Note: Descriptions are shown in the official language in which they were submitted.
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Field of the Invention
.
This invention relates to playing surfaces
for athletic games. More particularl~, this invention
relates to syntheitc turf playing sur~aces which
closely duplicate the appearance and physical
characteristics of natural turf playing surfaces.
Specifically, this invention relates to a playing
surface with a resilient, non-abrasive top-dressing
which is especially suitable for use on playing
fields for contact sports.
ackground o the Invention
A natural grass turf covering has tradi-
tionally ~een cultivated on most playing areas for
athletic games. Grass is considered highly desirable
both because it stabilizes the soil thereby limiting
problems with mud or dust, and also because of its
attractive appearance. Ho~ever, maintainence of
natural grass turf on athletic playing areas is
very expensive and is practically impossible on areas
subjected to continuous heavy usage.
In order to minimi~e the expense of maintaining
athletic playing areas as well as increase the durability
of the playing surfaces, attempts have been made
to substitute synthetic turf for natural turf. The
results of prior efforts have, however, left much to
be desired. Particulary severe problems arise in the
construction of fields for contact sports such as
football, rugby, soccerl field hockey, baseball and the like.
In an effort to achieve some degree of
resilience, many prior art synthetic turfs have
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incorporated an elastomeric foam underlay or backing
similar to a carpet pad. Synthetic turfs with
foam backing are typlified by the materials in Faria,
U.S. Patent No. 3,332,828 and Spinney, U.S. Patent
No. 3,661,687. Such turfs have an unnatural, springy or s~ongy
feel which reduces the surefootedness of players
running and making sharp turns thereon. The surface
may be slippery due to graininess or the presence of
moisture. Players falling on such surfaces may receive
severe rug-burns. The degree to which such
surfaces contribute to player injuries has been a
matter of substantial controversy.
Top dressed playing surfaces for athletic
games are disclosed in my prior U.S~ Pa-tents Nos.
3,995,079 and 4,04~,179. The '079 patent discloses
golf greens formed from a turf-like pile fabric
top dressed with non-compacting granular material
such as granulated coal slag, crushed flint or
crushed granite. Angular top-dressing materials
of this type are very abrasive and may scrape the
skin of a person falling on the surface. Moreover,
such top-dressing materials generally are not
readily available in all areas, and consequently,
undesirable expense and difficulty may be encountered
in installing such surfaces.
U.~. Patent No. 4,044,17~ shows a playing
surface comprising a pile fabric with piles resembling
grass disposed upon a firm, stable subsurface and
top-dressed with sand containing a small amount of
moisture modifying material. The sand top-dressing
compac-ts to form a dense, hard layer. This surface
is well suited for tennis courts and also can be
used for other games. Surfaces o~ this type are not
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entirely satisfactory for fields for contact spor-ts
because the compaction of the top-dressing limits
the shock absorbing ability of -the surface and because
the sand top-dressing is only sligh-tly less abrasive
than non-compacting angular particle dressings.
Playing surfaces have also been constructed
with compacted sand top-dressings and resilien-t under-
pads as described in U.S. Patent No. ~,389,435. These
surfaces have outstanding shock absorbing character
and provide a natural turf-like feel for players
walking or running thereon. They are particularly
well suited for ball control games such as golf,
tennis, lawn bowling, cricket and the like. However,
the abrasiveness of the compacted sand top-dressing
remains a problem in contact sports where players not
infrequently fall or are knocked down on ~he playing
surface. Moreover, the use of a resilient underpad
substantially increases the cost of the playing surface
and simultaneously decreases the service life of the
surface since the underpads deteriorate over time.
There remains a need for a highly durable,
less expensive synthetic turf playing surface which
closely slmulates the appearance and physical character
of natural turf without presenting an abrasive surfaceO
There is a particular need for a syn-thetic -turf playing
surface which does not give the -feeling of running or
walking across a springy or spongy surEace.
Objects of the Invention
:[t is therefore an objec-t of the present
invention to provide a playing surface for athletic
games which is particularly well adapted for use as
a playing field for contact sports where players may
fall or be knocked down on the playing surface.
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A further object of the present invention
is to pro~ide a playing sur:Eace for athletic games
which when used for contact sports provides good
shock absorption.
Another object of the present invention
is to provide a playing sur:Eace for athletic games
which does not present a highly abrasive surface.
A futher object of the present invention
is to provide a playing surface for athletic games
which is less expensive to construct and has a
longer service life than surfaces with resilient
underpads.
It is also an object of the present
invention to provide a playing sur~ace for athletic
games which is top-dressed with readily available
materials.
Another object of the invention is to
provide a playing surface which is safer than prior
art surfaces.
Another object of the present invention
is to provide a playing surface for athletic games
which is easier and less e~pensive to maintain than
natural turf.
It is also an object of the present
invention to pro~ide a playing surface for athletic
games which is more durable in use than natural
turf.
A further object of the present
invention is to provide a playing surface for athletic
games which provides a natural footing for a player
running or walking thereon.
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Summary of the Invention
These and other objects of the invention
are achieved by providing a playing surface for
athletic games comprising:
a firm, stable subsurface;
a pile fabric having a flexible backing
and normally upstanding pile elements resembling grass;
the length of said pile elements being
substantially uniform and lying in the range from about
1/2 to about 2 inches; and
a compacted top-dressing layer comprising
a mixture of from 25 to 95~ resilient particles and
from 5 to 75% fine sand interspersed on the backing
among the pile elements to a substantially uniform depth.
The combination of subsuxface, pile fabric
and top-dressing comprising resilient particles provides
excellent shock absorption and a natural foo-ting for
players without presenting an abrasive surface. It is
less expensive to construct than axtificial turfs having
resilient underpads and is more durable and easier to
maintain than natural turf. The playing surface of the
invention eliminates the feeling of walking or running on
a springy or spongy surface which is encountered with
conventional artificial turfs using foam underpads.
Br_ef Description of the Drawlng
The invention will be explained in further
detail with reference to the accompanying drawing
which is a sectional view through an athletic playing
surface according to the present invention.
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Detailed Description of Preferred
~mbodiments
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The figure depicts a sectional view
through a playing surface according to the present
S invention. Playing surface 1 starts with a
firm, stable subsurface 2 upon which the remainder
of the playing surface is constructed. A moisture
barrier layer 3 i5 disposed over subsurface 2.
A pile fabric 4 with yenerally upstanding pile
elements resembling grass is positioned on top of
moisture barrier 3. In the drawing, the pile
fabric 4 is depicted as a woven fabric backing 5
through which a plurality of segments of multi-
filament yarn 6 have been tufted to form the
upstanding piles. At the free ends of the tufts,
the individual filaments 7 can be seen. Among the
pile elemenls on the backing there is a compacted
layer of top-dressing 8 comprising a mixture of
from 25 to 95~ resilient particles and fxom 5 to 75
fine san~.
Subsurface 2 establishes the contour of the
playing surface. In order to provide a good playing
surface, the subsurface must be smooth. Subsurface
2 should be sufficiently compacted that lt will not
settle or shift after installation of the playing
surface but will provide a firm, stable foundation
for -the playing surface~ Subsurface 2 may consist
of concrete or asphalt pavement, compacted clay,
gravel rolled into ordinary dirt or any of a number of
other firm materials. A four inch thick la~er of
traffic bond provides a particularly suitable sub-
surface. Adequate subsurface drainage should be
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provided. For most games, a flat, generally
level surface is needed. A slight slope may be
provided to facilitate surface drainage.
Moisture barrier :Layer 3 functions to
reduce water penetration and heaving and to
protect the surface from ground moisture. If the
subsurface consists o~ concrete or asphalt pavement,
moisture barrier layer 3 may be dispensed with.
A suitable moisture barrier layer may be Eormed
with polyethylene sheeting between 2 and 10 mils
thick such as is sometimes used as a vapor barrier
in pouring concrete. A 6 mil thick sheet has been
found to produce excellent results. Another suit-
able material for the moisture barrier layer is
commercial asbestos roofing felt between 30 and
100 pound weight, preferably about 70 pound weight.
The pile fabric 4 may be a tufted or
knitted pile fabrlc or any other suitable construc-
tion. For reasons or cost as well as flexibility
of design, a tufted fabric is generally preferred.
~he fabric backin~ may be any suitable woven~
felted or extruded web. A particularly preferred
backing is a woven polypropylene fabric having a
weight of about 25 oz. per s~uare yard. Tufted
through the backing are segments of a multi-~ilament
yarn made from 3/8 gauge polypropylene ribbon 5 mils
thick which is slit and twisted to form a plurality
of thin filaments. Normally each strand of yarn
will compr:ise from 20 to 50 or more individual
filame~ts. In order to provide a pleasing natural
appearance, the polypropylene is typically dyed a
green color~ Suitable color stabilizers are in
corporated into the polypropylene to prevent
color degradation resulting from exposure of the
playing surface to the elements over a period of
time. The density of the tufts may vary depending
upon the weight of the multi-filament yarn and the
intended use of the playing surface. ~or the
previously mentioned 3~8 gauge,5 mil thick poly-
propylene ribbon yarns, tuft densities ranging
from 8 to 24 tufts per square inch are useful.
This corresponds to stitch rates from about 3 to
10 about 8 stitches per inch on conventional tufting
machines which produce 2 and 2/3 rows of tufts per
inch. The length of the pile elements may range
from about 1/2 to about 2 inches. In most
instances, -the pile length will be between about
15 1 and about 2 inches. The tufted piles function
to stabilize the top-dressing against shifting
and/or erosion and also give color to the playing
surface.
~he playing surface is top-dressed with
20 a layer of compacted material comprising a
mixture of resilient particles and fine sand.
Preferably the mixture comprises from 25 to 95
volume percent resilient particles and from 5 to
75 volume percent fine sand. Proportions are
25 expressed in terms of volume percent in order to
- compensate for the varying densities of different
types of resilient particlesO Most preferably,
the top-dressing comprises from about 50 to about
90 volume percent resilient particles and from
about 10 to about 50% fine sand.
~ variety of different resilient materials
may be used for the resilient particles. One
particularly preferred material is granulated cork.
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Commercially available cork granules such as used in
insulation materials or in the molding of gaskets are
generally suitable.
Another particularly preferred resilient
material is rubber particles. In addition to natural
rubber, synthetic rubbers may be used. Synthetic
rubbers such as styrene-butadiene rubber, butyl rubber,
cis-polyisoprene rubber, neoprene rubber, nitrile rubber
and urethane rubber may be used.
Beads of synthetic polymers not normally
considered to be rubbers may also be used. These include
the vinyls, e.g., vinyl chloride, vinyl ethers, vinyl
acetate etc., the acrylates and methacrylates, polyvinyli-
dene chloride, urethanes, polyamids and polyesters.
Synthetic polymer foam particles are also very
advantageous in the top-dressings of the invention. Vinyl
foams, e.g., polyvinyl chloride foams, polyvinyl ether foams
and the like, foamed polystryene, foamed polyurethanes and
foamed polyesters may be used. Of course, foamed natural
20 rubber is also useful. Foams may be either blown foams
or whipped foams. Preferred foams have particle densities
between about 12 and about 25 pounds per cubic foot.
Indoors or in an arid climate, sponge
granules and/or open-celled foam particles may be
25 used as or incorporated into the resilient particles.
Such particles may themselves take up and hold
moisture and thus, may reduce the need for special
moisture modifying materials in some cases.
Plasticizers, antioxidants, antistatic
30 agents and other additives known in the art may,
of course, be incorporated in the resilient particles.
Often it is desirable to use a mixture of
granules of two or more different resilient materials
as the resilient particle components of -the top-dressing.
35 For example, a mixture of cork granules and rubber
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particles formed by shedding rubber tire stock
with fine sand makes an excellent top-dressing.
The size of the resilient particles
may vary between about 4 and about 70 U.S. screen
mesh size. Preferably the resilient particles
will lie between about 6 and about 60 V.~. screen
mesh size. A range o sizes is preferred to a
single uniform size because it is easier to obtain
a suitably compacted surface with a range of
particle sizes. Fine sand is used in top-dressin~
the playing surface of the invention because large
sand granules tend to be more highly abrasive.
Fine sand particles also fill the interstices between
the resilient particles thereby forming a more dense
compacted top~dressing layer. The sand utilized
in the top~dressing of the invention is generally s~ller in
size than 30 U.S. screen mesh size. Preferably,
sand between about 40 and 200 U.S. screen mesh size
is used.
The depth of the top-dressing may range
between about 50% of the height of the piles and
substantially even with the tips of the pilesO
Preferably, the depth of the top-dressing will lie
between about 75~ and about 95~ of the height of
~he piles. q'he projection of the piles above the
top-dressing may range from as little as 1/1~ inch
to as much as 3/8 inch. Most preferably, the
projection of the pile elements above the top-dressing
will lie between about 1/8 and about 1/4 lnch.
Optionally, a portion of the resilient
particles may be replaced by a moisture modi~ying
material as described in U.S. Pa-tent No. ~,044,179.
A particularly preferred moisture modifying material
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is vermiculite. ~nother useful moisture modifying
material is calcined clay. The presence of a moisture
modifying material is helpful in arid climates,
such as the Southwestern United States, to maintain
a minimum moisture content in the dressing which
enhances cohesiveness of the compacted dressing and
prevents excessive dusting. As previously mentioned use
of sponge granules or open celled foam particles in
the resilient material may reduce the need for a
special moisture modlfying material. Use of 10~ or more
fine sand having a particle size smaller than about
60 U.S. screen mesh size also may reduce or eliminate the
need for the moisture modifying material, since the
fine sand also tends to hold molsture in the top-
dressing layer. In moist climates, such as the Gulf
Coast area of the United States, the use of a special
moisture modifying material generally will not be
necessary. The moisture modifying material may comprise
up to 20 volume percent of the -top-dressing. In most
cases where moisture modifying material is included in
the top-dressing, between about 2 and about 16 volume
percent will be utilized.
I~ desired, a small proportion of coloring
material may be incorporated in the dressing to enhance
the appearance ^f the playing surface.
The top-dressing functions to stabilize
the piles of the pile fabric and prevent graininess.
Qrdinarily, the pile elements of a pile fabric will
have a chacteristic grain (i.e.~ tendency to lay in a
given direction related to the direction in which
the material passed through the production machinery).
The top-dressing counteracts this tendency and prevents
the playing surface from having a noticeable grain. The
top~dressing also functions to absorb much of the shock of an
object impacting on the playing surface and improves the
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footing of a player running or walking across the
surface, particularly when making cuts or sharp
turns. The non abrasive character of the top-dressing
and the controlled pile height projecting above
the top-dressing make the playing surface of the
invention much less li]cely to produce rug burns or
abrasions when players do fall on the surface.
Optionally, the underside of the pile
fabric may be provided with a resinous coating
which functions to secure the tufts in place, to
increase the dimensional stability of the backing
and to increase the moisture resistance of the
backing. A preferred manner of coating the backing
is to contact the back of the pile fabric with a
solution of vinyl polymer in a volatile,non-aqueous
solvent and then subject the pile fabric to a heat
treatment to evaporate the solvent and cure the
vinyl polymer coating. Conventional polyvinyl
chloride, polyvinyl acetate or natural or synthetic
rubber latex coatings can be utilized. The resinous
coating is sometimes referred to as a secondary
backing. It may also be considered a moisture barrier.
Thu~, it may be possible to omit moisture barrier
3 if the back of the pile fabric is provided with a
suitable resinous coating.
The pile fabric may also be optionally
subjected to a heat treatment to induce a slight
crimping of free ends of the filaments of the piles.
Crimping the pile filaments provides the pile fabric
with a firmer, denser, slightly roughened surface which
results in a more natural appearance of the final
playing surface and also improves the footing for
athletes playing on the surface. Crimplng the piles
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may also be resorted to in order to increase the
resistance to objects rolling across the playing
surface and provide a "slower" playing surface.
For polypropylene yarn piles, suitable crimping
S may be effected by passing the pile fabric
through an oven at 285F. for a period of 10 to
12 minutes. Adjustments to temperature and time
may be required depending upon the charac-ter of
the multi-filament yarn used in the piles and
the degree of crimping desired.
The character of the playing surface
can be controlled by varying its construction.
For example, the shock absorbing character may be
increased without giving the surface a springy or spongy
feeling by increasing the length of the piles and
the depth of the top-dressingO Use of synthetic
polymer foam particles in place of rubber shavings
will increase the resilience of the surface. De-
creasing the projection of the pile elements above
the top-dressing will produce a "faster" surface.
It is thus possible to tailor the character of the
playing surface in order to provide the type cf
play desired.
Installation of the playing surface
according to the invention begins with proper
preparation of the subsurface to assure a stable,
firm surface which will not shift or settle and
which has smooth contours free of waves or ripples.
Once the subsurface is prepared, the moisture
barrier, if one is to be used, can be put down. The
pile fabric is then spread out over the moisture
barrier and trimmed as needed. ~d~acent sections
of the pile fabric must be seamed together~ Seaming
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can suitably be effected either with hot seaming
tape or with adhesive and tape. If the character
of the subsurface permits, spikes may be driven
through the pile fahric and moisture barrier to
further stabilize the playing surface against
shifting. This may be advisable in areas where
stress is repeatedly applied to the playing surface
such as near the goal line of a football field.
A series of 7 inch spikes arranged at 6 to 18 inch
intervals in a zig zag pattern has been found to
be helpful. After the pile fabric i5 in place,
the top-dressing is applied with conventional
spreading equipment. A mixture of the different
particles may be applied simultaneously from a
single spreader. However, it is important to guard
against segregation of the particles in the hopper
of the spreader which can lead to non-uniform
application. It is also possible to apply the dif-
ferent particles individually from separate spreaders
by passing the spreaders in sequence over the playing
surface, the relative proportions of part~cles
being controlled by corresponding adjustment of the
spreader outlet openings. Dual unit spreaders with
separate hoppers and flow controls for each spreader
unit can also be used. During application of the
dressing, the piles must be periodically brushed to
the upright position as needed. Brushing or sweeping
also helps to level out the top dressing. ~fter
application of the top-dxessing, the playiny surface
is ready for use.
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Example 1
A baseball field is constructed with
a tufted pile fabric having grass-like pile
elements 1 1/2 inches long laid over the infield
and base line areas. The pile fabric is top-dressed
with a dressing comprising ,a mixture of 56~ virgin
vinyl (polyvinyl chloride) foam beads having
a particle size between 10 and 40 U.S. screen mesh,
40% fine sand having a particle size between 40 and
140 U.S. screen mesh and 4% vermiculite having a
particle size between 10 and 40 U.S. screen mesh.
The depth of the top-dressing is 1 5/16 inches.
Example 2
A fsotball field is constructed by
laying a pile fabric having grass-like piles
2 inches in length over a firm subsurface and
dressing the pile fabric with a mixture of 40
volume percent cork granules having a particle
size between 6 and 20 U.S. screen mesh, 35%
shredded tire stock having a particle size between
12 and 45 U.S~ screen mesh and 25% fine sand
having a particle size between 60 and 170 UOS.
screen mesh. The depth of the top-dressing is
1 3/4 inches~
Example 3
A soccer field is constructed by
laying a pile fabric having grass-like pile elements
1 1/4 inches long over a stable subsurfac~ and
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applying a top-dressing comprising 50 volume percent
shredded urethane foam particles having a particle
size between 6 and ~0 U.S. screen mesh size and
50 volume percent fine sand having a particle size
between ~lO and 200 U.S. screen mesh size over the
pile fabric. The depth of the top-dressing is 1 inch.
Example 4
Another baseball field is construc-ted
similar to the field of Example 1 except that the top-
dressing comprises by volume 20% shredded tire stock,
10% vermiculite, 20% fine sand having a particle
size smaller than 60 U.S. screen mesh size, 25%
cork granules and 25% virgin vinyl foam. This
field is especially adapted to the climate of
Southern California.
Example 5
Another football field was constructed similar
to the field of Example 2 except the top-dressing
comprises by volume 25% shredded tire stock, 15%
vermiculite, 10% fine sand having a particle size smaller
than 60 UOS~ screen mesh size, 25% cork granules and
25% virgin vinyl foam. This surface is especially
adapted to the climate of the border states.
Example 6
_ =_
Another soccer field is constructed similar
to th~ field of Example 3 except that the top-dressing
comprises by volume 10% shredded tire stock, 15%
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vermiculite, 30~ fine sand having a particle size
smaller than 60 U.S. screen mesh size, 25% cork
granules and 20% virgin vinyl foam. The depth of the
top-dressing was 1 1/8 inch.
Playing surfaces according to the present
invention present a very attractive appearance closely
resembling the appearance of natural grass turf. Once
installed, the playing surfaces of the invention have
a very low maintenance cost because they require very
little upkeep. At the same time, the playing surfaces
of the invention are much more durable than natural
turf or earthen surfaces and can be used for virually
continuous play for lon~ periods without exhibiting
adverse wearO Playing surfaces of the invention
provide outstanding player feel. That is to say,
they feel to a player as though they were a natural
surface with none of the unnatural springiness or
sponginess hitherto characteristic of artificial turf.
Furthermore~ they are very comfortable and easy on
the legs and eet of the player, particularly in com-
parison with hard pavements. Another advantage is the
fact that the characteristics of the playing surface can
be readily adjusted according to the type of play de-
sired. Suitable top-dressing materials are readily
available. The surfaces-~f the invention are also
much less abrasive than prior top-dressed surfaces.
The foregoing embodiments have been
described merely as examples of the invention and are
not intended to limit its scope~ Since modifications
of the described embodiments ma~ occur to persons
s~.illed in the art, the scope of the invention is to
be limited solel~ by the scope of the appended claims.
