IL114510A - Material for covering an outdoor ground surface - Google Patents

Description

MATERIAL FOR COVERING AN OUTDOOR GROUND SURFACE The present invention relates to a material for covering an outdoor ground surface, e.g., a material for surfacing an outdoor play area for young children which is clean, safe and of attractive appearance.

Play areas, particularly for children of nursery school age, should be covered with a surface which makes falls less likely, and which, for those falls that inevitably do occur, minimizes child injuries. There is, however, a degree of contradiction between these two requirements. A hard, solid, high-friction surface such as asphalt is least likely to be the cause of a fall; however, a child who does fall down on such a surface will suffer injury to his knees, possibly also a scraped hand, and, in some cases, a bumped head. A smooth, but solid, surface such as marble or floor tiles is easy to keep clean and is less likely to cause injury to the skin, but such a surface may itself be the cause of slipping. A grass surface will almost certainly prevent injury to a falling toddler, but grass is difficult to maintain in good condition in all seasons, and it is practically impossible to keep clean. A gravel surface will prevent or reduce head injuries, but its appearance is not attractive; it will cause scrapes or skin injuries, and, if it is near white in color, will produce glare in strong sunlight. Sand is not suitable for running, and is subject to wind dispersal. Wood, linoleum and carpeting are not suitable for outdoor use.

Israel Patent 59357 describes and claims a multi-layer floor covering for sports areas. The upper layer is sand, red sand or ashes. A woven coconut fibre matting is used under the upper layer as a retainer. The covering is claimed to be suitable for tennis and other sports.

Bearing in mind the above-described state of the art, it is the object of the present invention to obviate the disadvantages of known outdoor ground surfaces and to provide such a surface which minimizes injuries to a falling child, is easy to keep clean, and is of attractive appearance.

The present invention achieves the above objectives by providing a material for covering an outdoor ground surface comprising a plurality of separate plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof.

In a preferred embodiment of the present invention, there is provided a material for covering an outdoor ground surface wherein the plastic coating has an average thickness of between 0.5 and 1.5 mm.

In a most preferred embodiment of the present invention, there is provided a plurality of separate plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof, for use as a covering for an outdoor ground surface, prepared by bringing heated gravel particles into contact with powdered plastic to individually coat the particles with an enveloping layer of plastic.

It will thus be realized that the novel material of the present invention serves to combine the benefits of deformability, low cost, and resistance to wind dispersal possessed by gravel, but with the coloring, smoothness and cleanliness associated with plastics, and can be used in playgrounds, for walkways, in parks, and in general for covering ground surfaces where children may play and run, as well as for aesthetic and decorative effect.

With regard to size, it is clear that small stones will have a high plastic: stone ratio, as well as being more difficult to coat and separate, thus raising costs. However, large stones over 15 mm are undesirable, being more likely to cause injury to a falling child. Preliminary tests with various sizes of stones have indicated that the best size range is gravel in the range of from .8-12 mm. Stones in the 12-15 mm range, if used, are advantageously processed before coating to remove sharp corners and edges.

No prior art methods of producing the material of the present invention have been found by the present inventor. Use of a material such as gravel, having irregular shape and size, poses its own problems when processed as a production component, and special consideration needs to be given to the requirement to produce individual articles at a low cost and to avoid the formation of a continuous mass. This presents a particular difficulty when dealing with small stones of less than 1 cm in size, as required in the present invention. It is clear that none of the standard methods used in the plastics industry, such as injection molding, extrusion, or blow-molding, is applicable. The present specification therefore details two suitable production methods .

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is an elevational view of a preferred embodiment of an outdoor ground surface covered with the material of the present invention; Fig. 2 is a view of one of the plurality of plastic-coated stones, pebbles, or rock fragments shown in Fig. 1; Fig. 3 is a diagrammatic representation of a first manufacturing method, and Fig. 4 is a diagrammatic representation of a second manufacturing method.

There is seen in Fig. 1 a covered outdoor ground surface 10, comprising a plurality of plastic-coated small stones, pebbles, rock fragments, or mixture thereof 12. Plastic coating 14 rounds off the sharp corners of each stone, softens its surface, and improves its optical properties. Suitably the surface 10 is 5 cm thick, thus providing sufficient deformability to cushion the fall of a child. The plastic coating 14 provides a clean surface, and is colored to provide an attractive appearance. A single color, or mixed colors, are used, depending on the desired visual effect. Each stone 12 prevents wind dispersal and reduces manufacturing costs.

Referring now to Fig. 2, similar reference numerals are used for identifying similar parts. Fig. 2 depicts one of the plastic-coated stones 12 referred to in Fig. 1. Stone 12 has at least one axis in the range of 4-15 mm.

A suitable soft, low-cost plastic for coating stones 12 is low-density polyethylene. Polyvinyl chloride may be preferable, depending on the production method to be used, as will be described further below.

Plastic coating 14 has an average thickness of between about 0.5-1.5 mm. The thicker the coating, the more effective is the rounding of the edges of the stones, and the softer the surface to be produced.

Fig. 3 is a diagrammatic illustration of a first method of producing a plurality of plastic-coated small stones, pebbles, rock fragments, or mixtures thereof for use in covering an outdoor ground surface 10. The material is prepared by bringing heated gravel or stone particles into contact with powdered plastic 16, to individually coat the particles with a plastic, enveloping layer, according to the following method: Step A The stones 12 are heated to a temperature of about 100°C.

Step B The hot stones 18 are charged, together with a plastic powder 16 such as low density polyethylene, into a mechanical rotating drum mixer 20. The plastic powder 16 becomes locally heated when it contacts the hot stones 18, and as a result, it sticks to the hot stones. The charge is then cooled until the coating is at a temperature which allows discharge of the stones without inter-adherence.

Step C Discharged stones 22 are received on a metal conveyor belt 24 which travels at sufficiently high speed to ensure spacing between the stones. Belt 24 moves through an oven 26, which radiates just enough heat to melt the plastic, causing it to flow over each stone surface.

Step D The coated stones 28 are cooled, advantageously by water spray 30, and are removed by gravity and vibration and, if necessary, by scraping, from the conveyor belt 24.

Fig. 4 represents a second method of preparing a plurality of plastic-coated small stones, pebbles, rock fragments, or mixtures thereof 12. The method includes bringing the stone particles into contact with molten plastic 32 to individually coat the stones with an enveloping layer of plastic, as follows: Step A Stones 12 are placed into metal cage 34 and are dipped into a liquid plastisol 32, such as a special polyvinyl chloride resin and a plasticizer. The plastisol can conveniently be at ambient temperature. ¾tep B Cage 34 is raised, to drain off excess liquid.

Step C Coated stones 36 are discharged onto a metal conveyor belt 38, which travels at a sufficiently high speed to ensure spacing between the stones. Belt 38 moves through an oven 40, which radiates just enough heat to solidify the plastic .

Step D Coated stones 36 are removed from belt 38 by gravity and vibration, and, if necessary, by scraping.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof . The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (9)

8 114 , 510/2 WHAT IS CLAIMED IS:

1. A material for covering an outdoor ground surface, comprising a plurality of separate, plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof.

2. The material according to claim 1 , wherein said stones, pebbles and rock fragments have at least one axis of a size in the range of from 4-15 mm.

3. The material according to claim 1 , wherein said plastic is low density polyethylene.

4. The material according to claim 1 , wherein said plastic is polyvinyl chloride.

5. The material according to claim 1 , wherein said plastic coating has an average thickness of between 0.5 and 1.5 mm.

6. The material according to claim 1 , wherein said plastic is colored. 9 114 , 510/2

7. A plurality of separate plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof, for use as a covering for an outdoor ground surface.

8. A plurality of separate plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof, for use as a covering for an outdoor ground surface, prepared by bringing heated gravel particles into contact with powdered plastic to individually coat said particles with an enveloping layer of plastic.

9. A plurality of separate plastic-coated individual small stones, pebbles, rock fragments, or mixtures thereof, for use as a covering for an outdoor ground surface, prepared by bringing gravel particles into contact with a molten plastic to individually coat said particles with an enveloping layer of plastic. For the Applicant WOLFF, BREGMAN AND GOLLER