The present invention relates to substructure for an artificial lawn, comprising an underlayer and a top layer of artificial grass fibres.

Such a substructure is known per se from Dutch patent No. 1021171, which discloses an artificial lawn made up of a comparatively hard underlayer, on which a flat layer of resilient and/or damping material is arranged, which layer may exhibit a thickness of about 10-40 mm. Arranged on the aforesaid resilient and/or damping layer is a top layer in the form of artificial turf consisting of a backing and synthetic grass blades connected thereto by tufting, knitting or weaving. The resilient and/or damping layer can be formed in different ways, for example by starting from a mixture of rubber granules, which are mixed with a liquid binder, for example polyurethane. The aforesaid resilient and/or damping materials are said to be exceptionally"bouncy", as a consequence of which in the case of ball games the bouncing behaviour of the ball is affected, which does not generally enhance the quality of the game. The excessive resilience of the synthetic turf field is moreover perceived by players as being unpleasant and tiring. Accordingly, the aforesaid Dutch patent proposes to form air chambers in the resilient and/or damping layer or between the resilient and/or damping layer and the underlayer, for example by forming recesses, applying a biodegradable material, removing material from the resilient and/or damping layer at various places, including a material having a low melting point in the resilient and/or damping layer, which material is removed by heating after the layer has been provided.

British patent publication GB 2 072 022 discloses a surface which can be used as an artificial putting area in the sport of golf. Such a surface consists of a plurality of segments of tubular air chambers arranged parallel to each other, which segments are arranged both perpendicularly and parallel to each other in said surface. Such tubular air chambers are interconnected within each segment and inflatable as a whole via a valve. To obtain a sloping surface, in which the air chambers extend over the entire width, for each segment, the air chambers within each segment have mutually different dimensions.

From International application WO 2006/007862 there is known a substructure for a sports floor, wherein a flat web or strip is passed between two rollers provided with a relief so as to form a cup structure in the web or strip, which cup structure consists of uniformly spaced recesses, which are open at the underside thereof.

From Dutch patent No. 1013987 there is known a substructure arranged on a foundation layer for a sports field at least partially covered with natural grass, which substructure partially consists of rock wool, which rock wool is at least partially made up of rock wool granulate. The substructure used therein also comprises sand, organic material, for example compost, or mould besides said rock wool.

From Dutch patent No. 1016193 in the name of the present applicant there is known an artificial lawn comprising a drainage layer built up of gravel, an underlayer arranged on top of the drainage layer, which underlayer comprises the earth that was originally dug off and subsequently removed, and an upper layer, in which fibres are present.

From International application WO 2006/007862 there is known a substructure for a sports floor in which a damping layer made of a deformed plastic material, in particular a thermoplastic foam, such as PE, PP or PVC, is used. The damping effect of such a layer is obtained by the cup structure of the plastic, which cups must exhibit a specific height-thickness ratio.

A drawback of the aforesaid artificial lawns is generally the fact that players experience the lawn as too "bouncy". As a result of the great resilience of the lawn, a ball that lands on the artificial lawn bounces too high and too quickly in comparison with a natural lawn. Because such an artificial lawn is used for sports purposes, players experience moving on the artificial lawn, in particular running and putting on spurts, as tiring and unnatural. In addition to that, the prior art constructions require a considerable investment, in particular on account of the cost of the materials used in the substructure.

Accordingly it is an aspect of the present invention to provide a substructure for an artificial lawn, which substructure exhibits a natural resilience in comparison with a usual lawn of natural grass fibres.

Another aspect of the present invention is to provide a substructure for an artificial lawn, which substructure possesses good thermal insulation properties, so that playing on the artificial lawn is possible also during cold winter months.

Another aspect of the present invention is to provide a substructure for an artificial lawn, which substructure exhibits a resilience that can be used over a wide range, which resilience is moreover substantially constant over the entire area of the substructure.

The substructure as referred to in the introduction is according to the present invention characterised in that an intermediate layer is disposed between said underlayer and said top layer, which intermediate layer comprises a matrix of plastic foil with separate chambers present therein, in which separate, regularly spaced-apart chambers, which are arranged in a single layer, a medium is present.

One or more of the above aspects is (are) met by using a matrix of plastic foil with separate chambers present therein. The term "separate" is to be understood to mean that the chambers are not interconnected via one or more common channels through which said medium can flow from one chamber to another chamber. Consequently, the term "chamber" is to be understood to mean a discrete space shut off from the outside environment, in each of which chambers the medium is retained. If a chamber in the matrix should spring a leak, for example as a result of a pointed object having pierced the wall of the chamber, only the chamber in question will "empty", so that the adjacent chambers will retain their resilient and insulating properties. The chambers are arranged in regularly spaced-apart relationship in a single layer in the foil, and consequently the foil exhibits a uniform damping characteristic over the entire surface area thereof, in contrast to a foam in which empty spaces are distributed at random over the foam material and will thus lead to non-uniform damping characteristics. The present chambers, in which a medium is present and which are fixed as separate chambers in the matrix of plastic foil, provide a natural resilience. Since the chambers are fixed, the resilient properties of the artificial lawn will be retained also after a prolonged period of time. The chambers can be regarded as closed, separate spaces which are fixed in the matrix layer, so that the medium present in the chambers cannot exit the discrete chambers when a force is exerted on the matrix layer. The matrix is not situated near the surface layer of the artificial lawn, so that the risk of the chambers springing a leak will be minimal. In addition, because of the use of the present matrix the position of the separate chambers in the substructure will be "fixed" for a long period of time, since there is no chance of the chambers shifting or even disappearing.

The medium has preferably been selected from the group consisting of air, nitrogen and aqueous fluid, with air and/or water being preferred. If an aqueous fluid is used, there is even a possibility to use a heating unit, which makes it possible to heat the substructure as such, which will make the lawn more pleasant to play on in the winter.

According to a special embodiment of the present invention, the amount of medium that is present in the chambers is adjustable. Depending on the purpose for which the substructure is intended, the amount of medium in the chambers or the number of chambers per square metre of matrix can vary. By reducing the amount of medium that is present in the chambers, for example, the resilient and insulating properties of the substructure will be influenced.

The underlayer used in the present substructure has preferably been selected from the group consisting of asphalt, lava, fly ash, sand, hardcore, granulated clay, foamed concrete and rubble, or a combination thereof. Such a selection of materials provides a stable sub basis which, in addition, exhibits good drainage characteristics. Good results have been achieved also with an underlayer of polystyrene and/or cellular concrete.

To protect the chambers against leakage, it is preferable in a special embodiment to provide the matrix with a protective coating on one or both surface sides, for example a geotextile, a foam layer or a combination thereof.

In a special embodiment, a cover layer selected from the group consisting of fly ash, lava, sand and rubble, or a combination thereof, is preferably disposed between the top layer and the intermediate layer. The use of such a cover layer is in particular desirable with a view to screen the intermediate layer somewhat from the top layer of artificial grass fibres.

Although it has been indicated in the foregoing that a top player of artificial grass fibres is used, it is preferable in a specific embodiment for the top layer to comprise natural grass fibres besides artificial grass fibres. The present inventors are moreover of the opinion that the present matrix can also be used in indoor applications, for example in a top layer of carpet, linoleum, PVC, polyurethane, vinyl, marmoleum, wood and the like for practising sports that do not require artificial grass fibres. In the case of such indoor applications, the present intermediate layer, viz. the matrix of plastic foil with the separate chambers present therein, may be added to sports halls provided with one of the aforesaid top layers, so that the resilient properties thereof can be influenced in dependence on the activities to be performed on the top layer.

The present invention will now be explained by means of a number of examples, in which connection it should be noted, however, that the present invention is by no means limited to such special examples.

• Figure 1 schematically shows a substructure according to the prior art.
• Figure 2 schematically shows a substructure according to the prior art.
• Figure 3 schematically shows a substructure according to the present invention.
• Figure 4 schematically shows a special embodiment of a substructure according to the present invention.
• Figure 5 is a top plan view of a special embodiment of the matrix according to the present invention.
• Figure 6 is a cross-sectional view of the matrix of Figure 5.

In figure 1 an artificial lawn (1) according to the prior art is shown, which is composed of artificial turf (3) as known from the prior art, in which upright stalks or blades (5) of a synthetic material are attached to a backing layer, whilst a resilient layer (4) of a damping material, for example bound or unbound natural or synthetic rubber granulate or rubber mats or a synthetic foam is disposed under the artificial turf (3). The resilient layer (4) is arranged on top of a moisture-permeable base layer (5) of, for example, sand, asphalt, broken rubble or lava beads. If desired, means for draining rain water or heating means may be provided in the base layer (5).

Figure 2 schematically shows an artificial lawn (11) known from the prior art, in which the artificial turf (3) is arranged on only a base layer (6) composed of a layer of sand, asphalt, broken rubble or lava beads.

Figure 3 schematically shows an artificial lawn (21) according to the present invention, in which the artificial turf (3) is arranged on a matrix (7) of plastic foil with separate chambers (10) present therein, which matrix (7) is disposed on an underlayer (8) selected from the group consisting of asphalt, lava, fly ash, sand, hardcore, clay granulate, foamed concrete and rubble, or a combination thereof. It will be understood that the chambers (10) are only schematically shown. A suitable medium is air, for example. The contents of each chamber (10) are not in communication with the contents of the other chambers (10), so that the matrix will still retain its resilient and insulating properties in case a few chambers (10) should spring a leak.

Figure 4 schematically shows an artificial lawn (31) according to a special embodiment of the present invention, in which the matrix (7) of plastic foil with separate chambers (10) present therein is provided with a foam layer (9) at the upper side, which foam layer (9) effects a further screening of the matrix (7). Although the chambers (10) are schematically shown in a random configuration in the matrix (7) both in figure 3 and in figure 4, a matrix of plastic foil with regularly spaced-apart chambers arranged in a single layer in the matrix will be used in practice.

Figure 5 and figure 6 are schematic views of an embodiment of the matrix (7) of plastic foil, which clearly show that the chambers (10) are evenly distributed in regularly spaced-apart relatoinship in a single layer over the foil (12). The chamber (10) is a discrete space sealed from the outside environment, and each chamber retains the medium that is present therein. In another embodiment of the present invention, it is also possible to use two or more such matrices of plastic foil in the substructure.