WO2008098905A2

WO2008098905A2 - Thermoplastic synthetic fiber for producing artificial grass mats or the like, process for the production thereof and mats incorporating said fiber

Info

Publication number: WO2008098905A2
Application number: PCT/EP2008/051621
Authority: WO
Inventors: Enrico Buriani; Francesco Zenoni
Original assignee: Tessiture Pietro Radici S.P.A.
Priority date: 2007-02-13
Filing date: 2008-02-11
Publication date: 2008-08-21
Also published as: WO2008098905A3; ITMI20070266A1

Abstract

Thermoplastic synthetic fiber for the production of mats, artificial grass and the like, comprising from 90 to 50% by weight of polyethylene and from 5 to less than 30% by weight of a plastomer having a modulus of flexural rigidity between 5 and 100 MPa, said plastomer being chosen from an ethylene copolymer obtained by single-site catalysis and a heterophasic copolymer containing prevalently propylene.

Description

THERMOPLASTIC SYNTHETIC FIBER FOR PRODUCING ARTIFICIAL GRASS MATS OR THE LIKE, PROCESS FOR THE PRODUCTION THEREOF AND MATS

INCORPORATING SAID FIBER DESCRIPTION

The present invention relates to a thermoplastic synthetic fiber to be used in the production of artificial grass mats or the like, to a process for the production thereof and to mats or the like incorporating said fiber. More in particular, the invention relates to a thermoplastic synthetic fiber constituting the bundles or tufts that protrude, in use, from the upper side of a backing layer in mats, particularly artificial grass mats.

Artificial grass mats, or artificial lawns, constitute a valid alternative to natural grass lawns in many cases, especially in the field of sporting facilities. Unlike natural grass lawns, artificial or synthetic grass mats do not require costly and constant maintenance operations and are not subject to easy wear and tear caused by intense mechanical stresses associated with sports use. This type of mats, for use as artificial grass, as a doormat or as a covering for walking surfaces in a domestic environment, an urban environment and the like, usually comprises a flat flexible backing composed of one or more layers of synthetic material, attached to which are a plurality of bundles or tufts, which project from the upper side of the backing and cover the entire surface thereof, to form a resilient and relatively soft walking layer. In the case of mats with the function of artificial lawn, the aforesaid bundles or tufts simulate the tufts of grass and perform the same function. These tufts are in turn composed of bundles of fibers or strips made of plastic material, produced separately from the flat backing and fixed thereto with techniques known to those skilled in the art. The fibers or strips intended to form these tufts must have properties of mechanical strength, flexibility and resilience suitable for the purpose for which they are intended.

Various embodiments of fibers or strips for artificial grass are described in the patent literature.

Patent application WO 99/04074 discloses the production of fibers or strips for artificial grass mats constituted by polymers or mixtures of polymers such as polyamide, polypropylene and LLDPE. There are described some structures of fibers or strips for artificial grass, for example, structures obtained by coextrusion of different polymers in order to form filaments having a polyolefin inner core and a polyamide surface layer, or vice versa. Preferred structures are composite structures in which fibers of different plastic materials are joined and twisted.

International patent application WO 93/06169 discloses the production of ternary blends of polyethylene and polypropylene compatibilized by adding a plastomer with low molecular weight obtained through metallocene catalysis. The quantity of plastomer with low molecular weight is below 40% in weight in relation to the mixture. The mixture is used in fields differing from those of artificial grass, in particular to produce fibers for nonwovens.

European patent application EP 1 378 592 Al discloses the production of fibers or strips for the production of artificial grass composed of a binary mixture of a polymer and a plastomer. The polymer is composed of polyethylene or polypropylene and the plastomer is composed of a homopolymer or copolymer of ethylene obtained with metallocene catalysis or in any case with single-site catalysts. The quantity of plastomer varies from 30 to 80% by weight with respect to the mixture.

Although these products are based on mixtures of polymers capable of giving the artificial grass a combination of characteristics of mechanical strength and resilience, the structures of fibers or strips proposed do not seem to achieve an optimal balance between properties and costs.

With regard to the fibers or strips for artificial grass mats described in the Patent application WO 99/04074, these do not appear to be totally satisfactory from the viewpoint of accident prevention and user comfort, as the stronger, but also harder, polymer is normally exposed at the surface of the fiber or strip and is therefore a potential source of abrasions and scratches in the event of a fall.

With regard to the fibers described in European patent application EP 1 378 592, it must be observed that the high plastomer content obtained with metallocene catalysis causes a significant increase in the cost.

The object of the present invention is therefore to provide a thermoplastic synthetic fiber for the production of mats, particularly artificial grass mats, provided with excellent properties of tenacity, resilience and softness, sufficient to eliminate or reduce possibilities of abrasion to the skin of persons who accidentally come into contact with the surface of the mat, and which is obtained with an inexpensive material.

Another object of the invention is to provide a mat, particularly an artificial grass mat, or a doormat, incorporating synthetic fibers provided with excellent properties of tenacity, resilience and softness, which are also such as to eliminate or reduce possibilities of abrasion to the skin of persons in the event of falls, slipping or more generally in the event of contact with the surface of this mat.

A further object of the invention is to provide a method for the production of these fibers which is efficient and advantageous from an economic viewpoint. The aforesaid and other objects and advantages of the invention, which will be apparent from the description below, are achieved with a thermoplastic synthetic fiber for the production of mats, artificial grass and the like, characterized in that it comprises from 90 to 50% by weight of polyethylene and from 5 to less than 30% by weight of a plastomer having a modulus of flexural rigidity between 5 and 100 MPa, said plastomer being chosen from an ethylene copolymer obtained by single- site catalysis and a heterophasic copolymer containing prevalently propylene.

More in particular, the polyethylene is chosen from high density or medium density polyethylene. Polyethylene with a density between 0.930 e 0.945 g/cc is particularly preferred.

When the plastomer is an ethylene copolymer obtained through metallocene catalysis or single-site catalysis, it can be an ethylene copolymer with a comonomer such as butene, hexene, 5-methylpentene-l or octene. Single-site catalysts are well known to those skilled in the art and are described, for example, in the patents EP 129 368 and US 4752597. They are capable of generating polymers with a narrow distribution of molecular weights, which, expressed as Mw/Mn, can be below 3. Plastomers having these characteristics are marketed, for example, with the trademark EXACT by ExxonMobil.

When the plastomer is a heterophasic copolymer containing prevalently propylene, it is typically composed of a mixture of copolymers obtained directly in the reactor, comprising a random copolymer of propylene with ethylene and an ethylene -propylene rubber, optionally also comprising a third monomer. These heterophasic copolymers, at times also called thermoplastic olefins (TPO), are marketed, for example, by Basell Polyolefins with the trademark SOFTELL.

The plastomer according to the invention is characterized by a modulus of flexural rigidity of between 5 and 100 MPa, preferably between 8 and 80 MPa, more preferably between 10 and 60 MPa, measured according to ASTM D - 790.

The plastomer according to the invention is preferably present in a quantity between 10 and 25% by weight of the total mixture.

The thermoplastic fiber obtained according to the invention is characterized by a tenacity between 3 and 1 gf/denier, preferably between 2 and 1.2 gf/denier, and by a breaking load between 3000 and 1000 gf, more preferably between 2500 and 1500 gf.

The aforesaid mechanical properties of the mixture of polymers according to the invention is such as to ensure that the fibers or strips have an adequate mechanical impact resistance, necessary to prevent the tufts of grass from breaking as a consequence of the continuous trampling and the violent mechanical stresses to which they are subjected, particularly in the event of the mat being used for sports. The mixture of polymers also has good properties of resilience, so that the tuft, which is stressed in compression when trampled, can regain its substantially erect position when compression ceases.

The thermoplastic fiber according to the invention can contain other components such as additives, colorants, stabilizers, fillers and the like, as it is known in the art.

With reference to Figure 1, the steps of a particularly advantageous method for the production of thermoplastic synthetic fibers according to the invention will now be schematically described.

The granules of polymer mixture 1 which are to form the fiber (10) according to the invention are fed, through loss-in-weight gravimetric feeders 2, into a Bandiera double screw extruder E at a temperature of 220-230⁰C. The mixture is formulated with suitable additive packages, as it is known in the art. The molten mixture is filtered through filters 3 to separate gels and any particles of dirt, and then fed to a flat headed spinnerette S, from which a molten film is delivered. The hot film delivered from the spinnerette S is then subjected to a cooling step C in a water tank kept at a constant temperature. Subsequently, the film is dried with a fan system and then cut into fibers or strips that are subjected to a hot stretching step D by means of two series of rollers 4, 4' and 5, 5' with different speeds, intercalated by a heating oven maintained at controlled temperature. To perform stretching, the speed Vi of the first series of rollers 4, 4' is lower than the speed V₂ of the second series of rollers 5, 5'. The fiber is then subjected to a thermosetting step TF in another two series of hot rollers at controlled temperature 6, 6' and 7, 7', in which the speed V₃ of the first series of rollers 6, 6' is greater than the speed V₄ of the second series of rollers 7, T. The subsequent step F is a lubrication step in which the fiber is lubricated by means of a finishing oil to make it suitable for the subsequent processing operations.

The final fiber obtained (10) has a count of between 200 and 2000 dtex, for the product named "monotape", and between 4000 and 15000 dtex for the product named "fibrillated". The difference between the two articles is due to the width of the final strip and the fibrillation, which is required to generate a particular mesh pattern in the fiber and which is produced between stretching and thermosetting by means of a roller provided with special needle inserts, not shown.

According to a preferred embodiment concerning the "monotape" product, this is joined in tufts of 4, 6 or 8 fibers, and these groups of fibers are twisted in a step T and optionally subjected to curling. A bundle of fibers (28) with a suitable count to form tufts of synthetic grass in a mat is thus generated.

Besides "monotape" and "fibrillated" products, a monofilament product can also be produced, with similar properties to the monotape, by direct extrusion in the spinnerette, i.e. without the need to cut a sheet as the fibers are delivered from several holes, of different shape, positioned on the extrusion head. Also with this product the monofilaments obtained are joined in bundles of 4, 6 or 8 fibers.

Due to the composition of the mixture, the final product is strong, flexible and soft, and therefore suitable to form the upper surface of a mat, for example an artificial grass mat. The cross section of a detail thereof is shown schematically in Figure 2. The fibers 10 grouped together and twisted in the bundles 28 are then fixed to one or more backing layers 30, 32 of a mat, in order to form a strong, flexible and soft upper covering layer simulating the properties of tufts of natural grass.

The bundles of fibers 28 are fixed to the backing layers of the mat 40 preferably by passing the bundles through one or more of these layers and making them protrude from the upper side thereof. Fibers can be fixed to the backing of the mat using other methods, as it is known to those skilled in the art. A filling material such as sand or granules of an elastic material 34, such as rubber, in particular recycled rubber, can be deposited on the upper surface of the mat backing, and which is capable of improving the general elastic properties of the mat, particularly in the case of an artificial grass mat intended for sports use. Examples

With the process described above, fibers were prepared from mixtures whose weight percentage compositions are indicated in Table 1:

Table 1

The fibers obtained had a count of 1350 denier. The tenacity of these fibers was determined with the method UNI EN ISO 2062 and the breaking load with the method UNI EN ISO 2062. The results are set down in Table 2:

Table 2

The data indicated above show that the mechanical properties are improved by the presence of at least 5% in weight of a plastomer, and that no significant improvement of the mechanical properties is obtained by increasing the quantity of plastomer to 30% or over. Below 5% the mechanical properties do not have values sufficient for the desired use. The interval from 5 to less than 30% instead ensures adequate values of the mechanical properties obtained with the use of a limited quantity of plastomer, thereby obtaining an optimal balance between properties and cost.

The embodiments described above for the thermoplastic synthetic fiber according to the invention allow the task and preset objects to be fully accomplished. In particular, the characteristics of mechanical strength and softness required to solve the technical problem highlighted in the preamble are obtained through the use of materials that allow a considerable reduction in the final production costs. Moreover, the production method of the synthetic fiber is simple and low-cost, although providing a fiber structure that associates, in an extremely advantageous manner, the characteristics of strength and durability with softness, which are very important from the viewpoint of accident prevention and comfort of the user.

The embodiments of the invention described above are susceptible to numerous modifications and variants, all falling within the scope of the same inventive concept, as defined in the accompanying claims.

Claims

1. Thermoplastic synthetic fiber for the production of mats, artificial grass and the like, characterized in that it comprises from 90 to 50% in weight of polyethylene and from 10 to 29% in weight of a plastomer having a modulus of flexural rigidity between 5 and 100 MPa, said plastomer being chosen from an ethylene copolymer obtained by single-site catalysis and a heterophasic copolymer containing prevalently propylene.

2. Fiber as claimed in claim 1, characterized in that said polyethylene is a HDPE or a medium density polyethylene.

3. Fiber according to claim 2, characterized in that said polyethylene has a density between 0.930 and 0.945 g/cc.

4. Fiber according to claim 1, characterized in that said plastomer is present in a quantity between 10 and 25% in weight.

5. Fiber according to claim 1, characterized in that said ethylene copolymer obtained through metallocene catalysis or catalysis of the single- site type, comprises an ethylene copolymer with a comonomer such as butene, hexene, 5-methylpentene-l or octene.

6. Fiber according to claim 1, characterized in that said heterophasic copolymer containing prevalently propylene, is composed of a mixture of copolymers obtained directly in the reactor, comprising a random copolymer of propylene with ethylene and an ethylene-propylene rubber, optionally also comprising a third monomer.

7. Fiber according to claim 1, characterized in that said plastomer has a modulus of flexural rigidity between 5 and 100 MPa.

8. Fiber according to claim 6, characterized in that said plastomer has a modulus of flexural rigidity between 8 and 80 MPa.

9. Fiber according to claim 7, characterized in that said plastomer has a modulus of flexural rigidity between 10 and 60 MPa.

10. Fiber according to claim 1, characterized by a tenacity between 3 and 1 gf/denier.

11. Fiber according to claim 9, characterized by a tenacity between 2.5 and 1.2 gf/denier.

12. Fiber according to claim 1, characterized by a breaking load between 3000 and 1000 gf-

13. Fiber according to claim 12, characterized by a breaking load between 2500 and 1500 gf-

14. Fiber according to claim 1, characterized by a count between 200 and 15000 dtex.

15. Fiber according to claim 1, of the monotape type, characterized by a count between 200 and 2000 dtex.

16. Fiber according to claim 14, of the fibrillated type, characterized by a count between 4000 and 15000 dtex.

17. Mat (40) comprising one or more backing layers (30, 32, 34) and an upper layer, characterized in that it comprises a series of bundles (28) of fibers (10) according to any one of claims 1-16 fixed to said backing layers.

18. Mat according to claim 17, characterized in that said bundles of fibers (28) are twisted.

19. Process for the production of thermoplastic synthetic fibers (10) for the production of mats, characterized in that it comprises the following steps: a) feeding into an extruder (E) a mixture comprising from 90 to 50% in weight of polyethylene and from 10 to less than 30% in weight of a plastomer having a modulus of flexural rigidity between 5 and 100 MPa, said plastomer being chosen from an ethylene copolymer obtained by single-site catalysis and a heterophasic copolymer containing prevalently propylene. b) melting said polymers in said extruder (E); c) extruding a thermoplastic film; d) cooling said thermoplastic film; e) cutting said thermoplastic film to form a series of fibers; f) stretching said fibers to obtain a count between 200 and 15000 dtex.

20. Process according to claim 19, characterized in that it also comprises: ao) a step of gravimetric feed of said mixture of polymers before said feeding a) to said extruder E; ei) a thermosetting (TF) and shrinkage step downstream of said stretching step f); e₂) a lubrication step (F) downstream of said thermosetting step (TF), to lubricate said fiber (10).

21. Process according to claim 20 or 21, characterized in that it also comprises a fibrillation step between said thermosetting step (TF) and said stretching step f).

22. Process according to claim 20, 21 or 22, characterized in that it also comprises a step (T) to join and twist said fibers (10) to form a bundle (28) of fibers with a count between 1400 and 16000 dtex.

23. Process according to claim 19, characterized in that it also comprises a step to curl said bundles of fibers (28).