Synthetic structure for covering a surface
United States Patent 3900656

A covering for a subsurface to provide a surface thereon suitable for recreational activities such as football, includes a top wear surface layer which may provide, for example, simulated grass, sometimes called synthetic turf and a moisture protected underlayment layer between the top surface layer and the subsurface composed of strands or noodles of a synthetic plastic material in an open celled foam binder, each strand being comprised of a multitude of closed cells containing encapsulated gas. The gas in the closed cells may be a non-toxic, non-corrosive heavy gas to which the strand material is not porous and so the underlayment can breathe by expelling air from the open celled foam binder when compressed and yet retains the pneumatic resilience of the trapped gas.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
428/17, 428/95, 428/305.5, 428/319.7, 428/398
International Classes:
D06N7/00; E01C13/08; (IPC1-7): B32B5/18
Field of Search:
161/21,62-67,159,160,161,162,170,178,190,231,55,57,60,143 273
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US Patent References:

Primary Examiner:
Mccamish, Marion E.
Attorney, Agent or Firm:
Dunn, Robert T.
What is claimed is

1. In a recreational surface covering a subsurface, including a top wear surface layer selected for a recreational activity, at least one underlayment layer between the top surface and the subsurface comprising,

2. A recreational surface as in claim 1 wherein,

3. A recreational surface as in claim 1 wherein,

4. A recreational surface as in claim 1 wherein,

5. A recreational surface as in claim 1 wherein,

6. A recreational surface as in claim 1 wherein,

7. A recreational surface as in claim 6 wherein,

8. A recreational surface as in claim 1 wherein,

9. A recreational surface as in claim 8 wherein,

10. A recreational surface as in claim 8 wherein,


The present invention relates to resilient surface coverings and more particularly, to surface coverings for recreational purposes for indoor or outdoor use such as football fields, baseball fields, tennis courts, tracks and gymnasiums. Heretofore, a number of synthetic turf recreational surface coverings have been used particularly for football fields. These coverings provide much needed shock dissipating qualities and at the same time they are rugged, have long life and require a minimum of maintenance. The combination of problems which is encountered in providing a suitable artificial turf particularly for a game like football are numerous. For example, turf must have the proper tactile properties which enable a player to feel reasonably secure on the playing field; the playing field must be shock absorbing to minimize injury to the players; the qualities of the playing field should not be unduly altered by changes in temperature and humidity and of course, the synthetic turf must be rugged and tough and should have long life and require a minimum of maintenance. A particular problem of synthetic turf used on a football field is that the turf must be sufficiently resilient to cushion the player and so minimize injury and at the same time, the turf must not be too resilient and must not "bottom-out" and it must have a high rate of recovery.

The artificial turf services provided heretofore generally include a top wearing layer which simulates grass and one or more underlayment layers which provide the shock absorbing qualities that contribute substantially to the "feel" of the turf. In the past, the underlayment in particular, has not exhibited the shock absorbing characteristics and the proper "feel" under the range of environmental temperature and moisture conditions such a field is normally exposed to.


In accordance with the primary purposes of the present invention an underlayment layer or layers is provided between the top surface or wearing layer which may have the texture and appearance of grass, and a subsurface such as asphalt or a bituminous covering. The underlayment disclosed in the present invention has effective use with a wide variety of surfaces, many of which simulate grass and is particularly effective for use with the simulated grass surface described in some detail herein. Furthermore, the subsurface may be asphalt, concrete, wood or other firm structure.

In accordance with the present invention, the underlayment layer or layers between the surface layer and the subsurface includes strands of a selected plastic material in a plastic binder such that the strands are substantially contiguous with each other and the thickness of the underlayment layer is many times the diameter of the strands. Each strand contains a multitude of closed cells which contain a selected relatively heavy non-toxic, non-corrosive gas and the binder is an open celled foam plastic material. Thus, when the underlayment is compressed, air is expelled from the open cells of the binder and yet the pneumatic resilience of the trapped gas in the closed cells in the strands is retained. Depending upon the resilience and the "feel" desired, the fraction of the volume of the underlayment provided by the strands can be varied. For example, where the strands constitute as little as 1% of the volume of the underlayment, substantial resilience is still provided.

It is one of the several objects of the present invention to provide a composite artificial surface for a recreational field having a synthetic underlayment which is substantially immune, in so far as resilience and "feel" are concerned, to environmental changes in temperature and humidity.

It is another object of the present invention to provide such a surface which has improved resilience characteristics compared to surface coverings available heretofore.

It is a further object of the present invention to provide a surface covering for the purposes described herein which is relatively more economical to manufacture than some of the surface coverings already in use.

It is another object to provide such a surface covering and particularly the underlayment using materials which are resistant to fungus, molds, mildew, moisture and normal ambient range of temperatures, the materials further being non-allergenic, non-toxic and odorless with readily predetermined density and resilience characteristics.

Other objects, features and advantages of the present invention will be apparent in view of the following description of embodiments of the invention which represent the best known uses of the invention. The invention accordingly, comprises the elements and combinations of elements, features of construction and arrangements of parts which are exemplified in the structures herein described and in the scope of the appended claims.

The several embodiments of the invention are described in the accompanying drawings.


FIG. 1 is a cross-section elevation view of a portion of a first embodiment of the invention;

FIGS. 2, 3, 4, 5 and 6 are cross-sectional elevation views of portions of respectively second, third, fourth, fifth and sixth embodiments of the invention; and

FIG. 7 illustrates greatly enlarged and somewhat schematically a portion of a strand used in making the underlayment mat that provides at least a part of the underlayments of the several embodiments to illustrate the general nature of the strand.

Throughout the drawings, like numerals indicate like parts and in the drawings, dimensions of certain other parts shown therein may have been modified and/or exaggerated for the purposes of clarity of illustration and understanding of the invention.


The resilient cushioning characteristics of the underlayment of the recreational surfaces described herein is provided by strands or noodles of a closed cellular plastic material in a binder of open cellular plastic material. Generally, the volumetric ratio of binder to strand is substantially greater than one and so the underlayment mat can be said to be an open cellular plastic material containing reinforcing strands or noodles of a closed cellular construction, the closed cells containing an encapsulated gas which is not permeant thereof. Toward this end, the encapsulated gas is preferably a relatively large molecule, non-allergenic, non-toxic gas.

The open celled binder or matrix makes its own contribution to the compression and resilience characteristics of the underlayment and of course, maintains the highly resilient strands in position with respect to each other and distributes externally applied loads uniformally to the strands.

A heavy load rapidly applied to the underlayment will quickly evacuate virtually all of the air from open cells under compression. The closed cells in the strands, however, even if they contain air are pneumatic in the sense that the air molecules enter and exit only by the relatively slow process of diffusion through the closed cell walls. Hence, if a load is rapidly applied, compression is resistant by the air within the closed cell as these cells act as miniature balloons. Where the closed cells are filled at least partially with a gas of high molecular weight there is practically no diffusion of the gas molecules through the closed cell walls. Thus, the parameters which are affective to determine the softness, resilience and "feel" of the synthetic recreational surface are numerous. The parameters include the volumetric ratio of binder to strand, the density of the binder, the density of the strand, the permeability of the closed cells to the gas contained therein and the ratio of impermeant gas to air contained in the closed cells.

Polymers suitable for preparing the binder or open celled resilient matrix are well known in the art and include polyester and polyether urethanes, and foam rubber, both natural and synthetic. Open celled polyurethane matrices are preferred since they may be prepared at very low densities and exhibit particularly satisfactory adhesion to the strands. The strands are prepared from polyethylene terephthalate which is charged into an extruder along with methylene chloride and extruded through cylindrical orifices about 15 mils in diameter. On entering atmospheric pressure the super heated methylene chloride flashes off, generating a micro-cellular terephthalate continuous filament with polyhedral celled walls less than 2 microns thick. Rapid diffusion of the methylene chloride vapor out of the closed cells leaves a substantially collapsed cell filament. These cells are post inflated by exposing the strands to a heated mixture of methylene chloride and perfluorocyclobutane for a prescribed interval. This treatment fully inflates the turgid closed cells with perfluorocyclobutane which is one impermeant inflatant.

The inflated strands are then placed in a mold in numerous layers and a polyurethane foam formulation is poured in and cured to provide the composite underlayment structure. This is an example of one technique for making the underlayment used in the present invention. Additional details of this technique and numerous other techniques imploying other open celled matrix materials and other impermeant inflatants for the closed cells of the strands are described in the prior art such as U.S. Pat. No. 3,503,840 which issued Mar. 31, 1970 to R. G. Parrish.

Referring now to FIG. 1, there is shown a portion of a first embodiment of the invention. It comprises a shock-absorbing resilient underlayment mat 2 which is attached by means of adhesive 4 to a supporting base or foundation 6, the latter being, for example, a layer of asphalt or concrete. The top layer of the structure, the wearing surface, is a layer of artificial turf 8, which is, for example, the kind shown in U.S. Pat. No. 3,661,687, which issued May 9, 1972 to Spinney, et al. Briefly, the turf may comprise a layer 10 of woven material as a backing, which may be made of a suitable thermoplastic material such as, for example, the polyesters, polypropylene or nylon fibers, or combinations thereof. Tufted, knitted or woven into the backing material 10 are upstanding fibers 12 rectangular in shape and of a size to approximate the size of natural grass, and having a suitable denier, which may, for example, range from 225 to 275 denier, (or may have an even higher denier, for example, 300 to 900 denier), and which have a ratio of width to thickness of approximately 5. In order to lock the fibers 12 into the backing material 10, a layer of latex sometimes designated plastisol, or other adhesive 14 is applied to the backing and allowed to cure. The turf structure 8 is attached to the mat 2 by means of a layer 16 of adhesive.

The adhesive layer 4 may be a suitable contact cement which has an affinity for the mat 2 and the underlying base or foundation 6.

In order to install the combined structure, the underlayment 6 is first prepared. A layer of adhesive 4 is spread thereon, and mat 2 is then rolled out upon it. On the top surface of mat 2 is then spread a layer of adhesive 16, and the previously prepared turf structure 8 is placed on top of the adhesive 16. The entire assembly is then allowed to set and/or cure before use.

The underlayment mat 2, made as described herein and as described in the above mentioned U.S. Pat. No. 3,503,840. A mat of this construction is available commercially bearing the designation pneumacel which is manufactured by E. I. DuPont de Nemours & Co. (inc.). The mat is a non-woven mat of cellular strands 20 (see FIG. 7) having the closed cells 22. The cells are filled with one or more gasses so adjusted as to give the individual strands a predetermined resistance to compression, as described in said patent. These strands are formed into the structure (illustrated in FIG. 1) having the open cells or voids 26 which are formed by the foam binder 27 all as described in said patent.

The basic chemical structure of the strand is that of a polyester. These strands bearing the designation pneumacel as manufactured and available, may have a density of approximately 0.2 lbs. per cubic feet to 3.5 lbs. per cubic feet. They are obtainable in thicknesses of .02 inches and up. The compression modulus of a typical example is approximately 2 lbs. per square inch to 40 lbs. per square inch loading-to-compression 50%. Its strip tensile strength is approximately 2 pli to approximately 30 pli, (0.25 inches thick), with an elongation of 20 to 25%. In the present invention strands 20 are preferably about 50 mils in diameter, and in a typical specimen of the material will be approximately 3 inches long. Cells 22 are small (that is, approximately 30 microns in diameter), are generally of uniform size, and polyhedral in shape. The side walls are approximately 0.2 microns in thickness, and are highly oriented. The strand itself has low density, being approximately 1 lb. per cubic foot. Its compression strength is essentially undamaged at 3,000 lbs. per sq. inch. Its chemical property is similar to polyester fiber and "Freon" fluorinated hydrocarbon and air blowing agents. It is supple because of its structure, and not because of its chemical composition.

The thickness of the underlayment mat 2 in an artificial football surface should lie between 0.5 and 1.0 inches. It is believed that the strands in this mat work in a manner similar to pneumatic tires in that the individual closed cells in the strand act as containers rather than beams and columns. The load supporting characteristic of the material is proportional to the "gauge" pressure of the impermeant gas in the cells.

Referring now to FIG. 2, a second embodiment of the invention is shown, in which the first layer 8 is the same as in the FIG. 1 embodiment. However, in this embodiment, instead of having a single mat of the strands, two mats 28 and 30 are used. Preferably mats 28 and 30 are of unequal thickness, but they can be of the same thickness. The total thickness of the combined mats 28 and 30 should be in the range of 0.7 inches to 1.0 inch (as in the first embodiment). One reason for using the two separate mats 28 and 30 is that it may be more economical to purchase the individual mats in standardized readily available form, and combine the two mats. For example, the first mat 28 may be 0.3 inches and the second mat 30 may be 0.5 inches, the total thickness being 0.8 inches. The materials of the two mats will be the same.

On the other hand, the volumetric proportions of strands in the two mats may be different. The bottom mat 30 may have a greater volumetric proportion of strands and so may not be as soft as the upper mat 28.

The respective layers of the total composite structure are assembled as follows: The base or foundation 6 is first provided, and on this is spread a layer of adhesive 4 as in the FIG. 1 embodiment. On top of this is then placed mat 30. On the upper surface of mat 30 is then spread a layer 32 of adhesive which is a contact cement which is suitable for the joint between the two mats.) On top of the adhesive 32 is then placed mat 28 which will adhere thereto because of the use of the adhesive. On the upper surface of the first mat 28 is then spread a layer of adhesive 16 the same as in the FIG. 1 embodiment, and on top of this is placed the composite turf structure 8. After the various adhesives have set firmly, then the surface may be used.

Referring now to FIG. 3, a third embodiment of the invention is shown. As in the FIGS. 1 and 2 embodiments, the turf structure 8 is the same as in the first embodiment, and has grass filaments 12, woven backing 10, and the latex locking coat 14. Next is a layer of adhesive 16 as used in FIG. 1. The next layer 36 is a layer of flexible polyvinyl chloride material. Adhesive 16 fastens the turf 8 to the top layer of the polyvinyl chloride material 36. Next in order comes a layer of adhesive such as the adhesive 4 of the FIGS. 1 or 2 embodiments. Next is a mat 2 of the strands which is similar to the layer 2 of FIG. 1, which is attached to the underground or base layer 6 by means of the adhesive 4.

The laying of this recreational surface can be conveniently done in two steps: In the first step, the layer of adhesive 4 is spread on the foundation 6, and the mat 2 is then placed on and adhered thereto. The turf material 8 has previously been prepared and is adhered thereto by means of the adhesive 16 to the upper surface or layer of polyvinyl chloride material 36. After the cement 16 has set, as well as the adhesive 4, then adhesive 4 is placed on the top surface of the mat 2, and the combined layers 8 and 36 are placed thereon and adhered.

In the FIG. 3 structure, as well as in the previous two embodiments, the layer of polyvinyl chloride material will prevent water seeping down through the top surface into the matting 2, as well as providing a firm load or impact spreading layer lying over the pad 2 as compared to the FIGS. 1 and 2 embodiment.

Referring now to FIG. 4, a structure somewhat like FIG. 3 is shown, but utilizing the two-layer mat system of FIG. 2 with the use of the polyvinyl chloride material 36 of FIG. 3. That is, starting with the top layer the structure 8 is shown just as in the FIG. 3 embodiment, and which is attached to the polyvinyl chloride layer 36 by means of the adhesive 16. Layer 36 is adhered by means of adhesive 4 to the first mat layer 28 as shown in FIG. 2. This first mat layer 28 is adhered by means of adhesive 16 to the second mat layer 30, the latter being in turn fastened by means of the adhesive 4 to the foundation 6. The use of the two layer mat system (28-30) may in some instances produce an economy of manufacture not possible with the single mat layer 2. As in the FIG. 3 embodiment, the layer 36 of solid but flexible polyvinyl chloride such as the PVC material described above, provides a load or impact distribution surface as compared to the FIGS. 1 and 2 embodiments.

Referring now to FIG. 5, structure 8 is the same as in the previous embodiments, and consists of the rectangular fibers or strands 12, the backing member 10 and the plastisol locking material 14.

On the foundation 6, is spread a layer of adhesive 4 on top of which is placed the single underlayment mat 2. On top of mat 2 there is provided a water-proof membrane such as Neoprene, or Adaprene (a Dupont product), Hypolon or other water-resistant elastomeric material. The thickness of the membrane 40 is in the order of 0.010 inch to 3/16 inch. It is poured or sprayed on the top of the mat 2, and allowed to set. After the membrane has set, then adhesive 16 is placed on the membrane, and the grass structure 8 is adhered to the membrane by the adhesive. The advantages of this structure is that a membrane 40 which is relatively thin is interposed between the grass structure 8 and the matting 2, this membrane being water-impervious so that moisture can not get into the voids of the mat.

Referring again to FIG. 3, one can construct a structure without having the grass turf structure, thus leaving the layer 36 as the wear surface. The resulting structure will be very suitable for gymnasium floors, or the floors and walls of rooms where it is desired to clean the rooms by washing with water. All that is necessary to do is to follow the structure of FIG. 3 except that the top grass layer 8 and adhesive 16 are not used.

The sixth embodiment shown in FIG. 6 includes a wear surface that does not simulate turf or grass. Here the wear surface layer 45 is a synthetic resin having a surface 46 sufficiently rough to provide traction for the user. This surface layer provides impact distribution to the mat 2 of strands 20.

The wear surface layer 45 is made of a durable synthetic resin such as an isocyanate which may be one of the commercially availably sheet materials bearing the designation adaprene, neoprene or hypolon. This layer is sufficiently thick to withstand the wear intended and is water-proof. The wear surface sheet could also be specially prepared with an inert filler that gives the surface 46 greater traction.

Installation of the surface shown in FIG. 6 begins with the underlayment or mat 2 which is rolled onto an adhesive layer 4 that is first spread on supporting base 6. Adhesive layer 16 is then put on the top of the mat and the wear surface layer 45 is rolled onto that and allowed to set or cure before use.

While the pneumacel material has been known, nevertheless, the unexpected advantages of using it for a sports playing field such as one use for football, soccer, basketball, track, tennis or baseball, are completely non-obvious. The reason for the non-obvious nature of the latter's use is that a football field, for example, has rather peculiar characteristics necessary for its proper functioning. One of these is the fact that it is outdoors, and as indicated earlier in discussing the background of the invention, it may become deleteriously affected by the retention of water in the pores of any resilient underlayment used. Furthermore, an outdoor playing field will be exposed to hot sun, and thus the artificial turf and underlayment may reach temperatures up to 160°F., in the warmer climates of the United States.

On the other hand, where a football field is used in a northern climate of the United States, during the winter, the field must be able to withstand without deterioration temperatures well below freezing. The pneumacel material provides the proper response and resistance to deterioration over such a wide range of temperatures. A further advantage of the underlayment provided is that so far as fire is concerned, it is self-extinguishing.

A further advantage is that by making up the plural layered materials, (where there are two underlayment mats of bonded strands superimposed on each other) by adjusting the individual densities per cubic foot of each mat, the total densities, in so far as load bearing and shock resistance of the combined pad are concerned, can be readily adjustable to meet given use requirements.

A further advantage of the underlayment mats of bonded strands which is important in, for example, football field applications, is that the structure of the mats spreads the impact loads over a much larger area than any other known foamed or open-pored type of material. The reason for this is that the peculiar mechanical structure of the mat itself, and the ability of the mat to cause the spreading of the impact loads is an unexpected advantage. Furthermore, for impact protection, the gas in the cells of the individual strands acts to cushion the impact shock. For example, the shoulder or elbow of a football player cannot "hit bottom" against any hard undersurface underlying the turf, such as the cement or asphalt 6. The cushioning characteristics stay fairly constant and therefore, regardless of whether a football game is played at below freezing temperature or as high as 100°F., the reaction of the football field surface remains essentially constant. This is not true of prior known composite structures.

In view of the above it will be seen that the several objects of the invention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the terminology employed herein is for the purpose of description and not of limitation. As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the spirit and scope of the invention.