WO2025094046A1

WO2025094046A1 - Infill material for turf systems, turf system and method of making the same

Info

Publication number: WO2025094046A1
Application number: PCT/IB2024/060645
Authority: WO
Inventors: Claudio Colombo; Andrea MARCASSOLI
Original assignee: LIMONTA SPORT SpA
Current assignee: LIMONTA SPORT SpA
Priority date: 2023-10-30
Filing date: 2024-10-29
Publication date: 2025-05-08
Anticipated expiration: 2026-04-30
Also published as: IT202300022791A1

Abstract

The invention relates to an infill material in granular form for artificial turf systems, comprising at least 50% by dry weight, preferably at least 55% by dry weight, more preferably at least 60% by dry weight, more preferably at least 65% by dry weight, more preferably at least 70% by dry weight of a main component of plant origin derived from the processing of pine cones and pine nuts, wherein the main component consists of: - between 0 and 95% by dry weight of ground pine cone flakes or petals, - between 5% and 100% by dry weight of ground pine nut shells, and - between 0 and 60% by dry weight of ground pine cone cores, to give 100% by dry weight of said main component. The main component has a grain size, measured according to standard EN933-1:2012, between 0.3 and 4.5 mm, preferably between 0.5 and 3.15 mm. The invention also relates to an artificial turf system (10, 100) comprising the aforementioned infill material, and to a method of making the same.

Description

Infill material for turf systems, turf system and method of making the same

DESCRIPTION

Field of the invention

The present invention relates to an infill material particularly suitable for use in artificial turf systems, whether fully synthetic or of the synthetic-natural hybrid type.

This infill material finds a preferred, though not exclusive, use in making turf systems for sports fields.

The invention also relates to a turf system that includes the aforesaid infill material, and to a method of making the same.

Background of the invention

Artificial grass, or synthetic turf, is used in a wide variety of applications. Of these, the one of greatest interest is certainly that of sports fields, but other common uses are in the decoration of residential spaces, gardens and exhibition areas, and more generally in the landscaping sector.

As is well known, an artificial turf generally comprises a support structure, in the form of a mat commonly referred to as primary or backing in the industry, which is made of synthetic or natural geotextile material, on which filaments of synthetic material similar to natural blades of grass in terms of shape, size and colour are attached. The synthetic filaments can be attached to the substrate in various ways, e.g. by tufting, weaving, gluing or welding.

In the case of hybrid turf systems, the support layer which the synthetic turf filaments are attached to has an essentially lattice or mesh structure, which allows the growth and passage of natural grass roots therethrough. More specifically, once laid on the substrate to be covered, the synthetic turf is covered with the seeding layer for the natural grass, possibly with a sandy infill therebetween. Once grown, the roots of the natural grass penetrate through the mesh of the synthetic turf down to the underlying substrate. This solution allows to achieve an interpenetration between the synthetic filaments and the natural grass, resulting in a denser grass effect and advantageously combining the benefits of both solutions.

As is well known, one or more layers of filling material, generally referred to as infill, - possibly interspersed with the natural grass in hybrid turfs - are then laid over the support layer and distributed between the synthetic grass filaments. The infill consists of material in granular form and performs various functions depending on the intended use of the turf, the environmental conditions of the installation site, the characteristics of the ground and more generally the design requirements of the turf.

For example, in order to impart to the artificial turf similar properties to those of natural turf in terms of mechanical response, stability and rainwater drainage, it is known to provide a stabilising infill consisting of inert granulates such as for example silica sand, or alternatively of an organic grit of natural origin, in particular of plant origin.

In all those applications where it is necessary to meet performance requirements, it is also known to provide one or more infill layers designed to impart to the finished turf the desired mechanical characteristics, e.g. related to elastic and bounce properties, to the ability to absorb shocks or traction/torsion stresses, or further related to the penetration resistance of external bodies. This is, for example, frequently the case for sports and playing fields, for the homologation of which it is necessary to comply with specific and stringent regulations.

In the construction of playing fields, the use of granular material made of plastics, such as granules obtained from specially produced thermoplastic elastomeric materials or recycled vulcanised rubber granules, e.g. from the shredding and appropriate treatment of end-of-life tyres, is well-known and widespread. Plastic granular materials can be used as such or may be coated, e.g. painted and encapsulated with a pollutant-free polyurethane resin film that does not alter the elasticity and strength characteristics of the core plastic material.

Although these materials provide good shock- absorbing properties to the turf, they give rise to a number of concerns in relation to environmental aspects as the use of plastics can cause the granules to be dispersed into the environment, the release of harmful chemicals into the soil and water as a result of the deterioration of the granules and the leaching effect caused by the water, as well as the dispersion of harmful volatile compounds (VOCs) into the air - a major problem especially for indoor sports facilities - as well as problems with the disposal of the granules once the turf has been decommissioned.

Another not secondary problem related to the use of these plastic-based materials is their very low hygroscopicity, which is reflected in the poor ability of the infill to counteract the heating effect of the sun’s rays through evaporation, as water absorption levels are very low. This is considered very negative aspect in relation to the feeling of comfort and “playability” of sports fields in which these infills are used, since in order to keep the thermal performance of these fields at an acceptable level, there is a need for copious and frequent wetting, which results in a considerable waste of water resources.

In recent years, there has been significant research and effort to address these issues and develop more sustainable and environmentally friendly alternatives to plastic-based infills.

However, the Applicant perceived that while the use of natural materials mitigates the environmental concerns raised by the use of granular materials made of plastic materials, this use is actually associated with additional stability and durability issues.

For example, patent application WO 2008/125895 Al discloses a filler material of natural origin comprising a granulate derived from grinding the granular and fibrous component of coconut shells. This filler material may include, in addition to a granulate derived from coconuts, other components of natural origin such as cork, or be further mixed with inert or synthetic materials such as sand and elastomeric rubber granules.

The Applicant has verified that the coconut fibre-based infill disclosed in this document has very high water absorption capabilities, which is positive in terms of counteracting the temperature rise of the field in the face of high outdoor temperatures and/or solar radiation; however, when this type of infill is used in sports fields installed in very rainy, humid and not very sunny geographical areas, it is possible that the high levels of water retention could modify the mechanical response of the sports field in the cold season, when there is little or no evaporation and localised freezing phenomena may occur, as compared to warmer periods.

With regard to cork, which in the above-mentioned document WO 2008/125895 Al is used as a filler for coconut fibre but which is also on the market as a stand-alone infill granulate, the Applicant noted that this material can trigger certain problems. In fact, the low density of the cork can, in the event of a sudden heavy rainfall on the field, lead to a risk of the infill washout due to the floating effect of the granulate, which can in turn imply the need for frequent refilling of the granulate. This problem is even more acute in view of the high costs of finding and processing cork.

Another material of natural origin present on the market as infill for artificial turf is olive stones, as described for example in EP 3 868 955 Al. This document discloses an artificial turf system comprising a plurality of turf fibres attached to a substrate, in which a filler material made entirely from ground olive stones is used.

The Applicant was able to verify that this infill material has limitations both in terms of elastic response, due to the high stiffness of the olive stones, and in terms of low hygroscopicity and consequently reduced ability to cool the playing field through water evaporation.

European patent application EP 4 220 054 Al discloses a process for the production of an infill material for an artificial turf surface wherein the infill material comprises a plurality of granules and wherein the process comprises the steps of providing particles made of plant material and of tumble drying the particles to obtain the granules.

According to this patent application, the aforesaid granules have a preferred size greater than or equal to 0.3 mm and lower than or equal to 3 mm, while the aforesaid plant material is preferably selected from the group of: olive stones, pine cones, walnut shells, cork or combinations thereof, more preferably olive stones.

International patent application WO 2014/049531 A2 discloses an infill material for synthetic turf and synthetic-natural “hybrid” turf based on organic material of plant origin, as well as turf thus obtained and a method of making such a turf.

The aforesaid infill material comprises in use a predetermined percentage by volume of a plant material consisting of the rachis of cereal ear and a predetermined percentage by volume of a ligninic and/or resinous material of vegetable origin, i.e. having a high content of lignin and/or resin, which makes this material highly resistant to the attacks of microorganisms.

According to this patent application, the rachis of cereal ears is not coated by a layer, or film, of material., while the lignin and/or resinous material of vegetable origin may be selected from the group consisting of: a loose material based on ground coconut, olive stones, tegument of cracked pine-kernels, material obtained by defibring the cones, in particular pine cones of arboreous species of the Pinus species, common reed, or Arundo donax, ground into fragments, or particles of predetermined size, teguments of pistachio seeds, barley grain, in particular devitalized for avoiding germination, teguments of sunflower seeds, shells of dried fruit, fragments of banana plant parts, grape seeds and/or grape stalks of Vitis vinifera, Aloe fibres, or a combination thereof.

Summary of the invention

In light of what was observed in the prior art, the Applicant aimed at providing an infill material in granular form for artificial turf systems, predominantly consisting of a main component of natural origin, more specifically plant-based, that has a high degree of environmental sustainability and at the same time is capable to ensure optimal performance, stability and durability characteristics of the turf system.

The Applicant perceived that it is possible to achieve this aim, addressing the problems observed in the prior art, by intervening on the selection of the natural material, its composition and the grain size parameters of the infill material. The present invention therefore relates, in a first aspect thereof, to an infill material in granular form for artificial turf systems.

The infill material according to the invention preferably comprises at least 50% by dry weight of a main component of plant origin derived from the processing of pine cones and pine nuts.

The aforesaid main component derived from the processing of pine cones and pine nuts preferably comprises:

- between 0% and 95% by dry weight of ground pine cone flakes or petals,

- between 5% and 100% by dry weight of ground pine nut shells, and

- between 0 and 60% by dry weight of ground pine cone cores, to give 100% by dry weight of said main component.

Preferably, moreover, said main component and/or said infill material have a grain size, measured according to EN933- 1:2012, between 0.3 and 4.5 mm, more preferably between 0.5 and 3.15 mm.

In a second aspect thereof, the present invention relates to an artificial turf system.

Such an artificial turf system preferably comprises a support layer for the artificial turf, adapted to be arranged above a substrate to be covered.

Preferably, the artificial turf system also comprises filaments made of synthetic material attached to said support layer so as to simulate a natural turf at an upper side of said support layer.

In addition, the artificial turf system preferably comprises a first infill layer distributed above the support layer between the filaments made of synthetic material, said first infill layer comprising an infill material as described herein.

In a third aspect thereof, the invention also relates to a method of making an artificial turf system.

Preferably, the method comprises providing an artificial turf.

Preferably, said turf comprises a support layer for the artificial turf.

Preferably, said turf comprises filaments made of synthetic material attached to the support layer so as to simulate a natural turf at an upper side of the support layer.

Preferably, the method comprises arranging said turf above the substrate to be covered.

Preferably, the method comprises distributing a first infill layer as described herein on said upper side of the support layer and between the filaments made of synthetic material.

In the present description and in the appended claims, with “pine cone” it is intended to indicate a plant strobilus, i.e., a cone-shaped woody plant structure typical of certain conifers belonging, for example, to one of the families Pinaceae (Pinoideae), Cupressaceae, Araucariaceae, Taxaceae, Podocarpaceae. As is well known in the botanical field, the pine cone comprises a central axis or rachis from which a series of scales or bracts radiates, i.e. modified leaves of a woody constitution that, in the case of reproductive pine cones, cover and protect the pine nuts. The pine nuts are encased in a hard, woody shell.

In the present description and in the appended claims, the scales or bracts of the pine cone will be referred to with the terms “flake” or “petal”, and the central axis or rachis of the pine cone will be referred to with the term “core”.

In the present description and in the appended claims, with “processing of pine nuts” it is intended to indicate all operations aimed at extracting pine nuts from their shells, which are therefore a by-product.

In the present description and in the appended claims, with “substrate” it is intended to indicate the top layer of the ground which forms the basis of the turf system of the invention. Such a substrate is, for example, natural terrain, e.g. rocky, mineral and/or organic soil, or artificial terrain, e.g. a cemented or asphalted surface.

In the present description and in the appended claims, with the clause “artificial turf system” it is intended to include both fully synthetic turf systems, in which the turf exclusively consists of synthetic filaments simulating natural grass, and synthetic-natural hybrid turf systems, in which synthetic turf filaments attached to a support layer are interspersed with natural blades of grass grown on a seeding substrate laid on top of the artificial turf.

In the present description and in the appended claims, with the clause “performance infill” it is intended to indicate an infill consisting of a material in granular form designed to impart certain mechanical and performance characteristics to the artificial turf, for example in connection with elastic and bounce properties, with the ability to absorb shocks or traction/torsion stresses, or still with the resistance to penetration of external bodies. In the case of sports fields, these mechanical and performance characteristics are often those required to comply with specific and stringent manufacturing standards in the field.

In the present description and in the appended claims, with the clause “stabilisation infill” it is intended to indicate an infill comprising a material in granular form designed to provide structural support to the turf system and to improve drainage and water run-off.

In the present description and in the appended claims, with “dry weight” of a filler or granular material it is intended to indicate the weight of the filler or granular material measured after it has been dried at 70°C for 48 hours in a drying oven equipped with forced convection heating (for example a Binder Model FD 115 oven or an oven with similar characteristics).

In the present description and in the appended claims, with “moisture” of a component or material it is intended to indicate the amount of water in parts by weight with respect to 100 parts by weight of the component or material in a moist conditions.

The infill material according to the invention represents a more environmentally sustainable alternative to plastic-based or elastomer-based infill materials, being predominantly made of a natural derivative from the processing of pine nuts and pine cones. This also allows the reuse as a secondary raw material of a material normally intended for use as biomass or as a fuel, which is further advantageous at least in terms of environmental sustainability.

Furthermore, the Applicant has experimentally verified that the infill material according to the invention has mechanical properties, in terms of elasticity, bounce capacity, impact resistance, resistance to traction/torsion, etc., that are at least comparable to those of a natural grass field, which makes the infill material particularly suitable for making performancetype infills for artificial turf systems, especially intended for installation in sports fields.

The Applicant also surprisingly found that the use of a granulate based on a derivative of pine nut and pine cone processing, including ground pine nut shells and one or more among pine cone flakes and pine cone cores, and having a particle size within the above-mentioned ranges is associated with numerous other advantageous effects.

Tests carried out by the Applicant have in fact shown that this infill material is associated with optimal water absorption and retention capacity capable to ensure a good cooling capacity through evaporation of the turf system thus made, and at the same time an adequate water release and drying speed capable to avoid potentially damaging stagnation, especially in the case of turf systems installed in cold and humid climates.

The Applicant has verified that the infill material comprising at least 50% by dry weight of a main component including at least 5% by dry weight of ground pine nut shells, in combination with ground pine cone flakes and/or ground pine cone cores, has optimum density values which are low enough to reduce the weight of the infill and allow it to be easily transported and distributed on the turf, but at the same time high enough to counteract the flotation effect during heavy rainfall observed with the use of predominantly cork-based infills.

Finally, the Applicant has found that the provision of an infill material according to the invention, which contemplates the presence of ground pine nut shells in combination with ground pine cone flakes and/or ground pine cone cores, allows to obtain ad hoc binary or ternary mixtures of such components, optimised according to the specific design requirements of the turf system, as well as to the environmental and meteorological conditions of the installation site.

The Applicant was also able to verify by means of appropriate microbiological tests that the infill material according to the invention is resistant to microbiological attack and mould development.

In at least one of the aforesaid aspects, the present description can present at least one of the preferred features described below considered singularly or in combination.

Within the framework of the present description and in the subsequent claims, all the numerical entities indicating quantities, parameters, percentages, and so on are to be considered preceded in every circumstance by the term “about” unless indicated otherwise. Furthermore, all the ranges of numerical entities include the maximum and minimum numerical values, all the possible combinations of maximum and minimum numerical values and all the possible intermediate ranges, in addition to those specifically indicated below.

Preferably, the component of plant origin derived from the processing of pine nuts and pine cones disclosed in this application is untreated and obtained by grinding the pine nut shells and pine cones.

For example, such a component preferably comprises natural pine nut shell particles, natural particles or fibres of pine cone flakes or petals and/or natural particles or fibres of pine cone cores, i.e. particles that have not been treated with antimicrobial additives (whether chemical, artificial, organic, natural, non-toxic or non-irritating antimicrobial additives).

Antimicrobial additives may be agents used to prevent the growth of bacteria, fungi, molds or other microorganisms (e.g. to prevent decay, contamination, etc.) and/or to strengthen the mechanical properties of treated materials or components (e.g. they can withstand more ultraviolet radiation, more friction before they break, etc.).

In some embodiments, the other layers or materials and components (e.g. turf fibres, turf substrate and additional infill materials) of the artificial turf system are also not treated with antimicrobial additives.

Preferably, the infill material according to the invention comprises at least 55% by dry weight, more preferably at least 60% by dry weight, more preferably at least 65% by dry weight, more preferably at least 70% by dry weight of a main component of plant origin derived from the processing of pine cones and pine nuts.

Preferably, said main component comprises an amount greater than or equal to 5%, more preferably greater than or equal to 10%, more preferably greater than or equal to 15%, more preferably greater than or equal to 20%, more preferably greater than or equal to 25%, more preferably greater than or equal to 30%, more preferably greater than or equal to 35%, more preferably greater than or equal to 40%, more preferably greater than or equal to 45%, more preferably greater than or equal to 50%, more preferably greater than or equal to 55%, more preferably greater than or equal to 60%, more preferably greater than or equal to 65%, more preferably greater than or equal to 70%, more preferably greater than or equal to 75%, more preferably greater than or equal to 80%, more preferably greater than or equal to 85%, more preferably greater than or equal to 90%, by dry weight of ground pine cone flakes or petals.

Preferably, said main component comprises an amount lower than or equal to 95%, more preferably lower than or equal to 90%, more preferably lower than or equal to 85%, more preferably lower than or equal to 80%, more preferably lower than or equal to 75%, more preferably lower than or equal to 70%, more preferably lower than or equal to 65%, more preferably lower than or equal to 60%, more preferably lower than or equal to 55%, more preferably lower than or equal to 50%, more preferably lower than or equal to 45%, more preferably lower than or equal to 40%, more preferably lower than or equal to 35%, more preferably lower than or equal to 30%, more preferably lower than or equal to 25%, more preferably lower than or equal to 20%, more preferably lower than or equal to 15%, more preferably lower than or equal to 10%, more preferably lower than or equal to 5%, by dry weight of ground pine cone flakes or petals.

Preferably, said main component comprises an amount greater than or equal to 10%, more preferably greater than or equal to 15%, more preferably greater than or equal to 20%, more preferably greater than or equal to 25%, more preferably greater than or equal to 30%, more preferably greater than or equal to 35%, more preferably greater than or equal to 40%, more preferably greater than or equal to 45%, more preferably greater than or equal to 50%, more preferably greater than or equal to 55%, more preferably greater than or equal to 60%, more preferably greater than or equal to 65%, more preferably greater than or equal to 70%, more preferably greater than or equal to 75%, more preferably greater than or equal to 80%, more preferably greater than or equal to 85%, more preferably greater than or equal to 90%, more preferably greater than or equal to 95%, by dry weight of ground pine nut shells.

Preferably, said main component comprises an amount lower than or equal to 95%, more preferably lower than or equal to 90%, more preferably lower than or equal to 85%, more preferably lower than or equal to 80%, more preferably lower than or equal to 75%, more preferably lower than or equal to 70%, more preferably lower than or equal to 65%, more preferably lower than or equal to 60%, more preferably lower than or equal to 55%, more preferably lower than or equal to 50%, more preferably lower than or equal to 45%, more preferably lower than or equal to 40%, more preferably lower than or equal to 35%, more preferably lower than or equal to 30%, more preferably lower than or equal to 25%, more preferably lower than or equal to 20%, more preferably lower than or equal to 15%, more preferably lower than or equal to 10%, by dry weight of ground pine nut shells.

Preferably, said main component comprises an amount greater than or equal to 5%, more preferably greater than or equal to 10%, more preferably greater than or equal to 15%, more preferably greater than or equal to 20%, more preferably greater than or equal to 25%, more preferably greater than or equal to 30%, more preferably greater than or equal to 35%, more preferably greater than or equal to 40%, more preferably greater than or equal to 45%, more preferably greater than or equal to 50%, more preferably greater than or equal to 55%, by dry weight of ground pine cone cores.

Preferably, said main component comprises an amount lower than or equal to 55%, more preferably lower than or equal to 50%, more preferably lower than or equal to 45%, more preferably lower than or equal to 40%, more preferably lower than or equal to 35%, more preferably lower than or equal to 30%, more preferably lower than or equal to 25%, more preferably lower than or equal to 20%, more preferably lower than or equal to 15%, more preferably lower than or equal to 10%, more preferably lower than or equal to 5%, by dry weight of ground pine cone cores.

Preferably, said main component comprises:

- between 50% and 90%, more preferably between 55% and 85% by dry weight of ground pine cone flakes or petals, and

- between 10% and 50%, more preferably between 15% and 45% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

In particularly preferred embodiments, said main component comprises:

- between 50% and 70%, preferably between 55% and 65%, more preferably about 60% by dry weight of ground pine cone flakes or petals, and

- between 30% and 50%, preferably between 35% and 45%, more preferably about 40% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

In other particularly preferred embodiments, said main component comprises:

- between 70% and 90%, preferably between 75% and 85%, more preferably about 80% by dry weight of ground pine cone flakes or petals, and

- between 10% and 30%, preferably between 15% and 25%, more preferably about 20% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

In particularly preferred embodiments, said main component comprises:

- between 10% and 60%, preferably between 20% and 40%, more preferably about 40% by dry weight of ground pine cone cores, and

- between 40% and 90%, preferably between 60% and 80%, more preferably about 60% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

In particularly preferred embodiments, said main component comprises:

- between 5% and 60%, preferably between 10% and 40%, more preferably about 10% by dry weight of ground pine cone cores,

- between 5% and 60%, preferably between 30% and 60%, more preferably about 30% by dry weight of ground pine nut shells, and

- between 20% and 60%, preferably between 30% and 60%, more preferably about 60% by dry weight of ground pine cone flakes or petals, to give 100% by dry weight of the main component.

The aforementioned balances between the quantity of ground pine nut shells and the quantity of ground pine cone flakes or petals and/or ground pine cone cores, confer to the infill material advantageous properties in terms of turf stability, maintenance of mechanical and drainage properties over time, resistance to flotation washout, resistance to dispersion of the infill as a result of contact with the ball during play, if the infill is used in a sports field, and a lower compaction of the ground, resulting in a reduced need of maintenance work to refill the infill as compared to infills predominantly or entirely made of other materials such as olive stones or cork.

In this respect, optimal results have been achieved when the main component of plant origin of the infill material is a ternary mixture of ground pine nut shells, ground pine cone flakes or petals and ground pine cone cores.

In particular and as will be better apparent hereinbelow, the results of the tests carried out by the Applicant show that an infill material comprising a binary mixture of ground pine nut shells and ground pine cone flakes or petals, a binary mixture of ground pine nut shells and ground pine cone cores or a ternary mixture of ground pine nut shells, ground pine cone flakes or petals and ground pine cone cores, has a better or significantly better heat reducing capacity than an infill material consisting of the aforementioned components taken individually and than an infill material consisting of ground pine cone components (ground pine cone flakes or petals and ground pine cone cores) disclosed in said European patent application EP 4 220 054 Al.

As is known to those skilled in the art, a higher heat reduction or radiation capacity keeps the artificial turf cooler (and thus keeps the overall sports field or stadium cooler to the players and audience), reduces heat damage to fibres, makes the artificial turf less susceptible to fire, allows organic and other particles to degrade more slowly, and reduces other heat- related problems.

In this regard, it should be noted that the heat-reducing characteristic is a particularly welcome improvement in an infill material that simultaneously meets or exceeds the required sports performance such as ball bounce, ball rolling, amount of vertical compression in response to an applied force, and amount of shock absorption in accordance with standards EN 15330-1:2013, EN 12235:2004, EN 12234:2003, EN 14808:2006, EN 14809:2006 and other standards and methods.

Tests carried out by the Applicant and as will be better apparent hereinbelow, also show that when the main component of plant origin of the infill material or the infill material itself essentially consists of ground pine nut shells, optimal results were also obtained in terms of flotation resistance and resistance to discolouration of the infill material.

The Applicant considers that the optimisation of these properties achieved by the binary and ternary mixtures according to the invention is related to the peculiar shape, density and weight characteristics of the granules of the mixture, which are linked to the co-presence of:

- a low-porous and high-density material, having an improved abrasion resistance, deriving from grinding pine nut shells,

- a high-porous and low-density fibrous material deriving from ground pine cone cores, and/or

- a mixture of woody and fibrous material deriving from ground pine cone flakes.

In particular, without wishing to be bound herein to any particular interpretation theory, the Applicant deems that the ground pine nut shells, which are more resistant to abrasion, play a role in containing the dustiness of the mixture that constitutes the main component, which decreases the occurrence of undesirable compacting phenomena of the turf.

The component having a higher porosity deriving from the ground pine cone cores and the more woody and fibrous component deriving from the pine cone flakes, on the other hand, would, in the Applicant's opinion, play a role in hygroscopicity and in lowering the density of the overall mixture, thereby improving the mechanical properties of the turf system, for example in terms of elasticity, shock absorption, ball rolling and bounce capacity and antisplash effect.

In particular, the Applicant deems that the ground pine cone cores, when present, exert beneficial effects in terms of water absorption and release, which in turn have significant effects on the thermal stability of the field, particularly in terms of cooling in the summer season.

Finally, the Applicant deems that the co-presence in the infill material both of the woody and fibrous material deriving from the ground pine cone flakes and of the fibrous material having high porosity and low density deriving from the ground pine cone cores, allows for a gradual release over time of the stored moisture with an advantageous prolongation of the cooling effect exerted by the infill material.

Preferably, said main component and/or said infill material have a bulk density, measured according to standard EN 1097-3: 1999, greater than or equal to 0.25 kg/dm³, more preferably greater than or equal to 0.3 kg/dm³, more preferably greater than or equal to 0.35 kg/dm³, more preferably greater than or equal to 0.4 kg/dm³, more preferably greater than or equal to 0.45 kg/dm³.

Preferably, said main component and/or said infill material have a bulk density, measured according to EN 1097-3: 1999, lower than or equal to 0.8 kg/dm³, more preferably lower than or equal to 0.75 kg/dm³, more preferably lower than or equal to 0.70 kg/dm³, more preferably lower than or equal to 0,65 kg/dm³, 0.6 kg/dm³, more preferably lower than or equal to 0.55 kg/dm³, more preferably lower than or equal to 0.50 kg/dm³, more preferably lower than or equal to 0.45 kg/dm³.

Preferably, said bulk density of the main component and/or of the infill material is measured on the main component and/or on the infill material in wet condition, more preferably said main component and/or infill material having a measured moisture content comprised between 10% and 50%, more preferably between 20% and 40%, more preferably between 30% and 35%, in parts by weight with respect to 100 parts by weight of the main component and/or of the infill material in wet condition.

The Applicant deems that the aforesaid bulk density values of the main component and/or of the infill material allow for an easy transport and distribution of the infill, reduce undesirable compaction of the turf over time and at the same time help to counteract the effects of washout by flotation as a consequence of a heavy rainfall.

Preferably, said infill material further comprises between 0% and 50%, more preferably between 0% and 40%, more preferably between 0% and 30%, by dry weight of a secondary component different from said main component.

Preferably, said secondary component is selected from plant fibrous material, cork, coconut shells, olive stones, walnut shells, hazelnut shells, cereal husks, rice husks, com cob, arboreal material chips, wood chips, sawdust; biodegradable or non-biodegradable polymeric granules, e.g. based on thermoplastic elastomer (TPE), styrene-butadiene copolymer rubber (SBR), ethylene propylene diene monomer rubber (EPDM), PLA; cellulosic copolymers; synthetic polymer resin, e.g. polyurethane (PU), polyvinyl chloride (PVC), polyethylene (PE), polyester, polypropylene, EVA; polymer resin of natural origin, e.g. flax-based, cornbased, oleoresins, turpentine resin (e.g. rosin), polymeric resin from conifers (e.g. larch, stone pine, Aleppo pine or scots pine), gluten-based polymeric resin (e.g. flour, starch, rice and/or wheat), polyurethane resin of plant origin (obtained from plant polyols such as soya, castor oil, turnip); or combinations thereof.

Preferably, said secondary component is of natural, more preferably, plant origin. Preferably, the main component and/or the secondary component of the infill material are obtained by a processing operation comprising one or more operations among grinding, shredding, fragmenting, screening, most preferably carried out by means of equipment known and commonly used for processing natural based infills. By way of non-limiting example, the grinding of the basic ingredients of the main component and/or of the secondary component may be carried out according to the method disclosed in patent application WO 2008/125895 Al.

Preferably, said infill material is essentially consisting of components of natural origin, more preferably of plant origin.

More preferably, said infill material is essentially consisting of components derived from the processing of pine nuts and pine cones as described herein.

In the present description and in the appended claims, with material “essentially consisting of (a certain component)” it is intended to indicate that the material consists essentially entirely of (said certain component), except for percentages of other elements that do not materially influence the desired characteristics.

In general, these additional elements, e.g. foreign matter or impurities, are present in essentially negligible percentages, for example in the order of 1-2% by dry weight or less.

In the present description and in the appended claims, moreover, the clause according to which a certain component comprises 100% by dry weight of ground pine nut shells is to be understood as equivalent to the clause according to which this component is essentially consisting of ground pine nut shells in the above-defined sense.

Preferably, said system additionally comprises a second infill layer adapted to stabilise the turf and aid drainage of liquids.

Said second infill layer preferably comprises a granular material, preferably selected from sand, clay, polymeric materials and grit of natural origin, more preferably of plant origin.

Preferably, an amount of the first infill is comprised between 2 kg and 35 kg per square metre of substrate to be covered.

Preferably, an amount of the second infill is comprised between 3 kg and 45 kg per square metre of substrate to be covered.

In some embodiments, the infill material according to the first aspect or the main component alone can be hydrated by adding an amount of rehydration water. The amount of rehydration water, if any, is determined according to the desired moisture content of the material or component, which in turn depends on the specific application of the material or component.

Preferably, said system further comprises a shock- absorbing mat adapted to be laid between the substrate to be covered and the support layer for the artificial turf. In particular, such a mat is configured to complement the mechanical properties of the turf system by, for example, optimising its elasticity, shock-absorbing and bounce capacity according to specific requirements.

In some embodiments, said system further comprises at least one geotextile separation membrane, arranged between the substrate and the shock- absorbing mat and/or between the shock-absorbing mat and the support layer for the artificial turf.

Preferably, providing said artificial turf comprises providing a support layer for the artificial turf.

Preferably, providing said artificial turf comprises providing filaments made of synthetic material.

Preferably, providing said artificial turf comprises attaching said filaments made of synthetic material to the support layer so as to simulate a natural turf at the upper side of the support layer.

In some preferred embodiments, arranging the artificial turf above the substrate to be covered comprises laying the artificial turf directly on the substrate to be covered.

In alternative embodiments, the method further comprises laying a shock- absorbing mat on the substrate to be covered.

In this case, arranging the artificial turf above the substrate to be covered comprises laying the artificial turf on the shock-absorbing mat.

In some preferred embodiments, the method of making an artificial turf system according to the invention further comprises a step of distributing a second layer of infill comprising a granular material on said upper side of the support layer and between the filaments made of synthetic material.

Preferably, said granular material is selected from sand, clay, polymeric materials and grit of natural origin, more preferably grit of plant origin.

Preferably, said second infill layer is laid first on the support layer and said first infill layer is laid above the second infill layer.

Additional features and advantages of the present invention will be better apparent from the following detailed description of some preferred embodiments thereof, made with reference to the accompanying drawings and provided by way of indicative and non-limiting example.

In the drawings, not to scale:

- FIG. 1 schematically illustrates an artificial turf system according to a first embodiment of the invention;

- FIG. 2 schematically illustrates an artificial turf system according to a second embodiment of the invention;

- FIG. 3 schematically illustrates an artificial turf system according to a third embodiment of the invention; and

- FIG. 4 schematically illustrates an artificial turf system according to a fourth embodiment of the invention.

Detailed description of currentlv preferred embodiments of the invention

FIG. 1 schematically illustrates an artificial turf system 10 according to the invention, shown in cross-section with respect to the surface development of the turf.

The turf system 10 comprises a support layer 12, for example made of a geotextile material, laid on a substrate 14 to be covered. Although the substrate layer 12 is represented as a layer with a continuous surface, the substrate layer 12 may have a lattice or mesh structure with openings connecting the substrate 14 to the upper layers of the turf system 10.

The turf system 10 further comprises a plurality of filaments 16 made of synthetic material attached to the support layer 12 in such a way as to extend upwards, distributed along the surface of the support layer 12 with appropriate spacings, so as to simulate a natural turf.

An infill layer 18 is placed above the support layer 12, distributed between the synthetic filaments 16. This infill layer 18 forms a performance infill and consists of an infill material in accordance with the present invention.

Preferably, the infill material comprises at least 70% by dry weight of a main component of plant origin derived from the processing of pine cones and pine nuts consisting of ground pine nut shells or a mixture of ground pine nut shells and one or more among ground pine cone flakes or petals, and ground pine cone cores.

Preferably, the infill material has a controlled grain size comprised between 0.3 and 4.5 mm.

This infill layer 18 imparts to the system 10 the desired performance, stability, and durability characteristics outlined in the introductory part of this application, and also helps to support the filaments 16 by preventing them from collapsing.

FIG. 2 schematically illustrates an artificial turf system 100 according to a further embodiment, which differs from that illustrated in FIG. 1 only insofar as it additionally includes a second infill layer 20 preferably consisting of inert materials, for example silica sand, and capable to realize a stabilising infill. The provision of the second infill layer 20 in addition to the previously described infill layer 18 contributes to improve the drainage capabilities of the system 10, by further decreasing the occurrence of waterlogging, and to support the synthetic filaments 16.

When present and as in the illustrated case, the second infill layer 20 is preferably laid first above the support layer 12 and the first infill layer 18 is laid above the second infill layer 20, but a reverse arrangement is possible. Furthermore, the first infill layer 18 and the second infill layer 20 are shown for the sake of simplicity as two separate layers, but it is reasonable to consider some degree of mixing between the two infill layers at least at the interface between the two.

When the second infill layer 20 is also provided, as in the case shown in FIG. 2, the quantities of the first infill layer 18 and of the second infill layer 20 are also dosed appropriately so as to achieve a predefined overall height of the infills, comparable to that achieved by the single infill layer 18 illustrated in FIG. 1. This height is in fact predetermined according to the length of the synthetic turf filaments 16 and to other specific characteristics of the field to be covered.

FIG. 3 schematically illustrates an artificial turf system 200 according to a further embodiment, which differs from that illustrated in FIG. 1 only insofar as it additionally includes a shock-absorbing mat 22 laid between the substrate 14 to be covered and the infill layer 18. The mat 22 is configured to optimise the elastic, shock-absorbing and bounce properties of the turf-covered field.

Similarly, FIG. 4 schematically illustrates an artificial turf system 300 according to a further embodiment, which differs from that illustrated in FIG. 2 only insofar as it additionally includes a shock- absorbing mat 22 entirely analogous to the one illustrated and described with reference to FIG. 3.

Examples 1-24 - Preferred compositions of infill material in granular form derived from processing pine cones and pine nuts

Table 1 below schematically shows examples of preferred compositions of an infill layer according to the present invention, prepared as described above, in terms of the percentage quantities by dry weight of the three components deriving from the processing of pine cones and pine nuts.

Table 1 - Compositions of infill material according to the invention

T = ground pine cone cores

G = ground pine nut shells

P = ground pine cone flakes or petals

Example 25 - Irradiation test

The Applicant carried out a number of experimental tests to verify the characteristics of the infill material in terms of water absorption and release, which in turn have a significant effect on the thermal stability of the field (both in terms of cooling in the summer season and in terms of preventing freezing in the winter season).

In particular, some irradiation tests were carried out according to the following experimental procedure.

Approximately 50g of each granular material to be tested, weighed using a laboratory scale (t-lab EU-C 7500), were placed in a cylindrical transparent plastic container with a diameter of 10 cm and a height of 10 cm with a volume of approximately 785 cm³.

The size of the granules, measured according to EN933-E2012, was between 0.5 and 3.15 mm.

In particular, the material was positioned to form a uniform layer of approximately 3.5 cm in height.

Subsequently, the layer of material was covered with tap water at room temperature (about 20°C) and stirred with a plastic stirring rod in order to ensure a uniform hydration of the granules and avoid the formation of air bubbles in the layer.

Subsequently, the water-covered layer of material was left to stand in free air for 24 hours, leaving the water-containing container away from heat sources.

Once the 24 hours had elapsed, the granular material was separated from the water by means of a 500 micron mesh sieve without applying mechanical force on the material itself so as to avoid total squeezing of the absorbed water.

The wet granular material was placed back into the aforementioned plastic container and distributed on the bottom of the container so as to form a uniform layer of approximately 3.5 and 4.5 cm in height, depending on the composition of the infill material.

The container was then placed and held in position on a support shelf having a 45° inclination with respect to the vertical and two high-power incandescent lamps of 1000 W each were placed side by side at a distance of about 50 cm from the support shelf, as measured perpendicularly to the support shelf itself.

30 minutes before starting the irradiation test, the two lamps were switched on in such a way as to ensure that a black (RAL 9011) thermal reference card reached a stable test temperature of 60 +/- 3°C.

During this pre-heating step of the lamps, the aforementioned black cardboard was exposed under the lamps at the same distance (approx. 50 cm) as for the test material samples.

During the irradiation test, the temperature of the granular material in the container was monitored every 15 minutes by means of a laser thermometer (infrared thermometer mod. Testo 83O-T1) taking care to mix uniformly the material in the container with the plastic rod before each measurement.

The irradiation test was considered complete after about 2h, or at any rate, when the measured temperature value of the material stabilised, i.e. had fluctuations of lower than 2°C.

According to the above procedure, irradiation tests were carried out on the following granular materials according to the invention: ground pine nut shells: Example 2, binary mixtures of ground pine nut shells/ground pine cone cores: Examples 22 and 23, binary mixtures of ground pine nut shells/ground pine cone flakes or petals: Example 17, and ternary mixtures of ground pine nut shells/ground pine cone flakes or petals/ground pine cone cores: Examples 14 and 24; as well as on the following comparative granular materials:

Comparative example 1: granular material consisting of ground pine cone cores,

Comparative example 2: granular material consisting of ground pine cone flakes or petals,

Comparative example 3: granular material consisting of ground pine cones (about 10-12% by weight of ground pine cone cores and about 88-90% by weight of ground pine cone flakes or petals), Comparative example 4: granular material consisting of 100% SBR nobilitated with polyurethane (commercial product Fun Rubber Verde - Pentaplast S.r.l., Albignano d'Adda - Italy).

The results of the radiation tests performed are shown in Table 2 below. Table 2

T = ground pine cone cores

G = ground pine nut shells

P = ground pine cone flakes or petals

From the results of the irradiation tests performed, it is evident that both the binary mixtures of Examples 17 (ground pine nut shells/ground pine cone flakes or petals), 22 and 23 (ground pine nut shells/ground pine cone cores), as well as the ternary mixtures of Examples 14 and 24 (ground pine nut shells/ground pine cone cores/ground pine cone flakes or petals) show a surprising synergistic effect between the respective components of the granular infill material in terms of heat reducing capacity with respect to an infill material comprising the aforementioned components taken individually (Example 2 according to the invention and Comparative Examples 1 and 2).

From the results of the irradiation tests performed, it also appears that all of the infill materials according to the invention (Examples 2, 14, 17, 22, 23 and 24) show an improved (Example 2) or much improved (Examples 14, 17, 22, 23 and 24) heat reduction capability with respect to an infill material according to Comparative example 3 consisting of ground pine cones, one of the possible plant materials described by EP 4 220054 Al.

In this respect, it should be noted that the improved results obtained with the material comprising ground pine nut shells according to the invention (Example 2) with respect to the material comprising ground pine cones according to the prior art appear quite surprising in view of the lower porosity and higher density of ground pine nut shells as compared to ground pine cones, which consist of fibrous materials with higher porosity and lower density, as such, more capable of absorbing and releasing water.

Furthermore, and in connection with the improved results obtained with the materials according to the invention, it should be noted that a reduced material temperature of even a few tenths of °C implies significant effects in case of the large surfaces in which the infill material is intended to be used, such as those of a football field. In this regard, for a football field of standard size, approximately equal to about 7500 m², and considering that generally 6 to 8 kg of performance infill are applied per m² of field, an amplification of the cooling effects can in practice be achieved, which can reach a few °C and in any case a level that reduces the heating effects and can be perceived by the athletes.

From the results of radiation tests carried out, it finally appears that all the infill materials according to the invention show a much improved heat reduction capacity with respect to known infill material based on polyurethane-nobilitated SBR.

It follows that the infill material deriving from the processing of pine cones and pine nuts according to the invention has a higher level of water absorption than synthetic materials such as SBR-based granulates and also than natural infill materials based on ground pine cones, one of the possible plant materials described by EP 4220054 Al, which renders such an infill material better capable to counteract excessive temperature increases as a result of solar radiation, due to increased evaporation.

From the tests performed, it was also observed that the infill materials according to the invention allowed a more gradual release of the stored moisture over time with an advantageous prolongation of the cooling effect exerted by the same.

Finally, the water absorption level of the infill material according to the invention was found to be lower than that of other known natural infill materials, for example coconut-based infill materials, which results in a lower decline of mechanical properties (elasticity, shock absorption, bounce, anti-splash effect, etc.) when the infill is exposed to very low temperatures, due to the lower degree of freezing, as ascertained by further tests carried out by the Applicant.

Example 26 - Floating test

The Applicant carried out some experimental tests to verify the ability of the infill material of Example 2 consisting of ground pine nut shells to resist runoff with respect to infill materials consisting of ground cork and, respectively, ground coconut.

Approximately 50g of the granular material of Example 2 according to the invention and an equal amount of two comparative granular materials consisting of ground cork and, respectively, ground coconut, weighed by means of a laboratory scale (t-lab EU-C 7500), were each placed in a cylindrical glass beaker having a volume of approximately 500 mL.

Also in this case, the size of all the tested granules, measured according to EN933-E2012, was between 0.5 and 3.15 mm.

Each beaker was filled with enough water to completely cover the granular material and everything was stirred with a plastic stirring rod.

After letting the water/granule mixture stand for about 30 minutes, the test showed that the ground pine nut shell granules remain at the bottom of the glass (they do not float in the water), while the cork and coconut granules float on the surface of the water or towards it.

This proves that ground pine nut shells are more stable than cork and coconut shells when filled with water or when their infill systems are filled with water.

As a result, the ground pine nut shell granules are more resistant to the action of rain runoff during rainy days and show a lower tendency to detach from the artificial turf.

Therefore, an infill material with ground pine nut shell granules is a better option to maintain the structure and appearance of the infill and to achieve a uniform surface when water is involved (e.g. ground pine nut shell granules are less likely to be moved from one area of the artificial turf to another).

Example 27 - Discolouration test

The Applicant carried out some experimental tests to verify the ability of the infill material of Example 2 consisting of ground pine nut shells to withstand discolouration with respect to infill materials consisting of ground cork and, respectively, ground coconut.

The discolouration test was carried out by placing ground pine nut shells, ground cork granules and ground coconut granules in respective containers with water and soaking or stirring the particles with water for about 2 hours.

In particular, about 50g of the granular material of Example 2 according to the invention and an equal amount of comparative granular material consisting of ground cork and ground coconut granules, weighed using a laboratory scale (t-lab EU-C 7500), were each placed in a cylindrical glass container having a volume of about 500 mL.

A new white cotton garment was then soaked in each of the containers to absorb the water contained therein and then removed from the respective container after 15 minutes.

The test showed that the ground pine nut shell granules leave almost no colour on the fabric of the white garment as compared to cork and coconut particles.

Coconut particles leave the darker colour.

Therefore, the ground pine nut shells are preferable and would make the athletes’ shirts, shorts and other clothing less dirty, e.g. in case of falls or slidings.

From the foregoing and from additional tests carried out on complete artificial turf systems (possibly also including the second stabilising infill layer 20 and/or the shock absorbing mat 22) in which the aforementioned infill compositions derived from the processing of pine nuts and pine cones are used, it appears that both the infill material and the artificial turf systems according to the invention comply with the national and international regulations in force in the field of sports fields (e.g., regulations imposed by the National Amateur League, LND in the Italian national context, or FIFA regulations at international level) in terms of mechanical response and performance.

Clearly, a person skilled in the art, in order to satisfy specific and contingent requirements, can make numerous modifications and variations to the invention described above while remaining within the scope of protection defined by the following claims.

Claims

1. Infill material in granular form for artificial turf systems, comprising at least 50% by dry weight, preferably at least 60% by dry weight, preferably at least 70% by dry weight of a main component of plant origin derived from the processing of pine cones and pine nuts, comprising:

- between 0% and 95% by dry weight of ground pine cone flakes or petals,

- between 5% and 100% by dry weight of ground pine nut shells, and

- between 0 and 60% by dry weight of ground pine cone cores, to give 100% by dry weight of said main component; and wherein said main component has a grain size, measured according to standard EN933- 1:2012, between 0.3 and 4.5 mm, preferably between 0.5 and 3.15 mm.

2. Infill material according to claim 1, wherein said main component comprises:

- between 50% and 90%, preferably between 55% and 85% by dry weight of ground pine cone flakes or petals, and

- between 10% and 50%, preferably between 15% and 45% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

3. Infill material according to claim 1, wherein said main component comprises:

- between 10% and 60%, preferably between 20% and 40% by dry weight of ground pine cone cores, and

- between 40% and 90%, preferably between 60% and 80% by dry weight of ground pine nut shells, to give 100% by dry weight of the main component.

4. Infill material according to claim 1, wherein said main component comprises:

- between 5% and 60%, preferably between 10% and 40% by dry weight of ground pine cone cores, - between 5% and 60%, preferably between 30% and 60% by dry weight of ground pine nut shells, and

- between 20% and 60%, preferably between 30% and 60% by dry weight of ground pine cone flakes or petals, to give 100% by dry weight of the main component.

5. Infill material according to any one of the preceding claims, further comprising between 0 and 50%, preferably between 0 and 40%, more preferably between 0 and 30%, by dry weight of a secondary component different from said main component, preferably selected from plant fibrous material, cork, coconut shells, olive stones, walnut shells, hazelnut shells, cereal husks, rice husks, com cob, arboreal material chips, wood chips, sawdust; biodegradable or non-biodegradable polymeric granules, e.g. based on thermoplastic elastomer (TPE), styrene-butadiene copolymer rubber (SBR), ethylene propylene diene monomer rubber (EPDM), PLA; cellulosic copolymers; synthetic polymer resin, e.g. polyurethane (PU), polyvinyl chloride (PVC), polyethylene (PE), polyester, polypropylene, EVA; polymer resin of natural origin, e.g. flax-based, com-based, oleoresins, turpentine resin (e.g. rosin), polymeric resin from conifers (e.g. larch, stone pine, Aleppo pine or scots pine), gluten-based polymeric resin (e.g. flour, starch, rice and/or wheat), polyurethane resin of plant origin (obtained from plant polyols such as soya, castor oil, turnip); or combinations thereof.

6. Infill material according to any one of the preceding claims, essentially consisting of components of natural origin.

7. Artificial turf system (10, 100), comprising:

- a support layer (12) for the artificial turf, adapted to be arranged above a substrate (14) to be covered,

- filaments (16) made of synthetic material attached to said support layer (12) so as to simulate a natural turf at an upper side of said support layer (12),

- a first infill layer (18) distributed above the support layer (12) between the filaments (16) made of synthetic material, said first infill layer (18) comprising an infill material according to any one of claims 1-6.

8. System (100) according to claim 7, further comprising a second infill layer (20) adapted to promote the drainage of liquids, arranged between said support layer (12) and said first infill layer (18) and comprising a granular material preferably selected from sand, clay, polymeric materials and grit of natural, more preferably plant, origin.

9. System (100) according to claim 8, wherein an amount of the first infill is comprised between 2 and 35 kg per square metre of a substrate to be covered, and/or wherein an amount of the second infill is comprised between 3 and 45 kg per square metre of a substrate to be covered.

10. System (10, 100) according to any one of claims 7-9, further comprising a shockabsorbing mat interposed between the substrate (14) to be covered and the support layer (12) for the artificial turf.

11. Method of making an artificial turf system (10, 100), comprising the steps of:

- providing an artificial turf, comprising a support layer (12) for the artificial turf and filaments (16) made of synthetic material attached to the support layer (12) so as to simulate a natural turf at an upper side of the support layer (12),

- arranging said artificial turf above a substrate (14) to be covered,

- distributing a first infill layer (18) comprising an infill material according to any one of claims 1-6 on said upper side of the support layer (12) and between the filaments (16) made of synthetic material.

12. Method according to claim 11, further comprising a step of distributing on said upper side of the support layer (12) and between the filaments (16) made of synthetic material a second infill layer comprising a granular material preferably selected from sand, clay, polymeric materials and grit of natural, preferably plant, origin.

13. Method according to claim 12, wherein said second infill layer (20) is laid first on the support layer (12), and said first infill layer (18) is laid above the second infill layer (20).