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United States Patent 
[n] 4,356,220  * Oct. 26,1982
 ARTIFICIAL TURF-LIKE PRODUCT OF THERMOPLASTIC POLYMERS
 Inventor: Joseph C. Benedyk, Highland Park, 111.
 Assignee: Brunswick Corporation, Skokie, 111.
[ * ] Notice: The portion of the term of this patent subsequent to Oct. 28, 1997, has been disclaimed.
 Appl. No.: 168,363
 Filed: Jul. 10, 1980
Related U.S. Application Data
 Continuation of Ser. No. 33,483, Apr. 26, 1979, abandoned.
 Int. CU A41G 1/00
 U.S. CI 428/17; 428/92;
 Field of Search 428/17, 92, 97
 References Cited
U.S. PATENT DOCUMENTS
3,332,828 7/1967 Faria 428/17
3,513,062 5/1970 Vinicki 428/17
3,551,263 12/1970 Carter 428/17
3,837,980 9/1974 Nishimura 428/17
3,940,522 2/1976 Wessells 428/92
3,987,228 10/1976 Hemming 428/92
4,061,804 12/1977 McCulloch 428/17
4,104,428 8/1978 Liu 428/97
4,230,752 10/1980 Benedyk 428/17
Primary Examiner—Marion McCamish
Attorney, Agent, or Firm—John G. Heimovics
An artificial grass product with pile fibers having a modulus of elasticity of from 25,000 p.s.i. to 100,000 p.s.i. and a moment of inertia of from 1.06 X 10~ 10in.4to 8:33 X 10~9 in4. For fibers of rectangular cross-section the fiber dimensions range from 0.004 in. to 0.010 in. in thickness and 0.020 in. to 0.100 in. in width.
18 Claims, 3 Drawing Figures
ARTIFICIAL TURF-LIKE PRODUCT OF
This is a continuation, of application Ser. No. 5 033,483, filed on Apr. 26, 1979 now abandoned.
CROSS-REFERENCE TO RELATED
This application is related to copending application 10 Ser. No. 17,465 of Joseph C. Benedyk, now abandoned, which is incorporated herein by reference.
This invention relates to an artificial grass product which simulates natural grass to a higher degree than commercially available artificial grasses. 15
BACKGROUND OF THE INVENTION
All of the commercially available fibers for the manufacture of artificial grass are made of either fibrillated or slit polypropylene, polyamides, polyesters, etc. Those 20 fibers are typically made from a film of 0.0015 to 0.002 inches (in.) thickness. It is known that the artificial grass pile fabric made from these materials has several disadvantages, including: a stiffness parameter inconsistent with the "feel" of natural grass, poor matting resistance, 25 poor abrasion resistance, poor fiammability qualities and poor ultraviolet resistance.
OBJECTS OF THE INVENTION
An object of the present invention is to provide arti- 30 ficial grass fiber, yarn and pile products made therefrom that closely simulate the "feel" and look of natural grass and do not suffer from the deficiencies of commercially available grass yarns and artificial grasses.
Another object of this invention is to provide a single 35 fiber pile product made of fibers comprising particular polymers and having a low elastic modulus and an area moment of inertia within a defined range.
A further object of this invention is to provide an artificial grass product having fibers with a modulus of 40 elasticity and an area moment of inertia closely approximating those properties of blades of Kentucky Blue Grass.
Still another object of the present invention is to provide an artificial grass product having superior ultra- 45 violet stability and weathering resistance in the absence or presence of an ultraviolet stabilizer or antioxidant.
A further object of the present invention is to provide an artificial grass containing additives, such as ultraviolet stabilizers or antioxidants, to improve ultraviolet 50 stability and weathering resistance.
Yet another object of the present invention is to provide an artificial grass product made from particular polymers in order to achieve the above-described objects and advantages.
SUMMARY OF THE INVENTION
The artificial grass product of the present invention is made of yarn comprised of fibers or a single fiber having an elastic modulus of from 25,000 pounds/inch2 (p.s.i.) to 100,000 p.s.i. and a moment of inertia about the x- or y-axis of from 1.06x10-10 inch4 (in.4) to 8.33 X10-9 in.4. The yarn of the invention is manufactured by extrusion/spinning through spinnerettes or by slitting or a polymer film. For specific details of this process reference is made to copending Benedyk application Ser. No. 17,465, now U.S. Pat. No. 4,181,762 previously referred to.
The elastic modulus and moment of inertia properties of the fibers of this invention allow use of yarn having substantially thicker fibers than are currently used in the art. Furthermore, the yarn may contain a mixture of fibers having varying cross-sectional shapes, elastic moduli and/or area moments of inertia. The yarn may be either twisted or braided from any number of the fibers described above.
Alternatively, the pile product of the invention may be made from single fibers having the properties described above.
The fibers of the artificial grass products of the invention closely simulate blades of Kentucky Blue Grass with respect to breaking load, ultimate tensile strength and elastic modulus. A turf product made with these fibers provides a surface more closely resembling natural grass than any conventional artificial grass product.
The invention may be better understood by reference to the appended drawings in which:
FIG. 1 is a cross-sectional view of a synthetic turf made by conventional methods using a braided yarn comprising fibers of the present invention. . FIG. 2 is a perspective view of a synthetic turf made by conventional methods using single fibers of the invention.
FIG. 3 is a cross-sectional view of the turf of FIG. 2 taken through section line 3'—3' of FIG. 2.
The fibers of the invention may be of rectangular, triangular or circular cross-section or combinations thereof. The fibers have an elastic modulus of from 25,000 p.s.i. to 100,000 p.s.i. and an area moment of inertia (bh3/12, where b is width and h is thickness of a rectangular cross-section taken perpendicular to the longitudinal axis of the fiber) of from 1.06x10-10 to 8.33 Xl0~9 in.4. For a rectangular cross-section, the fiber dimensions should range from 0.004 in. to 0.010 in. in thickness and 0.020 in. to 0.100 in. in width. These fibers may be extruded from commercially available polymers, including: ethylene-vinyl acetate copolymers, plasticized polyvinyl chloride, low density polyethylene, ethylene-ethyl acrylate copolymer, ethyleriebutylene copolymer, polybutylene and various copolymers thereof, certain ethylene-propylene copolymers, chlorinated polypropylene, chlorinated polybutylene and various compatible mixtures of these thermoplastics. The prior art has consistently viewed these polymers as unsuitable for use in fibers precisely because of their low elastic modulus and also because of their uniformly low tensile strength.
U.S. Pat. No. 3,573,147, which is incorporated herein by reference, discusses a method of making suitable ribbon-shaped fibers which may be used to produce the fibers of the invention.
The ribbon-like fibers can be made by extrusion from a rectangular, slotted orifice dimensioned to produce fibers having a thickness of between 0.004 in. and 0.010 in. and a width of between 0.020 in. and 0.100 in. since fibers having these cross-sectional dimensions possess good flexing and bending characteristics. However, as noted above, the cross-sections need not be rectangularshaped. Where the fibers have a generally circular cross-section, the diameter may be from about 0.003 in. to 0.006 in.
The ribbon-like fibers can also be made by slitting of plastic film or sheet having a thickness of between 0.004
in. and 0.010 in. to a fiber width of between 0.020 in. and 0.100 in.
It is also desirable to cross-link the fibers by use of 5 ionizing radiation, such as gamma rays emitted by radioactive elements and isotopes, x-rays, rays of subatomic charged particles including electrons, protons, deuterons, and rays of neutrons.
The dosage of radiation should be sufficient to cross- io link the molecules to the extent that they have a gel content greater than 30% but less than 90%. The preferred gel content is 45-55%. Gel content of the ethylene-vinyl acetate fiber, for example, is determined according to the following procedure: 15
Fibers are wound around a metal wire screen and subjected to solvent elution in hot xylene near the boiling point for 24 hours. Gel content is then calculated using the formula:
Where W0 is the initial weight of the sample and
W/is the final weight after elution.
To enhance cross-linking there may be distributed throughout the polymeric material fine particles of silicon dioxide, titanium dioxide or some other inorganic filler which enhances radiation cross-linking. The particle size of these oxides ranges between 100 angstroms and 1 micron and the amount used is below 1 volume percent. This small amount of inorganic filler improves ^ the efficiency of the irradiation step. For example, a polymeric material irradiated at a dosage of 10 megarads (MR) will have a gel content of 25-28%. When this same polymer includes 0.2 volume percent silicon dioxide and is irradiated at the same dosage, the gel content ^ is 40-45%. This increase in gel content represents a substantial increase in the melting point of the polymeric material. The addition of polyfunctional monomers also improves cross-linking. For example, triallyl cyanurate or triallyl acylate, alone or in combination 40 with the oxides, are additives which enhance the crosslinking yield for a given radiation dosage.
The thermoplastic materials of the invention may be cross-linked before, during or after the fibers are formed, or during or after the pile fabric is made. Miltz 45 and Narkis (J. Appl. Polymer Sci. 20: 1627-1633 (1976)) have described the synergistic effect which occurs when cross-linking, such as described above, and ultraviolet stabilization are combined in raising the ultraviolet resistance of low density polyethylene. 50
The yarn can be made by extrusion, by direct attenuation in the melt to final cross-sectional shape, by combined melt attenuation and solid phase drawing, or by 55 slitting of solid film. The yarn may consist of a combination of fibers having various cross-sectional shapes or dimensions.
Braiding or twisting of the fibers may be accomplished on any conventional braiding or twisting ma- 60 chine as, for example, one designed which accomodates from 4 to 8 carriers. The desired flexibility of the braided yarn for conventional tufting makes it preferable that no central fiber be included in the braid when it is subjected to tufting. Any conventional tufting tech- 65 nique may be used with the braided or twisted filaments. When tension is applied to the yarn by the maching during tufting, all of the ends pull together into a
tight yarn which easily passes through the machine elements.
THE PILE TURF
A detailed description of the production of artificial grass made from ribbon-like fibers can be found in U.S. Pat. No. 3,551,263, which is incorporated herein by reference. Basically, the invention described therein provides a cut pile-type synthetic turf having fibers of substantially rectangular cross-section.
Also discussed therein is a method of preparing a yarn consisting of the above-described fibers suitable for conventional cut pile tufting in the production of synthetic turf. Four to eight of the fibers are braided or twisted into a yarn which is secured by conventional cut pile tufting, weaving, knitting, or otherwise to form a structure consisting of a bacing having a cut pile face extending from one surface thereof. Where tufting, knitting or weaving is employed, a suitable latex formulation is applied to the other surface of the backing to render the complete structure dimensionally stable. A polymeric elastomer may then be applied to the latex backing to provide a more stable and improved structure.
FIG. 1 is a cross-sectional view of a synthetic turf produced by the conventional methods discussed in U.S. Pat. No. 3,551,263 using a braided yarn. Fibers 1 emerge from the fiber backing 2, the pile being anchored securely therein by a bonding agent 3. A polyvinyl chloride foam 4 has been applied to the backing to improve the physical properties of the turf.
In another embodiment, a single fiber pile is used in making the synthetic turf (see FIGS. 2 and 3) according to the process described in U.S. Pat. No. 3,332,828. A portion of the woven turf 5 is shown in which single fibers 6 extend upwardly from a woven synthetic fiber backing 7. The fibers 6 are anchored securely in the backing 7 by a bonding agent 8. A polyvinyl chloride foam 9 is applied on the backing 7 to improve the physical properties of the turf 5.
The mechanical properties of the low modulus, large diameter fibers of the invention were compared to the mechanical properties of blades of Kentucky Blue Grass as follows:
A table model Instron testing machine was used with Instron's "C" load cell at one pound (lb.) full scale deflection for the Kentucky Blue Grass with a crosshead speed of 0.2 inch/minute (in./min.), chart speed of 1 in./min. and a gauge length of 2 in. The fibers of the invention were tested in the same way with the exception of having the load cell at 2 lb. full scale deflection and a cross-head speed of 2 in./min., chart speed of 1 in./min., and a 2 in. gauge length.
Bending Modulus Test
The same Instron machine was used as previously described with the exception of a different gripping arrangement. The load cell used was an "A" cell at 10 grams full-scale deflection, 0.2 in./min. cross-head speed, 10 in./min. chart speed, and 1 in. gauge length.
Table I presents a summary of the tensile properties of Kentucky Blue Grass blades, fibers of the invention formed by drawing or extrusion, and polypropylene