Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR FORMING SYNTHETIC TURF GAME SURFACE
TECHNICAL FIELD
This invention relates to a method for forming a synthetic turf game playing
surface which closely simulates the feel and the playing characteristics of
natural
grass turf used for golf courses, tennis courts and other games played upon
grass
surfaces.
BACKGROUND OF INVENTION
Synthetic turf game playing surfaces are formed of pile carpets whose piles
or strands are fastened to a base or backing sheet. The piles or strands are
typically
formed of thin, flat, narrow strips of a suitable plastic material which may
be gathered
into tufts fastened to the base sheet. The base sheet may be a woven cloth,
formed
of suitable plastic material, with an adhesive type coating or binder applied
to the
base or backing to anchor the strands thereto. The particular construction of
the pile
carpet may vary considerably. In general, the carpet is made of a weather
resistant
or "outdoor" type of construction.
Such carpets are typically laid upon a prepared ground surface to form a game
playing surface intended to simulate a natural grass playing field surface.
For some
game purposes, a resilient underpad may be placed beneath the carpet and upon
a
firm support surface to provide some shock absorbent effects. In addition, in
some
instances, sand or other particulate materials may be placed in a layer upon
the upper
surface of the carpet base sheet and around the strands. An example of this
type of
construction is shown in U.S. Patent No. 4,389,435 issued June 21, 1983 to
Frederick
T. Haas, Jr. Another example is shown in U.S. Patent No. 4,637,942 issued
January
20, 1987 to Seymour A. Tomarin.
The synthetic plastic strips which form the blades, when made of an
appropriate plastic, such as stretch oriented polypropylene extruded, thin and
narrow
strands, tend to shred longitudinally during use. That is, during the
movements and
forces of players upon the surfaces thereof, the ends of the strands tend to
split into
a plurality of slivers. These intertangle with each other and, where used,
with the
sand of a sand layer located on the carpet. An example of this effect is
disclosed in
U.S. Patent No. 4,336,286 issued June 22, 1982 to Seymour A. Tomarin.
An attempt to substantially increase the shredding or fraying of the synthetic
blades to provide a dense, intertwined mat-like surface, by means of
sandblasting the
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blades, is disclosed in U.S. Patent No. 5,356,344 issued October 18, 1994 and
U.S.
Patent No. 5,373,667 issued December 20, 1994, both to Alain Lemieux for a
synthetic turf and a method of making a synthetic turf, respectively. In these
patent
disclosures, the grass-like synthetic blades are frayed by sandblasting the
blades from
above the carpet surface. Said blades may be made, for example, of
polypropylene,
nylon, polyester and the like, thin, narrow strips. Their upper, free ends are
frayed
or shredded by a blast of sand particles striking them. The frayed or shredded
ends
tend to intertwine or entangle to form a matted surface. However, the force of
the
sand blast, which is required to produce sufficient shredding, also tends to
crush or
permanently deform the blade strands downwardly against the base sheet of the
carpet. This affects the desired uniformity, pliability and feel of the
finished artificial
turf surface.
Therefore, this present invention relates to an improvement to the method for
shredding or fraying the artificial, plastic blade-like strands which avoids
crushing, or
permanently compressing or deforming or similarly damaging the blade strands
by the
sandblasting.
SUMMARY OF INVENTION
This invention contemplates shredding or fraying the upper end portions of the
synthetic plastic blades into finely divided slivers, which entangle and
intertwine with
each other to form a dense, matted surface, by supporting the artificial turf
carpet
upon a resilient, cushioning underpad during the sandblasting step. Further,
this
invention contemplates, as an option, further separating the finely divided
slivers of
each strand from each other while entangling the slivers of adjacent strands
better
and more densely packing the mat formed from the intertwined slivers of
adjacent
strands, by spraying the strands with high pressure water, after the
sandblasting step
or by brushing the sandblasted surface or by both water spraying and brushing.
An object of this invention is to provide a densely matted surface upon the
blade forming strands of the synthetic pile carpet by a sandblasting, or
similar sand
like particulate blasting procedure, without crushing or permanently
compressing the
strands as a result of the procedure.
Another object of this invention is to provide a simple sandblasting type of
procedure for shredding or fraying the upper ends of the pile strands of a
synthetic
turf carpet so as to form a densely matted playing surface comprising
entangled or
intertwined finely divided slivers formed on the ends of the strands and, in
addition,
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maintaining the sand layer deposited upon the base sheet of the carpet by the
covering mat.
Still another object of this invention is to provide a method for dividing
into fine
slivers the upper ends of the synthetic strands of a synthetic turf pile
carpet rapidly,
inexpensively, and without crushing, compressing or otherwise permanently
compacting the otherwise upright blades formed by the strands.
These and other objects and advantages of this invention will become
apparent upon reading the following description, of which the attached
drawings form
a party.
DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic, fragmentary, cross-sectional end view of a synthetic
turf
pile carpet.
FIG. 2 is a schematic view similar to FIG. 1, showing the carpet positioned
upon a cushioning underpad.
FIG. 3, is a view similar to FIG. 2, illustrating the step of sandblasting the
upper end portions of the blade forming strands of the carpet.
FIG. 4 schematically illustrates the dense mat formed by the upper, shredded
slivers and a layer of sand deposited by the sandblasting step upon the upper
surface
of the carpet base sheet.
FIG. 5 schematically illustrates the steps of water washing for further
severing
the slivers of the same strand while entangling or intertwining adjacent
slivers to form
the dense mat surtace, and also illustrates a rotary brush treating the upper
surface
of the mat.
FIG. 6 schematically illustrates a single U-shaped strand whose free upper
ends have been shredded into fine slivers by the sandblasting treatment.
DETAILED DESCRIPTION
FIG. 1 schematically illustrates a fragment of a synthetic turf pile carpet.
The
carpet has numerous, closely spaced, tufts 11 which are formed of U-shaped,
fiat,
narrow bent strips or strands 12 that form artificial grass blades. The turfs
are
fastened upon a base or backing sheet 14. This sheet may be made of a woven
cloth
or the like fabric material formed of stable, weather resistant, plastic such
as
polypropylene or nylon fibers or the like. The specific cloth must be flexible
but,
otherwise, may vary as to its composition.
As schematically illustrated in FIG. 1, the tufts are inserted around or
through
the fibers forming the base sheet. A suitable binder layer 16 may be applied
to bind
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the turfs and base sheet together. The binder may be formed of a polyurethane
adhesive
material or some other suitable, outdoor usable adhesive which remains
resilient or
flexible.
The carpet is placed upon a resilient cushion underpad 18. This underpad is
formed of a relatively thick sheet or pad of a resilient plastic material. A
preferred
underpad material is expanded bead polypropylene molded into an open cell pad
or sheet.
The sheet may be approximately between about l2mm to 50mm in thickness, with a
preferred density of approximately 0.038g/cm'. The density may be varied
within the
range of between about 0.024 to 0.048g/cm'. The thickness of the pad,
depending upon
the particular results desired, may also be varied to a slightly less than 6mm
thickness to
as much as up to 305mm thick.
The material utilized for the underpad may be varied. That is, other
resiliently
compressible plastic materials may be used, such as rubber-like polyurethane
or polyvinyl
chloride or the like materials.
With the carpet positioned upon the resilient cushion underpad 18, the upper
portions of the strands or blades are sprayed with a blast of sand 20 or
similar sand-like
particulate material from a pressurized nozzle 21 . This blast of sand shreds
each of the
strand upper end portions into numerous slivers 23 (see FIG. 6). The slivers
extend
laterally and intertwine and entangle together to form a dense mat 24.
The spray nozzle 21 may be moved back and forth from one side to the other in
a scanner-like movement across the upper end portions of the blades formed by
the
strands. The exact pressure of the sand blast spray may be varied. However, a
preferred
blast pressure is in the range of 690 to 830kPa. The blast may use silica sand
of a size
range of between about 1 6 to 40 mesh and, preferably, in the range of between
about
20 to 24 mesh or even more preferably in the approximate area of 24 mesh. The
sandblasting is conducted at a speed of movement and for a length of time
which is
sufficient to shred the strand end portions into finely divided slivers. For
example, the
upper, about one-fifth portions of the blades may be shredded into fine
slivers that remain
attached to their respective blades.
The force of the sand blast, depending upon how long, that is, how slowly the
blast is moved across the surface of the carpet, not only shreds the blades,
but also
forces the sprayed sand downwardly between the strands to deposit sand upon
the
surface of the base sheet of the carpet. The faster the movement of the
sandblast across
the surface of the pile carpet, the slower is the playing surface. That is,
the speed of
rebound and roll of a ball is inversely proportional to the speed of movement
of the
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sandblast across the blades. The sand layer 25 formed by the deposited sand
may be
kept upon the base sheet of the carnet where it is maintained in position by
the dense
intertwined or entangled sliver mat formed cn the upper ends of the blades.
By way of example, a blade height of approximately 16mm above the surface of
the base sheet, which is useful for a golf green surface may have its upper 20
to 33
percent of its length shredded into fine slivers. In this example, strands
which are about
1.78mm wide and about 0.051 mm thick, so that they are approximately
rectangular in
cross-section. The strands are bent in half to each form two blades, and are
gathered into
tufts of about 9-1 1 strands. These form about 18 to 22 blades per tuft. The
upper about
20 percent of each blade may be severed into about four slivers. Thus, each
tuft may
have as many as 70 to 80 slivers whose lower ends remain attached to the blade
body
and whose upper ends extend off into transverse directions to entangle with
the slivers
of adjacent strands. The slivers are about 0.51 mm in width and about 1.905mm
to
3.175mm long.
Following the sandblasting step, the carpet may be further treated with a high
pressure water spray 27 applied by a pressurized nozzle 28. The water spray,
which, for
example, could be at a roughly 690 to 1035kPa nozzle pressure, acts like a
wash which
further separates adjacent slivers that were shredded, but not fully separated
from each
other on the same strand, and simultaneously further twists, bends and
entangles the
slivers of one strand with slivers on its adjacent strand to further densify
the mat formed
by the intertwined slivers. This forms a denser and more uniform mat surface.
The mat surface may be further treated by brushing it with, for example, a
rotary
brush 29 applied upon the mat surface to make the mat surface more uniform.
The water
jet and the brushing also make the sand layer more uniform. The water jet and
the
brushing may be performed successively or at the same time as schematically
illustrated
in FIG. 5.
Significantly, the force of the sandblasting is sufficiently absorbed through
the
resilient cushioning pad beneath the carpet to prevent the strands from
becoming crushed
or permanently deformed or compacted by such force. That is, the strands
remain or
return to their upright positions after their upper ends are sand blasted. The
upright
positions are maintained, in part, by the deposited sand layer 25. Similarly,
the strands
and the mat 24 hold the sand layer 25 in place.
In the cases where the piles or upright strands of the pile carpet are tilted
or curved
in one direction relative to the plane of the carpet base sheet, the
sandblasting tends to
vertically straighten the strand portions that are located beneath the
slivers. Then, the
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sand layer helps to keep the mare vertical positioning of such strands.
The sand layer filling may be kept in place and the matted carpet may be
rolled and
transported to the site where it is to be spread and used with the sand layer.
This permits
the sand blast treatment to be performed either on the site of the game
playing field or
at any work site or factory area where the application of the sand, water and
brushing
treatments may be more conveniently performed. Thus, the treated carpet may be
unrolled and installed at the game surface site when desired and the sand
layer will remain
in place and additional sand at the use site for a sand filling may not be
needed.
As mentioned, the particular pile carpet construction may be varied. However,
an
example of a useful carpet for a golf green comprises synthetic grass of
approximately
7600 deniers, an approximate density of 0.142g/cm2, and a fiber height of
approximately
16mm combined with an underpad of 12mm to 50mm in thickness.
Similarly, an example of a fairway portion of a golf course may be in the
range of
approximately 7600 deniers synthetic grass, an approximate density of 0.142 to
0.187g/cm2, with a fiber height of about 16 to 50mm with an underpad of at
least about
25mm thick.
Still another example of the synthetic grass would be a weaving standard in
the
range of 3,600 to 10,000 deniers, with 13 to 22 stitches per 76mm, 3/1 6 gage
and a
density of about 0.1 15 to 0.220g/cm2~
The preferred beaded polypropylene material is commercially available for use
in
molding the underpads of the desired density. By way of example, expanded
polypropylene beads are available under the trade name of NEOPOLEN P, which is
a
trademark of BASF. This material is available at densities of 0.021, 0.030 and
0.045g/cm' and is referenced by BASF trademark EPERAN PP, types PP45, PP30 and
LBS
20. When the beads are molded in appropriate slab molding equipment at times
and
pressures known to those skilled in the art, the resulting pad, produced in
the desired
thickness, should have a density in the range of 0.024 to 0.048g/cm' with an
open cell
construction. The specific density selected may be varied for specific sport
activities. For
example, a density that has been found satisfactory for a golf green is in the
range of
approximately 0.038g/cm'.
The particular technique useful for the sandblast treatment involves
sandblasting
under pressure using commercially available sandblast equipment. A pressure in
the range
of 690 to 830kPa is preferred but the pressure may be varied somewhat, such as
a low
of about 560kPa. By moving the spray nozzle in back and forth movements across
the
surface of the carpet, the projected spray is sequentially concentrated upon
small portions
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of the carpet. The angle of the projected spray may vary but a preferred
angle, which
appears to be effective in a minimum of time, is an angle of about 70 to 80
degrees
relative to the plane of the carpet. The distance of the nozzle from the
strands may vary,
with the equipment operator selecting the optimum distance by visually
observing the
shredding action of the spray. An example of the distance may be in the range
of about
1 .2 to 1.5m, depending upon the speed of movement of the nozzle across the
carpet.
The resulting synthetic turf is particularly useful for golf courses, such as
the green
portions, approach portions, Tee-off portions and fairway. The turf surface
also may be
used for tennis courts, football or soccer as well as for other sports which
utilize grass
surfaces. Examples of these are grass hockey, croquet, grass bowling, children
playground, baseball, and the like. The surface of the artificial turf
produced by the
method herein, closely simulates the feel and action or rebound produced by a
natural
grass surfaced playing field. The completed, matted surface very closely
simulates the
natural grass surfaces required for golf courses and the similar playing
fields.
1 5 The turf produced by this method may also be useful as a covering upon a
rooftop
or patio or deck surface. As a covering, turf will form an insulation and a
waterproofing
material for such surfaces.
This invention may be further developed within the scope of the following
claims.
Accordingly, it is desired that the foregoing description be read as being
merely illustrative
of an operative embodiment of this invention and not in a strictly limiting
sense.
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