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Publication numberUS3597297 A
Publication typeGrant
Publication dateAug 3, 1971
Filing dateJun 25, 1968
Priority dateJun 25, 1968
Also published asDE1933048A1, DE1933048B2, DE1933048C3
Publication numberUS 3597297 A, US 3597297A, US-A-3597297, US3597297 A, US3597297A
InventorsTheodore Buchholtz, Timothy B Jensen, William H Penney
Original AssigneeMinnesota Mining & Mfg
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Synthetic turf material and method of making same
US 3597297 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

Aug. 3, 1971 T BUCHHOLTZ ETAL 3,597,297


United States Patent O U.S. Cl. 161--21 10 Claims ABSTRACT F THE DISCLOSURE rTurf-like surfacing formed from soft elastomeric base layer adhered to rigid substrate formed from 100% solids polyurethane having Shore A2 hardness of between 5 and 404 and containing to 75% by volume of voids, the major portion of which are in the 1/16 to 1A: diameter range and top surface of tough pile fabric adhered by means of adhesive which penetrates the back of said fabric and embeds the lower portion of the fibers therein, the base layer providing both viscous and elastic response to compression and being capable of slow recovery from indentation over a 2- to 20-second period.

This invention relates to novel very soft elastomeric materials containing large voids, to synthetic turf material utilizing the same as an integral component thereof, and to a method for preparing the same. More particularly the invention relates to synthetic turf materials which utilize very low durometer polyurethane elastomers containing voids, which may be formed by crushing of relatively large frangible fillers contained therein as a base layer.

Various attempts have been made to produce artificial turf having a grass-like surface for indoor or outdoor recreational and sports activities, or for use as a surfacing in other areas which receive hard wear. The currently most widely used form of such turfs is of the general type shown in U.S. Pat. 3,332,828, issued July 25, 1967, to Faria et al. Turfs are described in this patent which are formed by applying a conventional foam backing to the substrate by means of an adhesive such as a latex, and then applying a tufted fabric over the foam backing by means of a latex. Such constructions, however, suffer from several shortcomings, one of which is difficulty of adhesion to many substrates, particularly natural soils or gravel; the most serious shortcoming is the stiffness or hardness of the surface, even though covered by tufted fibers. The problem is particularly severe where outdoor surfacing is desired because, in order to minimize absorption of water, the base foam is disclosed as being of a closed cell structure. Chemically blown closed cell foams of this type, however, have a stiffness which is unwanted in the base layer of a turf type surfacing. Because of the difficulty of applying the base layers to asphalt or other substrates by means of Water or solvent based adhesives, it has become the actual practice to mechanically hold the surfacing in place. This is usually done by fastening the edges of the surfacing into trenches along the edges of the field to hold the surfacing tightly over the field.

It is an object of the present invention to provide resilient synthetic surfaces which resemble natural turf in appearance and performance, which are weather resistant. Such surfaces can be formed in accordance with the invention which are uniform and provide high traction. Surfaces of this invention are more durable than natural turf and previously proposed synthetic turfs, and thus can be maintained at low cost.

In accordance with the present invention, turf type surfacing is provided with an extremely soft yet resilient 3,597,297 Patented ug. 3, 1971 elastomeric base layer of a crosslinked polyurethane having Shore A2 durometers in the range of 5 to 40. These base materials are capable of being pushed down to onethird or less of their original volume by finger pressures, and exhibit a gradual but substantially full recovery over a period of 2 to 20 seconds and preferably 5 to l5 seconds after the application of such pressure. The resilient base layer is formed from a castable liquid material `which can be poured and cured in place on any suitable substrate such as concrete, asphalt, conventional flooring materials, and the like. The reaction mixture contains a frangible preferably hollow filler which is crushed after cure of the reaction mixture.

The finished turf surfaced material is formed by coating the soft base layer with additional liquid polyurethane material which functions as an adhesive to secure a top turf type surfacing to the base. The turf surfacing is a stretchable open fabric which may be either a woven, non-woven, or preferably a knitted backing to which fibers are secured. Knitted fabrics which are stretchable by virtue of their construction are prferred, but fabrics formed from elastic bers can be substituted. The open backed pile fabric is pressed into the reaction mixture while it is still liquid so that the reaction mixture penetrates the fabric portion of the pile material. The porous fabric and the lower ends of the pile fibers thus become embedded in the curing polyurethane mixture. The finished synthetic turf has an improved softness such that it is possible t0 jump with the full weight of ones body on the knees without shock or injury to the knees or legs. Thus, when used for athletic playing fields such as football fields, the synthetic turf of this invention minimizes leg injuries, which have become an increasing problem for athletes. Even though the finished surfacing is very soft, it is durable and can withstand the action of cleated or spiked shoes during rough athletic play in addition to being weather resistant. Because of the dead soft or slow recovery characteristic of the substrate layer, a quality similar to natural, which yields and receives a permanent impression, is provided. Synthetic turfs having a truly elastic recovery tend to be too rubbery to the extent that they work back against the action of cleats or shoes, thus producing an unwanted springiness. In contrast the substrate of this invention has the ability to yield a great amount and remain deformed for a period of time, thus resembling natural soils, but also has the ability to gradually recover its original shape over a period of seconds.

The invention will be further explained with reference to the accompanying drawing, wherein:

FIG. 1 is a cross-sectional view illustrating the crushing step in the preferred mode of forming the base layer 0f this invention, and

FIG. 2 is a cross-sectional view of the finished synthetic turf construction of this invention.

Referring more particularly to FIG. l, there is seen a base layer 10 preferably formed by pouring a liquid polyurethane-forming reaction mixture onto a solid substrate 12, which is preferably asphalt or concrete, and curing the same in situ to a solid state. Base layer 10 contains a frangible filler 14 which is crushed by means of any suitable device 16 for applying high localized pressures to the base layer. After crushing of the filler 14, voids 18 are provided in the base layer.

As seen in FIG. 2, the finished surface is provided by adhering a pile fabric 20 to the top of the base layer 10. Pile fabric 20 consists of an open base fabric 22 and a pile fabric 24 which simulates natural turf. The pile fabric 20 is adhered to base layer 10 by means of an adhesive 26 which uniformly coats the base layer 10 and penetrates the backing fabric 22 and preferably also surrounds the lower ends of the fibers 24.


The resilient base layer for the surfacing of the present invention is formed from pourable liquid reaction mixtures of organic polyisocyanates and coreactive materials which contain active hydrogen atoms (as determined by the well-known Zerewitinoff method), said coreactants being preferably organic polyols or blends of organic polyols and organic polyamines which contain a catalyst, if necessary, so that the reaction mixture will harden from a liquid state to a solid elastomeric state under ambient temperatures and pressures. The reaction mixtures contain approximately equivalent quantities, i.e., 0.7:l to about 1.2:1 of isocyanate groups to active hydrogens. The preferred reaction mixtures react rapidly at ambient temperatures so that within an hour or less the liquid mixture has cured to a slump resistant state. The reaction mixture is mixed shortly before casting. Known proportioning and mixing equipment is preferably used for mixng the components and dispensing the reaction mixture.

The preferred polyisocyanates are aromatic diisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, or chlorophenylene 2,4-diisocyanate. It will be apparent to those skilled in the art, however, that aliphatic, cycloaliphatic, or heterocyclic polyisocyanates or mixtures thereof can be substituted.

The preferred coreactant for the polyisocyanate is a polyalkylene ether polyol, preferably a polypropylene ether glycol either alone or mixed with an aromatic polyamine such as 4,4methylene bis 2-chloroaniline (MOCA). Small amounts of other polyols such as polyester polyols or polyether ester polyols can be substituted, but these are not preferred because of the greater hydrolyzin'g tendencies of the resulting polymers.

It is desirable to introduce some components having three or more reactive groups or atoms in order to provide some crosslinking as well as chain extension of the reaction mixture. This is readily accomplished by including some triisocyanate, triol, tetrol, pentol, triamine, etc. in the reaction mixture. It is usually preferable to prereact the polyisocyanate lwith a small amount of polyol to reduce the toxicity of the material and to improve the mixing ratio of the two-part system from which the base layer is cast.

Any known catalyst for the polyurethane reaction can be used. The preferred catalysts are soluble metal compounds, for example, mercury, lead, or tin salts of carboxylic acids or organo tin compounds. The preferred catalysts are organo rnercuric compounds such as phenyl mercurio acetate or phenyl mercuric hydroxide. The reaction mixture preferably contains at least 0.05% by weight of such a catalyst, or more as desired to produce the desired rapid ambient temperature cure rate.

The hardness of the rubber is controlled within the 5 to 40 Shore A-2 durometer range by adding to the reaction mixture predetermined amounts of a chain terminating agent such as butyl Cellulose (mono-butyl ether of ethylene glycol), butyl carbitol (mono-butyl ether of diethylene glycol), oleyl alcohol, ethylene glycol monoethyl ether, or similar mono-functional alcohols. Other compounds having a single active hydrogen can also be substituted.

The preferred frangible filler for forming the voidcontaining base layer is perlite. Other suitable materials are frangible hollow glass or plastic beads, expanded vermiculite, or even breakfast cereals. However, inorganic low density frangible llers are preferred in order to optimize the weather stability and fungal resistance of the structure. 'Ihe frangible filler preferably is a diameter range between about 1&6 and 1A, inch. The elastomer can also in addition contain some voids of a smaller size if desired. In practice such voids usually result from the entrainment of air with ya crushable filler, from CO2 generation due to moisture in the reaction mixture, or both. The finished base layer should contain between about and 75 percent by volume of voids. Optimum results have been obtained in the to 45 percent range.

The optimum void fraction will vary slightly among various systems of the invention depending on the size distribution of the voids, and the deformation characteristics of the elastomer. It appears that voids which are partially or slightly interconnected so that a bellows-type effect is achieved during localized compression of the elastomer are preferable because this bellows effect seems to contribute to the slow regain characteristic of the material by damping of the elastic recovery speed of the elastomer. While it is preferred to form the base layer by crushing of a frangible filler, it will be understood that equivalent structures can be formed by mechanical whipping in of the voids to the same volume content, preferably to form sli-ghtly interconnected voids of the type achieved by the addition and crushing of a frangible filler.

Where a frangible filler is used, a device which produces suicient localized pressure to cause thorough crushing of the filler can be used. For example, hammering or rolling devices can be employed so long as the polymer is not torn or otherwise injured. One suitable device is a weighted machine resemblng an agricultural disc in which the discs are blunt edged rather than sharp.

When the voids are made in the material by means of a frangible filler, it is preferred that the polymer contain an anti-settling agent. Such agents include finely divided materials, for example, finely divided silica or clays commercially available for this purpose, but we prefer to use small diameter, short asbestos fibers. Such agents provide thixotropy to the system and thus prevent floating of .the filler in the resin and assure a uniform distribution of voids in the base layer.

Because of the very soft and deformable nature of the base layer of this invention, it has been found that the tufted fabric `applied to form the top surface should also be of a highly stretchable nature. In order to form a durable composite structure, the fabric backing to which the fibers are attached must be capable of fiexing with the substrate. The preferred backing fabric is a circular knit polyester (preferably polyethylene terephthalate) fabric to which the grass simulating fibers are secured, preferably by looping. Other fibers or yarns can be used for forming the knitted fabric. |For example, nylon, polypropylene, rayon, or other fabrics can be substituted. The projecting fibers should be formed from durable weather resistant fibers, such as nylon, polypropylene, polyesters, or similar tough fibers can be used. Preferably the fibers are crimped to provide resilience and matting resistance to the tufted surface. The fibers can be dyed any desired color, but green is usually preferred to simulate grass. It will Ibe apparent that any dyes used should be color fast under weather exposure conditions. Ultraviolet light absorbers may also be added to the fibers as needed.

It is important that the fabric backing for the pile material be capable of stretching at least 50% in any direction. Most of this stretchability is provided by the manner in which the fabric is knitted. The preferred fabrics are capable of elongation of at least in at least one direction. Fabrics which do not elongate suitably have a tendency to act like a tightly stretched trarnpoline, and thus would lower the shock absorbing effect of the base layer. It is preferred that the pile fibers be apparently unoriented in the pile fabric, as fibers which are arranged in a regular or directional pattern tend to give an unwanted directionality to the response of the surface to balls, etc., bouncing or rolling thereon. Even distribution of crimped fibers of circular cross section has been found to provide such apparently unoriented piles.

The base layer should have a thickness of no less than 1A inch, and preferably `at least 1/2 inch. The quality that appears unique about the base layers of the present invention is that they are Visco-elastic in that they provide a retardation to impulse which is not purely elastic (Le. proportional to deformation), but which is also partly viscous (i.e. proportional also to the rate of deformation). Thus the base layer provides a deceleration rate which is much more nearly uniform than that provided by elastic substrates. The base layers of this invention have a coefficient of restitution in the range of 0.05 to 0.3 when using a 1 oz. steel weight dropped from a 16-inch drop height onto the surface. The coeflicient of restitution is a measure of the amount of energy returned to a falling object when it strikes the material. A coeicient of 1.00 would indicate 100% of the energy was returned and 0.00 Would indicate no energy was returned. A preferred balance of strength and kinetic properties has been found to occur in materials which have a coefiicient of restitution between 0.1 to 0.2, although the noted broader range is generally useful. As noted above the room temperature Shore A2 hardness of the base layer resin (without voids or fillers) material should be in the extremely low range of 5 to 40. The optimum hardness range has been found to be about a Shore A2 hardness of to 25.

The polymer used to bond the fabric to the base layer is preferably also a two-part polyurethane resin system of the type described above. It may be preferable to add an organic polyamine such as MOCA to improve the toughness and cut growth resistance of the polymer. Latex or solvent type adhesive can be substituted for applications where the surfacing is not anticipated to undergo severe use, but the two part solventfree systems are greatly preferred for athletic surfacing. The adhesive should be applied as a continuous impermeable layer. Because of the somewhat porous nature of the base layer, the adhesive serves as a sealant for the top of the base layer in addition to functioning as an adhesive to secure the pile fabric to the base layer.

While the above described method in which the base layer is poured onto the substrate and cured in situ is preferred for large athletic surfaces, for example football fields, it will be understood that in many applications the surfacing can be prepared by in-plant formation of a composite base layer to which the pile fabric is adhered as described above. Such a lcomposite. can later be applied to the rigid substrate by casting a relatively thin layer of adhesive, preferably a 100% solids urethane reaction mixture of the same type from which the base layer is formed. This alternative procedure is particularly advantageous when the surfacing is applied to relatively small areas, for example golf greens or tee areas, patios, or the like, where it would be impractical to utilize bulky crushing equipment. In -this alternative procedure the crushing step can be accomplished in the r suppliers plant.

By pile fabric as used herein we mean to include fabrics to which upstanding fibers are secured by looping, ocking, tufting, etc.

The invention will be further explained with reference to the following example in which all parts are given by weight unless otherwise indicated.

EXAMPLE The following ingredients, designated as Part A were mixed and evacuated separately:

Parts 2000 molecular weight polyoxypropylene glycol 50.33 Litharge 0.20 Green chrome oxide-yellow pigment mixture 1.30 Carbon black pigment 0.60 Kaolin clay 45.00 Hexogen calcium 0.40

Asbestos fibers, 10 to 35 mesh (Rotap screen analysis) 25,500 cm.2/ gm. surface area by Dyckerhoff system 0.25 Ethylene glycol monoethylene ether (ethyl Cellosolve) 2.10 Phenyl mercurio acetate 0.15

The following ingredients, designated as Part B were mixed separately:

Parts Toluene diisocyanate 86.7

Polyoxypropylene triol 6.0 432 molecular Weight (TP 440) trimethylol propane 7.3

Approximately eleven parts of B were mixed with one hundred parts of A. Following a thorough mixing of the part A and part B, twenty-seven parts of perlite (average diameter 1A; inch) were blended into the mixture. This mixture was poured over asphalt and screeded to approximately a one-half inch thickness. Following a three hour cure time, the material was subjected to a crushing load of approximately 400 p.s.i., repeated six times by means of a blunt bladed disc. This provided a soft base which exhibited elastico-viscous response to deformation.

A mixture of eleven parts B and one hundred parts A to be used as an adhesive was then spread over the cured, soft base at a rate of grams per square foot. Immediately the fiber pile top fabric was pressed into place so that the curing elastomer mixture wetted the backing fabric and that portion of the pile fibers in contact with the backing, thus providing a secure, tenacious bond upon completion of curing. The fiber pile top fabric consisted of a cut crimped nylon pile, 1/2 inch in height, placed into a knitted polyester backing having a total weight of approximately 2.2 pounds per square yard. The individual nylon bers were 2 inches long, circular in cross section, heat set crimped with 8 crimps per inch, so that their length after crimping was about 1 inch, weather resistant, and approximately 50 denier. The backing is made from 440 denier filament polyethylene terephthalate which is circularly knitted on a Wildman Co. knitting machine modified so as to include pile liber in the stitches. The nylon fibers were looped around the backing fibers with each end forming part of the pile. The pile fabric was lightly coated. on the back side with an acrylic latex to improve the dimensional stability and handleability of the fabric. The coating was light enough to just coat the fibers of the backing without closing off the spaces between the bers.

The physical properties of the construction were tested and found to have the following values: The base was found to have an elongation at break according to ASTM Test D-41261T of 137%, a compression modulus measured according to ASTM Test D-575-46 at a strain rate of 20 inches per minute of 3.17 p.s.i. for 10% compres sion and 40 p.s.i. for 50% compression, a coefficient of restitution as previously described of 0.13, and was found not to support the growth of fungi.

The completed surfacing was tested by means of a National Bureau of Standards machine described in volume 29 of the Journal of Research which was modified to simulate the action of football shoes. One pulley was used having 50 cleats mounted thereon in three circumferential rows. Each cleat was made of a hard rubber and had a rounded point of 3/16 inch radius, which flares out to a radius of 3/8 inch at its base.. The topped base distance is three-quarter inch. The surfacing Was subjected to 30,000 turntable revolutions. Negligible fiber loss was observed. The fibers were slightly matted in the direction of rotation, but gentle hand brushing restored the pile to substantially its original height. No loss of adhesion between the base and top was observed, and no damage was observed in the base layer after 30,000 revolutions.

What is claimed is:

1. An improved synthetic turf comprising a soft elastomeric polyurethane base layer containing from about 15 to 75% voids by volume and a top layer of liexible pile fabric, an elastomeric adhesive securing said top layer and said base layer to one another, said base layer having Visco-elastic properties, being capable of slow,

gradual and substantially complete recovery from indentation under ringer pressure in a period of about 2 to 20 seconds, and having a Shore A2 scale durometer in the range of 5 to 40 with a coeicient of restitution in the range of 0.05 to 0.3 when a l-ounce steel weight is dropped thereon from a 16-inch height.

2. The turf of claim 1 wherein said polyurethane is a cross-linked polyalkylene ether based polyurethane.

3. The turf of claim 1 wherein said pile fabric is capable of limited stretching in any direction.

4. The turf of claim 1 wherein said elastomeric ad hesive is polyurethane elastomer.

5. The turf of claim 1 wherein said base layer is at least 1A: of an inch thick. f

6. The turf of claim 1 wherein the fibers of said pile fabric are crimped synthetic bers of generally circular cross section.

7. A method for forming a synthetic turf which comprises (a) forming a base layer of soft Visco-elastic polyurethane elastomer containing from to 75% by volume of frangible particulate ller, (b) subjecting the base layer to compressive forces crushing said filler, and

(c) adhering a top layer of eXible pile fabric to said base layer with an elastomeric adhesive.

8. The method of claim 7 wherein said polyurethane elastomer is a cross-linked polyalkylene ether based polyurethane.

9. An improved synthetic turf comprising a soft elastomeric cross-linked polyalkylene ether based polyurethane base layer containing from about 15 to 75% voids by volume and a top layer of flexible pile fabric capable of limited stretching in any direction, an elastomeric adhesive securing said top layer and said base layer to one another, said base layer having Visco-elastic properties, being capable of slow, gradual and substantially complete recovery from indentation under 4finger pressure in a period of about 2 to 20 seconds, and having a Shore A2 scale durometer in the range of 5 to 40 with a coecient of restitution in the range of 0.05 t0 0.3 when a l-ounce steel weight is dropped thereon from a 16-inch height.

10. An improved synthetic turf comprising a soft elastomeric cross-linked polyalkylene ether based polyurethane base layer containing from about 15 to 75 voids by volume and a top layer of flexible pile fabric capable of limited stretching in any direction, an elastomeric polyurethane adhesive securing said top layer and said base layer to one another, said base layer having Visco-elastic properties, being capable of slow, gradual and substantially complete recovery from indentation under nger pressure in a period of about 2 to 20 seconds, and having a Shore A2 scale durometer in the range of 5 to 40 with a coecient of restitution in the range of 0.05 to 0.3 when a l-ounce steel weight is dropped thereon from a l6-inch height.

References Cited UNITED STATES PATENTS 2,515,847 7/1950 Winkler 161-64 3,325,338 6/1967 Geen 161-89 3,293,723 12/1966 Evans 161-62X 3,312,583 4/ 1967 Rochlis 161-62 3,238,156 3/1966 Kohrn 260-25 3,332,828 7/1967 Faria et al. 161-21 PHILIP DIER, Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 597,297 Dated August 3, 1971 Inventods) Theodore Buchnoltz, `Timothy B. Jensen 8c William H.

Penney It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 39, after "natural" insert soil Column 3, line 55, delete "Cellulose" and insert Cellosolve Signed and sealed this 7th day of March 1972.

(SEAL) Attest:

EDWARD M.FLETQHER,JR. ROBERT GOTTSCHALK Attestlng Offlcer' Commissioner' of Patents ORM DO-1050 (I0-59) uscoMM-Dc eoa7epe9 U,S GOVERNMENT PRINTING OFFICE: 1969 0-366-3S

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U.S. Classification428/17, 156/77, 428/369, 156/72, 428/317.9, 264/49, 428/95, 428/423.3
International ClassificationE01C13/08, B29B15/00, B32B5/18, B29C39/00, B29C39/10, B29C39/22, C08J9/00, B29C61/00, B29C65/00
Cooperative ClassificationC08J9/00, C08J2375/04, E01C13/08
European ClassificationC08J9/00, E01C13/08