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PROGRESS IN RUBBEt INSULATION J ~ T o 3 lake and R. Lyle Simlex wire and Garble Company Cambrldge, Ma~eachusetts tic versus Natural Pubber During 1946, although the available quantity of natural rubber increased,, the rubber industry in this country consumed very large quantitles of synthetic. The use for the year was 275 ~ 000 t one of natural rubber, and 750, 000 tons of synthe tic . The actual rate of use of natural rapper changed rabidly during the year. During the ftirat quarter of 1947, consumption of natural rubber was at the rate of 525, 000 tons, agile that of synthetic eras at the rate o' 66,000 tons. The latter consisted of 530~000 tons of ERAS, SO, 090 tons of buty1, and 4~3, 000 tons of neoprene. Congress he.s not yet determined a synthetic rubber pol icy for the United States . Sub_co;nmittees are now studying the problem, but it is expected that permanent legislation '.~il? not be enacted until early in 1948 ~ Temporary legislation genre the Government o'~e~ to controls the tine of natural rubber until March 3l, 194S,, or ,.~nti] permanent legislation is enacted, whichever occurs first. Congress did vote, however, to restore natural rubber to ~ free markets And on flay I, 1947, pri~rat.e trading in rubber took Mice f or the first t~ me in nears y 6 years . In the early cart of 1947 the Eric e of natural rubber eras an~roxima~cely (3 cents greater than that of EMS. With this ~ubstan~riaQ differential Against natural rubber (approximately 40'(), there eras only a moclera~Ge tendency to use natural rubber in electrical insulations, although the rubber controls in R-l ``rould have al] orated more to be used. Since May I, ho'.'re~rer, the price of natural rubber has decreased rapidly on the free market. It is now Belling at avarice below that of GR-~. In spite of the fact that the us e of BRAS in electrical insulation is desirable from the point of vies of quality in various respects, it is possible that the economic pressure brought about bar this, and ~ further revision in the price situation may increase the consumption of natural rubber in this field. Tt is to be honed that cohere there is a free choice, purchasers of. rubber in- su] ation will demand the higher quality available in electrical insulation made from GR-S. The nature of Permanent ~ egisiation to c on~crol and foster a synthetic rubber industry in this country is a highly 93 _

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con4Groversial subject. Tt seems that this country should main- tsin a synthetic rubber ir~ustry for an indefinite period. Two benefits drily be obtained from following such a policy. By maintaining an active synthetic rubber indus~crg, this country canon again be shu-t off from an adequate supply of rubber as it baa in 1942. This es Gentian commodity is a vital neces Piggy in event of war. The other benefit to be obtained from an active synthetic rubber industry in this country is the ~rtrt,ue of price stabiliza- tlon. The price of rubber in the Boast has fluctuated more widely than that of probably any other raw ~r.aterial. In the pest 25 years it has been as high as ~.20 per pound, and as loll a.a 2~3/4 cents per mound. Obviously t~s has been a tremendous factor in the profits and prosperity of manufacturers using natural rubber, since on. rising prices, substantial inventory profits ,vere pro_ duced, end con~reree~y on a falling !nerket, severe losses needed to be absorbed. Tt seems quite certain that; had not a synthetic rubber industry been in operation in this country during 1946, the price of natural rubber would have ri sen substantially . The selling price of natural rubber under these conditions id diffi_ cult to estimate, but it can be concluded that this country pro- bab]~y saved a substantial fraction of the cost of the ,~ar-time synthetic rubber ~1 ants as a result of this stabilizing influence. The cost of the r'le.nt~s con be consid.ered to be earned by ~.rinning the war. In addition to the ob']ecti~re of maintaining a synthetic rubber industry SO that there can be made eva.ile~ble sufficient Quantities of syn Emetic rubber in the event of an emergency, it is easen1;ial tha1; manufacturers of rubber products maintain the technical '~know-how'' of using synthetic rubber. The only method of maintaining such a condition is for each manufacturer to con- sume regularly a certain proportion of synthetic rubber,, since an art of this sort is lost rapidly through disusee Of course, it is to be honed the t research in the field will continue acti~re9 end that the quality of synthetic may be improved still further so that the element of compulsion in using synthetic rubber will be minim) z ed. ~ ~ ha ~ be en Or on o ~ e ~ the ~ a ~ art f ~ on n atu ral rubber would guarantee the consumption of a moderate amount of syn- thetic, and it has also been suggested that the Government should subsidize the eyn~Ghetic rubber industry Clinch the same objective in mind. Although Government regulate on is not pleasant to con- tem~late, it seems probable that this is the easiest way to in- sure the manufacture and consumption of synthetic rubber. Pro_ bably, not only should each manufacturer be required to consume a minimum fraction of synthetic rubber, but it should be con- sumed in all of his mayor products. In this event, a decrease in the vice of natural rubber would not affect the use of synthetic . An increase in the price of natural rubber woul increase the use of synthetic and this would do no harm. - 94

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Add; - ~ The most algr~cant development ~ ~ rubber insulation in ~ 946 was the gre-~-~l I of .the superiority of the synthetic fibers to natural rubber for many specific appliceti ore e In the field o~ hi gh temperature apn1ice~tione, Silicones continued to demonstrate their superiority over 8on~renti onal h.i go temperature rubber compounds. ~Qreden ~resertted data on the new polymers including their dielectric constant at 2500. arid 100C. and after 3 Libya at 2500., and 100~0 relative humidity. A flat curve fin the r~eighborhood of 3.~. was obtained for she range 10 to lot cycles per second. The 1Q8S factor at room temperature oven' the Bare frequency range was less. than sol,` from lO to lot cps. It rose sharply after IG7 cps. Dielectric strength is given as 595 volts Her mil on sheets 75 mile thick. The high ozone aback corona ~e$~sk%~e otb Silicone rubbers was stressed. Jenny revealed tn a eaten+' the curing agents used in Silicone rubbers. Lead monoxide may be used in the range of 1 to 100 on the Silicone. ~e result) ng physics ~ and electrical properti es are dependent anon the ~3~ tions used. . ~ . . . Eaton p~esented3 a comprehensive study of the property es of certain butyl rubber coonhounds at the Spring Meeting of the American Chemical Society, but tt has not yet been pubs ished. 13utyl Abler compounds are recommended especially for high Bold t age insulation . The physical ~roperti es of butyl are cl aimed to be greatly superior to those of natural rubber compounds in ozone resisting insulation' both initially and after drastic accelerated agingO In facts busy! is claimed to be superior 4n aging characteristics to heat resistant GRAB rubber comporancis. Tt ts stressed Chat -~he mcst important physical Property for ore resistant insulation is the percent elonga.~lon retained on aging. The busy-l formulation '~.s far superior to natural rubber oil base compounds, or to GR--S compounds, in this test. The low foes electrical properties of busy! we demonstrated with curves for the Over favor vs. temperature and Owe factor vs. voltage Which are lower for busy! than for other conventional power cable insulate ons. In both curves, buoyed rubber compounds give poorer factors between ~ and 2, There the cower factor of a typical oil base ozone resisting compound ~ ~ reported Go be between 3 and 54. The S . ~ . C ~ and Coffer factor of butt rubber compounds remain reasor~ab~ y constant after 1 ong time soaks ~ Only in di_ electric strength does the busy' compound Reeve something to be desired. No mention T'rRS mode of the lo~v modulus and high rate of cold. floor ''t ich are characteristic of buoys rubber* Simplex flare and Cable Co. ~ in its ''Third Ferret to Industry7'4 stresses the superior aging properties of properly formulated GR-S insu7 ati ons in accelerated angina tests oared those compared Faith eaui~ral ent natur al rubber compounds. I~ is cl aimed that nor- S c an be made e q ut v~ l e no t o no ~ t no tural ruby er c omit ounds in all respects except tensile strength, and superior to natural _ ~5 ~

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rubber filth regard to light checking and accelerated aging. Tensile strength is considered to be adequate. In heat rests_ Cant and ozone resistant compounds it can be made easily the equivalent of natural rubber. GR-S compounds are not as yet the equivalent of denroteinizea rubber in electrical stability in ~'rater-eoak, but they Abe better than conventional natural formulations. Data for typical GRASS and natural rubber compounds are given. Mctfillart and co-workers reports the successful production of a net. synthetic rubber ut, lizing standard GR-S equipment and using methyl ~entadiene as a monomer. It is reported to be very resistant to oxidation, but its initial tensile and per cent elongation are renor~ce.d as being lower than those of GR-~. An ad~itior~l aisaa~ran~Gage is its relatively high stifferdng ten_ Erasure Ice 3 ~ lot id said to extrude excellently, and is recommended for electrical insulation. No electrical data is given. Standard types of Tow water absorption GR-S polymers s,~i4Gable for electrical insulation are discussed by Brady. Pertinent data on GR-S 65, GR_S 16, and GR-B AC, the commercially produced rubbers are reported. The details of the manufacture of GR-S 65 are reported7 by Madigan and co-workers. GR-S 65 nonsenses Rater absorntions as low as 2 /a. cm. after 30 days at 70C. Carbon Black and Other Fillers In the fief ~ of fillers for rubber compounds, further data has been n;~blished9.10 on Shawinigan acetylene black for c inducting rubber compounds. Test data is given for compounds '`rith nature, rubber, GR-S, butt rubber, and neoprene. The use of e. cement technique was recommended for maximum conductivity for rubber compounds. Data is also given for Shawinigan acety_ Gene black in thermoplastics. A method of measuring electrical conductive ty is re_ porteai: by Newton for conducting rubbers. Dilute Sulfuric acid electrodes and electroplated copper electrodes are recommended to overcome the relatively high contact resistance. Morris and co_workers evaluated the effect of mineral nigment;s in GR-S insulationl2. Comme-clal. clays, whiting, zinc oxid e, titanium dioxide, litho~one, barium sulfate , zinc sulfide, calcium silicate, aluminum silicate, and hydrated alumina were studied. were the filler is produced by severe, manufacturers, the ,se~rern1~ ~rarieti ea were also evaluated. Electrical properties of 6" by 6" Dressed sheets using OR-S and 50 volume loadings of Figments included (1) specific resisti~rities, (II) dielectric _ 96

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strength at 60 CD8., (III) dielectric constant at 1 kilocycle end ~ me~ec,ycle, (IV) ~ Dower factor at 1 3~110cycle and 1 mega- cycle at O ho~ars and after 2 weeks in seater. Only 6 fillers retain specific resisti~rities greater than 2 x 10 4 ohms./cm. after soaking two creeks. These are Suprex Clay, Witcarb, Witcarb R-1!2,9 'ditcarb R. Ke.Ivan, and Ra.ycal. Fillers reported as herring a dielectric strength greater than 4Q0 V01~8 per mil before and- after soaking severe Witcarb, Witcarb R-12, Witcarb R. Atomite, and Cryntor~e ZE-SOO. All the fillers gave compounds whose di_ electric constants were fair, y stables The majority of the com- ~ouncIs had values of about 4 for ~ kilocycle which rose to 4e5 after 2 creeks soaking. At ~ megacycle the average E was about 3.0 rising +o 4~0 after 2 'reeks soe.kir~g. The poser factor was lowest high compounds containing 7~.rhiting, titanium dioxide, and zinc sul fide a They show little or no change at l kilocycle or 1 megacycle Stew soaking. Generally speaking, the clays severe found to be Door as 'vere the aluminum Gil icate and hydrated a? ~ur.ina. The British Admiral~G,y renorted}3 a study of the epic ~ of zi no oxide in womanized India rubber before and after aging, on strafer absorption and physical cro~ertiee. A series using zinc oxide arid one with French chalk as fillers were tested for tennis e aging,, oxygen absorption, =d water absorption. Zinc oxide has no deleterious effects. H~venhil]. and co-workers found:4 that the contact pox ten~cie1 of natural and synthetic rubber is highly electronegative, en cl Coitus ated that by the incorporation of highly electro- ~ositive rnate~ia's, closer boncling would result, increasing the tensil e s strength. This effect shoul ~ be especially noticeable nt hitcher temperatures where the electronegative potential of rubber is increased greatly. Proted ns, silicate, and sodium siJic?~t,e,, all highly electropositive, there found to increase the hot tensi ~ e of robber compounds ';hen used as fi] ~ ers. Tene' le ~ aid -wry ous temperatures are supplied together smith the descriptions of the Reprices used to measure contact potential. AguT~r re~orted~ 5 that reverse notentia] measurements con be rn-arie to severe es a. criterion of the Prague of an el ectri- cal~y ins,~t;ing !nateriP.le Reverse Potential measuremen~Ge are very sensitive to mois'Gure, and since moisture-cont~.ining materiel ~ are Door electrical insulating materials, the reverse Potential me~surement.s could serve to characterize the Prague of a metered! for insulation. Measurements are taken of samples 1n a moist and thoroughly dried condition. Data are Presented for caner, Buna S 9 and Minolam. C~b]~ Insulation In ogle fiel d of special aged ications ~ MiJ 1 er, in a pe tent to American Anode, disc'oses36 & method to air aid tinning copper spire which is to be used in con junction vrith a latex dip ~ 97 _

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roceas. The patent permits the use of a stranded wire on which is aimed a coating of neutral water soluble polyvalent salt such as zinc nitrate, and a water id oluble inert rookery material such as talc. Latex rubber is deposited on the above coatings. Rubber iB reported as being unimpaired physically or electrically after 28 days aging in a beer oven. Sigmund has patentea~7 an electroT,horetlc method of depositing latex on fine Conner wire after it has been assembled on a magnetizable core. Zinc, cadmium, tin, antimony, or lead, metals to which rubber latex will adhere readily, are deposited on the wire. Cox has natentedl8 a method to prevent the electrolysie or the lead in lead `sheathed cables by means of a rubber hydra_ hat ide film. The lead sheath is cooled to 250F. by means of fine welter morays The '`rater is volatilized at this temperature, leaving ~ d~y surface on which a rubber hydrohalide solution is Sprayers The high temperature quickly volatilizes the Solvent, leaving a '` ne Allen on the surface of the lead. The lead is then cooled further by a water Spray. Hamilton has patentedl9 the use of rubber hydrocarbon ir~iblt the crystallization of polyethylene during cooling. compound consisting of mineral oil,, and from 5 to 309` of rubber hydrocarbon 1a noura.Dle when hot and solid when at normal tem- n~rature . Scott has natented20 a cable Violet between a paper in- oulated cable and a rubber insulated cable. The Joint is made by impregnating a fibrous tape filth a mixture of rubber and poly_ styrene, and is wrapped over the connected cable. The rubber portion in basted smith a mixture of monostyrene and polystyrene. _ gS ~

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BIBLIOGRAPHY lo Mareden, ]. ~ Some Properties and Applications of Silicone Rubber ,, Rubber Age ,, 59, 691 ~ 1946 ~ 2. Jenny, Alfred L., (To Genera] Electric Co. ), U.S. Patent 2, 410, 737 ~ 1946 ~ 3. Eaton, T. C., Robert s9 Ae ll. ~ and Sheldon, E. E. ,, The Electrical Properties of Buoys Rubber, India Rubber World, ]~49 227 (1946), (Abstracted. March, 1946, A.C.S. Meeting, High Polymer Forum. 4. Simplex 11ire and Cobble Co., Cambridge, Mass. Third Annual Report to Rubber Industry Be McMillan, F. M. 9 Bishop, E. T. , Marple, K. E. , and Evans, T. WO New Synthetic Rubbers Based on Methyl Pentsaiene, India Rubber World, ~ 13 ~ 165 ~ 1 945 ~ 6. Brady, J. r., Available GR-S Polymers, India Rubber World, ll&, No . 4,, 5 ll ~ 1947 ~ 7. Madigan, J. C. , Borg, E. L. , Provost, R. L. and Mueller, lAr. J. , Development of GR-S 65, India Rubber World, ll4, 668 (1946), 15fAb1 tracts); Rubber Age, 59, 575 (1946) (AbBtrac~0s); ARCS. Fall S. GR-S 65, Release of,, Reconstruction Finance Corp. , Office Or Rubber Re ~ erve 9. Shenanigan Chemicela, Ltd. , Shawinigan Acetylene Black Sha~'inigan release. lo. Hall, R. L., Acetylene Black in Butyl Rubber, Canadian Chemistry and Process Industries, 29, 958 (1945) 11 e Newtons R. G., Electrically Conductive Rubber, kle~chods of Measuring Conductlvity, Journal of Rubber Research, 15, 35~60 (1946) 12. Morrle, Roas E., James, Robert R., and Evans, Edward R.> A Con~>arleon of Mineral Pigments in GR-S, Rubber Age 7 5S, 331 (1945) 13. Admiralty Eng. Lab., Influence of Zinc Oxide Content on Aging Qualities of Vir Cable, Journal of Rubber Research 9 lS 19 t 1946 ) 14. lIavenhill, R. S. , O'Brien, R. C., and Rankin, JO J., Electron static and Tensile Properties of Rubber and GR.S at Elevated Temperatures, Journal of Applied Physics, 17, 338 (1946); Rubber Chemistry arid Technology, 19, 428 t1946) _ 99 _

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; 50 Aguler, $Ielnz,, Reverse Potential Measurements, Zollold Zeitschritt ~ 107, 205 ( 1944 ) 16. Miller, Donald J., 2,411,284 (1946) - (to American Anode, Inc.), U.~. Patent 17. Sigmund, Frank J. and HIavin Willis S. (to Sigmund Corp.), U. 8. Patent 2,400,576 (19465 18e CON, Te Ke ( 1946) (to Western Electric), U. S. Patent, 2,395,024 I9. Hamilton, George Monty, (to Callenaer's Cable and Construction Co. ), U. S. Patent 2,414,500 (1947) 2Q. Scott, T. R., (~o Federal Telephone and Radio Corp. U. 8. Petent 2,393~935 (1946) _ 100 -