ARTIFICIAL TURF FIBER WITH LLDPE AND LDPE

Abstract

A method for manufacturing an artificial turf fiber includes creating a polymer mixture that includes, 60-99% by weight of an LLDPE polymer and 1-15% by weight of an LDPE polymer. The method further includes extruding the polymer mixture into a monofilament; quenching the monofilament; reheating the monofilament; and stretching the reheated monofilament to form the monofilament into the artificial turf fiber.

Claims

1-24. (canceled)

25. An artificial turf fiber comprising: 60-99% by weight of a linear low-density polyethylene (LLDPE) polymer; and 1-15% by weight of a low-density polyethylene (LDPE) polymer.

26. The artificial turf fiber of claim 25, wherein the LLDPE polymer has a density in a range of 0.918 g/cm.sup.3 to 0.920 g/cm.sup.3, and wherein the LDPE polymer has a density in a range of 0.919 g/cm.sup.3 to 0.921 g/cm.sup.3.

27. The artificial turf fiber of claim 25, wherein the LLDPE polymer comprises a first LLDPE polymer and a second LLDPE polymer, the first LLDPE polymer having a density in a range of 0.918 g/cm.sup.3 to 0.920 g/cm.sup.3 and the second LLDPE polymer having a density in a range of 0.914 g/cm.sup.3 to 0.918 g/cm.sup.3, and wherein the LDPE polymer has a density in a range of 0.919 g/cm.sup.3 to 0.921 g/cm.sup.3.

28. The artificial turf fiber of claim 27, wherein the artificial turf fiber comprises 60-99% by weight the first LLDPE polymer and 7-13% by weight the second LLDPE polymer.

29. An artificial turf comprising an artificial turf textile backing and the artificial turf fiber according to claim 25, the artificial turf fiber being incorporated into the artificial turf backing.

30. The artificial turf of claim 29, wherein the artificial turf fiber is an extruded and stretched monofilament.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0094] In the following embodiments of the invention are explained in greater detail, by way of example only, making reference to the drawings in which:

[0095] FIG. 1 shows an LDPE and an LLDPE molecule;

[0096] FIG. 2 shows an entanglement of one LDPE and multiple LLDPE molecules;

[0097] FIG. 3 shows the effect of shear forces during extrusion;

[0098] FIG. 4 shows a cross-section of a granular polymer mixture;

[0099] FIG. 5 shows a flowchart which illustrates an example of a method of manufacturing artificial turf fiber;

[0100] FIG. 6 shows a schematic drawing of a multi-phase polymer mixture;

[0101] FIG. 7 shows a cross-section of a small segment of the monofilament;

[0102] FIG. 8 illustrates the effect of stretching the monofilament;

[0103] FIG. 9 illustrates the extrusion of the polymer mixture into a monofilament; and

[0104] FIG. 10 shows an example of a cross-section of an example of artificial turf.

DETAILED DESCRIPTION

[0105] 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.

[0106] FIG. 1 shows a single LDPE molecule 102 as it may be used in embodiments of the invention. It comprises one or more long main chains and a plurality of small side chains extending from any one of the main chains. The small side chains are typically 2-8 carbon atoms long. In addition, FIG. 1 shows a single LLDPE molecule 104. The LLDPE molecule does not comprise larger side chains. It only comprises a single, long polyethylene main chain and a plurality of small side chains extending from the main chain.

[0107] Applicant has observed that the type of catalyst used during the polymerization reaction determines the tacticity and the branching properties of a PE molecule (number and distances of branches in a main chain, length of side chains, etc). Preferentially, metallocene catalysts are used for creating the LLDPE, because they result in a more regular branching pattern than other catalysts (which typically trigger the generation of LLDPE polymers whose number and distance of branches and the length of the individual branches follows a normal distribution). Generating LLDPE polymers with a defined, regular (not normally distributed) branching pattern can be beneficial as the properties of a monofilament resulting from a mixture of such an LLDPE polymer with an LDPE polymer can thus be predicted more clearly. Moreover, the density is then a more accurate indicator of the tacticity and the branching pattern.

[0108] In addition, the lower portion of FIG. 1 illustrates that the first, “medium density” LLDPE 104 is folded more densely than the second, “low density” LLDPE 106.

[0109] FIG. 2 shows chain entanglement between a single LDPE molecule 102 and multiple LLDPE molecules 104. The entanglement is achieved by Van-der-Waals forces between the larger and minor branches of the LPDE with the main chain and the minor side chains of one or more LLDPE molecules. Due to the lack of larger side chains, a polymer fiber solely consisting of LLDPE would be susceptible to splicing. By adding some LDPE molecules at a particular weight ratio to a polymer mixture largely consisting of LLDPE, and by choosing the LDPE and LLDPE polymers of a particular density, it is possible to manufacture a fiber that has a high split resistance and at the same time high tensile strength.

[0110] FIG. 3 shows a section through an area within a cylindrical extrusion nozzle. In a first area 302, the polymers of a liquefied polymer mixture are mostly in an amorphous state, i.e., there are only few or no crystalline regions and the polymer molecules do not show any preferred orientation in one dimension. In a second area 304 that corresponds to an area of increased shear forces, the polymer molecules are sheared and pulled at least partially in the direction of the opening 310 of the nozzle. In the area 306 corresponding to high shear forces, the LLDPE and partially also the LDPE molecules are at least partially disentangled, oriented and form crystalline portions 308. However, according to preferred embodiments, the majority of crystalline portions is created later in the stretching process.

[0111] Using the LLDPE-LDPE mixture according to embodiments of the invention are particularly beneficial for preventing splicing in artificial turf fibers which are stretched in the manufacturing process. The extrusion, and in particular the stretching, results in an at least partial disentanglement and parallel orientation of LLDPE molecules which again causes an increased susceptibility of the fiber to splicing. By adding the appropriate amount of LDPE, in particular LDPE of a particular density, to the polymer mixture, the splicing can be prohibited even in fibers that are stretched during manufacturing.

[0112] FIG. 4 shows a cross-section of a granular polymer mixture 470 according to one embodiment of the invention. The polymer mixture comprises the following components e.g. in the form of polymer granules that are molten later: [0113] a “pure” first LLDPE polymer 450 of a density of 0.919 g/cm.sup.3 and at an amount of 73% by weight of the polymer mixture. The first LLDPE polymer preferentially lacks any additives; [0114] a “master batch” 452 comprising the first LLDPE polymer having a density of 0.919 g/cm.sup.3 and at an amount of 10% by weight of the polymer mixture. The master batch may comprise additives. An LDPE polymer 454 of a density of 0.920 g/cm.sup.3 and at an amount of 7% by weight of the polymer mixture. [0115] a second, low density LLDPE polymer 456 of a density of 0.916 g/cm.sup.3 and at an amount of 10% by weight of the polymer mixture.

[0116] Depending on the embodiments, the amount of the filler material, the master batch, the LDPE and the first and second LLDPE polymer may vary. Preferentially, the amount of the first LLDPE polymer 450 lacking the additives is in this case adapted such that all components of the polymer mixture add up to 100%.

[0117] In the depicted example, the first LLDPE polymer in fraction 450 and in the master batch 452 and the additives contained in the master mix may constitute 83% by weight of the polymer mixture 470. In other embodiments (not shown), the polymer mixture 470 may comprise up to 39% filler material. In case the polymer mixture comprises 1% LDPE polymer and 99% LLDPE polymer (no filler or additives), an LDPE/LLDPE weight ratio of 1:99 is used. In case the polymer mixture comprises 15% LDPE polymer and 60% LLDPE polymer (a large amount of filler and additives may be used), an LDPE/LLDPE weight ratio of 15:60 is used. Preferentially, the LDPE/LLDPE weight ratio is between 5:95 and 8:60, i.e., between 5.3% and 13.3%.

[0118] In some embodiments depicted e.g. in FIG. 6, the polymer components 450-456 together form a first liquid phase 404 that may in addition comprise an additional polymer, e.g. PA, that may form a second phase 402 that forms beads 408 within the first phase. In this case, the amount of the first LLDPE is reduced in accordance with the amount of the other polymer.

[0119] FIG. 5 shows a flowchart which illustrates an example of a method of manufacturing artificial turf fiber. First in step 502 a polymer mixture is created. The polymer mixture is comprises at least an LLDPE polymer having a density of 0.918 g/cm.sup.3 to 0.920 g/cm.sup.3 and a first LLDPE polymer having a density of 0.920 g/cm.sup.3 in an amount of about 5-8% by weight of the polymer mixture. The LLDPE polymer may be added in the form of pure LLDPE granules 450 and master batch LLDPE granules 452 as depicted, for example, in FIG. 4. The master batch LLDPE polymer granules may comprise additives. Preferentially, the LLDPE polymer in the polymer granules 450, 452 is of an identical type. Optionally, the polymer mixture may comprise about 10% of a “low density” LLDPE.

[0120] Depending on the embodiment, it is possible that the polymer mixture comprises a small fraction of an additional polymer, e.g. PA, and optionally a compatibilizer, as depicted and discussed in further detail in FIG. 6.

[0121] The polymer mixture may at first have the form of a polymer granules mixture. By heating the granules, a liquid polymer mixture is created. Thereby, the polymer mixture may optionally be stirred at a stirring rate suitable to ensure that the molten polymers and additives are homogeneously mixed.

[0122] In the next step 504 the polymer mixture is extruded into a monofilament. Next in step 506 the monofilament is quenched or rapidly cooled down. Next in step 508 the monofilament is reheated. In step 510 the reheated monofilament is stretched to form the monofilament into the artificial turf fiber. Said step is depicted in greater detail in FIG. 3.

[0123] Additional steps may also be performed on the monofilament to form the artificial turf fiber. For instance the monofilament may be spun or woven into a yarn with desired properties. Then, the artificial turf fiber is incorporated into an artificial turf backing. For example be, this can be done by tufting or weaving the artificial turf fiber into the artificial turf backing. Finally, the artificial turf fibers are bound to the artificial turf backing. For instance the artificial turf fibers may be glued or held in place by a coating or other material. According to one embodiment, at least a portion of the artificial turf fibers extends through a carrier, e.g. a piece of textile, to the backside of said carrier. A fluid latex or polyurethane (PU) film is be applied on the backside of said backing (i.e., the side opposite to the side from which the larger portions of the fibers emanate) such that at least the portion of the fiber at the backside of the carrier is wetted and surrounded by said latex or PU film. When the film solidifies, the fibers are fixed in the latex or PU backing by mechanical, frictional forces. This effect is at least in part caused by the stretching process in which polymer crystals at the surface (and interior parts) of the fibers are generated which increase the surface roughness. Monofilaments generated according to embodiments of the invention have a higher surface roughness than e.g. polymer fibers generated by slitting polymer films into thin stripes, because the cutting of polymer films destroys the crystalline structures at the areas having contacted the blade of the cutting knife.

[0124] FIG. 6 shows a schematic drawing of a cross-section of a multi-phase polymer mixture 400. The polymer mixture 400 comprises at least a first phase 404 and a second phase 402. The first phase comprises a first dye and an LDPE-LLDPE polymer mixture according to embodiments of the invention as shown, for example, in FIG. 4. The second phase 402 comprises an additional polymer that is immiscible with the polymers in the first phase and a second dye. For example, the additional polymer may be PA which may provide for an improved resilience of the fibers. In the depicted embodiment, the polymer mixture comprises a third phase 406 that mainly or solely comprises a compatibilizer. The third phase may comprise the first or the second or a third dye or no dye at all. The first phase and the second phase are immiscible. The additional polymer and the second phase 402 are less abundant than the first phase (that mainly consists of the LLDPE-LDPE mixture). The second phase 402 is shown as being surrounded by the compatibilizer phase 406 and being dispersed within the first phase 404. The second phase 402 surrounded by the compatibilizer phase 406 forms a number of polymer beads 408. The polymer beads 408 may be spherical or oval in shape or they may also be irregularly-shaped depending up on how well the polymer mixture is mixed and the temperature. The polymer mixture 400 is an example of a three-phase system. The compatibilizer phase 406 separates the first phase 402 from the second phase 406. The additional polymer may be stiffer and more resilient than the polymers in the first phase, thereby increasing stiffness and resilience of the fiber.

[0125] Due to flow conditions during extrusion, the beads are formed into thread-like regions that are predominantly located in the interior parts of the monofilament. This particular location is advantageous as the increased stiffness of the threadlike regions (relative to the surrounding first polymer phase) may increase the risk of skin burns in case a person slides with his skin across a section of artificial turf if the threadlike regions would predominantly lie on the surface of a fiber.

[0126] In the context of manufacturing fibers comprising threadlike-regions of the additional polymer (that is preferentially more rigid than the polymers in the first phase), increasing the resistance to splicing in the first phase is particularly advantageous, as it prevents the rigid, thread-like regions (mainly located inside a fiber) being exposed to the surface due to delamination or other forms of splicing.

[0127] FIG. 7 shows a cross-section of a small segment of the monofilament 606. The monofilament is again shown as comprising the first phase 404 comprising the LLDPE-LDPE polymer mixture according to embodiments of the invention that may—as the case here—optionally comprise a second phase in the form of polymer beads 408 mixed in. The polymer beads 408 are separated from the second polymer by compatibilizer which is not shown. To form the thread-like structures a section of the monofilament 606 is heated and then stretched along the length of the monofilament 606. This is illustrated by the arrows 700 which show the direction of the stretching. The first and second polymer phases may comprise dies having different colors.

[0128] FIG. 8 illustrates the effect of stretching the monofilament 606. In FIG. 8 an example of a cross-section of a stretched monofilament 606 is shown. The polymer beads 408 in FIG. 7 have been stretched into thread-like structures 800. The amount of deformation of the polymer beads 408 would be dependent upon how much the monofilament 606′ has been stretched.

[0129] Examples may relate to the production of artificial turf which is also referred to as synthetic turf. In particular, the invention relates to the production of fibers that imitate grass both in respect to mechanical properties (flexibility, surface friction) as well as optical properties (color texture). The fibers according to the depicted embodiment are composed of first and second phases that are not miscible and differ in material characteristics as e.g. stiffness, density, polarity and in optical characteristics due to the two different dyes. In some embodiments, a fiber may in addition comprise a compatibilizer and further components. In other embodiments, the polymer mixture consists of only one liquid phase comprising one or more LLDPE polymers, one or more LDPE polymers and optionally one or more additives.

[0130] In a first step, the polymer mixture is generated comprising at least one LLDPE and one LDPE polymer in a particular density range corresponding to a particular tacticity and branching pattern.

[0131] In embodiments where the polymer mixture further comprises an additional polymer that forms a second phase, the quantity of the second phase may be 5% to 10% by mass of the polymer mixture and the quantity of an optional third phase being largely or completely comprised of the compatibilizers being 5% to 10% by mass of the polymer mixture. The amount of the LLDPE polymer in the first phase is adapted accordingly. Using extrusion technology results in a mixture of droplets or of beads of the second phase surrounded by the compatibilizer, the beads being dispersed in the polymer matrix of the first polymer phase and having a different color than the second phase.

[0132] The melt temperature used during extrusion is dependent upon the type of polymers and compatibilizer that is used. However the melt temperature is typically between 230° C. and 280° C.

[0133] A monofilament, which can also be referred to as a filament or fibrillated tape, is produced by feeding the mixture into an fiber producing extrusion line. The melt mixture is passing the extrusion tool, i.e., a spinneret plate or a wide slot nozzle, forming the melt flow into a filament or tape form, 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.

[0134] The monofilament or type is then annealed online in a second step passing a further heating oven and/or set of heated godets.

[0135] By this procedure the beads or droplets (optionally surrounded by a compatibilizer phase) are stretched into longitudinal direction and form small fiber like, linear structures, also referred to as thread-like regions. The majority of the linear structures is completely embedded into the LLDPE-LDPE-polymer matrix 404 but a significant portion of the linear structures is also at the surface of the monofilament.

[0136] The resultant fiber may have multiple advantages, namely softness combined with durability and long term elasticity and tensile strength in combination with resistance to splicing. The large amount of LLDPE polymer will ensure a high tensile strength while the LDPE polymer added in the specified LDPE/LLDPE ratio will promote chain entanglement and thus protect the fiber from splicing. In case of different stiffness and bending properties of the polymer phases, the fiber can show a better resilience (this means that once a fiber is stepped down it will spring back). In case of a stiff additional polymer 402, the small linear fiber structures built in the polymer matrix are providing a polymer reinforcement of the fiber.

[0137] Delimitation due to the composite formed by the polymers in the first and second phases is prevented due to the fact that the thread-like regions of the additional polymer are embedded in the matrix given by the LLDPE-LDPE polymer phase 404.

[0138] FIG. 9 illustrates the extrusion of the polymer mixture into a monofilament. Shown is an amount of polymer mixture 600. Within the polymer mixture 600 there is a large number of polymer beads 408. The polymer beads 408 may be made of one or more polymers that are not miscible with the LLDPE-LDPE polymer mixture in the first phase 404 and are separated from the first phase by a compatibilizer. A screw, piston or other device is used to force the polymer mixture 600 through a hole 604 in a plate 602. This causes the polymer mixture 600 to be extruded into a monofilament 606. The monofilament 606 is shown as containing polymer beads 408 also. The polymers in the first phase 404 and the polymer beads 408 are extruded together. In some examples the first phase will be less viscous than the polymer beads 408 comprising the additional polymer, e.g. PA, and the polymer beads 408 will tend to concentrate in the center of the monofilament 606. This may lead to desirable properties for the final artificial turf fiber as this may lead to a concentration of the thread-like regions in the core region of the monofilament 606. However, the composition of the first and second phases and in particular the polymers contained therein are chosen such (e.g. in respect to polymer chain length, number and type of side chains, etc.) that the first phase has a higher viscosity than the second phase and that the beads and the thread-like regions concentrate in the core region in the monofilament. In embodiments where the two different phases comprise dyes of different colors, the additional polymer is chosen such that its viscosity properties in combination with the viscosity properties of the polymers in the first phase ensures that there are still sufficient amounts of the beads and the thread-like regions on the surface of the monofilament to result in a marbled color texture on the surface of the monofilament.

[0139] FIG. 10 shows an example of a cross-section of an example of artificial turf 1000. The artificial turf 1000 comprises an artificial turf backing 1002. Artificial turf fiber 1004 has been tufted into the artificial turf backing 1002. On the bottom of the artificial turf backing 1002 is shown a coating 1006. The coating may serve to bind or secure the artificial turf fiber 1004 to the artificial turf backing 1002. The coating 1006 may be optional. For example the artificial turf fibers 1004 may be alternatively woven into the artificial turf backing 1002. Various types of glues, coatings or adhesives could be used for the coating 1006. The artificial turf fibers 1004 are shown as extending a distance 1008 above the artificial turf backing 1002. The distance 1008 is essentially the height of the pile of the artificial turf fibers 1004. The length of the thread-like regions within the artificial turf fibers 1004 is half of the distance 1008 or less. The coating may, for example, be a PU or latex film that is applied as a liquid film on the bottom side of the turf backing, that surrounds portions of the fibers at least partially, and that solidifies and thereby mechanically fixes the polymer fibers in the backing.

LIST OF REFERENCE NUMERALS

[0140] 102 LDPE molecule [0141] 104 LLDPE molecule [0142] 302-306 regions having different shear forces during extrusion [0143] 308 crystalline polymer portions [0144] 310 opening of extrusion nozzle [0145] 400 polymer mixture [0146] 402 second phase [0147] 404 first phase [0148] 406 third phase with compatibilizer [0149] 408 polymer bead [0150] 450 first LLDPE polymer [0151] 452 “master batch” LLDPE polymer (with additives) [0152] 454 LDPE polymer [0153] 456 second (“low density”) LLDPE polymer [0154] 470 polymer mixture [0155] 502-510 steps [0156] 600 polymer mixture [0157] 602 plate [0158] 604 hole [0159] 606 monofilament [0160] 606′ stretched monofilament [0161] 1000 artificial turf [0162] 1002 artificial turf carpet [0163] 1004 artificial turf fiber (pile) [0164] 1006 coating [0165] 1008 height of pile