Patent Application
20250092615
The invention relates to the field of artificial turf, and more particular to artificial turf fibers having a natural look and feel.
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.
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.
It is an objective to provide for an improved artificial turf fiber and artificial turf comprising the same. The objectives underlying the invention are solved by the features of the independent claims.
In one aspect an extruded artificial turf fiber is disclosed. The artificial turf fiber has an arced cross-sectional shape. The arced cross-sectional shape is defined by a boundary line consisting of uninterrupted undulations.
This may be beneficial, because the effect of a boundary line consisting completely of uninterrupted undulations is that 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.
As explained above, some prior art artificial turf fibers have a boundary line comprising a series of elevations or depressions to scatter incident light and provide a matt surface impression which is similar to the look of a natural grass fiber surface. However, some prior art fibers have fiber profile contours with multiple successive concave depressions or multiple successive convex elevations. Such an outline has several disadvantages: Series of concave depressions result in thin, pointed protrusions. These can lead to a very rough surface, especially when using relatively hard, mechanically robust polymer material, which in turn can lead to skin damage. In addition, these pointed protrusions are subject to high mechanical stress, resulting in a large amount of material being abraded in a short period of time. This abrasion can end up in the environment as unwanted microplastic waste. Series of convex bumps in turn create thin, conical depressions. Dirt and unwanted germs can accumulate in these depressions and negatively affect the appearance and hygiene of the artificial turf. In addition, such conical depressions, especially if they are large, represent a mechanical weak point where the fibers can easily tear (splice) under mechanical stress.
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, thereby minimizing the risk of splicing, the risk of skin burns, the generation of microplastic and the accumulation of dirt and debris.
A further benefit may be that the extrusion process can run true to shape. This means that the shape of the fiber cross section essentially matches the shape of the extrusion die profile opening. As the boundary line of the fiber profile is free of pointed protrusions or indentations, also the extrusion die profile is free of such pointed protrusions or elevations. As a consequence, the formation of speed differences of the extruded polymer mass during extrusion which may result in deformed fibers may be prevented.
According to some examples the fiber has ends, e.g., a first end and a second end.
The ends have a radius of curvature being at least as large as (or larger as) the smallest radius defining the undulations of the boundary line of the other parts of the cross-sectional shape.
For example, the ends may have a radius of curvature being at least 5%, e.g., at least 10%, e.g., at least 15% larger, e.g., 25% than the smallest radius defining the undulations of the boundary line of the other parts of the cross-sectional shape.
This may be beneficial as the ends will have a curvature based on a radius which is at least as large, and possible larger, than the smallest radius defining one or more of the undulations of the boundary line of other fiber parts, e.g., fiber arms or the center.
This may be beneficial as it protects the fiber against abrasion and also eases the manufacturing process: filigree fiber ends may result in a strongly reduced flow rate of the polymer matrix at the respective portions of the extrusion nozzle opening, which may result in a significant deviation of the shape of the extruded fiber from the shape of the extrusion nozzle opening. A further advantage of the above-mentioned fiber end curvature is that incident light is diffusely scattered even when it falls on the ends of the fibers. This is because a large radius of curvature at the fiber ends ensures that the incident light hits a relatively wide surface at the ends, so that the light scattering behavior of the fiber surface at its ends is similar to the scattering behavior at its wide inside and outside surfaces. With artificial turf, due to the industrial manufacturing process, there is always a risk that the synthetic lawn optics will depend on the viewing angle, as the fibers can have an unnatural-looking uniform orientation or distribution, for example. Because the ends have a comparatively large curvature radius, the light is scattered similarly at the ends as in the wide side and it is less noticeable if the majority of the fibers should have the same orientation.
According to some examples, the fiber has thickenings at the fiber ends. The ends are connected to the center of the fiber via fiber portions referred to as “fiber arms” or “arms”. The diameter of each of the thickenings is thicker than the thickest part of the fiber arm that connects said end to the center of the fiber.
For example, the diameter of each of the thickenings may be at least 5%, e.g., at least 10%, e.g., at least 15%, e.g., 25% thicker than the thickest part of the fiber arm that connects said end to the center of the fiber.
This feature may have similar beneficial effects like the use of the above-mentioned use of fiber end undulation having a radius of at least a certain size. It is possible, however, that the boundary line of the thickened ends comprises multiple undulations and hence cannot be described by the size of a single curvature radius.
According to some examples, the arced cross-sectional shape has an outer, convex boundary line and an inner, concave boundary line. At least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line are defined by first circles (508) having the same first diameter. At least 70%, in particular at least 80%, e.g., 100% of the undulations of the outer boundary line are defined by second circles having the same second diameter.
For example, the first and second diameters can be identical or similar, wherein a similar diameter lies in a range of plus or minus 10% of the other diameter.
The largely uniform wave shape of the bounding line may have the advantage that there are no particularly deep wave valleys where the fiber thickness is reduced to such an extent that weak points are created at which the fiber tears open under mechanical load. The risk of splicing is thereby further reduced. Likewise, there may not exist particularly high protrusions which may be particularly prone to wear and tear. This may further help to prevent the generation of microplastic waste.
According to some further examples, the fiber comprises a thickening at its center which forms a rounded protrusion to at least one side of the fiber. The curvature of the protrusion is defined by a circle having a radius selected such that a ratio of the said radius to the radius of the first circles is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.
According to some further examples, the radius of curvature of the fiber ends is selected such that a ratio of the radius of curvature of the fiber ends to the radius of the first circle is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.
According to a further example, the cross-section of the fiber is shaped like the arc of a segment of a circle. This circle is referred herein as the “fiber profile circle” and the radius of this circle the “fiber profile circle radius”. According to some embodiments, the ratio of the width of the fiber profile and the fiber profile radius is in the range of 1.40 to 1.80, in particular 1.50 to 1.70, in particular 1.55 to 1.68.
Applicant has observed that this ratio provides for a particularly “natural” look of a synthetic yarn made of respective fibers. Without the intention to be bound by any theory, applicant believes that this effect may be the result of said ratio value range approximately representing the “golden ratio”.
If one divides a stretch of an elongated object into two parts, of which the smaller part relates to the larger part as the larger part relates to the whole, then one speaks of the so-called ‘golden ratio’. In this case, the relationship of the larger part to the smaller part is: 1.618[ . . . ] and also the ratio of the whole to the larger part is 1.618[ . . . ]. In a circle, this “golden ratio” corresponds to an angle of 137.5 degrees. And this is exactly the most common arrangement of leaves and flowers around a plant stem in nature. For example, the golden ratio can be found in the arrangement of leaves and inflorescences of many plants. In these plants, the angle of two successive leaves divides the full circle in the ratio of the golden section. For example, the petals of the rose are arranged according to the golden ratio.
According to some examples, the fiber ends are connected to the center of the fiber via fiber arms, wherein each of the fiber arms is formed such that over a portion of at least 80% of the length of that arm, the fiber arm thickness has a thickness which is no more than 15% thicker or thinner than the average thickness of that fiber arm portion.
This may have the advantage that the fiber arms have an approximately uniform thickness. Hence, there do not exist particularly deep indentations or particularly high protrusions which may be associated with the above-mentioned problems concerning proneness to wear and tear, the generation of microplastic waste, splicing risk, etc.
According to some examples, the fiber comprises a nucleating agent.
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.
According to some examples, the cross-section of the fiber is shaped like the arc of a segment of a circle or an ellipse.
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.
According to some other examples, the cross-section of the fiber is shaped like a catenary. The catenary is a particular type of arced curve which is particularly robust against mechanical stress.
Using an artificial turf fiber having a cross-section shaped like a catenary may strengthen the ability of a downed fiber to straighten up quickly. With artificial turf, the problem exists that synthetic fibers that have been depressed by the ball or the players need several minutes or even hours to straighten up again. In some cases, the fibers do not straighten at all. This has the disadvantage that the footprints of the players are visible on the turf for a longer period of time, because the bent-down, essentially horizontally oriented fibers reflect the light differently. The footprints in artificial turf are therefore visible for a certain time as highly reflective, bright, shiny areas. This not only looks unnatural and unattractive; it can even lead to spectators and players being dazzled in strong sunlight. By using a fiber profile having a cross-section shaped like a catenary, the fiber becomes particularly mechanically stable. The tendency of the fiber to buckle under low loads is reduced, and the ability of the fiber to quickly straighten up again after a temporary load-induced buckling increases. Thus, this special shape not only supports the mechanical robustness of the fibers, but also has the particular effect of giving the turf a more natural-looking overall appearance, as footprints are no longer as strong or visible for as long.
According to some examples, the fiber comprises a thickening at its center.
This may help increasing the mechanical strength of the fiber and to increase the ability of the fiber to quickly straighten up again after a temporary load-induced buckling.
For example, the thickening at its center can be formed such that a round bulge is formed towards the outer surface of the fiber, wherein the thickening does not lead to a bulge towards the inner surface of the fiber.
According to some examples, the fiber has a width (w) measured as a straight line connecting the first and second ends of 0.7 to 2.5 mm, in particular of 0.9 to 1.5 mm.
According to some examples, the undulations are formed such that the fiber has at least 6, in particular at least 7, in particular 7-11, e.g., 9 round bulges on its outer surface, and/or such that the fiber has at least 6, in particular 6-10, e.g., 8 round bulges on its inner surface.
According to some examples, the majority of undulations form consecutive pairs of a round bulge and a round indentation, wherein each pair has a length of 0.10 mm to 0.30 mm, e.g. 0.10 to 0.20 mm.
According to some examples, at least 70% of the undulations of the inner surface and at least 70% of the outer surface have the same or a similar undulation length, wherein an undulation length is similar to a given length if it differs no more than plus or minus 10% from said given length.
The above-mentioned dimension and ranges have been observed to provide for artificial turf fibers capable to form a synthetic lawn that faithfully reproduces the look of natural grass.
In a further aspect, disclosed herein is an artificial turf comprising: a carrier; and a plurality of the artificial turf fibers described herein in various embodiments and examples integrated into the carrier and protruding therefrom to form an artificial turf.
In a further aspect, disclosed herein is the use of artificial turf fibers described herein in various embodiments and examples for providing artificial grass that looks like natural grass.
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, examples are described in greater detail making reference to the drawings in which:
In the following, similar elements may be denoted by the same reference numerals.
As can be inferred from
In the example shown, the undulations comprise alternating depressions 308 and elevations 312 on the outer fiber surface and alternating depressions 310 and elevations 314 on the inner fiber surface.
The thickness of the fiber at the thickenings 318 at the two ends is slightly greater than the thickness of the thickest portions of the fiber arms connecting the ends 302, 304 with the center 306. Moreover, there is a further thickening at the center of the fiber resulting in a protrusion/undulation 316 from the outer surface 312. In the depicted example, the central thickening does not result in a protrusion from the inner surface 102 of the fiber.
In other embodiments (not shown), D3 and D4 may be similar, but not identical.
In addition, or alternatively, D1 and D2 may be identical. For example, both D1 and D2 may represent a diameter which is chosen such that the ratio of D1 (or D2) to D3 (or D4) approximately is the golden ratio.
In the depicted example, w2 is the smallest with in the fiber arm and w3 is the largest width of the fiber arm.
In other examples, w1 and w2 may be identical, but preferably w1 is greater than the smallest width w2 of the fiber arms, and preferably also greater than the largest width w3 of the fiber arm.
According to some examples, the fiber profile is axisymmetric with respect to a vertical axis through the center of the fiber profile as shown in
The fiber profile can be scaled to provide fibers of different fiber weights. For example, by scaling the outer width of the fiber profile from 1.0 cm to 1.351 cm, and scaling all other dimensions given in
As can be inferred from
According to
According to
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.
