Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A common type of construction for electrical wires
or cables designed for medium-to-high voltage applications,
for example about 15 to 69 KV, as well as other classes of
electrical service, comprises combinations of one or more
insulating layers and semiconductive layers. In a typical
cable structure, for instance, the metallic conductor may be
provided with an organic polymeric insulation such as a
crosslinked polymer comprising ethylene, and an overlying
body of semiconducting material comprising an organic polymeric
material which has been rendered electroconductive by the
inclusion therein of electrical conductivity imparting agents
or fillers such as carbon black. Although these cable con-
structions may vary in certain elements, and often include t
intermediate components disposed between the metallic conductor
and the primary body of dielectric insulation, such as a layer
of separating tape and/or inner layer of semiconductive
material, or the overall cable assembly is enclosed within a -
covering sheath, all such cable constructions conventionally
include therein at least a body of primary dielectric in-
sulation surrounding the conductor and an overlying body of
semiconducting material in physical contact with the ins~
ation. However, this arrangement of a layer of insulation
with a superimposed layer of semiconductive material thereover
incurs certain handicaps.
For example, to prevent the occurrence of ion-
ization or corona ormation resulting from internal voids or
pockets within the cable construction and consequent ultimate ~-
breakdown of the insulation, it is necessary to eliminate
the presence or possible occurrence of any free space or
voids within or resulting from the interface between the
adjoining surfaces of the body of the insulation and the
body of semiconducting material. U.S. Patents Nos. 3,541,228-
Lombardi - issued November 17, 1970 and 3,677,849 - Lombardi -
'
;
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issued July 18, 1972 eal with this problem of intermediate void
spaces at the interface of the insulation and semiconductive
material by applying a heat treatment to the assembled product
to induce a shrinkage of the semiconductive materials tightly
about the insulation. U.S. Patent No, 3,259,688 - Towne, et al -~
issued July 5, 1966 proposes a different solution to this
problem comprising a distinctive construction and an irradiation
treatment. ~-
Further, the insulation layer for electrical cable
can be formed concurrently about the wire or metal conductor
by means of a continuous simultaneous extrusion process with
one extruder, such as shown in U.S. Patent No. 3,646,248 -
Ling, et al - issued February 29, 1972, or these layers can be
formed in ssquence employing tandem extruders such as shown
in U.S. Patent ~o. 3,569,610 - Garner, et al - issued March
9, 1971, and both layers are thereafter cured at the same time
in a single operation and unit to minimize manufacturing steps
and apparatus. Elowever, the simultaneous curing of both layers
together, or even the curing of only one layer alone while it
is in a contiguous arrangement with the other layer, can
result in the apparent formation of crosslinking bonds bridging
across the interface between the adjoining surfaces of each
phase as noted in U.S. Patents Nos. 3,569,610 and 3,792,1g2 -
Rye - issued February 12, 1974. This occurrence of such
crosslinking bonds bridging the interface between the surfaces
of the phases can render their subsequent separation very
difficult, such as during removal of a portion of the body
of semiconductive material from about the insulation by
stripping for the purpose of making splices or terminal
connections.
The separation of these layers often requires the
application of great force, and, upon being stripped or peeled
41D-1663
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off, the semiconductive material often is prone to leave a
substantial residue of its mass firmly adhering to the other
surface or the insulation. As is known in the art, it i9
necessary when splicing and treating cable ends that the semi-
conductive material be cleanly stripped or completely removed
from the terminal section of the cable end without any damage
or material loss to the underlying surface of the insulation,
and consequently the separation of these phases can require
an appreciable amount of added labor time and costs when the
semiconductive material is difficult to remove by stripping
and/or a residue thereof is retained tenaciously adhering to
the surface of the insulation. A solution to the difficulties
of this aspect of such cable constructions is the subject of
U.S. Patent No. 3,684,821 - Miyauchi, et al - issued August
15, 1972.
Other recent U.S. patents addressed to the foregoing
problem comprise the following: U.S. Patent No. 3,643,004 -
McKean - issued February 15, 1972 relates to a cable construction
wherein the semiconducting layer is adhering but unbonded-to
the insulating layer; No. 3,787,255 - Carini, et al - issued
January 22, 1974 which teaches attaching sulfonate groups to
the surface of the polyolefin insulation to deter migration of
the curing agent from the semiconductive layer across the
interface to the insulation and as a result thereof their
tenacious interlocking; and ~o. 3,793,476 - Misiura, et al -
issued February 19, 1974 which proposes a semiconductive
composition comprising a novel blend of ethylene-propylene
rubber and chlorine-containing polymers which forms a controlled
bonding upon curing with the underlying insulation of ethylene-
containing polymer.
This invention comprises a combination of specific
organic polymeric materials coupled with a curing sequence
.: . :- - . - .'- , ;.
- ' ' ' , ' '
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whereby an elastomeric blend, which may comprise a body of
semiconductive material, can be adheringly united to a
contacting surface of a body of a copolymer of ethylene and
propylene having an ethylene content of not more than about 50%
by weight of the copolymer, a conventional material for
dielectric insulations. The materials and curing sequence
of this invention provide a substantially continuous and
secure union of their contacting surfaces extending over
their common interface and thereby effectively obviating the
occurrence of intermediate void spaces, while at the same
time providing an interface union between the phases which is
easily separated with a relatively small pulling force where-
upon the components part from each other with clean surfaces
each free of any residue from the other.
The invention includes the combination of a first
body of a copolymer of ethylene and propylene of approximately
equal parts by weight of copolymerized ethylene and propylene,
adheringly joined with a second body composed of an elasto-
meric blend of a minor portion of ethylene-propylene rubber
admixed with a major portion of chlorosulfonated polyethylene,
wherein said second body of an elastomeric blend is in a
uncured condition and is applied to the first body of the
copolymer in a cured condition and said uncured second body
of the elastomeric blend is cured while a surface thereof is
in physical contact with a surface of the cured first body
of copolymer.
The compositions and their attributes of this
combination are uniquely suitable and advantageous for use in
the construction of electrical wires and cables in the function
of a composite of an insulation of ethylene-propylene co-
polymer or terpolymer with an easily and cleanly strippable
semiconductive material superimposed over the insulation
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when the polymeric material comprising the elastomeric blend
is rendered suitably electroconductive by appropriate filling
with a typical &lectrical-conductivity-imparting agent or
filler such as carbon black dispersed therethrough, or some
other electrically conductive particulate material such as
silicon carbide, iron, aluminum, and the like, in such amounts
so as to impart the desired degree of conductivity.
It is a primary object of this invention to provide
polymeric materials that can be joined in a contiguous
relationship with their interfacial surfaces adheringly united
together so as to eliminate the presence of any occurrence of
intermediate void spaces therebetween, and which thereafter -
can be separated by the application of a low pulling force
with the interfacial surfaces of the bodies cleaving cleanly ~;
and free of any adhering residual material.
It is also a primary object of this invention to
provide electrical conductors or wire, and a method of
manufacturing same, with coverings including a combination
of bodies of organic polymeric materials comprising a first
layer of insulation with a surface thereof adheringly joined
to a surface of a second layer which may be of any suitable
thickness down to less than about one millimeter, and wherein
the second layer of the polymeric material is easily and
cleanly strippable from the first layer of insulation with a
low peeling effort of preferably about 2 to 18 pounds pulling
force per one half inch wide strip of material, leaving the
separated surface of each layer intact, and clean and free
of any residue.
It is an additional and specific object of thig
invention to provide an electrical wire or cable, and method
of manufacturing same, having a multi-layered covering about
a metallic conductor comprising a combination of cured
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polymeric materials consisting of an insulation and an
overlying semiconductive shield which is free of intermediate
voids or spaces at the interface of said materials, and
wherein the material consisting of the semiconductive shield
comprises a polymeric carrier or matrix for particulate
conductive filler material dispersed therethrough can be
peeled or stripped off the underlying insulation with little
effort or pulling force and it separates or parts cleanly
from the surface of the insulation leaving it intact and
without adhering material.
It is a further object of this invention to provide
a method of joining polymeric materials in a contiguous re-
lationship with their interfacial surfaces adheringly united
so as to eliminate the presence or accurrence of intermediate
void spaces therebetween, and which thereafter can be separated
by the application of a low pulling force with the interfacial
surfaces of the bodies cleaving cleanly and free of any
adhering residual material.
FIGURE 1 comprises a perspective view of a portion of
an insulated condcutor having a semiconductive shield thereon;
and,
FIGURE 2 comprises a cross-sectional view of the
insulation and overlying semi-conductive layer about a portion
of metallic conductor.
This invention is hereinafter described in relation
to its principal field of application and utility, the
construction of electrical wire and cable, although other
areas of application are contemplated.
The invention specifically consists of a novel
combination of given polymeric materials, or combined bodies
composed thereof, coupled with a sequence of curing and
combining such polymeric materials, for adheringly joining
--6--
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them together with unique interfacial characteristics at
their mutual contiguous surfaces.
Polymeric materials of the invention comprise for
the one phase, a body or unit of a copolymer or terpolymer
of ethylene and propylene having an ethylene content of not
more than about 50% by weight of the polymerized material,
and preferably copolymers comprising approximately equal
parts by weight of ethylene and propylene, and for the other
phase or unit an elastomeric blend of about 20 to about 40
parts by weight of a copolymer or terpolymer of ehtylene
and propylene admixed with about 60 to about 80 parts by -
weight of chlorosulfonated polyethylene. Accordingly for the
purposes of this disclosure and the claims,-the term copolymers
of ethylene and propylene includes terpolymers comprising
such monomers.
The terpolymers of ethylene-propylene suitable for
this invention include commercially available rubbers produced
by the copolymerization of ethylene and propylene together
with minor proportions of dienes such as ethylidiene non~
bornene, dicyclopentadiene or 1,4-hexadiene or combinations
thereoif. The terpolymers of ethylene-propylene with dienes,
as is well known in the art, give greater latitude in the
available curing systems in relation to the copolymers of
only ethylene and propylene. Specifically, the copolymers
require a free radical curing mechanism as provided by a per- -~
oxide compound, whereas the unsaturated phase of the terpoly-
mers enables curing with a conventional suIfur-accelerator
curing system, as well as with a peroxide free radical system. -
An essential aspect of this invention comprises the
curing, by conventional means such as curing agents, of the
first phase or body of the copolymer of ethylene and pro-
pylene prior to the physical combining or joining together
41D-1663
of the first and second phases or bodies, and the curing,
by conventional means such as curing agents, of the second
phase or body of the elastomer blend while in physical contact
with the previously cured first phase or body. Thus the
curing and adjoining sequence required to achieve the advant- -
ages and benefits of the invention, comprises applying the
body or mass of the elastomeric blend while in an uncured
condition to the body or mass of the copolymer of ethylene
and propylene in a cured condition, and thereafter curing the
body or mass of elastomeric blend while a surface thereof
is in adjoining physical contact with a surface of the cured
copolymer of ethylene and propylene. This sequence of curing
and adjoining the respective polymeric components is necessary
to prevent formation of a tenacious union and bonding between -~
the interface of the polymeric components which can only be
separated with the application of very high pulling forces,
and does not separate cleanly with each unit free of residue
of the other.
The organic polymeric materials of each phase of the
combination of this invention, both the copolymer of ethylene
and propylene and the elastomeric blend, are typically cured
to a substantially thermoset condition by crosslinking with
a free radical forming peroxide according to conventional -~
practices such as described in U.S. Patents Nos. 2,888,424-
Precopio, et al - issued May 26, 1959 and 3,079,370 - Precopio,
et al - issued February 26, 1963, and in subsequent relevant
prior art. However, other curing systems or means known
to the art or prescribed by the polymer manufacturers or
suppliers can be applied, such as the use of sulfur-based
systems with terpolymers comprising ethylene and propylene.
For service in electrical applications such as a
semiconductive component in cable for medium to high voltage
41D-1663
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service, the elastomeric blends can be easily rendered
electroconductive to any appropriate degree d0sired by the
filling or inclusion therethroughout of a suitable amount of
an electrical conductivity imparting agent such as about 15
to about 75 parts of carbon black or metal particles by weight
of the polymeric ingredients according to conventional
practices. When aptly rendered electroconductive with a
suitable amount of a conductive material, dispersed there-
~ ughout, the elastomeric blend can fulfill the required
electrical functions of a semiconducting material in elec-
trical cable, and when combined with an ethylene-propylene
copolymer insulation and cured in accordance with the sequence
of this invention, the combination provides the unique inter-
facial properties which effectively eliminate the occurrence - -
of intermediate void spaces between the interface surfaces of
insulation and semiconductive material and also enables an
easy and clean separation of the semiconductive material from
the insulation.
Referring to the drawing, a typical cable of
medium-to-high voltage capacity of the type to which this
invention is especially applicable and advantageous, is
shown in perspective in Figure 1, and a short portion of such
a cable is also shown with the insulation and semiconductive
layer in longitudinal cross sec~ion about the conductor~in
Figure 2. The overall cable product 10, primarily comprises
a metallic conductor 12, a relatively thick first body of
dielectric insulation 14 surrounding the conductor, and
overlying the insulation is a second body or layer of semi- ~ -
conductive material 16. Other components can be included in
the cable structure following known designs. For example,
separating paper or tape can be provided on the conductor -
or a semiconductive layer can be located between the metallic
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conductor 12 and the primary insulation 14, such as shown in
the aforementioned U.S. Patents Nos. 3,259,688 and 3,684,821,
and the means of this invention apply thereto with its atten-
dant advantages whenever the insulation abuts the semiconductive
component as is conventional in medium-to-high voltage capacity
cables. Upon combining and curing the components in the
essential sequence of this invention as set forth herein-
above, the insulation and semiconductive material covering the
insulation become adheringly joined to each other, producing ~-
a united interface 18 of unique attributes which eliminates
intermediate voids, and upon the application of a small pulling
force of only a few pounds, the surfaces at the interface
separate cleanly leaving each surface free of adherents from
the other.
The following comprise specific examples of suitable
and preferred polymeric materials for the application of this
invention in the construction of high-voltage cable comprising
a body of ethylene-propylene copolymer insulation combined
with an overlying body of semiconductive material of a
polymeric carrier or matrix comprising an elastomeric blend
filled with particulate conductive material. -
The ethylene-propylene copolymer insulating com-
position of the following examples consisted of the following
ingredients, in parts by weight:
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Parts Bv Weiqht
Ethylene-Pr~pylene Copolymer t50% wt. ethylene) 100.0
Vistalon~404, Exxon Chemical Co.
Antioxidant - Flecto~ H, Monsanto 2.0
A polytrimethyldihydroquinoline
Zinc Oxide 3.0
Lead Dioxide 2.0
Polybutadiene homopolymer - Ricon 150 5.0
Clay 96.0
Petrolatum 5.0 -
Vinyl Silane 1.5
Dicumyl ~eroxide Curing A~ent 6.0
Di Cu ~40 KE, Hercules -
These ingradients of the dielectric insulation
were compounded in a suitable mixer, a Banbury mixer, until -
substantially homogeneously dispersed. However, pursuant to
conventional practices, all ingredients except the peroxide
curing agent were first admixed with the temperature of the
mixing ingredients maintained below about 400F. To prevent
precuring the peroxide curing agent was added to the admixed
ingredients while at a temperature of below about 200F. The --
compound was then ready for forming to a given shape and
curing to a thermoset condi~ion by the application of heat.
The elastomeric blend semiconductive composition
of the following examples consisted of the following ingred- -
ients, including an electrically conductive carbon black,
in parts by weight:
-. .. , - . ..
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Parts BY Weiqht
Chlorosulfo~ated Polyethylene 65.0
Hypalo~40S, duPont
A Ethylene-P~opylene Terpolymer 35.0
Nordel~1320, duPont
Conducting Carbon Black 45.0
Vulcan XC-72
Litharge (90$ in EPDM) 20.0
Naphthenic Oil 17.0
Circosol 4240 Oil
Crystalline ~ydrocarbon Wax 2.0
Sunocd~Anti-Chek
Antioxidant-Agerit~ Resin D, R.T. Vanderbuilt 0.5
Polymerized dihydrotrimethylquinoline
Trimethyl Propane Trimethacrylate 2.0
SR-350
Dicumyl Pero~ide Curing Agent 2.5
Di Cu~ R, Hercules
The foregoing ingredients of the semiconductive
20 cOmpQsitiOn were also compounded in a Banbury mixer until
substantially homogeneously dispersed. Also according to
conventional practice, all ingredients except the peroxide
curing agent were fixst admixed with the temperature of the
mixing ingredients maintained below about 250F. To prevent
precuring the peroxide curing agent was added to the admixed
ingredients while at a temperature of below about 200F.
The compounded elastomeric blend was then ready for forming
to shape and curing to a thermoset condition by activating
the curing agent ~ith heat.
Samples of both of the foregoing insulating and
semiconducting compounds were sheeted out on separate roll
mills and applied as follows. In the hereinafter described
Example I, strip specimens of each sheeted sample of uncured
insulation and uncured semiconducting material were combined
by super-imposing specimens of one sample sheet upon the
other and both cured together as a laminate in adjoining
-12-
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physical contact in a press at 310F for 45 minutes. After
cooling to room temperature and conditioning for at least 16
hours at room temperature, 1/2 by 4 inch strips of the simul-
taneously cured laminated samples were tested for strippability.
The results are given hereinafter.
Like samples of both of the same foregoing insulating ~`
and semiconducting compounds sheeted out on separate mill rolls
were applied as follows in accordance with this invention for
comparison. In Example II, the strip specimens of the sheeted `
insulating composition of ethylene-propylene copolymer were
first cured at 350F for 15 minutes in a mold. After cooling
to room temperature and conditioning for at least 16 hours at
room temperature, the precured strip specimens of the in-
sulating compound were combined with like sheeted specimens of
the uncured semiconducting compound by superimposing one
sheeted specimen on the other providing a laminate. The
semiconductive compound was thereafter cured as a laminate
while in adjoining physical contact with the precured insulat-
ing compound, at 310F for 45 minutes in a press.
2~ After cooling to room temperature, 1/2 by 4 inch
strips of the dissimilarly cured specimens of Example II were
tested for strippability in the same manner and conditions as
the simultaneously cured specimens of Example I. The combined
results were as follows: -
Example I Example II
Specimens could not be stripped Specimens stripped with
apart, semicon layer completely average pulling force of 2.32
bonded to insulation. lbs., and separated cleanly.
In the following examples illustrating the merits
of this invention, the foregoing insulating and semiconducting
compositions were combined under actual extrusion conditions
simulating the manufacture of high-voltage electrical cable
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having a metallic conductor covered with a body or layer of
dielectric insulation and an overlying body or layer of semi-
conducting material. The cable construction consisted of a
#2 AWG stranded metal core conductor, cpvered with a 0.150
inch thickness of the insulation and a 0.035 inch thickness
of the semicon with a total outside diameter of about 0.680
inches, each applied by extrusion in a conventional manner.
In each example, the insulating composition was
continuously formed on the core conductor by a first extrusion
operation and thereafter continuously cured by passing at a
rate of 14 feet per minute through a steam chamber 75 feet
in length maintained at a pressure of about 255 psig (209C)
for a swell period of about five minutes.
Following the continuous forming and curing of the
insulation composition on the core conductor, an overlying
covering of the semiconducting composition was continuously
applied in each example by a second extrusion operation and
thereafter continuously cured by passing at a rate of 15 feet
per minute through a steam chamber 75 feet in length main-
tained at a pressure of about 255 psig (209C) for a swell
period of about five minutes.
The four examples prepared as described according to
this invention were treated and tested for several properties
in addition to strippability as set forth in the following
table:
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Insulation Treatment Prior E X A M P L E S
To Semicon Extrusion III IV V VI Reauirements*
Insulation Ovenized ** No No Yes Yes
Spica oil applied to inter-
face ***Yes No No Yes
PROPERTIES
Outer Semicon Results
Tensile Strength, psi 16221615 19151858
Elongation, % 305327 295302
Seven Days Air Oven 121 C
Tensile Strength, psi ---1681 16261802
Elongation, % --- 223205193 100 minimum
Conductivity
Room Temperature - ohm-cm --- 525108 103 5000 maximum
90C - ohm-cm --- 2437055 50000maximum
Strippabilitv
Lbs. per 1/2 inch wide strip 4.755.75 5.38 5.64 4-minimum
18-maximum :
* IPCEA S-66-524 & AEIC 6-73
** Ovenizing conditions - 51 hrs. at 115C
*** Spica oil applied to insulation surface prior to semicon
extrusion to prevent nipple "plug-up".
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 the
invention.
