EPDM walkway pad compositions and uses therefor

A walkway pad composition comprises 100 parts by weight of an ethylene-propylene-diene terpolymer; from about 60 to 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 terpolymer; from about 40 to 175 parts by weight of a processing material and mixtures thereof, per 100 parts of the terpolymer; and from about 2 to 10 parts by weight of a cure package, per 100 parts of the EPDM terpolymer, the composition being devoid of any additional polymeric components. The 100 percent EPDM walkway pad composition has better low temperature properties and superior weathering resistance, and heat aging resistance compared to other walkway pad compositions which may include other polymeric components such as natural rubber, synthetic polyisoprene, styrene-butadiene rubber (SBR), polybutadiene, and butyl (IR) rubber. Up to about 25 parts by weight of ethylene-propylene copolymers may be substituted for the EPDM terpolymers.

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 (EPM) 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-diene 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, comprising other rubber or polymeric materials, directly onto the 
membrane defining a traffic pattern to areas of the roof to which travel 
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, such as set forth in U.S. Ser. No. 
08/606,119 owned by the Assignee of record, 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 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 walkway pad should show no signs of cracking or 
splitting when folded around a one-inch bending radius at 40.degree. F. 
The walkway pad should lay flat and remain flexible at temperatures as low 
as -20.degree. 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.degree. C. according to 
ASTM-D-2137; and a Shore "A" Hardness of between about 55 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.degree. 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. 
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. 
Other objects of the invention may be accomplished by providing a walkway 
pad comprising 100 parts by weight of an ethylene-propylene-diene 
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.

PREFERRED EMBODIMENT 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, 
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 20 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 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 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 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 diene monomer. Although not to be limited thereto, illustrative methods 
for preparing such terpolymers are found in U. S. Pat. No. 3,280,082 the 
disclosure of which is incorporated herein by reference. 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 John 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 5 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 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 diene 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.degree. 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 diene monomer utilized in forming the EPDM terpolymers is preferably a 
non-conjugated diene. Illustrative examples of non-conjugated dienes 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.RTM., 
from Uniroyal Chemical Co. under the tradename Royalene.RTM., and from DSM 
Copolymer under the tradename Keltan.RTM.. For example, one preferred 
amorphous EPDM terpolymer is Vistalon.RTM. MD-2727. This EPDM terpolymer 
has a Mooney viscosity (ML/1+4 at 125.degree. C.) of about 44.+-.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.degree. C.) of about 46.+-.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.degree. C.) of 
about 50.+-.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. 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 65 weight percent ethylene and from about 2 to about 4 weight 
percent of the diene 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.degree. C.) of about 45 to 50 and should have less than 
about 4 weight percent unsaturation. Non-conjugated dienes 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.RTM. 3708. This EPDM 
terpolymer has a Mooney Viscosity (ML/1+4 at 125.degree. C.) of about 
52.+-.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 5 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 term 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.RTM. 740. This EPM has a Mooney 
viscosity (ML/4 at 125.degree. C.) of about 63 and an ethylene content of 
about 60 weight percent. 
Other EPMs are available from DSM Copolymer under the tradename Keltan.RTM. 
and from Exxon Chemical Co. under the tradename Vistalon.RTM.. For 
instance, Keltan.RTM. 3300A and 4200A have Mooney viscosities (ML/4 at 
125.degree. C.) of about 35 and about 40, respectively, while 
Vistalon.RTM. 808 and 878 have Mooney viscosities (ML/4 at 125.degree. 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 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 1.80 g/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 coal 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.+-.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 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, Va. 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 ground rubbers are cryogenically or 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.+-.0.015 g/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.RTM., Barden R.RTM.; and LGB.RTM.. 
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.RTM. 
and K-78.RTM. or from Evans Clay Company under the tradename Hi-White 
R.RTM.. Particularly preferred is Hi-White R.RTM., an air-floated soft 
clay characterized as having a pH of about 6.25.+-.1.25, an oil absorption 
of 33 grams/100 grams of clay, a particle size of 68% (.+-.3) being finer 
than two microns, and a specific gravity of about 2.58. 
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.RTM. DL, Polyfil.RTM. F, Polyfil.RTM. FB, 
Polyfil.RTM. HG-90, Polyfil.RTM. K and Polyfil.RTM. 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.RTM. 40, 
Polyfil.RTM. 70, and Polyfil.RTM. 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.degree. C. The preferred chemically modified clays are 
commercially available from J. M. Huber Corporation and include those 
available under the tradenames Nucap.RTM., Nulok.RTM. and Polyfil.RTM.. 
Another preferred chemically modified clay is commercially available from 
Kentucky-Tennessee Clay Company under the tradenames Mercap.RTM. 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 m.sup.2 /g and a pH (5% solution) of 10. 
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 m.sup.2 /g, a 
refractive index at 20.degree. 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 
m.sup.2 /g, a refractive index at 20.degree. 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 
hereinabove. 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.RTM. and 
Silene.RTM.. Reinforcing silicas are generally characterized in terms of 
surface area (m.sup.2 /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 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-guanadine; 
N,N-di-(2-methylphenyl)guanadine; 2-mercaptobenzothiazole; 
2-(morpholinodithio)-benzothiazole disulfide; zinc 2-mercaptobenzothiazole 
and the like; a sulfur donor such 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 will 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 of 
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 
aid/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 tradename Struktol 40MS. This processing 
aid is used to improve the dispersion of the fillers such as carbon black, 
ground rubber particles, coal filler, mineral fillers and the like. 
Struktol 40MS has a softening point of about 100.degree. 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 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 40 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.degree. C. to about 250.degree. 
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.degree. 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.degree. 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 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.RTM. MD-2727, was added with 15 parts by weight of a second, 
semi-crystalline EPDM terpolymer, Vistalon.RTM. 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.RTM. 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. 
TABLE I 
__________________________________________________________________________ 
EPDM Walkway Pad Compositions (Parts per hundred rubber hydrocarbon by 
weight) 
Compound Nos. 
1 2 3 4 5 6 7 8 9 10 11 12 
__________________________________________________________________________ 
Amorphous EPDM.sup.a 
85 85 85 85 85 85 -- -- -- -- -- -- 
Semi-Crystalline 
15 15 15 15 15 15 -- -- -- -- -- -- 
EPDM.sup.b 
Amorphous EPDM.sup.c 
-- -- -- -- -- -- 100 100 100 100 100 50/50 
GPF Carbon Black.sup.d 
110 110 110 110 110 110 155.75 
155.75 
140 130 140 140 
HAF Carbon Black.sup.e 
-- -- -- -- -- -- 10 10 10 10 10 10 
Cryogenically ground 
100 200 300 400 500 600 -- -- -- -- -- -- 
Rubber.sup.f 
Processing Aid.sup.g 
-- -- -- -- -- -- 2.5 2.5 2.5 3 2.5 2.5 
Processing Oil.sup.h 
80 80 80 80 80 80 95 100 110 115 105 105 
Clay Filler.sup.i 
-- -- -- -- -- -- 15 15 25 30 25 25 
Coal Filler 
-- -- -- -- -- -- 20.05 
20.05 
20.05 
20.05 
20.05 
20.05 
Zinc Oxide 
5 5 5 5 5 5 5 5 5 5 5 5 
Stearic acid 
1 1 1 1 1 1 1.5 1.5 1.5 1.5 1.5 1.5 
Sulfur 0.95 
0.95 
0.95 
0.95 
0.95 
0.95 
0.95 
0.95 
0.95 
0.95 
0.9 0.95 
DPTH.sup.j 
0.4 0.4 0.4 0.4 0.4 0.4 -- -- -- -- -- -- 
TBBS.sup.k 
1 1 1 1 1 1 -- -- -- -- -- -- 
MBTS -- -- -- -- -- -- 2.3 2.3 2.35 
2.4 2.4 2.4 
ZDBDC -- -- -- -- -- -- 1.05 
1.15 
1.4 1.5 1.7 1.6 
TOTAL 398.35 
498.35 
598.35 
698.35 
798.45 
898.55 
409.1 
414.2 
418.75 
419.4 
414.1 
414.0 
__________________________________________________________________________ 
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 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 vulcanizing accelerators 
being incorporated in the walkway pad composition. 
Complete formulations for each example appear in Table I hereinabove with 
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 Rheometer 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.degree. 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.degree. 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 elongation at break measurements were obtained using 
the table model Instron.RTM. 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.degree. C. using the appropriate metal die (90.degree. 
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.degree. C. 
Shore "A" hardness, which measures the hardness of the cured rubber 
vulcanizate, was conducted at 23.degree. 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 vulcanizate 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.degree. 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.degree. 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.degree. 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.degree. C. were increased as the level of the sulfur vulcanizing 
accelerator increased and compound viscosity was reduced to the desired 
level (30-35 Mooney units at 135.degree. C.) by increasing the amount of 
paraffinic oil in the walkway pad (see Examples 11 and 12). These and 
other physical properties are presented in Table II hereinbelow. 
TABLE II 
__________________________________________________________________________ 
EPDM Walkway Pad Physical Properties 
Compound Nos. 
1 2 3 4 5 6 7 8 9 10 11 12 
__________________________________________________________________________ 
Rheometer at 320.degree. F. (160.degree. C.), mini-die, 3.degree. Arc 
Scorch time, minutes 
4:49 
4:44 
4:27 
4:45 
4:42 
4:45 
4:32 
4:26 
5:04 
6:51 
4:38 
3:25 
Time to 50% cure, minutes 
8:04 
7:57 
7:36 
7:42 
7:32 
7:09 
9:32 
9:23 
10:01 
11:55 
9:19 
7:08 
Time to 90% cure, minutes 
21:13 
21:08 
21:18 
21:54 
21:43 
21:20 
22:38 
22:54 
22:28 
22:37 
21:31 
19:1 
Minimum torque, lb.-inch 
9.1 12.95 
14.9 
16.9 
16.9 
19.5 
5.67 
5.34 
3.7 2.5 4.05 
4:23 
Maximum torque, lb.-inch 
30.7 
28.8 
28.6 
27.4 
26.9 
27.9 
43.16 
40.1 
35.5 
28.33 
37.7 
39.3 
Mooney Scorch at 275.degree. F. (135.degree. C.) - large rotor 
Minimum Viscosity, Mu 
40.6 
49.4 
57.7 
64.1 
66.1 
73.7 
-- 41.8 
-- -- 31.8 
32.5 
T5, minutes 18.85 
19.15 
20.2 
28.3 
26.5 
37.1 
-- 11.54 
-- -- 12.12 
11.1 
T35, minutes 28.5 
47.8 
&gt;60 &gt;60 &gt;60 &gt;60 -- 19.01 
-- -- 20.48 
19:6 
Stress-Strain Properties at 73.degree. F. (23.degree. C.) - slabs cured 
40 minutes at 320.degree. F. (160.degree. F.) 
100% Modulus, psi 
285 285 272 264 255 240 -- 555 -- -- 455 445 
300% Modulus, psi 
842 875 830 774 -- 710 -- 1240 
-- -- 1060 
1010 
Tensile at Break, psi 
1150 
1176 
1037 
886 665 790 -- 1326 
-- -- 1236 
1267 
Elongation at Break, % 
445 440 397 360 290 350 -- 370 -- -- 457 484 
Die C Tear Properties at 73.degree. F. (23.degree. C.) - slabs cured 40 
minutes at 320.degree. F. (160.degree. C.) 
Lbs./Inch 151 153 145 124 113 122 -- 199 -- -- 236 238 
Shore "A" Hardness 
Unaged - Tested at 73.degree. C. (23.degree. C.) 
63 63 64 65 65 65 74 72 63 59 64 65 
__________________________________________________________________________ 
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.