WO2018171911A1

WO2018171911A1 - Support mat for hybrid turf

Info

Publication number: WO2018171911A1
Application number: PCT/EP2017/067646
Authority: WO
Inventors: Stephan Sick; Ivo LOHR; Mark HEINLEIN
Original assignee: Polytex Sportbeläge Produktions-Gmbh; Technology Licensing Corp.
Priority date: 2017-03-23
Filing date: 2017-07-12
Publication date: 2018-09-27
Also published as: EP3601662A1

Abstract

The invention relates to a method of producing a support mat (200) for hybrid turf (312), the method comprising: - placing a degradable mesh (216) on top of a non-degradable (206), synthetic fiber mesh to form a multi-layer structure having an upper side (US) and a lower side (LS); - incorporating artificial turf fibers (222) into the multi-layer structure such that the artificial turf fibers penetrate the multi-layer structure as a whole and such that portions of the artificial turf fibers extend upwardly from the upper side of the multi-layer structure, each artificial turf fiber being a monofilament generated by an extruder or a bundle of extruder-generated monofilaments, - applying a liquid backing (220) to the lower side (LS) of the multi-layer structure; and - solidifying the liquid backing, the multi-layer structure with the incorporated artificial turf fiber and the backing forming the support mat.

Description

SUPPORT MAT FOR HYBRID TURF

Description

Field of the invention

This invention relates to artificial turf, and more particularly to hybrid turf.

Background and related art

Hybrid turf is generally understood to be a product that combines natural grass and synthetic elements. Hybrid turf is commonly used for constructing sports field surfaces because it has e a grass-like iook and feel, is more resistant to wear and tear than standard sports field sod and offers other advantageous properties. Hybrid turf is typically produced by generating a synthetic carrier structure having a horizontal mesh backing and vertical upright fibres tufted into the backing. This mat is often installed at a sod farm and infilled with growing medium. After natural grass has been grow within f the carrier structure the resultant hybrid turf is transplanted to the field of use.

There are several downsides to the commonly used process of growing and installing standard soil-based sod. Harvesting, transportation and re-installation costs are high and the natural grass easily becomes damaged in the transport and transplantation process. In particular, the roots of the natural grass plants will be damaged during harvest. The roots therefore need to be regenerated at the use site. This results in a significant delay between harvesting and usability because parts of the roots of the transplanted grass need to be regrown and need to penetrate the soil at the use site for firmly attaching the transplanted natural grass to the soil. For example, bentgrass greens are widely used in North America to provide golf course greens. Typical grow-in time for bentgrass golf greens is several months, and premature use of such greens can have serious adverse effects on the development and establishment of the roots for the natural grass plants. United States patent US 006035577 reduces the time needed to achieve playable but durable sports field or golf green by providing a support structure in the form of artificial turf as a base layer on top of which a further layer of natural grass is grown.

E0986674 B1 describes a piece of stabilized turf comprising a biodegradable and a synthetic mesh. However, the patent is based on fibers derived from a slit film. It has been shown that, at least for many materials commonly used for the production of artificial and hybrid turf, only fibers derived from slit films are sufficiently

"voluminous" to fill the wide mesh openings of the horizontal backing layer to a sufficient degree as to prevent the fibers from being pulled out during the process of filling the carrier structure with growing medium. This process, which includes brooming and raking the growing medium into the fibres of the carrier structure exerts considerable shear force on the fibers. If the fibres are not held or anchored sufficiently within the backing, they will be pulled out and the carrier structure damaged. Although fibers generated from slit film tapes typically are thick enough to be mechanically anchored to the backing, they have the disadvantage that they often do not faithfully reproduce the "look and feel" of natural grass. Summary

It is an objective of the present invention to provide an improved method of producing a support mat for hybrid turf and a corresponding support mat as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

In a first aspect, the invention relates to a method of producing a support mat for hybrid turf. The method comprises

- placing a degradable mesh on top of a non-degradable, synthetic fiber mesh to form a muiti-!ayer structure having an upper side US and a lower side LS;

- tufting artificial turf fibers individually into the multi-layer structure such that the artificial turf fibers penetrate the multi-layer structure as a whole and such that first portions of the artificial turf fibers extend upwardly from the upper side of the multi-layer structure, each artificial turf fiber being a monofilament generated by an extruder or a bundle of extruder-generated monofilaments;

- after having tufted the artificial turf fibers, applying a liquid backing to the lower side LS of the multi-layer structure such that the backing wets at least portions of the synthetic fiber mesh and second portions of the artificial turf fibers extending to the lower side of the multi-layer structure; and

- solidifying the liquid backing, the solidified backing mechanically fixing the

artificial turf fibers in the multi-layer structure, the multi-layer structure with the solidified backing and the tufted artificial turf fibers forming the support mat.

Embodiments of the invention may have multiple advantages:

Incorporating monofilaments or bundles of monofilaments rather than slit film based fibers into the multi-layer structure may have the advantage of providing artificial turf fibers which faithfully reproduce the look and feel of natural grass. This is because the shape of fibers consisting of a monofilament or a bundle of monofilaments have a comparatively thick, stiff and resilient central part, while the thickness and shape of fibers made from slit films is homogeneousiy thin (like that of a sliced thin polymer film). Meshes with a sufficiently narrow mesh width to firmly fix also monofilaments exist, but hitherto they could not be used as support mats in hybrid turf systems as this narrow mesh width would impede the growth and development of healthy grass roots, thus reducing downward water movement and the exchange of gases. Thus, embodiments of the invention may now allow to firmly incorporate monofilaments in a support mat for hybrid turf that would otherwise be too open to mechanically anchor the monofilaments, without risking that the natural grass plants die as a result of poor root growth, water-logging and so forth.

Incorporating the artificial turf fibers into a two-layered stack of meshes increases the stability of the natural grass layer, whose grass blades shall intermix with the artificial turf fibers. The resulting support mat may be more stable than a one- layered carrier material: the grids of the two meshes are typically shifted relative to each other. The mesh width of the two meshes may also slightly differ so that the "effective" mesh width for an artificial turf fiber penetrating both layers is typically much smaller than the mesh width of the individual meshes. Thus, a strong support structure for incorporating the artificial turf fibers is provided that firmly keeps the artificial fibers in place and vertically oriented. Using a combination of a degradable and a non-degradabie mesh is particularly advantageous, as at the beginning of hybrid turf production, when the artificial turf fibers are incorporated in a carrier structure, the two-mesh-layer structure provides a strong support for the artificial turf fibers, ensuring that said fibers extend basically vertically from the multi-layer structure (see above). The fact that one of the two meshes is degradable ensures that at a later stage of the method, when seeds of natural grass are added and the support structure is regularly watered at a sod farm, and when natural grass plants start go grow, the degradable mesh will have already started degrading by the time the roots of the grass plants start penetrating the support structure. This may be highly advantageous, as it has been observed that, in some prior art hybrid turf systems, the roots of the grass plants have clogged all openings of the carrier material of the artificial turf component. As a result, drainage rate is decreased, root development is impeded and grass health and quality are negatively affected. By contrast, as the degradable mesh is degraded when put in contact with water, microorganisms or another trigger of degradation, the roots have sufficient space for penetrating the multi-layer structure and for reaching a soil layer (consisting e.g. of earth or sand) without clogging the openings of the support structure. As the roots of the growing grass plants may continuously replace the space formerly occupied by the degradable mesh, and as the second mesh layer is of a non-degradable material, the artificial turf fibers may still be firmly fixed in the support structure when the degradable mesh has already partially or completely degraded. This is particularly advantageous in case the support structure for the hybrid turf is not directly installed at the use site for growing the natural grass plants there, but rather is installed first in a sod farm. In this case, once the natural grass has reached a desirable state of maturity the hybrid turf is transplanted to the use site. Because the synthetic components of the carrier structure provide support to the grass plants, damage from harvesting, transportation and re-installation is minimized. Thus, embodiments of the invention may provide one or more of the following advantages: a more "natural" look and feel of the artificial turf fibers as the artificial turf fibers are monofilaments or bundles of monofilaments; for example, the monofilaments are basically circular or ellipsoid in cross section as this shape is typically obtained for the products of an extrusion process for generating artificial turf fibers; improved stability and fixation of the artificial turf fibers in a carrier structure; prevention of water accumulation and moisture-induced decay of the roots and grass plants without reducing the quality of artificial fiber incorporation; and increased robustness of the hybrid turf against transport and transplantation damage. According to embodiments, the liquid backing is applied to the lower side LS of the multi-layer structure in an amount of more than 500 g/m², in particular 550 g/m² to 700 g/m². For example, 600 g/m2 of the liquid backing may be applied.

Compared to the amount of the secondary backing typically applied to artificial turf carriers, this is a particularly high amount. It may have the positive effect of firmly fixing even monofilaments and monofilament bundles in the multi-layer structure, even in case the liquid backing is applied such that it does not seal the whole lower side of the multi-layer structure but rather seals only some of the cells of the lower mesh.

According to embodiments, the liquid backing has a viscosity of 2000 mPa s - 5000 mPa-s. It has been observed that a viscosity of 2500 mPa s to 4000 mPa-s, in particular of 2800 mPa sto 3500 mPa s, is particularly suited for improving the fixing of monofilaments (including monofilaments lying in the inner of a monofilament bundle) in the two-layer structure without sealing and clogging the meshes.

This may be advantageous as the comparatively high viscosity may ensure that the liquid backing enters also the inner portion of monofilament bundles, thereby ensuring that also monofilaments completely surrounded by the other

monofilaments of the bundle are sufficiently wetted by the backing as to be firmly mechanically fixed in the backing.

According to embodiments, the liquid backing is applied to the lower side LS of the multi-layer structure such that less than 70%, preferentially less than 50% of the openings of the one of the two meshes facing to the lower side LS of the multi-layer structure is sealed by the backing.

This may be advantageous as the clogging of mesh holes may be prevented. Thus, it may be ensured that - at least after the degradable mesh has degraded - water can penetrate the mesh and does not cause a decay of the natural grass plants and their roots.

According to embodiments, the degradable mesh is a biodegradable mesh.

According to embodiments, the biodegradable mesh is a jute fiber mesh, a linen fiber mesh, a hemp fiber mesh, a polylactic acid fiber mesh, a sisal fiber mesh or a combination thereof. Jute fiber meshes have been observed to be particularly advantageous, since they are inexpensive, are available in many different mesh sizes, and degrade fast enough to ensure that during the growth period of many grass species, a sufficient portion, e.g. at least 40%, of the degradable mesh is degraded.

According to embodiments, the backing consists of or comprises degradable material. Using a combination of a degradable mesh and a degradable backing may be advantageous as a larger fraction of the overall mass of the hybrid turf is degraded, thereby leaving enough space for the roots to grow and penetrate the non- degradable mesh without clogging the mesh openings. The fraction of the

degradable backing material may vary depending on the desired price, physico- chemical properties and other factors. Preferentially, the backing comprises at least 30%, more preferentially at least 50% and even more preferentially at least 80% by weight of the backing a (bio-, pH- or water-) degradable material, in some

embodiments the backing essentially completely consists of a degradable material. According to embodiments, the degradable backing is a backing that degrades upon being exposed to water (irrespective of whether bacteria or other microorganisms are present). For example, a backing that degenerates upon being exposed to water can be made of a material that deteriorates within 6 month to at least 40% of its mass upon being regularly, e.g. daily, irrigated and contacted with water once or multiple times.

For example, the material that degrades upon being exposed to water can be a water-soluble form of polyvinylalcohol (PVA). Different forms of polyvinyl alcohol exist. Preferentially, a PVA form that degrades to at least 70% upon being repeatedly irrigated for at least three weeks is used. According to other examples, the material that disintegrates on contact with water is an inhomogeneous liquid mixture of a first latex and a second latex, the first latex in the dry state being less water-swellable than the second latex in the dry state.

According to other embodiments, the degradable backing essentially consists of a materia! that degrades upon being exposed to an acidic or a basic liquid, e.g. a liquid having a pH value above 7.5 or below 6.5. Appling a liquid with low pH value a single time may be sufficient to trigger the degradation (in this case: the solution) of the degradable material. It has been observed that most plant species survive a short time exposure of solutions, e.g. water, having a pH of 6, or 5.7 or even 5.4. Thus, by adding water comprising acetic acid or citric acid and having a pH value of below 6 (e.g. 5.4) at least a single time, a significant portion of the pH-degradabie material may be dissolved in the acidic water. For example, the degradable backing can consist of agar-agar having been observed to degrade if contacted with an acidic solution.

According to other embodiments, the degradable backing essentially consists of or comprises (e.g. by at least 30% or more) a bio-degradable material. For example, the bio-degradable backing can comprise a copolymer of starch with styrene- butadiene latex. The generation of said copolymers is described, for example, in US20130276245A1 , whereby embodiments of this invention differ from the method described in US20130276245A1 in that no pigments are used. For example, the starch-latex copolymer backing can be made from a mixture comprising starch and monomeric components. The monomeric components in the mixture that are copolymerized comprise: i. styrene or a substituted styrene,

ii. an acrylate and/or methacrylate,

iii. optionally: one or more further ethylenically unsaturated monomers.

For example, 5 to 40% by weight of the mixture may consist of starch and 50 to 95%, preferably 60 to 95%, by weight of the mixture may consist of the monomeric components. The starch is biodegradable and will allow the roots to penetrate also the mesh cells that are fully or partially sealed by the starch-latex copolymer backing after some weeks or month. According to other embodiments, the degradable backing is made of -degradable plastics whose components are preferentially derived from renewable raw materials, but which may also be made from petrochemicals containing degradable additives which enhance degradation. For example, most aliphatic polyesters are degradable due to their potentially hydrolysable ester bonds. According to preferred embodiments, the degradable backing and/or the degradable mesh is compostable. While "degradable" broadly means that an object can be broken down e.g. by microorganisms, water, a particular low or high pH value or other factors within a given time interval of, e.g. 6 month or, more preferentially, 6 weeks, "compostable" as used herein specifies that such a process will result in compost, or humus. For example, a "compostable material" is material that is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with that of known

compostable materials. Jute, linen, hemp, polylactic acid and sisal fibers are degradable as we!i as compostable. According to embodiments, the synthetic fiber mesh is a polymer fiber mesh, in particular a polyolefin fiber mesh.

According to some of said embodiments, the polyolefin fiber mesh is a polyethylene fiber mesh, a polyamide fiber mesh, a polypropylene fiber mesh, or a mesh of fibers comprising a mixture of two or more of the following polyolefins: polyethylene, polyamide and polypropylene.

According to embodiments, the incorporation of the artificial turf fibers comprises tufting the artificial turf fibers into the multi-layer structure.

Tufting is a type of textile processing in which a thread is inserted on a primary base. It is an ancient technique for making warm garments, especially mittens. Short U-shaped loops of extra yarn are introduced through the fabric from the outside so that their ends point inward (i.e., toward the hand inside the mitten). Usually, the tuft yarns form a regular array of "dots" on the outside. On the inside, the tuft yarns may be tied for security, although they need not be.

This may provide for a strong fixing of the artificial turf fiber in the multi-layer structure. Tufting may also be beneficial as it consumes less fiber material than weaving for achieving a desired density of artificial turf fibers emanating from a carrier. This is because it is not necessary to weave a portion of the fiber of significant length into the multi-iayer structure. Rather, only a comparatively small portion, typically below 20% or even below 15% of a fiber, is contained within or at the lower side of the multi-layer structure.

The two meshes are preferentially not glued or otherwise attached to each other at the moment when the artificial fibers are incorporated. This may be advantageous, as it eases the wetting of the degradable mesh when it is instailed at a sod farm and regularly watered for growing the natural grass, thereby boosting the

(bio)degradation process. Thus, the two meshes may be attached to each other merely mechanically by the incorporated artificial turf fibers and, optionally - in some comparatively small areas - by smaller amounts of a liquid backing that is applied to the lower side of the multi-layer structure that reaches the degradable mesh layer.

According to embodiments, the degradable mesh has the form of a first rectangular- shaped grid. The synthetic fiber mesh has the form of a second rectangular-shaped grid. In some cases, the first and/or second grid has a square shape. The artificial turf fibers are incorporated into the multi-layer structure such that the positions where the artificial turf fibers penetrate the multi-layer structure form multiple rows. Each row crosses two or more different grid rows of the first and the second grid. This may be advantageous, as the artificial turf fibers incorporated in the multi-layer structure may be mechanically fixed in the multi-layer structure more strongly. This may increase the overall stability of the support mat.

According to embodiments, each row has a zig-zag or S-form shape. This may increase the mechanical fixation of the artificial fiber within the multi-iayer structure and thus may increase the overall stability of the support mat.

According to some of said embodiments, the degradable mesh and the non- degradable, synthetic fiber mesh are aligned and positioned on top of each other such that the orientation of the x and y axes of the first and second grids are (basically) identical. The multiple rows are oriented at an angle within a range of 10- 80^D relative to the common x-axis of the first and the second grid. This may increase the mechanical fixation of the artificial fiber within the multi-layer structure, and thus may increase the overall stability of the support mat.

According to embodiments, the mesh widths of the degradable mesh and of the synthetic fiber mesh are large enough to allow water and roots of natural grass to penetrate the mesh.

According to embodiments, the mesh width of the degradable mesh is smaller than the mesh width of the synthetic fiber mesh. This may ensure that the degradation of the degradable mesh generates sufficient space for the grass plant roots to grow. According to embodiments, the openings of the degradable mesh and the openings of the synthetic fiber mesh have a width and a height of 5 mm - 8 mm. For example, the width x height of the mesh may be 7mm x 7mm.

Using a mesh with large openings may have the advantage that the grid lines of the mesh do typically not act as a bridge when the liquid backing is applied, thereby preventing the sealing of the openings by the liquid backing and a clogging of the hybrid turf generated from the multi-layer structure.

According to a first example, the non-degradable synthetic fiber mesh is made of a monofilament being 360pm thick. The overall pile weight of the support mat for the hybrid turf having already incorporated the artificial turf fibers but not the natural grass plants can be about 500 - 1000 g/m^z.

According to embodiments, the support mat is used for generating hybrid turf for installation at a golf course. This may be particularly advantageous for golf courses, which are irrigated frequently, so the risk that slack water damages the roots of the grass plants is particularly high. Said risk can be reduced by the multi-mesh-based mat whose degradable mesh largely deteriorates before it is installed at the use site.

According to embodiments, the method further comprises

- after having incorporated the artificial turf fibers, applying a liquid backing to the lower side of the multi-layer structure such that the backing wets the degradable mesh, the synthetic fiber mesh and portions of the artificial turf fiber extending to the lower side of the multi-layer structure; and

artificial turf fibers in the multi-layer structure. For example, the solidification may be performed actively, by applying heat, a catalyst or other factor to initiate or boost the solidification. Alternatively, the solidification may be performed passively by simply applying the liquid backing to the lower side of the multi-layer structure after having incorporated the artificial fibers, and then allowing the whole support mat with the liquid backing to dry and solidify for some number of minutes or hours at room temperature.

Adding a liquid backing to the lower side of the support mat (i.e., to the lower side of the multi-layer structure and opposite to the side from which the larger portions of the artificial turf fibers emanate as artificial grass blades) may have the advantage that the artificial turf fibers are more firmly fixed in the multi-layer structure.

For example, the artificial turf fiber may be a bundle of up to 6 monofilaments. The amount, application technique and viscosity of the liquid backing may be chosen such that also the monofilament in the inner part of the bundle is wetted.

According to embodiments, the method comprises creating the monofilament(s). The creation of the monofilaments comprises creating a liquid polymer mixture; extruding the polymer mixture into a monofilament comprising a marbled pattern of the first and second color; quenching the monofilament; reheating the monofilament; stretching the reheated monofilament to deform the polymer beads into threadlike regions and to form the monofilament into an artificial turf fiber. For example, the polymer mixture may comprise polyethylene or a mixture of polyethylene and po!yamide. The mixture may further comprise additives, e.g. dyes and flame retard ants. According to embodiments, the polymer mixture is at least a two-phase system. A first one of the phases comprises a first polymer and a first dye, a second one of the phases of the polymer mixture comprises a second polymer and a second dye. The second dye has a different color than the first dye. For example, the first dye may be yellow and the second dye may be green, or the two dyes may represent different shades of green. The second polymer may be of the same or of a different type as the first polymer depending on the way the phase separation is achieved. The first and the second phase are immiscible and the first phase forms polymer beads within the second phase.

This may be advantageous as an extrusion of said two phase system will result in the generation of a marbled monofilament that faithfully reproduces the color and texture of natural grass.

According to one embodiment, the phase separation is achieved by different polarities of the first and second polymers. For example, the second polymer is a non-polar polymer, e.g. polyethylene (PE), and the first polymer is a polar polymer, e.g. polyamide (PA). Optionally, the liquid polymer mixture is at least a three-phase system, the third phase being or comprising a compatibilizer. The first phase forms polymer beads surrounded by the third phase within the second phase. The compatibilizer may be, for example: a grafted maleic acid anhydride (MAH); an ethylene ethyl acrylate (EEA); a maleic acid grafted on polyethylene or polyamide; a maleic anhydride grafted on free radical initiated graft copolymer of polyethylene, SEBS, EVA, EPD, or polypropylene with an unsaturated acid or its anhydride such as maleic acid, glycidyl methacrylate, ricinoloxazoline maleinate; a graft copolymer of SEBS with glycidyl methacrylate, a graft copolymer of EVA with mercaptoacetic acid and maleic anhydride; a graft copolymer of EPDM with maleic anhydride; a graft copolymer of polypropylene with maleic anhydride; a polyolefin-graft- po!yamidepolyethylene or polyamide; and a polyacrylic acid type compatibilizer.

According to alternative embodiments, the phase separation of the first and the second phase is achieved by selecting the first and the second polymer such that the difference in melt mass-flow rate of the first and second polymer results in a phase separation of a molten mixture of the first and second polymer. For example, the first polymer may have a melt mass-flow rate that differs by at least 3 g/10 min measured at 190°C/2.16 kg from the melt mass-flow rate of the second polymer.

The first polymer may have a melt mass-flow rate - measured at 19CTC/2. 6 kg - of 0.5- 5 g/10 min. The second polymer may have a melt mass-flow rate - measured at 190X/2.16 kg - of 8- 100 g/10 min. According to embodiments, the extrusion is performed at a pressure of 40-140 bars, more preferentially between 60-100 bars. This may allow generating a marbled color pattern even in case a single type of polymer, e.g. PE, is to be used for generating the fiber. In combination with the use of a filamentous extrusion product as the monofilament, a particularly realistic synthetic turf fiber may be generated. According to embodiments, the method comprises adding a nucleating agent to the polymer mixture. The polymer mixture is extruded into a filamentous extrusion product which is stretched into the monofilament. The nucleating agent triggers, in particular during the stretching, the creation of crystalline portions in and at the surface of the monofilament. This may increase the surface roughness of the fiber and may increase the mechanical fixing of the fiber in the multi-layer structure and the backing. The nucleating agent may be, for example, talcum, kaolin (also known as "china clay"), calcium carbonate, magnesium carbonate, silicate, aluminium trihydrate, magnesium hydroxide, meta- and/or polyphosphates, and coal fly ash (CFA).

According to embodiments, the liquid backing is applied to the lower side of the multi-layer structure such that more than 10%, but less than 70% and preferentially less than 50%, of the lower side of the whole multi-layer structure is sealed by the backing. This may prevent an accumulation of water, which could cause the roots of the natural grass plants to rot.

According to some embodiments, the liquid backing is styrene-butadiene rubber (SBR) or another non-degradable material. Non-degradable material may be used, for example, in case the hybrid turf is to be installed on sandy ground or in regions with low annua! rainfall, as it may help to hold at least some of the moisture for some time. However, the holes in the solidified backing and the degradation of one of the mesh layers will ensure that the water does not accumulate to a degree that damages the plants. For example, the backing may be SBR applied in an amount of about 600 g/m^z to the lower side of the multi-layer structure.

According to alternative embodiments, the liquid backing is made of a degradabie material, e.g. a biodegradable material. For example, the liquid backing can be made of natural latex or starch-based latex: the liquid backing can be a copolymer of starch with styrene/butadiene latex as described above. Alternatively, the biodegradable backing can be made of natural rubber. Degradabie material may be used, for example, if the hybrid turf is to be installed on clay ground or in regions with high annual rainfall, as it may help to ensure that the water does not

accumulate to a degree that damages the plants.

In a further aspect, a method of producing hybrid turf is provided. The method comprises generating the support mat as described herein for embodiments of the invention. The method further comprises:

- placing the support mat on top of a layer comprising sand or earth or a mixture thereof;

- adding a fill layer comprising a fill material on top of the support mat; for example, the fill layer may comprise sand or earth or synthetic filler materials or a mixture thereof; the fill layer may optionally also comprise or may later be supplemented with fertilizers, minerals, fungicides, etc.; - adding seeds of natural grass to the upper side of the support mat; in some embodiments, the seeds may already be provided as a component of the fill layer; and

- growing the natural grass to provide natural grass fibers intermixing with the

artificial turf fibers to form the hybrid turf, thereby repeatedly watering the natural grass to stimulate growth of the grass; and

- applying a liquid on the natural grass for triggering the degradation of the

degradable fiber mesh. For example, in case the degradab!e mesh is

biodegradable or disintegrates or dissolves on water contact, the regular irrigation for watering the grass plants may at the same time slowly trigger the degradation (biodegradation or solution) of the degradable mesh. In case the mesh is of a material that dissolves or degrades upon being exposed to acidic liquids, this step may comprise applying water of a ph below 6, e.g. water having a pH of 5.4, at least once on the growing natural grass and the degradable mesh to trigger the degradation of the mesh.

The number of weeks or months during which the natural grass plants are grown in the sod farm may depend on the grass species and on the desired state of maturity of the grass as well as other conditions like temperature and humidity. Preferably, the degradable material of the degradable mesh is chosen such that a significant portion, e.g. at least 40%, of the degradable mesh is degraded when the natural grass plants have reached their desired state of maturity. This parameter is typicaliy known; data on the growth profile of various grass species can be derived from literature.

According to some embodiments, the grass species and the length of the artificial grass fibers extending from the multi-layer structure to the top are chosen such that the artificial and the natural fibers have approximately the same length or the artificial fibers have a slightly shorter length than the natural grass blades. This may ensure that the hybrid grass has a natural, grass-like appearance and touch, but is still more robust against transport damages and wear and tear than purely natural turf.

For example, the length of the portion of the artificial turf fiber extending the multilayer structure to the top is 3-7 cm. The natural grass blades intermix with the artificial turf fiber to form a hybrid turf that is supported by the artificial turf. Some grass species grow to the desired length within several weeks, e.g. 3 to 6 weeks, while others need 2 to 3 months.

According to embodiments, the placing of the support mat, the adding of the fill layer and the growing of the grass are performed in a sod farm. The method further comprises transplanting the support mat with the artificial turf fibers and the at least partially degraded degradable fiber mesh, parts of the first earth and/or sand layer bound by the roots of the natural grass, and the fill iayer to the use site.

In a further aspect, the invention relates to a support mat for hybrid turf. The support mat comprises

- a multi-layer structure having an upper side and a lower side and comprising:

_* a first Iayer of a non-degradable, synthetic fiber mesh; and

• a second Iayer of a degradable mesh placed on top of the first Iayer; and

- artificial turf fibers tufted individually into the multi-layer structure such that each artificial turf fiber penetrates the multi-layer structure as a whole and such that first portions of the artificial turf fibers extend upwardly from the upper side of the multi-layer structure, each artificial turf fiber being a monofilament generated by an extruder or a bundle of extruder-generated monofilaments; and

- a backing on the lower side LS of the multi-layer structure that surrounds and mechanically fixes at least portions of the synthetic fiber mesh and second portions of the artificial turf fibers extending to the lower side of the multi-layer structure (and optionally wetting also portions of the degradable mesh).

According to embodiments, the backing material is created by preparing an inhomogeneous liquid mixture of a first latex and a second latex. The first latex in the dry state is less water-swellable than the second latex in the dry state. After having incorporated the artificial turf fibers, the inhomogeneous liquid mixture is applied on the lower side of the multi Iayer structure such that the inhomogeneous liquid latex mixture wets at least portions of the incorporated fiber. The liquid backing is allowed to solidify to form the solid backing that mechanically fixes the artificial turf fibers.

Using a mixture of two different types of latex having different swelling capabilities for generating the backing may have the advantage that the different swelling properties will result in mechanical shear forces at the contact areas of the first and second latex when the backing contacts water. As the backing disintegrates when put in contact with water, the aeration of the ground is improved, and earthworms and roots have sufficient space for penetrating the multi layer structure without clogging the openings of the support mat.

Using a latex mixture that does not completely disintegrate but merely develops microscopic cracks may have the advantage that the roots of the growing grass plants may continuously replace the space formerly occupied by the backing. Thus, the artificial turf fibers may still be firmly fixed in the support structure when the backing is already partially or completely disintegrated. Embodiments of the invention may allow for providing a support mat for hybrid turf that ensures that natural grass plants do not die as a result of waterlogging.

In another beneficial aspect, the robustness of the support structure against transport and transplantation damage may be increased. Using a mixture of two different types of latex having different swelling capabilities for generating the backing may have the advantage that the different swelling properties will result in mechanical shear forces at the contact areas of the first and second latex when the backing contacts water. Typically, the backing contacts water when the support mat is installed and is exposed to rain or irrigation. The

mechanical shear forces resulting from the swelling of the first and second latex may be so high that the backing disintegrates into small pieces after just the first rainfall, if the difference in the swelling properties of the first and second latex is too low to result in a complete disintegration of the backing, at least microscopic cracks in the backing materia! are created that allow water to penetrate the backing and improve the aeration of the ground below the artificial turf. The effect of the water- induced microscopic cracks or the water-induced disintegration of the backing is that the clogging of the support mat is prevented.

By using a backing that consists of an inhomogeneous mixture of two types of latex with different swelling capabilities, said disadvantages may be avoided. Thus, embodiments of the invention may allow providing support mats for hybrid turf that ensures that rain can infiltrate the ground even after debris of all kinds may have accumulated on the hybrid turf over several years of use. According to embodiments, the first and/or second latex is an emulsion of a copolymer in an aqueous medium. The copolymer is a copotymerization product of a polymerizable polymer and one or more monomers. The one or more monomers are selected from a group comprising:

- styrene or a substituted styrene; and

- an acrylate and/or methacrylate.

According to embodiments, the polymerizable polymer is water-sweilabie.

According to embodiments, the polymerizable polymer is water-swellable and is a polymerizable starch or a polymerizable starch derivative. Using starch may be advantageous, as starch is a biodegradable substance. The backing can be disrupted very quickly by applying water to the hybrid turf or the artificial turf such that the water, e.g., rain or irrigation, contacts the backing. The resulting fragments of the backing can then be degraded at least partially by microorganisms over a longer period of time, typically weeks and months. Thus, the backing may largely or completely be degraded.

According to embodiments, the method further comprises generating the copolymer of the first (less water-swellable) latex by copolymerization of a first

copolymerization mixture. The first copolymerization mixture comprises:

- 20% to 40% by weight of the first copolymerization mixture of the styrene or the substituted styrene;

- 20% to 50% by weight of the first copolymerization mixture of the acrylate and/or methacrylate;

- 5% to 20% by weight of the first copolymerization mixture of one or more

ethylenically unsaturated monomers (e.g., acrylate, methacrylate, styrene); and - 1% to 15% by weight of the first copolymerization mixture of a not-yet- polymerizable form of the polymerizable polymer.

According to embodiments, the method further comprises generating the copolymer of the second (water-swellable) latex by copolymerization of a second

copolymerization mixture comprising:

20% to 40% by weight of the second copolymerization mixture of the styrene or the substituted styrene; - 20% to 50% by weight of the second copoiymerization mixture of the acrylate and/or methacrylate;

- 5% to 20% by weight of the second copoiymerization mixture of one or more ethyienically unsaturated monomers (e.g., acrylate, methacrylate, styrene); and 20% to 50% by weight of the second copoiymerization mixture of a not-yet- polymerizable form of the polymerizable polymer.

Thus, by increasing the fraction of the not-yet-polymerizable form of the

polymerizable polymer (e.g., naturally occurring starch), the swelling capabilities of the polymer generated by the copoiymerization are increased. By decreasing the fraction of the not-yet-poiymerizable form of the polymerizabte polymer, the swelling capabilities of the polymer generated by the copoiymerization are decreased.

According to further embodiments, the generation of the copolymer of the first latex comprises performing a copoiymerization of a first copoiymerization mixture and the generation of the copolymer of the second latex comprises performing a

copoiymerization of a second copoiymerization mixture. The first and the second copoiymerization mixture respectively comprise:

- 20% to 40% by weight the styrene or the substituted styrene;

- 20% to 50% by weight the acrylate and/or methacrylate;

- 5% to 20% by weight the one or more ethyienically unsaturated monomers, - 1 % to 50% by weight the not-yet polymerizable form of the polymerizable

polymer; thereby, the second copoiymerization mixture comprises at least 10% by weight more of the not-yet polymerizable form of the polymerizable polymer than the first copoiymerization mixture. Preferably, the second copoiymerization mixture comprises at least 20% by weight more of the not-yet polymerizable form of the polymerizable polymer than the first copoiymerization mixture. For example, the first copoiymerization mixture can comprise 35% of the not-yet polymerizable starch and the second copoiymerization mixture can comprise 50 % f the not-yet polymerizable starch. The higher the difference in weight structure of the not-yet polymerizable polymer, the stronger the mechanical shear forces resulting from water contact and the faster the degradation of any material generated from an inhomogeneous mixture of the two different latex forms. According to embodiments, the generation of the inhomogeneous liquid mixture of the first and second latex comprises stirring the first liquid latex with the second liquid latex under stirring conditions that are known to yield a liquid latex mixture having a desired degree of inhomogeneity. The desired degree of inhomogeneity is a degree of inhomogeneity that causes a solidified film of the first and second latex to disintegrate into fragments of a desired size in response to contact with water. For example, it may be desired to apply a secondary backing that disintegrates into pieces that are about a size of 0.2-2 cm after one hour of water contact. In order to determine the desired degree of inhomogeneity and the corresponding stirring conditions (duration, stirring speed, etc.), different mixtures (test mixtures) of the first and second latex may be created. Each of the test mixtures is stirred under different conditions (stirring speed, stirring duration, optionally also stirrer type or

temperature, etc.). The test mixtures are applied on an even layer and are allowed to dry to form a solid film. The film is then submerged in water. After a predefined time (e.g., one hour), the films will have disintegrated, and the sizes of the

fragments are determined. The stirring conditions that yield a desired degree of inhomogeneity and a corresponding desired fragment size are then used for generating the liquid mixture of the first and second latex.

According to embodiments, the method further comprises generating an

inhomogeneous test latex mixture, the test mixture comprising the first and second latex that will be used for producing the backing of the hybrid turf support mat. The test mixture is applied on an even surface and allowed to solidify and dry to form a test latex film. When the test latex film has dried, it is put in contact with water for a predefined time; e.g., one hour. The time of exposure is the desired backing disintegration time upon exposing the backing to water; e.g., to rainfall or irrigation. After the predefined time has elapsed, check whether the film has disintegrated, if the film has disintegrated, the first and second latex types used for generating the test latex mixture are used for manufacturing the backing of the artificial turf or the backing of the support mat. if the film has not disintegrated (to a sufficient degree), the composition of the first and/or second latex is changed in a way that the water- swelling capabilities of the first and second latex differ more strongly. Then, a new test latex mixture is generated comprising the first and/or second latex with modified composition. And the test is repeated to check whether the swelling capabilities of the different latex form in the new test latex mixture cause the backing to disintegrate in the water exposure test to a sufficient degree. The generation of the polymers can be performed, for example, as described in patent application

US20130276245A1 , which is incorporated in its entirety hereby by reference.

US20130276245A1 describes a composition for surface coloration of paper. It has nothing to do with artificial turf production. Embodiments of the invention are based on the surprising observation that the copolymerization described for generating the composition for surface coloration allows to exactly define the swelling capability of latex by choosing appropriate amounts of comonomers, whereby at least one of said comonomers is in fact a water-swellable polymer.

According to embodiments, the first copolymerization mixture and the second copolymerization mixture are free of pigments.

According to embodiments, the copolymerization is a radical emulsion

polymerization of the copolymerization mixture. According to embodiments, the inhomogeneous liquid latex mixture comprises about 50% by weight the first (less water-swellable) latex and comprises about 50% by weight the second (water-swellable) latex. However, other ratios of first to second latex are also possible; e.g., 1.4:1 or 1 :1.4.

In a still further aspect, the invention relates to a piece of hybrid turf comprising: - a layer of sand or earth or a mixture thereof;

- the support mat for natural turf mentioned above, with the degradable mesh at least partially degraded and wherein a solidified backing mechanically fixes the artificial turf fibers in the multi-layer structure;

- a fill layer comprising a fill material on top of the support mat; the fill layer may have a height of less than 2 cm, preferentially of less than 1 ,5 cm, and

- natural grass fibers whose natural grass blades intermix with the artificial turf fibers and whose roots penetrate the fill layer, the support structure and parts of the layer of sand or earth, or a mixture thereof.

Said piece of hybrid turf may be installed, for example, at a sod farm for growing the grass plants of the artificial turf, or at the use site, e.g., a sport field covered by the hybrid turf. According to embodiments, the artificial turf fibers protrude at least 20 mm, in some embodiments more than 40 mm from the upper side of the fill layer. The crowns of the natural grass plants protrude at least as far from the upper side of the fill layer as the artificial turf fibers. Thus, a comparatively large portion of the artificial grass fibers protrude from the fill layer. Contrary to many hybrid turf mats currently, it is possible to reduce the height of the fill layer (which protects the fibers from mechanical forces during a game) as the fibers are firmly fixed in the hybrid layer by the increased amount of the backing applied to the lower side of the multi-layer structure without sealing the carrier structure. Thus, a carrier for hybrid turf is provided that prevents damages of slack water and is also able to protect the artificial turf fibers from being pulled out.

The elements of the support mat and the hybrid turf may have features as described herein for embodiments of the invention, including embodiments of the inventive method of producing the support mat. According to embodiments, the "upper side" (US) of a multi-layer structure comprising a degradable mesh on top of a non-degradabie, synthetic fiber mesh is the outward side of the degradable mesh, with the inward side of the degradable mesh facing the non-degradabie mesh layer.

According to embodiments, the "lower side" (LS) of a muiti-layer structure comprising a degradable mesh on top of a non-degradabie, synthetic fiber mesh is the outward side of the non-degradabie mesh, with the inward side of the non- degradabie mesh facing the degradable mesh layer.

The term "hybrid grass" or "reinforced natural grass" as used herein refers to a product created by combining natural grass with artificial turf fibers, it is used, for example, for stadium fields and training fields used for association football, rugby, American football, golf and baseball. Reinforced natural grass can also be used for events and concerts. The incorporated synthetic fibers make the grass stronger and more resistant to damage.

The term "degradable" as used herein refers to materials which chemically or physically decompose upon being exposed once or regularly to a substance which triggers the chemical decomposition of a significant portion of said material within a predefined time. The predefined time is typically shored compared to the overall live expectancy of the material under the absence of the substance that triggers the chemical or physical decomposition. Thus, "degradable" as used herein is an umbrella term for "biodegradable", "water-induced disintegratable", water-soluble" and "pH soluble". Degradation times may vary strongly, but typical degradation times of materials used for generating the degradable mesh according to some embodiments of the invention range from a few minutes (in particular for pH degradable materials) to some days, weeks or month (in particular for water soluble and biodegradable materials). Typically, the degradable material is cased to degrade by maintaining it at a temperature of about 15-25°C and exposing it at least once or repeatedly to a suitable liquid that triggers the degradation of the

degradable mesh.

The term "biodegradable" as used herein refers to substances, e.g., plastics or natural substances such as jute, that decompose by the action of living organisms, usually bacteria.

The term "water-soluble" as used herein refers to substances, e.g., plastics or natural substances, that dissolve in water if once or repeatedly contacted with water over a broad pH range, including pH 7 even under the absence of living organisms which are able to digest the material. The expression "material that disintegrates on contact with water" as used herein refers to substances, e.g., plastics or natural substances, that mechanically disintegrate in water if once or repeatedly contacted with water over a broad pH range, including pH 7 even under the absence of living organisms which are able to digest the material. The disintegration may be caused by a partial dilution process or by mechanical forces, e.g. shear forces that may occur if a backing material that consists of an inhomogeneous mixture of two different latex types with different swelling capabilities is brought into contact with water.

The term "pH-soluble" as used herein refers to substances, e.g., plastics or natural substances, that dissolve in a liquid (typically water) if once or repeatedly contacted with a liquid having a pH lower than 6.5, e.g. a pH value of about 5.4, or with a liquid having a pH higher than 7.5. The term "mesh" as used herein is a material with essentially evenly spaced holes that allow air or water to pass through. For example, a mesh can be made from threads or wires. The threads or wires may be woven to form the mesh.

Alternatively, liquid materials, e.g. molten polymers, may be cast into a mesh. Thus, a mesh refers to a barrier made of connected strands ("fibers") of a flexible/ductile material. The mesh fibers may be attached to each other e.g. by weaving, gluing, knitting etc. A synthetic mesh can be, for example, a plastic mesh that may be extruded, oriented, expanded, woven or tubular.

The term "synthetic fiber" as used herein refers to a fiber that is mainly or entirely made from synthetic materials such as petrochemicals, unlike those man-made fibers derived from such natural substances as cellulose or protein. In particular, a synthetic fiber can be a synthetic polymer fiber, e.g., a synthetic polyo!efin fiber. A synthetic fiber can be made e.g. from polypropylene, polyethylene, nylon, PVC, PTFE or other materials. The term "sod farm" or "sod grass farm" as used herein refers to an agricultural company and farm that grows and sells turf.

The term "use site" as used herein refers to a location where natural, hybrid or artificial turf is to be installed and used. For example, turf is used in sports stadiums, lawns, golf courses and other facilities. A "monofilament" as used herein is a fiber generated by extruding a polymer mass through an opening of an extruder. It is not generated by slicing a polymer film into stripes. Extruded monofilaments tend to be more robust against splicing and shear forces than fibers generated from a slit film. Brief description of the drawings

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

Fig. 1 is a flow chart of a method for producing a support mat for hybrid turf.

Fig. 2 depicts a support mat for hybrid turf. Figs. 3a-d depict the use of a support mat for growing hybrid turf at a sod farm. Fig. 3e depicts the installation of the grown hybrid turf at the use site.

Fig. 4 is a photograph of the lower side of the support mat.

Fig. 5 is a photograph of the lower side of a rolled-up piece of support mat.

Fig. 6 is a photograph of the support mat against a bright background. Fig. 7 is a photograph illustrating the strength of the mechanical fixing of an individual artificial turf fiber in the multi-layer structure.

Fig. 8 is a photograph of the lower and upper sides of two rolled-up pieces of the support mat.

Fig. 9 is a photograph of two vessels filled with water and a film that

disintegrates on contact with water:

Fig. 10 shows a photograph of a film immediately after being contacted with water and a photograph of the same film one hour later.

Fig. 1 1 depicts two different copolymerization mixtures used for generating the polymer of the first and second latexes. Fig. 1 is a flow chart of a method for producing a support mat 200 as depicted, for example, in Fig. 2. The support mat is used as a mechanical support for hybrid turf as depicted, for example, in Fig. 3e. The method may be executed, for example, in a manufacturing plant for producing artificial turf. In the first step 102, a degradable mesh 216 such as a jute mesh is placed on top of a non-degradable, synthetic fiber mesh 206, e.g., a mesh of polyethylene (PE) yarn. Thus, a mu!ti-layer structure having an upper side US and a lower side LS is generated. In a further step 104, artificial turf fibers are incorporated into the multi-layer structure such that each artificial turf fibers penetrates the multi-layer structure as a whole one or multiple times. This means that the artificial turf fibers penetrate both layers 216, 206 at essentially the same position {slight shifts of a few mm caused e.g. by a shift of the two grids of the two meshes are permissible). Some first portions of the artificial turf fibers extend upward from the upper side US of the multi-layer structure and form artificial grass blades. Some U-shaped second portions of the artificial turf fibers extend to the lower side LS of the mufti-layer structure and may form U-turns generated by a tufting process. The fiber consists of a single monofilament or a bundle of multiple, typically up to 6, monofilaments. In an additional step, a liquid backing 220 may be applied on the lower side of the multi-layer structure.

Depending on the viscosity of the liquid backing, the multi-layer structure is oriented vertically or turned upside down to ensure that the liquid backing can wet at least the non-degradable mesh 206 and the U-shaped, lower portions of the incorporated artificial turf fibers, and optionally some smaller portions of the degradable mesh as well, before it is solidified and mechanically fixes or increases the mechanical fixing of the artificial turf fibers 222. The width of the synthetic mesh and the amount and viscosity of the liquid backing is chosen such that a comparatively high amount of backing is applied to the lower side of the multi-layer structure without sealing most of the holes of the mesh at the lower side of the structure. The viscous, liquid mass is distributed by a blade over the lower side of the multi-layer structure. However, due to the large size of the mesh openings in particular of the synthetic mesh, the sealing of the majority of the synthetic mesh openings can be prohibited to ensure that water can penetrate the multi-layer structure, in particular after the degradation of the degradable mesh.

The multi-layer structure 206, 216 with the incorporated artificial turf fiber and, optionally, the solidified backing 220, forms the support mat 200. The support mat is mechanically flexible and can adapt to a ground even if said ground is not totally level. The mat 200 is permeable to water and air and also to roots, in particuiar after the degradable mesh has started to degrade. Although the fibers are monofilaments or monofilament bundles, the comparatively high amount of backing applied per square meter may ensure that the fibers are strongly fixed in the multi-layer structure.

Figs. 3a-d depict the use of a support mat for growing hybrid turf at a sod farm.

The support mat 200 is transferred to a sod farm, where it is placed on top of a ground layer 302 comprising sand or earth or a mixture thereof. This step is depicted in Fig. 3a. The ground layer may also consist of synthetic filler materials and is of sufficient height to allow grass roots to mechanically penetrate the layer and extract nutrients and water, e.g. at least 2 to 3 cm. After the support mat 200 is installed on the ground layer 302 of the sod farm, a fill layer 306 is added on top of the support mat. This step is depicted in Fig. 3b. The fill layer comprises fill material. For example, the fill layer may comprise sand or earth or synthetic filler materials or a mixture thereof. The fill layer may optionally also comprise or may later be supplemented with fertilizers, minerals, fungicides, etc. According to embodiments, the fill layer has a height of 10-50 mm, preferably in the range of 20-40 mm. Depending on the embodiment, the fili layer may have a height of less than 20 mm, preferentially of less than 15 mm. Using a thin fill layer may be advantageous as the roots will penetrate and mechanically fix at least parts of the fill layer on top of the multi-layer structure. Thus, the fill layer will have to be moved at least partially from the sod farm to the use site. This increases the weight of the hybrid turf and thus increases transport costs. As the high amount of secondary backing firmly fixes the monofilaments in the multi-layer carrier structure, including the monofilaments contained in filament bundles, a thin fill layer may be sufficient to protect the fibers from being pulled out. Thus, transport costs may be reduced.

The fill layer supports the roots and crowns of the natural grass plants, and the grass blades of the natural grass plants as well as a large portion 304 of the artificial turf fibers 222 extend above the fili layer to create a hybrid grass surface that faithfully reproduces a natural grass surface. The support mat "carries" the natural grass plants and the fill layer. The roots of the natural grass plants extend

downward through the fill layer 306 and even penetrate the multi-layer structure and parts of the ground layer 302. This creates a unified mass, which also holds the fill layer of sand-based growth media in place. The support mat is root-, air- and water- permeable. Because the mesh 216 and optionally also the solidified backing 220 are degradable, the roots have sufficient space to grow without clogging the openings of the remaining mesh 206 and thus without making the support mat water- impermeable. However, the degradable mesh 216 stabilizes the support mat during the transport from the artificial turf factory to the sod farm, and in the early phase of growing the natural grass. The mesh 206 that is still intact when the natural grass has reached the desired length stabilizes the hybrid turf when it is transported from the sod farm to the use site, such as a golf course. As the roots remain largely intact, the overall time needed for achieving a playable and durable hybrid turf is reduced. According to embodiments, both the artificial grass blades as well as the natural grass blades extend more than 20 mm or even more than 40 mm above the upper surface of the fill layer. According to embodiments, the length of the portions of the natural grass fibers extending from the upper surface of the fill layer is typically identical to or at least 5 mm higher than the length of the portion of the artificial turf fibers extending from the upper surface of the fill layer.

As the support mat carries the filler material, e.g., sand-based growth media, only a comparatively small fraction of the roots will reach down to the base layer 302, so the root system can be transplanted in a comparatively intact form.

Fig. 3c depicts the process of growing the natural grass 310 to provide natural grass fibers 312 shown in Fig. 3d. The sod farm provides lighting and irrigation systems, 305 which allow for an optimum growth rate of the natural grass plants. Warm temperatures and constant humidity accelerate not only the growth of the plants but also the biodegradation of the degradable mesh 216 and, optionally, of the solidified backing 220 if it is made of a degradable material. Thus, the roots 308 of the grass plants have sufficient space to grow without clogging the non- degradable mesh 206.

A piece of hybrid turf whose natural grass blades 310 have reached the desired length is depicted in Fig. 3d. The natural grass blades 310 intermix with the artificial turf fibers 222 and form a piece of hybrid turf 312. When the natural grass has reached its desired length, significant portions of the degradable mesh have already degraded without a negative impact on the stability of the hybrid turf.

Fig. 3e depicts the installation of the grown hybrid turf at the site of use: the soil 314 at the site of use may be, for example, clay or sand or any other form of soil that supports the growth of grass. The fully grown hybrid turf 312 is formed into rolls at the sod farm, and a small fraction of the base layer 302 may be bound by the roots 308 of the plants and transported to the site of use. However, as can be inferred from figures 3d and 3e, the fraction of roots affected by the transplantation is comparatively small, so the damage to the roots will also be comparatively small.

Fig. 4 is a photograph of the LS of the support mat. It shows vertical 206.2 and horizontal 206.1 fibers of the synthetic mesh 206 in the foreground, and the fibers of a degradable jute mesh 216 in the background. The grid size of the mesh 206 is significantly larger than that of mesh 216, and the heights of individual cells/rows of the grid of the mesh 206 are indicated by reference number 224.

The artificial turf fibers are incorporated into the multi-layer structure such that the positions where the artificial turf fibers penetrate the multi-layer structure form multiple rows 202, 204. Each row 202, 204 crosses two or more different grid rows 224 of the first and the second grid. For example, a first knot 208 within the row 202 lies below the horizontal grid fiber 206.1 , a second knot 210 of the same row 202 lies above the grid fiber 206.1 , etc. Thus, each row 202, 204 has a zig-zag or S-form shape. The lower side of the support mat also comprises patches of the solidified backing 220. However, the backing does not cover the whole lower surface of the mat, to prevent a sealing of the mat. For example, the grid element below the arrow 216 is not covered by the backing, and the arrow 214 indicates a hole allowing water, air, roots and small earthworms to penetrate the support mat. Fig. 5 is a photograph of the lower side of a rolled-up piece of support mat. The distance 218 between two rows of artificial turf fibers, such as rows 202 and 204, typically lies in the range of 4-20 mm. The top region of Fig. 5 shows the US of the support mat, from which artificial turf fiber portions 304 extend outward. The jute mesh 216 and the non-degradable mesh 206 are also visible, whereby the jute mesh is at the border not fully covered by the synthetic fiber mesh.

According to one example, the non-degradable synthetic fiber mesh is made of a monofilament being 360pm thick. The distance 218 between two rows of artificial turf fibers is 3/4", the stitch rate is about 12/10 cm and the resulting artificial turf has a pile weight of about 1050 g/m². According to another example, the non-degradable synthetic fiber mesh is made of a monofilament being 360pm thick. The distance 218 between two rows of artificial turf fibers is 1 1/2", the stitch rate is about 12/10 cm and the resulting artificial turf has a pile weight of about 530 g/m².

Fig. 6 is a photograph of the US of the support mat against a bright, illuminated background. It can clearly be derived that the support mat has holes which are not covered by the backing, 220 and that the effective mesh width of the multi-layer structure is large enough to allow water, roots and small worms to penetrate said structure.

Fig. 7 is a photograph illustrating the strength of the mechanical fixing of an individual artificial turf fiber in the multi-layer structure. A sheet of the support mat having a size of approximately 30 cm x 21 cm is held by a single artificial turf fiber without pulling the fiber out of the multi-layer structure.

Fig. 8 is a photograph of the lower sides LS and upper sides US of two rolled-up pieces of the support mat. On the lower sides of the support mat, the non- degradable mesh 206 is visible. On the upper sides of the support mat, the artificial turf fibers 222 are visible. At the right sides of the roils, the jute mesh is visible. The support mat may be transported in this form from the artificial turf manufacturing plant to a sod farm.

Fig. 9 is a photograph of two vessels filled with water and a film made of an inhomogeneous mixture of two latex forms. As the two different latex forms have different water-sweiling capabilities, the film disintegrates in response to contact with water. The vessel 902 shows a single coherent piece of a test latex film that was created by hardening an inhomogeneous mixture of two different latex forms having different water-swelling capabilities. The test latex film in the vessel 902 is still intact because the photograph was taken immediately after the film was immersed in water. The vessel 904 shows fractions of another piece of the test film about one hour after being submersed in water. The fractions of the latex film in the vessel 904 were generated as a result of a disintegration process along the contact areas of the first and second latexes in the inhomogeneously mixed iatex fiim.

Fig. 10 shows a photograph of a piece of another test film. The other test film is also made of an inhomogeneous mixture of two latex forms that have different water- swelling capabilities. For example, the first latex type in dry form may swell by 10% of its size if put in contact with water for one hour, while the second latex type may swell by more than 100% of its size if put in contacted with water for one hour.

Figure 10 shows a photograph of a piece 1002 of the other test film that was made immediately after the piece of the other latex test film was submerged in a water bath. In addition, figure 10 depicts a photograph of a further piece 1004 of the other test film that was made about one hour after the piece of the other latex test film was submerged in a water bath.

The size of the fragments depends on the degree of in homogeneity of the latex mixture used for generating the backing and/or the test film. The longer the two latex forms are mixed and stirred together, the more homogeneous the latex mixture, and the smaller the fragments generated by contacting the hardened latex backing/film with water.

Figure 11 depicts two different copolymen^'zation mixtures used for generating the polymers 706, 708 of the first and second latexes used to generate the

inhomogeneous latex mixture that disintegrated on contact with water due to different swelling capabilities. The first mixture 702 is used for generating the polymer 706 of the first latex, and the second mixture 704 is used for generating the polymer 708 of the second latex. The polymers 706, 708 are copolymers generated in a copolymerization reaction. The type and/or relative amount of the comonomers 710, 712, 716 in the mixtures may be different and may be chosen such that the resulting polymers 706, 708 have different water-swelling properties.

The polymer 706 of the first latex is preferably a copolymer of: i. styrene or a substituted styrene 710; ii. an acrylate and/or methacrylate and/or butadiene 712; and iii. a polymerizable form 716 of a swel!able po!ymer; e.g., an ethylenically

unsaturated starch.

In the following, the generation of the first polymer 706 having a comparatively weak swelling capability according to one possible embodiment is described. The polymer 706 of the first latex can be obtained, e.g., by copolymerization of a degraded, oxidized anionic starch 7 6 which represents a polymerizable form of the

comparatively inert starch 714. For example, the polymer 706 of the first latex can be obtained by emulsion polymerization of a first mixture 702 of monomers. The polymerization can be a radical polymerization using hydroperoxide or A!BN

(azobisisobutyronitrile) as radical initiators. According to embodiments, the first mixture 702 of monomers consists of: i. from 20% to 40% by weight of the first copoiymerization mixture of styrene or a substituted styrene 712; ii. from 20% to 50% by weight of the first copoiymerization mixture of an

acrylate and/or a methacrylate and/or butadiene 712; iti. from 5% to 20% by weight of the first copoiymerization mixture of one or more ethylenically unsaturated monomers (e.g., acrylate, methacrylate, styrene); said monomers are given in addition to components i and ii and are added for generating polymerizable (grafted) forms of the not-yet- polymerizable polymer (starch); and iv. 1 % to 5% by weight of the first copoiymerization mixture of a not-yet- polymerizab!e form of the polymerizable polymer.

For example, the first mixture can comprise 40% styrene, 50% acrylate, 4% methacrylate, and 6% starch.

According to embodiments, the second mixture 704 of monomers consists of: i. from 20% to 40% by weight of the second copoiymerization mixture of

styrene or a substituted styrene 712; ii. from 20% to 50% by weight of the second copoiymerization mixture of

acrylate and/or methacrylate and/or butadiene 712; iti. from 5% to 20% by weight of the second copoiymerization mixture of one or more ethylenically unsaturated monomers (e.g., acrylate, methacrylate, styrene); said monomers are given in addition to components i and ii and are added for generating polymerizable (grafted) forms of the not-yet- poiymerizabie polymer (starch); and iv. 20% to 50% by weight of the second copoiymerization mixture of a not-yet- polymerizable form of the polymerizable polymer.

For example, the second mixture can comprise 30% styrene, 30% acrylate, 10% methacrylate, and 30% starch. Substituted styrenes may include, for example, a-methyl styrene, or styrenes substituted in the phenyl ring by aikyl groups, such as methyl, halogens, such as chlorine, or alkoxy groups, such as methoxy. However, styrene itself is the most preferred component. Acrylates or methacrylates are preferably lower alkyl esters such as methyl; ethyl; n- or isopropyl; and n-, iso-, sec-, or tert-butyl esters or their mixtures; with n-butyl acrylate being the most preferred component.

The ethylenically unsaturated comonomer may be selected from a wide variety of compounds containing one single unsaturated double bond; i.e., excluding dienes of starch/latex copolymers such as 1 ,3-butadiene or isoprene. Examples of suitable ethylenically unsaturated monomers are hydroxylated alkyl methacrylates, alkyi vinyl ketones, substituted acrylamides, methacrylic acid, N-methylol acrylamide, 2- hydroxyethyl acrylate, crotonic acid, itaconic acid, fumaric acid, maleic acid, maleic anhydride, vinyl halides, vinylidene halides, viny! esters, vinyl ethers, vinyl carbazole, N-vinyi pyrrolidone, vinyi pyridine, ethylene, propylene, isobutylene, vinyl triethoxy silane, and triphenyl vinyl silane.

For example, ethylenically unsaturated comonomers can be dimethyl amino ethyl acrylate, dimethyl amino propyl acrylamide, vinyl acetate, acrylic acid, acrylamide, maleic anhydride, and monovinyl silicon compounds including vinyl trimethyl silane, ethyl vinyl ether, butyl vinyl ether, 2-ethylhexyl acrylate vinyiidine chloride, butyl vinyl ether, and, especially, acrylonitrile.

According to embodiments, the not-yet-po!ymerizable polymer can be an oxidatively degraded anionic starch.

According to embodiments, the generated copolymers may advantageously be utilized in the form of aqueous dispersions ("latex"). These polymer dispersions generally contain between 20% and 50%, preferably between 25% and 35%, dry weight of solids. Aqueous dispersions of similar copolymers have been described in WO 00/46264, which document also discloses a process for their preparation.

Starch or starch derivatives suitable for incorporating into the final copolymer 706, 708 may include practically all thinned starches of plant origin including starches from corn, wheat, potatoes, tapioca, rice, sago, and sorghum. Waxy and high- amy!ose starches may also be suitable. The starches can be thinned by acid hydrolysis, oxidative hydrolysis, or enzymatic degradation. Further derivatized starches also suitable include those such as starch ethers, starch esters, cross- linked starches, oxidized starches, and chlorinated starches— for example, carboxymethyl cellulose and hydroxyethyl methyl cellulose. Typical examples are the commercially available amyiopectin and dextrin. A commercially available example of oxidized starch is Perfectamyl^® 4692.

According to embodiments, the first and/or second latex may contain further auxiliaries selected from fixing agents, dispersants, additional binder and binder resins, antifoams, and biocides.

Once the first and second latexes have been created, they can be combined in a tank and mixed by a stirrer under defined conditions for a defined time to ensure that the two latex forms are mixed but not homogeneously mixed to ensure that the inhomogenities of the latex composition of the backing will result in the desired size of the fragments when the backing contacts water. The inhomogeneous latex mixture can be applied to the lower side of the carrier or fiber layer by spraying, curtain coating, or conventional coating processes used for coating artificial turf and hybrid turf support mats. Optimal conditions for stirring speed and stirring duration for generating a desired degree of inhomogeneity can be easily determined experimentally by generating a latex film from a mixture of the first and second latexes that was stirred under defined conditions for a defined time, and then submerging the dried latex film in water for one hour. After one hour, the number and sizes of the fractions of the film generated by the swelling-induced expansion are examined. If the fragments are too large, the stirring speed or duration is increased, if the fragments are too small and optionally also incomplete, the stirring speed or duration is reduced. If no fragments appear at all, the stirring is either way too strong so that a homogeneous latex mixture was created or the difference in the swelling behavior of the first and second latexes is not high enough to disrupt the film. In this case, the composition of at least the first or the second latex is modified. The two different forms of a starch-latex copolymer described above are only one example for using an inhomogeneous mix of two different latex forms having different water-swelling capabilities. For example, there exist various ready-to-use !atex forms that are designed and used as binders in the pigmented paper industry. By experimentally determining the water-swelling capabilities of the available latex forms and by inhomogeneously mixing latex forms having different swelling properties, a backing layer for artificial turf and hybrid turf support mats can be generated that disintegrates upon contact with water. For example, the

commercially available latex BEL2102 can be used as the first latex that swells only very weakly, and BEL2100 can be used as the second latex that swells strongly if brought into contact with water. For example, a 1 : 1 mixture of the two latex forms may be used.

List of reference numerals 02 step

04 step

00 support mat

02 row of positions where artificial turf fiber penetrates multi layer structure

04 row of positions where artificial turf fiber penetrates multi layer structure

06 non-degradable, synthetic fiber mesh

06.1 horizontal fiber of mesh 206

06.2 vertical fiber of mesh 206

08 knot of tufted artificial turf fiber

10 knot of tufted artificiai turf fiber

14 opening

16 degradable mesh

8 distance between two rows of positions

20 solidified backing

22 artificial turf fibers

24 height of a grid row of mesh 206

02 base layer

04 upper portions of artificiai turf fibers extending from the degradable mesh

04' upper portions of artificiai turf fibers extending from the fil layer

05 illumination and/or irradiation systems

06 fill layer

08 roots

310 blades of natural grass

312 hybrid turf

902 vessel

904 vessel

1002 test film of in homogeneous latex mixture

1004 disintegrated test film of inhomogeneous latex mixture

Claims

C l a i m s

A method of producing a support mat (200) for hybrid turf (312), the method comprising:

- placing (102) a degradable mesh (216) on top of a non-degradable,

synthetic fiber mesh (206) to form a multi-layer structure having an upper side (US) and a lower side (LS);

- tufting (104) artificial turf fibers (222) individually into the multi-layer

structure such that the artificial turf fibers penetrate the multi-layer structure as a whole and such that first portions of the artificial turf fibers extend upwardly from the upper side of the mu!ti-layer structure, each artificial turf fiber being a monofilament generated by an extruder or a bundle of extruder-generated monofilaments;

- after having tufted the artificial turf fibers, applying a liquid backing (220) to the lower side (LS) of the multi-layer structure such that the backing wets at least portions of the synthetic fiber mesh and second portions of the artificial turf fibers extending to the lower side of the multi-layer structure; and

- solidifying the liquid backing, the solidified backing mechanically fixing the artificial turf fibers in the multi-layer structure, the multi-layer structure with the solidified backing and the tufted artificial turf fibers forming the support mat.

The method of claim 1 , the liquid backing being applied to the lower side (LS) of the multi-layer structure in an amount of more than 500 g/m², in particular 550 g/m² to 700 g/m².

The method of any one of the previous claims, the liquid backing being applied to the lower side (LS) of the multi-layer structure such that less than 70%, preferentially less than 50% of the openings of the one of the two meshes facing to the lower side (LS) of the multi-layer structure is sealed by the backing.

4. The method of any one of the previous claims, the backing being styrene- butadiene rubber (SBR).

5. The method of any one of the previous claims, the backing having a viscosity of 2000 mPa s - 5000 mPa s.

6. The method of any one of the previous claims, the backing comprising or consisting of a material that disintegrates on contact with water.

The method of claim 6, the material that disintegrates on contact with water being water-soluble materia!, in particular polyvinyl alcohol.

The method of claim 6, the material that disintegrates on contact with water being an inhomogeneous mixture of a first latex and a second latex, the first latex in the dry state being less water-swellable than the second iatex in the dry state.

The method of any one of the previous claims, the backing comprising or consisting of a pH sensitive materia! that degrades upon being contacted with an acid or basic liquid.

The method of claim 9, the pH sensitive material of the backing being agar- agar.

The method of any one of the previous claims, the backing comprising or consisting of a biodegradable material.

The method of claim 1 1 , the biodegradable material of the backing being selected from a group comprising: a copolymer of starch with styrene-butadiene Iatex; and

natural rubber Iatex.

13. The method of any one of the previous claims, the degradable mesh

comprising or consisting of a biodegradable material, in particular a jute fiber mesh, a linen fiber mesh, a hemp fiber mesh, a polyiactic acid fiber mesh, a sisal fiber mesh, a burlap fiber mesh, or a combination thereof.

1 . The method of any one of the previous claims, wherein the openings of the degradable mesh and the openings of the synthetic fiber mesh having a width and a height of 5 mm - 8 mm. 5. The method of any one of the previous claims, wherein the synthetic fiber mesh is a polyolefin fiber mesh. 16. The method of any one of the previous claims, the mesh width of the synthetic fiber mesh being large enough to allow water and roots of natural grass to penetrate the mesh.

17. The method of any one of the previous claims, further comprising generating the monofilaments, the generation comprising:

- creating a liquid polymer mixture, wherein the polymer mixture is at least a two-phase system, a first one of the phases comprising a first polymer and a first dye, a second one of the phases of the polymer mixture comprising a second polymer and a second dye, the second dye having a different color than the first dye, the second polymer being of the same or of a different type as the first polymer, the first and the second phase being immiscible, the first phase forming polymer beads within the second phase;

- extruding the polymer mixture into a monofilament comprising a marbled pattern of the first and second color;

- quenching the monofilament;

- reheating the monofilament;

- stretching the reheated monofilament to deform the polymer beads into threadlike regions and to form the monofilament into an artificial turf fiber. 8. The method of claim 17, wherein the polymer mixture that is extruded into the monofilament comprises a nucleating agent.

19. A method of producing hybrid turf (312), the method comprising:

- generating the support mat (200) according to the method of claim 1 ; - placing (102) the support mat on top of a layer comprising sand or earth or a mixture thereof;

- adding a fill layer (306) comprising a fill material on top of the support mat;

- adding seeds of natural grass to the upper side of the support mat; and

- growing the natural grass to provide natural grass fibers (310) intermixing with the artificial turf fibers to form the hybrid turf, thereby repeatedly watering the natural grass to stimulate the growth of the grass; and

- applying a substance on the support mat comprising the natural grass for triggering the degradation of the degradabie fiber mesh and of the degradable backing.

A support mat (200) for hybrid turf comprising:

- a multi-layer structure having an upper side (US) and a lower side (LS) and comprising:

• a first layer of a non-degradable, synthetic fiber mesh (206); and

• a second layer of a degradable mesh (216) placed on top of the first layer;

- artificial turf fibers (222) tufted individually into the multi-layer structure such that each artificial turf fiber penetrates the multi-layer structure as a whole and such that first portions of the artificial turf fibers extend upwardly from the upper side of the multi-layer structure, each artificial turf fiber being a monofilament generated by an extruder or a bundle of extruder-generated monofilaments; and

- a backing (220) on the lower side (LS) of the multi-layer structure that surrounds and mechanically fixes at least portions of the synthetic fiber mesh and second portions of the artificial turf fibers extending to the lower side of the multi-layer structure.

21 Hybrid turf (312) comprising:

- a layer of sand or earth or a mixture thereof;

- the support mat for natural turf of claim 20; - a fill layer comprising a fill material on top of the support mat, the fill layer having a height of less than 50 mm, preferentially of less than 15 mm; and

- natural grass plants, whereby at least portions of the blades of the natural grass plants intermix with the artificial turf fibers extending to the upper side of the support mat above the top of the fill layer, whereby roots of the natural grass plants penetrate the fill layer, the support structure and parts of the layer of sand or earth or a mixture thereof.

22. The hybrid turf according to claim 21 , wherein the backing seals less than 70%, preferentially less than 50% of the openings of the one of the two meshes facing to the lower side (LS) of the whole multi-layer structure; and/or the backing being made of a biodegradable material or material that disintegrates on contact with water or being pH-sensitive material.

23. The hybrid turf according to claim 21 , wherein the artificial turf fibers protrude at least 20 mm, more preferentially at least 40 mm from the upper side of the fill layer and wherein the crowns of the natural grass plants protrude at least as far from the upper side of the fill layer as the artificial turf fibers.