The invention relates to grass yarn for artificial grass coverings or turf coverings. Synthetic grass exists of synthetic blades or fibers that are attached to a support layer.

The market for artificial turf has seen a rapid development during the last years due to the numerous advantages of artificial turf above natural turf. Growth has been seen in several sport applications, especially in soccer, but also in several kinds of urban applications.

On artificial turf can be played more hours per day, than natural turf. A training pitch provided with artificial turf can be used more intense, such that the number of training pitches can be reduced.

In critical climate situations, like intense heat, very wet or extreme cold, artificial grass has proven to be a good solution over natural grass.

Where in the beginning of the installation of artificial turf the functional properties were mainly important, nowadays the natural look has become important as well. Especially in urban and landscape applications the optical performance of a grass field has become an important issue. With regard to the functional properties, the stiffness of the yarns is one of the important aspects. If the yarns are to flexible, they will fall down. If the yarns are too stiff, they could hurt the players playing on the artificial turf. Also for a sport field, like a soccer field, the ball - surface interaction is influenced by the stiffness of the yarns. For example how a ball will roll over the artificial turf. Player-surface interactions are also influenced by stiffness, for example a stiff yarn can injure players. In general stiffness is influenced by the Elasticity- modulus (or Young's modulus) and by the cross sectional inertia. Elasticity modulus is a result of two major properties; first the choice of the raw raw materials and secondly the processing conditions of the yarn. The first artificial turf coverings were mainly produced with a fibrillated tape fiber. These tapes have a rectangular shape, which has a relative low cross sectional inertia. To arrive at a desired stiffness of the yarns, the thickness will be such, that the appearance of the tape fibers does not

correspond with the appearance of natural grass.

A Second disadvantage of rectangular shapes is the shiny effect. Often described in the market as plastic look. Several kinds of polymers could be used for the production of blades for artificial turf. Polyethylene is at this moment the most used raw material for artificial grass yarns. Depending on the application also the usage of polypropylene and polyamide can be seen. Depending on the additives that are used and the

production method these polymers tend to give the product a shiny look. The plastic look makes the product look cheap.

Especially in applications where no sport properties and only optical properties are important the appearance of a grass field is important.

It is an object of the invention to provide a grass yarn for artificial grass coverings, which has an increased cross sectional inertia and has a reduced shiny effect.

This object is achieved with a grass yarn being a monofilament .

Monofilament yarns provide an increased design freedom, like in the cross sectional shape, compared to fibrillated tape yarns. Instead of the common rectangular cross section of fibrillated tape, monofilament yarns have the possibility of almost any desired cross section. A circular cross section or I- shaped cross section has for example a higher cross sectional inertia and subsequently a higher stiffness, than a rectangular cross section.

It has proven that a monofilament yarn having a cross section in the shape of a semi-circle with a spine in the middle has a good touch and a better stiffness. However, a disadvantage is that such yarns tend to split along the spine after a period of time. Subsequently the stiffness is no longer maintained and the yarns fall down easily.

According to a preferred embodiment of the invention, the grass yarn (or grass filament) has a sickle-shaped cross section. With a sickle-shaped cross section, the yarn has a curved cross section with a thick center part tapering to both ends. This results in an increased cross sectional inertia and thus higher stiffness. Also, due to the curved shape, light is reflected to different directions by the yarn, reducing the reflection.

Another embodiment of the grass yarn according to the invention comprises a plurality of ridges arranged on the surface of the grass yarn. These ridges disperse the light such that the reflection of the yarns is reduced.

Preferably the plurality of ridges are arranged in longitudinal direction of the grass yarn. In combination with monofilament yarns, the longitudinal ridges can be manufactures easily.

In yet another embodiment of the grass yarn according to the invention the height of the ridges is 0,5% - 15% of the main thickness of the grass yarn. With the main thickness it is understood the maximum thickness of the cross section of the yarn .

The grass yarn according to the invention is preferably of a material selected from the group high density polyethylene (HDPE) , polypropylene (PP) , polyamide (PA) , polyester and low density polyethylene (LDPE) . More preferred, the material of the grass yarn is linear low density polyethylene (LLDPE) .

In still another preferred embodiment of the invention the linear mass density of an individual filament is in the range of 50 - 300 tex.

The invention further relates to an artificial grass covering comprising a plurality of grass yarns according to the invention .

Preferably, the artificial grass covering according to the invention comprises a support layer to which the grass yarns are arranged.

These and other features of the invention, will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a cross sectional view of a first embodiment of a grass yarn according to the invention.

Figure 2 shows a cross sectional view of a second embodiment of a grass yarn according to the invention.

Figure 3 shows a semi perspective view of an artificial grass covering according to the invention.

Figure 4A and 4B show further embodiments of grass yarns according to the invention.

In figure 1 a cross sectional view of a first embodiment 1 of a grass yarn is shown. The shape of the grass yarn 1 is sickle-shaped. This sickle-shaped grass yarn 1 has a thick center portion with a maximum thickness ti and two ends tapering into edges 2. The convex side 3 of the sickle-shaped grass yarn 1 is provided with ridges 4. The concave side 5 of the grass yarn 1 is in this embodiment smooth.

The ridges 4 have a thickness t ₂ • This thickness t ₂ is typically 0,5% - 15% of the thickness ti of the sickle shape.

The ridges 4 will scatter light such that the grass yarns according to the invention will have a light reflection similar to natural grass. Furthermore the curved sickle-shape provides for a high cross sectional inertia resulting in a relative high stiffness of the grass yarn 1 relative to the maximum thickness ti of the yarn 1.

In figure 2 a second embodiment of a grass yarn 10 according to the invention is shown. The shape of this grass yarn 10 in cross section is also sickle shaped. In this

embodiment both the convex side 11 as the concave side 12 are provided with ridges 13 in order to reduce light reflection.

Figure 3 shows an embodiment of an artificial grass covering 20. This grass covering 20 has a support layer 21, in which tufts 22, 23 of grass yarns 24. The grass yarns 24 are shown schematically arranged in the support layer 21.

In this figure three grass yarns 24 per tuft 22, 23 are shown for explanation of the invention. Typically 4 - 12 grass yarns are used per tuft in standard applications of a grass covering according to the invention.

A typical application of an artificial grass covering according to the invention has the following characteristics:

- Width of a single yarn: 1.1 mm

- Highest thickness ti: 200 μm

- Yarn count individual filament: 195 tex

6 of these filaments are twisted or brought together by wrapping. With wrapping a yarn is wound around the 6 filaments.

- Raw material used for the yarns is LLDPE (linear Low density Polyethylene)

- The total tex count of a combined yarn after wrapping

6 yarns together is 1200 tex.

This combined yarn is used for tufting the following grass carpet construction:

- Gauge: 5/8'

- Stitches: 14 st/10 cm

- Pile height: 55 mm

- Yarn weight: 1230 g/m ²

It has proven that this product has a very natural look. The yarns do not exhibit any substantial shiny effects. The resulting product is tested according the Lisport test as described in standard NF EN 15306; ^Surfaces for outdoor sport areas - Exposure of synthetic turf to simulated wear' . After 12.200 cycles, no major wear or major yarn splitting was

visible. So it is clear that the sickle-shape of the yarns according to this embodiment reach the object of the invention. The ridges also do not increase the tendency for splitting.

Figure 4A shows a cross sectional view of third embodiment of a yarn 30 according to the invention. This yarn 30 has an ellipse shaped cross section, being provided with evenly distributed ridges 31 at the surface. Figure 4B shows a cross sectional view of fourth

embodiment of a yarn 35 according to the invention. This yarn 35 has a rectangular shaped cross section, being provided with evenly distributed ridges 36 at the surface.