Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-LAYER SECURITY MAT FOR PLAYGROUND SURFACE
FIELD OF THE INVENTION
The present invention relates to a multi-layer security mat for covering a
playground surface.
BACKGROUND OF THE INVENTION
U.S. Patent No. 5,916,034. granted to Steven A. Lancia on June 29, 1999
discloses a miniature golf hole system including an expanded polystyrene foam
base. A porous rubberized material is applied to an upper exposed side of the
expanded polystyrene base, and a porous outdoor carpeting is finally applied
to
the exposed surface of the rubber material.
A drawback of expanded polystyrene foam for this kind of application is
that its resiliency deteriorates with every shock absorbed by the polystyrene
material.
International patent application published under number WO 02/055299
A1 (Lemieux et al.) on July 13, 2002 describes a resilient floor surface that
can
be used for indoor and outdoor sporting applications. This floor surface
includes
a resilient underpad of expanded polypropylene suitable for being laid down
directly on the ground or other subfloor surface in a floating arrangement. A
floor
covering material is finally applied upon this resilient underpad. This floor
covering may comprise synthetic rubber tiles and panels, rubber flooring tiles
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and panels, residential and commercial carpets, crumb rubber surface coatings,
polyurethance surface coatings, etc.
The resilient floor surface of international patent application WO
021055299 A1 does not comprise, over the resilient expanded polypropylene
underpad, a proper arrangement of layers for optimal performance, in a
playground surface application, of a multi-layer security mat.
SUMMARY OF Tl-IE INVENTION
According to the present invention, there is provided, to overcome the
above-discussed drawbacks, a multi~-layer security mat for covering a
playground surface, comprising a top abrasion layer, an intermediate charge-
distributing layer, and a bottom shock-absorbing layer. The top abrasion layer
has a top surface and a first thickness, this top abrasion layer being made of
a
resilient material having a first density. The bottom layer absorbs shocks
applied
to the top surface of the top abrasion layer, this bottom shock-absorbing
layer
having a second thickness greater than the first thickness and being made of a
resilient material having a second density lower than the first density. The
intermediate layer is interposed between the top abrasion layer and the bottom
shock-absorbing layer for' distributing charges applied to the top surface of
the
top abrasion layer on the bottom shock-absorbing layer, this intermediate
charge-distributing layer having a third thicknes s intermediate the first and
second thicknesses and being made of a resilient material having a third
density
intermediate the first and second densities
The present invention also relates to a method of manufacturing a multi-
layer security mat for covering a playground surface, comprising lying a
prefabricated panel of expanded polypropylene generally horizontally to form a
bottom shock-absorbing layer having a first thickness and a first density, the
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prefabricated panel of expanded polypropylene having a top surface. A first
mixture of {a) granules of rubber material and (b) polyurethane is poured on
the
top surface of the prefabricated panel of expanded polypropylene, and is cured
to form an intermediate charge-distributing layer having a top surface, a
second
thickness smaller than the first thickness, and a second density higher than
the
first density. A second mixture of (a) granules of rubber material and (b)
polyurethane is poured on the top surface of the intermediate charge-
distributing
layer, and is cured to form a fop abrasion layer having a third thickness
smaller
than the second thickness, and a third density higher- than the second
density.
The foregoing and other objects, advantages and features of the present
invention will become more apparent upon reading of the following non
restrictive description of an illustrative embodiment thereof, given by way of
example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF TI-fE DRAINI~IGS
In the appended drawings:
Figure 1 is a partial, cross sectional elevation view of the non-restrictive,
illustrative embodiment of the rnulti-layer security mat according to the
present
invention;
Figure 2a is a graph of the dynar~nic cushioning performance of beads of
expanded polypropylene, this graph showing curves of the deceleration (G-
value) as a function of the static load (PSI) for expanded polypropylene beads
having a density of 20 gll for a first impact and for different H/t (Drop
HeightlCushion Thickness) ratios;
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Figure 2b is a graph of the dynamic cushioning performance of beads of
expanded polypropylene, this graph showing curves of the deceleration (G-
value) as a function of the static load (PSI) for expanded polypropylene beads
having a density of 20 g/l for the subsequent 2-5 impacts and for different
H/t
(Drop HeightlCushion Thickness) ratios;
Figure 3a is a graph of the dynamic cushioning perfiormance of beads of
expanded polypropylene, this graph showing curves of the deceleration (G-
value) as a function of the static load (PSI) for expanded polypropylene beads
having a density of 30 gll for a first impact and for different Hlt (Drop
Height/Cushion Thickness) ratios; and
Figure 3b is a graph of the dynamic cushioning pe~fiormance of beads of
expanded polypropylene, this graph showing curves of the deceleration (G-
value) as a function of the static load (PS1) for expanded polypropylene beads
having a density of 30 g/l for the subsequent 2-5 impacts and for different
Hlt
(Drop HeightlCushion Thickness) ratios.
DETAILED DESCRIPTION OF THE lLLUSTRAT1VE EMBODIMENT
The non-restrictive, illustrative embodiment of the rnulti-layer security mat
according to the present invention will now be described with reference to the
accompanying drawings.
Although the non-restrictive, illustrative embodiment of the mufti-layer
security mat will be described in the following description with reference to
covering of a playground surface, it should be kept in mind that the present
invention applies as wel! to other types of surface, for example a sport-
playing
surface.
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As illustrated in Figure 1, the multi-layer security mat for covering a
playground surface, generally identified by the reference 10, comprises a top
abrasion layer 11, an intermediate charge-distributing layer 12, and a bottom
shock-absorbing layer 13.
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Top abrasion layer
The top abrasion layer 11 is the denser layer of the non-restrictive,
illustrative embodiment of the multi-layer security mat 10 according to the
present invention. Its main function is to form an aesthetic, abrasion and
attrition=
resistant layer.
The top abrasion layer 11 is made of a mixture of (a) granules of rubber
materials and (b) polyurethane. According to the non-restrictive, illustrative
embodiment of the multi-layer security mat, the granules of the top abrasion
layer 11 are made of synthetic rubber material (E.~.D.M.) for presenting
better
abrasion and resistance to attrition.
These granules of synthetic rubber material are mixed, according to the
non-restrictive, illustrative embodiment of the multi-layer security mat 10,
with
liquid hydro-reactive, mono-component clear polyurethane. Of course, the
polyurethane constitutes a binder for the granules of synthetic rubber
material.
The top abrasion layer 11 may contain '18% to 22% (by weight) of
polyurethane, and the granules of synthetic rubber mafierial may have a
diameter
of 1-3 mm. It should be kept in mind that the present invention is not
restricted to
these values and the resulting density.
The synthetic rubber material of the granules of the top abrasion layer 11
can be colored as desired, for example depending on the intended use of the
multi-layer security mat 10.
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A suitable thickness of the top abrasion layer 11 of the non-restrictive,
illustrative embodiment of the mufti-layer security mat 10 is of the order of
8-10
mm, but the present invention is not restricted to this particular thickness.
Intermediate charge-distributing layer
The intermediate layer 12 is interposed between the top abrasion layer 11
and the bottom shock-absorbing layer 13 for distributing charges applied to
the
top surface 14 of the top abrasion layer 11 on the bottom shock-absorbing
layer
13. Accordingly, the intermediate charge-distributing layer 12 constitutes a
support layer for the top abrasion layer 11 and helps this top abrasion Payer
11 to
resist to extreme conditions, for example a person wearing high-heel shoes.
This
intermediate charge-distributing layer 12 has a thickness intermediate the
thickiiesses of the layers 11 and 13, and is made of a resilient material
having a
density intermediate the densities of these layers 11 and 13.
According to the non-restrictive, illustrative embodiment of the mufti-layer
security mat 10, the intermediate charge-distributing layer 12 is made of a
mixture of (a) granules of rubber material and (b) polyurethane. According to
this
illustrative embodiment, the granules of the intermediate layer 12 are made of
black recycled rubber material (S.B.R.) and are mixed with liquid hydro-
reactive,
mono-component clear polyurethane. Of course, the polyurethane constitutes a
binder for the granules of recycled rubber material.
The charge-distributing intermediate Payer 12 may contain 12% to 16%
(by weight) of polyurethane, and the granules of recycled rubber material may
have a diameter of 1-5 mm. it should be kept in mind that the present
invention
is not restricted to these values and the resulting density.
A suitable thickness of the intermediate charge-distributing layer 12 of the
non-restrictive, illustrative embodiment of the mufti-layer security mat 10 is
of the
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order of 20-30 mm, but the present invention is not restricted fio this
particular
thickness.
Bottom shock-absorbing layer
The bottom layer 13 absorbs shocks applied to the top surface 14 of the
top abrasion layer 11, iVlore specifically, the bottom layer 13 is made of
resilient
material capable of absorbing mechanical energy in order to damp, for example,
a child's fall on the multi-layer security mat 10.
The bottom shock-absorbing layer 13 is the thicker but less dense layer.
According to the non-restrictive, illustrative embodiment of the multi-layer
security mat 10, the resilient material of the bottom shock-absorbing layer 13
comprises a prefabricated panel of expanded polypropylene having a thickness
of the order of 25-50 mm and having a density of 0.7-1.0 PCP (Pounds per
Cubic Feet).
According to an alternative, the resilient material of the bottom shock-
absorbing layer 13 comprises a mixture of (a) granules and buffing (filaments)
of
rubber material and (b) polyurethane. According to this alternative, the
granules
of the bottom layer 13 are made of black recycled rubber material (S.S.R.),
and
these granules and the buffing are mixed with liquid hydro-reactive, mono-
component clear polyurethane. Again, the polyurethane constitutes a binder for
the granules of recycled rubber material and the buffing. The buffing
(filaments
of rubber material) also contributes to bind the granules together.
Also in accordance with this alternative, the density of the bottom shock-
absorbing layer 13 is lower than that of the intermediate charge-distributing
layer
12 and the thickness of this bottom shock-absorbing layer 13 is greater than
50
mm.
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Manufacture of the illustrative embodiment of the mufti-layer security mat
To manufacture the non-restrictive, illustrative embodiment of the multi
layer security mat 10 on the site of the installation, the following
operations can
be performed:
- lying one or many prefabricated panels of expanded polypropylene
generally horizontally and adjacent to each other over the whole surface
to be covered by the mat 10 to form the bottom shock-absorbing layer 13,
wherein the prefabricated panels) of expanded polypropylene can be
perforated to improve drainage;
- preparing a mixture of the granules of black recycled rubber material
(S.B.R.) and the liquid hydro-reactive, mono-component clear
polyurethane, pouring this mixture on the top surface of the prefabricated
panels) of expanded polypropylene, eventually pressing and finally
curing this mixture to form the intermediate charge-distributing layer 12;
and
- preparing a mixture of the granules of synthetic rubber material
(E.P.D.M.) with the liquid hydro-reactive, mono-component clear
polyurethane, pouring this mixture on the top surface of the charge-
distributing layer 12, eventually pressing and finally curing this mixture
to form the top abrasion layer 10.
Governmental regulations require that playground security mats meet
with a parameter Gmax<200 and a parameter HIC(P-fead Injury Criteria)<1000.
Gmax<200
Gmax is a parameter representative of the resiliency of the mufti-layer
security mat 10. Parameter Gmax is in tact representative of the capability of
the
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multi-layer security mat 10 to keep its initial properties notwithstanding the
number of shocks on the top surface 14 (Figure 1 ). Governmental regulations
require a Gmax<200 no matter the height.
in this respect, reference is made to Figures 2a and 2b showing the
dynamic cushioning performance of beads of expanded polypropylene, these
graphs showing curves of the deceleration (G-value) as a function of the
static
load (PSI) for expanded polypropylene beads having a density of 20 g/I for
different H/t (Drop Height/Cushion Thickness) ratios and for:
- a first impact (Figure 2a);
- the subsequent 2-5 impacts (Figure 2b).
Reference is also made to Figures 3a and 3b showing the dynamic
cushioning pertormance of beads of expanded polypropylene, these graphs
showing curves of the deceleration (G-value) as a function of the static load
(PSI) for expanded polypropylene beads having a density of 30 g/I for
different
H/t (Drop Height/Cushion Thickness) ratios and for:
- a first impact (Figure 3a);
the subsequent 2-5 impacts (Figure 3b).
Figures 2a, 2b, 3a and 3b show that the dynamic cushioning performance
does not significantly deteriorate from one impact to the other.
HIC<1000
HIC is a parameter representative of the energy absorbed by a child's
head upon a fall on the multi-layer security mat 10. Parameter HIC is in fact
representative of the capability of the multi-layer security mat 10 to absorb
and
dissipate energy when a child's head hits the top surface 14 (Figure 1 ).
Governmental regulations require a HIC<1000 for all heights.
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Advantages of fhe non-restrictive, illustrative embodiment of the multi-
layer security mat 70
A bottom shock-absorbing layer 13 made of expanded polypropylene is
5 very resilient and resistant to repeated shocks without significant damage,
and
efficiently absorbs and dissipates the energy of shocks for reducing as much
as
possible the energy absorbed by a child's head upon falling on the multi-layer
security mat 10. In this manner, the parameters Gmax<200 and HIC<1000 are
easily met by a multi-layer security mat 10 having a bottom shock-absorbing
10 layer made of expanded polypropylene.
A bottom shock-absorbing layer 13 made of expanded polypropylene
absorbs almost no water and constitutes an isolating material whereby a bottom
shock-absorbing layer 13 made of expanded polypropylene will not freeze when
the multi-layer security mat 10 is used outdoors to render the playground
surface
more comfortable all year long.
Although the present invention has been described in the foregoing
specification by means of an illustrative embodiment, this illustrative
embodiment
can be modified as will, within the scope of the appended claims without
departing from the nature and spirit of the subject invention.
