U.S. patent number 3,900,656 [Application Number 05/372,207] was granted by the patent office on 1975-08-19 for synthetic structure for covering a surface.
Invention is credited to John C. Schmidt.
United States Patent |
3,900,656 |
Schmidt |
August 19, 1975 |
Synthetic structure for covering a surface
Abstract
A covering for a subsurface to provide a surface thereon
suitable for recreational activities such as football, includes a
top wear surface layer which may provide, for example, simulated
grass, sometimes called synthetic turf and a moisture protected
underlayment layer between the top surface layer and the subsurface
composed of strands or noodles of a synthetic plastic material in
an open celled foam binder, each strand being comprised of a
multitude of closed cells containing encapsulated gas. The gas in
the closed cells may be a non-toxic, non-corrosive heavy gas to
which the strand material is not porous and so the underlayment can
breathe by expelling air from the open celled foam binder when
compressed and yet retains the pneumatic resilience of the trapped
gas.
Inventors: |
Schmidt; John C. (Haddonfield,
NJ) |
Family
ID: |
23467155 |
Appl.
No.: |
05/372,207 |
Filed: |
June 21, 1973 |
Current U.S.
Class: |
428/215; 428/95;
428/319.7; 428/17; 428/305.5; 428/398 |
Current CPC
Class: |
D06N
7/0089 (20130101); E01C 13/08 (20130101); B32B
11/10 (20130101); B32B 13/14 (20130101); B32B
2262/0276 (20130101); Y10T 428/24967 (20150115); Y10T
428/249992 (20150401); Y10T 428/23979 (20150401); Y10T
428/2975 (20150115); B32B 2305/02 (20130101); Y10T
428/249954 (20150401); B32B 2471/00 (20130101) |
Current International
Class: |
D06N
7/00 (20060101); E01C 13/08 (20060101); B32b
005/18 () |
Field of
Search: |
;161/21,62-67,159,160,161,162,170,178,190,231,55,57,60,143
;273/25,55R,176J ;260/2.5BE,2.5L,2.5B ;5/361B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: McCamish; Marion E.
Attorney, Agent or Firm: Dunn; Robert T.
Claims
What is claimed is:
1. In a recreational surface covering a subsurface, including a top
wear surface layer selected for a recreational activity, at least
one underlayment layer between the top surface and the subsurface
comprising,
an integral layer containing substantially uniform adhering
strands,
each strand being a closed cell gas inflated organic polymeric
material having polyhedral-shaped cells defined by film-like cell
walls about 2 microns thick, substantially impervious to the gas
contained therein,
each strand being about 50 mils in diameter and about 3 inches
long,
the strands being oriented substantially parallel to the plane of
the layer in crossing directions,
said strands being bound in a resilient open celled binder material
such that the underlayment can be compressed to expell air from the
open cells of the binder and yet retains the pneumatic resilience
of the trapped gas in the closed cells in the strands, and
means providing a moisture barrier between the underlayment and the
environment around the surface,
the thickness of the underlayment layers being at least about 0.5
inches, said thickness being selected to provide in combination
with other layers a recreational surface suitable for selected
recreational activity.
2. A recreational surface as in claim 1 wherein,
the strands are arranged substantially contiguous to each other in
the binder material.
3. A recreational surface as in claim 1 wherein,
the plastic material of which the strands are composed is a
compound of polyethylene terephthalate.
4. A recreational surface as in claim 1 wherein,
the open celled binder material is a polyurethane foam.
5. A recreational surface as in claim 1 wherein,
the gas trapped in the closed cells in the strand is
perfluorocyclobutane.
6. A recreational surface as in claim 1 wherein,
at least two separate underlayment layers are provided between the
top surface and the subsurface and
each of said separate layers is constructed of the same kind of
strands and binder material.
7. A recreational surface as in claim 6 wherein,
the two separate layers are different thicknesses.
8. A recreational surface as in claim 1 wherein,
the underlayment layers include a layer of non-porous flexible
plastic material immediately beneath the top wear surface.
9. A recreational surface as in claim 8 wherein,
the non-porous flexible plastic layer is polyvinyl chloride and is
attached to the layers adjacent thereto by an adhesive.
10. A recreational surface as in claim 8 wherein,
the non-porous flexible plastic layer is a water resistent
elastomeric material up to about 3/16 inches thick.
Description
BACKGROUND OF THE INVENTION
The present invention relates to resilient surface coverings and
more particularly, to surface coverings for recreational purposes
for indoor or outdoor use such as football fields, baseball fields,
tennis courts, tracks and gymnasiums. Heretofore, a number of
synthetic turf recreational surface coverings have been used
particularly for football fields. These coverings provide much
needed shock dissipating qualities and at the same time they are
rugged, have long life and require a minimum of maintenance. The
combination of problems which is encountered in providing a
suitable artificial turf particularly for a game like football are
numerous. For example, turf must have the proper tactile properties
which enable a player to feel reasonably secure on the playing
field; the playing field must be shock absorbing to minimize injury
to the players; the qualities of the playing field should not be
unduly altered by changes in temperature and humidity and of
course, the synthetic turf must be rugged and tough and should have
long life and require a minimum of maintenance. A particular
problem of synthetic turf used on a football field is that the turf
must be sufficiently resilient to cushion the player and so
minimize injury and at the same time, the turf must not be too
resilient and must not "bottom-out" and it must have a high rate of
recovery.
The artificial turf services provided heretofore generally include
a top wearing layer which simulates grass and one or more
underlayment layers which provide the shock absorbing qualities
that contribute substantially to the "feel" of the turf. In the
past, the underlayment in particular, has not exhibited the shock
absorbing characteristics and the proper "feel" under the range of
environmental temperature and moisture conditions such a field is
normally exposed to.
SUMMARY OF THE INVENTION
In accordance with the primary purposes of the present invention an
underlayment layer or layers is provided between the top surface or
wearing layer which may have the texture and appearance of grass,
and a subsurface such as asphalt or a bituminous covering. The
underlayment disclosed in the present invention has effective use
with a wide variety of surfaces, many of which simulate grass and
is particularly effective for use with the simulated grass surface
described in some detail herein. Furthermore, the subsurface may be
asphalt, concrete, wood or other firm structure.
In accordance with the present invention, the underlayment layer or
layers between the surface layer and the subsurface includes
strands of a selected plastic material in a plastic binder such
that the strands are substantially contiguous with each other and
the thickness of the underlayment layer is many times the diameter
of the strands. Each strand contains a multitude of closed cells
which contain a selected relatively heavy non-toxic, non-corrosive
gas and the binder is an open celled foam plastic material. Thus,
when the underlayment is compressed, air is expelled from the open
cells of the binder and yet the pneumatic resilience of the trapped
gas in the closed cells in the strands is retained. Depending upon
the resilience and the "feel" desired, the fraction of the volume
of the underlayment provided by the strands can be varied. For
example, where the strands constitute as little as 1% of the volume
of the underlayment, substantial resilience is still provided.
It is one of the several objects of the present invention to
provide a composite artificial surface for a recreational field
having a synthetic underlayment which is substantially immune, in
so far as resilience and "feel" are concerned, to environmental
changes in temperature and humidity.
It is another object of the present invention to provide such a
surface which has improved resilience characteristics compared to
surface coverings available heretofore.
It is a further object of the present invention to provide a
surface covering for the purposes described herein which is
relatively more economical to manufacture than some of the surface
coverings already in use.
It is another object to provide such a surface covering and
particularly the underlayment using materials which are resistant
to fungus, molds, mildew, moisture and normal ambient range of
temperatures, the materials further being non-allergenic, non-toxic
and odorless with readily predetermined density and resilience
characteristics.
Other objects, features and advantages of the present invention
will be apparent in view of the following description of
embodiments of the invention which represent the best known uses of
the invention. The invention accordingly, comprises the elements
and combinations of elements, features of construction and
arrangements of parts which are exemplified in the structures
herein described and in the scope of the appended claims.
The several embodiments of the invention are described in the
accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-section elevation view of a portion of a first
embodiment of the invention;
FIGS. 2, 3, 4, 5 and 6 are cross-sectional elevation views of
portions of respectively second, third, fourth, fifth and sixth
embodiments of the invention; and
FIG. 7 illustrates greatly enlarged and somewhat schematically a
portion of a strand used in making the underlayment mat that
provides at least a part of the underlayments of the several
embodiments to illustrate the general nature of the strand.
Throughout the drawings, like numerals indicate like parts and in
the drawings, dimensions of certain other parts shown therein may
have been modified and/or exaggerated for the purposes of clarity
of illustration and understanding of the invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The resilient cushioning characteristics of the underlayment of the
recreational surfaces described herein is provided by strands or
noodles of a closed cellular plastic material in a binder of open
cellular plastic material. Generally, the volumetric ratio of
binder to strand is substantially greater than one and so the
underlayment mat can be said to be an open cellular plastic
material containing reinforcing strands or noodles of a closed
cellular construction, the closed cells containing an encapsulated
gas which is not permeant thereof. Toward this end, the
encapsulated gas is preferably a relatively large molecule,
non-allergenic, non-toxic gas.
The open celled binder or matrix makes its own contribution to the
compression and resilience characteristics of the underlayment and
of course, maintains the highly resilient strands in position with
respect to each other and distributes externally applied loads
uniformally to the strands.
A heavy load rapidly applied to the underlayment will quickly
evacuate virtually all of the air from open cells under
compression. The closed cells in the strands, however, even if they
contain air are pneumatic in the sense that the air molecules enter
and exit only by the relatively slow process of diffusion through
the closed cell walls. Hence, if a load is rapidly applied,
compression is resistant by the air within the closed cell as these
cells act as miniature balloons. Where the closed cells are filled
at least partially with a gas of high molecular weight there is
practically no diffusion of the gas molecules through the closed
cell walls. Thus, the parameters which are affective to determine
the softness, resilience and "feel" of the synthetic recreational
surface are numerous. The parameters include the volumetric ratio
of binder to strand, the density of the binder, the density of the
strand, the permeability of the closed cells to the gas contained
therein and the ratio of impermeant gas to air contained in the
closed cells.
Polymers suitable for preparing the binder or open celled resilient
matrix are well known in the art and include polyester and
polyether urethanes, and foam rubber, both natural and synthetic.
Open celled polyurethane matrices are preferred since they may be
prepared at very low densities and exhibit particularly
satisfactory adhesion to the strands. The strands are prepared from
polyethylene terephthalate which is charged into an extruder along
with methylene chloride and extruded through cylindrical orifices
about 15 mils in diameter. On entering atmospheric pressure the
super heated methylene chloride flashes off, generating a
micro-cellular terephthalate continuous filament with polyhedral
celled walls less than 2 microns thick. Rapid diffusion of the
methylene chloride vapor out of the closed cells leaves a
substantially collapsed cell filament. These cells are post
inflated by exposing the strands to a heated mixture of methylene
chloride and perfluorocyclobutane for a prescribed interval. This
treatment fully inflates the turgid closed cells with
perfluorocyclobutane which is one impermeant inflatant.
The inflated strands are then placed in a mold in numerous layers
and a polyurethane foam formulation is poured in and cured to
provide the composite underlayment structure. This is an example of
one technique for making the underlayment used in the present
invention. Additional details of this technique and numerous other
techniques imploying other open celled matrix materials and other
impermeant inflatants for the closed cells of the strands are
described in the prior art such as U.S. Pat. No. 3,503,840 which
issued Mar. 31, 1970 to R. G. Parrish.
Referring now to FIG. 1, there is shown a portion of a first
embodiment of the invention. It comprises a shock-absorbing
resilient underlayment mat 2 which is attached by means of adhesive
4 to a supporting base or foundation 6, the latter being, for
example, a layer of asphalt or concrete. The top layer of the
structure, the wearing surface, is a layer of artificial turf 8,
which is, for example, the kind shown in U.S. Pat. No. 3,661,687,
which issued May 9, 1972 to Spinney, et al. Briefly, the turf may
comprise a layer 10 of woven material as a backing, which may be
made of a suitable thermoplastic material such as, for example, the
polyesters, polypropylene or nylon fibers, or combinations thereof.
Tufted, knitted or woven into the backing material 10 are
upstanding fibers 12 rectangular in shape and of a size to
approximate the size of natural grass, and having a suitable
denier, which may, for example, range from 225 to 275 denier, (or
may have an even higher denier, for example, 300 to 900 denier),
and which have a ratio of width to thickness of approximately 5. In
order to lock the fibers 12 into the backing material 10, a layer
of latex sometimes designated plastisol, or other adhesive 14 is
applied to the backing and allowed to cure. The turf structure 8 is
attached to the mat 2 by means of a layer 16 of adhesive.
The adhesive layer 4 may be a suitable contact cement which has an
affinity for the mat 2 and the underlying base or foundation 6.
In order to install the combined structure, the underlayment 6 is
first prepared. A layer of adhesive 4 is spread thereon, and mat 2
is then rolled out upon it. On the top surface of mat 2 is then
spread a layer of adhesive 16, and the previously prepared turf
structure 8 is placed on top of the adhesive 16. The entire
assembly is then allowed to set and/or cure before use.
The underlayment mat 2, made as described herein and as described
in the above mentioned U.S. Pat. No. 3,503,840. A mat of this
construction is available commercially bearing the designation
pneumacel which is manufactured by E. I. DuPont de Nemours &
Co. (inc.). The mat is a non-woven mat of cellular strands 20 (see
FIG. 7) having the closed cells 22. The cells are filled with one
or more gasses so adjusted as to give the individual strands a
predetermined resistance to compression, as described in said
patent. These strands are formed into the structure (illustrated in
FIG. 1) having the open cells or voids 26 which are formed by the
foam binder 27 all as described in said patent.
The basic chemical structure of the strand is that of a polyester.
These strands bearing the designation pneumacel as manufactured and
available, may have a density of approximately 0.2 lbs. per cubic
feet to 3.5 lbs. per cubic feet. They are obtainable in thicknesses
of .02 inches and up. The compression modulus of a typical example
is approximately 2 lbs. per square inch to 40 lbs. per square inch
loading-to-compression 50%. Its strip tensile strength is
approximately 2 pli to approximately 30 pli, (0.25 inches thick),
with an elongation of 20 to 25%. In the present invention strands
20 are preferably about 50 mils in diameter, and in a typical
specimen of the material will be approximately 3 inches long. Cells
22 are small (that is, approximately 30 microns in diameter), are
generally of uniform size, and polyhedral in shape. The side walls
are approximately 0.2 microns in thickness, and are highly
oriented. The strand itself has low density, being approximately 1
lb. per cubic foot. Its compression strength is essentially
undamaged at 3,000 lbs. per sq. inch. Its chemical property is
similar to polyester fiber and "Freon" fluorinated hydrocarbon and
air blowing agents. It is supple because of its structure, and not
because of its chemical composition.
The thickness of the underlayment mat 2 in an artificial football
surface should lie between 0.5 and 1.0 inches. It is believed that
the strands in this mat work in a manner similar to pneumatic tires
in that the individual closed cells in the strand act as containers
rather than beams and columns. The load supporting characteristic
of the material is proportional to the "gauge" pressure of the
impermeant gas in the cells.
Referring now to FIG. 2, a second embodiment of the invention is
shown, in which the first layer 8 is the same as in the FIG. 1
embodiment. However, in this embodiment, instead of having a single
mat of the strands, two mats 28 and 30 are used. Preferably mats 28
and 30 are of unequal thickness, but they can be of the same
thickness. The total thickness of the combined mats 28 and 30
should be in the range of 0.7 inches to 1.0 inch (as in the first
embodiment). One reason for using the two separate mats 28 and 30
is that it may be more economical to purchase the individual mats
in standardized readily available form, and combine the two mats.
For example, the first mat 28 may be 0.3 inches and the second mat
30 may be 0.5 inches, the total thickness being 0.8 inches. The
materials of the two mats will be the same.
On the other hand, the volumetric proportions of strands in the two
mats may be different. The bottom mat 30 may have a greater
volumetric proportion of strands and so may not be as soft as the
upper mat 28.
The respective layers of the total composite structure are
assembled as follows: The base or foundation 6 is first provided,
and on this is spread a layer of adhesive 4 as in the FIG. 1
embodiment. On top of this is then placed mat 30. On the upper
surface of mat 30 is then spread a layer 32 of adhesive which is a
contact cement which is suitable for the joint between the two
mats.) On top of the adhesive 32 is then placed mat 28 which will
adhere thereto because of the use of the adhesive. On the upper
surface of the first mat 28 is then spread a layer of adhesive 16
the same as in the FIG. 1 embodiment, and on top of this is placed
the composite turf structure 8. After the various adhesives have
set firmly, then the surface may be used.
Referring now to FIG. 3, a third embodiment of the invention is
shown. As in the FIGS. 1 and 2 embodiments, the turf structure 8 is
the same as in the first embodiment, and has grass filaments 12,
woven backing 10, and the latex locking coat 14. Next is a layer of
adhesive 16 as used in FIG. 1. The next layer 36 is a layer of
flexible polyvinyl chloride material. Adhesive 16 fastens the turf
8 to the top layer of the polyvinyl chloride material 36. Next in
order comes a layer of adhesive such as the adhesive 4 of the FIGS.
1 or 2 embodiments. Next is a mat 2 of the strands which is similar
to the layer 2 of FIG. 1, which is attached to the underground or
base layer 6 by means of the adhesive 4.
The laying of this recreational surface can be conveniently done in
two steps: In the first step, the layer of adhesive 4 is spread on
the foundation 6, and the mat 2 is then placed on and adhered
thereto. The turf material 8 has previously been prepared and is
adhered thereto by means of the adhesive 16 to the upper surface or
layer of polyvinyl chloride material 36. After the cement 16 has
set, as well as the adhesive 4, then adhesive 4 is placed on the
top surface of the mat 2, and the combined layers 8 and 36 are
placed thereon and adhered.
In the FIG. 3 structure, as well as in the previous two
embodiments, the layer of polyvinyl chloride material will prevent
water seeping down through the top surface into the matting 2, as
well as providing a firm load or impact spreading layer lying over
the pad 2 as compared to the FIGS. 1 and 2 embodiment.
Referring now to FIG. 4, a structure somewhat like FIG. 3 is shown,
but utilizing the two-layer mat system of FIG. 2 with the use of
the polyvinyl chloride material 36 of FIG. 3. That is, starting
with the top layer the structure 8 is shown just as in the FIG. 3
embodiment, and which is attached to the polyvinyl chloride layer
36 by means of the adhesive 16. Layer 36 is adhered by means of
adhesive 4 to the first mat layer 28 as shown in FIG. 2. This first
mat layer 28 is adhered by means of adhesive 16 to the second mat
layer 30, the latter being in turn fastened by means of the
adhesive 4 to the foundation 6. The use of the two layer mat system
(28-30) may in some instances produce an economy of manufacture not
possible with the single mat layer 2. As in the FIG. 3 embodiment,
the layer 36 of solid but flexible polyvinyl chloride such as the
PVC material described above, provides a load or impact
distribution surface as compared to the FIGS. 1 and 2
embodiments.
Referring now to FIG. 5, structure 8 is the same as in the previous
embodiments, and consists of the rectangular fibers or strands 12,
the backing member 10 and the plastisol locking material 14.
On the foundation 6, is spread a layer of adhesive 4 on top of
which is placed the single underlayment mat 2. On top of mat 2
there is provided a water-proof membrane such as Neoprene, or
Adaprene (a Dupont product), Hypolon or other water-resistant
elastomeric material. The thickness of the membrane 40 is in the
order of 0.010 inch to 3/16 inch. It is poured or sprayed on the
top of the mat 2, and allowed to set. After the membrane has set,
then adhesive 16 is placed on the membrane, and the grass structure
8 is adhered to the membrane by the adhesive. The advantages of
this structure is that a membrane 40 which is relatively thin is
interposed between the grass structure 8 and the matting 2, this
membrane being water-impervious so that moisture can not get into
the voids of the mat.
Referring again to FIG. 3, one can construct a structure without
having the grass turf structure, thus leaving the layer 36 as the
wear surface. The resulting structure will be very suitable for
gymnasium floors, or the floors and walls of rooms where it is
desired to clean the rooms by washing with water. All that is
necessary to do is to follow the structure of FIG. 3 except that
the top grass layer 8 and adhesive 16 are not used.
The sixth embodiment shown in FIG. 6 includes a wear surface that
does not simulate turf or grass. Here the wear surface layer 45 is
a synthetic resin having a surface 46 sufficiently rough to provide
traction for the user. This surface layer provides impact
distribution to the mat 2 of strands 20.
The wear surface layer 45 is made of a durable synthetic resin such
as an isocyanate which may be one of the commercially availably
sheet materials bearing the designation adaprene, neoprene or
hypolon. This layer is sufficiently thick to withstand the wear
intended and is water-proof. The wear surface sheet could also be
specially prepared with an inert filler that gives the surface 46
greater traction.
Installation of the surface shown in FIG. 6 begins with the
underlayment or mat 2 which is rolled onto an adhesive layer 4 that
is first spread on supporting base 6. Adhesive layer 16 is then put
on the top of the mat and the wear surface layer 45 is rolled onto
that and allowed to set or cure before use.
While the pneumacel material has been known, nevertheless, the
unexpected advantages of using it for a sports playing field such
as one use for football, soccer, basketball, track, tennis or
baseball, are completely non-obvious. The reason for the
non-obvious nature of the latter's use is that a football field,
for example, has rather peculiar characteristics necessary for its
proper functioning. One of these is the fact that it is outdoors,
and as indicated earlier in discussing the background of the
invention, it may become deleteriously affected by the retention of
water in the pores of any resilient underlayment used. Furthermore,
an outdoor playing field will be exposed to hot sun, and thus the
artificial turf and underlayment may reach temperatures up to
160.degree.F., in the warmer climates of the United States.
On the other hand, where a football field is used in a northern
climate of the United States, during the winter, the field must be
able to withstand without deterioration temperatures well below
freezing. The pneumacel material provides the proper response and
resistance to deterioration over such a wide range of temperatures.
A further advantage of the underlayment provided is that so far as
fire is concerned, it is self-extinguishing.
A further advantage is that by making up the plural layered
materials, (where there are two underlayment mats of bonded strands
superimposed on each other) by adjusting the individual densities
per cubic foot of each mat, the total densities, in so far as load
bearing and shock resistance of the combined pad are concerned, can
be readily adjustable to meet given use requirements.
A further advantage of the underlayment mats of bonded strands
which is important in, for example, football field applications, is
that the structure of the mats spreads the impact loads over a much
larger area than any other known foamed or open-pored type of
material. The reason for this is that the peculiar mechanical
structure of the mat itself, and the ability of the mat to cause
the spreading of the impact loads is an unexpected advantage.
Furthermore, for impact protection, the gas in the cells of the
individual strands acts to cushion the impact shock. For example,
the shoulder or elbow of a football player cannot "hit bottom"
against any hard undersurface underlying the turf, such as the
cement or asphalt 6. The cushioning characteristics stay fairly
constant and therefore, regardless of whether a football game is
played at below freezing temperature or as high as 100.degree.F.,
the reaction of the football field surface remains essentially
constant. This is not true of prior known composite structures.
In view of the above it will be seen that the several objects of
the invention are achieved and other advantageous results
attained.
It is to be understood that the invention is not limited in its
application to the details of construction and arrangement of parts
illustrated in the accompanying drawings, since the invention is
capable of other embodiments and of being practiced or carried out
in various ways. Also, it is to be understood that the terminology
employed herein is for the purpose of description and not of
limitation. As many changes could be made in the above
constructions without departing from the scope of the invention, it
is intended that all matter contained in the above description or
shown in the accompanying drawings, shall be interpreted as
illustrative and not in a limiting sense, and it is also intended
that the appended claims shall cover all such equivalent variations
as come within the spirit and scope of the invention.
* * * * *