CA1087779A - Heat resistant ethylene-propylene rubber and insulated conductor product thereof - Google Patents

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.

Description

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 - 10 108~7'79 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:

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.
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O O-- ~ ~I V h O a n -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

Claims (18)

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:
.

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:
.

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:
.

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:
.

.

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:

.

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:

.

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:

.

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.