U.S. patent application number 11/612431 was filed with the patent office on 2008-06-19 for artificial turf system and method of making.
Invention is credited to Bruce Cheskin, Joseph W. DiGeronimo, Henry A. Julicher.
Application Number | 20080145574 11/612431 |
Document ID | / |
Family ID | 39527641 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080145574 |
Kind Code |
A1 |
Julicher; Henry A. ; et
al. |
June 19, 2008 |
ARTIFICIAL TURF SYSTEM AND METHOD OF MAKING
Abstract
A recreational surface such as an artificial turf playing field
includes a pile fabric having a backing and a multiplicity of
generally upstanding pile elements, and an infill overlying the
backing and being interspersed between the upstanding pile
elements. The infill advantageously includes resilient particles as
well as particles of a rubber coated hard granular material such as
rubber coated sand. The particles of rubber and the particles of
rubber coated sand may be mixed together or they may be applied
separately in different courses or layers in which the relative
proportions of the two types of particles differ. Also disclosed is
a method of designing and constructing such a recreational surface
in which the properties of the recreational surface are specified
according to the intended use of the recreational surface. For
example, the impact resistance properties of the recreational
surface may be engineered by adjusting the relative proportions of
resilient particles and particles of rubber coated hard granular
material.
Inventors: |
Julicher; Henry A.; (Valley
Forge, PA) ; DiGeronimo; Joseph W.; (Sturbridge,
MA) ; Cheskin; Bruce; (Wayne, PA) |
Correspondence
Address: |
KNOBLE, YOSHIDA & DUNLEAVY
EIGHT PENN CENTER, SUITE 1350, 1628 JOHN F KENNEDY BLVD
PHILADELPHIA
PA
19103
US
|
Family ID: |
39527641 |
Appl. No.: |
11/612431 |
Filed: |
December 18, 2006 |
Current U.S.
Class: |
428/17 ;
428/87 |
Current CPC
Class: |
E01C 13/08 20130101;
E01C 13/02 20130101; Y10T 428/23921 20150401 |
Class at
Publication: |
428/17 ;
428/87 |
International
Class: |
A41G 1/00 20060101
A41G001/00 |
Claims
1. A recreational surface, comprising: a pile fabric having a
backing and a multiplicity of generally upstanding pile elements;
and an infill overlying said backing and being interspersed between
said upstanding pile elements, said infill comprising resilient
particles and particles of a rubber coated hard granular
material.
2. A recreational surface according to claim 1, wherein said infill
comprises a mixture of resilient particles and particles of a
rubber coated hard granular material.
3. A recreational surface according to claim 1, wherein said infill
consists essentially of resilient particles and particles of a
rubber coated hard granular material.
4. A recreational surface according to claim 1, wherein said infill
comprises more than one layer, and wherein at least one layer has a
composition that is different than a composition of another of said
layers.
5. A recreational surface according to claim 4, wherein one of said
layers has a first weight percentage of particles of rubber coated
hard granular material, and wherein another of said layers has a
second weight percentage of particles of rubber coated hard
granular material, and wherein said first weight percentage is
different from said second weight percentage.
6. A recreational surface according to claim 4, wherein said infill
comprises a first layer, said first layer being in contact with
said backing, and wherein said first layer is fabricated
predominantly of particles of a rubber coated hard granular
material.
7. A recreational surface according to claim 6, wherein said first
layer is at least 60% by weight particles of a rubber coated hard
granular material.
8. A recreational surface according to claim 6, wherein said infill
further comprises a second layer, and wherein said second layer is
fabricated predominantly of rubber particles.
9. A recreational surface according to claim 8, wherein said second
layer is at least 60% by weight rubber particles.
10. A recreational surface according to claim 1, wherein said
infill contains substantially no uncoated sand.
11. An artificial turf installation, comprising: a pile fabric
having a backing and a multiplicity of generally upstanding pile
elements; and an infill overlying said backing and being
interspersed between said upstanding pile elements, said infill
comprising a first layer that is predominantly fabricated from one
of either resilient particles or particles of a rubber coated hard
granular material, said infill further comprising a second layer
that is predominantly fabricated from the other of either resilient
particles or particles of a rubber coated hard granular
material.
12. A recreational surface according to claim 11, wherein said
infill consists essentially of resilient particles and particles of
a rubber coated hard granular material.
13. A recreational surface according to claim 11, wherein said
first layer is fabricated predominantly of particles of a rubber
coated hard granular material.
14. A recreational surface according to claim 13, wherein said
first layer is at least 60% by weight particles of a rubber coated
hard granular material.
15. A recreational surface according to claim 11, wherein said
second layer is at least 60% by weight rubber particles.
16. A recreational surface according to claim 11, wherein said
infill contains substantially no uncoated sand.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to the field of synthetic
recreational surfaces and processes that are used to fabricate such
surfaces. More specifically, this invention relates to an improved
artificial turf system and methods that may be used to fabricate
such a system.
[0003] 2. Description of the Related Technology
[0004] Synthetic recreational surfaces include indoor and outdoor
surfaces that are designed for walking, running, sporting events or
other recreational activities. They include walkways, running
tracks, and artificial turf installations.
[0005] Processes for fabricating an early synthetic grass or turf
for applications such as outdoor miniature golf courses have been
known since at least the 1930s, but it was not until the mid-1960s
that an artificial turf system was developed that was adequate to
serve as a playing surface for rigorous sports such as football and
baseball. This first truly modern artificial turf system, which was
eventually installed in the Houston Astrodome, was developed by
Monsanto and was disclosed in U.S. Pat. No. 3,332,828 to Faria et
al.
[0006] Early artificial turfs such as that disclosed in the Faria
et al. patent relied upon one or more layers of elastomeric
material to provide cushioning against impact with the turf. This
tended to give the turf a spongy feel that players felt was
unpleasant. It also made early artificial turfs unsuitable for
certain sports related applications, such as golf greens. The
solution to this problem was first introduced in the mid-1970s in
U.S. Pat. No. 3,995,079 to Haas, Jr., which disclosed a synthetic
turf like product that included a pile fabric having a relatively
flexible backing and generally upstanding pile elements resembling
grass as well as a granular infill or top dressing material
interspersed on the backing among the pile elements of the pile
fabric. The granular infill or top dressing was disclosed as
preferably being installed to a depth that was sufficient to
substantially absorb the shock of objects impacting thereon.
[0007] The motivation for the use of the infill technique in the
Haas, Jr. patent was to provide an artificial turf surface that had
property suitable for use as a golf course green. However, it was
soon recognized that the infill technique provided superior
characteristics for artificial turf playing surfaces for more
rigorous sports as well. The preferred material for use in the
infill, however, continued to evolve. The original Haas, Jr. patent
described the use of relatively coarse, hard materials such as
crushed granite to form the infill, which gave the resulting turf a
crunchy feel and tended to abrade against the pile elements or
artificial grass blades. Haas, Jr. improved on the original
technology in U.S. Pat. No. 4,044,179, which disclosed the use of
multiple layers of granular material to form the infill.
Specifically, a fine sand layer was first laid directly upon the
backing material, dispersed among the upstanding pile elements. A
coarse sand layer was then applied over the fine sand layer. The
use of a moisture retention material such as vermiculate was also
discussed in order that the sand would retain moisture to restrict
it from shifting.
[0008] While an all sand infill was found to be superior in many
respects to in infill formed of coarser hard materials, it also had
disadvantages. After extended use, the sand would tend to compact
and become quite hard, losing its resiliency. The turf would
increasingly become less comfortable for the players and would
eventually have to be replaced. Sand compaction also tends to
negatively impact the ability of the artificial turf to drain
itself during heavy rains.
[0009] Impact testing (commonly referred to as Gmax testing) is
used to measure the shock-absorbing properties of recreational
surfaces, including artificial turf. Gmax values express a ratio:
the ratio of the maximum acceleration (deceleration) experienced
during an impact with the surface undergoing testing, to the normal
rate of acceleration due to gravity. The higher the Gmax value, the
lower the shock-absorbing properties of the surface. Gmax
measurements are an important measurement of the playability and
safety of an artificial turf playing field. The most commonly used
Gmax testing standard is the one established by the American
Society for Testing and Materials (ASTM). For synthetic surfaces,
the ASTM specifies that the average Gmax value of one or more test
points on a field should not exceed 200 Gmax (as measured in
accordance with ASTM procedures F355-A and F1936). If Gmax level of
over 200 is measured, the field is considered unsafe and
remediation is required.
[0010] Removal and replacement of the compacted sand top dressing
is a difficult, time-consuming and expensive process because the
compacted top dressing material becomes closely packed together
with the upstanding artificial grass fibers and is difficult to
remove.
[0011] In the early 1980s, Haas, Jr. developed an infill or top
dressing, as disclosed in U.S. Pat. No. 4,337,283, which included
resilient particles, preferably fabricated from granulated cork or
synthetic rubber, that were mixed with harder granular materials
such as sand. This improved the cushioning of the artificial turf
and reduced frictional abrasion to players and objects when
impacting the turf. The sand that was used in such infills was raw
uncoated silica sand, which in practice has been found to be
potentially unsafe because it can cause silicosis.
[0012] U.S. Pat. No. 5,958,527 to Prevost discusses an artificial
turf assembly includes having a top dressing or infill having a
base course that is first placed upon the top surface of the
backing and consists exclusively of hard sand granules. A middle
course of intermixed hard sand and resilient rubber granules is
then placed upon the base course. A top course exclusively of
resilient rubber granules is then placed upon the middle course.
The base sand course is represented to hold the turf in place and
to quickly drain the surface. The middle layer of mixed sand and
rubber granules was said to act as a buffer to keep the base sand
and top rubber courses separated.
[0013] It has been found by those in the industry that artificial
turf systems that utilize a mixed sand and rubber infill will
eventually degrade so as to have undesirable shock absorbing
characteristics. Such systems are typically measured to have Gmax
ratings approximately within the range of about 180 to about 200.
While these values are not so high as to require immediate
remediation, they represent close to the minimum acceptable
standard of impact resistance for an athletic field. Concerned
coaches, athletes and administrators typically prefer an athletic
field that has greater impact resistance (which will be expressed
as a lower Gmax rating) than is commonly achieved using a mixed
sand and rubber infill because of safety and performance
issues.
[0014] Sprinturf of Wayne, Pa. has more recently pioneered a top
dressing or infill that is fabricated entirely from elastomeric
materials. This is commonly known as the all rubber infill. An all
rubber infill can be more expensive than using sand or a mixture of
sand and rubber, but it provides certain distinct advantages and
may be cooled if the rubber is colored. An all rubber infill feels
and reacts more like a natural turf soil base than a mixture of
sand and rubber does. It will not overcompact like sand, so the
shock absorbing characteristics of the all rubber infill turf will
not significantly degrade over time. In other words, the measured
Gmax rating of the artificial turf using an all rubber infill will
not increase dramatically over time like those systems that utilize
a sand infill or a mixture of sand and rubber. Artificial turf
systems utilizing an all rubber infill are commonly tested to have
a Gmax rating that is approximately within a range of about 100 to
about 130.
[0015] Another advantage of eliminating sand from the infill
material stems from the fact that sand is a relatively porous
material that is believed by some to be susceptible to absorption
of biocontaminants (fungus, algae, bacteria, urine, blood, saliva,
excrement, etc.) that can cause bacterial and viral infestation,
leading to an offensive odor or other potentially dangerous
unhygienic conditions. Sand also commonly ends up in players' eyes,
where it can cause abrasion damage, particularly in the case of
players who wear contact lenses. An all rubber infill is much less
abrasive to players and objects than is an infill utilizing
sand.
[0016] U.S. Pat. No. 5,041,320 to Meredith et al., which issued in
1991, disclosed an infill or top dressing for artificial turf that
uses loose mineral grains such as sand that have been coated with a
polymeric material. This is commonly referred to in the industry as
rubber coated sand. WO 2004/022853 to Jensen also discloses a
method of making artificial grass utilizing a rubber coated sand.
Rubber coated sand is well suited for artificial turf as an infill
material in many respects. Because a particle of rubber coated sand
tends to be denser than a particle that is fabricated entirely from
rubber, theoretically rubber coated sand could provide a firmer
surface in comparison to pure rubber. However, it is generally
considered to be uneconomical to fabricate an infill for larger
artificial turf projects such as a football field out of rubber
coated sand because it is very expensive. In addition, because no
coating process is perfect, rubber coated sand still tends to be
more abrasive than an infill or top dressing that is fabricated
entirely from rubber.
[0017] A need exists for an improved artificial turf system and a
method for constructing such a system that is economical, resists
compaction, minimizes abrasiveness and that provide superior shock
impact resistance and stability in comparison to conventional
artificial turf systems.
SUMMARY OF THE INVENTION
[0018] Accordingly, it is an object of the invention to provide an
improved artificial turf system and a method for constructing such
a system that is economical, resists compaction, minimizes
abrasiveness and that provide superior shock impact resistance and
stability in comparison to conventional artificial turf
systems.
[0019] In order to achieve the above and other objects of the
invention, a method of fabricating a recreational surface according
to a first aspect of the invention includes steps of determining a
desired property of the recreational surface; and fabricating the
recreational surface using a mixture comprising resilient particles
and particles of a rubber coated hard granular material. The step
of fabricating the recreational surface preferably includes
selecting a relative proportion of the resilient particles with
respect to the particles of a rubber coated hard granular material
based on said desired property.
[0020] A method of fabricating artificial turf according to a
second aspect of the invention includes steps of installing a pile
fabric having a backing and a multiplicity of generally upstanding
pile elements; installing a first infill layer on the backing, the
first infill layer being predominantly fabricated from one of
either resilient particles or particles of rubber coated hard
granular material; and installing a second infill layer over the
first infill layer, the second infill layer being predominantly
fabricated from the other of either resilient particles or
particles of rubber coated hard granular material.
[0021] According to a third aspect of the invention, a method of
fabricating an artificial turf installation includes determining an
intended use of the artificial turf installation; calculating an
optimum shock absorbing property specification for the artificial
turf installation, the step of calculating an optimum
shock-absorbing property specification being performed in reliance
upon the determined intended use; calculating an infill composition
in reliance on the shock-absorbing property specification, the
infill composition comprising a mixture of first particles having a
first hardness and second particles having a second hardness that
is different from the first hardness, and wherein the step of
calculating an infill composition comprises determining a ratio of
the first particle to the second particles; installing a pile
fabric having a backing and a multiplicity of generally upstanding
pile elements; and installing an infill constructed according to
said calculated infill composition on the backing.
[0022] A recreational surface according to a fourth aspect of the
invention includes a pile fabric having a backing and a
multiplicity of generally upstanding pile elements; and an infill
overlying the backing and being interspersed between the upstanding
pile elements, the infill comprising resilient particles and
particles of a rubber coated hard granular material.
[0023] An artificial turf installation according to a fifth aspect
of the invention includes a pile fabric having a backing and a
multiplicity of generally upstanding pile elements; and an infill
overlying the backing and being interspersed between the upstanding
pile elements, the infill comprising a first layer that is
predominantly fabricated from one of either resilient particles or
particles of a rubber coated hard granular material, the infill
further comprising a second layer that is predominantly fabricated
from the other of either resilient particles or particles of a
rubber coated hard granular material.
[0024] These and various other advantages and features of novelty
that characterize the invention are pointed out with particularity
in the claims annexed hereto and forming a part hereof. However,
for a better understanding of the invention, its advantages, and
the objects obtained by its use, reference should be made to the
drawings which form a further part hereof, and to the accompanying
descriptive matter, in which there is illustrated and described a
preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a fragmentary perspective diagrammatical view of
an artificial turf installation that is constructed according to a
preferred embodiment of the invention;
[0026] FIG. 2 is a fragmentary cross-sectional view of an
artificial turf installation according to a modified embodiment of
the invention;
[0027] FIG. 3 is a diagrammatical cross-sectional view of a first
type of infill particle according to a preferred embodiment of the
invention;
[0028] FIG. 4 is a diagrammatical cross-sectional view of a second
type of infill particle according to a preferred embodiment of the
invention;
[0029] FIG. 5 is a diagrammatical fragmentary cross-sectional view
of an artificial turf assembly that is constructed according to one
embodiment of the invention;
[0030] FIG. 6 is a diagrammatical fragmentary cross-sectional view
of an artificial turf assembly that is constructed according to a
second embodiment of the invention; and
[0031] FIG. 7 is a flow chart depicting a method that is performed
according to a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0032] Referring now to the drawings, wherein like reference
numerals designate corresponding structure throughout the views,
and referring in particular to FIG. 1, an artificial turf
installation 10 that is constructed according to a first preferred
embodiment of the invention includes a first layer of compacted
subgrade soil 12 having a plurality of trenches 14 defined therein,
each of which contains a perforated drainage pipe 16. Perforated
drainage pipe 16 is preferably fabricated from a plastic material.
Adjacent to the trenches 14 and placed on an upper surface of the
compacted subgrade 12 are a plurality of perforated panel drain
members 18, which are generally oriented so as to be substantially
perpendicular to the axis of the trench 14 and are designed to
carry drainage water to the trench 14 and the perforated drainage
pipe 16. The perforated panel drain members 18 may be wrapped in a
geotextile fabric in order to prevent clogging.
[0033] A layer of coarse aggregate material 20 is preferably
provided on top of the panel drain members 18. The coarse aggregate
material 20 is preferably crushed stone. A second layer 22 of fine
aggregate material, also preferably fabricated from crushed stone,
is preferably installed on top of the layer of coarse aggregate
material 20. An artificial turf assembly 24, which will be
described in greater detail below, is installed on top of the fine
aggregate material 22.
[0034] In an alternative embodiment of the invention that is
depicted in FIG. 2, the artificial turf assembly 24 may be
supported by a base installation 32 having a first sub base layer
34 that is preferably fabricated from crushed stone and a second
layer 36 that is preferably fabricated from a hot mix asphalt
material. A nonwoven geotextile pad 37 is placed on top of the hot
mix asphalt material, and a layer of shock absorbing material 39 is
installed between the nonwoven geotextile pad 37 and the artificial
turf assembly 24. The layer 39 of shock absorbing material 39 is
preferably comprised of synthetic rubber, an inorganic-based
moisture-retaining component and a binder mixture obtained by
mixing an isocyanate polyurethane and an acid.
[0035] In a preferred embodiment, the synthetic rubber may be a
butadiene rubber comprising from about 100% to about 60% by weight
of the composition. More preferably, the butadiene rubber is
polybutadiene or styrene-butadiene rubber that preferably comprises
from about 88% to about 86% by weight of the composition. Most
preferably, however, the butadiene rubber is a styrene-butadiene
that comprises about 86% by weight of the composition. The
synthetic rubber is preferably granulized with the granules having
a diameter that allows for maximum sized air voids while giving the
desired degree of softness-hardness and strength. Preferably, the
granule size ranges from about 6 millimeters to about 2 millimeters
in diameter. A preferable source for the granulized synthetic
rubber is recycled tires that are commercially available from
numerous sources, such as American Recycled Tires, Midland, Mich.;
TLJ, Inc., St. Louis, Mo.; W & W Recycling Rubber, Saugus,
Mass. and Tire Incorporated, Charlotte, N.C. The granulized rubber
is preferably comprised of granulized reinforced polycord tires
with no steel present and with the polycord being comprised of
nylon or polyester.
[0036] To provide an underlayment with the desirable amount of
shock absorbency and traction, it is preferred that the synthetic
rubber have a certain degree of softness-hardness and resiliency.
To that end, it is preferable that the recycled tires have a Shore
"A" hardness of about 40 to about 70 as measured by the American
Standard Test and Measurements ("ASTM") scale for tire hardness,
ASTM No. D2240-68. This shore gives the granulized rubber the
desired amount of softness-hardness and resiliency required in most
applications. More preferably, however, the tires have a shore A of
about 45 to about 65, and most preferably, have a shore A of about
50 to about 60.
[0037] The layer 39 of shock absorbing material 39 preferably has a
thickness that is substantially within the range of about 12 mm to
about 60 mm and more preferably within a range of about 19 mm to
about 38 mm. This embodiment of the invention is preferably
constructed according to the teachings that are provided in U.S.
Pat. No. 5,605,721 to DiGeronimo, the entire disclosure of which is
incorporated by reference as if set forth fully herein.
[0038] Referring again to FIG. 1, artificial turf assembly 24
preferably includes a pile fabric having a web like backing
material 26 and a multiplicity of generally upstanding pile
elements or fibers 28. Artificial turf assembly 24 also preferably
includes an infill 30 that is overlying the backing material 26 and
interspersed between the upstanding pile elements 28.
[0039] According to one particularly advantageous feature of the
invention, infill 30 includes both resilient particles and
particles 40 of a rubber coated hard granular material. A resilient
particle is defined as a particle that is fabricated from a
material or materials that are substantially compressible at
pressures that will be applied thereto when a person is walking or
running on an artificial turf installation. A resilient particle in
the preferred embodiment of the invention is embodied as a rubber
particle 46, but could alternatively be fabricated from another
resilient material such as cork or vermiculate. A rubber particle
46 is shown diagrammatically in FIG. 4. The term "rubber" as used
within this document in relation to either rubber particles or
rubber coated particles is hereby defined to encompass any
resilient elastomeric material, including natural and artificial
rubbers and polymers such as thermoplastic polymers and equivalent
materials. The rubber particle 46 that is depicted in FIG. 4 may be
fabricated from any such material. Rubber particle 46 is preferably
constructed so as to be substantially homogeneous in its density
and composition.
[0040] A particle 40 of rubber coated hard granular material is
shown diagrammatically in FIG. 3. Particle 40 includes a core 42 of
hard granular material, which may be fabricated of a metallic
material, a ceramic material, a stone material, a mineral material,
a hard plastic material or any other hard material. The core 42 of
hard granular material preferably exhibits a Brinell hardness that
is greater than about 10 and a specific gravity that is greater
than 1, meaning that it would not float in water. Preferably, the
core 42 of hard granular material is a particle of sand, and most
preferably quartz sand. Particle 40 further includes an outer
coating 44 of a rubber material as the term is defined above.
[0041] The rubber particles 46 and the particles 40 of rubber
coated hard granular material are preferably of substantially the
same size, and preferably have a median size that is within a range
of about 8 to about 42 mesh (about 0.0937 to about 0.0139 inches).
More preferably, both types of particles have a median size that is
substantially within a range of about 10 to about 42 mesh (about
0.0661 to about 0.0139 inches).
[0042] Preferably, the particles 40 of rubber coated hard granular
material are fabricated so that the rubber coating comprises about
2% to about 8% by weight of core 42 of hard granular material, and
more preferably about 4% to about 6% by weight of the core 42 of
hard granular material.
[0043] The core 42 of hard granular material is preferably quartz
sand and is preferably of an overall grain diameter in the range of
about 0.0039 inches to about 0.0787 inches, more preferably in the
range of about 0.0078 inches to about 0.059 inches, and most
preferably in the range of about 0.0156 inches to about 0.0354
inches.
[0044] Both the rubber particles 46 and the particles 40 of rubber
coated hard granular material preferably have a specific gravity
greater than 1, meaning that they will not float in water.
Preferably, the specific gravity of the rubber particles 46 is
substantially the same as the specific gravity of the particles 40
of rubber coated hard granular material.
[0045] The particles 40 of rubber coated hard granular material are
preferably fabricated according to the process that is described in
WO 2004/022853 to Jensen, the entire disclosure of which is hereby
incorporated by reference as if set forth fully herein. In the
preferred embodiment, the core 42 is a particle of quartz sand. The
rubber coating material 44 in the preferred embodiment is a
thermoplastic polymer having a melt index that is substantially
within a range of about 20 to about 40 g/10 min and more preferably
within a range of about 25 to about 35 g/10 min. The melt index is
measured as grams of melt in 10 minutes according to the test
procedure defined in the ASTM standard D1238 Procedure A.
[0046] The material from which the rubber particles 46 and/or the
particles 40 of rubber coated hard granular material is fabricated
may be impregnated with a substance that inhibits the growth of
bacteria and/or mold. Alternatively, a coating of such a substance
may be applied to the external surface of the rubber particle 46
and/or to the external surface of the particles 40 of rubber coated
hard granular material.
[0047] The material from which the rubber particles 46 and/or the
particles 40 of rubber coated hard granular material is fabricated
preferably has a static frictional coefficient relative to other
particles of the same composition that is within a range of about
0.9 to about 3.0 and is more preferably within a range of about 1.0
to about 2.5. This relatively high frictional engagement between
the individual particles reduces the amount of mixing and settling
of the particles that will occur after installation and as a result
of extended use of the recreational surface.
[0048] The hardness testing of plastics is most commonly measured
by the Shore test. The Shore hardness is measured with an apparatus
known as a Durometer and consequently is also known as Durometer
hardness. The ASTM test number is ASTM D2240 while the analogous
ISO test method is ISO 868. This method measures the resistance of
the material against indentation and provides an empirical hardness
value that is the preferred method for quantifying the hardness of
natural and artificial rubbers as well as other elastomers and is
also commonly used for `softer` plastics such as polyolefins,
fluoropolymers, and vinyls. The Shore A scale is typically used for
`softer` rubbers while the Shore D scale is used for `harder` ones.
The rubber coating material 44 in the preferred embodiment is
preferably a thermoplastic polymer that has a Shore A hardness that
is substantially within a range of about 40 to about 90, more
preferably within a range of about 50 to about 80, and most
preferably within a range of about 60 to about 75.
[0049] Referring now to FIG. 5, artificial turf assembly 24
according to a first embodiment of the invention includes a pile
fabric having a backing 26. Backing 26 preferably includes a first
layer 50 of a woven material and a second layer 52 of a nonwoven
material, and a multiplicity of generally upstanding pile elements
or fibers 28, which are preferably tufted to the backing material
26 as is illustrated in FIG. 5. Artificial turf assembly 24 also
preferably includes an infill 30, which is preferably a
substantially homogeneous mixture of particles 40 of rubber coated
hard granular material and rubber particles 46. The rubber
particles 46 and the particles 40 of rubber coated hard granular
material preferably are size to have outer diameters that are
substantially the same. The rubber material that is used in the
particles 40 of rubber coated hard granular material is preferably
a different material than the rubber material that is used to
fabricate the rubber particles 46, with the material that is used
to fabricate the rubber particles 46 preferably having a greater
weight density than the rubber material that is used to fabricate
the particles 40 of rubber coated hard granular material. The core
particles 42 of hard granular material are likely to have greater
weight density than either of the rubber materials that are used to
fabricate the rubber particles 46 and the outer rubber coating 44
of the particles 40 of rubber coated hard granular material.
Accordingly, by using a denser material for the rubber particles 46
the average weight density of the rubber particles 46 and the
particles 40 of rubber coated hard granular material may be
constructed so as to be substantially the same. This is considered
preferable, as it will minimize post installation layering and
separation between the two types of particles, which could
otherwise change or degrade the performance of the artificial turf
installation.
[0050] In order to improve the binding between the grain and the
coating material, so that the particulate material is less
sensitive to wear, it is considered preferable to provide a
coupling agent between the silica sand grains and the rubber
coating material. Such coupling agents are characterized by having
an improved adherence to the surface of the sand grain as well as
to the elastomeric coating material as compared to the adherence
between the elastomeric coating material and the grain surface when
being in direct contact. One preferred coupling agent is
bifunctional silane comprising a reactive amino group and a
hydrolyzable inorganic triethoxysilyl group, so that the silane
binds to inorganic materials, i.e. the sand grains, as well as to
organic polymers, i.e. the elastomeric coating material. A
preferred bifunctional silane is 3-aminopropyltriethoxysilane
(H.sub.2N--(CH.sub.2).sub.3--Si(OC.sub.2H.sub.5).sub.3), which is
sold by the company Degussa under the trade name of Dynasylan Ameo.
The silane is typically applied in a thin layer on the surface of
the sand grains in an amount of about 0.05 to about 0.5% by weight
of the sand, and more preferably in an amount of about 0.1 to about
0.3% by weight. Other preferred coupling agents are EDA-based
terpolymers (ethylene-acrylic derivatives) ethylene-acrylic
ester+maleic anhydride terpolymer, in particular defined as
terpolymer comprising glycidyl methacrylate (GMA) groups or
terpolymer comprising maleic anhydride (MAH) groups. One
particularly preferred material is ethylene-butyl acrylate-maleic
anhydride terpolymer, sold by the company Atofina under the trade
name of Lotader 3410. Typically, this terpolymer is applied in a
thin layer on the surface of the sand grains in an amount of 0.3-2%
by weight of the sand, preferably in an amount of 0.5-1.5% by
weight. The coupling agent constitutes a part of the
above-mentioned coating material, so that the indicated preferred
weight range of the coating material includes the thermoplastic
polymer as well as the coupling agent. These coupling agents may
preferably be applied on the surface of the sand grains, but may
alternatively be mixed in a polymer, such as a phenolic, furan or
melamine resin which is applied to the sand grain in a thin layer
before the coating with the elastomeric coating material, or the
coupling agent may be admixed with the elastomeric coating material
before it is applied as a coating to the sand grains. Combinations
of the mentioned coupling agents with each other or with other
coupling agents may alternatively be applied.
[0051] The rubber coated sand particles may be produced by a method
that is disclosed in WO 2004/022853 to Jensen, namely by heating a
portion of silica sand to a temperature within the range of about
200.degree. to about 300.degree. C., and more preferably about
230.degree. to about 270.degree., placing the portion of sand in a
mixer, adding a portion of a thermoplastic polymer to the content
of the mixer, adding a predetermined amount of water to the content
of the mixer as it continues to operate, and directing an airflow
through the content of the mixer so as to lower the temperature
thereof. By heating the sand to such a high temperature, a very
advantageous and even distribution of the coating is obtained. By
adding water to the mixture of sand and the thermoplastic polymer,
a rapid cooling to just above about 100.degree. C. may be obtained,
whereby the distribution as well as the properties of the coating
is secured. The water is dried out of the mixture by means of the
airflow through the content of the mixer and the temperature is
lowered further, e.g. below 80.degree. C. and more preferably below
60.degree. C., so that the coated grains are no longer mutually
bonded and a loose, particulate product is obtained. The
predetermined amount of water may be about 3 to about 15% by weight
of the sand, more preferably about 5 to about 10% by weight of the
sand, and most preferably between about 6.5 to about 8.5% by weight
of the sand.
[0052] A coupling agent as discussed above may be added to the
mixer prior to the thermoplastic polymer, so as to provide a layer
of the coupling agent on the surface of the silica sand grains
before the thermoplastic polymer is added to the content of the
mixer, thereby improving the binding between the grain and the
thermoplastic polymer.
[0053] A recreational surface according to a second embodiment of
the invention is depicted in FIG. 6. In this embodiment, a pile
fabric having a backing 26 and a multiplicity of generally
upstanding pile elements 28 that are otherwise identical to those
described above with reference to the first embodiment are first
installed. An infill 56 is then installed in separate and distinct
layers. In the embodiment of FIG. 6, this is performed by first
installing a first infill layer 58 that is predominantly fabricated
from particles 40 of the rubber coated hard granular material. More
preferably, the first infill layer 58 is at least 60% by weight of
the particles 40 of the rubber coated hard granular material. Most
preferably, the first infill layer 58 consists entirely of the
particles 40 of rubber coated hard granular material.
[0054] After installation of the first infill layer 58, a second
infill layer 60 is installed directly on top of the first infill
layer 58. Preferably, the second infill layer 60 is predominantly
fabricated of rubber particles 46. More preferably, the second
infill layer 60 is at least 60% by weight made up of the rubber
particles 46. Most preferably, the second infill layer 60 consists
entirely of rubber particles 46. The second infill layer 60
accordingly will preferably have different composition than the
first infill layer 58, and the weight percentage of particles of
the rubber coated hard granular material in the second infill layer
60 will be different than in the first infill layer 58.
[0055] Both the rubber particles 46 and the particles 40 of rubber
coated hard granular material are preferably pigmented with a
colorant that gives the particles a surface coloration that is
preferably an earth tone color such as tan, light green or brown.
This coloration helps keep the artificial turf assembly cool and
also gives it an attractive appearance.
[0056] After installation of the second infill layer 60, a third
infill layer 62 is installed directly on top of the second infill
layer 60. Third infill layer 62 is preferably predominantly
fabricated from particles 40 of the rubber coated hard granular
material. More preferably, the third infill layer 62 is at least
60% by weight of the particles 40 of the rubber coated hard
granular material. Most preferably, the third infill layer 62
consists entirely of the particles 40 of rubber coated hard
granular material.
[0057] After installation of the third infill layer 62, a fourth
infill layer 64 is preferably installed directly on top of the
third infill layer 62. The fourth infill layer 64 is preferably
predominantly fabricated of rubber particles 46. More preferably,
the fourth infill layer 64 is at least 60% by weight made up of the
rubber particles 46. Most preferably, the fourth infill layer 64
consists entirely of rubber particles 46.
[0058] In this embodiment of the invention, each of the infill
layers 58, 60, 62, 64 is preferably constructed so as to be
substantially devoid of any abrasive material such as uncoated
sand.
[0059] The embodiment of the invention described above may be
modified by installing fewer or more than four separate layers of
infill material. For example, an infill according to the invention
may include a first infill layer that is predominantly fabricated
of particles of rubber coated hard granular material and a second
infill layer that is predominantly fabricated of rubber particles
without the installation of additional layers.
[0060] According to another important aspect of the invention, a
method of fabricating a recreational surface includes determining a
desired property of the recreational surface and fabricating the
recreational surface using a mixture of rubber particles and
particles of a rubber coated hard granular material. The relative
proportion of the rubber particles with respect to the particles of
rubber coated hard granular material is, according to the
invention, selected in accordance with the desired property of the
recreational surface. The desired property of the recreational
surface may be a shock absorbing property of the recreational
surface. The shock absorbing property of the recreational surface
may be adjusted by varying the relative proportion of the rubber
particles with respect to the particles of rubber coated hard
granular material, with a greater proportion of rubber particles
being associated with increased shock absorption properties.
[0061] As has been described above, impact testing (commonly
referred to as Gmax testing) is used to measure the shock-absorbing
properties of recreational surfaces, including artificial turf.
Gmax values express a ratio: the ratio of the maximum acceleration
(deceleration) experienced during an impact with the surface
undergoing testing, to the normal rate of acceleration due to
gravity. The higher the Gmax value, the lower the shock-absorbing
properties of the surface. Gmax measurements are an important
measurement of the playability and safety of an artificial turf
playing field. The most commonly used Gmax testing standard is the
one established by the American Society for Testing and Materials
(ASTM). For synthetic surfaces, the ASTM specifies that the average
Gmax value of one or more test points on a field should not exceed
200 Gmax (as measured in accordance with ASTM procedures F355-A and
F1936). If Gmax level of over 200 is measured, the field is
considered unsafe and remediation is required.
[0062] According to another important aspect of the invention as is
depicted in FIG. 7, a method of fabricating an artificial turf
installation may be performed by determining an intended use of the
artificial turf installation, installing a pile fabric having a
backing 26 and a multiplicity of generally upstanding pile elements
28 as described above, determining a specification for an infill in
a manner that considers or relies at least partially on the
intended use of the artificial turf installation, and installing an
infill according to that specification. More specifically, the
specification of the infill may be selected according to the type
of recreational or athletic activity that is intended to take place
within the artificial turf installation. In addition, the length of
the multiplicity of generally upstanding pile elements 28 and the
depth and weight density of the infill may be selected in a manner
that considers or relies at least partially on the intended use of
the artificial turf installation.
[0063] Preferably, the Gmax value of the playing field for lower
impact sports such as field hockey and baseball would be selected
to be within a range of about 115-200, with a more preferred range
being about 135-165. For higher impact sports such as lacrosse,
football and soccer, a preferred Gmax value of the playing field
would be about 90-160, with a more preferred range being about
100-145.
[0064] The Gmax value of the playing field may be adjusted to the
desired value by selecting a base installation for the playing
field and by adjusting the proportion of rubber particles to
particles of rubber coated hard granular material in the infill of
the playing field. By selecting the base installation that is
described with reference to FIG. 2 and that has a layer of shock
absorbing material 39, it is possible to achieve a lower Gmax
rating than it is with the base installation that is described
above with reference to FIG. 1, all other factors being equal. When
the base installation described with reference to FIG. 2 is used, a
Gmax range from about 80 to about 150 is achievable depending on
infill thickness and weight density, the proportion of rubber
coated hard granular material to rubber particles in the infill,
and the composition and thickness of the layer of shock absorbing
material 39. Such a low Gmax value is particularly suitable for
higher impact sports such as lacrosse, football and soccer when
being played by younger athletes such as children. A more preferred
Gmax rating for high impact children's sports would be about
80-135, while a more preferred Gmax rating for high impact adult
sports using the base installation described with reference to FIG.
2 would be about 100-150.
EXAMPLE 1
[0065] A playing field was fabricated using artificial turf that is
constructed of a pile fabric having a backing and a multiplicity of
generally upstanding pile elements, with each of the generally
upstanding pile elements being approximately 2 inches in length,
plus or minus about 1/8 of an inch. A base installation was
provided according to the embodiment of FIG. 1 described above. An
infill was installed that is made up of a homogeneous mixture of
approximately 75% by weight particles of rubber coated hard
granular material and 25% by weight rubber particles. The infill
was applied over the backing of the pile fabric so as to be
interspersed between the multiplicity of generally upstanding pile
elements and at a density of approximately 4 pounds per square
foot. This installation yielded a Gmax rating of about 138. This
particular installation is considered to have particular utility
for higher impact sports such as lacrosse, football and soccer.
[0066] A comparable installation to that described in Example 1
utilizing an infill made up of all rubber particles applied at a
weight density of 3 pounds per square foot was measured to have
Gmax rating of 115. Another comparable installation utilizing an
infill made up of all rubber coated hard granular material
particles applied at a weight density of 4 pounds per square foot
was measured to have Gmax rating of 172. These examples show how it
is possible according to the teachings of the invention to adjust
the Gmax rating of the artificial turf installation by adjusting
the relative proportions of rubber coated hard granular material
and rubber particles that are used in the artificial turf in
infill. The higher the relative proportion of rubber coated hard
granular material particles to rubber particles, the higher the
Gmax rating of the artificial turf installation will be.
EXAMPLE 2
[0067] A playing field was fabricated using artificial turf that is
constructed of a pile fabric having a backing and a multiplicity of
generally upstanding pile elements, with each of the generally
upstanding pile elements being approximately 1.5 inches in length,
plus or minus about 1/8 of an inch. A base installation was
provided according to the embodiment of FIG. 1 described above. An
infill was installed that was made up of a homogeneous mixture of
approximately 50% by weight particles of rubber coated hard
granular material and 50% by weight rubber particles. The infill
was applied over the backing of the pile fabric so as to be
interspersed between the multiplicity of generally upstanding pile
elements and was applied at a density of approximately 2 pounds per
square foot. This installation yielded a Gmax rating of about 160.
This installation is considered to have particular utility for
lower impact sports, such as baseball and field hockey. A
comparable installation having an infill made up of all rubber
particles applied at a weight density of 1.5 pounds per square foot
had a Gmax rating of 148.
EXAMPLE 3
[0068] A playing field would be fabricated using artificial turf
that is constructed of a pile fabric having a backing and a
multiplicity of generally upstanding pile elements, with each of
the generally upstanding pile elements being approximately 2 inches
in length, plus or minus about 1/8 of an inch. A base installation
would be provided according to the embodiment of FIG. 2 described
above. An infill would be installed that was made up of a
homogeneous mixture of approximately 50% by weight particles of
rubber coated hard granular material and 50% by weight rubber
particles. The infill would be applied over the backing of the pile
fabric so as to be interspersed between the multiplicity of
generally upstanding pile elements and at a density of
approximately 2 pounds per square foot. This installation would be
expected to yield a Gmax rating of about 90. This particular
installation would be considered to have particular utility for
higher impact sports such as lacrosse, football and soccer and
particularly for children playing such sports.
[0069] It is to be understood, however, that even though numerous
characteristics and advantages of the present invention have been
set forth in the foregoing description, together with details of
the structure and function of the invention, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size and arrangement of parts within the
principles of the invention to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed.
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