Recyclable artificial grass and HDPE backing layer for recyclable artificial grass

Abstract

The present invention relates to a polyethylene backing layer for an artificial turf base consisting essentially of highly oriented high density polyethylene filaments forming the warp and weft yarns, the highly oriented high density polyethylene filaments having a tensile strength of at least 945 kg / m 3 and a melt flow index of up to 2 g / 10 min. The invention further relates to filaments for making such a backing layer, to a method for producing such filaments, and to an artificial turf base comprising such a backing layer.

Description

[Technical field]

[0001]

[0001] The present invention relates to artificial turf, and in particular to backing layers for artificial turf made from high density polyethylene filaments, and methods for their manufacture. [Background technology]

[0002]

[0002] Artificial turf is well known from various publications and has been developed through several generations up to its current form. In general, such systems try to achieve the same properties as their natural counterparts, but in certain areas may already surpass them, at least in terms of predictability of behavior. Here, a distinction is made between artificial turf intended for use in sports and competitions and artificial turf used purely (or mainly) for landscaping.

[0003] First generation systems were typically made with green nylon yarn. The pile was very short and dense and not very comfortable for sports use. Second generation systems, initially made with nylon yarn, more recently moving to PP and PE, have longer pile and use sand as an infill layer to keep the pile upright. Although second generation systems were more suitable for sports use, they still did not resemble natural grass very well.

[0004] A typical third generation turf system comprises a carpet-like layer having upright pile fibres and an infill layer disposed between the pile fibres. The carpet has a backing layer which may consist of a woven fabric of suitable material into which the artificial turf fibres are tufted to provide the pile fibres oriented in an upward position. The pile fibres may comprise fibrillated tapes or monofilaments of a suitable polymeric material or mixture of materials. The pile fibres may be fixed to the woven fabric by a coating of latex or polyurethane to reduce fibre pull-out. The infill provides the required elasticity of the pitch and may comprise soft granules such as synthetic rubber and / or natural materials such as sand or cork.

[0005] In fourth generation turf systems, the shock absorbing function of the filler can be integrated with the fiber structure of the carpet. This can be achieved, for example, by careful selection of different fibers to produce a thatch layer of curled fibers that does not extend much further than the pile fibers. In fourth generation systems, weaving of complete artificial turf carpets is popular as an alternative to tufting. The backing layer and the pile fibers are therefore produced simultaneously by weaving on a loom. There is now considerable freedom in the location of the pile fibers and the backing structure.

[0006]

[0006] In both third and fourth generation systems, several different classes of materials are used to achieve the correct mix of properties in each layer of the final product. The term "layer" is used here merely for convenience. It will be understood that a given function may be achieved by several layers, and that one layer (and function) may be partially coextensive with another layer, such as a fill layer may extend through a pile layer.

[0007]

[0007] At least the following layers and functions relevant to the present discussion can be distinguished (although certainly more exist): - the backing layer, generally a woven fabric, provides structural integrity in the horizontal direction and holds the pile fibers; -The pile layer provides sports performance (ball-rolling, ball-bouncing, sliding performance, etc.) - The locking layer prevents the pile from being pulled out of the backing layer, -The elastic layer provides elasticity and keeps the pile layer upright.

[0008]

[0008] Although the patent publications indicate that any one or more of many different selected materials can be used for any of these layers or functions, this is not the case. In reality, a limited number of materials can acceptably accomplish the required functions of each layer. In particular, it should be recognized that artificial turf is primarily expected to be used outdoors where it is exposed to all possible environmental conditions.

[0009] For this reason, in existing third and fourth generation systems, the backing layer is generally formed from woven polypropylene fibres. Typical fabric weights are between 80 and 400 g / m 2 and the fibres have a linear density of 300-1500 dtex. Polypropylene exhibits good stability to outdoor conditions, shows high creep resistance and has a good life span. Stability is important because temperatures on the pitch can vary between freezing and 85°C if exposed to direct sunlight without proper cooling facilities. Sufficient creep resistance is particularly important for artificial turf applied to sports fields that have even a small slope for drainage, otherwise static forces may result in deformation of the artificial turf over time.

[0010]

[0010] The pile layer is typically formed from polyethylene, although polypropylene and polyamide materials may also occasionally be used. Polyethylene has been found to have the most optimal properties, especially elasticity, to achieve the required functions of the pile layer. Attempts have been made to improve these functions further by using coatings and mixtures of other materials, but PE currently accounts for about 95% of the market for sports surfaces.

[0011]

[0011] The lock layer is currently primarily provided by a latex coating on the back side of the backing layer, although in North America polyurethane is preferred.

[0012]

[0012] The infill layer is currently perhaps the most varied layer in terms of material choice. Many existing pitches still use crumb rubber from recycled car tyres. This is now being phased out, with new installations favouring natural materials such as cork. In the case of fourth generation turf systems, the infill layer / function can be provided by thatch fibres, for example fibrillated, curled, knit-de-knit (KDK) or textured (TXT) yarns made from polyolefins.

[0013]

[0013] Although such systems provide superior sports performance, the presence of multiple materials poses significant additional difficulties and costs during removal and disposal. The present invention seeks to further improve such artificial turf systems by providing a comparable level of functionality while enhancing the ability to recycle the product at the end of its life. Summary of the Invention

[0014]

[0014] There is therefore provided a polyethylene backing layer for an artificial turf base consisting essentially of highly oriented high density polyethylene (HDPE) filaments forming warp and weft yarns, the highly oriented high density polyethylene filaments having a modulus of at least 945 kg / m 3 and a melt flow index of up to 2 g / 10 min.

[0015]

[0015] In this context, "consisting essentially of" means that at least 99% by weight of the backing layer consists of highly oriented HDPE filaments. In each HDPE filament, at least 90% or even at least 95% by weight of the total weight of the filament may be a high density polyethylene composition. In addition, the HDPE filaments may comprise additives such as fillers, pigments, UV stabilizers or processing aids. The term "highly oriented filaments" is used to indicate filaments formed in an extrusion process using a draw ratio greater than 4, preferably greater than 5, and more preferably a draw ratio between 6 and 7.

[0016]

[0016] As described above, conventional artificial turf uses different classes of polymer materials for the backing on the one hand and for the pile fibers on the other hand. According to the present invention, polyethylene is used for both layers and / or functions. Although this may seem trivial in theory, the solution is not so in practice. As indicated above, the backing layer has been made up to now from polypropylene (PP), precisely due to its stability against temperature fluctuations during use and its good creep resistance. Polypropylene, however, cannot be effectively used as pile fiber, since it is too stiff and it was still not possible to achieve the required sports performance properties with this material.

[0017]

[0017] Currently, polyethylene (PE) is the most preferred material for pile fibers. It has the appropriate physical properties (e.g., flexibility) to exhibit acceptable sports performance properties for the range of fiber dimensions required. On the other hand, it has not been considered possible to use PE in the backing layer due to the fact that it is not adequately temperature stable when exposed to high temperatures such as those found in use, or even when encountered during production, e.g., during the application of coating layers. In addition, attempts to produce polyethylene backings have failed thus far, mainly due to insufficient creep resistance and dimensional stability with respect to the tufting process. In fact, the ability to extrude polyethylene backing filaments, especially filaments of sufficient strength to be used as a replacement for polypropylene, has been relatively limited so far.

[0018] According to the invention, the creep resistance of the artificial turf is improved by providing a backing layer made from a high density polyethylene material. 3The density can be measured, for example, according to ISO 1183-1 or ISO 1183-2. The advantage of using HDPE is the relatively high tensile strength, good creep resistance and good heat resistance compared to polyethylene materials with a higher degree of branching, such as LDPE. More precisely, by using HDPE, a backing layer can be formed that has at least the same dimensional stability with regard to weather, strength and creep resistance as a backing layer made from PP.

[0019]

[0019] In an embodiment, the filaments have one or more ribs along their length. This advantageously increases the surface roughness so that the filaments are less prone to distortion, both in use and during the tufting process. In an embodiment, the filaments may be provided with ribs or grooves on one or both sides. These may be imparted by an extrusion die which may have shape features in the range of 0.01 mm to 1 mm, particularly 0.1 mm to 0.6 mm. It will be appreciated that such features are proportionally reduced during drawing of the filaments and may be present in the final filaments merely as light streaks or ripples. Nevertheless, they may help provide stability to the woven backing.

[0020] In an embodiment, the polyethylene has a viscosity of at least 950 kg / m 3 It has a density of 945kg / m 3 HDPE having a density of 100% may be sufficient, but the mechanical properties of the backing layer, such as strength and dimensional stability, e.g., shrinkage and creep resistance, may be improved for higher densities due to the lower degree of branching and higher crystallization rate.

[0021] In an embodiment, the density is 950 kg / m 3 ~970kg / m 3For some types of HDPE, a lower density may improve the processability of the HDPE in the extrusion process that may be used to form the filaments. It will also be understood by those skilled in the art that the strength of the lining filaments is highly dependent on their degree of orientation and the draw ratio to which they are exposed. It should be recognized that higher density polyethylenes can be better stretched, but are also more susceptible to shrinkage during use. Thus, heat stabilization of the lining prior to use is recommended, as further detailed below. Higher density is also associated with a higher melting point, which is desirable for reasons further discussed below.

[0022]

[0022] In an embodiment, the molecular weight of HDPE is 200000-500000 g / mol. As well as the effect of higher density, a higher molecular weight also contributes to a higher melting point and improved creep resistance. Nevertheless, too high a molecular weight may result in poor processability in the extrusion process.

[0023]

[0023] In an embodiment, the HDPE has a moderate or moderately broad molecular weight distribution (MWD). HDPE with too narrow a molecular weight distribution will reduce the processability of HDPE in the extrusion process, since it will make the processing window too narrow. Nevertheless, a narrow MWD may be associated with a more distinct melting temperature, which may be advantageous for reasons further given below. HDPE with too broad a molecular weight distribution may also be less favorable in terms of its mechanical properties. Therefore, preferably, the HDPE has a molecular weight distribution (MWD) as narrow as possible, while maintaining good processability of HDPE in the extrusion process. Preferably, the HDPE has a monomodal weight distribution curve.

[0024]

[0024] The melt flow index (MFI) of the HDPE of the filament is at most 2 g / 10 min. The MFI is measured according to ISO 1133-1. Such a relatively low MFI is advantageous because the creep resistance of the backing layer is lower for a higher MFI. It will be understood by those skilled in the art that the HDPE composition also has a certain minimum melt flow index (MFI). In an embodiment, the MFI is at least 0.7 g / 10 min or at least 1.2 g / 10 min.

[0025] In an embodiment, the melt flow index (MFI) of the HDPE composition of the filament is 1.5g / 10min to 2g / 10min, preferably 1.7g / 10min to 1.9g / 10min. HDPE compositions with MFI within these ranges have good processability in the extrusion process. A lower MFI may result in too high die pressure in the extruder and, as a result, a lower throughput. Conversely, a higher MFI may cause problems during the stretching of the filament or extruded film, resulting in non-uniform stretching. Thus, an MFI within these ranges is favorable for both the processability of the HDPE composition in the extrusion process and the stability characteristics of the backing layer.

[0026] According to an embodiment, the HDPE has a melting point of at least 125°C, preferably at least 128°C, more preferably about 130°C. This is advantageous for the subsequent use of a backing layer in the artificial turf backing when melting the pile fibers of the artificial turf backing to increase the fiber bond strength, as will be discussed in connection with further aspects of the invention below. Since the melting point of the backing layer is higher than the melting point of the pile fibers in the artificial turf backing, the pile fibers can be melted together but the backing layer remains intact. Preferably, an HDPE with the highest possible melting point is selected. Currently available HDPE compositions have a melting point of about 130°C.

[0027]

[0027] Those skilled in the art will recognize that for polymeric materials, melting actually occurs over a range of temperatures. In the following, melting temperature will refer to the peak temperature measured by differential scanning calorimetry (DSC). This is different from the onset temperature, which is sometimes called the extrapolated onset temperature (according to DIN EN ISO 11357-1:2010-03). This is the calculated intersection of the extrapolated baseline and the inflection tangent at the beginning of the melting or crystallization peak. According to an embodiment of the present invention, the HDPE composition may be selected to have an onset temperature that is above the melting temperature of the pile fibers.

[0028] The warp and weft filaments in the backing layer may be monofilaments or slit films. In an embodiment, at least some of the filaments are tapes. The term "tape" refers to a unidirectionally oriented polymeric product, preferably having a linear density (or titer) of 100 dTex to 2500 dTex. The tape may have a rectangular or square cross section and is preferably formed by slitting an extruded film. The tape typically has a thickness of 50 to 120 μm, preferably 70 to 100 μm, and a width of 0.5 to 5 mm, preferably 1 to 3 mm. These thicknesses and widths refer to the thickness and width of the tape stretched during the extrusion process and ready for weaving. Wider tapes may cause obstructions to the woven backing layer, whereas narrower tapes will not be effective due to their insufficient strength.

[0029]

[0029] In a further embodiment, the backing layer is a primary backing layer suitable for tufting. The primary backing layer is defined as the layer in which the pile fibers are located after tufting. Preferably, the filaments of the primary backing layer are formed by tapes. Alternatively, the backing layer can be part of a three-dimensionally woven artificial grass backing. Weaving of a complete artificial grass carpet is common as an alternative form of tufting. Woven artificial grass comprises a backing layer and pile fibers that are simultaneously produced by weaving on a loom. Woven artificial grass backing comprises warp and weft threads. Most preferably, woven artificial grass is produced in a face-to-face weaving process, in which pile fibers are also present in the warp threads.

[0030] In an embodiment, the backing layer is woven using a plain weave, which is well suited for tufting.

[0031]

[0031] In an embodiment, the number of warp filaments per unit length is different from the number of weft filaments per unit length. This is advantageous for the tuftability of the backing layer. In the manufacture of artificial turf, an important goal is to avoid unnatural appearances such as overly regular patterns. The variation between warp and weft yarns reduces the so-called moiré effect in tufting, thereby also reducing aesthetic defects.

[0032] In an embodiment, the ratio of the number of warp filaments to the number of weft filaments is substantially the same as the inverse of the ratio of the linear density of the warp filaments to the linear density of the weft filaments. Here, "substantially the same" refers to a maximum difference between the ratios of 15%. This results in a backing layer with good tuftability and similar strength in the warp and weft directions. The effect in terms of strength is similar when the number of warp filaments per unit length and the number of weft filaments per unit length are substantially the same, and the warp and weft filaments have substantially the same linear density. Such a so-called square structure, where the arrangement of the warp filaments and the arrangement of the weft filaments are substantially the same, contributes to the dimensional stability of the backing layer (see, for example, US Pat. No. 6,897,170 B2) and ensures that the individual tapes lie flat in the fabric without twisting. This results in a backing layer with low fabric shrinkage and hence better dimensional stability. In addition, the backing layer may have similar strength in both the warp and weft directions. A fabric in which the ratio of the number of warp filaments to the number of weft filaments is substantially the same as the inverse of the ratio of the linear density of the warp filaments to the linear density of the weft filaments combines the beneficial effects of a square structure with a non-square structure that has good tuftability. This arrangement is called a "biased square structure." Alternatively, in an embodiment, a perfect square structure can be used, in which the number of warp filaments per unit length and the number of weft filaments per unit length are substantially the same, and the warp and weft filaments have substantially the same linear density.

[0033]

[0033] In an embodiment, the backing layer may comprise multiple sub-layers. The multiple sub-layers may be stacked on top of each other or stitched or bonded together to together perform the function of the backing layer providing structural integrity in the horizontal direction and holding the pile fibers. The multiple sub-layers together form a primary backing layer suitable for tufting. The preferred method of joining such layers is by warp knitting. In an embodiment, the backing layer consists of two sub-layers that are identical to each other.

[0034]

[0034] In another embodiment, the filaments of the backing layer have a linear density of 100 to 2500 dtex, preferably 200 to 1700 dtex. Illustrative values ​​can be between 600 dtex and 1200 dtex.

[0035]

[0035] The filaments should be as strong as possible, subject to other constraints. In an embodiment, the filaments have a tensile strength of at least 20 cN / Tex, preferably the filaments have a tensile strength of at least 25 cN / Tex. More importantly, the filaments may have a tensile strength of greater than 10 cN / Tex at 5% elongation, or greater than 12 cN / Tex at 5% elongation.

[0036] In an embodiment, the backing layer has a thickness of 80 to 400 g / m 2 , preferably 100 to 300 g / m 2 Such a weight allows applicability as a backing layer in most sports applications and in artificial turf that is primarily used in landscaping.

[0037] In an embodiment, the filaments may further comprise one or more additives, preferably selected from the group consisting of antioxidants, UV stabilizers, pigments, processing aids, acid scavengers, lubricants, antistatic agents, fillers, nucleating agents, and clarifiers. These additives may preferably be added as a masterbatch to the melt before extrusion. In an embodiment, the filaments comprise 3-6 wt. % pigments and UV stabilizers, and / or 0-2 wt. % processing aids. The amount of fillers is typically 2-6 wt. % and may vary for filaments used in warp and weft directions, depending on the properties required.

[0038] In an embodiment, the filaments have a strain at break of 10-40%, preferably 20-35%. It will be appreciated by those skilled in the art that low strain values ​​of the individual filaments generally correspond to high creep resistance of the backing layer, which is therefore advantageous for use in the backing layer of artificial turf. Nevertheless, some elasticity is required to prevent the filaments from breaking during weaving. Alternatively, the creep of the backing layer itself can be measured. According to an embodiment, the backing layer has a creep strain rate of at most 1.0% / h, preferably at most 0.5% / h, more preferably at most 0.1% / h after 5 hours. The creep strain rate can be determined in a Zwick tensile tester by applying a constant load at 50°C for 5 hours. After 5 hours, the creep strain rate can be determined as the difference between the 4-hour gauge length and the 5-hour gauge length divided by the 4-hour gauge length.

[0039] In an embodiment, the backing layer is heat-stabilized by heating the backing layer above the initiation temperature of the HDPE. Heat stabilization relaxes the strains generated in the filaments during the weaving process. It will be understood that weaving is generally performed at ambient temperature where the filaments have a given elastic modulus. The weaving action induces bends and twists in the filaments, which remain after the process is completed. When the temperature of the backing layer is increased, the induced strains can be restored by relaxation and straightening of the bends in the filaments. In an embodiment, heat stabilization can be performed in combination with locking of the pile fibers, for example in a melting process as described in more detail below. This is particularly important in the case of artificial turf woven in three dimensions.

[0040] According to a second aspect of the present invention, and in accordance with the advantages described above, there is provided a method for producing a backing layer, the method comprising the steps of: 3and a melt flow index of up to 2 g / 10 min; and weaving a backing layer, the backing layer being preferably obtained according to the present invention, wherein the highly oriented high density polyethylene filaments are used as both warp and weft yarns.

[0041]

[0041] In an embodiment, the method further comprises heat stabilizing the backing layer. Heat stabilization can be carried out using a variety of different methods.

[0042] In an embodiment, heat stabilization is accomplished by feeding the backing along a body having a heated surface, with the first surface of the backing layer being placed in contact with the heated surface, which may be a roller or a calender as is commonly known in the art.

[0043] In another embodiment, heat stabilization is carried out by guiding the backing layer through one or more ovens without direct contact with a heated surface. For example, a tenter frame can be used to guide the backing layer through the ovens. In one embodiment, the backing layer is guided through an oven having a temperature of 135-155 degrees with a residence time of 10-120 seconds.

[0044] It will be appreciated that the exact details of the heat stabilization process will generally be tailored to the particular artificial turf product being manufactured, the specific type of HDPE being used, and the method of heat stabilization. Typically, the process will ensure that the backing layer is heated to a temperature above the initiation temperature of the polyethylene.

[0045]

[0045] According to a further aspect of the present invention, and in accordance with the advantages set forth above, there is provided a method of manufacturing a polyethylene heat stabilized artificial turf base, the method comprising providing a high density polyethylene backing layer according to the present invention, the backing layer having an upper surface and a lower surface, and integrating pile fibers into the backing layer so as to stand upright from the upper surface, wherein the pile fibers comprise polyethylene, and bonding the pile fibers to the backing layer to prevent fiber pull-out.

[0046]

[0046] The pile fibers are preferably integrated into the backing layer through tufting. The pile fibers can protrude through the backing layer as loops, or the loops can be cut open. Alternatively, a fully woven artificial turf backing can be formed, with the backing layer being formed simultaneously with the integration of the pile fibers.

[0047]

[0047] In this context, bonding of pile fibers is intended to refer to mechanical, physical, or chemical bonding in addition to the step of integrating the pile fibers to the backing layer, which results in a greater pull-out strength than after the integration of the pile fibers resulting from the tufting or weaving step alone. It may involve melting, fusing, gluing, encapsulation, coating, etc., subject to the restriction that no different materials are introduced and the resulting backing remains a single polymer artificial turf backing.

[0048] In the following, the term "fusion" is used to refer to the situation where two components or fibers are completely melted together, i.e., to form an integral component. Melting may simply cause one component to mold around the other, without actual bonding or fusion occurring. In this case, upon cooling, there may simply be a mechanical bond between the two components, e.g., the pile fibers and the woven backing layer.

[0049] In one embodiment, bonding of the pile fibers is accomplished by feeding the backing along a body having a heated surface, the underside of the backing layer being placed in contact with the heated surface. This can be accomplished using conventional machines as described above. It is noted that it may nevertheless be desirable to adapt the process to achieve the results currently described. In particular, the time and temperature required to achieve the pile bonding may differ from the time and temperature required to achieve a heat-stabilized backing layer. For bonding, it is necessary to exceed the melting point of the pile fiber material. Preferably, this is done instantaneously and locally to avoid significant damage to the backing structure and fiber properties. In a particular embodiment, the heated surface contacts only the pile fibers, without direct contact with the backing material itself. In the case of heat stabilization, a lower temperature is required to penetrate more generally into the backing structure to the areas where distortion exists.

[0050] In an embodiment, the heated surface is at 135-155°C and the contact period is 20-35 seconds, preferably 25-30 seconds. This period is long enough to bond the pile fibers together without damaging the backing layer. The heated surface is preferably at about 145°C.

[0051] In an embodiment, a roller is placed against the heated surface to press the backing layer, preferably applying a pressure of 2-8 Bar. The roller, preferably a laminating roller, ensures that all pile fiber bundles under the backing layer are in good contact with the heated surface. When no pressure or insufficient pressure is applied, not all pile fibers may melt.

[0052]

[0052] Alternatively or additionally, bonding may comprise applying a hot melt or powder melt to the underside of the backing layer, or laminating the underside of the backing layer with a polyethylene film, whereby the lamination is carried out by melting the film. Again, in all of these cases it is a mandatory requirement that this additional layer comprises polyethylene. The only exception to this would be if the additional layer is easily removable during or before the recycling process. The additional layer may further strengthen the bond between the pile fibres and the backing, making the artificial turf suitable for applications where high demands are made on the fibre pull-out strength.

[0053] In one embodiment, the method comprises actively cooling the backing, thereby fixing the pile fibers to the backing layer. After thermal bonding or stabilization, the backing may be cooled by removing the heat source, e.g., a heated surface, an infrared beam, or a hot air blower. Alternatively, the backing may be actively cooled, e.g., by conveying the carpet along a cool surface or by supplying cool air along the underside of the backing layer.

[0054] According to a further aspect of the present invention, and in accordance with the advantages and benefits set out above, there is provided an artificial turf backing consisting essentially of a polyethylene material, the artificial turf backing comprising a backing layer comprising backing filaments and pile fibres upstanding from the backing layer, the backing filaments comprising polyethylene having a first density and the pile fibres comprising polyethylene having a second density, the ratio between the first density and the second density being at least 1.01, preferably at least 1.02. The backing layer typically has a density of at least 945 kg / m 3 whereas the density of the pile fibres is preferably 945 kg / m 3 significantly lower than, for example, 915-935 kg / m 3 The difference in density generally translates into a difference in melting temperature.

[0055] According to yet a further aspect of the present invention, and in accordance with the advantages and effects described above, there is provided an artificial turf backing consisting essentially of a polyethylene material, the artificial turf backing comprising a backing layer with backing filaments and pile fibres upstanding from the backing layer, the backing filaments comprising polyethylene having a first melting temperature and the pile fibres comprising polyethylene having a second melting temperature, the difference between the first and second melting temperatures being at least 2°C, preferably at least 3°C ​​and may be higher than 5°C. The backing layer preferably has a melting temperature of at least 130°C, whereas the melting temperature of the pile fibres is typically less than 127°C. The different melting temperatures allow the pile fibres to be fixed to the backing layer through melting of the pile fibres, without melting or even softening the filaments of the backing layer.

[0056]

[0056] Those skilled in the art will appreciate that the properties imparted to the filaments and fibers during the extrusion process may be nullified upon melting. In particular, in this manner, the molecular orientation of the backing filament material may be preserved if subsequent processing remains away from the melting temperature of the filaments. In an embodiment, the bonding of the pile fibers may be performed without exceeding the initiation temperature of the backing filaments. This may be the case when the melting temperature of the pile fibers is below the initiation temperature of the backing filaments.

[0057]

[0057] In an embodiment, the backing layer is a backing layer according to the present invention.

[0058] In an embodiment, the backing layer has an upper surface and a lower surface, the polyethylene pile fibers stand up from the upper surface, and the pile fibers are tufted into the woven backing layer and bonded to each other and to the backing layer at the lower surface. As explained above, polyethylene is a preferred material for the pile fibers due to its elasticity, and forming both the backing layer and the pile fibers from the same material facilitates recycling, as explained above.

[0059]

[0059] In one embodiment, the artificial grass backing comprises at least 90% by weight or at least 95% by weight or at least 98% by weight of polyethylene, preferably at least 99% by weight of polyethylene. It will be understood that for recycling purposes, the weight percentage of the polymer material will be as close to 100% by weight as possible. It will be understood that nevertheless, various additives may be present and other contamination may occur. At the very least, it is important that the weight percentage is high enough so as not to cause significant disadvantages during recycling.

[0060] In one embodiment, the pile fibres comprise a bundle of monofilaments, preferably with different properties, more preferably the bundle is between 10000 dtex and 15000 dtex. The monofilaments themselves may be between 1000 and 3000 dtex per filament. In a preferred embodiment, at least the cross-sectional shape varies between the monofilaments, but the colour, stiffness and pile height may also vary to mimic natural grass. The cross-sectional shape may be, for example, flat, V-shaped, lenticular, curved, wavy, trilobal, hollow, etc. Alternatively or additionally, the pile fibres may comprise fibrillated tapes.

[0061]

[0061] In one embodiment, the monofilament bundles are at least partially melted together. This prevents individual pull-out of the pile fibers and fixes the pile fibers in the backing layer. For example, as described with respect to the method for producing an artificial turf backing, such melting can be achieved by feeding the backing along a body having a heated surface having a temperature above the melting point of the polyethylene in the pile fibers, and the underside of the backing layer is placed in contact with the heated surface to cause melting or softening of the pile fibers.

[0062] According to a further aspect of the present invention, and in accordance with the advantages and effects described herein above, there are provided highly oriented high density polyethylene filaments suitable for producing a backing layer according to the present invention. They have been specifically designed for this purpose, since HDPE filaments for producing a backing layer were not readily available. Any HDPE composition cannot be easily processed in an extrusion process to form a tape by slitting the extruded film. It is therefore a further object of the present invention to provide an HDPE composition having both good processability, and the desired strength, stability and creep resistance as required for its application in artificial turf.

[0063] According to a further aspect of the present invention, and in accordance with the advantages and benefits described hereinabove, there is provided a method for producing high density polyethylene filaments for a back layer of an artificial turf base, the method producing a high density polyethylene filament yield of at least 945 kg / m 3 and a melt flow index of 1.5 to 2 g / 10 min to an extruder, forming filaments, and stretching the filaments in the machine direction to obtain a tape having a linear density of 100 to 2500 dTex. Preferably, the HDPE has a medium or medium broad molecular weight distribution.

[0064] According to an embodiment, the filaments are tapes and the step of forming the filaments comprises extruding a polyethylene composition into an extruded film and slitting the film into a tape. The HDPE composition is provided to an extruder, which extrudes the HDPE into a film. Such a film can be prepared by any conventional film-forming process, including an extrusion procedure such as cast film extrusion. After the film is formed, it is subsequently slit into a tape and stretched. The film can be stretched before cutting it into tapes, the film can be first cut and then stretched, or cutting and stretching can be performed simultaneously. Preferably, the film is first cut into tapes, and the tape is subsequently stretched in the machine direction at the desired draw ratio to form the final tape. In an embodiment, the film is extruded through a profiled die having at least one ribbed surface.

[0065] In an embodiment, the draw ratio in the machine direction is at least 4, preferably at least 5, more preferably at least 6. For example, the draw ratio can be from 6 to 7. The draw ratio indicates the number of times the tape is stretched in the machine direction compared to its original length.

[0066]

[0066] The present invention will now be discussed in more detail with reference to the accompanying drawings. [Brief description of the drawings]

[0067] [Figure 1A]

[0067] A perspective view of a portion of a heat-stabilized artificial turf backing according to a first embodiment is shown diagrammatically. [Figure 1B]

[0068] 1B is a schematic side view of the artificial turf base of FIG. 1A as viewed from the IB direction. [Diagram 2]

[0069] 1 illustrates diagrammatically a method for producing a heat-stabilized artificial turf backing according to a first embodiment. [Diagram 3]

[0070] 3 shows a first embodiment of an apparatus that can be used for the pile fiber bonding step according to the method shown in FIG. 2. [Figure 4]

[0071] FIG. 2 shows a cross-sectional view of a portion of an extrusion die for forming filaments according to the present invention. [Diagram 5]

[0072] 1 shows a typical differential scanning calorimetry curve for a filament material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068]

[0073] The drawings are intended for illustrative purposes only and do not serve as a limitation on the scope or protection defined by the claims.

[0069]

[0074] Following is a description of certain particular embodiments of the invention, given by way of example only and with reference to the drawings.

[0070]

[0075] FIG. 1A shows a schematic perspective view of a heat-stabilized artificial grass base 1 according to the invention, made only of polyethylene. FIG. 1B shows a side view of the artificial grass base of FIG. 1A. The artificial grass base 1 comprises a backing layer 2 having an upper surface 3 and a lower surface 4. The backing layer 2 is a woven fabric with warp tapes 21 and weft tapes 22, each formed as an HDPE extruded tape. From the upper surface 3 stand polyethylene pile fibers 5 and thatch yarns 7. The pile fibers 5 are provided as bundles 6 of monofilaments, each having different properties such as cross-sectional shape, green color, stiffness, and / or pile height, in order to mimic natural grass as much as possible. The pile fibers 5 are tufted into the backing layer 2, and at the lower surface 4 of the backing layer 2, the bundles 6 of pile fibers 5 are fused together to provide pile fiber bundles 8 melted below the backing layer 2. A polyethylene coating layer 9 is provided on the lower surface 4 to provide additional strength.

[0071]

[0076] The pile fibres 5 are tufted into the carpet along the warp direction such that molten bundles 8 of pile fibres 5 extend along the warp direction below the lower surface 4 of the backing layer 2. The molten bundles 8 have a width of a few millimetres and therefore extend across the width of several warp tapes 21. This makes the fibre bonds quite strong and the pile fibres break before being pulled out. The molten pile fibre bundles 8 are arranged in a zigzag pattern below the backing layer 2, zigzagging across a total width of about 5 mm. The warp tapes have a width of about 1 mm and the weft tapes have a width of about 2 mm. As a result, the molten bundles of pile fibres span the width of at least two or three tapes.

[0072]

[0077] The artificial grass backing 1 has similar mechanical properties as conventional artificial grass backings made with a PP backing layer and retains the pile fibres equally well. Advantageously, due to the product only comprising PE, the product can be easily recycled at the end of its life.

[0073]

[0078] FIG. 2 shows diagrammatically a method for producing such an artificial grass backing 1. First, a plurality of tapes 21, 22 are produced from an HDPE composition in a tape-forming step 10, which are then used to form a backing layer 2 in step 11. The pile fibers 5 are then integrated into the backing layer 2 in an integration step 12, preferably through tufting. Alternatively, the woven backing 2 and the pile fibers 5 can be integrally formed by weaving the pile fibers 5 into the woven backing 2 using a weaving technique to produce a three-dimensional artificial grass structure 1. The backing layer 2 with the integrated pile fibers 5 is called an intermediate product 17, which generally looks quite similar to the artificial grass backing 1 illustrated in FIG. 1, but the pile fibers 5 are not fixed to the backing layer 2, and therefore the intermediate product 17 has inferior mechanical properties compared to the final artificial grass backing 1. To increase fiber bond strength and prevent fiber pull-out, the intermediate product 17 undergoes a bonding step 13 in which the underside 4 of the backing layer 2 is heated to a temperature above the melting point of the PE in the pile fibers to thermally bond the pile fibers 5 in the bundles 6 to each other and / or to the backing layer 2, strengthening the fiber bonds. During the bonding step 13, the backing layer 2 is heated to a temperature and for a time sufficient to stabilize the backing layer 2 to the temperatures that will be encountered in use. After the bonding step 13, the product is cooled to room temperature in a cooling step 14.

[0074]

[0079] The artificial turf backing 1 of Figure 1 is made from a mixture of different polyethylene compositions, where the term "polyethylene composition" is used to indicate the composition of the raw polyethylene which is extruded to form the tapes for the backing layer 2 and to form the pile fibres 5 for the pile layer.

[0075]

[0080] The tape in the backing layer 2 is made of an HDPE composition. As explained above, HDPE has good tensile strength, good creep resistance, and good heat resistance compared to polyethylene materials with higher branching such as LDPE. Lining filament - Example 1

[0076]

[0081] According to a first embodiment, the HDPE is ELTEX B4020N1332, a high density polyethylene copolymer manufactured by INEOS Olefins & Polymers Europe, having a strength of 952 kg / m when measured according to ISO 1183-1. 3 HDPE has a unimodal weight distribution curve and a sufficiently broad molecular weight distribution (MWD) to allow good processability of HDPE in extrusion processes.

[0077]

[0082] The HDPE composition has a melt flow index (MFI) of 1.9 g / 10 min. Preferably, the MFI is selected between 1.5 and 2 g / 10 min. A lower MFI may result in too high a die pressure in the extruder and, as a result, a lower throughput. Conversely, a higher MFI may cause problems during stretching, resulting in non-uniform stretching. Thus, an MFI between 1.5 and 2 g / 10 min is favorable for the processability of HDPE through the extruder. In addition, a higher MFI reduces the creep resistance.

[0078]

[0083] The HDPE composition is provided to an extruder, which extrudes the HDPE into a film. Such films can be prepared by any conventional film-forming process, including extrusion procedures such as cast film or blown film extrusion. After the film is formed, it is quenched in water and subsequently slit into tapes and stretched. The film can be stretched before cutting it into tapes, the film can be cut first and then stretched, or cutting and stretching can be performed simultaneously. Preferably, the film is first cut into tapes, which are subsequently stretched longitudinally at the desired stretch ratio to form the final tape. A stretch ratio of 6 is used, which indicates that the tape is stretched longitudinally 6 times compared to its original length. The tape is then relaxed and annealed on a roll.

[0079]

[0084] FIG. 4 illustrates a portion of an extruder die 50 with an overall width of about 1 meter. The die opening 52 has a nominal opening of 0.6 mm, but is provided on its underside with a pattern of rectangular ribs 54 and grooves 56 with a depth of 0.15 mm and a width of 0.5 mm. The film exiting the die 50 has a cross-sectional shape corresponding to the die opening 52. When stretched, the cross-section of the film will be reduced accordingly and the shape features will be reduced by the square root of the stretch ratio. In addition, the flow of the extrudate will tend to soften all the features, so that the final tape will have a shallow rippled surface on its underside spaced about 0.2 mm apart. The formed tape has a tensile strength of about 25 cN / Tex.

[0080]

[0085] The formed tapes are used to weave a backing layer for artificial turf. Preferably, the warp and weft tapes in the backing layer are woven in a plain weave and arranged to resemble a so-called biased "square structure". This means that the average number of tapes, tape width, tape thickness, and tape linear density are typically similar in both the warp and weft directions, which has a beneficial effect on the dimensional stability of the backing layer. Nevertheless, non-square weave patterns can also be used. Lining layer - Example 1

[0081]

[0086] According to a first example, the backing layer 2 is a single layer woven fabric, for example as shown in Figures 1A and 1B. The backing layer 2 has a plain weave pattern using tapes as described in the first example. The warp tapes have a linear density of 670 dtex and the weft tapes have a linear density of 1200 dtex. On average, about 860 warp tapes and 610 weft tapes are provided per metre. The warp tapes have a width of 1.2 mm, the weft tapes have a width of about 2.2 mm and both the warp and weft tapes have a thickness of 58 μm. This gives a weight of about 129 g / m 2 yields fabric weight of Lining layer - Example 2

[0082]

[0087] According to a second example, the backing layer is also formed from a tape as described in the first example. The backing layer comprises two substantially identical sublayers stacked on top of each other and bonded to each other, for example by warp knitting the first and second sublayers together. The woven backing layer thus comprises two layers of warp and weft tapes which together form one backing layer which functions as a pile support layer. The warp tapes 21 in each sublayer have a tape width of 1.2 mm, a linear density of 670 dtex and about 840 threads per meter. The weft tapes 22 each have a tape width of 2.2 mm, a linear density of 1200 dtex and about 420 weft threads per meter. The warp threads have a thickness of about 59 μm and the weft threads have a thickness of about 57 μm.

[0083]

[0088] In both examples, the backing layer 2 has a different number of tapes in the warp and weft directions. This has been found to be advantageous for the tuftability of the backing layer 2. In order to balance the variation in the number of tapes while still obtaining a backing layer 2 with the favorable dimensional stability of the square structure, the linear density and tape width of the weft tape 22 are approximately twice as large as those of the warp tape 21. More precisely, per meter of width, the linear density in the warp direction is 670*840=562800 dTex / m and the linear density in the weft direction is 1200*420=504000 dTex / m. Thus, the deviation is less than 15% and thus an approximately biased square structure is obtained in the backing layer according to the second example.

[0084]

[0089] In the second example, the number of warp tapes multiplied by the linear density of the warp tapes is slightly greater than the number of weft tapes multiplied by the linear density of the warp tapes, which is advantageous because it can compensate for the reduction in strength in the warp direction due to filament damage from the weaving process.

[0085]

[0090] The fabrics according to the first and second examples have sufficient strength and dimensional stability to be used as backing layers in artificial turf. The mechanical properties of the first and second examples are summarized in Table 1. Optionally, the backing layer can be heat-stabilized before tufting to improve its stability. Table 1 shows the results for Example 1 both before and after heat setting.

[0086] [Table 1]

[0087]

[0091] The strength at Fmax refers to the force [N] required to break or tear a strip of thickness 5 cm in the machine direction (MD, warp direction) or cross direction (CD, weft direction), respectively. The elongation at Fmax refers to the corresponding strain that occurs while performing this test. In general, stronger fabrics are more stable and have a higher creep resistance.

[0088]

[0092] Shrinkage at 90 degrees refers to the shrinkage expected in the field when the artificial grass is exposed to direct sunlight. It is measured by marking a sample with a specified length and exposing it to 90°C for a period of 15 minutes. After cooling, the marked length is measured again and the shrinkage is determined. Due to the method of making the woven backing, inherent stresses are created in the fibers of the woven backing layer. When exposed to heat, the fibers relax and the woven structure "expands". This phenomenon has different names but can be called creep, stretching, or expansion. It is not a simple matter of thermal expansion since it does not necessarily reverse on cooling. Expansion can cause a carefully laid artificial grass pitch to wrinkle or crease unacceptably. Therefore, the shrinkage rate is preferably as low as possible.

[0089]

[0093] To form the artificial turf, the pile fibres 5 are integrated into a backing layer according to the invention to form an intermediate product 17. The PE composition for the pile fibres has a lower density and a lower melting point than the HDPE composition applied to the backing layer. Preferably, the melting point of the pile fibres 5 is below 115°C. This difference in melting point between the bundles 6 of the pile fibres 5 and the backing layer 2 allows the bundles 6 to be melted to each other during the bonding step 13, while the backing layer 2 does not melt.

[0090]

[0094] In a particular embodiment, the pile fibres 5 are made of PE with a melting temperature of 110° C. The bundles 6 tufted into the HDPE backing layer 2 are different monofilaments each having a linear density of 900 dtex resulting in a total linear density of 12600 dtex. These pile fibres 5 extend over a height of 4.3 cm and may have different properties to mimic the appearance of natural grass.

[0091]

[0095] In addition, textured or curled thatch yarns 7 are integrated into the backing layer 2 which do not extend too far. The thatch yarns 7 are arranged in bundles with a total linear density of 5000 dtex each comprising 8 yarns. The thatch yarns 7 are made of PE with a melting temperature of 125°C.

[0092]

[0096] Generally, the fiber bond strength of the intermediate product 17 is insufficient, and therefore in prior art artificial turf systems a locking layer, e.g. a latex coating, is typically applied. As this impairs the recyclability of the artificial turf backing, the intermediate product 17, according to the present invention, undergoes a bonding step 13, in which the underside 4 of the backing layer 2 is heated to fuse the pile fibers 5 in the bundles 6 to each other and / or to the backing layer 2, strengthening the fiber bonds. During the bonding step, the backing layer 2 is simultaneously heat set to reduce expansion of the artificial turf backing during use and improve dimensional stability. This type of bonding is referred to herein as a "heat setting" step.

[0093]

[0097] Figure 3 shows an illustrative embodiment of an apparatus 20 that can be used to perform the fibre bonding step 13. An intermediate product 17 consisting of an HDPE backing layer 2 with integrated pile fibres 5 is provided by a feed roller 21 and guided through the apparatus 20 using a number of guide rollers 22. The intermediate product 17 is conveyed through the machine at a speed of 1-30 m / min and guided along the heated surface 25 of a roller 24. The heated roller 24 melts the individual pile fibres 5 in the bundle 6, thereby also increasing the bond between the pile fibres 5 and the backing layer 2. Importantly, the backing layer 2 itself does not engage the roller 24, but remains spaced from it by the pile fibres 5.

[0094]

[0098] Optionally, a hot melt adhesive or powder melt can be applied to further increase the fiber bond strength. A device 23, for example a spreading device, can be arranged in the apparatus 20. The device 23 can spread hot melt adhesive powder on the underside 4 before the intermediate product 17 is conveyed along the heated roller 24. This hot melt or powder melt can consist essentially of polyethylene so that the recyclability of the artificial grass base is not compromised. Alternatively, no hot melt adhesive or powder melt is applied, which makes the production process less complicated and therefore cheaper and less error-prone.

[0095]

[0099] To process the backing layer 2 having the HDPE composition as described above, the heated surface 25 is heated to a temperature in the range of 135-155°C. The heated surface 25 is typically a drum made of a non-adhesive material to prevent the intermediate product 17 from sticking to the surface 25. The guide rollers 22 are arranged to place the intermediate product 17 under tension and to control the residence time of the intermediate product 17 on the heated surface 25. Typically, the rollers 22, 24 are arranged relative to each other to allow a residence time of 10-40 seconds. Preferably, the residence time is 22-35 seconds, for example 25 seconds. This contact period allows the backing layer 2 and / or the pile fibers 5 to melt sufficiently and partially fuse with each other to provide a sufficiently high fiber bond strength. The partially melted intermediate product 17 is subsequently carried away by the guide rollers 22 and transported out of the apparatus for further processing. Such further processing may include accelerated cooling of the artificial turf backing or lamination of the underside of the backing layer. In an embodiment, the product after cooling is the final product.

[0096]

[0100] The guide roller 22 may not only guide the intermediate product 17 through the apparatus 20, but may also be used as a pressure roller, arranged adjacent to the heated roller 24, which may increase the pressure against the underside 4 of the backing layer 2 to better spread the molten polymer material between the warp and weft fibers of the backing layer 2 and the pile fibers 5. It will be understood by those skilled in the art that the temperature of the heated roller 25 and the pressure applied to such a pressure roller should be optimized depending on each other and on the properties and texture of the intermediate product 17 to achieve good results. Fiber Bonding Methods - Example 1

[0097]

[0101] According to a first example of the method, the temperature of the roller is set at 145° C., measured on a heated cylinder, and a residence time of 25 seconds. A pressure of 5 Bar is applied. The method was tested on a first exemplary backing layer after it had undergone a heat stabilization step. Fiber bonding method - Example 2

[0098]

[0102] According to a second example of the method, the roller temperature is set at 145° C., measured on a heated cylinder, and a residence time of 30 seconds. A pressure of 5 Bar is applied. This method was tested on a second exemplary backing layer.

[0099]

[0103] The mechanical properties of the artificial turf substrates according to the first and second examples are summarized in Table 2.

[0100] [Table 2]

[0101]

[0104] The second backing layer was not heat stabilized before applying the heat fixing step. This reduces the cost and complexity of production. Nevertheless, it will be understood that embodiments in which the backing layer is first heat stabilized before the heat fixing step are not excluded.

[0102]

[0105] Figure 5 illustrates a typical Differential Scanning Calorimetry (DSC) trace. The melting point of the material is determined as the peak value for heat flow. The onset temperature at point D is defined as the intersection of the extrapolated baseline and the inflection tangent at the beginning of the melting or crystallization peak. The inflection tangent is shown between points B and D. The extrapolated baseline is shown between points A and C.

[0103]

[0106] The HDPE filaments according to the first example have an onset temperature of about 125°C and a melting point of about 130°C.

[0104]

[0107] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Those skilled in the art will be able to conceive and practice alternative and equivalent embodiments of the invention. All changes that come within the meaning and range of equivalence of the claims are to be embraced within their scope.

Claims

1. 1. A polyethylene backing layer for an artificial turf base consisting essentially of highly oriented high density polyethylene filaments forming warp and weft yarns, said highly oriented high density polyethylene filaments having a strength of at least 945 kg / m 3 and a melt flow index of up to 2 g / 10 min, said backing layer being heat stabilized.

2. The highly oriented high density polyethylene filaments have a strength of at least 950 kg / m 3 Preferably, the density is 950 kg / m 3 ~970kg / m 3 The backing layer of claim 1 having a density of

3. 2. The backing layer of claim 1, wherein the highly oriented high density polyethylene filaments have a melt flow index of 1.5 to 2 g / 10 min, preferably 1.7 to 1.9 g / 10 m.

4. 10. The backing layer of claim 1, wherein the high density polyethylene has a medium or medium broad molecular weight distribution.

5. 2. The backing layer of claim 1, wherein the high density polyethylene has a melting point of at least 125°C, preferably at least 130°C.

6. The backing layer of claim 1 , wherein at least a portion of the highly oriented high density polyethylene filaments are tape.

7. The backing layer of claim 6 , wherein the backing layer is a primary backing layer suitable for tufting.

8. The backing layer of claim 7 , wherein the backing layer is woven using a plain weave.

9. 9. The backing layer of claim 8, wherein the number of warp filaments per unit length and the number of weft filaments per unit length are different.

10. 10. The backing layer of claim 9, wherein the ratio of the number of warp filaments to the number of weft filaments is the reciprocal of the ratio of the linear density of the warp filaments to the linear density of the weft filaments.

11. 7. The backing layer of claim 6, wherein the backing layer comprises a plurality of sub-layers, preferably the backing layer consists of two sub-layers which are identical to each other.

12. 2. The backing layer of claim 1, wherein the highly oriented, high density polyethylene filaments have a linear density in the range of 100 to 2500 dtex, preferably 200 to 1700 dtex, optionally 600 dtex to 1200 dtex.

13. 2. The backing layer of claim 1, wherein the highly oriented high density polyethylene filaments have a tensile strength of at least 20 cN / Tex, and preferably the highly oriented high density polyethylene filaments have a tensile strength of at least 25 cN / Tex.

14. 80-400g / m 2 , preferably 100 to 300 g / m 2 2. The backing layer of claim 1 having a fabric weight of

15. The backing layer of claim 1, wherein the individual highly oriented high density polyethylene filaments have a strain at break of 10 to 40%, preferably 20 to 35%.

16. 10. The backing layer of claim 1, wherein the highly oriented high density polyethylene filaments may further comprise one or more additives, preferably selected from the group consisting of antioxidants, UV stabilizers, pigments, processing aids, acid scavengers, lubricants, antistatic agents, fillers, nucleating agents, and clarifiers.

17. 2. The backing layer of claim 1, wherein the highly oriented high density polyethylene filaments have one or more elongated ribs of grooves along their length.

18. 1. A method for producing a high density polyethylene backing layer, the method comprising: at least 945 kg / m 3 providing a plurality of highly oriented high density polyethylene filaments having a density of at least 100 nm and a melt flow index of at most 2 g / 10 min; weaving said high density polyethylene backing layer, wherein said plurality of highly oriented high density polyethylene filaments are used as both warp and weft yarns; Equipped with The method further comprising heat stabilizing the high density polyethylene backing layer by heating the high density polyethylene backing layer above the melting temperature of the high density polyethylene.

19. The method according to claim 18, wherein the high density polyethylene backing layer is a backing layer according to any one of claims 1 to 17.

20. 20. The method of claim 18, wherein the heat stabilization is performed by feeding the high density polyethylene lining layer along a body having a heated surface, a first surface of the high density polyethylene lining layer being positioned in contact with the heated surface.

21. 19. The method of claim 18, wherein the heat stabilization is carried out by guiding the high density polyethylene backing layer through an oven, preferably having a temperature of 135-155°C, and preferably the high density polyethylene backing layer has a residence time of 10-120 seconds.

22. 1. A method for producing a polyethylene heat stabilized artificial turf backing, the method comprising: Providing a high density polyethylene backing layer according to any one of claims 1 to 17, wherein the backing layer has an upper surface and a lower surface; incorporating pile fibers into said backing layer so as to extend upright from said top surface, said pile fibers comprising polyethylene; bonding said pile fibers to said backing layer to prevent fiber pullout; A method comprising:

23. A method for producing a polyethylene heat stabilized artificial turf backing, the method comprising: forming a backing layer according to any one of claims 18, 20 or 21, wherein the backing layer has an upper surface and a lower surface; incorporating pile fibers into said backing layer so as to extend upright from said top surface, said pile fibers comprising polyethylene; bonding said pile fibers to said backing layer to prevent fiber pullout; A method comprising:

24. 23. The method of claim 22, wherein bonding is accomplished by feeding the polyethylene heat stabilized artificial grass backing along a body having a heated surface, the lower surface of the backing layer being positioned in contact with the heated surface.

25. The method of claim 23, wherein bonding is accomplished by feeding the polyethylene heat-stabilized artificial turf backing along a body having a heated surface, and the underside of the backing layer is positioned in contact with the heated surface.

26. 25. The method of claim 24, wherein the heated surface is at 135-155°C and the contact period is 20-35 seconds, preferably 25-30 seconds.

27. The method of claim 25, wherein the heated surface is at 135-155°C and the contact period is 20-35 seconds, preferably 25-30 seconds.

28. The method according to claim 24, wherein a roller is placed against the heated surface to press the backing layer, preferably applying a pressure of 2 to 8 Bar.

29. The method of claim 25, wherein a roller is positioned against the heated surface to pressurize the backing layer, preferably applying a pressure of 2 to 8 Bar.

30. 25. The method of claim 24, further comprising applying a hot melt or powder melt to the underside of the backing layer which comprises the same polymeric material.

31. The method of claim 25, further comprising applying a hot melt or powder melt to the underside of the backing layer, the underside being made of the same polymeric material.

32. 25. The method of claim 24, further comprising laminating the lower surface of the backing layer with a polyethylene film, the lamination being accomplished by melting the polyethylene film.

33. The method of claim 25, further comprising laminating the underside of the backing layer with a polyethylene film, the lamination being accomplished by melting the polyethylene film.

34. 1. An artificial turf backing consisting essentially of a polyethylene material, the artificial turf backing comprising a backing layer having backing filaments and pile fibers upstanding from the backing layer, the backing filaments comprising polyethylene having a first density and the pile fibers comprising polyethylene having a second density, the ratio between the first density and the second density being at least 1.

01.

35. 1. An artificial turf backing consisting essentially of a polyethylene material, the artificial turf backing comprising a backing layer having backing filaments and pile fibres upstanding from the backing layer, the backing filaments comprising polyethylene having a first melting temperature and the pile fibres comprising polyethylene having a second melting temperature, the first melting temperature being at least 2°C higher than the second melting temperature, preferably at least 3°C ​​higher.

36. The artificial turf base fabric according to claim 34 or 35, wherein the backing layer is a backing layer according to any one of claims 1 to 17.

37. 36. The artificial turf base of claim 34 or 35, wherein the backing layer has an upper surface and a lower surface, and the pile fibers are tufted into the backing layer and bonded to each other or to the backing layer at the lower surface.

38. 36. The artificial turf backing of claim 34 or 35, wherein the artificial turf backing comprises at least 98% by weight polyethylene, preferably at least 99% by weight polyethylene.

39. The artificial turf base fabric of claim 34 or 35, wherein the pile fibers are arranged in bundles of monofilaments, each bundle having a linear density of 10,000 dtex to 15,000 dtex.

40. 36. The artificial turf base of claim 34 or 35, wherein the monofilament bundles are at least partially fused to one another.

41. Highly oriented high density polyethylene filaments suitable for use in the backing layer according to any one of claims 1 to 17.

42. 1. A method for producing high density polyethylene filaments for a backing layer of an artificial turf backing, the method comprising: at least 945 kg / m 3 and a melt flow index of 1.5 to 2 g / 10 min. - forming a filament; stretching said filaments in the machine direction to obtain a tape having a linear density of from -100 to 2500 dTex; A method comprising:

43. 43. The method of claim 42, wherein the stretching step has a stretch ratio of at least 4, preferably at least 5, more preferably at least 6.

44. The filament is a tape, and the forming step of the filament comprises: - extruding the high density polyethylene composition into an extruded film; - slitting the extruded film into tapes; 44. The method of claim 42 or 43, comprising:

45. 45. The method of claim 44, wherein the extruded film is extruded through a profiled die having at least one ribbed surface.

46. The method according to claim 42, wherein the high density polyethylene filaments are suitable for application in a backing layer according to any one of claims 1 to 17.

47. The method described in claim 42, wherein the high density polyethylene filaments are suitable for application in an artificial turf base fabric as described in claim 34 or 35.

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