Artificial Turf Fiber and Method of Manufacturing Thereof

The invention relates to the field of artificial turf, and more particular to artificial turf fibers and the manufacture thereof.

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

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

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

US patent U.S. Pat. No. 10,793,973 B2 relates to a synthetic monofilament fiber for use in an artificial lawn which has multiple tapered elevations which are believed be associated with increased risk of skin abrasion, and an increased proneness to wear and tear and the associated generation of microplastic waste.

EP 1 950 350 A1 discloses various fibers, some of which have large bulbs at the center and on the ends. These fibers have stress points at the point the bulbs are connected to the fiber. As a result, these types of fibers have a tendency to fray or split along these stress points.

A further fiber is disclosed in US006491991B2 which has a curved cross section with a series of flat, planar sections which may lead to decreased mechanical stiffness and other undesired properties.

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

It is an objective to provide for an improved manufacture of artificial turf fibers, improved artificial turf fibers, and artificial turf comprising the same. The objectives underlying the invention are solved by the features of the independent claims.

In one aspect, a method of manufacturing an artificial turf fiber includes extruding a polymer mixture through at least one fiber profile opening of an extrusion plate to form an artificial turf fiber, the fiber profile opening including: first and second end portion openings, and a curved middle portion opening connected with the first and second end portion openings, the curved middle portion having at least a first spine opening proximate to the first end portion opening and a second spine opening proximate to the second end portion opening; allowing the extruded polymer mixture to travel along a distance between the at least one fiber profile opening of the extrusion plate to a quenching unit, where the first and second spine openings are sized and positioned such that a net polymer mass flow in the extruded polymer mixture from a position of the first spine opening to a first end portion of the fiber and from a position of the second spine opening to a second end portion of the fiber occurs before the fiber is quenched; and quenching the extruded polymer mixture in the quenching unit to form the artificial turf fiber.

Advantageously, manufacturing an artificial turf fiber by extruding a polymer mixture through at least one fiber profile opening of an extrusion plate including at least a first spine opening proximate to the first end portion opening and a second spine opening proximate to the second end portion opening results in a fiber that has less thinning of the fiber end portions, more resistance to curling of the end of the fiber, and hence more mechanical stability and/or strength. The fiber end portions are defined as the end portions in a cross-section of the fiber, whereas the end of the fiber refers to the end of the length of the fiber (i.e. the tip of the fiber). The one or more spine openings of the extrusion plate result in a net polymer mass flow, which occurs between extrusion of a polymer mass from the extrusion plate (in the form of an unquenched polymer fiber) and quenching of the fiber via, for example, a quenching unit. For example, the extruded fiber may travel a specified distance before entering the quenching unit. The net polymer mass flow, which is in the direction from a region of the extruded fiber (corresponding to the spine opening of the extrusion plate) to the closest end portion of the fiber, mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of the end of the quenched fiber.

According to some examples, the first spine opening is positioned in the middle portion opening on a first arc length defined by a first angle of less than or equal to 60°, or between 35°-55°, or between 40°-50°, or at 45°, where the first arc length is measured along the curved middle portion opening from the first end portion opening, and the second spine opening is positioned in the middle portion opening on a second arc length defined by a second angle of less than or equal to 60°, or between 35°-55°, or between 40°-50°, or at 45°, where the second arc length is measured along curved middle portion opening from the second end portion opening.

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

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

According to examples, the ratio of an area of the first spine opening to an area of the first end portion opening is larger than the ratio of a cross-sectional area of the first spine of the quenched fiber to a cross-sectional area of the first end portion of the quenched fiber, the first end portion of the fiber being created by extruding the polymer mass through the first end portion opening, and/or the ratio of an area of the second spine opening to an area of the second end portion opening is larger than the ratio of a cross-sectional area of the second spine of the quenched fiber to a cross-sectional area of the second end portion of the quenched fiber, the second end portion of the fiber being created by extruding the polymer mass through the second end portion opening.

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

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

According to yet other examples, a width of the first end portion opening is larger than a width of a first section of the middle portion opening adjacent to the first end portion opening, a width of the second end portion opening is larger than a width of a second section of the middle portion opening adjacent to the second end portion opening, and/or a width of the first end portion of the quenched fiber is larger than a width of a first section of a middle portion of the quenched fiber adjacent to the first end portion of the quenched fiber, and a width of the second end portion of the quenched fiber is larger than a width of a second section of the middle portion of the quenched fiber adjacent to the second end portion of the quenched fiber.

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

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

According to examples, a center of the curved middle portion opening includes a bulge opening, and a maximum width of the middle portion opening including the bulge opening is greater than a maximum width of the first and second end portion openings.

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

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

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

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

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

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

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

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

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

According to some examples, the polymer mixture includes a polyethylene or a polyethylene-polyamide blend, where the quenching unit is a water bath, where the distance between the extrusion plate openings (also referred to as the fiber profile opening) and the quenching unit is 3.0-5.0 cm, and where a temperature of the water bath is 28° C.-34° C.

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

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

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

According to some examples, the polymer mixture is at least a two-phase polymer mixture, where a first phase of the polymer mixture includes a first polymer and a first dye and a second phase of the polymer mixture includes a second polymer and a second dye, where a color of the second dye is different than a color of the first dye, where the second polymer is of a same or of a different type as the first polymer, where the first and the second phases are immiscible, and where the extruded fiber has a marbled appearance.

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

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

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

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

In one aspect, an extrusion plate for artificial turf fibers includes at least one fiber profile opening, the fiber profile opening including first and second end portion openings, and a curved middle portion opening connected with the first and second end portion openings. The curved middle portion opening has at least a first spine opening proximate to the first end portion opening and a second spine opening proximate to the second end portion opening.

The features of the extrusion plate result in a fiber that has less thinning of the fiber end portions, more resistance to curling of the end of the fiber, and hence more mechanical stability and/or strength. The one or more spine openings of the extrusion plate result in a net polymer mass flow, which occurs between extrusion of a polymer mass from an extrusion plate (in the form of an unquenched polymer fiber) and quenching of the fiber via, for example, a quenching unit. For example, the extruded fiber may travel a specified distance before entering the quenching unit. The net polymer mass flow, which is in the direction from a region of the extruded fiber (corresponding to the spine opening of the extrusion plate) to the closest end portion of the fiber, mitigates or prevents a reduction in width of the first and second end portions of the quenched fiber in comparison to a width of the end portion openings of the extrusion plate, thereby increasing dimensional stability and/or mitigating or preventing curling of the end of the quenched fiber.

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

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

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

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

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

It is understood that one or more of the aforementioned embodiments and examples may be combined as long as the combined embodiments are not mutually exclusive.

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

is a perspective 3D view of the inside of a section of an artificial turf fiber. For example, the fiber may be made of polyethylene or polypropylene or polyamide or a mixture of two or more of these polymers. The fiber may be generated in an extrusion process and the cross-sectional areaof the fiber may have essentially the same shape along the entire length of the fiber.shows the inner surfaceof the fiber defined by the concave part of the boundary line of the shape of the fiber profile. Depending on the type of artificial turf, the length of the fiber (measured from the upper surface of a carrier to the free ends of the fibers) may be different. For example, the fiber length may be in the range of e.g., 2.0 cm to 9.0 cm, preferably 3.0 cm to 7.0 cm.

is a perspective 3D view of the outside of a section of the fibershown already in.shows the outer surfaceof the fiber defined by the outer, convex part of the boundary line of the shape of the fiber profile.