf fiber 1502extrusion dye 1504photo of artificial turf fiber 1506outline (i.e., shape) of extrusion dye 1508outer boundary line 1510inner boundary line 1512end portion 1518first baseline 1520second baseline 1600artificial turf fiber 1602extrusion dye 1604photo of artificial turf fiber 1605end potions 1606center 1608end portions 1618first baseline 1620second baseline 1700artificial turf fiber 1702extrusion dye 1703first end portion opening 1704photo of artificial turf fiber 1706center 1710first spine 1712second spine 1714bulge 1716end portions of photo 1704 1718first baseline 1720second baseline 1800artificial turf fiber 1801middle portion 1802first spine 1804second spine 1900artificial turf fiber 1901middle portion 1902first spine 1904second spine 2000artificial turf fiber 2001middle portion 2002first spine 2004second spine 2100artificial turf fiber 2200artificial turf fiber 2300artificial turf fiber 2400artificial turf fiber 2500artificial turf fiber

Claims

1. An extruded artificial turf fiber (100; 800-1200; 2100-2500) comprising: - first and second end portions (1605, 1608); and - a middle portion (2001, 1901) having a curved cross-sectional shape, ∘ wherein the curved cross-sectional shape is defined by a first boundary line (1222) and a second boundary line (1226) opposite the first boundary line, ∘ wherein the first boundary line consists of first uninterrupted undulations and the second boundary consists of second uninterrupted undulations, and ∘ wherein either: ▪ a width of the curved cross-sectional shape as measured between the first and second boundary lines is constant along a 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.

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

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

4. The extruded artificial turf fiber of claim 3, wherein widths of the first and second end portions of the fiber are greater than a 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 first and 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 uninterrupted undulations 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 the curved 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 second boundary line is an inner, concave boundary line, - wherein at least 70%, in particular at least 80%, e.g., 100% of the undulations of the 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 of the 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 a center 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 first boundary 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 an amplitude of the spine is larger than amplitudes of the neighboring first uninterrupted undulations.

11. The extruded artificial turf fiber of any one of the previous claims, wherein the fiber is 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 polymer beads within the second phase.

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

14. The extruded artificial turf fiber of any one of claims 11-13, wherein the first polymer is any one of the following: polyamide, polyethylene terephthalate, and polybutylene terephthalate, and wherein the second polymer is any one of the following: polyethylene, polypropylene, and a mixture thereof.

15. An artificial turf comprising: - a carrier; and - a plurality of artificial turf fibers, each artificial turf fiber comprising the extruded 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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