ARTIFICIAL AND SEMI-ARTIFICIAL SURFACES The present invention relates to artificial and semi-artificial surfaces for leisure activities. More specifically, the present invention is concerned with providing improved surfaces for use in competitive games such as tennis, cricket, football, rugby and golf. Equally, the artificial or semi-artificial surfaces of the present invention may find use in running tracks or horse racing tracks at stadia. The present invention is thus advantageously employed in applications in which normal grass surfaces usually suffer heavy wear or where a normal grass surface is not appropriate. The artificial and semi-artificial surfaces of the present invention also find use in landscaping work as a consequence of their ability to stabilise the ground upon which they are provided.

In the prior art, GB 2 292 091 relates to a surface for a sports ground which is formed by mixing sand, wood chip and/or chopped geotextile material, and natural or synthetic fibres. The geotextile material is made from a flexible sheet or web of material which is water-permeable and non-biodegradable, of which spun bonded polyethylene or polypropylene are examples.

This material can be laid on top of soil or on top of a prepared drainage base, to form a surface.

US Patent No. 4 073 753 relates to an outdoor surface composition for playing areas or other utility areas. This surface comprises a mixture of particulate reclaimed rubber and inorganic particulate solids such as sand. The amount and particle size range of the reclaimed rubber and of the inorganic particulate solids are important in providing the desired characteristics of the surface, for example drainage, shock absorbency and resistance to shear.

GB 814 885 relates to a surface for tennis courts which is maintenance free and porous. This patent

describes a material which includes a layer of fine chippings, fibre and a binding solution which comprises a mixture of linseed oil and a compatible natural or synthetic resin. The chippings may be chips of brick, sand, granite or similar material and the fibre is preferably coconut fibre.

GB 2 184 765 discloses an artificial surface for equestrian events which comprises a layer of material made from sand and uncrimped synthetic fibres having a specified length dispersed therein. This patent claims to achieve adequate mixing and random distribution of the straight fibres within the sand. In addition, this patent states that the random dispersion of fibres reinforces the sand and creates resistance to particle movement under load so as to minimise spreading and penetration when under load from horses hooves.

GB 2 274 997 relates to an all weather grass surface in which the root zone is stabilised with synthetic fibres. In this patent, grass is grown in a layer of growing material which comprises sand, an organic growth supporting medium, and elongate synthetic fibres which are randomly dispersed in the growing material. Again, the straight fibres are claimed to provide resistance to particle movement and it is essential to use straight fibres of specified length to ensure adequate dispersion of the fibres in the growing material.

Those of the above compositions which contain fibres suffer the common disadvantage that the fibre distribution is not always random because of the problem of adequate mixing of the materials. One consequence of inadequate dispersion is that there is insufficient crosslinking between the individual fibres. The nature of the straight fibres results in inadequate cross-linking and interlocking into the matrix of all the components, and as a result

insufficient resistance to movement or deformation in use. Insufficient interlocking between the components results in a higher risk in use of disturbance without recovery or even movement or loss of the components.

In addition, it appears to be essential that the lengths of the prior art fibres present in the fibre mixtures is carefully controlled in order to achieve distribution of the fibres. In the case of GB 2292091 there is the further problem of having to provide and incorporate a geotextile material in the mixture in such a way as to ensure random distribution. The present invention seeks to overcome the various disadvantages of the prior art surfaces and to provide surfaces which are improved but simple to prepare and maintain. The present invention also seeks to provide surfaces having improved uniformity and stability in comparison with conventional surfaces.

Surprisingly, we have discovered that the incorporation of crimped fibres in artificial or semi- artificial surfaces provides surfaces which benefit from improvements in one or more of the following characteristics: strength, resilience, and stability when compared with surfaces available previously.

Conventional crimped fibres cannot be incorporated in such mixtures and are difficult to handle because of the tendency to tangle and form balls of single or multiple fibres. Satisfactory mixing cannot then be achieved.

We have found that the difficulties in mixing conventional crimped fibres in such surfaces can be overcome by careful control of the type of fibre crimping employed. It is thus important to ensure that the fibres are crimped so as to give the desired advantages over straight fibres whilst ensuring that dispersion can still be achieved. The crimped fibres of the present invention allow mixing and interlocking

of the fibres thereby giving rise to superior characteristics when compared with straight fibres.

In addition, we have also found that crimped fibres can be incorporated in materials for artificial or semi-artificial surfaces in such a manner that a very significant proportion of the fibres may be considered to be randomly dispersed, thus giving rise to improved uniformity of the surface. We have also discovered that the crosslinking between the randomly distributed crimped fibres contributes in part to a surprising improvement in the surface stability and uniformity. Thus, for example, surfaces according to the present invention are less likely to give rise to unexpected ball movements during the playing of ball games because the whole playing area formed by the surface is more uniform than in the case of conventional surfaces. This is particularly important for cricket pitches, tennis courts and the like where unexpected"bounces"are undesirable or dangerous.

According to one aspect of the present invention there is provided an artificial surface comprising a layer of material which is formed from a mixture of inorganic particulate solid material and crimped fibres, wherein individual crimped fibres are randomly dispersed throughout the inorganic particulate material and wherein the fibres have a length of 5-100 mm when measured in crimped form.

In a second aspect of the present invention there is provided a semi-artificial surface which comprises a layer of material formed from a mixture of grass and/or grass seed, an inorganic particulate material, a grass support medium and crimped fibres, wherein individual crimped fibres are randomly distributed throughout the mixture of the grass support medium, the inorganic particulate material and the grass, and wherein the fibres have a length of 5-100 mm when measured in

crimped form.

In an embodiment of the invention, the crimped fibres of the artificial or semi-artificial surfaces of the present invention preferably have a length of 20-90 mm, and more preferably from 35-70 mm, when measured in crimped form.

Suitably, the fibres are from 6-300 denier (0.030 to 0.215 mm). More preferably, the fibres are in the range 8-150 denier (0.035 to 0.153 mm), and more preferably in the range 20-100 denier (0.055 to 0.125 mm).

Ideally, the fibres are made from a synthetic material such as a polymeric material. For example, polyolefins such as polypropylene and polyethylene, polyesters such as polyacrylates, and polyvinyl chlorides are suitable for use in the present invention. Polypropylene is most suitable. Equally, natural fibres, such as cellulose, may be utilised in the present invention provided that they can be suitably crimped.

The term crimping refers to the process of imparting corrugations and/or other variations and/or projections which occur along the lengths of the fibre in a direction perpendicular to a hypothetical longitudinal axis of a corresponding straight fibre.

The crimping process puts waves in an otherwise straight fibre which can have a measurable amplitude and frequency along the fibre length. The amplitude and frequency can be adjusted as appropriate to the denier and length of the fibre. The combination of crimp, fibre length and diameter ensures that the required random distribution and interlocking properties referred to above are present in the resulting artificial or semi-artificial surfaces of the present invention. Thus, these properties are optimised as required for a given fibre.

A crimped fibre has a generally wavy, spiked and/or jagged appearance when compared with a normal straight fibre. The corrugations or waves present in each fibre may take the form of smooth curves or may be more angular and jagged or spiked, depending on the resilience and strength of the material and the method of crimping employed. Fibres having smooth curves are preferred because of the reduced tendency to tangle and/or form balls.

The frequency of the wave peaks is such that there are from not more than 8 crimps per inch of fibre to more than 1 crimp per inch of fibre, with the proviso that each fibre contains at least 2 crimps.

Preferably, the fibres contain from not more than 4 crimps to more than 1 crimp per inch. If there are more than 8 crimps per inch it becomes difficult to ensure adequate mixing of the fibre. Equally, if there are to few crimps in the fibre the desired advantageous properties cannot be obtained.

The amplitude of the crimps in two, or even three, dimensions reduces the otherwise straight length of the fibre by an amount of from 5% to 30%, and preferably by 10% to 20% of the length of the straight fibre. In the case of a sine wave shaped crimp, the maximum amplitude corresponding to a 30% reduction in length is approximately 1S of the wavelength. As is evident from above, the crimps can be present in two dimensions in the form of waves etc, or in 3 dimensions in the form of helices of the like.

One method of obtaining crimped fibres employs the stuffer box method. In this method, a bundle of continuous filaments is overfed under pressure into a confined chamber from which its eventual access is restricted. The combination of speeds, temperatures and pressures applied to a thermoplastic fibre enable the desired crimp to be produced in a controlled and

repeatable fashion.

The inorganic particulate material used in the artificial or semi-artificial surfaces of the present invention comprises sand, soil, clay, brick, granite, limestone, aggregate, ash, coke or cinders, or a mixture of any of these. Preferably, the inorganic particulate material is sand, soil or cinders, and most preferably sand, on the basis of surface stability and uniformity. In addition, sand, soil and cinders have the advantages of being cheap and readily available materials.

The particle sizes of the above materials typically lie within the ranges 0.1 to 2.0 mm.

The proportion of crimped fibres in the artificial surface of the present invention typically comprises 0.1 to 5.0% by weight of the inorganic particulate material. When the inorganic particulate material is relatively light material such as ash or cinder, the percentage of fibre present in the mixture lies towards the top of this range, whereas for a heavier inorganic particulate such as sand or brick, the percentage of fibre will be at the lower end of this general range i. e. from 0.1 to 1.0 % by weight.

In the semi-artificial surface of the present invention the inorganic particulate material, preferably sand or brick and most preferably sand, comprises 40-90% by volume of the semi-artificial surface. The grass growth medium represents 60-10% by volume of the semi-artificial surface and the crimped fibre represents 0.1 to 1.0 % by weight (i. e. approximately 0.1 to 1.0% by volume) of the semi- artificial surface.

The grass in the semi-artificial material of the present invention may be in the form of grass seed which is capable of forming a cultivated grass surface or may be in the form of existing grass growth derived

from turf or the like and originating from a grass support medium.

The grass support medium may be any organic material which is capable of supporting the growth of grass whether it arises from existing grass growth or from seed implanted therein. Suitably, the grass support medium may be soil, humus, peat or a mixture of any of these. Additives such as fertiliser, selective weed killer etc may be included in the grass support medium prior to forming the semi-artificial surface to enhance growth and/or prevent undesirable additional growth of non-grass plant material.

In order to prepare an artificial surface according to the present invention, an appropriate quantity of crimped fibres having the desired length are added to the inorganic particulate material in a conventional bulk powder mixer, such as pan, rotary or cyclone type mixers or conventional sand-mixing plant machinery. The quantity of fibres added is calculated depending on the intended end use of the artificial surface and the particular properties sought.

Thus, within the above mentioned range of fibre contents, a higher proportion of fibre will lead to improved shear resistance in the surface but may be detrimental to the uniformity of the surface. We have found that the reduction in uniformity of the surface as the proportion of fibre is increased arises because it becomes more difficult to ensure random distribution of individual crimped fibres as the proportion of the fibres is increased. On the other hand, the use of a lower proportion of crimped fibres within the above mentioned range in an artificial surface will ensure substantially random distribution of the individual fibres. The result is a uniform surface having consistent playing characteristics but which has less resistance to shearing. Cost may, of course, also be

an important factor in determining the proportion of added fibre in the surface material.

In order to prepare a semi-artificial surface according to the present invention, the inorganic particulate material is mixed with the appropriate quantity of suitable crimped fibres in a suitable mixer such as a pan, rotary or cyclone type mixers or conventional sand-mixing plant machinery. The resulting mixture is a homogenous mixture in which the fibres are randomly distributed throughout the particulate material. As is the case with the artificial surfaces of the present invention, the proportion of crimped fibres incorporated in the surface will depend upon the intended end use of the surface.

The homogenous mixture of inorganic particulate material and crimped fibre is then mixed with the grass support medium, which is either in the form of organic material already supporting grass growth i. e. in the form of turf and the like, or is mixed with a grass support medium in the form of organic material incorporating grass seed. Grass seed may also be added to the resulting mixture as appropriate if required as a supplement.

The present invention will now be illustrated, by way of example only, by the following mixtures which can be made in accordance with the present invention.

Example 1 0.1'-. by weight of 60 denier crimped polypropylene fibre in which the average length of the individual fibres is 60mm when crimped is combined until mixed with 100kg of quarry sand to form an intimate mixture of sand and fibre. The fibre has 3.5 crimps per inch and is readily incorporated into the sand.

Example 2 0.3t by weight of 70 denier crimped polypropylene

fibre in which the average length of the individual fibres is 55mm when crimped is combined until mixed with 100kg of quarry sand to form an intimate mixture of sand and fibre. The fibre has 3.0 crimps per inch and is readily incorporated into the sand.

Example 3 0.5% by weight of 70 denier crimped polypropylene fibre in which the average length of the individual fibres is 55mm when crimped is combined until mixed with 100kg of quarry sand to form an intimate mixture of sand and fibre. The fibre has 2.5 crimps per inch and is readily incorporated into the sand.

Example 4 0.8% by weight of 75 denier crimped polypropylene fibre in which the average length of the individual fibres is 50mm when crimped is combined until mixed with 100kg of quarry sand to form an intimate mixture of sand and fibre. The fibre has 2.0 crimps per inch and is readily incorporated into the sand.

The playing characteristics of an artificial or semi-artificial surface according to the present invention will, of course, depend on the foundations upon which the surface is laid. Thus the preparation which has been effected prior to application of the surface to an area of ground is important. However, it should be noted that the artificial or semi-artificial surfaces of the present invention require no special foundation work in advance of their application to an area of ground. Accordingly, the provision of suitable foundations for a given application would be apparent to the skilled person depending upon the local conditions and intended use of the surface.

The artificial surfaces of the present invention find particular applicability where the quality of the surface is important and surface shearing is

undesirable. Thus, such surfaces are ideal for"loose" tennis courts, arenas for horse trials, and footpaths.

The semi-artificial surfaces of the present invention find particular applicability where substantial and prolonged traffic over an area of grass gives rise to high wear and tear. In such situations damage even occurs to the root system of the grass.

Thus, footpaths across golf courses, areas to and from golf tees, and even the golf tees themselves, represent particularly advantageous applications for semi- artificial surfaces according to the present invention.

In addition, some or all areas of football pitches and grass tennis courts show marked improvements in surface quality when use of a semi-artificial surface according to the present invention is made.