HEAT RESISTANT ETHYLENE-PROPYLENE RUBBER AND INSULATED CONDUCTOR PRODUCT THEREOF

CAOUTCHOUC RESISTANT A LA CHALEUR, A BASE DE PROPYLENE ET D'ETHYLENE, ET CONDUCTEUR ISOLE

English Abstract

ABSTRACT OF THE DISCLOSURE
A crosslink curable ethylene-propylene rubber composi-
tion with improved resistance to heat, the cured rubber
composition and electrical conductors insulated with said
cured rubber composition. The improved rubber composition
comprises a combination of ethylene-propylene rubber,
chlorosulfonated polyethylene, zinc oxide, a combination
selected from the group consisting of talc with carbon black
and hydrated alumina with amorphous silica each constituent
being in particular proportions, and can include optional
components which enhance the overall attributes of the rubber
composition.

Claims

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:
1. A curable ethylene-propylene rubber composition
having improved resistance to heat and apt electrical and
physical properties, consisting of the combination
in approximate parts by weight of:
<IMG>.
2. The crosslink cured product of the ethylene-
propylene rubber composition of claim 1.
3. A curable ethylene-propylene rubber composition
having improved resistance to heat and apt electrical and
physical properties, consisting essentially of the combination
in approximate parts by weight of:
<IMG>.
12

4. The crosslink cured product of the ethylene-
propylene rubber composition of claim 3.
5. A curable ethylene-propylene rubber composition
having improved resistance to heat and apt electrical and
physical properties, consisting essentially of the combination
in approximate parts by weight of:
<IMG>.
6. The crosslink cured product of the ethylene-
propylene rubber composition of claim 5.
7. A curable ethylene-propylene rubber composition
having improved resistance to heat and apt electrical and
physical properties, consisting of the combination in approximate
parts by weight of:
<IMG>.
13

<IMG>.
8. The crosslink cured product of the ethylene-
propylene rubber composition of claim 7.
9. An electrical conductor having an insulating
covering thereon comprising the composition defined in claim
2, 4 or 6.
10. An electrical conductor having an insulating
covering thereon comprising the composition defined in claim 8.
Claims Supported by the Supplementary Disclosure
11. A curable ethylene-propylene rubber composition
having improved resistance to heat and suitable electrical and
physical properties, consisting essentially of the combination in
approximate parts by weight of: ethylene-propylene rubber, 100;
chlorosulfonated polyethylene, 3 to 10; zinc oxide, 15 to 30;
a combination selected from the group consisting of talc, 75 to
200 with carbon black, 10 to 30, and hydrated alumina, 35 to
100 with amorphous silica, 35 to 100; vinyl silane, 1 to 3;
antimony oxide, 2 to 10; antioxidant, 0.5 to 6; and peroxide
curing agent, 2 to 8.
12. A curable ethylene-propylene rubber composition
having improved resistance to heat and having apt electrical
and physical properties, comprising the combination in
approximate parts by weight of:
14

<IMG>.
13. The crosslink cured produce of the ethylene-
propylene rubber composition of claim 12.
14. A curable ethylene-propylene rubber composition
having improved resistance to flame and heat and having apt
electrical and physical properties, consisting essentially of
the combination in approximate parts by weight of:
<IMG>.
15. The crosslink cured produce of the ethylene-
propylene rubber composition of claim 14.

16. A curable ethylene-propylene rubber composition
having improved resistance to flame and heat and having apt
electrical and physical properties, consisting of the combination
in approximate parts by weight of:
<IMG>.
17. The crosslink cured product of the ethylene-
propylene rubber composition of claim 16.
18. An electrical conductor having an insulating
coating thereon comprising the composition defined in claim 13,
15 or 17.
16

Description

21WC-1862
HEAT RESISTANT ETHYLENE-PROPYLENE RUBBER
AND INSULATED CONDUCTOR PRODUCT THEREOF
BACKGROUND OF THE INVENTION
Loss of elasticity, or embrittlement, upon exposure to above amhient
temperatures has been a longstanding impediment of many common elastomers. The
deteriorating effect of heat upon elastomers has prompted continuing efforts
and the use of a variety of remedial measures to improve their resistance to
heat, such as the development and use of antioxidants or agents which block
the action of oxygen or free radical forming ingredients, and new compound
formulations
The characteristic loss of elasticity or embrittlement of
elastomers is a particularly significant and critical problem in the electrical
insulating field wherein conductors insulated with heat degradable elastomers
are utilized in areas which are exposed to high temperatures, such as leads
or wires in or about motors and transformers, or within apparatus containing
heating elements or which are otherwise disposed in locations encountering
high temperatures.
SUMWARY OF THE INVENTION
This invention comprises a novel rubber composition of a specific
combination of compounded ingredients and proportions thereof which has
significantly improved resistance to heat, or heat aging, along with
satisfactory physical and electrical properties. The heat resistant rubber
composition of this invention is composed of an essential combination of
ethylene-propylene rubber, chlorosulfonated polyethylene, zinc oxide, talc
and carbon black in particular proportions, and can include optional components
which enhance the overall attributes of the rubber composition. The invention
additionally includes electrical conductors insulated with the highly heat
resistant ethylene-propylene rubber compound.
OBJECTS OF THE INVENTION
It is a primary object of this invention to provide a novel rubber
composition having increased resistance to high temperatures.
It is a further object of this invention to provide a novel curable
rubber composition and products thereof which withstand high temperatures and
3~

2lWC 1862
`` 10877'79
exhibit stable chemical, physical and electrical properties
over extended periods of exposure to elevated temperatures.
It is an additional object of this invention to
provide a crosslink cured ethylene-propylene rubber composi-
tion that is resistant to embrittlement and 108~ of elasti-
ctty upon prolonged heating and posses~es physical and
electrical attributes which render it advantageously suitable
for use as an electrical insulating material for conductors
such as wire and cable.
It is also a primary object of this invention to
provide a new and improved heat resistant electrical conductor
product insulated with a cured elastomer composition having
a high tolerance to elevated temperature and apt physical
and electrical properties whereby the insulating material
substantially maintains its original elastic, flexible and
dielectric characteristics through its service life
regardless of temperature conditions.
It i8 a specific object of this invention to
provide an ethylene-propylene rubber composition posseæsing
apt electrical properties, abrasion and tear resistance,
flexibility and elasticity, and which retains these attri-
butes notwithstanding high temperature conditions, and an
improved heat stable electrical insulation thereof.
This invention specifically consists of a novel
combination of compounded ingredients and relative proportions
thereof which in total produce an elastomeric composition
having outstanding stability and resistance to deterioration
upon subjection to elevated temperatures over extended periods.
The rubber composition of this invention comprises
the combination, in approximate parts by weight, consisting
essentially of:
Ethylene-propylene rubber 100
Chlorosulfonated polyethylene 3 - 10

21WC-1862
108~7'79
Zinc Oxide 15 - 30
Talc 75 - 200
Vinyl silane 1 - 3
Carbon black 10 - 30
Antimony oxide 0 - 10
Antioxidant 0.5 - 6
Peroxide curing agent 2 - 8
Curing Coagent o - 3
The ethylene-propylene rubber component comprises ethylene-propylene
copolymers and terpolymers of typical commercially available compositions con-
stituting about 25 to about 75 parts by weight of ethylene nomer copoly~merized
with about 75 to about 25 parts by weight of propylene nomer. Terpolymers of
ethylene-propylene include those commercial rubbers produced by the copolymeriza-
tion of ethylene and propylene together with minor proportions of dienes such asethylidene norbornene, dicyclopentadiene and 1,4-hexadiene.
Talc, of course, consists of a well known but distinctive mineral
form of hydrated magnesium silicate. It is preferred that the talc component
of this invention be of the plate type in its physical fo~m.
Antioxidants for use in the composition of this invention should be
of the amine, hydroquinoline, or other heterocyclic types. Amine type anti-
oxidants include, for example, di-B-naphthyl-p-phenylenediamine, and hydro-
q~inoline type comprise the polymerized 1,2-dihydro-2,2,4-trimethylquinolines.
Other types of heterocyclic antioxidants include, for exa~ple, zinc salt of
2-mercaptobenzimidazole.
Peroxide crosslink curing agents for the ethylene-propylene rubber
compound of this invention comprise the free radical forming organic peroxides
such as tertiary peroxides characterized by at least one unit of the structure
f cl `
C C-- o o C C
C C
which is activated by its decomposition at temperatures in excess of about 295F.
The use of such peroxides in crosslinking polymers is described in detail in U.S.

~ ~ ~ 21WC-1862
patents 2,888,424 issued May 26,1959 to Precoplo et al; 3,079,370 issued
February 26, 1963 to Precopio et al; and 3,214,422 issued October 26, 1965
to Mageli et al. A commonly used and preferred curing agent for this
invention is dicumyl peroxide. Other useful peroxide curing agents include
the tertiary diperoxides such as 2,5-dimethyl-2,5(t-butyl peroxy) hexane,
and 2,5-dimethyl-2,5 di (t-butyl peroxy) hexyne-3, and the like diperoxy
compounds.
The use of a peroxide curing coagent in the crosslinking of the novel
composition of this invention is strongly preferred to increase the efficiency
of the cure in accordance with the technology in this art. Apt curing coagents
include, for example, trimethylol propane trimethacrylate and other esters of
methacrylic acid such as ethylene glycol dimethacrylate and 1,3 butyl glycol di-
methacrylate. Additional examples of coagents are set forth in an article
entitled "Evaluation Of Cross-Linking Coagents In Ethylene-Propylene Rubber"
by Lenas, I&EC Product Research & Development, Volume 2, No. 3, September, 1963,
pages 202 - 208.
A processing aid is generally desirably included in the rubber composition
of this invention to facilitate the compositions preparation and handling such
as the mixing or compounding of its ingredients and/or its forming and consoli-
dation into a product shape by molding or extrusion. Processing aids include
oils, waxes and jellies derived from petroleum or hydrocarbon sources and they
serve to unite the ingredients into a coherent and uniform workable plastic
mass and~or to provide a lubricant therein.
The following comprise examples illustrating specific embodiments of
this invention and demonstrating their improved resistance to heat in relation
to a control comprising a prior art heat resistant composition.
The compounds of the control and each example of this invention were
all prepared in an identical manner, comprising first admixing all components,
except the peroxide curing agent and curing coagent, in a Banbury for about 12
minutes while heating to about 250~. After cooling to room temperature, the
curing coagent was added to the admixture on a two roll rubber mill followed
by the addition of the peroxide and dispersed through the other ingredients.
The compositions of the control and the examples of this invention
C were as follows in approximate parts by weight:
-- 4 --

21WC-1862
108m9
CONTROL ExAMpr~Fs
A B C I II III
Ethylene-propylene-diene
terpolymer (du Pont-
Nordel* 1145) 100 100 100 100 100 100
Chlorosulfonated polyethylene
(du Pont-Hypalon* 40) - - - 5 5 5
Zinc Oxide 5 5 20 20 20 20
Talc - hydrated magnesium
silicate (Sierra Talc -
Mistron* Vapor) 179 179 179 179 179 179
Vinyl Silane 3 3 3 3 3
Carbon Black 20 20 20 20 20 20
Antimony Trioxide - - - - 5 5
Antioxidants -- Reaction product
of acetone & diphenylamine
(Uniroyal - B.L.E.*-25) 2 - - - - -
Zinc Salt of 2-mercaptobenzi-
midazole (Mobay Chemical-
Z.M.B.*~ 2 2 2 2 2
Polymerized 1,2-dihydro-2,2,4-
trimethylquinoline (R.~.
Vanderbilt - Agerite* MA) - 2 2 2 2 2
Diisodecyl phthalate - - - - - 0.5
Processinq lubricant oil
(Sun Oil - Sunpar* 2280)54 54 54 54 54 54
Dicumyl peroxide curing agent
(Hercules - Di Cup* R)4.19 4.19 4.19 4.19 4.19 4.19
Curing Coagent - trimethylol pro-
pane trimethacrylate
(Sartomer* Resin - SR-350) 2 2 2 2 2 2
Samples of each composition of the controls and of the examples of
this invention were prepared and crosslink cured by molding identical quantities
for 3 minutes at 200F-220F in a press and then curing in an open steam
vulcanizer for 1 minute at 250 pounds per square inch gauge stea~ pressure.
The tensile strength and percent elongation were determined for the
original crosslink cured composition of each control and example and for each
of said compositions after an accelerated heat aging for 13 days at a temperat~re
*Trade Mark
C

~ ~ ~ 21WC-1862
of 175C. The measured properties were as follows:
CO~rROLS EXPMPLES
A B C I II III
Original Properties
S Tensile Strength,lbs/in21002 1111 1005 1009 1001 1011
Elongation, percent 262 213 227 271 233 280
13 Days In Air Oven At 175C
Tensile strength,lbs/in2 BrittleBrittle 371 756 1121 786
Percent retention BrittleBrittle 36.9 74.9 112 77.7
Elongation, percent Brittle Brittle 22 S7 58 - 58
Percent retention BrittleBrittle 9.7 21 26 20.7
: Additional samples of unaged compositions of Control A and Exa~ples
II and III were subjected to long term aging tests under the ~ollowing conditions
and their resultant tensile strength and elongation properties were dete~mined
lS as follows:.
CONTROL EXAMPLES
A II III
Long Term Aging
30 Days In Air Oven at 136C
Tensile, lbs/in2 1112 1141 - 1202
Percent retention 111 114 119
Elongation, percent 193 223 217
Percent retention 74 95.8 77.5
60 Days In Air Oven at 136C
Tensile, lbs/in21048 1166 1228
Percent retention 104.6 116.5 121~5
Elongation, peTcent 133 212 20S
Percent retention S0.8 91.1 73.2

1 ~ ~ 21WC 1962
90 Days In Air Oven at 136C
Tensil, lbs/in 953 1119 1201
Percent retention 95.1 111.8 111.8
Elongation, percent 102 117 187
Percent retention 38.9 76 66.8
Although the invention has been described with
reference to certain specific embodiments thereof, numerous
modifications are possible and it is desired to cover all
modifications falling within the spirit and scope of this
invention.
SUPPLEMENT DISCLOSURE
Additionally, in another aspect of the invention,
the heat resistant rubber composition is composed of a
composition of ethylene-propylene rubber, chorosulfonated
polyethylene, zinc oxide, a combination seIected from the
group consisting of talc with carbon black and hydrated alumina
with amorphous silica each constituent being in particular
portions, and can include optional components which enhance
the overall attributes of the rubber composition.
Further, when the heat resistant rubber composition
has the element selected from hydrated alumina and amorphous
silica the rubber composition has an increased resistance
to flame.
In one embodiment of the invention the rubber
composition comprises the combination, in approximate parts by
weight, consisting essentially of:
Ethylene-propylene rubber 100
Chlorosulfonated polyethylene 3-10
Zinc oxide 15-30
Hydrated alumina 35-100
Vinyl silane 1-4
Amorphous silica 35-100

1~79 21WC-1962
Antimony oxide 2-10
Antioxidant 0.5-6
Peroxide curing agent 2-8
Curing coagent 0-3
Hydrated alumina, of course, consists of a well
known but distinctive mineral form of hydrated alumina oxide.
The amorphous silica comprises silicas synthetically
produced by precipitation, such as the commercial product silene*
D, sold by Pittsburgh Plate Glass Company.
Antioxidants for use in the composition may comprise,
in addition to those previously mentioned, tetrakis[methylene
3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane
(Irganox* 1010) and in general the aforementioned amine,
hydroquinoline, or other heterocyclic types.
The following comprise examples illustrating specific
embodiments of this invention and demonstrating their unique
resistance to flame in relation to controls comprising similar
compositions.
The compounds of the control and each example of this
invention were all prepared in an identical manner, comprising
first admixing all components, except the peroxide curing agent
and curing coagent, in a Banbury for about 10 minutes while
heating to about 25~F to 300F. After cooling to room
temperature, the curing coagent was added to the admixture
in a Banbury followed by the addition of the peroxide and
dispersed through the other ingredients.
*Trade Mark

21WC 1962
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10~77 79
Samples of each composition of the controls and of the
examples of this invention were prepared and extrusion molded on
copper wire, #18 Awg. in a wall thickness of 3/64 of an inch, then
crosslink cured by exposure to steam at a temperature of about
406F for about 1.25 minutes.
The flame resistance of the composition of each
control and each example of this invention as applied to the
wire was determined and evaluated by subjecting samples of each
of the composition on wire as set forth to Underwriter's Labora-
tories Flame Travel Test 758, which measures the rate of flame
spread or travel along a horizontally supported insulated wire,
and also dripping or discharge of burning particules. The U.L.
7~8 Travel Test results for samples of each composition of the
control and examples of this invention applied as insulation to
wire, measured as rate of flame travel between the seven inch
mark and the ~hirteen inch mark in inches per minute and
ignition of underlying cotton due to dripping, were as follows:
CONTROL EXAMPLES
A B C I II III
Inches/min. 0.75 Flame 0.83 Flame 0.87 0.93
Out Out
Before Before
7" 7"
Dropping Burning
Particles or
~aterial No Yes Threw No No No
Sparks
-- 11 --