MAT

FIELD OF THE INVENTION

This invention relates to mats and the process for producing the mats. The invention has particular application to resilient mats for use as artificial turf and as floor coverings, and to mats utilising recycled rubber material as a constituent thereof.

BACKGROUND OF THE INVENTION Convention artifical turf matting as used, for example for playing surfaces, typically comprises an upper turf carrying sheet affixed to a substrate. The upper sheet is often formed of plastic grass, typically thin strips of plastic material, tufted into a flexible backing of, for example, polyurethane. To retain the grass in the sheet and to provide additional strength a secondary backing sheet may also be provided. This turf carrying sheet is then glued to a substrate, normally a resilient flexible rubber sheet. The process of glueing the turf sheet to the substrate is normally carried out manually, with operators spreading a layer of glue over the substrate and then laying the other turf sheet over the glue coated surface.

When spreading the glue, care must be taken to provide a uniform thickness over the surface such that the resulting bond is uniform. Also, conventional glues used for this purpose must be left for a predetermined period before the mat and substrate are combined. This presents problems where a large area is to be coated with glue, as it will take an operator possibly several minutes to coat the surface with glue, such that the time between applying the initial area of glue and the final area of glue leads to a difference in dwell times between different areas of the surface. This may result in a bond of inconsistent quality.

Artificial turf is most frequently used in outdoor locations and may, therefore, be subject to large variations in temperature. As the upper turf sheet and the rubber backing often have difference coefficients of expansion, the join between the two must withstand the forces experienced when the components of the mat expand and contract at differing rates. Also, where the artificial turf is used, for example, to provide a driving surface on a golf range, the grass layer will be subject to considerable abuse and must, therefore, be fixed securely to the backing to prevent separation.

There are many other surface and floor coverings similarly composed of at least two sheets of different materials. In gymnasiums, for example, floor matting is often provided with a hard wearing upper sheet of flexible material affixed to a thicker substrate of resilient material.

Examples of such artifical surfaces are disclosed in U.S. Patent No. 4,614,686 to Coke et al, U.S. Patent No. 4,637,942 to Tomarin, and U.S. Patent No. 4,810,560 to Sell.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a mat comprising a first layer including a first material and a second layer including a second material and a third material. At the boundary between the two layers there is chemical bonding between the first material and the second material.

The first layer may be relatively thin and may form an upper surface of the mat. The second layer may be relatively thick and resilient to provide a lower substrate for the mat. The third material may be formed of granules bound together by the second material.

According to a further aspect of the present invention there is provided a process for producing a mat comprising the steps: providing a first layer having a first side and including a first material; coating the first side of the first layer with a second layer including a second material and a third material; and curing the second material to form a boundary between the first and second layers at which the first material and the cured second material are chemically bonded together.

The curing of the second material may be carried out in the presence of a catalyst.

According to a still further embodiment of the present invention there is provided a mat comprising granules of rubber dispersed in a polymeric binding.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of an artificial turf mat in accordance with the present invention; and

Figure 2 is a side view of apparatus for use in producing the mat of Figure 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to Figure 1 of the drawings, which illustrates a mat 10 of artificial turf. It will be noted that the mat comprises three identifiable layers: a first or upper layer 12 which contains the artificial grass 14; a second or lower layer 16 in the form of a resilient substrate; and an intermediate layer 18.

In this example, the upper layer 12 is formed of a polyurethane sheet carrying tufts of artificial grass 14 in the form of thin olefin strips. Typically, the upper layer 12 will be formed of two layers of polyurethane, a first layer 12A into which the grass 14 is tufted, and a

second layer 12B applied to the rear surface of the first layer to assist in retaining the grass and to provide greater mechanical strength.

The lower layer 16 is formed of a mixture of granules of rubber 17 dispersed throughout a polyurethane binder 19. The process of producing the layer 16 will be described later.

The intermediate layer 18 is formed of polyurethane which is crosslinked to the polyurethane in the upper and lower layers 12, 16.

The crosslinking between the layers 12, 16, 18 provides a substantially unitary mat. In other embodiments it is possible to form the mat without the intermediate layer 18, using crosslinking between the polyurethane in the upper layer 12 and the polyurethane in the lower layer

16 to provide the bond. However, it has been found that providing an intermediate layer of polyurethane allows the mat to be formed more quickly and efficiently as will be described below. Reference is now also made to Figure 2 of the drawings which illustrates, in somewhat schematic form, the apparatus used for producing the mat in accordance with the present invention. The upper layer 12 is provided in the form of a turf mat 21 on a reel 20 from which the mat 21 may be dispensed, with the grass 14 extending downwardly. The raw material for the lower layer 16 is granulated rubber 23, conveniently from shredded scrap tires, urethane 25 and a catalyst 27. The rubber 23 is

contained in a feedstock hopper 22, from which it is transferred into a batch weight hopper 24 by a suitable conveyor, in this case an 18' length, 6" diamater screw auger conveyor 26. The batch weight hopper 24 is mounted on scales 28 which may be set to deactivate the conveyor 26 when a desired weight of rubber has been deposited in the hopper 24.

From the batch weight hopper 24, the rubber is released into a ribbon mixer 30 which includes a further inlet through which the urethane 25 and catalyst 27 may be introduced. A separate mixer 32 is also provided for containing only urethane and catalyst.

Measured amounts of rubber, urethane and catalyst are introduced into the mixers 30, 32 where they are mixed for a predetermined time sufficient to disperse the urethane and catalyst throughout the rubber and thoroughly mix the urethane and catalyst, respectively. While the mixing operation proceeds, a length of mat 21 from the reel 20 is pulled across a screet table 36 above which the mixers 30, 32 and the batch weight hopper 24 are mounted. The urethane and catalyst mix are then released from the mixer 32, through an outlet 38 onto the turf, where the polyurethane and catalyst mix are spread evenly over the mat by a screet blade 40. Generally, the volume of urethane and catalyst mix released will be sufficient to completely coat the rear surface of the turf mat 21. The volume required will vary depending on the surface finish of the mat, a rough or irregular surface requiring a

greater volume of urethane and catalyst mix. This relatively thin layer will eventually form the intermediate layer 18.

After the urethane and catalyst mix has been spread evenly over the mat 21, the rubber, urethane and catalyst mix is released from the mixer 30 through outlet 42 onto the turf mat and the urethane and catalyst mix layer. The screet blade 40 is raised slightly and used to level the mix to form an even coating. The thicker layer will eventually form the lower layer of the finished mat. The coated turf is then moved to the right (as seen in Figure 2) between the platens 44, 46 of a hydraulic press 48. The platens 44, 46 of the press illustrated are oil heated, self-lubricating and the press is capable of producing 100 psi over 6912 square inches (96" long x 72" wide). For ease of illustration, the hydraulic system 50 and the oil heater 52 of the press 48 are shown as separate units. It should also be noted that the trailing edges 54, 56 of the platens 44, 46 are unheated.

The coated turf mat 21 is compressed and heated in the press 48 to compress and cure the urethane in the urethane and catalyst mix and the rubber, urethane and catalyst mix, and to compress the mixes to a predetermined degree. During curing, the urethane polymerizes such that a first boundary 58 (Figure 1) is created between the turf mat 21 and the urethane and catalyst mix, now the polyurethane intermediate layer 18. At this boundary 58

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- 8 - there is crosslinking between the polyurethane of the turf mat 21 and the polyurethane formed by curing of the urethane in the urethane and catalyst mix. A similar second boundary 60 (Figure 1) is formed between the urethane and catalyst mix, and the rubber, urethane and catalyst mix, now the lower layer 16. At this second boundary 60 there is also crosslinking between the polyurethane formed in the layers 16, 18.

The temperatures to which the platens 44, 46 are heated are chosen so as not to damage the turf mat 21, particularly the grass 14 which is normally more susceptible to heat damage. Similarly, the pressures are chosen so as not to damage the mat 21.

After the urethane present in the mixes has cured, the platens 44, 46 are separated and the resulting mat pulled onto a cutting table 62, where the mat is cut to size. The unheated edges 54, 56 of the platens slow the curing operation at the trailing edge of the mat 21 such that the cured layers 16, 18 appear as continuous layers along the length of the finished mat 10. While the cutting operation is taking place, subsequent trailing portions of the mat 21 may be subject to curing in the press 48, or being coated on the screet table 36.

The properties of the substrate 16 may be varied by using different sizes of rubber granules and different forms or densities of urethane. Conveniently, the rubber used may be from 200 mesh up to outsize (3/8" diameter). Also, the proportions of rubber to urethane may be varied,

the mix including up to 50% weight urethane. Curing time is governed by the proportion of catalyst present, the use of the intermediate layer of urethane between the upper and lower layers also serving to accelerate the bonding process between the layers.

It will be clear to those skilled in the art that similar mats may be created using materials other than polyurethane, and where a different polymer is present in the upper layer 12, a compatable monomer, or partly polymerized ; olymer, mixed with the rubber material, should provide the desired bonding or crosslinking between the layers.

Also,it is possible to produce a mat formed only of the rubber and urethane mix, without the upper layer. Three embodiments of the invention may be prepared in the following manner.

EXAMPLE 1

468.2 ozs. of rubber, in the form of small buffings (approximately 5 mesh) is mixed with 30 ozs. of 2000 c.p.s. polyether based polyurethane prepolymer, commercially available from Uniroyal Chemical Ltd. under the Vibrathane B843C Trade Mark and 1.8 oz . alkanolomine catalyst, commercially available from Dow Chemical Canada Inc. as Triethylolamine 85, a mixture of 85% triethanolamine and 15% diethanolamine, is mixed for three minutes before being spread over a polyurethane mat 60" wide by 60" long (total area 25 square feet). The mat

and mix are then placed in a press and subject to compression of 47 psi between platens heated to 100 C for three minutes. The resulting layer has a thickness of 1/4" and a gross weight of 31.25 lbs.

EXAMPLE 2

468.2 ozs. of 5 mesh rubber granules and 468.2 ozs. of oversize (3/8" diameter) rubber granules is mixed with 16 ozs. of Vibrathane B843C urethane and 3.6 ozs. of Triethanolamine 85 for three minutes. The mix is then spread over a polyurethane mat 60" wide by 60" long. The mat and mix are than placed in a press and subject to compression at a pressure of 47 psi between platens heated to 100 C for 10 minutes. The resulting layer has a thickness of 2 1/4".

EXAMPLE 3

1404.6 ozs. of 5 mesh rubber granules is mixed with 20 ozs. of Vibrathane B843C urethane and 5.4 ozs. of Triethenolamine for three minutes. The mix is then spread over a polyurethane mat 60" wide by 60" long. The mat and mix are then placed in a press and subject to compression of 47 psi for between platens heated to 92° C 6 minutes.

The resulting layer is 3'4" thick.