(1) Field of the Invention

THIS INVENTION relates to a method of making artificial snow from cross-linked polymers. The artificial snow is then maintained and used as a surface suitable for skiing.

(2) Prior Art

The addition of cross-linked polymers to water and the resultant gel have been used to form surfaces suitable for both snow skiing and ice skating. Bucceri (International Publication No. WO86/02936) describes a method where water swellable cross-linked polymers are used to absorb up to 70% of their maximum capacity, by aerating the mixture to cause void spaces, the individual gel particles are then frozen to form a skiing surface. Walker (U.S. Patent No. 3,251,194), describes a method where cross-linked polymers are used to absorb up to their maximum capacity and are then laid on sub-zero surface to produce a solid sheet of ice suitable for ice skating. It is the express intention of this invention to cause the particles to shatter, in that way, there is no need to either aerate the mixture as in the Bucceri Patent or produce an undesirable solid sheet of ice as in the Walker Patent.

SUMMARY OF THE PRESENT INVENTION The object of this invention is to produce a frozen surface suitable for snow skiing, where the surface may be indoor or outdoor. It is preferably maintained in a state suitable for snow skiing by the use of either sub-zero ambient ground temperatures or an underlying refrigerant grid.

The frozen surface is produced by taking water swellable, water insoluble materials such as polymers and co-polymers of acryla ide, acrylic acid, poly-

acrylate salts, vinyloxazolidinane, methylacrylate salts, styrene, vinyl ether and salts of styrene sulphonates, together with polymers and co-polymers polymerised with cellulosic fibres. The polymer material is mixed with water in such a ratio so that substantially maximum absorbancy is preferably reached, with preferably no free water remaining. Maximum absorbancy varies from polymer type to polymer type and on the exact chemical composition of the water used. Water, preferably of potable grade and not greater than 600 parts per million total dissolved solids, is preferably used. It is preferable that polymers be chosen with absorbancies in the range of 60 to 120 to 1 with water on a weight by weight basis. Compounds or various chemical types may be added to the swollen gel to inhibit the growth of bacteria and fungi and such compounds include carbamate thiones and cyano butanes. (These are products commonly used for inhibiting growth in shampoos, detergents and a wide range of cosmetic products.)

The resultant gel is then preferably placed on the sub-zero ground or refrigerant grid. It is the preferred aim of this invention to produce a final skiing surface where each individual grain of frozen gel remains discrete and unattached to all other grains in its vicinity. This is achieved by the specific choice of gel strength, that is the density of cross-linking in the gel and the particle size. Upon freezing, the internal forces associated with the expansion of water is less than 0°C conditions overcomes the strength of the gel. The gel will thus shatter into fine particles, The resultant product is a frozen surface comprised of many small individual particles of frozen gel. Each particle is separate from the other. During the process of freezing and shattering, each small resultant gel

particle is forced away from those in immediate contact with it. This causes a volumentric increase due to the inclusion of large void, air filled spaces. The resultant surface mimics the appearance and physical properties of a surface of distinct snow crystals.

The surface is preferably physically groomed to ensure all of the frozen gel particles are of a relatively small size consistent with natural snow crystals. Various physical characteristics of. the frozen surface can be changed by altering either the density of cross-linking or particle size. Each time one of these variables is changed so the strength of the gel alters and thus the amount of shattering which takes place. Hard densely packed snow can be produced by using particles of high cross-linked density and small particle size likewise soft powdery snow can be produced by using polymers of low cross-link density and very large particle size. BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood, a preferred embodiment will now be described with reference to the accompanying drawing, which shows a. schematic layout of the equipment used to produce a skiing slope.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE METHOD

The water swellable polymer to be mixed with water and frozen to produce individual ice crystals may be formed from the following ingredients, by way of example:

(a) 100 mis water

(b) 30 mis acrylate monomer

(c) 1 ml tetramethylethylenediamine (d) 4 mis 7% ammonium persulphate

(e) 200 up to 2000 parts per million methylene bisacrylamide (based on acrylate monomer)

For "soft" snow, the mixture may include (b) 30 mis acrylate monomer and (e) 400 parts per million bisacrylamide. For "hard" snow, -the (b) acrylate monomer may be replaced by (b) a mixture of 25 mis acrylate monomer/5 mis acrylamide monomer and (e) the concentration of bisacrylamide increased to 1800 parts per million.

The ingredients are mixed well and allowed to react exothermically to produce a cross-linked polymer matrix capable of retaining 50-100 times its own weight in water based on solids. The production of the skiing surface using the cross-linked polymer will now be described.

A slope 10 is laid on either the side of a hill or on a an internal structure. The slope is delineated by side walls 11 which, control run-off of gel and avoid damage to the surrounding environment. Refrigerant pipes 12 are laid on the surface. The pipes 12 are provided with manifolds 13 connected to a refrigeration unit 14. Brine, glycol or refrigerant is pumped through the pies 12 and then passed through a heat exchanger 15 and returned via a pump 16. The heat from the refrigerant is dissipated by liquid circulated through the heat exchanger 15 and a cooling tower 17 by a pump 18.

Water 20 is supplied to a large tank 21 into which is added the cross-linked polymer 22 in a ratio of between 60 to 120 to 1 by weight. The cross-linked polymer is allowed to absorb all of the water in the tank 21. Only after no free water remains can the gel be used. If any free water remains undesirable bridging of particles will occur upon freezing to produce an icy

surface rather than a surface suitable for snow skiing.

The resultant gel is pumped by way of a positive displacement pump 23 e.g. a rotary or piston pump through a line 24 and onto the refrigerant grid 10. A total depth of gel 25 of approximately 100-200 millimetres is used. This may be laid as several layers of approximately 10-20 millimetres. The gel is allowed to freeze and undergo a volu entric increase due to shattering and expansion. The surface 26 is then physically groomed and the gel particles are encouraged to further shatter by mechanical abrasion -such as running over the surface with a tractor or grooming machine 27 fitted with rotary cutters. The surface 26 is maintained by the refrigerant pipes 12 at less than -2°C. The slope 10 can be regularly groomed or more gel may be added as patching and allowed to freeze.

As hereinbefore described, the physical characteristics of the frozen surface can be varied e.g. to produce a surface 26 which mimics hard-packed snow or light powdery snow. It will be readily apparent to the skilled addressee that various changes and modifications may be made to the embodiments described without departing from the scope of the present invention as defined in the appended claims.