PRODUCTION OF AN ARTIFICIAL TURF FIBER WITH A NON-CIRCULAR CLADDING

Abstract

A method for producing an artificial turf fiber, comprising: preparing a core polymer mixture from a core polymer and a thread polymer forming beads within the core polymer; coextruding the core polymer mixture with a cladding polymer component into a monofilament, the core polymer mixture forming a cylindrical core, The cladding polymer component forming a cladding encompassing the core with a non-circular profile; quenching the monofilament; reheating the quenched monofilament; stretching the reheated monofilament to deform the beads into threadlike regions; and providing one or more of the stretched monofilaments as the artificial turf fiber.

Claims

1. An artificial turf fiber, comprising: a core; and two protrusions, each protrusion extending from the core, each protrusion including a cross-sectional profile, the cross-sectional profile of each protrusion including an undulated side.

2. The artificial turf fiber according to claim 1, wherein the cross-sectional profile of each protrusion further includes a smooth side.

3. The artificial turf fiber according to claim 2, wherein the smooth side is either a straight smooth side or a concave smooth side.

4. The artificial turf fiber according to claim 3, wherein each protrusion has a rounded tip, and wherein a curvature of the concave smooth side of each protrusion is configured such that a thickness of each protrusion is decreasing in a direction towards its respective tip.

5. The artificial turf fiber according to claim 1, wherein the undulated side comprises uninterrupted undulations.

6. The artificial turf fiber according to claim 1, wherein the undulated side consists of uninterrupted undulations.

7. The artificial turf fiber according to claim 1, wherein the undulated side includes an undulated section, the undulated section spanning at least 60% of the undulated side.

8. The artificial turf fiber according to claim 7 wherein the undulated section comprises uninterrupted undulations.

9. The artificial turf fiber according to claim 7 wherein the undulated section consists of uninterrupted undulations.

10. The artificial turf fiber according to claim 1, wherein the undulated side includes 4 notches along a straight baseline of the undulated side.

11. The artificial turf fiber according to claim 1, wherein each protrusion encloses an angle of between 100 and 180 degrees towards the undulated side of the profile.

12. The artificial turf fiber according to claim 11, wherein each protrusion encloses an angle of about 135 degrees towards the undulated side of the profile.

13. The artificial turf fiber according to claim 1, wherein the core has a thickness, and wherein each protrusion has an extension of about 3 times the thickness of the core.

14. The artificial turf fiber according to claim 1, wherein the core has a circular cross-sectional profile.

15. The artificial turf fiber according to claim 1, further comprising a cladding encompassing the core, wherein the cladding comprises the two protrusions.

16. The artificial turf fiber according to claim 15, wherein cladding further comprises two circular sections on two opposite sides of the core, and wherein the two protrusions extend from two other opposing sides of the core.

17. The artificial turf fiber according to claim 15, wherein the core has a diameter of 50 to 600 micrometers, the cladding has a minimum thickness of 25 to 300 micrometers in all directions extending radially from the core, and each protrusion has a radial extension, measured from a perimeter of the core, of the cladding thickness plus 2 to 10 times a radius of the core.

18. The artificial turf fiber according to claim 15, wherein the core comprises a core polymer and a thread polymer, the thread polymer including any one of polyamide, polyethylene terephthalate, polybutylene terephthalate, polyester, and polybutyrate adipate terephthalate.

19. The artificial turf fiber according to claim 18, wherein the cladding comprises a cladding polymer, and wherein the core polymer and the cladding polymer include any one of polyethylene, polypropylene, and a mixture thereof.

20. An artificial turf, comprising: an artificial turf backing; and the artificial turf fiber according to claim 1.

Description

SHORT DESCRIPTION OF THE FIGURES

[0112] In the following, embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings in which:

[0113] FIG. 1 shows a radial cross-section of a monofilament for producing an artificial turf fiber;

[0114] FIG. 2 visualizes the composition of a three-component core polymer mixture;

[0115] FIG. 3 shows a schematic axial cross-section of a monofilament before stretching;

[0116] FIG. 4 shows a schematic axial cross-section of a monofilament after stretching;

[0117] FIG. 5 shows a monofilament, the cladding being transparent such that the contact layer between core and cladding becomes visible

[0118] FIG. 6 is a cross-sectional diagram of an artificial turf comprising artificial turf fibers made from monofilaments;

[0119] FIG. 7 is a cross-sectional profile of an artificial turf fiber with protrusions comprising an undulated and a straight section

[0120] FIG. 8 is a cross-sectional profile of an artificial turf fiber with protrusions comprising an undulated and a concave section; and

[0121] FIG. 9 is a cross-sectional detail of a coextrusion device with a joining path.

DETAILED DESCRIPTION

[0122] Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

[0123] Bicomponent artificial turf fibers have each of their components designed to fulfill the opposing requirements of providing artificial grass blades which are soft but resilient at the same time. While the resilience of an artificial turf fiber can be provided by selecting a rigid material for the core strand, its cladding can provide a soft surface which is better fit to reduce the risk of injuries and imitate the haptic and visual behavior of natural grass. However, no material combination of core and cladding polymers is known to date which meets these demands, but is also miscible in a liquid state during manufacturing such that the two materials can be laminated together. For this reason, the core and cladding of bicomponent artificial turf fibers are typically joined together by an interfacing layer of a third polymer which is cohesive to the two otherwise immiscible components. However, cohesive forces between the adjacent layers are not strong enough to provide sufficient protection against splicing of the three layers. Against this background, the invention seeks to provide a bicomponent artificial turf fiber which is less prone to delamination and provide a more cost-effective surface-to-mass ratio as well as a closer resemblance of natural lawn.

[0124] FIG. 1 shows a schematic diagram of a cut through a monofilament 100 according to embodiments of the invention, the cut being oriented perpendicularly with respect to the central axis of the monofilament 100. It comprises a cylindrical core 110 and a non-circular cladding 102 surrounding the core 110. The core 110 comprises a core polymer 112 and threadlike regions which are embedded in the core polymer 112. The threadlike regions are formed from a thread polymer 202 which is preferably a polymer with a high bending rigidity or stiffness such as polyamide. The threadlike regions permeate the core polymer 112 in axial directions and at random radial positions and/or orientations.

[0125] The core polymer 112 makes up the majority of the core volume and may be any polymer which is miscible with the cladding polymer forming the cladding 102. As the core polymer 112 makes up the largest portion of the core 110, it is preferably chosen to be a comparably inexpensive material such as polyethylene. The core polymer 112 may be immiscible with the thread polymer 202. In this case, the threadlike regions are surrounded by a compatibilizer 204, which is another polymer material with the capability to emulsify the thread polymer 202 with the liquid core polymer 112. After manufacturing, the threadlike regions remain cohesively coupled to the core polymer 112 in the solidified monofilament 100.

[0126] The core 110 may comprise 1 to 30 percent by its weight the thread polymer 202 and, if any, an additional thread polymer combined. Particularly, the thread polymer 202 and, if any, the additional thread polymer combined may be 1 to 20 percent by weight of the core 110. More particularly, the core 110 may comprise 5 to 10 percent by its weight the thread polymer 202 and, if any, the additional thread polymer combined. The core 110 may for instance have a diameter of 50 to 600 micrometer in size. It may typically reach a yarn weight of 50 to 3000 dtex.

[0127] The threadlike regions may have a diameter of less than 50 micrometers. Particularly, the threadlike regions may have a diameter of less than 10 micrometers. More particularly, the threadlike regions may have a diameter between 1 and 3 micrometers.

[0128] The cladding 102 is formed by a cladding polymer which is chosen to be miscible with the core polymer 112 in fluid state. The cladding polymer may be identical to the core polymer 112. The annular cylindrical zone or area where the cladding polymer contacts the core polymer 112 is a contact layer 114 where both polymers are mixed with each other. Hence, the contact layer 114 may bond core 110 and cladding 102 together with stronger forces than the long-range forces which occur typically within arrangements with a purely cohesive bonding.

[0129] The cladding 102 completely surrounds the core 110 with two circular sections on two opposite sides of the core 110 and two flat, thin, long protrusions 104 on two other opposing sides of the core 110. The cladding 102 is preferably formed by a polymer such as polyethylene which may provide a soft and smooth surface characteristic. The cladding 102 may comprise additives which support its interfacing function to the environment and/or a user. Typical additives to the cladding 102 may be, for example, pigments providing a specific color, a dulling agent, a UV stabilizer, flame retardant materials such as aramid fibers or intumescent additives, an anti-oxidant, a fungicide, and/or waxes increasing the softness of the cladding 102.

[0130] Providing the cladding 102 with additives may have the advantage that these can be left out from the core 110. This way, a smaller content of expensive additive material per mass unit is required. As an example, it is not necessary to add pigments to the core 110 because only the cladding 102 is visible from the outside. By way of a more specific example, it may be beneficial to add a green pigment, a dying agent and a wax to the cladding 102 to gain a closer resemblance of natural grass blades.

[0131] The non-circular profile of the cladding 102 may be symmetric or irregular; polygonal, elliptic, lenticular, flat, pointed or elongated. Preferably, the cladding 102 resembles a blade of grass by encompassing the circular-cylindrical core 110 with two convex segments extending in two opposite directions from the geometric center of the monofilament and two flat protrusions 104 extending in two further opposite directions from the geometric center of the monofilament, the convex segments and the flat protrusions 104 being alternatingly joined by concave segments. The two flat protrusions 104 may also add to the biomimetic properties of the monofilament 100 and may increase the surface-to-mass ratio for each monofilament 100 and, accordingly, may provide an improved surface coverage for an artificial turf manufactured from artificial turf fibers on the basis of such monofilaments 100.

[0132] A monofilament 100 as shown in FIG. 1, which can also be referred to as a filament, can be produced by feeding a core polymer mixture 200 and a cladding polymer component into a fiber producing coextrusion line. The two polymer melt components are prepared separate from each other and then joined together in the coextrusion tool, i.e., a spinneret plate, forming the two melt flows into a filament which is quenched or cooled in a water spin bath, dried and stretched by passing rotating heated godets with different rotational speed and/or a heating oven.

[0133] The thread polymer 202 is prepared by first mixing it with the compatibilizer 204. This may result in granular material which consists of a two-phase system in which the thread polymer 202 is surrounded by the compatibilizer 204.

[0134] Then, a three-phase system is formed by adding the core polymer 112 to the mixture whereby in this example the quantity of the core polymer 112 is about 80-90 mass percent of the three-phase system, the quantities of the thread polymer 202 being 5% to 10% by mass and of the compatibilizer 204 being 5% to 10% by mass. Using extrusion technology results in a mixture of droplets or of beads 210 of the thread polymer 202 surrounded by the compatibilizer 204 that is dispersed in the polymer matrix of the core polymer 112. In a practical implementation a so called master batch including granulate of the thread polymer 202 and the compatibilizer 204 is formed. The master batch may also be referred to as a polymer mixture herein. The granulate mix is melted and a mixture of the thread polymer 202 and the compatibilizer 204 is formed by extrusion. The resulting strands are crushed into granulate. The resultant granulate and granulate of the core polymer 112 are then used as the core polymer mixture 200 in the coextrusion process described below.

[0135] FIG. 2 shows a diagram which illustrates a cross-section of a core polymer mixture 200. The polymer mixture comprises a thread polymer 202, a core polymer 112 and a compatibilizer 204. The thread polymer 202 and the core polymer 112 are immiscible. The thread polymer 202 is less abundant than the core polymer 112. The thread polymer 202 is shown as being surrounded by compatibilizer 204 and being dispersed within the core polymer 112. The thread polymer 202 surrounded by the compatibilizer 204 forms a number of polymer beads 210. The polymer beads 210 may be spherical or oval in shape or they may also be irregularly-shaped depending on how well the polymer mixture is mixed and the temperature.

[0136] The core polymer mixture 200 shown in FIG. 2 is an example of a three-phase system. The core polymer mixture 200 is free of color pigments, UV and thermal stabilizers, process aids and other additive substances that are known as such from the art. However, the core polymer 112 may contain more than three phases, such as e.g. a four-phase system comprising the thread polymer 202, the core polymer 112, an additional thread polymer, and the compatibilizer 204. In such a four-phase system, the thread polymer 202 and the additional thread polymer may be not miscible with the core polymer 112. The compatibilizer 204 then separates the thread polymer 202 from the core polymer 112 and the additional thread polymer from the core polymer 112. In this example the same compatibilizer 204 is used for both the thread polymer 202 and the additional thread polymer. In other examples, the compatibilizer 204 used for the thread polymer 202 may be different from the compatibilizer 204 used for the additional thread polymer. In a four-phase core polymer mixture 200, the polymer beads 210 may be formed by both the thread polymer 202 and additional thread polymer.

[0137] The compatibilizer 204 may be 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 compatibilizer. As a consequence of its interfacing topology, the compatibilizer 204 may be a major portion (up to 60% by weight) of the core polymer mixture 200 in order to enable a full encasement of the threadlike regions 400 after stretching. Notwithstanding the above, it is emphasized that the liquid core polymer mixture 200, and equivalently, the core 110 formed from the liquid core polymer mixture 200 during manufacturing, is at least a two-phase system comprising the thread polymer 202 as a first one of the at least two phases, and the liquid core polymer 112 as a second one of the at least two phases. This includes the example that the liquid core polymer mixture, or respectively, the core, is a two-phase system, i.e., the core is free of the compatibilizer.

[0138] The thread polymer 202 and the core polymer 112 are two chemically different polymers. In any case, each of the core polymer 112 and the thread polymer form a phase, i.e. a macroscopic, continuous volume filled with a plurality of molecules of the respective polymer.

[0139] Consequentially, any beads 210 or threadlike regions 400 formed from the thread polymer 202 are macroscopic phases embedded in the macroscopic core polymer phase 112. More precisely, any one of the threadlike regions 400 is not to be understood as a single stretched polymer molecule.

[0140] The cladding polymer component is prepared by mixing the pure cladding polymer granulate with additives as desired for the resulting artificial turf fibers. Suitable additives may be one or more of a wax, a dulling agent, a UV stabilizer, a flame retardant, including aramid fibers and/or an intumescent additive, an anti-oxidant, a fungicide, an antimicrobial agent, such as a silver salt, and/or a pigment, including an infrared- (IR-) reflective pigment or combinations thereof. The core polymer mixture 200 and the cladding polymer component are then melted in two single-component extrusion units and fed to a coextrusion head or die, a spinneret, or a similar coextrusion device. The melt temperature used during extrusion is dependent on the types of polymer and compatibilizer 204 that are used. The melt temperature is typically between 230 C. and 280 C. A preferable choice of process parameters for the combination of polyamide being the thread polymer and polyethylene being both the core polymer and the cladding polymer, is a pressure of 80 bar and a temperature of 240 C.

[0141] The coextrusion includes joining the cladding polymer component to the core polymer mixture 200 such that they form a polymer strand of two components which are connected by a contact layer 114 comprising a mixture of the core polymer 112 and the cladding polymer. The joining process makes use of a controllable small-scale turbulence to avoid purely laminar surface-to-surface joining. The control of this turbulence involves process parameters such as temperature and/or feed rates to influence the rheological behavior (including e.g. viscosity, melt flow index, flow velocity profile) of the two components to be joined. The strand can be extruded through an extrusion opening to form a bicomponent polymer monofilament 300 of a desired contour. Preferably, the monofilament 300 is quenched after extrusion to fix its structure thus formed.

[0142] FIG. 3 shows a cross-section of a small segment of a quenched monofilament 300 before stretching. The monofilament 300 is again shown as comprising the core polymer 112 with the polymer beads 210 mixed in and the cladding polymer surrounding the core polymer 112. The polymer beads 210 are separated from the core polymer 112 by compatibilizer 204 which is not shown. To form the threadlike regions, a section of the monofilament 300 is heated and then stretched along an axial direction of the monofilament 300. This is illustrated by the arrows which show the direction of stretching 310.

[0143] FIG. 4 illustrates the effect of stretching the monofilament 300 with an example of a cross-section of a stretched monofilament 100. The polymer beads 210 in FIG. 3 have been stretched into threadlike regions. The amount of deformation of the polymer beads 210 would be dependent upon how much the monofilament 300 has been stretched.

[0144] The polymer beads 210 may comprise crystalline portions and amorphous portions. Stretching the polymer beads 210 into threadlike regions may cause an increase in the size of the crystalline portions relative to the amorphous portions.

[0145] Core 110 and cladding 102 are joined together by a contact layer 114 where the core polymer 112 and the cladding polymer are mixed. As can be seen in FIG. 5, the threadlike regions comprised by the core 110 may locally extend into the contact layer 114 as a consequence of turbulent mixing during joining and of stretching. Preferably, the thread polymer 202 amounts to not more than 30% by weight of the core, such that the cohesion provided by the contact layer 114 remains equal or stronger than in conventional three-component artificial turf fibers with a compatibilizing layer interfacing core and cladding, even if thread polymer 202 and cladding polymer are not miscible with each other. The contact layer 114 may extend radially up to 50 percent of the minimum thickness of the cladding 102 in all directions extending radially from the core 110.

[0146] FIG. 6 shows a schematic cross-section of an exemplary piece of artificial turf 600. The artificial turf 600 comprises an artificial turf backing or carpet 602. Artificial turf fiber 604 has been tufted into the artificial turf backing 602 to form a pile 608. On the bottom of the artificial turf backing 602 a coating 606 is shown. The coating may serve to bind or secure the artificial turf fiber 604 to the artificial turf backing 602. The coating 606 may be optional. For example, the artificial turf fibers 604 may be alternatively woven into the artificial turf backing 602. Various types of glues, coatings or adhesives could be used for the coating 606. The artificial turf fibers 604 are shown as forming the pile 608 by extending a distance 610 above the artificial turf backing 602. The distance 610 is essentially the height of the pile 608 of the artificial turf fibers 604. The length of the threadlike regions within the artificial turf fibers 604 is preferably half of the distance 610 or less.

[0147] Providing the artificial turf fiber 604 may comprise weaving, spinning, twisting, rewinding, and/or bundling one or more of the stretched monofilament 100 into the artificial turf fiber 604. The incorporating may comprise weaving or tufting the artificial turf fiber 604 into the artificial turf backing 602.

[0148] An effect of designing the protrusions with a slight concave curvature can be demonstrated by comparison of FIGS. 7 and 8. FIG. 7 shows a normal cross-sectional profile of an undulated artificial turf fiber comprising a round bulge 700 at the center and two protrusions with rounded tips. The profile extends over an overall thickness t between the front central bulge 700 and the rear tip of the protrusions. The distance between the two tips is the overall width w of the fiber. Both protrusions have a profile with one straight side 704 and, opposite to the straight side 704, one undulated side 702 with four notches along a straight base line. Taking into account the axial extension of the fiber, this profile corresponds to protrusions with one flat face and one grooved face.

[0149] The protrusions may include an angle between 100 and 180 degrees. In the non-limiting example shown, the protrusions enclose an angle of about 135 degrees towards the undulated side 702 of the profile. Both protrusions have a radial extension of about three times the thickness of the bulge 700. For the purpose of demonstration only, assuming an exemplary overall profile width w=1.35 mm and overall thickness t=0.45 mm, the profile of FIG. 7 would have a cross-sectional area of 0.216 mm.sup.2. At an exemplary average density of 0.92 g/mm.sup.2, this corresponds to a yarn weight of about 2000 dtex.

[0150] FIG. 8 shows a normal cross-sectional profile of an undulated artificial turf fiber similar to the one shown in FIG. 7, the difference being that the straight sides 704 of the profile are replaced by concave sides 804, corresponding to protrusions with one concave face and one grooved face. The curvature has been designed such that the thickness of the protrusions (measured between the concave side 804 and the base line of the undulated side 702) is gradually declining towards their respective tip. For comparison with the non-limiting example above, with an overall width w=1.35 mm and overall thickness t=0.45 mm as above, the profile of FIG. 8 would have a cross-sectional area of 0.180 mm.sup.2. At the assumed average density of 0.92 g/mm.sup.2, this corresponds to a yarn weight of about 1650 dtex. A fiber with the concave profile of FIG. 8 would thus have a weight reduction of about 17% compared to a fiber with the straight profile of FIG. 7. As the concave profile has a slightly larger perimeter than the straight profile, a fiber with the concave profile would also have an increased surface-to-mass ratio compared to a fiber with the straight profile.

[0151] FIG. 9 illustrates coextrusion of two polymer components in a coextrusion device with a joining path 910 located upstream of a coextrusion opening 908. The setup comprises a hole 906 which receives a free end of a capillary tube 905. Opposite to the inserted capillary tube 905, hole 906 ends in coextrusion opening 908. A clearance between capillary tube 905 and the walls of hole 906 hydraulically connects the hole to a second channel system 904. Capillary tube 905 is hydraulically connected to a first channel system 902 and is not fully inserted into hole 906, such that a section 910 of hole 906 is hydraulically connected both to first channel system 902 and to second channel system 904. This section 910 is the joining path 910 of the depicted coextrusion setup. Joining path 910 extends from capillary tube 905 to extrusion opening 908, as is indicated by dotted lines.

[0152] During coextrusion operation, capillary tube 905 receives a molten core polymer component from first channel system 902 and hole 906 receives a molten cladding polymer component from second channel system 904. The respective transport directions of the polymer components are indicated by arrows. The two polymer components flow separated from each other until they come into contact in joining path 910. The two joined polymer components pass joining path 910, which narrows to the cross section of coextrusion opening 908, and exit coextrusion opening 908 as a bicomponent monofilament.

[0153] In cases where core and cladding are to be joined together with a contact layer comprising a mixture of the core polymer mixture and the cladding polymer component, the dimensions of the joining path are suitably chosen such that a stable contact layer of homogeneous thickness is formed. In an example, the contact layer is formed within an axial length of the joining path of 3 to 7 times the diameter of the liquid core polymer mixture at the upstream end of the joining path. In a more specific example, the diameter of the liquid core polymer mixture at the upstream end of the joining path is between 0.5 and 1.5 mm, the axial length of the joining path is between 1.5 and 10.5 mm, causing the melted core polymer mixture to mix with the cladding polymer component in a contact layer with a radial thickness between 10 and 150 m.

LIST OF REFERENCE NUMERALS

[0154] 100 stretched monofilament [0155] 102 cladding [0156] 104 protrusion [0157] 110 core [0158] 112 core polymer [0159] 114 contact layer [0160] 200 core polymer mixture [0161] 202 thread polymer [0162] 204 compatibilizer [0163] 210 polymer beads [0164] 300 raw monofilament [0165] 310 direction of stretching [0166] 400 threadlike regions [0167] 600 artificial turf [0168] 602 artificial turf backing [0169] 604 artificial turf fiber [0170] 606 coating [0171] 608 pile [0172] 610 height of pile [0173] 700 central bulge [0174] 702 undulated side [0175] 704 straight side [0176] 804 concave side [0177] 902 first channel system [0178] 904 second channel system [0179] 905 capillary tube [0180] 906 hole [0181] 908 coextrusion opening [0182] 910 joining path section