ARTIFICIAL TURF WITH TEXTURIZED FACE YARN AND TEXTURIZED THATCH YARN

Abstract

 The invention relates to an artificial turf (200, 300, 500, 520, 530) comprising textured thatch yarn fibers (206), textured face yarn fibers (204), and a carrier (202). The face yarn fibers are integrated in the carrier such that the thatch yarn fibers protrude from the carrier by a shared thatch yarn fiber height (L2). The thatch yarn fibers are integrated in the carrier such that the face yarn fibers protrude from the carrier by a shared face yarn fiber height (L3). The face yarn fiber height being larger than the thatch yarn fiber height.

Description

Field of the invention

[0001] The invention relates to the field of synthetic surfaces and the production thereof, and more particularly to artificial turf.

[0002] Background and related art

[0003] Artificial turf or artificial grass is surface that is made up of fibers which is used to replace grass. The structure of the artificial turf is designed such that the artificial turf has an appearance which resembles grass. Typically, artificial turf is used as a surface for sports such as soccer, American football, rugby, tennis, golf, or for other playing fields or exercise fields. Furthermore, artificial turf is frequently used for landscaping applications. An advantage of using artificial turf is that it eliminates the need to care for a grass playing or landscaping surface, like regular mowing, scarifying, fertilizing, and watering.

[0004] Some artificial turf types are known which comprise a combination of fibers of two different lengths. For example, US patent application US 6,299,959 B1 describes synthetic grass having both surface forming non-textured fibers and textured thatch zone forming fibers to add resilience and to lock in rubber granules which are distributed more densely near the base of the fibers. In one embodiment of this arrangement, the covering rubber like particles are used to stabilize the synthetic surface fibers in their upright position.

[0005] However, it has been observed that the longer "pile yarn" fibers often are not resilient enough to raise up again after being repeatedly pressed down by players and playing equipment. Adding an infill for stabilizing the pile yarn, as suggested by US patent application US 6,299,959 B1, may have the disadvantage that costs are increased and that those parts of the pile yarn fibers protruding from the infill layer may still be permanently depressed soon after heavy use. In a further disadvantageous aspect, it has been observed that tufted pile yarn fibers of several state of the art artificial turf types do not protrude orthogonally (in a 90° angle) from the carrier, but rather in an angle that of about 83°-97°. This is because the tufting process is typically performed on a moving carrier structure, so the tufting needle releases the tufted fibers in a slightly skewed direction. As the direction of the moving carrier remains the same during the tufting process, all pile yarn fibers are tilted in the same direction. This tilt is also referred to as "turf grain" (or "Polneigung" in German). This tilt may result in a significant anisotropy of the roll resistance of the artificial turf and thus in an inhomogeneous and unpredictable movement of the ball over the artificial turf surface, in particular when the ball moves with slow speed. The lack of rigidity of the pile yarn fibers and the tufting-induced tilt of the pile yarn fibers in one direction may alone or in combination result in inhomogeneous and unpredictable movement of any object that rolls or slides along the surface of the artificial turf. This movement behavior is considered highly undesirable in almost all types of application scenarios, in particular in any kinds of ball sports like soccer, golf, or the like.

Summary

[0006] It is an object of the invention to provide for an improved artificial turf and methods for producing the same. The problem is solved by the features as specified in the independent claims. Embodiments of the invention are given in the dependent claims. The embodiments and examples described herein can freely be combined with each other unless they are mutually exclusive.

[0007] In one aspect, the invention relates to an artificial turf comprising textured thatch yarn fibers, textured face yarn fibers, and a carrier. The face yarn fibers are integrated in the carrier such that the thatch yarn fibers protrude from the carrier by a shared thatch yarn fiber height (L2). The thatch yarn fibers are integrated in the carrier such that the face yarn fibers protrude from the carrier by a shared face yarn fiber height (L3). The face yarn fiber height is larger than the thatch yarn fiber height.

[0008] Said features may be advantageous for multiple reasons.

[0009] In one advantageous aspect, an artificial turf is provided that may allow for predictable, straight movement trajectories of a ball. As not only the thatch yarn fibers, but also the face yarn fibers are texturized, the tilt of the fibers generated by the tufting process is "randomized". The texturized face yarn fibers still have a tufting-induced tilt, but as they are texturized, the direction of the tilt of all face yarn fiber is randomized such that no net effect of the tilt of the fibers on the movement of a ball is observable.

[0010] In a further beneficial aspect, the texturization-induced randomization of the orientation of the thatch yarn fibers and of the face yarn fibers reduces the light reflection on the surface of the artificial turf fibers. This is desirable for acquiring high-quality photographs (e.g. of children playing on ground made of artificial turf) and TV broadcasts of soccer games and other types of sport.

[0011] In a further beneficial aspect, it has been observed that the texturization-induced randomization of the orientation of the thatch yarn fibers and of the face yarn fibers helps preventing skin-burns. It is assumed, this effect results from the uneven surface generated by the random orientation of the texturized fibers. The uneven surface reduces the contact surface of the fibers and the skin of the players.

[0012] In a further beneficial aspect, the rigidity of the face yarn fibers is increased even if no infill is present or if the height of the infill layer is lower than the height of the face yarn fibers. This may allow providing an artificial turf that is particularly robust against wear and tear.

[0013] In a further beneficial aspect, an artificial turf is provided with a "thatch yarn zone" and a "face yarn zone" whose fibers respectively have a defined, common length. In state of the art artificial turf systems, a defined, particular pile height is created by cutting non-texturized fibers which do not change their length after the cutting. To the contrary, embodiments of the invention use texturized fibers for generating the face yarn fibers of a particular, defined, common length. This is not trivial, because texturized fibers may have an inhomogeneous distribution of their mass and of other relevant parameters which may have an impact on their length when being cut.

[0014] The thatch yarn fibers and face yarn fibers protrude in the same direction, respectively generate a "layer" or "zone" of a predefined height. Preferably, all face yarn fibers have basically the same length (measured from the point where the fiber is integrated in the carrier and the end of the fiber protruding from the carrier). For example, at least 90%, more preferably at least 99% of the thatch yarn fibers have a thatch yarn length that differs from a median thatch yarn fiber length not more than +/- 10%. Analogously, at least 90%, more preferably at least 99% of the face yarn fibers have a face yarn length that differs from a median face yarn fiber length not more than +/- 10%.

[0015] According to embodiments, the first and second texturized fibers respectively have a molecular memory of a textured state, wherein a textured state can be, for example, a curled, crumpled and/or wrinkled state. A "molecular memory" means a tendency to turn into a particular state, i.e., the textured state, if the fiber is allowed to do so. For example, the tufting needle may exert a force on the tufted fiber, thereby stretching the fiber and turning the fiber into a stretched, partially or completely "non-texturized" shape. However, as soon as the stretching force has disappeared, e.g. as a result of cutting the stretched fibers, the fibers turn into their "texturized" shape, which is typically a curled, crumpled and/or wrinkled state. Thus, a texturized state of a fiber is a state in which the length of the fiber protruding from a particular object, e.g. a carrier, is shorter than in the non-texturized state of the fiber, whereby the non-texturized state can be a state before the fiber was texturized or can be a state after the texturization when a stretching force is applied on the fiber.

[0016] According to embodiments, the artificial turf is a playing field surfaces for athletic games such as tennis, football, soccer, baseball, field hockey and golf, or is a landscaping artificial turf. In particular, the artificial turf may be a high-usage artificial turf.

Alternative A: Generating thatch yarn and face yarn fibers from fibers having been texturized to a different degree

[0017] In a further aspect, the invention relates to a method of producing an artificial turf. The method comprises:

• integrating texturized first fibers and texturized second fibers in a carrier such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first fibers are stronger texturized than the second fibers;
• stretching the first and second texturized fibers during and/or after their integration such that they are prevented from contracting to their respective default length;
• cutting the stretched first and second texturized fibers at the same length (L0);
• allowing the cut first and second fibers to contract to their respective default lengths, the contracted first texturized fibers providing texturized thatch yarn fibers protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second texturized fibers providing texturized face yarn fibers protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

[0018] Said features may be advantageous, as they allow using the same type of polymer material for the first and second fibers. The length difference may be achieved solely by different degrees of texturization of the fibers. Thus, for a given fiber material, different degrees of contraction and thus, different lengths of the fibers in their default state are achieved. This may allow choosing the polymer type freely in dependence on the particular needs of a given use case scenario, and freely defining the respective end length of the thatch yarn fibers and the face yarn fibers by differential texturization of the first and the second fibers. Thus, according to some embodiments, the first and second texturized fibers are made of the same material, e.g. PE or a particular form of PE or a particular PE comprising thread-like regions of PA surrounded by a compatibilizer as described for example in EP 3122942. According to other embodiments, the first and the second texturized fibers are made of different materials which may have identical or different capabilities to contract, e.g. shrink, in response to being exposed to a contraction-inducing condition as described later. However, the length differences of the first and second fibers are caused, according to embodiments of the invention, solely or partially by texturization of the first and second fibers differently.

[0019] Optionally, the length difference may in addition be modulated by differences in the material properties and/or by exposing the tufted fibers to condition which may reduce the length of the first and second fibers differently. Thus, embodiments of the invention represent a combination of the alternative A and the alternative B described below.

[0020] The stretching of the first and second fibers is a reversible stretching and the first and second fibers are adapted to contract, upon being cut, to their respective contracted state whose length is at least partially determined by the degree of their respective texturization.

Alternative B: Generating thatch yarn and face yarn fibers from fibers reversibly stretched such that the first fibers are stretched stronger than the second fibers

[0021] In a further aspect, the invention relates to a method of producing an artificial turf that comprises integrating texturized first fibers and texturized second fibers in a carrier such that the first and second texturized fibers protrude from the carrier in the same direction. The first fibers are texturized as strongly as the second fibers or are texturized stronger than the second fibers.

[0022] The method further comprises (reversibly) stretching the first and second texturized fibers during and/or after their integration such that they are prevented from contracting to their respective default length, whereby the first fibers are stretched stronger than the second fibers.

[0023] The method further comprises cutting the stretched first and second texturized fibers at the same length. For example, this can be performed right after or during the tufting process and the first and second texturized fibers may be stretched by the tufting needle(s) while being firmly fixed in the carrier.

[0024] The method further comprises allowing the cut first and second fibers to contract to their respective default lengths. The contracted first texturized fibers provide texturized thatch yarn fibers protruding from the carrier by a shared thatch yarn fiber height L2. The contracted second texturized fibers provide texturized face yarn fibers protruding from the carrier by a shared face yarn fiber height L3. The face yarn fiber height is larger than the thatch yarn fiber height.

[0025] Said features may be advantageous, because this approach may allow generating a two-layered artificial turf from first and second fibers which may be of identical or different materials and which may have identical or different degree of texturization. The height of the thatch yarn and of the face yarn is solely or predominantly determined by the different degree of the (reversible) stretching of the first and second fibers when being cut. In some examples, the first fibers are texturized stronger than the second fibers and/or the first fibers are made of a material that is adapted to (irreversibly) contract stronger when exposed to a contraction inducing condition, e.g. heat).

[0026] According to embodiments the stretching of the first and the second fibers is performed such that at least the second fibers are not stretched to their maximum length (i.e., to their fully expanded state) when being cut. Optionally, also the first fibers are not stretched to their maximum length (i.e., to their fully expanded state) when being cut.

[0027] The expression "first fibers being stretched stronger than the second fibers" as used herein implies that a larger "stretching force" (measured e.g. in Newton) is applied to the first fiber than to the second fiber.

[0028] To give one illustrative example, the first and second fibers are texturized to identical degree. 10 cm of the non-texturized first fibers may correspond to 5 cm of the texturized first fibers in their default (non-stretched) state. Likewise 10 cm of the non-texturized second fibers may correspond to 5 cm of the texturized second fibers in their default (non-stretched) state. The first and second texturized fibers are tufted in the carrier and a stretching force of 30 Newton is applied to the first fibers and a stretching force of 20 Newton is applied to the second fibers. As a result, 5 cm of the texturized first fiber may be (reversibly) stretched into 8 cm stretched texturized first fibers and 5 cm of the texturized second fiber may be (reversibly) stretched into 6.5 cm stretched texturized second fibers. When the first and second fibers are cut at a cutting height L0 6.5 cm away from the surface of the carrier, the first fibers will contract to their default length corresponding to a thatch yarn height of 3.5 cm and the second fibers will contract to their default length corresponding to a face yarn height of 5 cm.

Alternative C: Generating thatch yarn and face yarn fibers from fibers made of different materials with different capabilities to contract

[0029] In a further aspect, the invention relates to a method of producing an artificial turf. The method comprises:

• integrating first texturized fibers made of a first material and second texturized fibers made of a second material in a carrier such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first material is adapted to contract stronger than the second material upon being exposed to a contraction inducing condition;
• cutting the integrated first and second texturized fibers at the same length;
• exposing the cut first and second texturized fibers to the contraction inducing condition, the contraction inducing conditions causing the first and the second texturized fibers to contract, the contracted first fibers providing texturized thatch yarn fibers protruding from the carrier by a shared thatch yarn fiber height, the contracted second fibers providing texturized face yarn fibers protruding from the carrier by a shared face yarn fiber height, the face yarn fiber height being larger than the thatch yarn fiber height.

[0030] For example, the first and second fibers at the time of cutting are integrated in the carrier such that they are stretched and are prevented from contracting to their default length as described for embodiments of the invention according to alternative A or B. Likewise, the first and second fibers at the time of cutting are integrated in the carrier such that they are relaxed. In this case, the cutting will generate fibers which have identical length. However, the length of the first and second fibers will differ significantly in response to exposing the first and second fibers to the contraction inducing condition.

[0031] According to embodiments, the contraction inducing conditions cause the first and the second texturized fibers to irreversibly contract.

[0032] Embodiments according to alternative C may have the advantage that the tufting process is facilitated as it may not be necessary to stretch the fibers such that are not in their "default", i.e., contracted", length. Rather, it may be sufficient to cut the tufted fibers at a particular length and then chose the contraction inducing conditions such that a desired length difference between the first and second texturized fibers is achieved. This method may further have the advantage that it is more robust against undesired stretching effects that may be caused by the godets used for transporting the fibers during the fiber production, texturization and tufting process: In case one fiber should undesirably be textured stronger than desired during the tufting process due to a temperature or rotation speed of one or more godets that deviates from a desired temperature or rotation speed, this may easily be compensated by adjusting the contraction inducing conditions, e.g. raising or decreasing the temperature of an oven used for shrinking the fibers and/or prolonging or shortening the residence time of the artificial turf in the oven.

[0033] In a further beneficial aspect, generating fibers of different length based on different material properties of the fibers may increase the robustness of the production method against process parameter changes during fiber production and/or tufting.

[0034] According to embodiments, the method further comprises stretching the first and second fibers during and/or after their integration such that they are prevented from contracting to their respective default length. The first fibers are stretched as strongly as the second fibers or are stretched stronger than the second fibers when being cut. The first fibers and second fibers are cut to the same length L0 (cutting length, e.g. length between the surface of the carrier where the fibers are integrated and the cut).

[0035] Said features may be advantageous as cutting fibers in the stretched state may provide for a more fine-grained control of the resulting length than cutting a non-stretched fiber. This is because the material in a non-stretched, textured fiber is inhomogeneously distributed due to the curling and/or wrinkling of the textured fibers. Therefore, cutting a stretched fiber may ensure that the vast majority of the first fibers will have identical or very similar length and that the vast majority of the second fibers will have identical or very similar length right after the cutting and after the exposing of the fibers to the contraction inducing condition.

[0036] According to some embodiments, the first material is a polymer that is identical to a second polymer. The second polymer is used as the second material. The first fibers are texturized stronger than the second fibers. The contraction inducing condition is heat of a temperature adapted to irreversibly contract the stronger texturized first fibers to the thatch yarn fiber height L2 and adapted to irreversibly contract the less texturized second fibers to the face yarn fiber height L3.

[0037] According to some embodiments, the first material is different from a second polymer used in the second fibers as the second material. The degree of texturization of the first and second fibers is identical. The first polymer is adapted to contract stronger than the second polymer when heated. The contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height L2 and adapted to irreversibly contract the second fibers to the face yarn fiber height L3.

[0038] According to some embodiments, the first material is a first polymer that is different from a second polymer used in the second fibers as the second material. The first polymer is adapted to contract stronger than the second polymer when heated. The first fibers are texturized stronger than the second fibers. The contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height L2 and adapted to irreversibly contract the second fibers to the face yarn fiber height L3.

[0039] According to embodiments, the heat is a temperature in the range of 60°C-100°C, more preferentially in the range of 80°C-90°C.

[0040] In the following, features and steps will be described for alternative C that can likewise be applied for alternative A and alternative B unless they are incompatible with the features of the alternative A or the alternative B.

[0041] According to embodiments, the integration of the first and second fibers comprises tufting the first fibers, the second fibers, and one or more further fibers into the carrier.

[0042] For example, the further fibers can be stitch-in yarn fibers, and/or a lay-in yarn fibers.

[0043] The carrier can be, for example, an existing mesh, e.g. a synthetic fiber mesh or a plant fiber mesh (e.g. a jute mesh, a sisal mesh, or the like). Alternatively, the carrier can be a mesh generated dynamically by interweaving the first fibers, the second fibers, and/or one or more further fibers with each other such that parts of the first and second fibers form the mesh and other parts of the first and second fibers protrude from the mesh.

[0044] According to embodiments, the first fibers are integrated in the carrier in the form of first rows selectively comprising first dots. Each first dot selectively comprising first fibers. The second fibers are integrated in the carrier in the form of second rows selectively comprising second dots, each second dot selectively comprising second fibers. The first rows and second rows alternate and run in parallel to each other.

[0045] This may be advantageous as it eases or allows to expose the first and second fibers selectively to different contraction inducing conditions, e.g. exposing the first fibers in the first rows to higher temperatures than the second fibers in the second row, thereby triggering a stronger shrinkage of the first fibers than of the second fibers.

[0046] According to embodiments, the first and second rows respectively are straight lines.

[0047] According to embodiments, the first and second rows respectively are zig-zag lines. This may be advantageous as the first and second fibers are distributed more homogeneously in the artificial turf, thus preventing an unpredictable movement pattern of a ball along the artificial turf, preventing the formation of visible "stripes" in the artificial turf and letting the artificial turf appear more "natural".

[0048] According to embodiments, the exposing of the cut first and second texturized fibers to the contraction inducing condition comprising heating the first and the second rows such that contraction of the first and second fibers is induced. The first rows are heated to higher temperatures than the second rows for inducing a stronger contraction of the first fibers than the second fibers.

[0049] For example, the first rows can selectively be heated to 130-140°C and the second rows can selectively be heated to 75°C-85°C.

[0050] According to embodiments, the generation of the artificial turf further comprises applying a liquid backing on the side of the carrier opposite to the side from which the first and second fibers protrude. For example, the backing can be a liquid polyurethane reaction mixture or a latex mixture. The backing is applied to prevent, when solidified, detachment of the fibers after extended use of the artificial turf; and an underlayment positioned beneath the backing such that a stable base is provided for the artificial turf.

[0051] For example, the generation of the artificial turf can comprise, after having tufted the first and second textured fibers in the carrier such that the first and second textured fibers protrude from the upper side of the carrier, applying a liquid backing on the lower side of the carrier. Thereby, the liquid backing gets in contact with and wets the "U" shaped portions of the tufted fibers. The liquid backing can be, for example, polyurethane (PU) or latex. When the liquid backing solidifies, it firmly fixes the first and second fibers in the carrier. According to preferred embodiments, the solidification is performed in an oven. The artificial turf is transported, e.g. by a conveyor belt, continuously through the oven. The backing is in liquid state when the artificial turf enters the oven and is in solid or semi-solid state when it leaves the oven.

[0052] According to preferred embodiment, the process of heating the backing for accelerating its solidification is performed in an oven that is adapted to dynamically identify the position of the first and second rows of the artificial turf that is continuously transported through the oven. The oven comprises a plurality of heating elements that can be dynamically aligned with the different tuft rows of the artificial turf such that the heat generated by each of the heating elements selectively and predominantly reaches the one of the tuft rows that was aligned with said heating element. The heating elements can be controlled such that they apply higher temperature to the first rows than to the second rows, thereby inducing a stronger contraction of the first fibers than of the second fibers. The heating elements are positioned such that they apply the heat on the side of the carrier from which the thatch yarn fibers and the face yarn fibers protrude in basically orthogonal direction.

[0053] According to embodiments, the heating is performed in an oven which comprises a plurality of first and second heating elements. The oven further comprises a camera, a controller (e.g. one or more integrated circuits comprising the control logic, or a computer comprising software implementing a control logic) and a positioning element (e.g. robotic arms, a conveyor belt or combinations thereof). The heating comprises:

• continuously capturing, by the camera, images of the artificial turf while being moved through the oven;
• continuously analyzing, by the controller, the images for determining current positions of the first and second rows;
• continuously controlling, by the controller, the positioning element such that the positioning element positions the artificial turf and/or the first heating elements such that the first heating elements are aligned with the first rows and such that the positioning element positions the artificial turf and/or the second heating elements such that the second heating elements are aligned with the second rows;
• continuously controlling, by the controller, the first and second heating elements such that the first heating elements generate a higher temperature than the second heating elements.

[0054] For example, the heating elements can be infrared heating lamps that can be controlled individually. For example, the heating elements can be operatively coupled to the controller and can be configured to receive a control command from the controller, the control command being indicative of a desired temperature that is to be generated by the heating element receiving the control command. Each heating element is adapted to generate a temperature in its respective environment (e.g. within a radius of about 0.5-2 cm around the heating element) and the control command may specify any temperature in a range of 50°C-150°C.

[0055] In some embodiments, the heating elements can be re-positioned relative to each other and relative to a dynamically determined position of the tuft rows at the upper side of the artificial turf. The heating elements are positioned in the oven such that the heat generated by the heating elements is applied selectively or at least predominantly to the tuft row at the upper side of the carrier that was aligned to this heating element.

[0056] According to other embodiments, the position of the heating elements is not modified dynamically when the artificial turf is transported through the oven. For example, the heating elements can be fixed or can be re-positionable only when the oven is not in use. In this case, the distance and configuration of the heating elements must be adapted to the tuft row distance of the artificial turf that is to be transported through the oven. The adaptation can be performed permanently or in a configuration process that precedes the processing of a particular artificial turf in the oven.

[0057] Optionally, the oven may further comprise a heating element positioned below the lower side of the carrier for heating and solidifying the liquid backing.

[0058] Said features may be advantageous, because they allow applying different contraction inducing conditions on the first and second fibers, respectively, thereby inducing a different degree of contraction (here: shrinkage) of the first and second fibers. In a further beneficial aspect, energy may be saved as the heat is generated in spatial proximity to the tuft rows where the heat is used to cause the fibers to contract, and the heat is re-used for solidifying the backing. Thus, no extra step for generating different fiber length and for solidifying the backing may be required, thereby saving energy and increasing the speed of artificial turf production.

[0059] For example, the first heating elements may dynamically or statically be configured to heat the first texturized fibers contained in the first rows to 130-140 ° Celsius and the second heating elements may be configured to heat the second texturized fibers contained in the second rows to 75-85°C, preferably 80 °C.

[0060] According to embodiments, the first fibers and the second are integrated in the carrier in the form of rows, whereby each row comprises first and second dots in alternating order ("dot-wise-mixed rows"). Each first dot selectively comprises first fibers and each second dot selectively comprising second fibers. According to alternative embodiments, the first fibers and the second are integrated in the carrier in the form of rows, whereby each row comprises a random mixture of first and second fibers ("randomly mixed rows"). Mixed rows may be heated selectively by a single type of heating element as described above, thereby saving energy, but no differential heating can be applied in this case. However, the material of the first and second fibers may have a different shrinkage behavior at high temperatures. Thus, also fibers contained in mixed rows can be exposed to a contraction inducing condition that results in the generation of thatch yarn fibers and face yarn fibers having different, defined lengths.

[0061] The rows can have a distance to each other in a range of 7.5mm-11.5 mm, preferably in the range of 9mm-10 mm, for example.

[0062] According to embodiments, the method further comprises generating the first texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the first texturized fibers are created. Each first texturized fiber does not extend to its full potential height in the absence of a stretching force. In addition, or alternatively, the method comprises generating the second texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the second texturized fibers are created. Each second texturized fiber does not extend to its full potential height in the absence of a stretching force.

[0063] For example, the texturization of the first and/or second fibers can be performed with a venture nozzle as described, for example, in EP 17202272.5 and US4282637 A whose respective disclosure is incorporated herewith by reference. For example, a polymer fiber can be transported via a plurality of godets having different temperatures and/or rotation speeds, can be stretched, heated or otherwise processed for generating a texturized fiber. After the texturization, the texturized fibers are tufted or otherwise integrated in the carrier.

[0064] According to embodiments, the first and second texturized fibers respectively have a molecular memory of a curled, crumpled and/or wrinkled state.

[0065] According to embodiments, the shared thatch yarn fiber height (L2) is in the range of 10 mm to 30mm, preferably in the range of 15 mm to 25 mm.

[0066] According to embodiments, the shared face yarn fiber height (L3) is in the range of 31 mm to 50 mm, preferably in the range of 35 to 45 mm.

[0067] This may be advantageous, as this comparatively narrow tuft row width was observed to allow a good compromise between allowing to apply heat selectively to individual rows and providing a homogeneous, carpet-like surface that provides for a predictable, steady movement of objects, e.g. balls, over the surface.

[0068] According to embodiments, the first fibers are made of a first polymer and the second fibers are made of a second polymer, the first polymer being adapted to contract stronger than the second polymer in response to being exposed to the contraction inducing condition. The exposing of the cut first and second texturized fibers to the contraction inducing condition comprises heating the first and the second rows such that contraction of the first and second fibers is induced.

[0069] According to some embodiments, the first polymer is HDPE (high density polyethylene) and the second polymer is LLDPE (linear low density polyethylene).

[0070] According to alternative embodiments, the first polymer is PE, whereby the PE is free of PA. The second polymer is PE comprising thread-like regions of PA as described, for example, in EP 3122942.

[0071] According to alternative embodiments, the first polymer is PE comprising thread-like regions of PA as described, for example, in EP 3122942. The second polymer is polypropylene (PP) or polyamide (PA) or a mixture thereof.

[0072] The fibers can be heated, for example, in an oven for about 5 minutes to at least 80°C, preferably to 130°C-140°C.

[0073] Said exemplary combinations of different polymers may allow generating thatch yarn fibers and face yarn fibers having a clearly defined height simply by applying heat as the contraction inducing condition. In all three cases, the polymer type the first fibers are made from shrinks stronger under heat than the polymer type used for generating the second fibers.

[0074] According to embodiments, the first and second fibers are made of the same polymer or of different polymers. In case the first and second fibers are made of the same polymer, the first fibers must be stronger texturized than the second fibers in order to provide for thatch yarn and face yarn fibers having different length. However, even in case the materials used for the first and second fibers differ, the texturization of the two fibers may also differ. In this case, the different shrinkage behaviors of the materials and the differing degree of texturization may both contribute to the length difference of the fibers. In general, the stronger texturization of a fiber, the stronger the contraction of the fiber after the cutting of the fiber in stretched state.

[0075] According to one example, the first polymer is adapted to contract at least 20%, preferably at least 35% more than the second polymer upon heating the artificial turf fibers to a predefined temperature, e.g. above 80°C. the heating may be performed such that first and second fibers are heated to the same temperature. The heating can be performed in an oven, whereby the oven may in addition be used for hardening a liquid backing having been applied on the lower side of the artificial turf.

[0076] Applicant has observed that the shrinkage of artificial turf fibers strongly depends on the type of material (typically a polymer, e.g. a polyolefin) the fiber is made of. The different shrinkage properties of different polymers is partly due to the difference of density of polymers from the melt state and the cooled, rigid state. Shrinkage is a rate, so it is expressed in percent. Semi-crystalline polymers (e.g. polybutylene-terephthalate (PBT) or polypropylene (PP) show a higher shrinkage than amorphous polymers (e.g. polystyrol (PS) or polycarbonates (PC)), because when cooled down semi-crystalline polymers will see part of their macromolecular chains re-arranged to form crystallite, that is a well-organized structure, leading to less space needed for the same amount of atoms.

Artificial turf and fibers with low texture reversion

[0077] According to embodiments, the first texturized fiber and/or the second texturized fiber can be made of a polymer material that shows no texture reversion or a particularly low texture reversion. As a result thereof lifetime and/or durability of the artificial turf may be increased.

[0078] According to a first embodiment, the bulk polymer is polyethylene (PE) and the thread polymer is polyamide (PA). According to a second embodiment, the bulk polymer is polyethylene (PE) and the thread polymer is polyester. According to a third embodiment, the bulk polymer is polypropylene (PP) and the thread polymer is polyester. According to a fourth embodiment, the bulk polymer is polypropylene (PP) and the thread polymer is polyamide (PA). Said embodiments may have the advantage of delayed and/or reduced texture reversion of the thatch yarn fibers and/or the pile yarn fibers made from this polymer material.

[0079] For example, the first fiber and/or the second fiber can comprise (or consists of) a mixture of a bulk polymer and a thread polymer with an optional compatibilizer. The polymer mixture can comprise at least 30 weight percent of the bulk polymer and/or at least 10 weight percent of the thread polymer.

[0080] According to one embodiment, the bulk polymer is polyethylene (PE) and a thread polymer being polyamide (PA) and. The thread polymer may comprise at least 90 weight percent of PA. The bulk polymer can comprise at least 90 weight percent of PE. The polymer mixture used for generating the first and/or second fiber can comprise at least 30 weight percent of PE and/or at least 30 weight percent of PA. This embodiment can be advantageous, because it can provide for the textured artificial turf yarn with the aforementioned delayed and/or reduced texture reversion.

[0081] In another embodiment, the thread polymer comprises (or consists of) polyester and the bulk polymer comprises (or consists of) PE. The thread polymer may comprise at least 90 weight percent of polyester. The bulk polymer can comprise at least 90 weight percent of PE. The polymer mixture can comprise at least 30 weight percent of PE and/or at least 30 weight percent of polyester. This embodiment can be advantageous, because it can provide for the textured artificial turf yarn with the aforementioned delayed and/or reduced texture reversion.

[0082] In another embodiment, the thread polymer comprises (or consists of) polyester and the bulk polymer comprises (or consists of) polypropylene (PP). The thread polymer may comprise at least 90 weight percent of polyester. The bulk polymer can comprise at least 90 weight percent of PP. The polymer mixture can comprise at least 30 weight percent of PP and/or at least 30 weight percent of polyester. This embodiment can be advantageous, because it can provide for the textured artificial turf yarn with the aforementioned delayed and/or reduced texture reversion.

[0083] In another embodiment, the thread polymer comprises (or consists of) PA and the bulk polymer comprises (consists of) PP. The thread polymer may comprise at least 90 weight percent of PA. The bulk polymer can comprise at least 90 weight percent of PP. The polymer mixture can comprise at least 30 weight percent of PP and/or at least 30 weight percent of PA. This embodiment can be advantageous, because it can provide for the textured artificial turf yarn with the aforementioned delayed and/or reduced texture reversion.

[0084] In another embodiment, the polymer mixture further comprises a compatibilizer. The compatibilizer comprises any one of the following: 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 its 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; a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graft-polyamidepolyethylene or polyamide; and a polyacrylic acid type compatibalizer. The SEBS is styrene-ethylene-butylene-styrene. The EVA is ethylene-vinyl acetate. The EPD is polyamide-6 polymer. The EPDM is ethylene propylene diene monomer (M-class) rubber. The polymer mixture may comprise at least 10 weight percent of the compatibilizer. This embodiment may be advantageous, because it can provide for the polymer mixture which utilization results in manufacturing of the textured artificial turf yarn with the aforementioned delayed and/or reduced texture reversion.

[0085] In another embodiment, the polymer mixture is at least a four-phase system as described above and/or further in the text. This mixture can be prepared as described above and further in the text. The third polymer in this mixture may be any one of the following: polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The polymer mixture may comprise at least 20 weight percent of the third polymer. Utilization of these polymers and/or the aforementioned concentration of the third polymer may facilitate delaying and/or reducing texture reversion of the textured artificial turf yarn.

[0086] In another embodiment, the method comprises the following steps: extruding the polymer mixture into a monofilament yarn; quenching the monofilament yarn; heating the quenched monofilament yarn; stretching the heated monofilament yarn to deform the polymer beads into threadlike regions and to form the heated monofilament yarn into a stretched monofilament yarn; and texturing the stretched monofilament yarn to form the textured and stretched monofilament yarn to be used as the first and/or the second texturized fiber. This embodiment may be advantageous, because the deformation of the polymer beads into threadlike regions can facilitate delaying and/or reducing texture reversion of the textured artificial turf yarn.

[0087] According to embodiments, the method further comprises adding infill material on the already installed artificial turf such that the infill material fills the space between the thatch yarn fibers and filling at least 20% of the space between the face yarn fibers extending above the ends of the thatch yarn fibers. Thus, the infill layer may be as high as the pile height of the turf, but does not have to be so high, because the face yarn fibers are texturized and thus have a high rigidity and resilience and thus may not need the presence of an infill as high as the pile height of the artificial turf in order to stabilize the face yarn fibers.

[0088] In a further aspect, the invention relates to artificial turf generated by a method according to any one of the embodiments and examples described herein. Thus, any description of a method step that implicitly corresponds to a feature of the generated artificial turf shall also be considered as a specification of a feature of the resulting artificial turf and its components.

[0089] An "infill" as used herein is material, typically sand or rubber granules that is added on top of an artificial turf layer and fills the space between fibers for ballast and cushion.

[0090] "Extrusion" as used herein is the process of transforming liquid plastic into individual solid fibers by pushing the liquid plastic through a fixed cross sectional profile that is designed to form a monofilament or film that may then be processed to generate an artificial turf yarn fiber.

[0091] A "thatch yarn" as used herein is yarn used with different colors that is situated below the face yarn to enhance recovery.

[0092] A "face yarn" (or "pile yarn") as used herein is the yarn that forms the pile of the artificial turf and that protrudes from the carrier of the artificial turf farther than any other type of yarn contained in the artificial turf, if any, thereby determining the pile height of the artificial turf.

[0093] The term "tufting" as used herein is a sub-process in the manufacturing of artificial turf that comprises pressing (e.g. by using pneumatic force) a U-shaped piece of yarn through a carrier, e.g. a carrier mesh or other form of carrier structure. In state of the art tufting processes, the height of the pile is altered solely by cutting the yarn shorter or leaving it longer. To the contrary, according to embodiments of the invention, artificial turf fibers are stretched while being cut and/or are subjected to contraction inducing condition that modulates the height of first and second fibers differently such that a thatch yarn layer with a homogeneous fiber length and a face yarn layer with a different homogeneous fiber length is generated.

[0094] The length "L0" may also be referred to as "cutting length" and is the distance between the point where the first and second texturized fibers are respectively integrated in the carrier and the point where they are cut.

[0095] A "texturized" fiber as used herein is a fiber that has a molecular memory of a textured state, wherein a textured state can be, for example, a curled, crumpled and/or wrinkled state. The expression "fibers sharing a fiber height" as used herein means that the fibers have identical or basically identical height. Preferably, the height deviations of the fibers is below 6% of the fiber length, preferably below 2.5% of the fiber length.

[0096] A fiber that is "stronger texturized" than another fiber is a fiber that, provided that both fibers have the same length in their non-textured, fully expanded state, contracts to a contracted length that is shorter than the contracted length of the other fiber. A fiber that is texturized 10% stronger than another fiber is a fiber that, provided that both fibers have the same length in their non-textured, fully expanded state, contracts to a contracted length that is 10% shorter than the contracted length of the other fiber.

[0097] The "texture reversion" (or "texturing reversion") of a textured (curled) artificial turf yarn is, as understood herein, a process of smoothing out of the crimps of the textured (curled) artificial turf yarn, when the textured (curled) artificial turf yarn is subjected to a mechanical and/or weathering stress. The mechanical stress can be caused by sportsmen using the artificial turf with the textured (curled) artificial turf yarn. The weathering stress can be caused by weather conditions at place where the artificial turf with the textured (curled) artificial turf yarn is installed. The weathering stress comprises at least one of the following: temperature changes, water exposure, snow exposure, icing, light exposure (in particular ultraviolet light exposure). For instance, the properties of the textured turf yarn of an artificial turf (e.g. softness and voluminous appearance) can degrade throughout its lifetime/utilization due to the texture reversion. The phenomenon of the texture reversion is a newly observed effect, which is not yet reported in the state of art literature. For instance the publication "Ribbon curling via stress relaxation in thin polymer films" discloses an observation that the texturing of the filament made of polymer film remains permanent ("Ribbon curling via stress relaxation in thin polymer films", Proceedings of the National Academy of Sciences of the United States of America, vol. 113, no. 7, pp. 1719-1724, http://www.pnas.org/content/113/7/1719). The texture reversion of a fragment of a single textured artificial turf yarn, which may be integrated into an artificial turf backing, can be assessed by employing the following example method: hanging the fragment, such that the fragment is unfolded by gravity in a vertical direction; measuring a distance D1 between the ends of the hanged fragment; subjecting the fragment to a mechanical and/or weathering stress, which may be caused by utilization of an artificial turf comprising said fragment and said artificial turf backing; performing the following after the subjecting of the fragment to the mechanical and/or weathering stress: hanging the fragment, such that the fragment is unfolded by gravity in the vertical direction; measuring a distance D2 between the ends of the hanged fragment. A first value characterizing the texture reversion can be determined according to the following equation: (D2-D1)/D1. A second value characterizing the texture reversion can be determined according to the following equation: (D2-D1)(/D1*T), wherein T is a time interval between the aforementioned measurements of distances D1 and D2. The first and/or the second value can be used for optimization of manufacturing tools for manufacturing of the textured artificial turf yarn, parameters of processes for manufacturing of the textured artificial turf yarn, phase and/or chemical composition of filaments used as an ingot for manufacturing of the textured artificial turf yarn. The optimization can be targeted towards reduction in the first and/or second value, whereas fragments of different filaments are subjected to the same (test) mechanical and/or weathering stress, wherein the different filaments are manufactured using different tools, different process parameters, and/or different ingots. A similar approach can be implemented using characteristic values of fiber texturing generated using the aforementioned optical means.

Brief description of the drawings

[0098] In the following embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings in which:

Figure 1

depicts a cross-sectional view of a state-of-the-art artificial turf.

Figure 2

depicts a cross-sectional view of an artificial turf according to an embodiment of the invention.

Figure 3

depicts a cross-sectional view of an artificial turf according to another embodiment of the invention.

Figure 4

depicts flowcharts of three alternative methods of producing artificial turf according to embodiments of the invention.

Figure 5

depicts three alternative ways how first and second textured fibers can be integrated in a carrier.

Figure 6

depicts the process of tufting, stretching and cutting textured fibers according to embodiments of the invention.

Figure 7

depicts a block diagram of an oven adapted to heat fibers contained in different tuft rows differently.

[0099] Figure 1 depicts a cross-sectional view of a state-of-the-art artificial turf 100. It comprises straight, non-texturized face yarn fibers 104 having a pile height L3, and a zone of texturized thatch yarn fibers 106. The thatch yarn fibers have a height L2 that is shorter than the height L3 of the face yarn fibers. The difference between the height of the face yarn fibers and of the thatch yarn fibers is depicted as "L1".

[0100] Figure 2 depicts a cross-sectional view of an artificial turf 200 according to an embodiment of the invention. The artificial turf 200 comprises texturized thatch yarn fibers 206 having a height L2 and texturized face yarn fibers 204 having a height L3. The thatch yarn fibers are shorter than the face yarn fibers by a length L1. The face yarn fibers and thatch yarn fibers are integrated, e.g. tufted, in a carrier 202, e.g. a mesh made of synthetic or plant-based materials. In addition, the artificial turf 200 may comprise a fill layer and/or a backing as depicted, for example, in figure 3.

[0101] The face yarn defines the pile height of the artificial turf and provides the rolling resistance for the rolling ball. The thatch yarn serves the purpose of holding or immobilizing the infill, if any, and prevent or reduce splashing and limit redistribution of the infill when the artificial turf is in use, thereby preventing an uneven distribution of the infill.

[0102] Figure 3 depicts a cross-sectional view of an artificial turf 300 according to another embodiment of the invention. The artificial turf 300 comprises a backing 310, e.g. a layer of solidified latex or polyurethane having been added in liquid state onto the lower side of the carrier 202 after the fibers 204, 206 have been tufted into the carrier. The side of the carrier 202 from which the fibers 204, 206 protrude is referred herein as the "upper side" of the carrier/of the artificial turf, while the other side, where only u-shaped portions of the fibers forming tuft knots and/or a secondary backing 310 may be visible, is referred herein as the "lower side" of the artificial turf.

[0103] The artificial turf 300 comprises a backing 310, e.g. a layer of hardened latex or polyurethane, that contacts and surrounds the U-shaped fibers on the lower side of the artificial turf, thereby strongly fixing the fibers in the carrier.

[0104] In addition, the artificial turf 300 comprises a filler material 308, e.g. a sand-rubber-granule mixture. The infill may fill free space between thatch yarn fibers and/or face yarn fibers in the thatch yarn zone as well as in the face yarn zone. As the face yarn is texturized, it is not necessary to have an infill height that almost reaches the tips of the face yarn fibers in order to stabilize the fibers. Rather, it may be possible to use an infill layer whose upper surface is one or more cm below the pile height L3. Thanks to a combination of textured face yarn fibers and thatch yarn fibers, the infill granules are stabilized and are protected from being delocalized by a ball or other object hitting the surface of the artificial turf. Moreover, thanks to the random orientation of the texturized face yarn fibers, an artificial turf with a more homogeneous surface is provided that increases the predictability and directional stability of any object rolling or sliding over the surface of the artificial turf.

[0105] Figures 2 and 3 show the texturized fibers 204, 206 in their relaxed, default state. The length of the fibers in this state is shorter than in a stretched, expanded state, due to their texturization.

[0106] The fibers 204, 206 can be textured monofilaments or textured split film tapes or bundles of textured monofilaments or textured split film tapes. Preferably, the fibers of the face yarn are made of a mixture of PE/PA with compatibilizer as disclosed in EP 3122942. Surprisingly PE/PA monofilaments have the following advantages in this context: the texturing has more long term stability even if subjected to mechanical stress and weathering (sunshine). The thatch yarn can be made of PE monofilaments (in particular LLDPE) or another material as it is less stressed both mechanically and by weathering. Moreover, thatch yarn lacking PA may shrink stronger if exposed to heat. This effect may be used for generating an artificial turf with two types of texturized fibers which are adapted to form a thatch yarn zone of a clearly defined, uniform fiber height L2, and for generating face yarn fibers having a defined, uniform fiber height L3 although also the face yarn fibers are texturized.

[0107] Figure 4 depicts flowcharts of three alternative methods of producing artificial turf according to embodiments of the invention.

[0108] Figure 4A depicts a method of producing an artificial turf 200, 300, 500, 520, 530 according to "alternative A" embodiments. This alternative is based on length difference of the thatch yarn fibers and the face yarn fibers which completely or at least partially result from a different degree of texturization of first and second fibers.

[0109] First in step 402, texturized first fibers 602 and texturized second fibers 604 are integrated, e.g. tufted, in a carrier 202 such that the first and second texturized fibers protrude from the carrier in the same direction. This direction is also referred to as the "upper side" of the artificial turf. The first fibers are stronger texturized than the second fibers. According to embodiments, the first fiber is texturized at least 10%, preferably at least 20%, preferably, at least 30% stronger than the second fiber.

[0110] For example, the first and second fibers can be air texturized, for example, with a venture nozzle adapted to generate a texturizing air jet. For example, US4282637A describes a Venturi type nozzle for the texturization of yarns. The nozzle includes a hollow body which compressed air is fed, a needle housed therein to which yarn is fed, and a plug. The needle is provided with a longitudinal passage for the yarn. The air passes between the body and the needle, and yarn and air pass through a passage shaped like a Venturi cone in the plug. Mutually facing portions of the needle head and of the plug have frusto-conical surfaces. The nozzle is adapted to produce a texturization effect on the yarn.

[0111] Next in step 404, the first and second fibers are stretched. The stretching in step 404 is performed while or after the first and second texturized fibers are integrated in the carrier. For example, the stretching can be performed by a tufting needle that still holds the fibers after their integration in the carrier. Preferably, the first and second fibers are respectively stretched to their maximum possible length (their fully expanded length) when they are cut to allow for a tight control of the length of the resulting thatch yarn and face yarn fibers. When fully stretched, the first and second fibers may appear to be non-texturized, but the fibers have a molecular memory that will cause the fibers to contract to their default, texturized state as soon as the stretching force is no longer applied on the fibers. The stretching force applied in step 404 prevents the first and second fibers from contracting to their respective default length. In some embodiments, it is necessary to apply different stretching forces on the first and the second fibers in order to ensure that the first and second fibers respectively are stretched and expanded to their respective maximum possible length.

[0112] Next in step 406, the stretched first and second fibers are cut at the same length L0. The "same length" here means the length of the fibers in fully expanded state. For example, a tufting needle used for tufting the fibers may comprise or be coupled to a knife or a scissor adapted for automatically cutting the tufted, maximally stretched first and second fibers at the same length.

[0113] Next in step 408, the cut first and second fibers are allowed to contract to their respective default (contracted) lengths. The contraction is induced by the molecular memory of the fibers that causes the fibers to contract into the curled state defined during the texturization of the respective fibers. The contracted first texturized fibers provide texturized thatch yarn fibers 206 protruding from the carrier by a shared thatch yarn fiber height L2. The contracted second texturized fibers provide texturized face yarn fibers 204 protruding from the carrier by a shared face yarn fiber height L3. The face yarn fiber height is larger than the thatch yarn fiber height.

[0114] Figure 4B depicts a method of producing an artificial turf 200, 300, 500, 520, 530 according to "alternative B" embodiments. This alternative is based on length differences of the thatch yarn fibers and the face yarn fibers which completely or at least partially result from different degrees of reversibly stretching the first and second fibers, whereby the first fibers are reversibly stretched stronger in step 430 than are the second texturized fibers. The first and second fibers may be made of the same material or of different materials. The first and second fibers may be texturized to the same degree or the first fibers may be texturized stronger than the second fibers. Alternative B is characterized in that the length difference of the face yarn fibers and of the thatch yarn fibers are solely or at least partially generated by the stronger reversibly stretching of the first than of the second fibers in sep 430. All other steps correspond to the steps described for alternative A, whereby in step 402 it is also possible to use first and second fibers having the same degree of texturization.

[0115] Figure 4C depicts a method of producing an artificial turf 200, 300, 500, 520, 530 according to "alternative C" embodiments. This alternative is based on length differences of the thatch yarn fibers and the face yarn fibers which completely or at least partially result from different materials used for producing the first and the second fibers, whereby the different materials have different capabilities to contract in response to a contraction-inducing condition.

[0116] In step 420, first texturized fibers made of a first materiel and second texturized fibers made of a second material are integrated in a carrier 202. For example, the fibers can be integrated by a respective tufting needle in a tufting process. The first and second texturized fibers are integrated such that the first and second texturized fibers protrude from the carrier in the same direction. The first material is adapted to contract stronger than the second material upon being exposed to a contraction inducing condition.

[0117] Next in step 424, the integrated first and second texturized fibers are cut at the same cutting length L0 as described already for alternative A.

[0118] Next in step 426, the cut first and second texturized fibers are exposed to a defined contraction inducing condition. The contraction inducing conditions causes the first and the second texturized fibers to contract. For example, the contraction inducing condition may be heat of 80°C or higher, as described with reference to figure 7. In some embodiments, the contraction inducing condition may be chosen differently for the first and second fibers. For example, the first fiber may be heated to higher temperatures and/or for a longer duration than the second texturized fibers, thereby causing the first texturized fibers to contract stronger than the second texturized fibers. The contracted first fibers provide texturized thatch yarn fibers 206 protruding from the carrier by a shared thatch yarn fiber height L2. The contracted second fibers provide texturized face yarn fibers 204 protruding from the carrier by a shared face yarn fiber height L3. The face yarn fiber height is larger than the thatch yarn fiber height.

[0119] As is indicated by the dotted boxes of steps 404 and 408 in figure 4B, the method of producing artificial turf according to embodiments of the invention can comprise combinations of the steps of both methods, thereby providing a better control of the length difference of the textured thatch yarn fibers and the texturized face yarn fibers.

[0120] Figure 5 depicts three alternative ways how first and second textured fibers can be integrated in a carrier 202.

[0121] Figure 5A depicts an artificial turf 500 wherein texturized face yarn fibers and texturized thatch yarn fibers are tufted in straight parallel rows. Thatch yarn fiber rows ("B"), 502 and face yarn fiber rows ("A") 504 are alternating in the plane of the artificial turf. The face yarn fibers are longer than the thatch yarn fibers. The fibers are integrated into the carrier 202 by a tufting process, whereby bundles of fibers of the same type are tufted into the carrier and are then cut. Each row 502, 504 comprises only fibers of one particular type, i.e., either thatch yarn fibers or face yarn fibers.

[0122] The distance between tufting rows of the same fiber type can be e.g. 1.9 cm and can be about 0,95 cm between neighboring rows of face/thatch yarn.

[0123] Figure 5B depicts another artificial turf 520 wherein texturized face yarn fibers and texturized thatch yarn fibers are tufted in parallel, zig-zag rows. Thatch yarn fiber rows 508 and face yarn fiber rows 506 are alternating in the plane of the artificial turf. Each row 506, 508 comprises only fibers of one particular type, i.e., either thatch yarn fibers or face yarn fibers.

[0124] Using texturized face yarn fibers reduces the anisotropy of the roll resistance of the artificial turf. Zigzag rows are particularly advantageous in this context as they reduce the anisotropy of the roll resistance of the artificial turf even more.

[0125] Figure 5C depicts another artificial turf 530 wherein face yarn fibers and thatch yarn fibers are tufted in parallel, mixed type (or "mixed") rows 510, 512 Each row comprises a mixture of both texturized face yarn fibers and texturized thatch yarn fibers. For example, each row may comprise a mixture of thatch yarn fiber bundles and face yarn fiber bundles. Alternatively, each row may comprise a mixture of face and thatch yarn fibers which are individually tufted into the carrier. Still alternatively, each row may comprise tuft bundles respectively comprising a mixture of thatch yarn fibers and face yarn fibers.

[0126] Figure 6 depicts the process of tufting, stretching and cutting textured fibers according to embodiments of the invention.

[0127] A first tufting needle (not shown) can tuft a first texturized fiber 602 into a carrier 202. During the tufting, or after the first fiber was tufted into the carrier, the first fiber is stretched. Preferably, the stretched, expanded first fiber is at least 10%, more preferably at least 20%, more preferably at least 50% longer than in its default, contracted state. The stretching can be performed, for example, by a plurality of godets 608 within or external to the tufting needle which apply a pulling force on the tufted first fiber in basically orthogonal direction away from the carrier 202.

[0128] A second tufting needle (not shown) can tuft a second texturized fiber 604 into the carrier 202. During the tufting, or after the second fiber was tufted into the carrier, the second fiber is stretched. Preferably, the stretched, expanded second fiber is at least 10%, more preferably at least 20%, more preferably at least 50% longer than in its default, contracted state. The stretching can be performed, for example, by a plurality of godets 610 within or external to the tufting needle which apply a pulling force on the tufted second fiber in basically orthogonal direction away from the carrier 202.

[0129] The tufting process is illustrated for individual fibers. However, the tufting process can likewise be performed for bundles of fibers.

[0130] Then, the stretched texturized first and second fibers 602, 604 or one or more bundles thereof are cut, preferably in a single cutting operation at the same length L0 above the carrier as indicated by the scissor and the dotted lines.

[0131] The cut first fiber 602 contracts to its default state, thereby providing a texturized thatch yarn fiber 602' having a height L2 above the carrier structure 202'.The fiber 604 contracts to its default state, thereby providing a texturized face yarn fiber 604' having a height L1+L2=L3 ("pile height") above the carrier structure 202'.

[0132] According to preferred embodiments, the first and the second texturized fibers are stretched to their full length such that they appear to be non-texturized fibers. Thus, the first and the second fibers are cut when stretched to their maximum possible, fully expanded length. Thus, the first and second fibers are cut to the same, fully expanded length. Only in response to the fibers contracting to their respective default states and/or by exposing the fibers to a contraction inducing condition, a defined length difference of the two fiber types is generated. Cutting the first and second fibers when expanded completely to their respective maximum length may have the advantage that the fibers are cut in a clearly reproducible state and that the effective lengths L1, L3 of the contracted fibers are identical or highly similar, i.e., show only a very low length variability.

[0133] For example, stretched, texturized first and second fibers 602, 604 may be cut when respectively being in fully expanded state. The texturized look of the expanded fibers 602, 604 in figure 6 is just for illustration that the first and second fibers are texturized and have a "molecular memory" of a texturized fiber. When the fibers are expanded to their maximum expandable length, they may still have a slightly wrinkled appearance, but in many cases the fully expanded fibers will have the same or a similar appearance as a non-texturized fiber. In this case, the tufted face yarn fiber 604' and the tufted thatch yarn fiber 602' have different lengths in their default, contracted state, but have identical lengths if stretched to their completely expanded state. For example, the thatch yarn fiber length L1 in default, contracted state can be about 20 mm and the face yarn fiber length L3 in default, contracted state can be about 40 mm.

[0134] In some embodiments, the first and the second fibers are made of the same material. In this case, the length difference of the face yarn and the thatch yarn is obtained solely based on the different degrees of texturization of the first and second fibers, because stronger texturization results in a stronger contraction of the fibers upon being cut, and in a shorter length in the contracted default state of a fiber.

[0135] This may be accomplished by using identical yarn for the thatch and pale portions and using different degrees of texturing to produce the different lengths when relaxed. It can also be done by using different yarn using an identical texturing process or varying both the material and the texturing.

[0136] The first and second texturized fibers can be made of the same type of polymer, e.g. polyethylene (PE), or of a mixture of miscible polymers, or a polymer mixture of immiscible polymers.

[0137] In accordance with embodiments, the polymer mixture used for generating the second fibers to be turned into face yarn fibers is at least a three-phase system, wherein the polymer mixture comprises a first polymer, a second polymer, and a compatibilizer. The first polymer and the second polymer are
immiscible. The first polymer forms polymer beads surrounded by the compatibilizer within the second polymer as disclosed in EP3122942 the entirety of which being expressly herein incorporated by reference. The second polymer may be a PE and the first polymer can be polyamide (PA). The polymer mixture used for generating the first fibers to be turned into thatch yarn fibers can be made of PE that is free of any PA. The PAs beads may provide some stability and rigidity to the second fibers, thereby reducing the ability of the second fibers to contract, e.g. in response to heat.

[0138] Figure 7 depicts a block diagram of an oven 700 adapted to heat fibers contained in different tuft rows differently. The artificial turf may be generated in a fully or semi-automated process. For example, the carrier may be transported, via godets and/or conveyor belts, to a tufting unit where first and second fibers are tufted into the carrier as illustrated, for example, in figures 5 and 6. Also the cutting of the tufted fibers may be performed in the tufting unit. Then, the carrier comprising the tufted fibers is transported further to a further unit where the liquid backing is applied on the lower part of the artificial turf. For example the backing can be applied via a "knife over roll" technique and/or can be sprayed on the backing. The liquid backing is allowed to wet the U-shaped portions of the fibers at the lower side of the carrier and may even be allowed to partially penetrate the openings of the carrier 202, e.g. a carrier mesh. Then, the artificial turf with the still liquid backing is transported automatically into the oven 700.

[0139] According to one embodiment, the oven comprises a camera 706 adapted to continuously capture images of the turf that is currently transported through and processed in the oven. The oven further comprises a plurality of heating elements 702, 704 and a controller. The Heating elements may comprise first heating elements 702 and second heating elements 704. The oven may further comprise one or more positioning elements 710 that are interoperatively coupled with the controller 708 and are adapted to position the individual heating elements and the tufting rows 502, 504 relative to each other such that first heating elements are selectively aligned to first rows and second heating elements are selectively aligned to second rows.

[0140] Optionally, the oven can in addition comprise a backside heating element 712 for heating the backing of the artificial turf in order to accelerate the hardening of the liquid backing. In some embodiments, the solidification of the backing is performed in a different oven than the heating of the fibers for inducing a differential contraction of the fibers. However, performing both steps in the same oven may be advantageous as this allows to save energy and accelerate the production process.

[0141] The controller 708 is configured to control the first and second heating elements such that the first heating elements generate a higher temperature than the second heating elements. As a result, the texturized artificial turf fibers in the first rows contract stronger in response to the heat than the second fibers. The first texturized fibers provide the texturized thatch yarn fibers and the second texturized fibers provide the texturized face yarn fibers. Thus, the stronger heat-induced contraction of the first fiber may alone or in combination with differences in the degree of texturization contribute to the length difference of the face yarn fibers and the thatch yarn fibers.

[0142] According to embodiments, the first heating elements generate heat that is adapted to selectively or predominantly heat the first tuft rows 502 to about 130-140 °C. The second heating elements generate heat that is adapted to selectively or predominantly heat the second tuft rows 504 to about 80 °C, thereby causing the first texturized fibers in the first rows to shrink stronger than the fibers in the second rows. Moreover, in some embodiments, the first texturized fibers in the first rows can be of a material that shrinks stronger at a given temperature than the material of the second fibers. For example, the material of the first texturized fiber can be pure PE and the material of the second texturized fibers can be a mixture of PE/PA. The first fibers can be made of PE (in particular LLDPE) or a similar material as it is less stressed both mechanically and by weathering. Moreover, in some embodiments, the first texturized fibers in the first tuft rows are texturized stronger than the texturized fibers in the second rows.

Listofreferencenumerals

[0143] 

100

state-of-the-art artificial turf

104

straight, non-texturized face yarn fibers

106

texturized thatch yarn fibers

200

artificial turf with texturized face yarn and thatch yarn fibers

202

carrier

204

texturized face yarn fibers

206

texturized thatch yarn fibers

L0

cut height above the tuft knot

L1

height of the portion of the face yarn fibers extending above the ends of the thatch yarn fibers

L2

height of the thatch yarn fibers

L3

pile height

300

artificial turf with texturized face yarn and thatch yarn fibers

308

filler material

310

backing

402-408

steps

420-430

steps

500

artificial turf with straight, alternating tuft rows

502

first rows comprising thatch yarn fibers

504

second rows comprising face yarn fibers

520

artificial turf with zig-zag turf rows

506

second rows comprising face yarn fibers

508

first rows comprising thatch yarn fibers

530

artificial turf with mixed-type turf rows

510

tuft row comprising a mixture of first and second fibers

512

tuft row comprising a mixture of first and second fibers

602

stretched, texturized first fiber

604

stretched, texturized second fiber

608

godets for the first fiber

610

godets for the second fiber

700

oven

702

first heating elements

704

second heating elements

706

camera

708

controller

710

positioning elements

712

backside heating element

Claims

1. An artificial turf (200, 300, 500, 520, 530) comprising:

- textured thatch yarn fibers (206);

- textured face yarn fibers (204); and

- a carrier (202),

wherein the face yarn fibers are integrated in the carrier such that the thatch yarn fibers protrude from the carrier by a shared thatch yarn fiber height (L2), wherein the thatch yarn fibers are integrated in the carrier such that the face yarn fibers protrude from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

2. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- Integrating (402) texturized first fibers (602) and texturized second fibers (604) in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first fibers are stronger texturized than the second fibers;

- Stretching (404) the first and second texturized fibers during and/or after their integration such that they are prevented from contracting to their respective default length;

- cutting (406) the stretched first and second texturized fibers at the same length (L0);

- allowing (408) the cut first and second fibers to contract to their respective default lengths, the contracted first texturized fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second texturized fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

3. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- integrating (402) texturized first fibers (602) and texturized second fibers (604) in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first fibers are texturized as strongly as the second fibers or are texturized stronger than the second fibers;

- stretching (430) the first and second texturized fibers during and/or after their integration such that the first fibers are stretched stronger than the second fibers;

- cutting (406) the stretched first and second texturized fibers at the same length (L0);

- allowing (408) the cut first and second fibers to contract to their respective default lengths, the contracted first texturized fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second texturized fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

4. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- integrating (402) first texturized fibers made of a first materiel and second texturized fibers made of a second material in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first material is adapted to contract stronger than the second material upon being exposed to a contraction inducing condition;

- cutting(406) the integrated first and second texturized fibers at the same length (L0);

- exposing(426) the cut first and second texturized fibers to the contraction inducing condition, the contraction inducing conditions causing the first and the second texturized fibers to contract, the contracted first fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

5. The method of claim 4, the first material being selected from a group comprising:

- a polymer that is identical to a second polymer, the second polymer being used as the second material, wherein the first fibers are texturized stronger than the second fibers, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the stronger texturized first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the less texturized second fibers to the face yarn fiber height (L3);

- a first polymer that is different from a second polymer used in the second fibers as the second material, wherein the degree of texturization of the first and second fibers is identical, wherein the first polymer is adapted to contract stronger than the second polymer when heated, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the second fibers to the face yarn fiber height (L3);

- a first polymer that is different from a second polymer used in the second fibers as the second material, wherein the first polymer is adapted to contract stronger than the second polymer when heated, wherein the first fibers are texturized stronger than the second fibers, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the second fibers to the face yarn fiber height (L3).

6. The method of producing an artificial turf according to claim 4, further comprising:

- stretching the first and second fibers during and/or after their integration such that they are prevented from contracting to their respective default length;

wherein the first fibers are stretched as strongly as the second fibers or are stretched stronger than the second fibers when being cut.

7. The method of any one of claims 2-6, the integration of the first and second fibers comprising tufting the first fibers, the second fibers, and one or more further fibers into the carrier.

8. The method of any one of claims 2-7,

- the first fibers being integrated in the carrier in the form of first rows (502) selectively comprising first dots, each first dot selectively comprising first fibers;

- the second fibers being integrated in the carrier in the form of second rows (504) selectively comprising second dots, each second dot selectively comprising second fibers;

- the first rows and second rows alternating and being parallel to each other.

9. The method of claim 8, the first and second rows respectively being straight lines.

10. The method of claim 8, the first and second rows respectively being zig-zag lines.

11. The method of any one of claims 4-10, wherein the exposing of the cut first and second texturized fibers to the contraction inducing condition comprising heating the first and the second rows such that contraction of the first and second fibers is induced, whereby the first rows are heated to higher temperatures than the second rows for inducing a stronger contraction of the first fibers than the second fibers.

12. The method of claim 11, the heating being performed in an oven, the oven having a plurality of first heating elements (702), a plurality of second heating elements (704), a camera (706), a controller (708) and a positioning element (710), the heating comprising:

- continuously capturing, by the camera, images of the artificial turf while being moved through the oven;

- continuously analyzing, by the controller, the images for determining current positions of the first and second rows;

- continuously controlling, by the controller, the positioning element such that the positioning element positions the artificial turf and/or the first heating elements such that the first heating elements are aligned with the first rows and such that the positioning element positions the artificial turf and/or the second heating elements such that the second heating elements are aligned with the second rows;

- continuously controlling, by the controller, the first and second heating elements such that the first heating elements generate a higher temperature than the second heating elements.

13. The method of any one of claims 2-7,

- the first fibers and the second being integrated in the carrier in the form of rows, each row comprising first and second dots in alternating order, each first dot selectively comprising first fibers, each second dot selectively comprising second fibers; or

- the first fibers and the second being integrated in the carrier in the form of rows, each row comprising a random mixture of first and second fibers.

14. The method of any one of claims 2-13, further comprising:

- generating the first texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the first texturized fibers are created, each first texturized fiber not extending to its full potential height in the absence of a stretching force; and/or

- generating the second texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the second texturized fibers are created, each second texturized fiber not extending to its full potential height in the absence of a stretching force.

15. The method of any one of claims 2-14, wherein the first and second texturized fibers respectively have a molecular memory of a curled, crumpled and/or wrinkled state.

16. The method of any one of claims 2-15, wherein the shared thatch yarn fiber height (L2) is in the range of 10 mm to 30mm, preferably in the range of 15 mm to 25 mm; and/or wherein the shared face yarn fiber height (L3) is in the range of 31 mm to 50 mm, preferably in the range of 35 to 45 mm.

17. The method of any one of claims 2-16, wherein the first fibers are made of a first polymer and the second fibers are made of a second polymer, the first polymer being adapted to contract stronger than the second polymer, the exposing of the cut first and second texturized fibers to the contraction inducing condition comprising heating the first and the second rows such that contraction of the first and second fibers is induced.

18. The method of claim 17,

- wherein the first polymer is HDPE and the second polymer is LLDPE; or

- wherein the first polymer is PE being free of PA and the second polymer is PE comprising thread-like regions of PA; or

- wherein the first polymer is PE comprising thread-like regions of PA and the second polymer is PP or PA or a mixture thereof.

19. The method of any one of claims 2-18, wherein the first and second fibers are made of the same polymer or of different polymers and wherein the first fibers are stronger texturized than the second fibers.

20. The method of any one of claims 2-19, further comprising adding filler material (308), the infill material filling the space between the thatch yarn fibers and filling at least 20% of the space between the face yarn fibers extending above the ends of the thatch yarn fibers.

21. The method of any one of claims 2-20, wherein the first and/or the second texturized fiber is made of a polymer mixture comprising a bulk polymer and a thread polymer,

- wherein the bulk polymer is polyethylene (PE) and the thread polymer is polyamide (PA); or

- wherein the bulk polymer is polyethylene (PE) and the thread polymer is polyester; or

- wherein the bulk polymer is polypropylene (PP) and the thread polymer is polyester; or

- wherein the bulk polymer is polypropylene (PP) and the thread polymer is polyamide (PA).

Amended claims

Amended claims in accordance with Rule 137(2) EPC.

1. An artificial turf (200, 300, 500, 520, 530) comprising:

- textured thatch yarn fibers (206) made of a first material;

- textured face yarn fibers (204) made of a second material; and

- a carrier (202),

wherein a textured fiber is a fiber having a molecular memory of a textured state, wherein the textured state is a curled, crumpled and/or wrinkled state, wherein the molecular memory is a tendency to turn into the textured state if the fiber is allowed to do so, wherein the length of a fiber in texturized state is shorter than in the non-texturized state of the fiber;
wherein the face yarn fibers are integrated in the carrier such that the thatch yarn fibers protrude from the carrier by a shared thatch yarn fiber height (L2), wherein the thatch yarn fibers are integrated in the carrier such that the face yarn fibers protrude from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height, wherein the first material is adapted to contract stronger than the second material upon being exposed to a contraction inducing condition.

2. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- Integrating (402) texturized first fibers (602) and texturized second fibers (604) in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first fibers are stronger texturized than the second fibers, wherein a textured fiber is a fiber having a molecular memory of a textured state, wherein the textured state is a curled, crumpled and/or wrinkled state, wherein the molecular memory is a tendency to turn into the textured state if the fiber is allowed to do so, wherein the length of a fiber in texturized state is shorter than in the non-texturized state of the fiber;

- Stretching (404) the first and second texturized fibers during and/or after their integration such that they are prevented from contracting to their respective default length to their respective maximum possible length;

- cutting (406) the stretched first and second texturized fibers at the same length (L0);

- allowing (408) the cut first and second fibers to contract to their respective default lengths, the contracted first texturized fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second texturized fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

3. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- integrating (402) texturized first fibers (602) and texturized second fibers (604) in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first fibers are texturized as strongly as the second fibers or are texturized stronger than the second fibers, wherein a textured fiber is a fiber having a molecular memory of a textured state, wherein the textured state is a curled, crumpled and/or wrinkled state, wherein the molecular memory is a tendency to turn into the textured state if the fiber is allowed to do so, wherein the length of a fiber in texturized state is shorter than in the non-texturized state of the fiber;

- stretching (430) the first and second texturized fibers during and/or after their integration such that the first fibers are stretched stronger than the second fibers;

- cutting (406) the stretched first and second texturized fibers at the same length (L0);

- allowing (408) the cut first and second fibers to contract to their respective default lengths, the contracted first texturized fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second texturized fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

4. A method of producing an artificial turf (200, 300, 500, 520, 530), the method comprising:

- integrating (402) first texturized fibers made of a first materiel and second texturized fibers made of a second material in a carrier (202) such that the first and second texturized fibers protrude from the carrier in the same direction, wherein the first material is adapted to contract stronger than the second material upon being exposed to a contraction inducing condition, wherein a textured fiber is a fiber having a molecular memory of a textured state, wherein the textured state is a curled, crumpled and/or wrinkled state, wherein the molecular memory is a tendency to turn into the textured state if the fiber is allowed to do so, wherein the length of a fiber in texturized state is shorter than in the non-texturized state of the fiber;

- cutting(406) the integrated first and second texturized fibers at the same length (L0);

- exposing(426) the cut first and second texturized fibers to the contraction inducing condition, the contraction inducing conditions causing the first and the second texturized fibers to contract, the contracted first fibers providing texturized thatch yarn fibers (206) protruding from the carrier by a shared thatch yarn fiber height (L2), the contracted second fibers providing texturized face yarn fibers (204) protruding from the carrier by a shared face yarn fiber height (L3), the face yarn fiber height being larger than the thatch yarn fiber height.

5. The method of claim 4, the first material being selected from a group comprising:

- a polymer that is identical to a second polymer, the second polymer being used as the second material, wherein the first fibers are texturized stronger than the second fibers, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the stronger texturized first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the less texturized second fibers to the face yarn fiber height (L3);

- a first polymer that is different from a second polymer used in the second fibers as the second material, wherein the degree of texturization of the first and second fibers is identical, wherein the first polymer is adapted to contract stronger than the second polymer when heated, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the second fibers to the face yarn fiber height (L3);

- a first polymer that is different from a second polymer used in the second fibers as the second material, wherein the first polymer is adapted to contract stronger than the second polymer when heated, wherein the first fibers are texturized stronger than the second fibers, wherein the contraction inducing condition is heat of a temperature adapted to irreversibly contract the first fibers to the thatch yarn fiber height (L2) and adapted to irreversibly contract the second fibers to the face yarn fiber height (L3).

6. The method of producing an artificial turf according to claim 4, further comprising:

- stretching the first and second fibers during and/or after their integration such that they are prevented from contracting to their respective default length;

wherein the first fibers are stretched as strongly as the second fibers or are stretched stronger than the second fibers when being cut.

7. The method of any one of claims 2-6, the integration of the first and second fibers comprising tufting the first fibers, the second fibers, and one or more further fibers into the carrier.

8. The method of any one of claims 2-7,

- the first fibers being integrated in the carrier in the form of first rows (502) selectively comprising first dots, each first dot selectively comprising first fibers;

- the second fibers being integrated in the carrier in the form of second rows (504) selectively comprising second dots, each second dot selectively comprising second fibers;

- the first rows and second rows alternating and being parallel to each other.

9. The method of claim 8, the first and second rows respectively being straight lines.

10. The method of claim 8, the first and second rows respectively being zig-zag lines.

11. The method of any one of claims 4-10, wherein the exposing of the cut first and second texturized fibers to the contraction inducing condition comprising heating the first and the second rows such that contraction of the first and second fibers is induced, whereby the first rows are heated to higher temperatures than the second rows for inducing a stronger contraction of the first fibers than the second fibers.

12. The method of claim 11, the heating being performed in an oven, the oven having a plurality of first heating elements (702), a plurality of second heating elements (704), a camera (706), a controller (708) and a positioning element (710), the heating comprising:

- continuously capturing, by the camera, images of the artificial turf while being moved through the oven;

- continuously analyzing, by the controller, the images for determining current positions of the first and second rows;

- continuously controlling, by the controller, the positioning element such that the positioning element positions the artificial turf and/or the first heating elements such that the first heating elements are aligned with the first rows and such that the positioning element positions the artificial turf and/or the second heating elements such that the second heating elements are aligned with the second rows;

- continuously controlling, by the controller, the first and second heating elements such that the first heating elements generate a higher temperature than the second heating elements.

13. The method of any one of claims 2-7,

- the first fibers and the second being integrated in the carrier in the form of rows, each row comprising first and second dots in alternating order, each first dot selectively comprising first fibers, each second dot selectively comprising second fibers; or

- the first fibers and the second being integrated in the carrier in the form of rows, each row comprising a random mixture of first and second fibers.

14. The method of any one of claims 2-13, further comprising:

- generating the first texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the first texturized fibers are created, each first texturized fiber not extending to its full potential height in the absence of a stretching force; and/or

- generating the second texturized fibers by curling, crumpling, and/or wrinkling of a non-texturized monofilament or split-film tape upon itself so that the second texturized fibers are created, each second texturized fiber not extending to its full potential height in the absence of a stretching force.

15. The method of any one of claims 2-14, wherein the first and second texturized fibers respectively have a molecular memory of a curled, crumpled and/or wrinkled state.

16. The method of any one of claims 2-15, wherein the shared thatch yarn fiber height (L2) is in the range of 10 mm to 30mm, preferably in the range of 15 mm to 25 mm; and/or wherein the shared face yarn fiber height (L3) is in the range of 31 mm to 50 mm, preferably in the range of 35 to 45 mm.

17. The method of any one of claims 2-16, wherein the first fibers are made of a first polymer and the second fibers are made of a second polymer, the first polymer being adapted to contract stronger than the second polymer, the exposing of the cut first and second texturized fibers to the contraction inducing condition comprising heating the first and the second rows such that contraction of the first and second fibers is induced.

18. The method of claim 17,

- wherein the first polymer is HDPE and the second polymer is LLDPE; or

- wherein the first polymer is PE being free of PA and the second polymer is PE comprising thread-like regions of PA; or

- wherein the first polymer is PE comprising thread-like regions of PA and the second polymer is PP or PA or a mixture thereof.

19. The method of any one of claims 2-18, wherein the first and second fibers are made of the same polymer or of different polymers and wherein the first fibers are stronger texturized than the second fibers.

20. The method of any one of claims 2-19, further comprising adding filler material (308), the infill material filling the space between the thatch yarn fibers and filling at least 20% of the space between the face yarn fibers extending above the ends of the thatch yarn fibers.

21. The method of any one of claims 2-20, wherein the first and/or the second texturized fiber is made of a polymer mixture comprising a bulk polymer and a thread polymer,

- wherein the bulk polymer is polyethylene (PE) and the thread polymer is polyamide (PA); or

- wherein the bulk polymer is polyethylene (PE) and the thread polymer is polyester; or

- wherein the bulk polymer is polypropylene (PP) and the thread polymer is polyester; or

- wherein the bulk polymer is polypropylene (PP) and the thread polymer is polyamide (PA).

Drawing