CA1136312A - Heat resistant ethylene-propylene rubber with improved tensile properties and insulated conductor product thereof - Google Patents

Abstract

HEAT RESISTANT ETHYLENE-PROPLYENE RUBBER WITH IMPROVED
TENSILE PROPERTIES AND INSULATED CONDUCTOR PRODUCT THEREOF

ABSTRACT OF THE DISCLOSURE
A cross-link curable ethylene-propylene rubber composition with improved tensile and related properties and resistance to heat, the cured rubber composition and electrical conductors indulated with said cured rubber composition. The improved rubber composition comprises a combination of ethylene-propylene rubber, chlorosulfon-ated polyethylene,finyl silane, antimony oxide, peroxide and a combination of antioxidants, zinc oxide, talc and carbon black in particular proportions.

Description

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HEAT RESISTA~T ETHYLENE-PROPYLENE RUBBER WITH IMPROVED
TEN.S ILE PROPERTIES AND INSULATED CONDUCTOR PRODUCT THEREOF

B~CKGROUND OF THE INVENTION
The present invention relates generally to compositions of ethylene-propylene rubber adapted or use as insulation compositions and to conductors insulated with such compositions. More specifically the in~ention relates to an ethylene-propylene composition having a desired and needed cornbination of properties as an insulator including improved ten.sile proper~ies in com-bination with heat resistant properties and to insulated conductors having such composition orming the insulation thereo~.
It is well-known that polymeric compositions, when used fcr insulating purposes, are used in many different environments including temperature en~ironments, and that no one composition is suitable for all uses. To a large degree the use, which is made of an insulating ~: composition, places important requirements on the compo-sition and there are many s~andards which have been established in ~he industry, and by standards organizations such as the Underwriters Laboratories,ASTM,IPCEA, for wire insula~ion compositions. In all of the standards whieh are established there is a close correlation between the requirements of the insulated composition and of the insulated wire or cable and the use to which the composi-tion or cable is to be put. Accordingly, it is well-established in the wire and cable ~echnology and indus~ry that direrent combinations o~ ~nsulating properties and .

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physical properties are required in different cables where such cables are to be used in applica-tions having particular criteria such as temperature criteria, atmospheric criteria, voltage criteria and other measurable criteria of compositions and of cables.
Another important criteria of insulating compositions, and o~ cables formed with such composltions, is the economic criteria or more specifically the ability to prepare such compositions and cables at reasonable costs.
In some other cases a composition can be prepared in a bulk form, or an extruded form, or a sheet form and have good properties but the same properties are not retained when a product is put on a conductor to form a wire or cable. For still other compositions the process ; 15 by which the material is applied to a conductor may give deleterious results in the finished product or may make the application process uneconomical.
Compositions which have been prepared in the past of ethylene-propylene rubber and which have very ` 20 desirable heat resistance and other properties for use as wire and cable insulation are disclosed in U.S. patents 4,069rl90, dated January 17, 1978 and ~,133,936, dated January 9, 1979, both patents being assigned to the same assignee as the subject application. As is brought out in ~; 25 these patents the insulating composition and the cable made with the insulating composition has a combination of proper-ties, values of which are set forth in the data included in -- the patents. Further, the composition is made up of a number of ingredients which are set forth in range values also explicitly included in the data of the preferred embodiments.
One of the desirable properties which is achieved in the compositions and product of the U.S. patents referenced above is heat resistance.
In developing the composition, the heat resistance needed was not as great as that of silicone rubbers which had been used in prior compositions but the .:
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One of the criteria in achieving heat resis-tance as is brought out in t~le patents is the avoidance of cracking and deterioration of the composition when employed at the elevated temperatures. The heat resistant properties of the composition of the reference patents are attributed to a number of factors. In this regard it is important to appreciate that a COTnpOSitiOn made up of such a combination of materials achieves a combination of properties based on the proper blending and curing of the components as prescribed in the patent. With regard to the heat resistant properties one of ~he elements or components which contribute.s to the development of the heat resistant property, but not the only component, is the inc].usion of the antioxidants in the overall combina-tion in the ranges set forth in the reference patents.
Other components are deemed significant in achieving the overall beneficial combineti~n of properties of the composition both by itself and also as a wire insulation.
However, with reference to the antioxidant the combina-tion o.~ ingredients includes the antioxidant which is present in order to inhibit such reactions at elevated temperatures as cause deterioration of the composition and product. As is evident from the text of the prior art patents,there is also present in the overall composi-tion a peroxide material which is added according to the prescribed method to provide the cross-linking as set out - in the patent. Such cross~linking gives the compositions of the refe.rence patents some of their higher temperature properties. It has generally been understood with respect to higher temperature compositions formed by peroxide curing that the presence of the peroxide and the ,~

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4lWC-2043 presence of the antioxidant material can be antagonistic to each other in the sense that their functions in the overall composition are for inconsistent purposes. More specifically the peroxide material is present to include cross-linking. By contrast the antioxidant material is present as generally contemplated to l'imit or inhibit the post-cured oxidation of the composition at the elevated temperatures at which it is used.
With reference to the aforementioned U.S. patents 10' 4,069,190 and 4,133,936 the compositions and products are referred to as heat resistant and this heat resistance is indicated in the statement of the background of the in~en tion to pertain to the loss of elasticity or to increase embrittlement upon exposure to temperatures above ambient temperatures. As stated in the patent: "The deteriorating effect of heat on elastomers has prompted continuing efforts -~, and the use of a variety of remiedal measures to improve their resistance to heat, such as the development and use of antioxidant or agents which block the action o~ oxygen or free radical forming ingredients~ and new compound formulations."
It is well known that different applications for wires require that the wires have different sets of ~,~ properties depending on the application to be made of the ' 25 wire.
For motor lead and apparatus lead applications the particular combination of properties which is required include a basic heat resistance of the insulation compound.
For such applications a preferred combination includes an economical heat resistant, tough, fle~ible insulation with a moderate tensile strength and also with good tear resistance and good abrasion resistance. For such motor lead and apparatus lead applications the insulation jacket is integral in the sense that there is no outer jacket applied over the insulation jacket having these properties. In other words there is only a single .",~
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insulating jacket appli.ed and that jacket is the one ~ which must have the desirable combination of properties ;~ recited above. Of course, the composition must also have a needed or standard set of electrical properties.
In general heat res,istant properties o~
polymers may be increased by cross-linking of the i~ polymer molecules. Such cross-linking can be accomplished for some polymer syste~ by use of thermally unstable peroxide compositions. However the aging properties of polymer systems at high temperature may be adversely affected by presence of peroxide curing agents and anti-oxidant compositions ha~e been added to polymer syste~ls to inhibit or overcome such deleterious effects.
Mechanisms for antioxidant use are discussed in the following exerpt from a booklet entitled "Handbook On Antioxidant And Antiozonants" for rubber and rubber like products published by Goodyear Chemicals. Two exerpts from page 11 of th~ booklet are as follows:
"~y adding an ant:ioxidant of one or more typesS
the oxidation of polymers can be interrupted and the degradation slowed down considerably.
There are two ways this can usually be accom-plished. The first way is to introduce an antioxidant that will eliminate peroxides before they can do damage.
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The antioxidants which will do this ar~ the phenolics and the aromatic amines. The amines include most of the staining antioxidants and the antiozonants.' * * * * * * *
"Another way of disrupting the oxidative action is ~o des~roy the hydroperoxides before then can cause problems.
ROOH ~ AH ~ Stable Products Two ~ypes of antioxidants do this. They are ~ lWC-2~43 '' the phosphites and the thioesters~ The mos t ~,' common phosphi~e .i.s ~risnonylphenylphosphite and a well known thioester is dilaurylthio~
dipropionate, frequently called simply ..................... '', DLTDP.
The thioesters are most widely used in ',;,,:
plastics, principally polyolefi.ns, while the phosphites are used in the rubber industry almost exclusively as emulsi,on polymer .,;
stabilizers. Both phosphite and thioesters are affected by vulcaniza~ion systems, losing ,,' most of their activity. ,', Often an antioxidant from each of the two 's groups is used in a polymer to form a :'", synergistic combination. By combining the , ,-two, they can work hand in hand to destroy ;,' both types of destructive radicals. , A~tually, such a combination almost always w ~rks much better than simply increasing ,'' t Le concentration of a singl.e antioxidant.".
O~JECTS OF THE INVENTION
It is accordingly one object of the present ~"
invention to provide a wire product suitable f~r use '' ; as a motor lead or a~paratus lead wire. i~ !
Another object is ~o provide an i~proved j ' insulation composition for disposition and curing on a ' conductor to form a motor lead type of wire.
Another object is to provide an impr~ved cured ! ~ i insulation composition for use on motor lead t~pe ~ ; '-30 conductors. , ~, Another object is to provide a novel ,rubber composition having a novel combinati~n of properties ,';
including, a resistance to deterioration of such properties at high temperatures.
It is another object of thijs invention to provide a novel curable composition a~d products thereof which have an improved combination o~ proper~ies for use .

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~: It is another object of this inven~ion to pro-vide A new and improved electrical conductor having an insulation wi.th a novel combination of physical properties and having apt electrical properties.
It is another object of this invention to provide an ethylene-propylerle rubber composition possess~
ing a novel combination of physical properties which make it particularly suitable for use as an ele~trical insulation for motor lead type conductors.
Other objects and advantages of the invention will be in part pointed out and in part apparent from lS the description which follows.
S~IARY OF THE INVENTION
The invention comprises a novel rubber compo-sition o~ a specific combination of compounded ingredients and proportions thereof which has a significantly improved combination of physical properties for use as an insulation of motor lead type of wlre together with satisfactory other physical and electrical properti.es.
The novel rubber composition of this invention is composed o an essential combination of ethylene-propylene rubber, chlorosulfonated polyethylene, zincoxide, talc, carbon black, vinyl silane, antimony oxide, amine antioxidan~, imidazole antioxidant, peroxide curing agent and curing coagent, and can include other optional components which enhance the overall at~ributes of the rubber composition. The invention additionally includes electrical conductors insulated with the novel ethylene-propylene rubber compound.
BRIEF DESCRIPTION OF ~HE DRAWING
.. .. . _ _ ,rhe figure comprises a perspective view o a section of an electrical conductor insulated with the novel and ~mproved rubber composition of this invent~on.

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DEl'AILED _~,S RtPTION C~ A r~E~ D EMBODIMENT
This inven~ion specifically consists of a ~! novel combination of compolmded ingredients and relative proportions thereoflwhich in total produce an elastomeric composition having an outstanding combina-~, tion of physical and electrical properties including ~' stability and resistance to deterioration upon subjection to elevated ~emperatures over extended periods sui~able for use in a motor lcad or apparatus lead wire, The rubber cornposition of this invention com-prises the combinatlon, in approximate parts by weight, consisting essentially of:
Ethylene-propylene rubber 100 Chlorosulfonated polyethylene 3 - 10 lS Zinc Oxide 15 30 Talc SO ~ 125 Vinyl silane 0.5 - 3 Carbon black 10 - 32 Antimony oxide 3 - 10 20 Amine antioxidant 1 - 4 Imidazole antioxidant 0.~. - 4 Peroxide curing agent 2 - 8 Curing coagent 2 - S
The ethylene-propylene rubber component com-p ises ethylene-propylene copolymers and terpolymers of typical commercially available compositions constituting about 25 to about 75 parts by weight of ethylene monomer copolymerized with about 75 ~o about 25 parts by weight of propylene monomer. Terpolymers of ethylene-propylene include those commercial rubbers produced by the copoly-merization of ethylene and propylene together with minor proportions of dienes such as ethylidene norbornene, dicyclopen~adiene and 1,4-hexadiene.
Talc~ of course, consists of a well-known but distinctive mineral form of hydrated magnesium silicate.
It is preEerred that the talc component of this invention be of the plate type in its physical form.

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_ g _ In practicing this invention two special categories of antioxidant must be employed in combination to achieve the combination of desired physical and electrical properties in insulation material of the invention. The first category is the amine antioxidants and this category is exemplified by reaction products of diphenyl amine and acetone. The second category is the imidazole antioxidants and this category is examplified by a zinc salt of 2-mercaptotolylimidazole.
Peroxide cross-link curing agents for the ethylene propylene rubber compound of this invention comprises the free radical forming organic peroxides such as tertiary peroxides characterized by at least one unit of the structure C C

C C
which is activated by its decomposition at temperatures in excess of about 295F. The ufse of such peroxides in cross-linking polymers is described in detail in U.S.
patents 2,888,424, Precopio et al, issued May 26, 1959;
3,079,370, Precopio et al, issued February 26, 1963; and 3,214,422, Mageli et al, issued October 26, 1965. A
commonly used and preferred curing agent for this invention is dicumyl pero~ide.
The use of a peroxide curing coagent in the cross-linking of the novel composition of this invention is required to increase the efficiency of the cure in accordance with the technology in this art. Apt curing coagents include, for example, polybutadiene homopolymer.
The following comprise examples illustrating specific embodiments of this invention and demonstrating their improved combination of properties in rela~ion to a control comprising a prior art composition.

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The cornpounds of th~ control and each example of this invention were all p~epared in an identical manner, comprising first admixing all components, exc ep k the peroxide curing agent and ouring coagent, in a Banbury for about 10 minutes while heating to about 300F. After cooling to room temperature, the curing eoagent was added to the admixture on a two roll rubber mill. This was followed by the addit:ion of the peroxide by dispersal through the other in~redients.
The following comprise examples illustrating specific embodiments of this invention in rela~ion to control compositions and ilLustrating by comparison of the embodiment~ with the control examples the benefits and advantages made possible through the invention. l~e improvements which are made are not confined to improve-ment of a single property and accordingly cannot be measured by a single criteria of the composition or cable. Rather, the lmprovements involve beneficial chang~s in a combination of properties and particularly those combinations which are needed and beneficial for the favorable performance of -the composition and cable in the use applications for which they are prepared.
; One such cormnon use of these materials and cables is in the motor lead and apparatus lead applications where cables prepared pursuant to this invention have shown superior performance and ha~e solved some of the problems which are particularly associated with such end applica-tion use.
The compounds of the control examples listed in Tables I, II, and III and of each listed test example of this invention are all prepared in an essentially identical manner. The preparation invol~ed first admixing all of the components excep~ the peroxide curing agent and the curing coagent in a Banbury mill for about ten minutes wh:ile heating to about 300F. After cooling to room temperature, a curing coagent was added to the admixture on a two roll rubber mill followed by the . .
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addition of the peroxlde. The addition was made so as '~ to disperse the coagent and the peroxide through the other ingredients, A firs~ set of test and control compositions was made and the combinations of the ingredients of these composi~ion.s and some of the ~est properties found are listed in the following chart ldentified as TABLE I.
All amounts are given in parts per lOU parts of base copolyrner and/or terpolymer.

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'i ~ 14 - 41WC-20~3 r'~ Samples of each composition of the controls .;. and of the test exLInlples of thls invention were prepared ;~ from the Banbury into sheet form having a thickness 4f ' approximately 1/~l" al.though ~he thickness is not .;, 5 critical in rela~ion to ~he propertles of the material which result from processing o~ the sheet material. The only requiremen~ is that the t~ickness of the sheet material be greater than the thickness of a platen in which the sheet is to be pressed at an elevated tempera-ture. A quantity of the sheet mater;al is cut and wei~hed and it is then placed in a heated platen having width and length dimenslons greater than that o the sample of cut sheet materlal but which has thickness dimensions thinner than that of the cut sample of sheet material.
The platen is preheated at the time of intro-duction of the cut sample to a temperature o 350F. The platen is premounted in a press which is then closed to appl.y a pressure to the composition and to ~t least partially cure the composition, to exclude air from the composition and to compact it to a final thickness of approximately 80 or 85 mils and a pressure across the members of the platen of approx. 400~-5000 psi. The total time during which the sample remains under pressure in the platen at 350F. temperature is 45 minutes.
The platen press is opened to release and remove the pressed sample. The prepared test sample is allowed to cool to room ~emperature. Normally a waiting period of at least four hours follows the press heat curing of the composition in the platen before the physical tests are performed. The three physical pro-perties, namely ~ensile s~rength, per cent elongation and 200% modulus, are measured in the units as indicated in Table I. The measurements were made for the cross-link cured compositi.on of each control and of the test sample.
Wi~.h regard to the results reported in Table I
it is evident ~hat there was also an accelerated heat .

- lS ~ ~lWC-2043 ! ~ging test conducted for 18 hours in an air oven at 200C. In this test the ends of a 4" x 1/2l' strip . which had heen subjected to the heat a&ing te~t were bent together. The measured values obtained were as set out in Table I. From the data which is presented in Table I, it is clear that strikingly different physic~l property values were obtained Eor the example ID 80-87C
as compared to those obtained for ~.he other test samples.
Sample ID 80-87C is ~he only one of the four test samples listed in Table I which contain Vulkanox ZMB-2 in addition to ~ . L. E . -25 antioxidant materi.al.
With further regard to the results pre~ented in Table 1, it will be realizecl that one of the principle problems which was being addressed in undertaking the studies, the results of which are reported in Table I, was the problem of improving the tensile strength and related properties of the resulting cured composition. The tensile strength properties tested are really those which refer to th~ tensile strength property of the insulation for use on a wire, such as a motor lead wire. The insulation compo-sition is prepared for deposition as an insulating layer on a wire as an ~mcured composition. After deposit on the wire the composition is cured.
Experience prior to this invention has shown that there are numerous compositions for use or cure and that such prior art compositions had a highly desirable set of properties as an insulation for motor lead wire or for si.Dilar applications. However, it has also been known that the combination of properties desirable for such applications might be improved with particular regard to the tensile streng~h and related properties of the insula-tion. Referring to Table I and comparing the results of the tests of the properties of the co~positions reported, an attempt was made to improve the tensile strength by increasing the amount of the terpolymer present so that the amount of the EPDM rubber and particularly the Nordel 1040 was increased by 25 parts with a con-,~

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The results of the test Il) 8()-87A which had the 'higher concentration of terpolymer show that the tensile property was not improved and also there ~laS no improve-ment in the modulus. Accordingly this approach towardimproving the tensile strength property was essentially unsuccessful. It will be noted that the other components of the ID 80-87A composition are identical with those of the control 1852 -19-07.
With regard to the test sample ID 80-87B it is noted from Table I that the Vistalon, Nordel and other ingredients are the same as those given for the control 1852 -19-07 but that a change was made in the peroxide employed from the Di Cup T to Di ~wp R. The amount o Di Cup R used in 87B is slighly less than the amount of Di Cup T used in 87A. However because of the higher active level of dicumyl peroxide available from Di Cup R
the dicum~l peroxide contetlt of each compositi.on is about equal. The use of Vi Cup R was tested to determine whether the dicumyl peroxide present would be more effecti.ve in generating a higher degree of cross-linking - because of the ease of processing to a homogeneous mix using ~he Di Cup R, However,no difference in effective-ness was found.
Turning now to example ID 80~87C the ingredients ~, of this test example were essentially the same as those of ID 80-87B with ~he exception that there was an increase in the amount of Di Cup R employed but also there was a substan~ial increase in the amount and composition of the antioxidant which was employed. The results in TabLe I
show a very substanti.al increase in both tensile strength and modulus for the ID 80~87C test example. In act, the de~ree of increase was quite surprising and unexpected, particularly inasmuch as the addition of the particular antioxidant material had the surprising apparent effect of increasing the degree of cross~linking of the ethylene propylene material of th~ base composition. In other ' ~
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' ' ' ' ' ~ ' - 17 - ~ C 2043 words, improvements in the tensile properties are normally associated with increases in the cross-linking and increases in the cross-l:inking are normally associated with increases in the amount of cross-linking agent employed. In this polymer systern the cross-linking agent is the peroxide and no~ the antioxidant. What is surprising is the finding that an increase in antioxidant coupled with a modification :in antioxidant content apparently gave rise to a substantial. increase in cross-linking as evidenced by the .increase in the tensi'lestrength and tensile strength related properties.
In fact, in run ID 80 87C the peroxide had been increased and further sampl.es were prepared to test whether the increased ter.si'le stren~,th fo~md showld be attributed to the peroxide or to the modification of antioxidant or possibly to both.
A second set of trial rulls were made by pre-paring both control and novel compositions and by testing them using the procedures and the format which has been described with reference to the compositions and their preparation and testing as set out with reference to Table I.
The results achieved in such tests are listed in Table II benea~h the compositions which were tested.
; 25 Here again the amounts of the ingredients of tlle composition are given in parts per 100 parts of base polymer.
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20 ~ /JC-2043 ,-~ It is no~eworthy irst that the eontrol sampleof Table I, namely 1852-19-07 was repeated in rnaking the ,' runs for e~aluation of compositions as carried out with ~ reference to the tests and test results listed under ,~ 5 Table II.
., In this regard please note that although the components of the composition were essentially identical for the control sample of Table I and the control sample of Table II nevertheless there are somewhat different test results obtained from the measurements of phy~ical properties. Thus, the tensi:le strength of the control sample of Table II W2S 866 psi while that o Table I
was 787 psi. Similarly the elongation of Table II was 730~/O whereas that of Table I was 573%. Further, the modulus of Table II was 532 psi while that of Table I
is 502 psi. It should be understood that in running tests of this sort different values will be obtained in the test results due to slight variations in some of the val-iables of processing or of the mixing or ofthe testing.
The tested property value numbers of the control sample of Table II are deemed to be entirely compatible and consistent with the values found for the con~rol of Table I. However, what is quite remarkable and striking are the very large di.fferences which are found in the comparison of the tes~ values of the physical properties of the control sample of Table II and the test values for the physical properties measured for the other test samples of Table II.
Turning now more specifically to the illustra-tive examples of Table II, the compositions are as set forth in the Table and are described here principally with reference to the differences rather than to recitation of all of the components which were employed in the sample.
Please note that in the test ID 80-87C of Table II, two parts of Vulkanox ZMB-2 antioxidant were employed together with one part of B.L.E. -25 an~ioxidant. The same ratios of Vulkanox ZMB-2 and the B.L.E. -2S are employed in the .

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; exarnple I~ 80-90A and the only difference in composikion ~s ln the slightly different peroxide content. With . reference spee:Lfically to the peroxide the purpose of , using 4.71 parts of Di Cup R in example ID 80~87C is to , 5 increase the amount of peroxide employed in a manner and in an amount identical to the increase of peroxide employed in the example ID 80-87C of Table I. In fact, the compositions of the two ID 80-87C examples are identical for the test of Table I and the test of Table II. However, to demonstrate tha~ the improved results in physical proper~ies of the ID 80~87C sample was not the result of increase in peroxide over other samples of Table I the peroxide content of samples of Table II was reduced to a level which approximates that of the control, namely 1852 -19-07 of bo~h Table I and Table II. As is evident from the reading of the tensile strength elonga-tion and modulus given in Table II, the improvement in properties of the novel composition of this invention is not the result of a modiEication o ~he concentration of peroxide alone. This last reference is of course to the example ID 80-90~ as shown in Table II inasmuch as the peroxide content of example ID 80-9OA of Table II
corresponds closely to that of the control of Table I
and Table II, namely 1852 -19-07.
Considering next the examples ID 80-9OB and ID 80-SOC, it is evident that these two examples employ a smaller amount of Yulkanox ZMB-2 than the two previous examples, namely ID 80-87C and ID 80-9OA. However, as is evident from the results of the measurements of the tensile strength, elongation and modulus the values obtained for measurement of these physical properties ~re very s~bstantially improved over those of the control 1852 -19-07. Further, there is a demonstration of the relatively low or insignificant effect of the change of 3~ peroxide concentration as between the ID BO-9OB and ~D 80-9OC examples. This confirms again the results recited above with reference to the ID 80-87C and 3~s~
- ~2 ~ lWC--20l~3 ID 80-9OA examples concerning peroxide conce~tration.
Accordingly it is clear that the improvement in physical properties is the resul~ of the inclusion of the i.midazole antioxidan~ in the composition together with the amine S antioxidant and not a change in peroxide or peroxi~le concentration.
Considering next the ID ~0-9OD example, this is precisely the composition which was employed in examples described below used in the production o an insulation which was applied to a wire. In this example it will be noted that the concentration of the Vulkanox Z~-2 was reduced still further below that in ~he ID 80-90B and 90C and specifically down to a concentration of l/2 part of the Vull;anox Z~-2 Nevertheless, very suhstantial improvernent in tensi.le strength is observed with reference to the control sample 1852 -1~-07. Also, substantial decrease in the elongation is found where the ID 80-9OD sample is compared wit-h the same control of Table II. Further, a substantial increase in the 200~/~
modulus was achieved al~hough the concentration of the Vulkanox ZMB-2 was at the relatively low level used and listed in the example ID 80-90D. In fact, the choice of the composition of the sample ID 80-9OD was made based on the overall combination of properties of the composition and was not made based on onlythe tensile strength, or on'y the elongation, or only on any other single one of the properties. The value of the tear resistant property was influential in the choi.ce which was made inasmuch as it is desirable to have favorable tear resistant proper-ties and higher tear resistant properties are generally favorable. In this regard it is noted that the reduction in tear resistant properties is smallest for ~he ID 80-9OD
example of Table II when comparison is made with the tear resistant properties of the control 1~52 -19~07.
Considering next the examples and the technical data which is assembled as Table II, here again there was a repetition for the purpose of experimental ~ : . . . . . . .. . .. . . . .. .. ....

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- ~3 - ~lWC-2043 verification and control. of two of the examples which are given above in Table I. The first is the control 1852 -19-07. The second is the ID 80-87C. The identity of these two runs with respect to ~he runs listed in Table I, Table II and Table III are self~Pvident from a comparison of the content of the three Tables.
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' ` . -~ ' ~6 - ~lWC~2043 Turning next to the example ID 80-96A, in this example the test of ID 80-87C is repeated in essence with the small variation in the Di Cup R component as has been discussed above. Otherwise the compositions are essentially iden~ical.
Lastly and significantly, the example ID 80-96B
has a composition which matches that of ID 80-96A with the exception that the Vulkanox ZMm-2 of example ID 80-96A is absent from ID 80-96B but the Vanox ZMTI anti-oxidant component is present in example ID 8~-96B in an amount which is equivalent to the amount of Vulkanox ZMB-2 present in ID 80-96A.
Again by comparison of the results obtained there is a significant reaffirma~ion of the improvement in the test values for tensile strength, elongation and modulus properties based on the repetition o~ these respective tests and comparison o~ the values with those for the control sample 1852 -19-07 of Table III. Further in Table III there is reported the repetition and con~
firmation of the results for example ID 80-87C as listed in Tables I and II.
These two examples 1852 -19-07 and ID 80-87C, are repeated as part of the sets of tests conducted and reported in each of the three tables and the three independent confirmatory tests appear in each of the three tables. Because of the similarity of values '- ;
obtained in each of the three 1852 -19-07 examples and the similarity of values obtained in the ID ~0-87C
examples coupled with the. substantial differences between values for the 1852 control and the repeated 80-87C test example the validity of the improvements obtained by the coml~ination and addition of Vulkanox Z~2 antioxidant mat.erial is verified and by the combination of the Vanox ZMTI, each of which materials is a zin~ salt of 2-mercapto-~olylimidazole.
~le significance of 96B test is that it confirms : that the improved resul~s obtained in the data of Tables I

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3~ 2 ~ 27 - 41WC~-2043 and II is not limitecl to the employment of the Vulkanox ~MB-2 alone in the composition which is prepared, bu~ is tied to and dependent on the use o~ a zinc salt of 2-mercaptotolylimidazole.
Considering next the pertinency and relevancy of the discovery of the uniquely beneficial effect of the addition of even small amounts of the combination of antioxidant compounds, zinc salt of 2 mercap~otolyli-midazole such as Vul.kanox ZMB-2, and the amine antioxidant such as B.L.E. - 25 to the compositions as recited in the tables, the compositions and parti.cularly that of example ID 80-9OA, were em210yed in preparing insulated wire samples. In general, the data obtained from the platen cured materials as recited in the tables do not correspond, value for value, to the values o~ data obtained from compositions formèd and deposited on wire.
However, it has been fo~ld that the beneficial effects which are evident from the study and comparison of the platen sample data of Tables I, II and III are available and are present in the cable samples which are prepared with thesc compositions and particularly with the selected composition of test example I~ 80-9OD.
As has been indicated previously, the composi-tions of the present invention are improvements over those previously known. The results achieved in preparing the novel compositions and in curing and testing them are drawn from the labora~ory preparation, cure and test of platen samples performed with the objective in developing ; the new compo~md not only to provide the novel cured compound itself and the novel precured composition, but also to formulate the material for application to wire ~
as the insulation therefor. ~;
Prior art compositions similar to that of the ' control composition of Tables I, II and III have been known and have been used in the past for a number of years. Such prior art composition was known and is -shown in the tables with thc identification 1852 -19-07.
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A sample of such prior art composition was applied to a cable and the composition was cured on the cable by subjecting ~he composition and cable to a steam atmosphere at an elevated temperature. Generally the steam pressure for cure of such prior art compositions on cable is between about 225 to 250 psig. Saturated steam, such as may be used in curing such a composition on a wire or cable would have a temperature of 395F. with a pressure of 220 psi~. Alternatively, saturated steam at a temperature of ~06F.and having a pressure of 250 psig may be used. Using a prior art composition illustrated by the 1852 -19-07 composition of Tables I, II and III
and using a steam curing procedure in the temperature and pressure range recited above, a cured insulation was prepared on a ca~le.
The particular cable is American Wire Gauge size No. 2/0 AWG. The conductor was stranded tinned copper and there were 325 strands each having a diameter of .0~01 inches. An insulation wall thickness of approx.
0.155 inches was deposit.ed and steam cured on the con-ductor. This construction was the construction for both a prior art composition according to sample 1852 -19-07 and was also the construction for a sample identified as T1~52 -19-07C. This latter composition is the same as the composition identified in Table III as ID 80-9OD.
Subsequent to its preparation of the prior art cable the insulation was stripped from the cable so that test samples could be prepared to study the physical properties of the insulation. The test samples were prepared in the conventional manner known in the polymer testing art and the following results were obtained using the prior art composition. The tensile streng~h based on '~
measuring five samples was 675 psi. Elongation again ;
based on the use of five samples was 819~/o. A tensile stress a~ 200~/o elongation, also known as 200~/o modulus, based on a test of five samples was 425 psi.
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29 - ~lW~-~043 Tear resistance of this cured prior art composition was tested on six samples and fln average tear resistance of 37.83 pounds per inch was :Eound. The test used is the ASTM D470 tear resistance test.
For an insulated cable prepared from the ID 80-9OD composition, extruded onto conductor and steam cured as described above, folLowed by stripping and testing of the cured insulation the following physical properties were found: the tensile strength wa~ 828 psi, elongation was 881%, the 200% modulus was 502 psi, each value being based on measurement of three samples.
Tear resistance measurements ~ere made on six samples and an average tear resistance of 35.9 lbs/in.
was found. The cable was tested for dielectric breakdown and a value of over 58kv was found.
The properties of the insulation of a second prior art cable were compared with those of a cable insulal:ion formed with the preferred composition of sample ID 80-9OD of Table IL above. The cable construc-tion for each cable was onP for a 2 AWG made up ofnineteen 7 strand bundles, each strand of which had a diameter of 0.0223 inches. An insulation wall thickness of approx. 0.155 inches was formed and steam cured. The outside diameter was 0.670 inches or the prior art cable and 0.683 inches for the novel cable of this invention.
The tensile strength of the prior art insulation was found to be 662 psi and the per cent elongation was 876 based on five tPSt samples. The 200% modulus was 400,psi again based on five test samples. A tear resistance of 35.88 psi was found based on a measurement of six samples.
A comparable cable was prepared insulated with the ID 80-9OD composition. The cable was a 2 AWG having nineteen 7 strand bundles each strand of which had a diameter of 0.0223 inches. The insulation thiclcness was approx. 0.155 inches and the insulation was steam cured following eY~trusion of the insulating wall onto the cable.

_ 30 - ~lWC-~043 On stripping of the cured insulation and measuremen~ of i~s properties in the conventlonal manner it was fo~md that the tensile strength was 818 psi and the per cent elongation was 905 based on a test of three samples. Also the 200% modulus was 475 psi based on a test of three samples. A tear resistance o~ 33.8 lbs.
per inch was found based on a test of six samples.
The cables prepared pursuant to this invention were found to have acceptably apt electrical properties at least as good as t:hose of prior art cables but having a combination of significantly superior physical properties as set forth above.
For most prior art and other cable constructions it is frequently desirable and often mandatory to include a film or strip of separator between the stranded con-ductor and the deposited o~lter layer ofinsulation. A
strip of Mylar having a t~ickness of about 2 mils was employed as a separa~or on the cable products described herein. The electrical properties of the cable reported above are based on a cable made with the Mylar ribbon sellarator.
Referring to the drawing, there is shown a typical construction for an insulated electrical wire or cable product 10, comprising a metallic conductive 25 element 12 and an overlying body of cured elastomeric ~.
insulation 14 extending ~hereabout or covering the conductor. In the drawing, the product 10 is illustrated as a short section with the insulation 14 removed from the end portion of the conductor 12. According to one embodiment of this invention, the novel ethylene-propylene rubber composition thereo~ can be used to provide or form the insulation 14 on a conductor 12 of wire or cable product 10. It is to be understood from the ~oregoing, however, that the lnsulation can comprise 35 a coatillg on any portion of a conductive element and that .:
the insulation need not com?letely enclose the element where such is not necessary for a desired insulative effect.
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- 31 - 41WC-~043 Althowgh the invention has been described with reference ~o certain specific embodiments thereof, numerous modifications are possible and it is desired to cover all modifications alling within the spirit and scope of this invention.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A curable ethylene-propylene rubber composi-tion having improved tensile and related physical proper-ties, resistance to heat and apt electrical and physical properties, consisting essentially of the combination in approximate parts by weight of:
Ethylene-propylene rubber 100 Talc-hydrated magnesium silicate 50 - 125 Vinyl silane 0.5 - 3 Thermal carbon black 10 - 32 Reaction product of acetone and diphenylamine 1 - 2.5 Zinc salt of 2-mercaptotolylimidazole 0.2 - 3 Chlorosulfonated polyethylene 3 - 10 Antimony trioxide 3 - 10 Zinc oxide 15 - 25 Dicumyl peroxide curing agent 2 - 8 Polybutadiene homopolymer 2 - 5

2. The cured composition of claim 1.

3. A cable coated with the cured composition of claim 1.

4. A curable ethylene-propylene rubber composition having improved tensile and related physical properties, resistance to heat and apt electrical and physical properties, consisting essentially of the combination in approximate parts by weight of:
Ethylene-propylene copolymer 50.
Ethylene-propylene-diene-terpolymer 50.
Talc-hydrated magnesium silicate 76.
Vinyl silane .77 Medium thermal carbon black 30.4 Reaction product of acetone and diphenylamine 2.
Zinc salt of 2-mercaptotolylimidazole .5 Chlorosulfonated polyethylene. 5.

Antimony trioxide 5.
Zinc oxide 20.8 Dicumyl peroxide curing agent 98-100% active 4.71 Polybutadiene homopolymer 3.
5. The cured product of claim 4.
6. A cable coated with the cured product of

claim 5.