The invention relates to a yarn containing polyamide for producing artificial grass. The invention furthermore relates to a method of manufacturing said yarn and to a field of artificial grass in which said yarn is incorporated.

Such a yarn for a field of artificical grass is known from Japanese patent publication JP 7048778A. The field of artificial grass is obtained by intertwining polyamide fibre and PE fibre in a base layer.

More in particular, the method comprises the provision in a base layer, in a pile length of 25 mm, of a yarn by twisting split yarn made of 5000d polyamide and split yarn made of 5000d high density PE.

Such a yarn is also known from Japanese patent publication JP 09119036A, wherein a yarn for artificial turf pile is formed by melt-spinning a polyamide resin composition comprising 70-99 % by weight of a polyamide resin and 1-30 % by weight of a polyethylene resin.

From EP-A-0 648 868 a yarn is furthermore known which is used for making artificial grass, which yarn is manufactured of polypropylene or of a block copolymer of polypropylene and polyethylene.

It has now become apparent that the properties of yarn for artificial grass, in particular its wear-resistance, flexibility and processibility, can be improved by manufacturing the artificial grass of a specified combination of polymers, and consequently the yarn according to the invention is characterized in that the yarn, in addtion to polyamide, also contains a polyolefin compound selected from the group consisting of polypropylene, LLDPE and a block copolymer of polypropylene and polyethylene.

In particular it is preferred for the yarn to contain 20-80 % by weight of polypropylene and 80-20 % by weight of polyamide.

The use of this specific mixture of polypropylene and polyamide leads to improved mechanical properties of the artificial grass, which mechanical properties are considerably better than those of polypropylene and polyamide individually.

In a preferred embodiment of the yarn according to the present invention, a block copolymer of polypropylene and polyethylene is used. A particularly suitable block copolymer is the polypropylene/- polyethylene block copolymer as described in European patent application No. 0 359 321, which document may be considered to be incorporated herein, which block copolymer is marketed by Solvay, Belgium with a melt flow index of about 4. Such a preferred yarn is preferably composed of 20-80 % by weight of block copolymer of polypropylene and polyethylene, and 20-80 % by weight of polyamide.

In specified embodiments it is also possible, however, to produce a yarn which, in addition to polyamide, contains the polymer LLDPE (Linear Low Density Polyethylene). Such a yarn is preferably composed of 20-80 % by weight of LLDPE and 20-80 % by weight of polyamide.

Although a polyamide resin composition of polyamide resin and a poly- ethylene composition containing 50-100 % by weight of LLDPE and 0-50 % by weight of a maleic acid anhydride modified polyethylene resin is known from Japanese patent publication JP 09119036A, it should be understood that the present composition of 20-80 % by weight of LLDPE and 20-80 % by weight of polyamide is essentially different from the composition which is mentioned in said Japanese patent publication.

From JP-A-5,171,613 it is known to manufacture artificial grass from various polymers. Said Japanese patent publication mentions a large number of polymers, among which polypropylene and Nylon.

It does not describe a yarn which is made from the present combination of polypropylene and/or polyethylene and polyamide, however. Nor does said Japanese patent publication disclose a method of manufacturing the yarn as used in accordance with the invention.

JP-A-3,279,419 discloses a fibre which consists of Nylon which is mixed with polypropylene. Said fibre has been used for making clothes. Said Japanese patent publication does not describe the use of such a mixture of polymers for manufacturing artificial grass.

US patent No. 5,597,650 discloses a carpet yarn having special properties as regards flame retardation and resistance to stains.

Said yarn consists of a polyolefin matrix, preferably polypropylene, in which smaller polyamide fibrils are embedded. Said US patent does not describe the use of such a yarn for manufacturing artificial grass.

According to the method which is used in particular for producing yarns which are used for manufacturing artificial grass, the polymer is extruded to form monofilaments, which are subsequently processed into bands, with several bands being twisted to form a yarn, and possibly with several yarns being twined to form a composite yarn.

This method is characterized in that monofilaments are extruded from one of the polyolefins from the group of polypropylene, LLDPE and a block copolymer of polypropylene and polyethylene, and that monofilaments are extruded from polyamide, or in that monofilaments are extruded from a mixture of one of the polyolefins from the group of polypropylene, LLDPE and a block copolymer of polypropylene and polyethylene on the one hand and polyamide on the other hand. Furthermore it is preferred to process in particular the monofilaments of the block copolymer of polyethylene and polypropylene into a first yarn containing the block copolymer of polyethylene and polypropylene, and to process the monofilaments of polyamide into a second yarn containing polyamide, after which the two yarns are joined to form a composite yarn. Then the artificial grass is manufactured of said composite yarn. In specified embodiments, however, it is preferred to use a yarn of the block copolymer of polypropylene and polyethylene on the one hand and a yarn of polyamide on the other hand as separate yarns for producing a field of artificial grass. Experiments have shown that fields of artificial grass produced in this manner exhibit better mechanical properties than fields of artificial grass according to the prior art as described above. Such a method of producing monofilaments is described in European patent No. 0 648 868, which document may be considered to be incorporated herein.

Furthermore it is preferred to use co-extrusion in manufacturing the yarn according to the present invention. According to such a method, the core is built up of one of the polyolefins from the group of polypropylene, LLPDE and a block copolymer of polypropylene and polyethylene, and the cladding is built up of polyamide. Under certain circumstances it is preferred to exchange the aforesaid core and cladding materials, so that a core of polyamide is obtained.

The present invention is not limited to the use of monofilaments, and in a special embodiment it is preferred to use one of the yarns from the group of fibrillated yarn of the block copolymer of polyethylene and polypropylene, fibrillated yarn of HDPE, fibrillated yarn

of LLDPE, fibrillated yarn of polypropylene on the one hand and a yarn of fibrillated polyamide yarn on the other hand. The method of producing fibrillated yarn is described in European patent application No. 0 263 566, which application may be considered to be incorporated herein. Thus, in a special embodiment of the method according to the present invention a foil is made from a polymer which, in addition to polyamide, also contains a polyolefin compound selected from the group of polypropylene, LLDPE and a block copolymer of polypropylene and polyethylene, which foil is cut into bands, with several bands being twisted to form a yarn, and possibly with several yarns being twined to form a composite yarn. According to such a method it is also possible on the one hand to make a foil from one of the polyolefins from the group of polypropylene, LLDPE and a block copolymer of polypropylene and polyethylene and on the other hand to make a foil from polyamide, after which the bands obtained from said two foils may be processed to form said composite yarn. A combination of mono- filaments and fibrillated yarns, preferably monofilaments of polyamide and fibrillated yarn of the block copolymer of polypropylene and polyethylene, is also suitable for manufacturing the composite yarn.

The invention will be explained in more detail hereafter by means of the following examples.

Example 1 Monofilaments were obtained by extrusion of the block copolymer of polyethylene and polypropylene on the one hand and by extrusion of polyamide on the other hand, and after stretching said monofilaments, bands were obtained. A method as indicated in example 1 of EP-A-0 648 868 was thereby used for the block copolymer. The bands were processed to form a yarn, thus producing the block copolymer of poly- ethylene and polypropylene yarn consisting of four non-twisted bands each having a yarn number of 1100 dtex on the one hand and a polyamide yarn consisting of non-twisted bands each having a yarn number of 666 dtex on the other hand. Said two yarn types were twined to form a composite yarn having a yarn number of 8400 dtex. Said composite yarn was then knitted and fixed so as to obtain a teasing effect, after which the teased composite yarn was used for obtaining a carpet for artificial grass.

To this end the yarn was tufted with 300 stitches per running metre, and a pile height of 12.5 mm, resulting in a pile insert weight of 1750 g/m2.

The carpet thus obtained was subjected to various tests in order to determine the mechanical properties, such as the tretrad test for determining the fibrillation, the Taber test for determining the weight loss and the Leroux test for determining the sliding properties.

The data that were obtained are shown in table A.

Table A BlockcopolymerPolyamideCompositeyarn ofofpolyamide polypropyleneandblock andcopolymerof polyethylenepolypropylene and polyethylene tretradpost-nopost-nopost- fibrillationfibrillationfibrillation Taber (g/m2)loss 2000t0.380.560.32 5000t0.931.490.76 slidingLeroux dry0.7900.7600.772 wet0.5370.4400.390 The data in this table show that the artificial grass made from the combination of the block copolymer of polyethylene and polypropylene and polyamide did not exhibit any post-fibrillation, so that a much better result is obtained than with artificial grass made from a polypropylene-containing polymer, that the weight loss results as measured by means of the Taber test are much better than with the artificial grass made from the block copolymer of polyethylene and polyethylene and with the artificial grass made from polyamide, that the sliding results as measured by means of the Leroux test are much better in wet conditions, and that the sliding results of artificial grass made from polyamide are slightly better only in dry conditions. Furthermore it has become apparent that burn tests in accordance with BS 4790 show a low value for the artificial grass according to the invention, which value is comparable

with that of artificial grass made from polyamide, but which is better than that of artificial grass made from polypropylene-containing polymer.

Summarizing the above it can be stated, therefore, that the results obtained with the artificial grass according to the invention are better than the results that could be expected with artificial grass of polyamide or with artificial grass of polypropylene-containing polymer.

This shows that a synergetic effect is obtained with the combination of starting materials according to the invention.

Example 2 The artificial grass was manufactured in the same manner as in Example 1. A field of artificial grass scattered in with sand was composed, to which end the yarn was tufted with 140 stitches per running metre and a pile height of 34 mm, as a result of which a pile insert weight of 970 g/m2 was obtained. The carpet thus obtained was subjected to tests comparable with the tests of Example 1. It has become apparent thereby that, also in the case of a field of artificial grass scattered in with sand, the mechanical properties of the yarn composed of the block copolymer of polyethylene and polypropylene and polyamide were much better than those of yarns for fields of artificial grass which were made from polypropylene and from polyamide.

Example 3 Monofilaments were obtained by extrusion of the block copolymer of polyethylene and polypropylene on the one hand and by extrusion of polyamide on the other hand, and after stretching said monofilaments, bands were obtained. A method as indicated in example 1 of EP-A-0 648 868 was thereby used for the block copolymer, so as to obtain a block copolymer having a yarn number of 8800 dtex consisting of 8 bands, each having a yarn number of 1100 dtex. Then a polyamide having a yarn number of 4000 dtex, which consisted of 6 bands, was twined with a polyamide having a yarn number of 4000 dtex, which consisted of 6 bands, to form a yarn having a yarn number of 8000 dtex, which consisted of 12 bands. In order to be subjected to a tufting operation, the block copolymer yarn was preferably threaded on the uneven positions on the creel of the tufting machines, whilst the polyamid yarn was threaded on the even positions. It is also possible, however, to use other position settings.

The carpet for artificial grass, which was built up of separate yarns of block copolymer and polyamide, was tufted with 310 stitches per running

metre, and a pile height of 12.5 mm, resulting in a pile insert weight of 1750 g/m2.

The carpet thus obtained was subjected to tests comparable with the tests of Example 1. It has become apparent thereby that, also in the case of a field of artificial grass, whether or not scattered in with sand, the mechanical properties of the field of artificial grass made from the block copolymer of polyethylene and polypropylene and polyamide were much better than those of fields of artificial grass made from polypropylene and from polyamide.