HELICAL ARTIFICIAL TURF FIBER WITH ANTI-SPLICING AGENT

Abstract

Disclosed is a helical artificial turf fiber comprising an anti-splicing agent.

Claims

1. An artificial turf fiber comprising an anti-splicing agent, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape.

2-21. (canceled)

22. A helical artificial turf fiber, comprising an anti-splicing agent.

23. The artificial turf fiber of claim 1, wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve.

24. The artificial turf fiber of claim 1, wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis.

25. The artificial turf fiber claim 1, wherein the anti-splicing agent is or comprises a compatibilizer.

26. The artificial turf fiber according to claim 25, wherein the compatibilizer is selected from a group comprising: an anhydride modified polyethylene, a maleic acid grafted on polyethylene or polyamide; a maleic anhydride grafted on free radical initiated graft copolymer of polyethylene, SEBS, EVA, EPD, or polypropylene with an unsaturated acid or it's anhydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate, a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; Ethylene Ethyl Acrylate (EEA), Maleic Acide Anhydride grafted PE, a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graftpolyamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer; and a combination of two or more of the aforementioned substances, wherein the compatibilizer is in particular Ethylene Ethyl Acrylate (EEA) or Maleic Acide Anhydride grafted PE.

27. The artificial turf of claim 25, the fiber comprising the compatibilizer in an amount of 0.5-5.0 weight %, in particular 0.5-2.0 weight %, wherein in particular the compatibilizer is EEA or Maleic Acid Anhydride grafted PE.

28. The artificial turf fiber claim 1, wherein the anti-splicing agent is or comprises a low-density polyethylene-LDPE.

29. The artificial turf fiber according to claim 28, wherein the fiber comprises the LDPE polymer in an amount of 0.1-15% by weight of the fiber, in particular in an amount of 1.0-8.0% by weight of the fiber, in particular in an amount of 5.0-8.0% by weight of the fiber.

30. The artificial turf fiber of claim 1, wherein the artificial turf fiber has a longitudinal cross-sectional profile, in particular a cross-sectional profile with a central bulb and two wings extending in different directions.

31. The artificial turf fiber of claim 1, wherein the fiber comprises a different polymer material at its core compared to its peripheral regions, wherein the polymer materials are selected such that the polymer material at the core exhibits greater shrinkage than the polymer material in the peripheral regions in response to heat treatment.

32. The artificial turf fiber of claim 1, comprising: 0.1-15%, in particular 1.0-8.0% by weight of low-density polyethylene (LDPE), and optionally 0.1-15% by weight HDPE; and 60-99% by weight of linear low-density polyethylene (LLDPE).

33. The artificial turf fiber of claim 1, wherein at least 60% by weight of the fiber, preferably at least 75% by weight of the fiber, comprises one or more polymers having a density in the range of 0.910 to 0.928 g/cm.sup.3, more preferably in the range of 0.913 to 0.925 g/cm.sup.3.

34. The artificial turf fiber of claim 1, wherein the fiber comprises an hydrophilization agent, in particular hydrophilic fumed silica.

35. The artificial turf fiber of claim 1, wherein the fiber comprises a nucleating agent, wherein the nucleating agent is in particular an inorganic substance selected from a group comprising: talcum; kaolin; calcium carbonate; magnesium carbonate; silicate; silicic acid; silicic acid ester; aluminium trihydrate; magnesium hydroxide; meta- and/or polyphosphates; and coal fly ash; fumed silica; and/or wherein the nucleating agent is in particular an organic substance selected from a group comprising: 1,2-cyclohexane dicarbonic acid salt; benzoic acid; benzoic acid salt; sorbic acid; and sorbic acid salt.

36. An artificial turf, comprising: a carrier a plurality of helical artificial turf fibers according to claim 1, wherein the fibers are integrated into the carrier and extend to one side of the carrier.

37. The artificial turf according to claim 36, wherein the helical artificial turf fibers are texturized fibers, wherein the artificial turf further comprises non-texturized fibers, wherein in particular the non-texturized fibers have approximately the same length or a larger length than the helical, texturized fibers.

38. The artificial turf according to claim 36, further comprising: an infill layer, wherein the number of twists per fiber and the height of the infill is chosen such that in at least 80% of the helical fibers, the part of the helical fibers that protrudes above the infill layer makes at least 1.0 turns.

39. A method for manufacturing an artificial turf fiber that is under internal stress, the method comprising: creating a polymer mixture, the mixture comprising an anti-splicing agent; extruding the polymer mixture into a monofilament; quenching the monofilament; controlling equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; stretching the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing the internal stress into the fiber, wherein the internal stress is adapted to cause the artificial turf fiber, upon receiving heat treatment, to assume a helical shape.

40. The method of claim 39, further comprising: heating the monofilament, thereby causing the artificial turf fiber change its 3D shape to form a helical artificial turf fiber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0134] In the following, examples are described in greater detail making reference to the drawings in which:

[0135] FIG. 1 is a flow chart of a method of manufacturing helical artificial turf fibers;

[0136] FIG. 2 is a diagram illustrating artificial turf comprising a helical, texturized and a straight fiber;

[0137] FIG. 3 is a photo of an artificial turf comprising a helical, texturized and a straight fiber;

[0138] FIG. 4 is a photo of an artificial turf comprising a helical, texturized and a straight fiber and infill;

[0139] FIG. 5 is a collection of cross-sectional profiles of a helical fiber;

[0140] FIG. 6 is a photo of a Lisport Test apparatus adapted to test mechanical fiber stability in many thousand test cycles;

[0141] FIG. 7 is a photo of two different types of artificial turf;

[0142] FIG. 8 shows photos of the two different types of artificial turf and a helical artificial turf fiber comprised therein after 0 cycles;

[0143] FIG. 9 shows photos of the two different types of helical artificial turf fiber after different numbers of cycles;

[0144] FIG. 10 is a photo of the artificial turf shown in FIG. 4 after 50.000 cycles; and

[0145] FIG. 11 is an illustration of the impact of the LLDPE anti-splicing agent on the extrusion process;

[0146] FIG. 12 is a cross sectional drawing of a co-extrusion device used for the manufacturing of artificial turf fibers with a core-cladding structure;

[0147] FIG. 13 shows different types of temperature gradients used for inducing a helical structures in different groups of fiber profiles;

[0148] FIG. 14 is a block diagram of a manufacturing line for manufacturing artificial turf yarn;

[0149] FIG. 15 is a photo of a cross-section of a fiber; and

[0150] FIG. 16 shows various cross-sectional fiber profiles.

DETAILED DESCRIPTION

[0151] In the following, similar elements are denoted by the same reference numerals.

[0152] FIG. 1 shows a flow chart of a method of manufacturing artificial turf fibers comprising stress which, upon receiving heat treatment, causes the artificial turf fiber change its 3D shape to form a helical artificial turf fiber (steps 102 to 110), and for manufacturing helical artificial turf fibers (step 112). The steps in this process are as follows:

[0153] In a first step 102, a polymer mixture is created. The polymer mixture is formulated with an anti-splicing agent. The mixture serves as the raw material for the artificial turf fibers, with the anti-splicing agent playing a crucial role in preventing the fiber from splitting or fraying under mechanical stress.

[0154] A base polymer is selected that will form the bulk of the artificial turf fiber. Preferably, polyethylene (PE) is chosen for its softness, flexibility, and UV resistance. In some embodiments, the PE may be or comprise low-density polyethylene (LDPE) or high-density polyethylene (HDPE). In applications requiring greater durability or heat resistance, polypropylene (PP) or polyamide (PA) may be used as base polymer. The polymer(s) are mixed with the anti-Splicing agent(s) to prevent the fiber from splitting or unraveling under mechanical stress. The anti-splicing agent may comprise, for example, elastomers or other substances that provide flexibility and bond strength within the fiber matrix. In particular, a compatibilizer and/or a significant portion of LLDPE may be used as anti-splicing agent.

[0155] Various further additives may be incorporated into the mixture before extrusion: UV Stabilizers, Colorants, processing aids (like lubricants and stabilizers that help improve the flow properties of the polymer during extrusion, reducing friction and preventing thermal degradation) and/or anti-static agents may be used.

[0156] Once the base polymer and additives are selected, the materials are combined in a melt mixing process. This typically occurs in an industrial extruder where the polymer granules and additives are fed into the extruder's barrel and mixed together under heat and pressure. The extruder temperature is precisely controlled to ensure proper melting and blending of the polymer and additives. Typical processing temperatures range from: Polyethylene (LDPE/HDPE): 160-250 C., Polypropylene: 180-280 C. and Polyamide (Nylon): 230-290 C. The mixing speed and time is chosen as to ensure uniform blending of polymers and additives.

[0157] In a next step 104, the polymer mixture is extruded to form a monofilament. In this step, the polymer is pushed through a die, resulting in a continuous, uniform fiber that will be further processed. The extrusion defines the initial dimensions (cross sectional fiber profile) and properties of the fiber.

[0158] After extrusion, the monofilament undergoes rapid cooling, also referred to as quenching 106. This step solidifies the fiber and helps lock in its shape, establishing its basic structural properties. Quenching is preferably performed in a water bath set to a particular temperature, e.g., about 4-20. The temperature of the water bath and/or the temperature of godets used for transporting the fibers from the water bath to other fiber processing units may be set to a defined temperature chosen such as to ensure the formation of a stable, reproducible temperature gradient. The temperature differential is key to inducing internal stresses that lead to the fiber's twisting or coiling behavior. The temperature gradient ensures that the stretching will introduce stress in the fiber, which will finally result in the formation of a helical structure in response to heat treatment.

[0159] Next in step 108, equipment used for processing the extruded fiber is controlled such that a temperature gradient is formed reproducible across the cross-section of the extruded monofilament. For example, the temperature of the quenching bath, the temperature of godets used for transporting the fiber from the quenching unit to a stretching unit, to a texturization unit and/or to a winding unit for winding the fiber onto a bobbin, are chosen such that the temperature gradient is formed during transportation and/or while the fiber is processed in the stretching chamber.

[0160] Next in step 110, the monofilament is stretched while the temperature gradient is present. Stretching the fiber will increase its length and enhance the proportion of crystalline regions relative to amorphous regions in the polymer material. This stretching process also introduces stress into the fiber.

[0161] Introducing stress during the transport and/or during the stretching while the temperature gradient is present will usually not immediately result in a helical structure, but will cause the fiber to adapt helical shape upon heat treatment. The orientation of the temperature gradient may be chosen in dependence of the cross-sectional profile of the fiber. For example, a dorsoventral gradient may be chosen for fibers with a maximum-length to maximum-thickness ratio in the cross-sectional profile of below 3.0, while a central-radial temperature gradient may be introduced for fibers whose ratio is 3.0 or higher.

[0162] Preferably, the equipment used for fiber processing is controlled such that both the height and orientation of the temperature gradient and the amplitude and direction of the mechanical stress applied while the temperature gradient is present are applied in a defined, controlled and reproducible manner as to ensure a regular periodicity of the turns of the helix to be created in response to heat-treatment.

[0163] For example, the stretching may be performed by using godets with differential speed such that the stretching is executed during the transport of the fiber. In addition, or alternatively, the stretching may be performed in a stretching chamber. This stretching process not only strengthens the fiber but also primes it for taking on its helical shape.

[0164] After stretching, the monofilament is heated in step 112. The heating step may comprise heating the artificial turf fiber (or the artificial turf or greige good comprising the same) to a temperature above 70 C., in particular a temperature between 70 C. and 130 C., in particular a temperature between 80 C. and 90 C. The heating step will cause the fiber to change it's 3D shape into a helical configuration.

[0165] FIG. 2 is a detailed cross-sectional representation of an artificial turf 200 comprising a helical, texturized fiber 204 and a straight fiber 208. The artificial turf also comprises an infill layer 208. This configuration is designed to enhance the durability, aesthetic appeal, and functionality of the artificial turf.

[0166] A carrier 202 is a sheet-like structure for carrying the artificial turf fibers. The carrier layer serves as the foundation into which the fibers (both helical and non-helical) are anchored, providing structural stability to the turf system. The carrier is typically composed of a flexible yet durable material that supports the fibers and accommodates the infill layer. For example, the carrier can be a mesh, e.g., a methos of synthetic and/or natural fibers.

[0167] Helical, texturized fibers 204 are shown extending upward from the carrier 202. These fibers are formed in a twisted, helical shape to mimic the appearance of natural grass blades and offer enhanced resilience. The helical shape provides elasticity and helps maintain the turf's upright position, ensuring that the turf retains its appearance and cushioning properties even after repeated use. The helical shape also allows to keep infill particles in place.

[0168] The length of the helical fibers 204 is indicated as L1, representing the vertical extension from the carrier to the top of the helical fiber. These fibers typically extend to a height that contributes to the overall softness and bounce of the turf and that is preferably higher than the height L3 of the infill layer 208.

[0169] Alongside the helical fibers, the turf 200 also comprises non-helical, straight fibers 206. These fibers contribute to the fiber's optical properties. The length of the non-helical fibers is denoted as L2, which may vary depending on the design of the turf. These straight fibers in the depicted example extend higher as the helical fibers, contributing to a balanced appearance and feel.

[0170] Surrounding and partially covering both the helical and non-helical fibers is the infill layer 208. The infill is typically composed of granular materials such as rubber or sand, which help to provide cushioning, stability, and weight to the turf system. The infill also contributes to the overall performance of the turf, aiding in shock absorption and maintaining the vertical alignment of the fibers. The infill layer extends to a height indicated as L3, filling the space between and around the fibers. The height of the infill layer is carefully controlled to ensure it provides adequate support while allowing the fibers to extend above it for a natural look and feel. In particular, the number of turns in the helical fibers, the height of the infill L3 and the height L1 of the helical fibers are chosen such that the helical fibers extend at least 1 whole turn, preferably at least 1.5 to two turns above the infill. This is to ensure that the helical fibers can sufficiently contribute to optical and playing properties of the artificial turf such that the turf does not have grain.

[0171] A common problem of artificial turf is that the synthetic fibers forming the artificial turf surface have a grain. The grain of an artificial turf as used herein encompasses the natural tendency of turf fibers to lie at a slightly slanted angle. The term grain is also alternatively known as the pile direction. In German the grain is known as Florrichtung. The grain of artificial turf refers to the direction in which the synthetic grass blades are oriented and lie. The grain of artificial turf affects its appearance, texture, and performance, and is typically undesired: the grain may have negative effects on the visual appearance, as the turf can look patchy or show stripes due to differences in how light reflects off the fibers when viewed from different angles. In can also contribute to inhomogeneous ball roll characteristics and even an increased risk of injuries for the players. That L1, L3 and the manufacturing properties influencing the number of terns per length unit of the helical fibers are chosen as specified above ensures that the twisted, helical nature of the helical fibers can have a sufficient effect on the optical properties and playing characteristics.

[0172] The helical fibers may be integrated into other types of artificial turf as well. For example, they may be integrated into an infill-less artificial turf. They may be helical and texturized or helical and non-texturized. The helical fibers may be the only type of fibers in the turf, or they may be combined with other fiber types, e.g. non-helical texturized or non-helical non-texturized fibers.

[0173] FIG. 3 is a photo of an artificial turf 300 comprising a helical, texturized and a straight fiber. The line 302 indicates the height L2 of the non-helical, straight fibers, and the line 304 indicates the length L1 of the texturized and helical fibers.

[0174] FIG. 4 is a photo of an artificial turf 400 comprising a helical, texturized fiber and a straight fiber and infill. For example, the turf 400 may be created by adding infill to turf 300 after installation at the use site.

[0175] FIG. 5 is a collection of cross-sectional profiles 502-510 of different helical fibers. Applicant has observed that the cross-sectional fiber profile has a strong impact on the capability of a fiber to acquire a helical shape, and has developed different, profile-specific techniques for integrating stress into the fiber profiles in order to force the fibers to acquire helical shape. The different types of profiles, their impact on the ability to form helical structures, and suggested procedural adaptations of the manufacturing process for generating artificial turf fibers having a helical structure will be discussed in the following.

[0176] Diamond/Rhomboid profiles: Fiber profile 502 is an example of a fiber profile with longitudinal shape having a central bulb with wings (protrusions) extending in different directions, wherein the fFiber profile 502 has a maximum length (Lmax) to maximum thickness (Tmax) ratio of approximately 2.5.

[0177] The applicant has observed that for fiber profiles with a maximum length to maximum thickness ratio of less than 3.0, a dorsoventral temperature gradient (1302, 1304) across the fiber's cross section, as shown in FIG. 13, during stretching or compression is preferred. This temperature gradient may ensure that the fibers will adopt a helical structure when subjected to heat treatment. A radial temperature gradient may not be sufficient to induce a strong helical structure as any induced length difference between the core and the peripheral regions may not be sufficient to overcome the rigidity imposed by the massive central region. Hence, a dorso-ventral temperature gradient is preferred for this type of fiber profile.

[0178] Fiber profiles 504-510 are examples of longitudinal artificial turf fiber profiles that feature a central bulb with wings extending in different directions which have a cross-sectional profile with a maximum length to maximum thickness ratio greater than 3.0. In certain embodiments, fiber profiles with a central bulb and wings extending therefrom in different directions, particularly those with a maximum length to maximum thickness ratio of 3.0 or higher, are induced to form helical structures by establishing a core-to-radial temperature gradient (1306, 1308), as illustrated in FIG. 13. In all fiber profiles 504-510, the maximum length is indicated with the label Lmax, the maximum thickness (or width) is indicated with the label Tmax, the central bulb is indicated with the label c and the wings (protrusions) extending therefrom are indicated with the label p.

[0179] The profiles 504-510 are particularly suitable for manufacturing helical fibers as these profiles have been observed to facilitate and boost the formation of a helical structure, possibly because the wings are comparatively thin compared to the thickness of the central bulb, so the stress having been introduced into the polymer material faces less resistance by the polymer mass of these whole fiber cross section.

[0180] Fiber profiles 504, 506-510 may be manufactured using a single extrusion nozzle or using a co-extrusion nozzle as illustrated in FIG. 12. If a co-extrusion nozzle is used, the fiber may have a core-cladding structure. The core-cladding structure may in some cases be easily visible if different dyes are used for the cladding and the core polymer, and may in other cases be determinable by a more detailed optical or chemical analysis of the polymer material. The fiber profile 507 is an example of a fiber having a core-cladding structure as a result of a co-extrusion process, wherein the core polymer is visibly separated from the cladding polymer.

[0181] Fiber profile 507 comprises a cylindrical core and a non-circular cladding surrounding the core. The core comprises a core polymer. In some embodiments, the core polymer is a blend of an aged polymer and a virgin polymer. In addition, or alternatively, the core polymer may be a polymer material that will shrink stronger than the cladding polymer upon heat treatment. The heat treatment can be, for example, a step of heating the artificial turf after having applied a liquid polyurethane or latex mass or other type of liquid backing material on order to harden and solidify the liquid backing.

[0182] The core polymer may be a polymer which is miscible with the cladding polymer. For example, the core polymer can be polyethylene and the cladding polymer can be polyamide or polypropylene. The use of a compatibilizer as an anti-splicing agent may be particularly useful for core-cladding fiber profiles having different, immiscible core and cladding polymers, as the compatibilizer helps to prevent delamination and splicing at the contact surface of the core and cladding polymer.

[0183] The core may for instance have a diameter of 50 to 600 micrometer in size. It may typically reach a yarn weight of 50 to 3000 dtex.

[0184] In other embodiments, the cladding is formed by a cladding polymer which is chosen to be miscible with the core polymer in fluid state. The cladding polymer may be identical to the core polymer. The annular cylindrical zone or area where the cladding polymer contacts the core polymer is a contact layer where both polymers are mixed with each other. Hence, the contact layer may bond core and cladding together with stronger forces than the long-range forces which occur typically within arrangements with a purely cohesive bonding.

[0185] The cladding completely surrounds the core with two circular sections on two opposite sides of the core and two flat, thin, long wings on two other opposing sides of the core.

[0186] The cladding may be based on a polymer such as polyethylene which may provide a soft and smooth surface characteristic, or on polyamide which has the benefit of a reduced shrinkage in response to heat treatment relative to a PE-based core polymer. The cladding may comprise additives which support its interfacing function to the environment and/or a user. These additives to the cladding may be, for example, pigments providing a specific color, a dulling agent, a UV stabilizer, flame retardant materials such as aramid fibers or intumescent additives, an anti-oxidant, a fungicide, and/or waxes increasing the softness of the cladding.

[0187] Providing the cladding with additives may have the advantage that these can be left out from the core. This way, a smaller content of expensive additive material per mass unit is required. As an example, it is not necessary to add pigments to the core because only the cladding is visible from the outside. By way of a more specific example, it may be beneficial to add a green pigment, a dying agent and a wax to the cladding to gain a closer resemblance of natural grass blades.

[0188] Preferably, the cladding resembles a blade of grass by encompassing the circular-cylindrical core with two wings extending in two opposite directions from the geometric center of the monofilament.

[0189] A fiber 507 having a core-cladding structure can be produced by feeding a core polymer mixture and a cladding polymer component into a fiber producing coextrusion line. The two polymer melt components are prepared separate from each other and then joined together in the coextrusion tool, i.e., a spinneret plate, forming the two melt flows into a filament which is quenched or cooled in a water spin bath, dried and stretched by passing rotating heated godets with different rotational speed and/or a heating oven.

[0190] The two wings may have various forms and orientations. For example, the wings in profile 504 and 508 protrude in opposite (180) directions while the wings in profiles 508 and 510 protrude in an angle of about 135. The wings of profile 508 have an undulated and a non-undulated, straight side, while the wings of profile 510 have an undulated side and a non-undulated, concave side.

[0191] FIG. 6 is a photo of a Lisport Test apparatus adapted to test mechanical fiber stability in many thousand test cycles. The Lisport Test is a specialized testing method used to assess the durability and wear resistance of artificial turf. The test simulates the effects of long-term use on artificial turf by subjecting it to repeated mechanical abrasion and impact, mimicking the conditions experienced in real-life scenarios over several years. A machine equipped with rollers or studs repeatedly moves across the surface of the artificial turf, exerting pressure and friction, similar to the effect of people walking, running, or playing on the turf. The test is conducted in cycles, and the number of cycles simulates the number of years of use. A standard Lisport Test might simulate several years of wear in a matter of hours or days. After the test, the turf is evaluated for wear, such as fiber flattening, splitting, or loss of resilience. This helps manufacturers and users understand how the turf will hold up under long-term usage. The Lisport Test is an industry-standard test for evaluating artificial turf's durability (FIFA QUALITY PROGRAMME FOR FOOTBALL TURF, TEST MANUAL I: TEST METHODS, April 2024 edition, p. 52).

[0192] FIG. 7 is a photo of an area 700 that shall undergo a Lisport test. The upper half of the area is covered with artificial turf incorporating helical fibers that include an anti-splicing agent (in the following anti-splicing(+) turf), while the lower half is covered with artificial turf containing helical fibers manufactured without the anti-splicing agent (in the following anti-splicing() turf).

[0193] The compositions of the two compared turfs are as follows:

TABLE-US-00001 Anti-splicing(+) turf Anti-splicing() turf Polymer 83% by weight LLDPE, 95% by weight LLDPE, density: 0.918 g/cm.sup.3 density: 0.918 g/cm.sup.3 Anti-splicing 2% by weight: agent 1 Compatibilizer (Maleic Acid Anhydride grafted PE) Anti-splicing 10% by weight LDPE agent 2 Further additives 5% by weight of the 5% by weight of the (UV-stabilizer, fiber fiber pigments)

[0194] FIG. 8 shows a photo 800 of artificial turf comprising helical anti-splicing (+) turf fibers one of which being depicted in greater detail in photo 804 after 0 cycles of the Lisport test. FIG. 8 also shows a photo 802 of artificial turf comprising helical anti-splicing() turf fibers one of which being depicted in greater detail in photo 806 after 0 cycles of the Lisport test. As can be seen, both types of fibers look intact and do not show any signs of splicing.

[0195] FIG. 9 shows photos 902-906 of the helical anti-splicing(+) turf fibers after 10.000, 30.00 and 50.000 Lisport test cycles and photos 908-912 of the helical anti-splicing() turf fibers after 10.000, 30.00 and 50.000 Lisport test cycles. As can be seen from the photos, the helical fiber without the anti-splicing agent is severely damaged by lateral splicing already after 10.000 cycles, and is completely destroyed after 50.000 cycles, while the artificial turf fiber comprising the anti-splicing agent is still intact and does not show signs of splicing.

[0196] FIG. 10 is a photo of the artificial turf 700 shown in FIG. 7 after 50.000 cycles. It can be seen that the artificial turf 702 comprising the helical anti-splicing(+) turf fibers is still largely intact, while the artificial turf 704 comprising the helical anti-splicing() turf fibers is severely damaged. The splicing damage has introduced fiber edges that cause diffuse light reflection, resulting in turf 704 appearing white, with a bleached and visibly deteriorated appearance (whitening). As can be inferred from the photos in FIGS. 9 and 10, the helical fibers lacking an anti-splicing agent degrade rapidly, the helical fiber gets lost, and the fibers are lying flat or breaking into longitudinal fragments.

[0197] FIG. 11 shows a section through an area within a cylindrical extrusion nozzle. This figure shall illustrate the impact of the LDPE anti-splicing agent on the extrusion process and on the mechanical characteristics of the resulting fibers. Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene having a density in the range of 0.910-0.940 g/cm3. Embodiments of the invention are based on LDPE whose density range is within the above specified sub-range.

[0198] Linear low-density polyethylene (LLDPE) as used herein is a substantially linear polymer (polyethylene), with significant numbers of short branches. LLDPE differs structurally from LDPE because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and alpha-olefins.

[0199] Manufacturing an artificial turf fiber comprising a mixture of LLDPE and LDPE in the amount ranges described may be advantageous for multiple reasons:

[0200] The method allows manufacturing artificial turf fibers which are at the same time soft, flexible, resistant to shear forces (e.g. applied during extrusion or during stretching), have a high tensile strength and are resistant to splicing. Applicant has observed that not all plastomers are well suited for preventing splitting in artificial turf fibers, presumably because plastomersat least if provided in some particular amount ranges and/or having a particular densityappear not to generate a chain entanglement that can reliably prevent splicing and/or have negative side effects like making a fiber that has decreased tensile strength or flexibility and/or an increased brittleness. Applicant has observed that an optimal compromise between a high splicing resistance on the one hand and high tensile strength on the other hand can be achieved by combining specific amounts of LLDPE and LDPE polymers for generating an artificial turf fiber. Said fiber may in addition have a decreased brittleness, decreased splicing risk, and increased flexibility.

[0201] Applicant has also observed that the amount of LDPE used should be comparatively low, preferentially in the range of 0.1%-15%, more preferentially in the range of 5-8% by weight of the polymer mixture to ensure a high resistance to splicing in combination with a high tensile strength and high flexibility of the generated fiber.

[0202] Applicant has observed that the lack of long-chain branching in LLDPE allows the chains to slide by one another upon elongation without becoming entangled. As a result, fibers completely consisting of LLDPE are susceptible to splicing if a pulling force is applied on the surface of a fiber. Applicant has also observed that LLDPE has a higher tensile strength and a higher puncture resistance than LDPE and many plastomers.

[0203] Applicant has further observed that, upon applying strong shear forces on a polymer mixture comprising LLDPE and LDPE polymers, e.g. by extruding a polymer mixture comprising LLDPE and LDPE polymers, LDPE molecules are deformed, the side branches of the LDPE molecules get entangled with the ones of other LDPE molecules and/or with LLDPE molecules. As a consequence of chain entanglement, the viscosity raises. Applicant found that an artificial turf fiber manufactured from a particular mixture of specific amounts of LDPE and LLDPE is soft and flexible and has high tensile strength (thanks to the LLDPE component) and is at the same time resistant against splicing (thanks to chain entanglement caused by the LDPE component). Applicant has observed that if the ratio of LLDPE to LDPE is too large, splicing may occur, and if said ratio is too low, the flexibility and tensile strength of the fiber may significantly decrease.

[0204] FIG. 11 shows a section through an area within a cylindrical extrusion nozzle. In a first area 1102, the polymers of a liquefied polymer mixture are mostly in an amorphous state, i.e., there are only few or no crystalline regions and the polymer molecules do not show any preferred orientation in one dimension. In a second area 1104 that corresponds to an area of increased shear forces, the polymer molecules are sheared and pulled at least partially in the direction of the opening 1110 of the nozzle. In the area 1106 corresponding to high shear forces, the LLDPE and partially also the LDPE molecules are at least partially disentangled, oriented and form crystalline portions 1108. However, according to preferred embodiments, the majority of crystalline portions is created later in the stretching process.

[0205] Using a LLDPE polymer that comprises also LDPE as an anti-splicing agent, and optionally also a compatibilizer as a further anti-splicing agent, may prevent splicing in artificial turf fibers, because LDPE (in contrast to LLDPE) has side-chains which result in an entanglement of the linear, parallel oriented LLDPE-molecules. The extrusion, and in particular the stretching, results in an at least partial disentanglement and parallel orientation of LLDPE molecules which again causes an increased susceptibility of the fiber to splicing. By adding the appropriate amount of LDPE, in particular LDPE of the preferred density range, to the polymer mixture, the splicing can be prohibited even in helical fibers that are stretched during manufacturing.

[0206] FIG. 12 illustrates coextrusion of two polymer components in a coextrusion device for manufacturing an artificial turf fiber with a core-cladding structure. The coextrusion device comprises a joining path 1210 located upstream of a coextrusion opening 1208. The setup comprises a hole 1206 which receives a free end of a capillary tube 1205. Opposite to the inserted capillary tube 1205, hole 1206 ends in coextrusion opening 1208. A clearance between capillary tube 1205 and the walls of hole 1206 hydraulically connects the hole to a second channel system 1204. Capillary tube 1205 is hydraulically connected to a first channel system 1202 and is not fully inserted into hole 1206, such that a section 1210 of hole 1206 is hydraulically connected both to first channel system 1202 and to second channel system 1204. This section 1210 is the joining path 1210 of the depicted coextrusion setup. Joining path 1210 extends from capillary tube 1205 to extrusion opening 1208, as is indicated by dotted lines.

[0207] During coextrusion operation, capillary tube 1205 receives a molten core polymer component from first channel system 1202 and hole 1206 receives a molten cladding polymer component from second channel system 1204. The respective transport directions of the polymer components are indicated by arrows. The two polymer components flow separated from each other until they come into contact in joining path 1210. The two joined polymer components pass joining path 1210, which narrows to the cross section of coextrusion opening 1208, and exit coextrusion opening 1208 as a bicomponent monofilament.

[0208] In cases where core and cladding are to be joined together with a contact layer comprising a mixture of the core polymer mixture and the cladding polymer component, the dimensions of the joining path are suitably chosen such that a stable contact layer of homogeneous thickness is formed. In an example, the contact layer is formed within an axial length of the joining path of 3 to 7 times the diameter of the liquid core polymer mixture at the upstream end of the joining path. In a more specific example, the diameter of the liquid core polymer mixture at the upstream end of the joining path 1210 is between 0.5 and 1.5 mm, the axial length of the joining path is between 1.5 and 10.5 mm, causing the melted core polymer mixture to mix with the cladding polymer component in a contact layer with a radial thickness between 10 and 150 m.

[0209] The extrusion opening 1208 defines the capillary length 1211 of the extrusion nozzle. The extruding is performed via an extrusion opening, also referred herein as extrusion channel, having a capillary length of less than 8 mm, in particular a capillary length of less than 5.0 mm, in particular a capillary length of less than 2.5 mm, in particular a capillary length of less than 2.0 mm, in particular of 1.0 to 3 mm, e.g., 1.4 to 1.6 mm. This may ensure a more turbulent flow, which provides further protection of the helical fiber against splicing.

[0210] The capillary length in an extrusion nozzle refers to the length of the narrow, cylindrically shaped passage (capillary) through which the molten material (e.g., polymer) flows as it is forced out of the extrusion die or spinneret. The capillary length determines the shear stress, flow rate, and final properties of the extruded material.

[0211] FIG. 13 illustrates different temperature gradients used for generating a helical structure in fibers having different fiber profiles.

[0212] For fiber profiles having a maximum length to maximum thickness ratio of less than 3.0, preferably a dorso-ventral temperature gradient is established during the post-processing of the extruded fiber when the fiber is stretched, according to embodiments of the invention.

[0213] A dorso-ventral (or lateral) temperature gradient is a gradient that extends from the lower to the upper surface of the two longitudinal sides of a fiber cross-sectional profile, or from the upper to the lower surface, see the two temperature gradients 1302 and 1304. In general, a dorso-ventral temperature gradient refers to a temperature distribution along the dorsal (back or top) to ventral (top or back) axis, typically seen in non-cylindrical or asymmetrical structures. The temperature difference in this gradient occurs from one side (e.g., dorsal) to the opposite side (e.g., ventral), rather than uniformly radiating outward.

[0214] A radially symmetric temperature gradient refers to a temperature distribution that radiates from a central point or axis outward in all directions. In this type of gradient, the temperature changes consistently as one moves away from the center towards the peripheral regions/outer surface.

[0215] A dorso-ventral temperature gradient is generated preferably for fibers having a maximum-length to maximum thickness ratio of below 3.0, because the stress introduced via a radial temperature gradient 1306, 1308 has been observed to be in some cases insufficient to outperform the torsion-resistant forces exerted by the massive body of fibers having the above-mentioned length-to-thickness ratio.

[0216] However, the dorsoventral temperature gradient typically results in helical fibers which comprise a significant lateral component in their helical turns, meaning that the helical structures generated via a dorso-ventral temperature gradient are wound around a (virtual) cylinder. However, in some cases, it may be more desirable to have a helical fiber that is twisted essentially only around its own axis, i.e., it may be more desirable to have a helical fiber that is twisted like a screw, with basically no lateral component in the helical turns. For those types of applications, and in particular for fibers having a maximum-length to maximum thickness ratio of above 3.0, or above 4.0, or above 5.0, and in particular for fiber profiles having a central bulb and two wings extending in different directions, a radial temperature gradient is preferably established according to embodiments. For example, the temperature gradients 1306 and 1308, which are both examples for radial temperature gradients from the central part to the peripheral regions of the fiber profile cross section, are used for causing fiber profiles 504-510 of FIG. 5 to acquire helical shape. Applicant has observed that the helical shape caused by the radial temperature gradients 1306, 1308 and a stretching or compression of the fibers when this temperature gradient is present results in helical structures which have no or only a small lateral component in their helical rotations, meaning they look more like screws and less like helices coiled around a virtual cylinder. Applicant has observed, however, that a radial temperature gradient 1306, 1308 is less suitable for creating a helical structure in fibers with a maximum length to maximum thickness ratio of less than 3.0. Rather, a radial temperature gradient is preferably established for fiber profiles having a ratio of 3.0 or higher, e.g., 4.0 or higher, or 5.0 or higher.

[0217] FIG. 14 is a block diagram of a manufacturing line for manufacturing artificial turf yarn 422. The manufacturing line (or manufacturing system) comprises: an extruder 403 (e.g. a screw-extruder), one or more drawing devices 415, 418, one or more thermosetting (or heating) devices (e.g. godets, ovens) 417, one or more cooling devices (e.g. godets, bathes with cooling liquid) 416, 420, 497, and one or more rollers 421.

[0218] The extruder 403 comprises at least one hopper 401 for feeding components of a monofilament yarn (e.g. a blend of polymers) into the extruder and one outlet 402 for the monofilament yarn. The outlet 402 can be implemented as a wide slot nozzle or a spinneret. A polymer melt formed in a chamber of the extruder is pressed through the outlet 402 to form a monofilament yarn of a specific shape.

[0219] The monofilament yarn can be cooled down after the extrusion using the cooling device 497. When the cooling device is implemented as a godet, it can comprise two rollers 499 and 498 for winding the monofilament yarn 419. The cooling process can be implementing by maintaining a temperature of the rollers 499 and 498 within the specified range and/or by air cooling and/or by water cooling. A temperature of water (or air) can be kept within a specified range as well. Alternatively, the cooling device can be a bath with a cooling liquid (e.g. water) in which the monofilament yarn is cooled. The monofilament yarn is cooled down using the cooling device 497 to a temperature where crystallization can take place. The cooling device 497 may be, for example, a water bath (quenching bath). In the crystallization process the crystallites are forming to a percentage, which depends on the cooling rate. The higher the cooling rate, the less is the crystallinity and vice versa. The temperature of one or more of these devices, the environment temperature and/or the speed of transportation of the fiber from one processing unit to the next may be chosen such that a stable temperature gradient is reproducibly established across the cross section of the fiber.

[0220] The monofilament yarn can be further drawn using the drawing device 415. The drawing device can comprise three rollers 404, 403, 405. The drawing ratio is defined as the ratio of linear speeds of a pair of rollers 403 and 404 (or 404 and 405). The drawing device 415 can be operable for heating the monofilament yarn 419 during or before the drawing process such that a temperature gradient is established in the cross-sectional profile of the fiber. This can be implemented by differentially heating, e.g., heating and/or cooling one or more the rollers in order to keep their temperature within a predetermined temperature range and/or by air heating, wherein the hot air has a temperature within a predetermined temperature range, whereby the hot air is applied selectively to one side of the fiber. The elongation of the monofilament yarn in the drawing device can force the macromolecules of the monofilament yarn to parallelize and will introduce stress in the polymer material, because the molecules will reorganize in response to the mechanical stretching forces in a temperature-dependent way and the temperature gradient results in different molecular re-organization in different parts of the fiber cross section. This results in an overall higher degree of crystallinity and increased tensile strength, compared with undrawn monofilament yarn, but the crystallinity is not uniformly distributed in the fiber cross-section.

[0221] According to an alternative example not depicted in a figure, the drawing device may comprise one or more feeding rollers, an oven, and one or more receiving rollers. The one or more feeding rollers are configured to feed the monofilament yarn 419 into the oven. The one or more receiving rollers are configured to receive the monofilament yarn from the oven. The oven is configured to heat the monofilament yarn. The drawing ratio is determined by a ratio of the linear speeds of the feeding roller being the last roller before the oven and the receiving roller being the first after oven. The thermosetting process (drawing process) is performed in the oven 480, in which the monofilament yarn in stretched and heated simultaneously.

[0222] The monofilament yarn can be further cooled using the cooling device 416. The cooling device, when implemented as a cooling godet can have rollers 406 and 407. Alternatively, the cooling device 416 can be built and/or function in the same way as the cooling device 497. Afterwards the monofilament yarn can be further drawn using the drawing device 418 having rollers 410, 411, and 412. The drawing device 118 can be built and/or function in the same way as the drawing device 415.

[0223] The monofilament yarn can be further heated using one or more heating devices or elements (e.g. device 417). The heating device comprises a heater (or a heating element) and a temperature sensor for sensing a temperature of the heater (or the heating element). The heater can be implemented as an electrical resistance heater. The heating device is controlled by a controller (e.g. controller 452) such that the temperature of the heater is kept at a desired temperature (this temperature is mentioned herein as the third desired temperature as well). The controller comprises a computer processor 453 and memory 454 comprising instructions executable by the computer processor. The controller is communicatively coupled to the heating device and the temperature sensor configured to sense a temperature of the heating device. The communicative coupling can be implemented via a computer network 455.

[0224] The controller is operable to hold an actual temperature of the heating device at the desired temperature. The desired temperature can be selected such that a stable temperature gradient is established in the cross-section of the yarn during a transportation from the heater to the texturing apparatus (e.g. distance 456) has a temperature of the texturing process when it enters the texturing apparatus 414, or its inlet port 424 for receiving the yarn. The execution of the computer instructions by the computer processor 453 causes the controller to maintain the desired temperature gradient.

[0225] The heating device 417, when implemented as a godet, comprises a pair of rollers 408 and 409. The heating of the monofilament yarn can be made by keeping a temperature of the rollers within a predetermined temperature range and/or by hot air having a temperature within a predetermined temperature range. For instance the roller 409 can be equipped with a heater 150 and a temperature sensor 451 both communicatively coupled to the controller 452.

[0226] A controller 470 comprises a computer processor 472 and memory 473 comprising instructions executable by the computer processor.

[0227] The controller may optionally be configured to control a temperature of an optional texturing apparatus 414. The controller is communicatively coupled to the temperature sensor 458 configured to sense a temperature of the texturing apparatus 414, and a heating device, 429. The heating device can be configured to heat the texturing device through physical contact between the texturing device and the heating device or by electromagnetic induction. The physical contact can be a direct physical contact or a contact in which a thermally conductive paste is used between the heating device 429 and the texturing apparatus 414. At least a portion of the texturing device can be placed inside or in the proximity of the electromagnet of the heating device configured to heat the texturing device by electromagnetic induction. The heating device can be implemented as an electrical resistance heater. Further heating devices and temperature sensors can be operated by the controller 470 (or other controllers). The communicative coupling can be implemented via a computer network 471. The controller is operable to hold an actual temperature of the texturing apparatus at a desired temperature which can be the temperature required for the texturing process. The desired temperature can be specified as a temperature range. In this case the holding of the actual temperature at the desired temperature comprises keeping the actual temperature within the specified range, in particular the actual temperature is kept as close as possible to a middle temperature of the temperature range. The middle temperature is equal to an average of a lower boundary of the temperature range and an upper boundary of the chosen temperature range. The execution of the computer instructions by the computer processor 472 causes the controller to hold the texturing apparatus temperature at the desired temperature.

[0228] After the heating using one or more heating devices 417 the monofilament yarn is textured (curled) in the texturing apparatus 414. The textured (curled) monofilament yarn 422 is cooled using a cooling godet 420. And is forwarded further to another roller 421 for further processing.

[0229] FIG. 15 is a photo of a cross-section of a short segment of a longitudinal, helical fiber 1500. The depicted fiber is made of only a single PE-based polymer. According to some embodiments, the area within the dotted ring of FIG. 15 may represent a central region of the cross-sectional profile of the fiber 1500 and the area outside of the dotted ring of the fiber 1500 may represent the peripheral region of the cross-sectional fiber profile. The periphery of the artificial turf fiber may comprise the two wings and a thin layer within the central bulb that surrounds the core polymer. The central region may consist of a core polymer, and the peripheral region may consist of a cladding polymer (also referred to as wing polymer).

[0230] FIG. 16 shows various examples of cross-sectional profiles of artificial turf fibers 1602-1618 according to embodiments of the invention. The artificial turf fibers 1602-1618 have a longitudinal cross section, meaning the longest cross-sectional diameter of the fiber is at least twice the length of the shortest cross-sectional diameter. According to some embodiments, the fiber comprises a central bulb, which may be only slightly thicker than the wings of the fiber (as shown e.g. in 1602-1606) or which may be significantly, e.g., at least 10%, or at least 15%, or at least 20% thicker than the wings (measured at the thinnest portion of any of the two wings). For example, the central bulb in fiber profiles 1608-1618 is significantly thicker than the wings. Preferably, the fiber profiles comprise a core polymer at the center of the central bulb, and a cladding polymer at the periphery of the artificial turf fiber. According to some embodiments, the fiber profile is axially symmetrical with respect to the x and y axis (see e.g. fiber profiles 1602-1610). According to some embodiments, the fiber profile is rotational symmetric (see profiles 1616 and 1618).

[0231] Disclosed herein are also the following fibers and methods for manufacturing the same, which are described as clauses which can freely be combined with each other and with the other examples and embodiments disclosed herein as long as they are not mutually exclusive:

[0232] Clauses related to fibers comprising an anti-splicing agent: [0233] 1. An artificial turf fiber (204, 502-510, 804, 902-906) comprising an anti-splicing agent, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape. [0234] 2. A helical artificial turf fiber, comprising an anti-splicing agent. [0235] 3. The artificial turf fiber of any one of the previous clauses, wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve. [0236] 4. The artificial turf fiber of any one of the preceding clauses, wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis. [0237] 5. The artificial turf fiber according to any one of the preceding clauses, wherein the anti-splicing agent is or comprises a compatibilizer. [0238] 6. The artificial turf fiber according to clause 5, wherein the compatibilizer is selected from a group comprising: an anhydride modified polyethylene, a maleic acid grafted on polyethylene or polyamide; a maleic anhydride grafted on free radical initiated graft copolymer of polyethylene, SEBS, EVA, EPD, or polypropylene with an unsaturated acid or it's an-hydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate, a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; Ethylene Ethyl Acrylate (EEA), Maleic Acide Anhydride grafted PE, a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graftpolyamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer; and a combination of two or more of the aforementioned substances, [0239] wherein the compatibilizer is in particular Ethylene Ethyl Acrylate (EEA) or Maleic Acide Anhydride grafted PE. [0240] 7. The artificial turf of clause 5 or 6, the fiber comprising the compatibilizer in an amount of 0.5-5.0 weight %, in particular 0.5-2.0 weight %, wherein in particular the compatibilizer is EEA or Maleic Acid Anhydride grafted PE. [0241] 8. The artificial turf fiber according to any of the preceding clauses, wherein the anti-splicing agent is or comprises a low-density polyethylene-LDPE. [0242] 9. The artificial turf fiber according to clause 8, wherein the fiber comprises the LDPE polymer in an amount of 0.1-15% by weight of the fiber, in particular in an amount of 1.0-8.0% by weight of the fiber, in particular in an amount of 5.0-8.0% by weight of the fiber. [0243] 10. The artificial turf fiber of any one of the preceding clauses, wherein the artificial turf fiber has a cross-sectional profile with a central bulb and two wings extending in different directions. [0244] 11. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises a different polymer material at its core compared to its peripheral regions, wherein the polymer materials are selected such that the polymer material at the core exhibits greater shrinkage than the polymer material in the peripheral regions in response to heat treatment. [0245] 12. The artificial turf fiber according to any one of the preceding clauses, comprising: [0246] 0.1-15%, in particular 1.0-8.0% by weight of low-density polyethylene (LDPE), and [0247] optionally 0.1-15% by weight HDPE; and [0248] 60-99% by weight of linear low-density polyethylene (LLDPE). [0249] 13. The artificial turf fiber according to any one of the preceding clauses, wherein at least 60% by weight of the fiber, preferably at least 75% by weight of the fiber, comprises one or more polymers having a density in the range of 0.910 to 0.928 g/cm.sup.3, more preferably in the range of 0.913 to 0.925 g/cm.sup.3. [0250] 14. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises an hydrophilization agent, in particular hydrophilic fumed silica. [0251] 15. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises a nucleating agent. [0252] 16. An artificial turf, comprising: [0253] a carrier [0254] a plurality of helical artificial turf fibers according to any one of the previous clauses 2-15, wherein the fibers are integrated into the carrier and extend to one side of the carrier. [0255] 17. The artificial turf according to clause 16, [0256] wherein the helical artificial turf fibers are texturized fibers, [0257] wherein the artificial turf further comprises non-texturized fibers, wherein in particular the non-texturized fibers have approximately the same length or a larger length than the helical, texturized fibers. [0258] 18. The artificial turf according to clause 16 or 17, further comprising: [0259] an infill layer, [0260] wherein the number of twists per fiber and the height of the infill is chosen such that in at least 80% of the helical fibers, the part of the helical fibers that protrudes above the infill layer makes at least 1.0 turns. [0261] 19. A method for manufacturing an artificial turf fiber that is under internal stress, the method comprising: [0262] creating (102) a polymer mixture, the mixture comprising an anti-splicing agent: [0263] extruding (104) the polymer mixture into a monofilament; [0264] quenching (106) the monofilament; [0265] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0266] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing the internal stress into the fiber, wherein the internal stress is adapted to cause the artificial turf fiber, upon receiving heat treatment, to assume a helical shape. [0267] 20. A method for manufacturing a helical artificial turf fiber, comprising: [0268] creating (102) a polymer mixture, the mixture comprising an anti-splicing agent: [0269] extruding (104) the polymer mixture into a monofilament; [0270] quenching (106) the monofilament; [0271] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0272] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing stress into the fiber; and [0273] heating (112) the monofilament, thereby causing the artificial turf fiber change its 3D shape to form a helical artificial turf fiber. [0274] 21. The method according to clauses 19 or 20, wherein the extruding is performed via an extrusion channel having a capillary length of less than 8 mm, in particular a capillary length of less than 5.0 mm, in particular a capillary length of less than 2.5 mm, in particular a capillary length of less than 2.0 mm, in particular of 1.0 to 3 mm, e.g., 1.4 to 1.6 mm. [0275] 22. The method according to clauses 19, 20 or 21, wherein the stretching (110) is performed such that the ratio of the fiber length before the stretching to the fiber length after the stretching is in the range of 1:3 to 1:6, e.g., in the range of 1:4 to 1:5.

[0276] Clauses related to fibers comprising a hydrophilization agent [0277] 1. An artificial turf fiber (204, 502-510, 804, 902-906) comprising an hydrophilization agent, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape. [0278] 2. A helical artificial turf fiber, comprising a hydrophilization agent. [0279] 3. The artificial turf fiber of any one of the previous clauses, wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve. [0280] 4. The artificial turf fiber of any one of the preceding clauses, wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis. [0281] 5. The artificial turf fiber according to any one of the preceding clauses, wherein the hydrophilization agent is or comprises hydrophilic fumed silica. [0282] 6. The artificial turf fiber according to any one of the preceding clauses, [0283] wherein the hydrophilization agent is or comprises a surfactant, in particular polyenthylene glycol-PEG, and/or [0284] wherein the hydrophilization agent is or comprises Maleic Acide Anhydride grafted PE. [0285] 7. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises a nucleating agent. [0286] 8. The artificial turf fiber according to clause 7, wherein the nucleating agent is an inorganic and/or an organic substance or a mixture thereof, wherein the inorganic substance acting as the nucleating agent consists of one or more of the following: [0287] talcum; [0288] kaolin; [0289] calcium carbonate; [0290] magnesium carbonate; [0291] silicate; [0292] silicic acid; [0293] silicic acid ester; [0294] aluminium trihydrate; [0295] magnesium hydroxide; [0296] meta- and/or polyphosphates; and [0297] coal fly ash; [0298] fumed silica; wherein the organic substance acting as the nucleating agent consists of one or more of the following: [0299] 1,2-cyclohexane dicarbonic acid salt; [0300] benzoic acid; [0301] benzoic acid salt; [0302] sorbic acid; and [0303] sorbic acid salt. [0304] 9. The artificial turf fiber according to any one of the preceding clauses, wherein the artificial turf further comprises an anti-splicing agent. [0305] 10. The artificial turf fiber according to clause 9, wherein the anti-splicing agent is or comprises a compatibilizer. [0306] 11. The artificial turf fiber according to clause 10, wherein the compatibilizer is selected from a group comprising: an anhydride modified polyethylene, a maleic acid grafted on polyethylene or polyamide; a maleic anhydride grafted on free radical initiated graft copolymer of polyethylene, SEBS, EVA, EPD, or polypropylene with an unsaturated acid or it's an-hydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate, a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; Ethylene Ethyl Acrylate (EEA), Maleic Acide Anhydride grafted PE, a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graftpolyamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer; and a combination of two or more of the aforementioned substances, [0307] wherein the compatibilizer is in particular Ethylene Ethyl Acrylate (EEA) or Maleic Acide Anhydride grafted PE. [0308] 12. The artificial turf of clause 10 or 11, the fiber comprising the compatibilizer in an amount of 0.5-5.0 weight %, in particular 0.5-2.0 weight %, wherein in particular the compatibilizer is EEA or Maleic Acid Anhydride grafted PE. [0309] 13. The artificial turf fiber according to any of the preceding clauses, wherein the anti-splicing agent is or comprises a low-density polyethylene-LDPE. [0310] 14. The artificial turf fiber according to clause 13, wherein the fiber comprises the LDPE polymer in an amount of 0.1-15% by weight of the fiber, in particular in an amount of 1.0-8.0% by weight of the fiber, in particular in an amount of 5.0-8.0% by weight of the fiber. [0311] 15. The artificial turf fiber of any one of the preceding clauses, wherein the artificial turf fiber has a cross-sectional profile with a central bulb and two wings extending in different directions. [0312] 16. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises a different polymer material at its core compared to its peripheral regions, wherein the polymer materials are selected such that the polymer material at the core exhibits greater shrinkage than the polymer material in the peripheral regions in response to heat treatment. [0313] 17. The artificial turf fiber according to any one of the preceding clauses, comprising: [0314] 0.1-15%, in particular 1.0-8.0% by weight of low-density polyethylene (LDPE), and [0315] optionally 0.1-15% by weight HDPE; and [0316] 60-99% by weight of linear low-density polyethylene (LLDPE). [0317] 18. The artificial turf fiber according to any one of the preceding clauses, wherein at least 60% by weight of the fiber, preferably at least 75% by weight of the fiber, comprises one or more polymers having a density in the range of 0.910 to 0.928 g/cm.sup.3, more preferably in the range of 0.913 to 0.925 g/cm.sup.3. [0318] 19. An artificial turf, comprising: [0319] a carrier [0320] a plurality of helical artificial turf fibers according to any one of the previous clauses 2-18, wherein the fibers are integrated into the carrier and extend to one side of the carrier. [0321] 20. The artificial turf according to clause 19, [0322] wherein the helical artificial turf fibers are texturized fibers, [0323] wherein the artificial turf further comprises non-texturized fibers, wherein in particular the non-texturized fibers have approximately the same length or a larger length than the helical, texturized fibers. [0324] 21. The artificial turf according to clause 19 or 20, further comprising: [0325] an infill layer, [0326] wherein the number of twists per fiber and the height of the infill is chosen such that in at least 80% of the helical fibers, the part of the helical fibers that protrudes above the infill layer makes at least 1.0 turns. [0327] 22. A method for manufacturing an artificial turf fiber that is under internal stress, the method comprising: [0328] creating (102) a polymer mixture, the mixture comprising a hydrophilization agent: [0329] extruding (104) the polymer mixture into a monofilament; [0330] quenching (106) the monofilament; [0331] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0332] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing the internal stress into the fiber, wherein the internal stress is adapted to cause the artificial turf fiber, upon receiving heat treatment, to assume a helical shape. [0333] 23. A method for manufacturing a helical artificial turf fiber, comprising: [0334] creating (102) a polymer mixture, the mixture comprising a hydrophilization agent: [0335] extruding (104) the polymer mixture into a monofilament; [0336] quenching (106) the monofilament; [0337] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0338] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing stress into the fiber; and [0339] heating (112) the monofilament, thereby causing the artificial turf fiber change its 3D shape to form a helical artificial turf fiber. [0340] 24. The method according to clauses 22 or 23, wherein the extruding is performed via an extrusion channel having a capillary length of less than 8 mm, in particular a capillary length of less than 5.0 mm, in particular a capillary length of less than 2.5 mm, in particular a capillary length of less than 2.0 mm, in particular of 1.0 to 3 mm, e.g., 1.4 to 1.6 mm. [0341] 25. The method according to clauses 22, 23 or 24, wherein the stretching (110) is performed such that the ratio of the fiber length before the stretching to the fiber length after the stretching is in the range of 1:3 to 1:6, e.g., in the range of 1:4 to 1:5. [0342] 26. The method according to any one of clauses 22-25, wherein the temperature gradient is a dorso-ventral gradient or a radial gradient. [0343] 27. The method according to clause 26, wherein the fiber has a maximum-length-to-maximum-thickness ratio below 3.0 and wherein the temperature gradient is a dorsoventral gradient. [0344] 28. The method according to clause 26, wherein the fiber has a maximum-length-to-maximum-thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0, and wherein the temperature gradient is a radial gradient. [0345] 29. The method according to any one of clauses 22-28, [0346] wherein the manufacturing equipment comprises godets; and [0347] wherein the controlling (108) of the equipment for generating the temperature gradient comprises: controlling the temperature of the godets or parts thereof such that a temperature gradient within the fiber cross-section is reproducibly introduced into the material of the fiber. [0348] 30. The method of clause 29, wherein the stretching of the fiber comprises stretching the fiber by the godets while transporting the fiber. [0349] 31. The method according to any one of clauses 22-30, [0350] wherein the manufacturing equipment comprises a stretching chamber; and [0351] wherein the controlling (108) of the equipment for generating the temperature gradient comprises: controlling the temperature of the stretching chamber or parts thereof such that a temperature gradient within the fiber cross-section is reproducibly introduced into the material of the fiber. [0352] 32. The method of clause 31, wherein the stretching chamber comprises at least one heating element, and wherein the introduction of the temperature gradient within the fiber cross-section comprises: controlling the heating element in the stretching chamber so that a temperature gradient within the fiber cross-section is reproducibly introduced into the material of the fiber.

[0353] Clauses related to fibers comprising a longitudinal cross-sectional shape with different polymers: [0354] 1. An artificial turf fiber (204, 502-510, 804, 902-906, 1500, 1602-1618) comprising a longitudinal cross-sectional profile, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape, wherein the fiber comprises a core polymer in its core and a cladding polymer its periphery, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment. [0355] 2. A helical artificial turf fiber (204, 502-510, 804, 902-906, 1500, 1602-1618) comprising a longitudinal cross-sectional profile, wherein the fiber comprises wherein the fiber comprises a core polymer in its core and a cladding polymer its periphery, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment. [0356] 3. The artificial turf fiber according to clause 1 or 2, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0, [0357] 4. The artificial turf fiber according to any one of the previous clauses, wherein the cross-sectional fiber profile has a central bulb and two wings extending from the central bulb in different directions. [0358] 5. The artificial turf fiber according to clause 4, wherein the core polymer is comprised in the core of the central bulb and wherein the cladding polymer is comprised in the wings and optionally also in peripheral regions of the central bulb. [0359] 6. The artificial turf fiber of any one of the previous clauses, wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve. [0360] 7. The artificial turf fiber of any one of the preceding clauses, wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis. [0361] 8. The artificial turf fiber according to any one of the preceding clauses, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of below 3.0, and wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve. [0362] 9. The artificial turf fiber according to any one of the clauses 1-7, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0, and wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis. [0363] 10. The artificial turf fiber according to clause 9, wherein the helical fiber does not comprise a lateral component as it rotates and advances along its own central axis, resulting in a three-dimensional spiral curve having the shape of a straight screw. [0364] 11. The artificial turf fiber according to any one of the preceding clauses, wherein the artificial turf has a core-cladding structure as the result of a co-extrusion step of a stream of the core polymer concentrically surrounded by a stream of the cladding-polymer. [0365] 12. The artificial turf fiber according to any one of the preceding clauses, wherein the core polymer is or predominantly comprises polyethylene and the cladding polymer is or predominantly comprises polyamide. [0366] 13. The artificial turf fiber according to any one of clauses, wherein the core polymer is a blend of aged polymer and a first virgin polymer, wherein the cladding polymer is made of a second virgin polymer, and wherein in particular the first and the second virgin polymers are both polyethylene polymers. [0367] 14. The artificial turf fiber according to any one of the previous clauses 8-10, wherein the cladding polymer comprises a higher amount of HDPE than the core polymer. [0368] 15. The artificial turf fiber according to any one of the preceding clauses, wherein the artificial turf comprises an anti-splicing agent. [0369] 16. The artificial turf fiber according to clause 15, wherein the anti-splicing agent is a compatibilizer, and/or a low-density polyethylene-LDPE. [0370] 17. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises an hydrophilization agent, in particular hydrophilic fumed silica. [0371] 18. The artificial turf fiber according to any one of the preceding clauses, wherein the fiber comprises a nucleating agent. [0372] 19. An artificial turf, comprising: [0373] a carrier [0374] a plurality of helical artificial turf fibers according to any one of the previous clauses 2-18, wherein the fibers are integrated into the carrier and extend to one side of the carrier. [0375] 20. The artificial turf according to clause 19, [0376] wherein the helical artificial turf fibers are texturized fibers, [0377] wherein the artificial turf further comprises non-texturized fibers, wherein in particular the non-texturized fibers have approximately the same length or a larger length than the helical, texturized fibers. [0378] 21. The artificial turf according to clause 19 or 20, further comprising: [0379] an infill layer, [0380] wherein the number of twists per fiber and the height of the infill is chosen such that in at least 80% of the helical fibers, the part of the helical fibers that protrudes above the infill layer makes at least 1.0 turns. [0381] 22. A method for manufacturing an artificial turf fiber that is under internal stress, the method comprising: [0382] creating (102) at least one polymer mixture comprising at least a core polymer and a cladding polymer, wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment; [0383] extruding (104) the at least one polymer mixture into a monofilament via an extrusion nozzle causing the monofilament to have a longitudinal cross-sectional profile, in particular a cross-sectional profile with a central bulb and two wings extending from the central bulb in different directions, wherein the extrusion is performed such that the core polymer is exclusively or predominantly located in the core of the cross-sectional fiber profile and wherein the cladding polymer is exclusively or predominantly located in peripheral regions of the cross-sectional profile; [0384] quenching (106) the monofilament; [0385] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0386] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing the internal stress into the fiber, wherein the internal stress is adapted to cause the artificial turf fiber, upon receiving heat treatment, to assume a helical shape. [0387] 23. A method for manufacturing a helical artificial turf fiber, comprising: [0388] creating (102) at least one polymer mixture comprising at least a core polymer and a cladding polymer, wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment; [0389] extruding (104) the at least one polymer mixture into a monofilament via an extrusion nozzle causing the monofilament to have a longitudinal cross-sectional profile, in particular a cross-sectional profile with a central bulb and two wings extending from the central bulb in different directions, wherein the extrusion is performed such that the core polymer is exclusively or predominantly located in the core of the cross-sectional fiber profile and wherein the cladding polymer is exclusively or predominantly located in peripheral regions of the cross-sectional profile; [0390] quenching (106) the monofilament; [0391] controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; [0392] stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing stress into the fiber; and [0393] heating (112) the monofilament, thereby causing the artificial turf fiber to assume a helical shape and become a helical artificial turf fiber. [0394] 24. The method according to clauses 22 or 23, wherein the extruding is performed via an extrusion channel having a capillary length of less than 8 mm, in particular a capillary length of less than 5.0 mm, in particular a capillary length of less than 2.5 mm, in particular a capillary length of less than 2.0 mm, in particular of 1.0 to 3 mm, e.g., 1.4 to 1.6 mm. [0395] 25. The method according to clauses 22, 23 or 24, wherein the stretching (110) is performed such that the ratio of the fiber length before the stretching to the fiber length after the stretching is in the range of 1:3 to 1:6, e.g., in the range of 1:4 to 1:5. [0396] 26. The method according to clauses 22-25, wherein the extrusion nozzle is a coextrusion nozzle for co-extruding a core polymer and a cladding polymer, wherein the core polymer is or comprises the first polymer, wherein the cladding polymer is or comprises the second polymer, wherein the central bulb is made of the core polymer and a layer of cladding polymer surrounding the core polymer, wherein the wings are made of the cladding polymer. [0397] 27. The method according to clauses 22-26, wherein the method comprises: [0398] Generating a three-phase polymer mixture, the polymer mixture comprising mainly a first polymer, in particular PA, comprising a second polymer, in particular PE, and a compatibilizer, wherein the second polymer forms beads within the first polymer, the beads being surrounded by the compatibilizer, wherein the three phase polymer mixture is used as the extruded at least one mixture; and [0399] Performing the extrusion, wherein the polymer beads are located predominantly in the core region of a central bulb during extrusion, wherein the polymer beads are deformed into thread-like regions in the extrusion process, wherein the thread-like regions of the polymer located mainly in the core of the cross-sectional fiber profile to undergo greater shrinkage upon being subject to heat-treatment than the peripheral regions of the cross-sectional profile. [0400] 28. The method of any one of the previous clauses 22-27, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of below 3.0, and wherein the equipment is controlled such that a dorso-ventral temperature gradient is formed. [0401] 29. The method of any one of the previous clauses 22-27, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0, and wherein the equipment is controlled such that a radial temperature gradient is formed.

REFERENCE SIGNS LIST

[0402] 102-110 steps [0403] 200 artificial turf [0404] 202 carrier [0405] 204 texturized and helical fiber [0406] 206 straight fiber [0407] 208 infill [0408] 300 artificial turf [0409] 302 height of layer of texturized, helical fibers [0410] 304 height of straight fibers [0411] 400 artificial turf [0412] 401 Hopper [0413] 402 Outlet [0414] 403 Extruder [0415] 404 Roller [0416] 405 Roller [0417] 406 Roller [0418] 407 Roller [0419] 408 Roller [0420] 409 Roller [0421] 410 Roller [0422] 411 Roller [0423] 412 Roller [0424] 414 Texturing apparatus [0425] 415 Drawing device [0426] 416 Cooling device [0427] 417 Heating device [0428] 418 Drawing device [0429] 419 Monofilament yarn [0430] 420 Cooling godet [0431] 421 Roller [0432] 422 Artificial turf yarn [0433] 424 Inlet port [0434] 429 Heating device [0435] 451 Temperature sensor [0436] 452 Controller [0437] 453 Computer processor [0438] 454 Memory [0439] 455 Computer network [0440] 456 Distance (from heater to texturing apparatus) [0441] 458 Temperature sensor (texturing apparatus) [0442] 470 Controller [0443] 472 Computer processor [0444] 473 Memory [0445] 480 Oven (thermosetting process) [0446] 497 Cooling device [0447] 498 Roller [0448] 499 Roller [0449] 502-510 artificial turf fiber profile [0450] 600 Lisport Test apparatus [0451] 700 area covered with two different types of artificial turf [0452] 702 artificial turf with artificial turf fibers with an anti-splicing agent [0453] 704 artificial turf with artificial turf fibers without an anti-splicing agent [0454] 800 artificial turf with artificial turf fibers with an anti-splicing agent [0455] 802 artificial turf with artificial turf fibers without an anti-splicing agent [0456] 804 artificial turf with fiber with an anti-splicing agent [0457] 806 artificial turf fiber without an anti-splicing agent [0458] 902-912 photos of fibers [0459] 1102 first area [0460] 1104 second area [0461] 1106 area 1106 corresponding to high shear forces [0462] 1108 crystalline portions [0463] 1110 nozzle opening [0464] 1202 First channel system [0465] 1204 Second channel system [0466] 1205 Capillary tube [0467] 1206 Hole [0468] 1208 Coextrusion opening [0469] 1210 Joining path [0470] 1302 dorsoventral temperature gradient [0471] 1304 dorsoventral temperature gradient [0472] 1306 central, radial temperature gradient [0473] 1308 central, radial temperature gradient [0474] 1500 photo of cross-sectional fiber profile [0475] 1602-1618 cross-sectional fiber profiles [0476] L1: Height of the helical fiber [0477] L2: Length of the non-helical fiber [0478] L3: Height of the infill layer