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OCR for page 79
79
SYNTHETIC PLASTIC INSULATICN
R. P0 Boyer and P. 5. ~oodiand
The Don Chemical Company
Midiandg Michigan
Introduction .
~ ,
The 1946 Tariff Commission report shoes a total production of synthetic
resins for that year of approximately one billion pO]~3S9 exclusive of cellulosics
and synthetic rubber. There was a time when the electrical industr~t constituted a
major outlet for synthetic plastics and provided strong stimulus for the development
·of new plastics In fact' much of the drive for the development of polystyrene in
this country came from the fact that this material was an outstanding dielectric
substance which.should demand considerable use in the electrical industry. It is
aifficult,to tell...~hat fraction of current polystyrene production finds its ultimate
use in the,-electrica1 ~.ndustry9 but the fraction must be small. A similar case
preva~.s With polythen£,.~hose 'arge scale development arose from an urgent war-time
requirement for a dielectric materia.]O Fo~.~ever9 it is.safe to predict that the non-
electrica]. peace-.t~me uses for pol~thene are already or will dwarf any d.ie~ectr~c
applications. ~hi~e'.~ese't~o important plastics, pol,ythene and pol-~rstyrene9 mere
both sti.mulaued'primarily on tile basis of e]..ect.,r~cal properties, yet the character
of the plastics industry leas so changed in magnitude and outlook that it mill prob-
ably be d~.fficu~t in tine future to encourage plastics developments solely on the.
basis of their possible use in the electrical field. Protective coatings' synthetic
fibers 9 molding ponders and structural materials are suck. large volume ventures as
to attract the major research effort. If the new material' developed for these
fields happen also to possess good electrical properties, no much the better.
A second important consequence of the growth in the plastics industry is
that its.rav! materials requirements aloe so tremendous as to disturb the equil~.br~um
of 'Ghe entire c'nemical industry. Phenol, G. R. S. Rubber and polystyrene combined
can cons.~me over half of the benzene ~rod.uced, ~h~..le ~hthalic anh.-ydrid.e for aDkyd-
'resins and,for ~htLalate plasticizers requires a.~.arge notion of the available
rlaphthalen~e. Various peop]..e are express ng concern over this vital. dependence. of;
plastics on coal. tar chemistry, and also on the ::etro].eum industry It is signifi-
can+ to this situation that Nylon production has alr~es.d;y turned for one of its major
raw materials to furf-ara' g an agricultural cl~e?nica~ O
Genera] Articles
Kline3 has prepared his cu.s~vomary anml.a] review articles which attempts to
give a broad picture of develo-.~ments in the ent re plrsti.cs field during 1947.
Kline4 has al so presented a gener`ai revile article concernln~ recent
developments of plastics for use on corrosion resistance equipment. Mar of the
nester plastic materials, as ;;'el~ as the snore standard ones, fire countered as to
properties and acrlic,~-~tions. ' '
r
OCR for page 80
so
An excel:l ent, reviews ent' tle.d "pylon 2nd Other fJonce.2 lu? os7 c Synthetic
Fibers'' by Ruth Peterson, is to be recommended because f hers ser-'e not only as Ire
covering and on ~ aminat~es for Eke e~ ectr;.~3 industr.,r9 but gene-ra~3y those sy~thei,ics
which hare desirable properties for fibers may be of direct interest as molding and
extruding materials for elec-~rj.c~al ~nsu3=t~ors. T-n:~s survey covers both the mote
generally ~ ecognized synthetic fibers (ny].on:., hi n"`T;on9 Area on ~ g3.ass, etc ~ ) bill al so
gives the available background on the never fibers. (acryIoni tr~.le, Ter~y].ene .
aig~nates, etch
An excellent book g "The Chili strv o:E Coi~nerci.21 Elastic s t, by ~lakerr.a~ i is
scholarly and well writtan9 and gives a broad. pi.ct~we of the entire pias~1cs iridustry
include ng the .nerier plastic mater~ais.
,.. . . ..
. A report from the IT, ,, Pureau of Minxish on ti~:oxici.~: and inflame Resistance
of~rTher~iosetting Plastics' is obvic~usl~y of consid.erable i~Aportar~e to the entire
insulation field. . Reports from UO SO Fleet un~.~s concerning battle damage :suggestied
that., toxic fumes are generated! then tt~er~iosett~ng ple.stic ~ns<~]at~cn ?s.burned or .
decomposed in enclosed spaces. La-~orat,ory .f] ame-~esistar3ce tests modified to study
-these toxic f~lmes9 re~ea'ea t,k~e fo310t~in~ factse Ph=~1~,c-~t,~?~-ics-fa-~c fi3~1ed.
materials end phenolic~fabric-cotton fil~edmc~.ded~nauer~a.ls give off rollgh].y equal
volumes of NED,` CO, and c,Fan,.de~. Iibe quantity, of &11 three- toxic gases Was greater
for me].am~ne-m~neral filled molding materials .-7hich d;.ri not ignite, than for the
:?heno1ic-n'.inera1 f~.1led materials. For the same torte of filler, me1an~inc;.s veered more
flange resistant Chars -~ohenolics,` for the same -e of desire' inQrgar~ic f~13.ers pros
vided more flame resistance than organic fillers,
A methq] was described fcr`,det=rr:~ning the surface ten:~e~rat.~.re.at the
moment of ignition of rig~.plastics;~'. ~lamm.abi.lity data are r~resented..for over
twenty~five different materials uncle' a variety obtest condition.s. A n-~okabJe
mechanism of ignition is included in the discussion.
A Literature Survey on the Properties of Plastics Infl~encl.n~ Their
Stabijity in Storage" Zla.s been prepared tv members of the Battelle Mc~o;-ial Insti-
tut~o C~timum storage conditions, as extra~.ted from publ.shed.~.~"y.$~l nroper-
ti.es, are. an oxygen-free atmosphere of 50-70 per cent relative..hum~.oi~,~yg and tem-
perature between Roland. SO° F.' the absence of '.ight9 and a minions of cyc.~.-icai
variations. Fore rea1~sti.c cond.it~ons are given as ,~:ir9 50-80 per cent. re1ati`.,e
hum~dity9 30-100° F., absence of light and a r.r~inimum of cyclical ~rariciticn.
Delmonte1O has presented further results based on his ph.ot~dielect.ric
arat.~;sis of plast~icso In this method ~ transparent plastic its v-.;e~,Ted by colariz,ed
light as increasing voltage ~ to tile dielectric strength or the material is arrI.ied.
Strains resulting in the material, from the high voltages and. the effects of mechan
~cally induced strains con the dielectric breakdown can Act? fo]1ored. Eventually
sac'': studies should lead to a belter un.derstandirig of insu]a.tor design.
Standard P3 ass'' c ~ -~qateria] s
~.,~_,~ ~^ ~ _ ~ ~ _.
Pherlol:Lcs. The stiriLnka(~;e Cal various pLeno1ic Mastics d~.ririg prolonged
~ . ~
heating It 1~° C. D8.S been investigated.- 1 A 30 minute preheating of the mod cling
panders at 90° C. gives more beat-s+..a'n].e moldings than parts mol.der5. from the regular
pander as received from the manu~actu.rerO
OCR for page 81
gl
A study of the dielectric properties of pure and modified phenol-formal-
dek~rde resins in the frequency range 10: circles to 2,5 megacycles has been reportedi2
The power factor and dielectric constant are lowered substantially by the benzy~a~
tion of the hyc~rox] group or by substituting an alkyl or ary] group either in the
methylene bridge or in the pare position of the benzene ring.
A study of the rate and event of cross-li.=ing pheno1.-Porme.~deh~J4e resins
has been made by the joint use of electrical resistance and density measurement
The former is sensitive to internal molecular arrangements while the latter appears
to fcl1 0757 the gross properties of the resin.
Comprehensive articles on fillers for phenolicsl4 and for ureas and me]a
_ r
mi nes- -7 have appeared. Mood flours, cotton, asbestos, sisal, di~atomaceo~.'s earth,
and sheJ1 fillers are among the types discussed.
.
~ . Cellulose Derivatives. Th.ermo~lastic laminates have been prepared by
_~._, .. . ~.~ ., .
adhering molten cellulose acetate or ethy~cellulose to fabric sheets and then mold-
~ng several. of these sheets together into the finished laminate. The toughness and
'neat resistance of these thermoplastic laminates has found use in electr~.ca].. hous-
irgs9 solenoid covers, etc.1
Ce]lulose acetate propionate has recently been offered for sale under the
trade name of Penile III.17; This material is said to have better impact strength
and dimensional stability than.cel]^ulose acetate and less odor than cellulose -
acetate-but~yrate.
~ general article -reviewing the history of ethyl cellulose stresses the
part which this material played in the VT-fuze program^3 and how this program lead
to a bette~gand more general knowledge of the molding cha.rac;tel~istics of ethyl
cellu10se.
Acr:;lates. Plexigas A is an acrylic injection molding powder With a heat
A__ ~ . t.
distortion temperature of 90-94`' C. It possesses improved ~oldab~li+vy by virtue ~5
low f1c,~r temperature and. yet,, it shows little tendency for shr..nkage up to lOOiC.
PolYstYren.e. A mod.if~.ed po~yst~rene9 knowers as Lustrex shores a measured
_ . ~ .. ~
heat distortion temperature of S7-~° C., but is actually able to withstand bolting
Hater for short periods. Some lmproveme~G,-'n toughness and a 30%.reduction in
molding cycle are additional a.~vante~esO
A copolymer of styrene and fumarodinitr~le is claimed to have higher heat
resistance and better solvent resistance than polystyrene This patent is possibly
the basis of Cerex, a high heat distortion s Serene base material Chick has been
mentioned in previous issues of this Digest. ...
~ ! ~i
The perennial 'out never too promising subject GO plasticizers for polysty-
rene finds expression in a patent Filch mentions alk,yi napkthalenes where the alk,vl
chain is five carbon atoms or le.ssO
OCR for page 82
~2
Pclyvin~1 CarkazGle Resin. The general. properties of polyvi.nylcarba7Jole
have been known for some time - particularly its high heat dis~vor~;on temperature
and excellent electrice.1 character.-,.sti.cs. Its v~ar-time development under the name
of Polectron as a mica replacement, leas been mentior~ed in nrevicus reviews. A
recent arti21e describes monomer properties end nietliods of using 3.t to impregnate
condensers. 3 The polymer itself suffers from bri1;tl:eness' although compression
moldings of pl.astici.zed pol--yvinyl carbazole containing or~ent,ed fibers of flare
polyvin''1 carbazole shoe.' improved t~ougI~ness. Just as T?ll~h polystyrene, the presence
of a plasticizer lowers the flow tempera+ure9 but does not: increase toughness.
Silicones. A plastic dielectric comprising a major Portion of a liquid
polymer of an organosilicone, eg9 dimethy' silicone mixed Ruth p~ inorganic a~rogel,
is used in aircraft ignition-cable to prevent corona discharge.~~ This its a 'i~is-~ori.c
patent whose importance cannot be gauged by the simple description above. not only
did it solve an important aircraft ignition problem for the armed forces' but9
being perhaps one of the first commercial appli.cat~on for silicones' it gave con-
siderable impetus to the development of this indust.,ry~.
Recent developments in the use of silicone resin DC2103 as a heat stable
bonding agent for fibers and fined divided ponders such as Ordered metals, micas
SiO2 have been listed. A generate review of the silicone .¢ield has been given.
The Navy27 in its search for more ordeal electrical. insul.at~.on is nor
encore aging development of silicone-glass laminates as high strength' non-toxic,
heat and arc resistant materials. Thile some mechanical properties of the present
silicone laminates are inferior to those ob+,ainabJe from melamine-~ass cloth
laminates9 it Was felt that most of tI:e outstanding problems could yield to further
research. ~
, ..
-Polvtef,raflurorcethylene (Teflon). Inoreased Production, bore experience
in fabrication, and greater appreciation of its chemical inertness' held resistane,e
Arid dielectric strength' charact,er~ze recense developments with Teflon. Shale it,s
electrical properties are ideals yet its remark&tile chemical resistance has perhaps
Excited even more interest for use in gaskets.
New Plastics
Te~Q_ene is ~ crystalline polyester prepared from terephthalic aced And
ethylene glycol (or their equiva]~ents.) ~hil..e it is being protected primarily As
textile fiber material, yet like nylons it may find use for wire covering and as a
thermoplastic molding m&serial because of its heat and ligh' stability chemical
resistance, and low moisture absorption. 9, 30, Al
. . . . . .
Dually] Phenol Phoschonate. This interesting monomer can be co~ol.~ymernzed
with other monomers such as methyl methac~ylate or styrene to give both cross-li.~:ing
action and flame resistance. Polymerized by itself' it forms an insoluble resin
With a refractive index of l.57O It is-said to form transparent laminates with
glass cloth.32
A general discussion of the monomeric and polymeric bent aky1 ethers has
been presented. These polymers are finding use as plasticizers and modifiers for
other polymers, and as aid. in latex dip coating applicat~.ons.
OCR for page 83
83
Stable polymer oils, greases and waxes have been prepared by the poly-
merization of chlorotrifluoro~e~G_~lene.34' 35 Electrical properties were not. reported
for these materials.
High polymers of this type were not discussed although one would suspect
developments along this line to be in progress. Such a polymer would be similar in
general structure to ~oly~in.~l chloride without the nossibi~i.ty of PCI evolutions
and it would constitute a modification of Teflon, probably in the direction of
greater ease in molding and inferior dielectric properties.
A patent, claims that in in.teroo3~ymer of ethylene and chlorotr~fluore-~-
lene in 1:1 mol. ratio this a higher softening point than that of either component
when pol',r~nerized.alorle.
A copolymer of tetrafluoreth..,vlene with SO2 is said to have a lacer melting
point and improved workability as compared With Boll etrafluorethylene.~'
The dielectric proper"' s of ch].ori.nated po],ythenes in the range from 104
.3.j ~ _~ __ a. . ~ ~ :~ . . ~ . ,,~. _ -
to 10~ cycles has been reportedly The increased rigidity of the material resulting
from the addition of chlorine is reflected in an increased dipole relaxation time.
It should prove extremely interesting to follow developments.in the family
of compounds: Polyethylene, chlorinated ~olyethyIene9~ pol~,rtetraf~uoroethylene,
Polych2~orotrifluorethylene' tetrafluorethylene-S,Q2 ,copol~,mers, . and the trifluor-
ettl~rlene-ettlylene copol,ymers. 'Cr,~r,stallinit,T, solvent resistances high meltir~g
points and dielectric properties can ar)~arently,be.,,controlled in a region of' im-
portance to the elec~tric'd;l;'industr~r. ' ' ' "
A brief note on a new method of synthesizing extremely high molecular
Height proteins by an ionic chain polymerization method has. occasioned considerable
lo. _.. ma., .~ A_ . . . . . . . . ..
interest among pl.ast,ic chemists. There is annarerlt~v 'no cQmmerci~;3 activity in
this field as yet, but such developments may '~11' be anticipe.*ted.
Wire and Cable Nation
~· ~, ,
~ discuss:.on4° of tile voltage characteristics of.pol~ell~tlene cables has
been given2by Davis, Austin and Jackson. They have made an experimental ~nveStiga-
ti.on of breakdown voltage, Dower factor, life with pulse voltages, and discharge
characteristics at power frequencies and performance Edith 6~)0 me radio frequency
pulse operation. Tentative voltage ratings based on this work.are proposed,
A .patent4) has been issued for a coating of high dielectric strength Bale
from ~ solution of l-5 carts of polyLutene in 30-2C parts of benzene and .2-5~ of
dodecy1 arr.ine acetate.
. . . .
A tab]:p has been publ-'shc36.42 showing the comparative properties of natural.
arid synthetic polymer used in ~nsul~-..ted. afire.
Polymeric Plasticizers
Po1:Trneric plasticizers have been mentioned in previous issues of this
review but the past year has witnessed ~ considerable amount of scientific and
OCR for page 84
AL
industrial acti~rit,7 in this field. Perhaps the first co~neric.~1 use of a polymeric
plasticizer novas the ~nccr~cratior~ of ~nol~vrisobutylL!er~e with polystyrene to form a
aemi-flexible insulation for coaxial cables during the early days of the car before
clythene became avai.laLle. Polvisob'~t,y].en.e was also used as a r:L`ast:.cizer or
softening agent for polyethylene. Toward tile end of the car, polyester resins were
used ~n the vinylite jacket on coaxial cabbies to~replace conversional pasters
Which migrated into and ruined the dielectric cro~er+,ies of tee po~yi;lene cable
core. The Federal significance of this deve'onr~ient to aid. types of `~-asticizec
problems was soon realized with the result Chaff an i.1nt-Jortant new trench in p3.asti-
c izers i s row eve
.; ~
An exact definition of a polymeric plasticizer has not been formulated.
The following somewhat arbitrary def~niticn V'7il] describe the essential features:
an inherently flexible polymer or copolynner with ~ molecular wei~g.~t in excess of
5,000-IO9OQO such that both the vapor pressure and the diffusion rate are negI-~ble.
In general, a cot~b~natlon of flexible elements along the chair (met,h~ylLene or ester
DLink~ages) to ensure 1 sow temperature f ~ exibi~it~, and of polar groups f -G = C, -C
N) to promote compatibility with the polymer: appear to be necessary at leas' with
the vinyls. The three types of polymeric pl$st~'cizers*which haste received most
attention; thus. far for use With polyvinyl chloride are
. ~ .
a) Polyesters43
b) ~Copoly~ers of but&diene and acrylonitr:~e44s 45
c ~ Copolymers of styrene and i sobutylene46
The major di~ficu:~ties inherent in the use of such pl.asticizere are:
al Difficulty of i.ncorporation:~:n the r301y-.er.
b) Not as efficient, on a Weight basis, in Ic~b;7erir~g the brit~3.e
temperature as are con~rentiona] ].o~ ~no.lecul.ar weight plasti.-
cizers or the same chemical s tructu-re.
c) Tendency for phase separation Beading to loss of flexibility
of the plasticized polymer.
d) Sensitivity to light and oxygen of the o~efin linkages in
butadiene contai.nin..g polymeric plast,.ci7.ers.
e)
The apparent necessity of using small amounts of I molecular
Weight plasticizers to supplement the action of the polymeric
Plasticizer.
Some of these difficulties will undoubtedly-disappear as more experience
is gained in handling such Plasticizers. They should not detract from the ~m~cbr-
tance of this new development.
For examples 1 '0 5,ci of tet;raalkyl thiura~ d~s,'~fid.e is recommended as a
stabilizer against the effects of li-ght~ and air for v:: nay resins compounded ~,~.th
butadiene acrylonitrile polymers . 47
` , ~
OCR for page 85
~5
what is prot;ably one of the basic po3 Anemic p3 asticizer patents clad me
a linear polyester of 1,2-prcrylene glycol and sebaccic acid havlug a molecular
weight between 1700 and 20,000 as a non-m~gratlug plasticizer for pol~-in:~]ckloride,
polyvi.ryl acetate g or copolymers thereof a ~
A spectra' var:i~t~on on the po'ymoric plas+,nc~zers consists in using a
~Tin,yl chloricn~e--20 per cent vinyl acetate copo~yr`'er of molecular weight S,OOO -
159G(") as a processing aid for v:inylite co'co:Lymers containing up to 7 per cent vinyl
acetate and haling molecular Eights in excess of lS,O00.5°
Internal po]~neric plast~ic~-zers have been used to toughen phenol forma]-
deL~Tde resins.51 Polyolefins9 or 3or molecular weight, vinyl or butadiene pol',~ners,
or fatf,y acids are condensed with phenol in tile presence of BF3 to form compounds
having trTo or more phenol groups per mo~ecu]~. these in learn are condensed with
fo,~ma]del~yde. Con~renticnal inert r?lastic~ze~rs added to phenolic resins do not cite
elastic products v'Pe'-eas the interna:l~ly lineal. p~l.ast-.c3zers appear able to take
d=-~:Corn~ation forces elasc~cally and reversibly.
A symposium on conventional type plasticizers has served to review this
fiel¢2and bring out some special work performed for the armed services during the
war.' ~ dielectric idc?~..tit; test has began developed for plasticiscrs of the three
used in polyvinyl chloride, 5 Reprod.uclble loss factor-ten~perature, and dielectric
constant~t~mpera~ure curares Were obtained at 70 megacycles on a number of typical.
plasticizers.
D; c- ~ ec~tr~ c Tahiti nil
The FCC on Dece~ncer 3, 3,947, altered the frequencies alloca.t,ed for in-
dustrial dielectric heating use. It non has provided the frequencies of i~.569
27.12 encl. 40.68 r^,ogacyc~es for this use. On comparing the reed allocations r?i.th the
old, it will be observed that the new ~requer~cies differ only slightly from the
pre~r:~ous allocations. ~n addition bc these three Preq~enc~- banish the commission
has also allocated a nu~nb=~ or' frequencies in tier? ~ltra-hiph frequency region.
Re.diation Chicle may be produced by electronic heating equipment can inters
fere seriously r~it,h radio con~rnun~cations' thus posing a problem for both industry
and the Federal Communications Com~r;iss.~on. This; along raith other !?rokJ ems, is
discussed by the ~{,F,,~. subco~i~i.t tee on e]octronic 'neati.ng and. reported by'--. CO
Rude. 54
The Pritish55 have published a repour on the in~erferer~ce from :industrial
radio frequency heating equipment. T'ney "Lnvest.ige.t~?d Foul different p:.ecc;s of appa-
r~J~us ranging in pouch -Strom 2.5 lo 45 T`~.r and operating corer a frequency range from
600 KC to 20 MCo
For the study of the application of dielectric heating in various indus-
tri.al processes ~hi+,ehead5 suggests t:Lle use of a calorimetric substitution method
for the ~Teasuroment of losses in dielectrics.
OCR for page 86
With the ever increasing demand for greater production and speed, the use
of hi.giler end. higher frequencies is being pursued. The ''nor~'ledge and teehni.ques
gained in racer Fork during the solar are now being applied to radio frequency, heating
as a means of increasing heating rates.
In a recent article57 by Farce and R:nn, techniques are discussed for
generating and handling microwave energy! Methods are suggested for utilizing wave
guides for applying microwaves to moving or sta+,io~lary hires and threads, sheets or
irregularly shaped objects to achieve uniform diel.ectric.heat,~ng. A survey of tubes
offering possibilities for continuous ope^~.~ion at n,.icro~re frequencies is also
givers.
Development of a magnetron and horn antenna technique :for Cookir.g has
resulted in a practical. design of a mode:! having an oven 13 inches wide, 14 inches
deep, and 15 inches high.5 A number of these.units are non in commercial use in
restaurants throughout the country. Perhaps '=~its of this general type could be
used for high speed heating of p]-astic'pre~orms.
Force and Bevercomb have described59 a magnetron of the continuous Have
type capable of providing five kilowatts of output poller at ],000 megacycles.
Brown and Baylor have published a kook6° on the theory and application of
radio :frequenc~y heating. The authors have placed .~.n ore volume the basic princl-
,ples' design equations, and practical applications data for both Induction and di-
e].ectric heatnugO Eight chapters are devoted to tile 'nearing of poor conductorsO
'l'hese include wood gluing pressed radio ~requenc~',~ se~'i.ng mach.;nes.for sheet , .-
~iastacs, ref. dehydration' pasteurization, ster~.~ation; ccok~ng of'food 'end the ''
heating of drugs and other materials.
. . . . · .
A. P. Pock exclains61 the.factors involved l.?hen.heatirlg a substance by
induction or die2.ect,ric heating. Examples are given for calculating the power re-
quiremer~ts for the heating of plastic preforms. Si~ilar'Galculations Here also
made by Courval. ~ '
Finder outlines63,the fundamental principles of induction and dielectric
heating and points out ~rario~ls.gerleral types of operaticns.~rrhere Induction or d
electric heating can be Used to save time, crest? equipment and materials
. ~.
A British patented has been issued claiming Improved dielectric scaling
of.' superficial ch].orinated po].yeth~r].ene films.
~ , ~ .
' J. F. Capner65 discusses methods and advantages c!f automatic loading
control in generators used in the dielectric beating.~.eld. ~ .'..',, .. '
. · . . . .
Surface Effects
An OSRD,reporu (.-i'To. 5324, PB-11955) from Johns i~'opki.ns Un;.versi+.y has
attempted to collect from! various government and indvstria]. research.laboratories
data pertaining to the effect of moisture and fungus on the electrical and mechani-
ca3. properties of plastic ~ns~.Jat=ng materials. As the author recognizes, the data
avai3.able to him at the time of the -deport (Cctober, 1945) was too incomplete to
OCR for page 87
~7
a]]or: many general conclusions. Most of the data presented refers to filled pk~enol-
"ics, but, there are some data on r.~ethy~ methacryxate and glass bonded mica.
^ti stud.-r66 has appeared on tile surface conductivity of mica, glassy methyl
met7~clc~vlategpolystyrene and pol~risc~butylene, in vacua and in the presence of acid9
alkaD!i and. range of water vapor concentrations. No surface conductivity is observed
in vacuum even With aced or alkali or the surface. Mica9 methyl. methacr~rlate and
polystyrene shoe: no surface conductivity up to saturation Linen distillated Water
valor is used, but minute traces of acids in the hater vapor do produce conductivity
at high rater vapor pressures.
A nerT surface coating material for polystyrene, known as Logoquantg its
reported. to give an l8% increase ire scratch resistance, 14% greater transmission of
incident..light,g ~ reve-rsec] electrostatic charge' and better resistance to to~uene9
carbon tet~acI]oride, and gasoline. This coating, which can be applied by spraying
Or dippings becomes integra'3iy borld.od~'to the base polystyrene. The coating material
is a}?7~are--ltly a cede derivatively
A study of the mechanism of current creep and tracking conclud.es Thai; an
irregular dis~;ibu.tion of surface condtlcti.v~ty is necessary for the occurrence of
current creep. a
A stud, has been made of contribution of moisture to the high frequency
e].ectr~cal characteristics of, a synthetic resin. About half of the Icss angle at
room temperature is ascribed to l~ygrosco~icity.69
Pott~.n~ Conmounds
fifth the increasing produc+~..on of home television receivers, With their
I~i.gh voltage components, there should be increasing activity in potting resin A.
r.t'he JAN T-27 specs. covers the testing of potted transformers. The follo~eir~g has
been given70 as the best National. Bureau of Standards casting mixture.
33 . ON 2- 5 di c h] oro s Anyone
2] ~ 5~ poll ~rdichiorostyrene
21. 0% st!',~rene monomer
~ l. ~polystyrene
hydroge:rlated terphenyl
di viny]: of 60~ strength
OCR for page 88
fig
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Representative terms from entire chapter:
chemical company
