Note: Descriptions are shown in the official language in which they were submitted.
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EPDM WALKWAY PAD COMPOSITIONS AND
USES THEREFOR
TECHNICAL FIELD
The present invention relates generally to roof walkway pads which are
placed over a roofing membrane in order to protect the membrane from foot
traffic,
necessitated by excursions onto the covered roof to service, for instance,
HVAC units,
exhaust fans, smoke hatches, condenser units, window washing equipment,
lightning
protection units and the like. More particularly, the present invention
relates to
walkway pads comprising a polymer composition of matter containing 100 percent
ethylene-propylene-diene terpolymers (EPDMs) or blends of EPDM with at least
one
ethylene-propylene copolymer (E~'M) as the polymeric component therein.
Specifically,
the present invention relates to a cured walkway pad composition comprising
from about
75 to 100 parts by weight ethylene-propylene-dime terpolymer and optionally
from 0
up to about 25 parts by weight ethylene-propylene copolymer as the sole
polymeric
components. The walkway pad composition has excellent low temperature and heat
aging properties as well as superior weathering resistance as compared to
other walkway
pad compositions which include other polymeric components such as natural
rubber,
synthetic polyisoprene, styrene-butadiene rubber (SBR), polybutadiene, and
butyl (IR)
rubber. The walkway pads of the present invention also meet the physical
performance
requirements desired of walkway pad compositions.
BACKGROUND OF THE INVENTION
Polymeric roof sheeting is often used as single-ply roofing membrane for
covering industrial and commercial flat roofs. Such membranes are typically
applied
to the roof surface in a vulcanized or cured state.
Because of outstanding weathering resistance and flexibility, cured EPDM
based roof sheeting has rapidly gained acceptance as an effective barrier to
prevent the
penetration of moisture through the roof being covered. While this material is
suitable
for covering the roof, and although it is capable of withstanding most
traffic, it is
customary to apply walkway pads, comerising other rubber or polymeric
materials,
directly onto the membrane defining a traffic pattern to areas of the roof to
which travel
CA 02246013 2005-03-10
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is required. Typically, it is common to specify the use of walkway pads in
areas where
the frequency of traffic exceeds one excursion per month.
Presently, such walkway pads are typically made from various scrap
rubber or claimed rubber materials such as recycled tires, or uncured workaway
or
uncured off specification rubber compounds available from tire manufacturing
facilities
or various other industrial facilities which have various off specification
mechanical
rubber goods available for use. These rubber compositions generally include
such rubber
materials as natural rubber, synthetic polyisoprene, styrene butadiene rubber
(SBR),
polybutadiene, butyl rubber (IIR) or the like or mixtures and blends thereof.
Still other
walkway pads have been produced from polymeric materials such as neoprene,
polyvinyl
chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene
and
other similar olefin-type polymers.
Walkway pads are generally about 30 inches square and about 0.3 inches
thick, although thicknesses generally range between about 0.25 and 0.5 inches.
The pad
provides upper and lower surfaces. The lower surface is generally relatively
smooth
while the upper surface may be textured in order to improve traction.
Walkway pads are currently applied to roofing membranes and other
forms of roof covering material with the use of liquid adhesives or tape
adhesives which
are applied to the walkway pad prior to installing the walkway pad on the roof
surface.
This method typically involves cleaning and/or priming the walkway pad and
then
applying the liquid or adhesive tape to the pad, although alternative methods,
are being
explored. The applied adhesive, which is oftentimes used in the form of a seam
tape
which itself may include EPDM or EPM, keeps the walkway pad in place on the
roof
surface, and the walkway pad serves to protect the roof system, especially the
membrane
from foot traffic.
While various walkway pad compositions are known, the art has not
heretofore recognized the benefit of a walkway pad composition containing 100
percent
ethylene-propylene copolymers and terpolymers as the polymeric material used
in the
walkway pad composition. Such a walkway pad would certainly be compatible with
the
necessary adhesive tapes typically used to adhere the walkway pad to a roofing
membrane, especially where the roofing membrane composition includes EPDM as
its
base polymer. Given the rapid acceptance of EPDM as the base rubber component
in
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many roofing membranes today, the use of a similar EPDM as the sole polymer,
or as
the major component (with a minor amount of EPM) in a walkway pad composition
would also appear desirable. Moreover, given the excellent weathering
characteristics
of EPDM, such an EPDM walkway pad composition would appear to provide a
significant improvement in the art over current walkway pad compositions
containing
various other rubber or polymeric materials such as natural rubber, synthetic
polyisoprene, styrene butadiene rubber (SBR), polybutadiene, butyl rubber
(IIR) or the
like or mixtures and blends thereof, as well as those compositions containing
polymeric
materials such as neoprene, polyvinyl chloride (PVC), chlorinated polyethylene
(CPE),
chlorosulfonated polyethylene and other similar olefin-type polymers.
Walkway pads should also meet standard physical property requirements.
For instance, a preferred wa.kway pad should show no signs of cracking or
splitting
when folded around a one-inch bending radius at 40°F. The walkway pad
should lay
flat and remain flexible at temperatures as low as -20°C. Still
further, the pad should
be free of any mold release on the non-dimpled or textured side. Additional
desirable
physical properties include an elongation of at least 100 percent using ASTM-D-
412; a
brittleness temperature of at least -40°C according to ASTM-D-2137; and
a Shore "A"
Hardness of between about SS to 70 as tested in accordance with ASTM-D-2240.
Thus, the need exists for a walkway pad composition which has excellent low
temperature and heat aging properties as well as superior weathering
resistance as
compared to other walkway pad compositions which include other polymeric
components
such as natural rubber, synthetic polyisoprene, styrene-butadiene rubber
(SBR),
polybutadiene, and butyl (IR) rubber. The walkway pads should also meet the
physical
performance requirements desired of walkway pad compositions. Desirably, such
a
fully compounded EPDM walkway pad composition would have a Mooney viscosity
ranging between about 45 and about 60 Mooney units (ML/4 at 100°C), and
an
elongation at break of at least 100 and, more preferably, at least 250
percent.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a walkway pad
containing 100 percent ethylene-propylene-diene terpolymers and copolymers of
ethylene
and propylene as the polymeric component thereof.
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It is another object of the present invention to provide a walkway pad
containing 100 percent EPDM.
It is yet another object of the present invention to provide a walkway pad
comprising a polymer blend having a major amount of EPDM and a minor amount of
EPM.
It is still another object of the present invention to provide a walkway pad,
as above, which is both flexible and weather resistant.
It is a further object of the present invention to provide a walkway pad, as
above, which provides superior weathering resistance, water absorption
resistance, and
heat aging performance as compared to other walkway pads containing natural
rubber,
synthetic polyisoprene, styrene butadiene rubber (SBR), polybutadiene, butyl
rubber
(IIR), or mixtures thereof.
It is yet a further object of the present invention to provide a walkway pad,
as above, which may provide better adhesion to the seam adhesive tape used to
attached
the bottom surface of the walkway pad to the roofing membrane.
It is still a further object of the present invention to provide a walkway
pad,
as above, which can have a seam tape adhered to it without the use of a primer
or
adhesive.
In general, the objects of the present invention are accomplished by
providing a walkway pad comprising 100 parts by weight of a polymeric material
containing from about 75 to 100 parts by weight of an ethylene-propylene-diene
terpolymer and from 0 to about 25 parts by weight of an ethylene-propylene
copolymer;
from about 60 to about 700 parts by weight of a filler selected from the group
consisting
of reinforcing and non-reinforcing materials and mixtures thereof, per 100
parts of the
polymeric material; from about 40 to about 175 parts by weight of a processing
material
and mixtures thereof, per 100 parts of the polymeric material; and from about
2 to about
10 parts by weight of a cure package per 100 parts of the polymeric material,
the
walkway pad being devoid of any additional polymeric components. Preferably,
the
cure package contains sulfur and at least one organic (sulfur vulcanizing)
accelerator.
Moreover, it is preferred that from about 60 to 275 parts by weight carbon
black or
other reinforcing filler (per 100 parts of the polymeric material) be
employed, while up
to about 700 parts by weight of non-reinforcing filler such as clay, coal
filler, or
cryogrind EPDM material, per 100 parts of the polymeric material, may be
employed.
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9707044(175) - $ -
Other objects of the invention may be accomplished by providing a walkway
pad comprising 100 parts by weight of an ethylene-propylene-dime terpolymer;
from
about 60 to about 700 parts by weight of a filler selected from the group
consisting of
reinforcing and non-reinforcing materials and mixtures thereof, per 100 parts
of EPDM
terpolymer; from about 40 to about 175 parts by weight of a processing
material and
mixtures thereof, per 100 parts of EPDM terpolymer; and from about 2 to about
10
parts by weight of a cure package, per 100 parts of EPDM terpolymer, the
walkway pad
being devoid of any additional polymeric components.
At least one or more of the foregoing objects which shall become apparent
to those skilled in the art are described in greater detail with reference to
the drawings
and specification which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top plan view of a portion of a roof covered with a roofing
membrane and carrying a plurality of walkway pads;
Fig. 2 is an enlarged side elevation, taken substantially along the lines 2-2
of Fig. 1, and depicting the roofing membrane and overlying walkway pad; and
Fig. 3 is a perspective view of a walkway pad with seam tape pre-applied
thereto.
PREFERRED 1FMBODIMENT OF THE INVENTION
With reference to the drawings, Fig. 1 depicts a portion of a flat roof 10,
covered by a plurality of roof sheeting membranes 11. Upon the roof is a unit
of roof-
mounted equipment, such as an air conditioning apparatus 13. A plurality of
walkway
pads, generally 20, have been applied on the membranes 11 along a traffic path
to
apparatus 13.
Fig. 2 depicts a section of the roof in cross-section, revealing the roof deck
14, which typically comprises metal, wood, concrete or the like, and a layer
of
insulation 15, placed thereover. The roof sheeting membranes 11 are placed
down next,
to which are applied the walkway pads 20, where desired. It is to be
appreciated that
the roof construction depicted is exemplary only and is not to be construed as
constituting a limitation of the present invention. On the contrary, the
walkway pads
of the present invention can be employed on virtually any membrane covered
roof,
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irrespective of the construction or method of applying and finishing the roof.
Thus, for
example, where membrane roofs are ballasted, it is customary to move aside the
ballast
in order to maximize the bond between the membrane and walkway pad. Subsequent
to application of the pads, the ballast can be re-distributed over the
membrane and
around the walkway pads.
In Fig. 3, the walkway pad 20 is depicted. As noted hereinabove, the
walkway pad is about 30 inches square and 0.3 inches thick, although
thicknesses
generally range between about 0.25 and about 0.5 inches. The pad provides
upper and
lower surfaces, 21 and 22 respectively. Typically, the lower surface is
relatively
smooth while the upper surface can be textured to improve traction. An
adhesive tape
25 is preferably applied in a series of strips such as at two of the edges 28
and 29, and
at the center of the pad 20, adhered directly to the lower surface 22. The
adhesive tape
provides upper and lower surfaces, 30 and 31 respectively, the upper surface
30
being applicable to the lower surface 22 of the pad, and the lower surface 31
being
15 applicable to the roofing membrane 11. The adhesive or seam tape 25 may be
added
to the bottom surface 22 of the walkway pad 20 in the field just prior to
positioning the
walkway pad 20 on the roofing membrane 11, or the tape 25 may be applied to
the
bottom surface 22 of the walkway pad 20 at the factory, as part of the
manufacturing
operation. As the walkway pad is relatively clean shortly after manufacturing
the
20 factory applied version thereof, it is not necessary that separate cleaning
and/or priming
operations be made prior to adhering the tape 25 to the pad. However, adhesion
between the tape and pad is maximized where there are clean and controlled
conditions
for application of the tape to the pad. Thus, as opposed to "in the field"
applications,
i. e. , those on a roof, where the pads may become soiled or contaminated
which, in turn,
may interfere with the adhesion of the seam tape to the pad, manufacturing
based
application of the tape to the pad is preferred.
Typically, the adhesive or seam tapes employed have a release paper 32
applied to the lower surface 31 of the tape 25. If not pre-applied, there may
also be
another release paper (not shown) applied to the upper surface of the tape.
The release
paper 32 prevents exposure of the surface 31 to dust and the like prior to
installation on
the roof and, in certain instances, prevents adjacent stacked walkway pads
from adhering
together. Once in the field, i. e. , the rooftop, all that is required is for
the installer to
prime the pad, if necessary, strip away the release paper(s), and place the
adhesive on
CA 02246013 2005-03-10
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the walkway pad and/or onto the roof and then apply pressure which can be
accomplished merely by walking over the pads or with the use of a roller,
where such
equipment is available and/or desirable.
The walkway pad of the present invention preferably contains 100 percent
EPDM as the sole polymeric component of the composition. Optionally, however,
the
walkway pad may include minor amounts of EPM, generally up to about 25 percent
of
the polymeric component and more preferably, from about 5 to about 25 parts by
weight.
In any event, the composition of the walkway pad is devoid of any other rubber
components or polymers. For example, there are no adhesive enhancing polymers
or
tackifiers.
The term EPDM is used in the sense of its definition as found in ASTM
D-1418-94 and is intended to mean a terpolymer of ethylene, propylene and a
dime
monomer. Although not to be limited thereto, illustrative methods for
preparing such
terpolymers are found in U. S. Pat. No. 3,280,082. Other illustrative methods
can be
found, for example, in Rubber and Chemistry & Technology, Vol. 45, No. 1,
Division of
Rubber Chemistry (March 1992); Morton, Rubber Technology, 2d ed., Chapter 9,
Van
Nostrand Reinhold Company, New York (1973); Polymer Chemistry of Synthetic
Elastomers, Part II, High Polymer Series, Vol. 23, Chapter 7, John Wiley &
Sons, Inc.
New York (1969); Encyclopedia of Polymer Science and Technology, Vol. 6, pp.
367-
68, Interface Publishers, a division of John Wiley & Sons, Inc., New York
(1967);
Encyclopedia of Polymer Science and Technology, Vol. 5, p. 494, Interface
Publishers, a
division of Johm Wiley & Sons, Inc., New York (1966); and Synthetic Rubber
Manual,
8th ed., International Institute of Synthetic Rubber Producers, Inc. (1980).
The preferred terpolymers of the present invention are substantially
amorphous. That is, at least one EPDM terpolymer employed to make the walkway
pad
of the present invention should have less than about two percent
crystallinity. More
particularly, the EPDM walkway pad composition of the present invention should
have
about 85 to 100 parts by weight of at least one EPDM terpolymer having up to
about two
percent crystallinity, and 0 to about 15 parts by weight of an EPDM terpolymer
having
more than about two percent crystallinity. More preferably, the composition
should
include at least 95 parts and even more preferably 100 parts, by weight of
amorphous
EPDM having up to 2 percent crystallinity and, optionally, only up to about
CA 02246013 1998-08-21
9707044(175) _ g _
parts by weight of crystalline or semi-crystalline EPDM having more than 2
percent
crystallinity.
Any EPDM containing up to 2 percent crystallinity from the ethylene
component and exhibiting the properties discussed hereinbelow should be
suitable for
5 use in the present invention. Typically, amorphous EPDMs having less than
about 65
weight percent ethylene and from about 1.5 to about 4 weight percent of the
dime
monomer with the balance of the terpolymer being propylene or some other
similar
olefin type polymer is desired. Such EPDMs also preferably exhibit a Mooney
viscosity
(ML/1 + 4 at 125°C) of about 40 to 60 and more preferably, of about 45
to 55.
Preferably, the EPDM has from about 2 to about 4 weight percent unsaturation.
The dime monomer utilized in forming the EPDM terpolymers is preferably
a non-conjugated dime. Illustrative examples of non-conjugated dimes which may
be
employed are dicyclopentadiene, alkyldicyclopentadiene, 1,4-pentadiene, 1,4-
hexadiene,
1,5-hexadiene, 1,4-heptadiene, 2-methyl-1,5-hexadiene, cyclooctadiene, 1,4-
octadiene,
1,7-octadiene,5-ethylidene-2-norbornene,5-n-propylidene-2-norbornene,5-(2-
methyl-2-
butenyl)-2-norbornene and the like.
Typical EPDM terpolymers having less than 2 weight percent crystallinity
are available from Exxon Chemical Co. under the tradename Vistalon~, from
Uniroyal
Chemical Co. under the tradename Royalene~, and from DSM Copolymer under the
tradename Keltan~. For example, one preferred amorphous EPDM terpolymer is
Vistalon~ MD-2727. This EPDM terpolymer has a Mooney viscosity (ML/ 1 + 4 at
125°C) of about 44 t 5, an ethylene content of about 56 weight percent
and about 2.1
weight percent unsaturation.
Another example of an EPDM having less than 2 weight percent crystallinity
is available from Uniroyal Chemical Co. under the Royalene tradename and has a
Mooney viscosity (ML/4 at 125°C) of about 46 t 5, an ethylene content
between 69
or 70 weight percent and about 2.8 weight percent unsaturation.
Still another example of an EPDM having less than 2 weight percent
crystallinity is available from DSM Copolymer under the Keltan tradename. Such
an
amorphous EPDM has a Mooney viscosity (ML/4 at 125°C) of about 50 t 5,
an
ethylene content of about 69 weight percent and about 2.6 weight percent
unsaturation.
It will be appreciated that the subject walkway pad may comprise 100 parts
by weight of an amphorous EPDM as the sole elastomeric polymer for the
composition.
CA 02246013 1998-08-21
9~o~oaa~ms~ - 9
However, it is also contemplated that more than one EPDM having less than 2
weight
percent crystallinity may be employed.
When EPDM terpolymers having more than 2 percent crystallinity from the
ethylene component are employed, these EPDMs preferably should contain at
least about
S 65 weight percent ethylene and from about 2 to about 4 weight percent of the
dime
monomer with the balance of the terpolymer being propylene or some other
similar
olefin-type polymer. Although not necessarily limiting, such EPDMs also should
exhibit
a Mooney viscosity (ML/1 + 4 at 125°C) of about 45 to 50 and should
have less than
about 4 weight percent unsaturation. Non-conjugated dimes like those
exemplified
above can also be used for these types of EPDMs as well.
A typical EPDM having more than 2 percent crystallinity is available from
Exxon Chemical Co. under the tradename Vistalon~ 3708. This EPDM terpolymer
has
a Mooney Viscosity (ML/1 + 4 at 125°C) of about 52 t 5, an ethylene
content of
about 69 weight percent and about 3.2 weight percent unsaturation.
By reducing the amount of crystalline, high ethylene-containing EPDM
terpolymer to less than about 15 parts by weight, and more preferably, to 0 to
about S
parts by weight in combination with increasing the amount of non-crystalline,
amorphous
EPDM terpolymer to at least about 85 parts by weight, and more preferably, to
about
95 to 100 parts by weight, the resulting cured walkway pad will lay flat and
be more
flexible as compared to commercial walkway pad compositions currently
available.
The tet~rrt EPM is used in the sense of its definition as found in ASTM D-
1418-94 and is intended to mean a copolymer of ethylene and propylene. The
preferred
copolymers contain from about 60 to 72 weight percent ethylene with the
balance, to
total 100 weight percent, being propylene. A typical EPM suitable for use in
the
present invention is available from DSM Copolymer under the tradename Keltan~
740.
This EPM has a Mooney viscosity (ML/4 at 125°C) of about 63 and an
ethylene content
of about 60 weight percent.
Other EPMs are available from DSM Copolymer under the tradename
Keltan~ and from Exxon Chemical Co. under the tradename Vistalon~. For
instance,
Keltan~ 3300A and 4200A have Mooney viscosities (ML/4 at 125 °C) of
about 35 and
about 40, respectively, while Vistalon~ 808 and 878 have Mooney viscosities
(ML/4 at
125°C) of about 46 and 53, respectively. These ethylene-propylene
copolymers are
available in either crumb or pellet form. The advantage of using an EPM is
that the
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9707044(175) - 1Q -
resultant walkway pads should be flexible and exhibit excellent long-term
rooftop aging
properties.
In addition to the EPDM terpolymers and EP copolymers employed, the
walkway pad composition of the present invention may also include fillers,
processing
oils and curatives as well as other optional components including cure
activators, all of
which are discussed hereinbelow.
With respect to the fillers, suitable fillers are selected from the group
consisting of reinforcing and non-reinforcing materials, and mixtures thereof,
as are
customarily added to rubber. Examples include both inorganic and organic
materials
such as carbon black, ground coal fines, cryogenically or ambiently ground
EPDM
rubber, and clay as well as other mineral fillers, and the like. Generally,
preferred
fillers include carbon black and cryogenically or ambiently ground rubber.
Carbon black, a reinforcing filler, is used in an amount of from about 60
parts to about 275 parts per 100 parts of polymer (phr), preferably in an
amount of
about 85 to about 175 phr. The carbon black useful herein may be any carbon
black
suitable for the purposes disclosed hereinbelow. Preferred are furnace blacks
such as
GPF (general purpose furnace), FEF (fast extrusion furnace) and SRF (semi-
reinforcing
furnace). Most preferred is N650 HiStr GPF black, a petroleum-derived, black
reinforcing filler having an average particle size of about 60 nm and a
specific gravity
of about 1.80g/cc.
The ground coal utilized as a filler in the walkway pad compositions of the
present invention is a dry, finely divided black powder derived from a low
volatile
bituminous coal. The ground colt has a particle size ranging from a minimum of
0.26
microns to a maximum of 2.55 microns with the average particle size of 0.69 t
0.46
as determined on 50 particles using Transmission Electron Microscopy. The
ground
coal produces an aqueous slurry having a pH of about 7.0 when tested in
accordance
with ASTM D-1512. A preferred ground coal of this type is designated Austin
Black
which has a specific gravity of about 1.255 ~ 0.03, an ash content of about
4.58 % and
a sulfur content of about 0.65 % . Finely ground coal is commercially
available from
Coal Fillers, Inc. of Bluefield, Virginia. Amounts range from about 5 to about
65 phr
with about 15 to about 35 phr being preferred when used.
Essentially any cryogenically or ambiently ground rubber may be employed
as a filler in the composition of the invention. The preferred cryogenically
or ambiently
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9707044( 175) - I 1 -
ground rubbers are cryogenically ur ambiently ground EPDM, butyl, neoprene and
the
like. A preferred cryogenically or ambiently ground rubber is a ground EPDM
rubber.
The preferred ground EPDM rubber is a fine black rubbery powder having a
specific
gravity of about 1.16 t O.OlSg/cc and a particle size ranging from about 30 to
about
300 microns with an average particle size ranging from about 40 to about 80
microns.
When carbon black is included in the walkway pad composition, the amount of
ground
rubber may range from about 25 to about 100 parts per 100 parts of polymeric
material,
i.e., EPDM and, optionally, EPM. In the absence of any carbon black, the
amount of
cryogenically or ambiently ground rubber may exceed 600 parts by weight per
100 parts
polymeric material (phr).
Non-black mineral fillers may also be employed and, in the past, have
included those fillers selected from the group consisting of hard clays, soft
clays,
chemically modified clays, calcined clays, mica, talc, alumina trihydrates,
calcium
carbonate, titanium dioxide, silica, and certain mixtures thereof. In some
instances.
these fillers may completely or partially replace "black" fillers, i. e.
carbon black and
other petroleum-derived materials.
Some four basic types of clays are normally used as fillers for rubber
elastomers. The different types of clay fillers include airfloated, water
washed, calcined
and surface treated or chemically modified clays.
The airfloated clays are the least expensive and most widely used. They are
divided into two general groups, hard and soft, and offer a wide range of
reinforcement
and loading possibilities. Hard Clays may be used in the amount of about 20
parts to
about 300 parts per 100 parts of rubber (phr), preferably in an amount from
about 65
to 210 phr. Preferred airfloated hard clays are commercially available from
J.M. Huber
Corporation under the tradenames Suprex~, Barden R~; and LGB~.
The airfloated soft clays may be used in amounts ranging from about 20 parts
to about 300 parts per 100 parts of rubber (phr), preferably in an amount from
about 75
to 235 phr. The preferred airfloated soft clays are available from J.M. Huber
Corporation under the tradenames Paragon~ and K-78~ or from Evans Clay Company
under the tradename Hi-White R~. Particularly preferred is Hi-White R~, an air-
floated
soft clay characterized as having a pH of about 6.25 t 1.25, an oil absorption
of 33
grams/100 grams of clay, a particle size of 68 % ( t 3) being finer than two
microns,
and a specific gravity of about 2.58.
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Water washed clays are normally considered as semi-reinforcing fillers. This
particular class of clays is more closely controlled for particle size by the
water-
fractionation process. This process permits the production of clays within
controlled
particle size ranges. The preferred amounts of water washed clays are very
similar to
the preferred amounts of airfloated soft clays mentioned hereinabove. Some of
the
preferred water washed clays include Polyfil~ DL, Polyfil~ F, Polyfil~ FB,
Polyfil~ HG-
90, Polyfil~ K and Polyfil~ XB; all commercially available from J.M. Huber
Corporation.
The third type of clay includes the calcined clay. Clays normally contain
approximately 14 percent water of hydration, and most of this can be removed
by
calcination. The amount of bound water removed determines the degree of
calcination.
The preferred ranges of calcined clays are very similar to the preferred
amounts of
airfloated hard clays mentioned hereinabove. Some of the preferred calcined
clays
include Polyfil~ 40, Polyfil~ 70, and Polyfil~ 80, all commercially available
from J.M
Huber Corporation.
The last type of clay includes chemically modified reinforcing clays. Cross-
linking ability is imparted to the clay by modifying the surface of the
individual particles
with a polyfunctional silane coupling agent. Chemically modified clays are
used in the
amount of from about 20 parts to about 300 parts per 100 parts of rubber(phr),
preferably in an amount from about 60 to 175 phr. Normally, the specific
gravity of
most of these clays is about 2.60 at 25° C. The preferred chemically
modified clays are
commercially available from J.M. Huber Corporation and include those available
under
the tradenames Nucap~, Nulok~ and Polyfil~. Another preferred chemically
modified
clay is commercially available from Kentucky-Tennessee Clay Company under the
tradenames Mercap~ 100.
As an alternative to the clays, a silicate may have utility in the present
invention. For example, synthetic amorphous calcium silicates such as those
which are
commercially available from the J.M. Huber Company under the trademark
Hubersorb
600 may be utilized. Hubersorb 600 is characterized as having an average
particle size
of 3.2 micrometers (by the Coulter Counter Method), oil absorption of 450
ml/100 g
of calcium silicate, a BET (Brunaver-Emmet-Teller nitrogen adsorption
procedure)
surface area of 300 m2/g and a pH (5 % solution) of 10.
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Other silicates which may be used in the composition of the present invention
include precipitated, amorphous sodium aluminosilicates available from the
J.M. Huber
Company under the tradenames Zeolex 23 and Zeolex 80. Zeolex 23 has a BET
surface
area of about 75 m2/g, a refractive index at 20°C of about 1.51, and a
pH of about 10.2
determined by slurring 20 grams of silicate with 80 grams of deionized water.
In
comparison, Zeolex 80 has a BET surface area of about 115 m2/g, a refractive
index
at 20°C of about 1.55, and a pH of about 7. The average particle size,
density,
physical form and oil absorption properties are similar to each other.
Reinforcing silicas may also be used as non-black fillers, preferably in
conjunction with one or more of the chemically modified clays noted
heTeinabove.
Silica (silicon dioxide) utilizes the element silicon and combines it in a
very stable way
with two oxygen atoms. Generally, silicas are classed as wet-processed,
hydrated silicas
because they are produced by a chemical reaction in water, from which they are
precipitated as ultrafine, spherical particles. However, there are in reality
two different
forms of silica, crystalline and amorphous (noncrystalline). The basic
crystalline form
of silica is quartz, although there are two other crystalline forms of silica
that are less
common -- tridymite and cristobalite. On the other hand, the silicon and
oxygen atoms
can be arranged in an irregular form as can be identified by X-ray
diffraction. This
form of silica is classified as amorphous (noncrystalline), because there is
no detectable
crystalline silica as determined by X-ray diffraction. The most preferred
forms of silica,
i.e., a fine particle, hydrated amorphous silica, are available from PPG
Industries, Inc.
and J.M. Huber Corporation in a low dust granular form. These silicas
typically are
available from PPG Industries under the tradenames HiSil~ and Silene~.
Reinforcing
silicas are generally characterized in terms of surface area (m2/g by the BET
procedure)
or particle size as determined by either electron microscopy or the Coulter
Counter
Method.
These silicas can be employed in the amount of about 10 parts to about 110
parts per 100 parts of rubber (phr), preferably in an amount from about 10 to
30 phr.
The useful upper range is limited by the high viscosity imparted by fillers of
this type.
Still other fillers include calcium carbonate, titanium dioxide, talc
(magnesium silicate), mica (mixtures of sodium and potassium aluminum
silicate) and
alumina trihydrate. The amount of these fillers may vary significantly
depending upon
the number and amount of other particular fillers employed, but typically are
employed
CA 02246013 1998-08-21
9707044(175) - 14 -
in amounts ranging from about 5 to about 200 parts by weight, per 100 parts of
polymeric material.
With respect to the processing material, it is included to improve the
processing behavior of the composition (i. e. to reduce both mixing time and
compound
viscosity as well as to increase the rate of sheet formation) and includes
processing oils,
waxes and the like. The process oil is included in an amount ranging from
about 40
parts to about 125 parts process oil phr, preferably in an amount ranging from
about 75
parts to about 115 phr. A preferred processing oil is a paraffinic oil, e.g.
Sunpar 2280,
which is available from the Sun Oil Company. Other petroleum derived oils
including
naphthenic oils are also useful.
In addition to the above ingredients which are mixed to form a masterbatch
in the preferred embodiment, cure activators such as zinc oxide and stearic
acid may
optionally be added to and made a part of the rubber masterbatch. Amounts of
these
activators can vary depending upon processing needs, but it is conventional to
add about
5 phr zinc oxide and about 1 phr stearic acid to the rubber masterbatch.
A cure package may also be included. Preferably, the cure package contains
sulfur and one or more organic, preferably sulfur vulcanizing, accelerators.
The cure
package is typically prepared and added to the EPDM walkway pad composition
after
mixing the masterbatch. The cure package for the walkway pad composition of
the
present invention may range from about 2 phr to about 10 phr with the
preferred
amounts ranging from about 3 to about 7 phr.
As part of the cure package, sulfur is preferably employed in amounts of
about 0.7 to 1.5 phr, with about 1 phr being most preferred. This amount of
sulfur is
similar to the amount of sulfur used in other EPDM rubber compositions.
In addition, the cure package provides one or more vulcanizing accelerators
including thiuram monosulfides and disulfides such as tetramethylthiuram
monosulfide
(TMTMS); tetrabutylthiuram disulfide (TBTDS); tetramethylthiuram disulfide
(TMTDS);
tetraethylthiuram monosulfide (TETMS); and the like; benzothiazole
sulfenamides such
as N-oxydiethylene-2-benzothiazole sulfenamide; N-cyclohexyl-2-benzothiazole
sulfenamide; N,N-diisopropyl-2-benzothiazolesulfenamide; N-tert-butyl-2-
benzothiazole
sulfenamide (TBBS) and the like; 2-mercaptoimidazoline; N,N-diphenyl-
guanidine;
N,N-di-(2-methylphenyl)guanadine; 2-mercaptobenzothiazole; 2-
(morpholinodithio)-
benzothiazole disulfide; zinc 2-mercaptobenzothiazole and the like; a sulfur
donor such
CA 02246013 1998-08-21
9707044(175) - 15 -
as 4,4'-dithiodimorpholine and the like; benzothiazyl disulfide (MBTS);
dithiocarbamates
such as tellurium diethyldithiocarbamate; copper dimethyldithiocarbamate;
bismuth
dimethyldithio-carbamate; cadmium diethyldithiocarbamate; lead
dimethyldithiocarbamate; zinc diethyldithiocarbamate; zinc
dimethyldithiocarbamate and
zinc dibutyldithiocarbamate (ZDBDC).
It should be appreciated that the foregoing list is not exclusive, and that
other
vulcanizing agents known in the art to be effective in the curing of EPDM
terpolymers
may also be utilized. For a list of additional vulcanizing agents, see The
Vanderbilt
Rubber Handbook, referenced hereinabove. However, it wilt be appreciated that
thioureas such as ethylene thiourea; N,N-dibutylthiourea; N,N-diethylthiourea
and the
like as well as various hexasulfides such as dipentamethylene thiuram
hexasulfide
(DPTH) are not specifically listed above. That is because the present
invention may be
devoid of thioureas and hexasulfides in the walkway pad composition, but still
maintain
its physical properties.
Moreover, it has been found that the use of a combination of MBTS and
ZDBDC as accelerators offers a number of advantages over other accelerators
such as
the thiuram accelerators including tetramethylthiuram monosulfide (TMTMS) and
tetramethylthiuram disulfide (TMTDS), and certain sulfenamide accelerators
such as,
for example, t-butyl-2-benzothiazyl sulfenamide (TBBS). This combination has
been
found to improve tear resistance. Still further, this combination provides a
lower raw
material cost than these other accelerators listed hereinabove.
Other optional ingredients include, for example, conventional amounts ~f
other conventional additives, such as zinc oxide, stearic acid, antioxidants,
processing
aids, homogenizing agents, antiozonants, flame retardants, and the like. For
instance,
one particular processing aidi homogenizing agent suitable for use in the
present
invention is a mixture of dark aromatic hydrocarbon resins available from the
Struktol
Company of Stow, Ohio under the tradenanle Struktol 4OMS. This processing aid
is
used to improve the dispersion of the fillers such as carbon black, ground
aubber
particles, coal filler, mineral fillers and the like. Struktol 40MS has a
softening point
of about 100°C, an ash content of less than 2 percent by weight, a bulk
density of about
650 grams/liter and a specific gravity of about 1.06.
The compounding ingredients can be admixed, utilizing an internal mixer
(such as a Banbury mixer), an extruder, and/or a two-roll mill, or other
mixers suitable
CA 02246013 1998-08-21
9707044(175) - 16 -
for forming viscous, relatively uniform admixtures. When utilizing a type B
Banbury
internal mixer, in a preferred mode, the dry or powdery materials such as the
mineral
fillers as well as zinc oxide, stearic acid and antioxidant of the present
invention are
added first, followed by the liquid process oil and finally the polymer, i.e.,
EPDM (this
type of mixing can be referred to as an upside-down mixing technique). The
resultant
mixture forms a masterbatch to which the cure package can then be added. The
cure
package typically includes sulfur and one or more organic accelerators.
The resulting admixture may then be sheeted to a thickness ranging from
about 0.25 inches to about 0.50 inches, and preferably to about 0.3 inches, by
conventional sheeting methods, for example, milling, calendering or extrusion.
The
sheeting may then be cut into thick, resilient mats or pads having widths
ranging from
about 20 to about 40 inches and lengths ranging from about 20 inches to about
4U
inches. Preferably, the resultant walkway pad is about 30 inches square.
The unvulcanized rubber walkway pad composition thus prepared is shaped
into a desired form by, for instance, extruders, calender rolls, or
compression presses,
and is vulcanized simultaneously by either compression molding or injection
molding
techniques. Ordinarily, it is common practice to cure the unvulcanized rubber
walkway
pad by heating the vulcanizate to a temperature of about 150°C to about
250°C for
anywhere from about 5 to about 20 minutes.
The resultant walkway pad of the present invention will show no signs of
cracking or splitting and will remain flexible at temperatures as low as -
20°C.
Moreover, the pad will be free of any mold release on the non-dimpled side
thereof.
Other physical properties include a minimum percent elongation of 100 upon
testing in
accordance with ASTM D-412, a brittleness temperature of at least -40°C
when tested
in accordance with ASTM D-2137, and a Shore A hardness of about 55 to 70 as
tested
in accordance with ASTM-D-2240. Since it is made from EPDM, the resultant
walkway pad is known to exhibit excellent weathering properties and water
absorption
resistance as well as outstanding heat aging performance.
The walkway pad of the present invention is also compatible with various
adhesives and sealants commonly used to adhere EPDM membranes together. It is
believed that this will make it easier for the installer to place the walkway
pad onto the
roof. The walkway pad of the present invention may be applied to roofing
membranes
or other forms of roof covering material by one of at least two ways using
liquid
CA 02246013 1998-08-21
9~o~oaa(ms~ _ 17 _
adhesives or tape adhesives such as seam tapes. Seam tapes typically are about
3 to 7
inches wide and are wound on release paper in roll form. These tapes may be
made
from an EPDM composition as well and may be applied to the bottom or lower
surface
of the walkway pad immediately after removal of the pad from the mold during
the
manufacturing process, in which case no cleaning or priming of the walkway pad
may
be required. Alternatively, the tape may be applied to the walkway pad prior
to
installing the walkway pad on the roof surface. This method typically involves
cleaning
and/or priming the walkway pad and then applying the liquid or adhesive tape
to the
pad. The walkway pad may then be applied to the rooftop membrane. The adhesive
keeps the walkway pad in place on the roof surface, and the walkway pad serves
to
protect the roof system, especially the membrane from foot traffic.
In order to demonstrate practice of the present invention, several test
walkway pad compositions were prepared and subjected to various physical
property
tests, as will now be set forth in detail. In the first six Examples, 85 parts
by weight
of one particular amorphous EPDM terpolymer, Vistalon~ MD-2727, was added with
15 parts by weight of a second, semi-crystalline EPDM terpolymer, Vistalon~
3708, to
form the polymeric component of the present invention. In Example Nos. 7-11,
100
percent of an amorphous EPDM terpolymer, available from Uniroyal Chemical Co.
under the tradename Royalene~ was used as the sole polymeric material of the
composition.
The following examples are submitted for the purpose of further illustrating
the nature of the present invention and are not to be considered as a
limitation on the
scope thereof. Parts and percentages are by weight, unless otherwise
indicated.
CA 02246013 1998-08-21
9707044(175) _ ~ g _
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CA 02246013 1998-08-21
9707044(175) - 19 -
a. Vistalon MD 2727
b. Vistalon 3708
c. Royalene spac Proprietary Amporphous EPDM available from Uniroyal Chemical
under the tradename Royalene. In example 12, this EPDM is blended with
proprietary, wide-spec.amorphous EPDM available from Goldsmith and Eggleton of
Wadsworth, Ohio.
d. N-650 HiStr GPF Black
e. N-330 HAF Black
f. EPDM Cyrogrind (100 Mesh)
g. Struktol 40 MS
h. Sunpar 2280 Process Oil
i. Hi-White R Clay
j. Sulfads
k. Santocure NS
The examples illustrated in Table I comprise EPDM walkway pad
compositions. Examples 1-6 comprise 100 parts by weight of EPDM terpolymer,
about
110 parts carbon black, from about 100 to about 600 parts cryogenically ground
EPDM
rubber, about 80 parts processing oil, about 5 parts zinc oxide, and about 1
part stearic
acid to form a rubber masterbatch. About 0.95 parts by weight sulfur with
about 1.4
parts, in total, of sulfur vulcanizing accelerators are then added to the
rubber
masterbatch.
Examples 7-11 include 100 parts amorphous EPDM, and from about 140 to
about 165.75 parts by weight of two types of carbon black. From about 95 to
about 115
parts by weight of a processing oil and about 2.5 parts of a processing aid is
also
included in these compositions. Further, about 20 parts of coal filler is
included, along
with about 5 parts zinc oxide, and about 1.5 parts stearic acid to form the
rest of the
rubber masterbatch. The cure package again includes about 0.95 parts by weight
sulfur
with about 3.35 to about 4.1 parts, in total, of sulfur vulcanizing
accelerators being
added. The cure package in these compositions do not include a hexasulfide
(DPTH).
Lastly, Example 12 includes about 50 parts of the same amorphous EPDM
employed in Examples 7-11 and about 50 parts of a different amorphous EPDM.
However, the rest of the ingredients essentially parallel those provided in
Example 12.
These include about 150 parts by weight of two types of carbon black, about
105 parts
by weight of a processing oil and about 2.5 parts by weight of a processing
aid.
Further, about 20 parts coal filler is included, along with about 5 parts zinc
oxide and
CA 02246013 1998-08-21
9707044(175) - 20 -
1.5 parts stearic acid. The cure package again includes about 0.95 parts by
weight
sulfur with about 4 parts, in total, of sulfur wlcanizing accelerators being
incorporated
in the walkway pad composition.
Complete formulations for each example appear in Table I hereinabove with
S all parts given on the basis of parts per hundred parts of rubber (phr) by
weight, unless
otherwise specified.
The cure characteristics, viscosity and scorch measurements, stress-strain
data, Die C tear properties, and hardness of the walkway pad compositions were
then
determined for each example of the present invention. The cure characteristics
(cure
rate, cure state, etc.) of the fully compounded walkway pad compositions were
determined by means of a Monsanto Oscillating Disc Rlleometer in accordance
with
ASTM Method D 2084-81. The specific conditions employed involved using a mini-
die
attachment operating at 100 rpm, with the die oscillating at a three degree
arc at 160°C
during actual testing.
The compound processing characteristics of the walkway pad compositions
were determined using a Monsanto Mooney Viscometer (MV-2000E) Tester. The
specific test conditions involved using a large rotor (1.5-inches in diameter)
die
attachment operating at 135°C during the test procedure. The Mooney
viscometer
provided useful information involving the compound viscosity and processing
(scorch)
safety of the fully compounded EPDM walkway pad compositions. This test method
can
also be used to determine incipient cure time and the rate of cure during the
very early
stages of vulcanization.
In testing, each of the walkway pad compositions (Examples 1-12) were
compression molded to a thickness of about 45 mils and cut into a plurality of
test
specimens as discussed hereinbelow. The initial Instron jaw separation was two
inches.
Each test specimen was tested using a crosshead speed of 20 inches per minute
on a
table model 4301 Instron Universal Tester. The Universal Tester (a testing
machine of
the constant rate-of jaw separation type) is equipped with suitable grips
capable of
clamping the test specimens, without slippage.
For testing purposes, dumbbell-shaped specimens were also cut from
individual 45-mil thick flat sheets of the walkway pad material according to
ASTM D-
412 (Method A - dumbbell and straight specimens). Modulus, tensile strength
and
CA 02246013 1998-08-21
9707044(175) - 21 -
elongation at break measurements were obtained using the table model Instron~
Tester,
Model 4301, and the test results were calculated in accordance with ASTM D-
412. All
dumbbell test specimens were allowed to set at room temperature for about 24
hours
before testing was carried out at 23°C using the appropriate metal die
(90° angle die C).
Die C tear specimens were also cut and tested under the same conditions as the
dumbbell-shaped specimens. Again, the test specimens were allowed to set for
about
24 hours before testing was carried out at 23°C.
Shore "A" hardness, which measures the hardness of the cured rubber
wlcanizate, was conducted at 23°C in accordance with ASTM D-2240-91.
Hardness
is measured by penetrating the surface of a cured rubber vulcanizate with an
indentor.
Hardness measurements are based upon initial (instantaneous) indentation or
indentation
after a specified period of time (dwell time), or both. Each cured rubber
wlcanizate
is allowed to set for about 24 hours prior to testing.
Physical properties of each of the rubber compounds were measured and
have been reported in Table II hereinbelow. The resultant walkway pad
compositions
in Examples 1-6 (Table I) can be characterized as having tensile at break in
excess of
665 psi or higher and die C tear values ranging between 113 and 153 lbs./inch
at 23°C.
The hardness of Examples 1-6 ranged between about 63 and 65. The elongation at
break values certainly exceeded the minimum limit of 100% elongation at break
at
23°C.
Examples 7-12 also displayed excellent physical properties. Examples 7-12
feature two types of carbon black, replacing the cryogenically ground rubber,
i.e.,
EPDM Cryogrind (100 mesh). The Examples also include higher paraffinic process
oil
loadings and an increased amount of sulfur vulcanizing accelerators. Tensile
strength
values for Examples 8, 11 and 12 ranged between 1236 and 1326 psi, while the
die C
tear properties at 23°C were about 199 lbs./inch or higher. Increasing
the load of
process oil reduced cured compound hardness values to about 65. Die C tear
properties
were enhanced by replacing the cryogenically ground EPDM rubber, a filler,
with two
types of carbon black. The overall cure rates at 160°C were increased
as the level of
the sulfur wlcanizing accelerator increased and compound viscosity was reduced
to the
desired level (30-35 Mooney units at 135°C) by increasing the amount of
paraffinic oil
CA 02246013 1998-08-21
9707044(175) - 22 -
in the walkway pad (see Examples 11 and 12). These and other physical
properties are
presented in Table II hereinbelow.
CA02246013 1998-08-21
9707044( 75) 23
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CA 02246013 1998-08-21
9~0~o44~ms) -24-
Compared to walkway pads produced using various conventional elastomers,
i.e., natural rubber, synthetic polyisoprene, styrene-butadiene rubber (SBR),
polybutadiene and butyl (IR) rubber, walkway pads featuring EPDM have
excellent tear
properties, harden at a much slower rate under normal rooftop aging conditions
as well
as indoor accelerated aging conditions, and develop less shrinkage over an
extended
period of time at elevated temperatures. The process (paraffinic) oil used in
an EPDM
walkway pad is less volatile compared to an aromatic process oil commonly used
in
other walkway pads. The EPDM walkway pad compositions of the present invention
are flexible and show excellent weathering performance properties including
heat and
ozone aging resistance. The EPDM walkway pad compositions also show better
physical properties performance retention compared to other conventional
polymeric
walkway pads.
It is to be understood that the invention is not limited to the specific type
of
amorphous EPDM exemplified herein or by the disclosure or other EPDMs or EPMs,
the examples having been provided merely to demonstrate practice of the
subject
invention. Those skilled in the art may readily select other EPDMs (and, in
certain
instances, EPMs) having the desired crystallinity characteristics. Similarly,
the
invention is not necessarily limited to the particular fillers and processing
oil exemplified
or the amounts thereof. In fact, with respect to the ground rubber, the
processing aid,
the carbon blacks, coal filler, and clay, it will be appreciated that these
ingredients are
essentially optional.
In conclusion, it should be clear from the foregoing examples and
specification disclosure that a walkway pad containing 100 percent EPDM or a
polymer
blend of EPDM and EPM is highly desirable. With respect to the EPDMs, those
EPDMs having up to 2 percent by weight crystallinity are particularly
desirable,
although a minor amount of EPDM having more than 2 percent by weight
crystallinity
may be employed. This composition provides a walkway pad which is suitable for
use
on the roof of a building.
It will be appreciated that any variables disclosed herein can readily be
determined and controlled without departing from the scope of the invention
herein
disclosed and described. Moreover, the scope of the invention shall include
all
modifications and variations that fall within the scope of the attached
claims.
