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Патент USA US3100141

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Aug. 6, 1963
R. c. D'ASCOLI ETAL
3,100,136
METHOD OF MAKING POLYETHYLENE-INSULATED POWER CABLES
Filed June 18, 1959
INVENTOR.
RALPH GREGORY D'ASCOLI
E CHARLES EBEL
W
4&2,’
Limos M4 474+
AIM/HHS
United States Patent 0
Ice
1
3,100,136
Ralph Gregory D’Ascoli, Yonkers, and Lawrence Charles
Ehel, Hastings on Hudson, N.Y., assignors to Anaconda
Wlre and Cable Company, a corporation of Delaware
Filed June 18, 1959, Ser. No. 821,074
(Cl. 18-59)
3,l00,l36
Patented Aug. 6, 1963,
2
METHOD OF MAKING POLYETHYLENE
INSULATED POWER CABLES
6 Claims.
\
.
temperature of at least 250° F. and at a pressure from
200 to 1200 pounds per square inch so that molten poly
alkylene is forced under pressure into all of the surface
irregularities in the semiconductive ?lm, thereby forming
an intimate bond between the semiconductive ?lm sur
rounding the conductor and the inner face of the poly
alkylene insulation. If desired, an additional shielding
layer of semiconductive ?lm coating may be intimately
bonded to the outer ‘face of the insulation merely by.app1y
This invention relates to a method forlm-aking shielded
ing the same or an equivalent shielding composition to
electric conductors which are insulated with polyethylene 10 the insulation as it leaves the extruder but while it is still
and, more particularly, to a method for intimately bond
in an amorphous and near-molten state, thereby ?rmly
ing an electrostatic shield to either the inner or the outer
bonding the shield to the insulation.
face of a layer of polyethylene insulation surrounding an
The particular semiconductive shielding compositions
electric conductor, to protect the insulation against the 15 which may be intimately bonded to polyethylene or to
formation or development of any focal points at which
polypropylene insulation in accordance with the invention
corona discharge might occur. This application is a con
tmuation-in-part of our copending application Serial No.
565,609, ?led @February 15, 1956, on which United States
hgeétgers Patent No. 2,913,515 was granted ‘November 17,
l’olyethylene is a rigid, waxy, translucent, synthetic
include those described in our copending application Serial
No. 565,609, ?led February 15, 1956. These shielding
compositions have excellent adherence to both polyethyl
20 ene and polypropylene. Basically, the shielding composi
tion contains methylated paral?n combined withjeit-her a
polyvinyl acetate or chlorinated paraf?ns, both of which
resin having excellent dielectric properties, ozone resist
modify the inherent brittleness and tackiness of methylated
ance, moisture resistance, and chemical stability. It has
para?in without impairing its adhesive properties. The
been extensively used in recent years for insulating high 25 composition also contains a su?icient ‘amount of conduct
frequency conductors which normally carry ‘only small
ing or semiconducting particles, such as carbon black, to
currents. Although it possesses excellent chemical, phys
render it electrically conductive. In general, the semi
lcal, and electrical properties ‘as an insulating material for
conductive shielding compositions contain from 25 to 50
high voltage power cables which carry relatively large
percent ‘by weight of methylated para?fin, from 20‘ to 60
currents, its use for this purpose has been limited due to
percent by weight of modi?er (e.g., polyvinyl acetate or
the tendency of polyethylene to separate slightly from the 30 chlorinated para?ins), and from about 10 to about 50
conductor or conductive shield and to form small air gaps
percent by weight of carbon-black particles.
which become focal points ‘for ionization and corona dis
The unique properties of this composition are-‘largely
charge, the ultimate result of which is electrical break
attributable to the combination of methylated paraf?n
down of the cable.
Using a semiconductive shielding composition consisting
essentially ‘of methylated para?in combined with a modi
?er of its inherent brittleness ‘and tackiness and containing
a su?‘icien-t amount of carbon black ‘or equivalent mate
rial to render it electrically conductive, we have found
that by bringing the semiconductiveshielding composition
in contact with molten polyethylene which is in an amor
phous state, using su?icient pressure to force the molten
polyethylene into intimate contact with the shielding com
with the other components. Methylated paraf?n is the
polymerization product obtained by catalytic reaction of
a mixture of monomers having an average molecular
weight of about Y90 and composed ‘of dienes and reactive
ole?ns. The polymerization product, which is -a methylat
ed para?inic hydrocarbon chain, is a ‘hard, brittle, thermo
plastic resin having an average molecular weight between
1000 and 1400 and a softening point of about 100° C. as
measured by the ball and ring method. The methylated
para?in manufactured by the Pennsylvania Industrial
position, it is possible to form an intimate bond between
Chemical Corporation under the trade name “Pi'ccopale”
45
the shielding composition and the polyethylene. Intimate
is a typical example of a methylated para?‘in and has
bonds may also be formed between the shielding com
been found to give very-satisfactory results.
'
" i
'
position and polypropylene insulation when molten poly
A large proportion of carbon black in the shielding
propylene is used in place of the polyethylene. These
composition produces a semiconductive loomposition of
bonds are so resistant to rupture that no voids or ?ssures
or air gaps ‘are formed at the bond interface even when
the polyethylene is subject to stresses and strains compara
ble to those which occur in cable insulation.
Based on these discoveries, the invention provides an
improved method for forming an intimate bond between
an electrostatic shield and polyethylene or polypropylene
insulation surrounding an electrical conductor to protect
the insulation against the development of any focal points
relatively high conductivity. Although decreasing the
amount of carbon blioclk results in an increase in the ?lm
strength of the composition, the amount of carbon black
cannot be reduced to less than about 10 percent by weight,
(below which concentration the carbon black particles be
come so dispersed that they lose contact with one an
other, thus reducing the conductivity of the composition
to an excessively low level.
/
The shielding composition used to coat the metallic
at which corona discharge might occur. In essence, the
conductor is conveniently prepared by heating a mixture
method of the invention comprises coating a metallic con
of the methylated para?’in and chlorinated para?ins until
60
ductor with a continuous semiconductive ?lm consisting
the mixture lbeoornes ?uid, at which point the carbon
essentially of from 2.5 to 50 percent by weight of methylat
ed para?in, from 20 'to 60‘ percent by weight of either
polyvinyl acetate or chlorinated paraiiins (both of which
modify the inherent brittleness and tackiness of methylated
para?in without impairing its adhesion to polyethylene
or to polypropylene), and from about 10 to 50 percent by
weight ‘of carbon-black particles uniformly dispersed
black is added and thoroughly dispersed throughout the
mixture. Upon cooling, the composition‘soli-di?es to a
soft solid, which, when brought into contact with a heated
conduct-or, melts to form a smooth, continuous coating
around the conductor.
-
-.
To intimately Ibond thesemiconductive shielding com
position to the inside surface :of a layer of ‘polyethylene
throughout the ?lm coating to render it electrically con
insulation about a conductor in accordance with the in
ductive, and then extruding a molten polyalkylene of the
vention, the metallic conductor is coated with a con
70
group consisting of molten polyethylene and polypropylene
tinuous ?lm of the shielding composition by heating the
in an ‘amorphous state about the coated conductor at a
conductor and passing it through the shielding compo
3,100,186
3
sition just before it enters the extruder by which the
polyethylene insulation is applied. Upon entering the
extrusion head, the semiconductive ?lm coating sur
rounding the conductor comes in contact with the molten
polyethylene as it' is extruded around the conductor. By
maintaining the temperature of the polyethylene
the
extrusion head at not less than about 250° F., which
temperature is above the normal melting point of the
'4
tion 5, leaving a semiconducting coating 7 on the in_
sulation. The insulated‘and icoated conductor then passes
through a cooling trough 8.
Table I lists the formulations of two semiconductive
shielding compositions which were used in examples of
the invention described below. One of thesecomposi
tions (Composition A) was used to form an electrostatic
shield about the inner face of a layer of polyethylene
insulation surrounding an electrical conductor, while a
polyethylene; and by employing extrusion pressures from
200 to 1200 pounds per. square inch, it is possible to
?orce moltenpolyethylene into. all of the surface irregu
solution of the other (Composition B) was employed
to form an electrostatic shield around the outer face of
the insulation.
TABLE I
larities in the semiconductive ?lm coating and to inti
mately bond the ?lm to the inner face of the extruded
layer of polyethylene insulation. This bond is so strong
that even though the conductor may loosen within the
Semiconductive Shielding Compositions
[Parts by Weight]
semiconductive ?lm coating, the ?lm ooating remains in
contact with the inner ‘face of the polyethylene insula
tion and thereby protects the insulation against the for
mation and‘ development of any voids at which ionization
A
Methylated parai?n _________________________________ __
20 Polyvinyl acetate- _ _
and corona discharge might occur.
Chlorinated paraillns (40-42% chl0rine)____
Where polyethylene insulation is used, then as a gen
Chlorinated para?lns (68~73% ch1orine)_____
eral rule, we prefer to extrnde the polyethylene insula
B
40
20
40
Wax _____________________________________ __
Acetylene black
tion about the coated conductor at temperatures in ex
cess of 300° F. at extrusion pressures from 600 to 1200
A heated conductor was coated with a conductive ?lm
pounds per square inch to insure that the molten poly 25
of the shielding composition (Composition A) and then
ethylene will be forced» into all of the surface irregulari
passed into and through an extrusion head where molten
ties in the semiconductive ?lm, and to obtain an exceed
polyethylene ‘was extruded around the coated conductor
ingly ?rm bond of the polyethylene to the semiconductive
at a temperature in excess of 300° F. and at a pressure of
coating.
about 1000* pounds per square inch. Upon leaving the
extrusion head, the outer surface of the insulation, which
A shielding layer of the semiconductive ?lm coating
may, also be applied to- the outer face of the polyethyl
was still in a near-molten and substantially amorphous
state, was coated with an additional layer of semiconduc
ene. insulation as it leaves the extrusion head while the
insulation is still in a near-molten and amorphous state,
tive shielding composition (Composition B) by spraying
no pressure being required tobond this shielding layer
to the outer surface of the insulation provided the pol - 35 an ethylene dichloride solution ct this composition about
the outer surface of the polyethylene prior to its entry into
ethylene is still‘ in an amorphous state. In such case,
a cooling trough.
. the shielding composition or a solution of it in a volatile
The shielded, insulated conductor thus made was tested
solventmay be applied to the outer surface of the insula
successfully, without ionization, at 18 kv. Even upon
tion by spraying or pouring it over the outer surface of
40 stretching the conductor to loosen within the insulation,
the insulation.
the cable operated without ionization at voltages up to
The coatingcomposition for the outside of the insula
7.8 kv. By way of contrast, a polyethylene-insulated con
tion is conveniently prepared by dissolving the methylated
ductor
which was identical in all respects except that it
para?in andi polyvinyl acetate in a mutual solvent, such
did not contain electrostatic shields bonded to the inner
asethylene dichloride, butyl acetate, or methyl isobutyl
or outer faces ot the insulation showed ionization even at
ketone, the solvent reducing‘ the viscosity sui?ciently so
that the shielding composition may be applied by dip~
voltages below 1.0 kv. after the conductor had been
stretched and loosened from the insulation.
ping, brushing, or even spraying. The amount of the
solvent is varied to suit the method of application, evap
orating from the coating soon after application to the
outer surface of the amorphous insulation. After dis
Although the foregoing example has illustrated the ef
fectiveness with which polyethylene insulation may be
intimately bonded to a shielding composition in accord,
ance with the invention, excellent results have also been
obtained by using molten or amorphous polypropylene as
the insulation in place of the polyethylene.
We claim:
solving the methylated paraf?n and polyvinyl acetate in
the solvent, the carbon black is then. added to the solu~
tion, using an- additional amount‘ of solvent to impart
the desired viscosityito the composition.
The drawing is a schematic representation of a pre
ferred embodiment of‘ the PPOlCeSSlOf this invention.
In the process illustrated‘- by the drawing a heated‘ elec
trical conductor 1-‘ passes through a container 2' of shield
55
1. A method for forming an intimate bond between an
electrostatic shield and polyethylene insulation surround
ing an electrical conductor to protect the insulation
against the ‘development of focal points at which corona
ing composition comprising methylated paraf?n, chlo
discharge might occur which comprises coating a metal;
to render the compositionsemiconducting. A coating 2a
of the shielding composition adheres to the emerging
conductor, which then passes through the extrusion head
sisting essentially of from 25 to 50 percent by weight of
methylated para?in, irom 20 to 60 percent by weight of
a polymer selected from the group consisting of polyvinyl
ethylene. The polyethylene leaves the extrusion head
dispersed throughout the ?lm coating to
rinated paraffin, and a sufhcient quantity of carbon black 60 lic conductor with a continuous semiconductive ?lm con
3 of an» extrnder 4 where it‘ is covered‘ with hot poly 65 acetate and chlorinated para?‘ins, and from about 10 to
50 percent by weight of carbon-black particles uniformly
as a concentric wall' of amorphous insulation 5 around
the conductor 1 and its shielding 2a. Before the poly
ethylene 5 has cooled from its amorphous state it is
sprayed with a semiconducting solution 6 comprising
methylated‘ para?in and polyvinyl acetate dissolved in a
solvent such as ethylene, dichloride, and having semi
conducting particles of carbon black suspended therein.
thereto
semiconductive properties, extruding molten polyethylene
in an amorphous stateabout the coated conductor at a
temperature of at least 250° ‘F. and at a pressure of 200
to 12001 pounds per square inch to force molten poly
ethylene into all of the surface irregularities in the semi
conductive ?lm, thereby intimately bonding said ?lm to
the inner face of the polyethylene, and applying an outer
layer of the semiconductive ?lm coating to the outer face
The solvent evaporates from the solution ‘(Sunder the in
?uence of, the sensible heat of. the polyethylene insula 75 of the polyethylene while it is still in an amorphous, near
5
3,100,136
h
molten state to intimately bond the outer layer of the
semiconductive ?lm- to the outer face .of the polyethylene.
to render it electrically conductive, thereby intimately
bonding the outermost shielding composition to the
2. A method for forming an intimate bond between an
outer face of the polyethylene.
5. A method for forming an intimate bond between
electrostatic shield and polyethylene insulation surround
ing an electrical conductor to protect the insulation
against the development of focal points at which corona
an electrostatic shield and polyethylene insulation sur
rounding an electrical conductor to protect the insulation
against the development of focal points at which corona
discharge might occur which comprises coating a metal
lic conductor with a continuous semiconductive ?lm
discharge might occur which comprises extruding molten
polyethylene in an amorphous state about the conductor,
and applying to the outer face of the polyethylene while
it is still in an amorphous, near-molten state a continuous
consisting essentially of 40 parts by weight of methylated
semiconductive ?lm consisting essentially of from 25 to 10 paraffin, about 40 parts by weight of chlorniated par
50 percent by weight of methylated paraf?n, from 20 to
a?ins, about 20 parts by weight of wax, and from 10
60 percent by weight of a polymer selected ?nom the
to 20 parts by weight of carbon-black particles uni
group consisting of polyvinyl acetate and chlorinated
para?ins, and from about 10 to 50 percent by weight of
formly dispersed throughout the ?lm coating to impart
thereto semiconductive properties, extruding molten poly
carboneblack particles uniformly dispersed throughout
ethylene in an amorphous state about the coated con
ductor at a temperature of at least 250° F. and at a
pressure from 200 to 1200 pounds per square inch to
the ?lm coating to impart thereto semiconductive prop
erties, whereby said outer layer of semiconductive ?lm
is intimately bonded to the outer face of the polyethylene.
force molten polyethylene into all of the surface irregu
3. A method for forming ‘an intimate bond between an
larities of the semiconductive ?lm, thereby intimately
electrostatic shield and polyethylene insulation sun-pound
ing an electrical conductor to protect the insulation
bonding said ?lm to the inner face of the polyethylene,
and applying to the outer face of the polyethylene while
against the development of focal points at which corona
discharge might occur which comprises coating a metal
layer of a semiconductive shielding composition consist~
it is still in a near-molten, amorphous state an outer
ing essentially of about 20 parts by weight of methylated
para?in, about 40 parts by weight of polyvinyl acetate,
lic conductor with a continuous semiconductive ?lm con
sisting essentially of from 25 to 50 percent by weight of
methylated par-ai?n, ‘from 520 to 60 percent by weight of
chlorinated paraffins, and ‘from 10' to 50 percent by weight
and from 10 to 50 parts by weight of carbon-black
particles uniformly dispersed throughout the composition
of carbon-black particles uniformly dispersed throughout
to render it electrically conductive, thereby intimately
bonding the outermost shielding composition to the outer
face of the polyethylene.
the ‘?lm, coating to impart thereto semiconductive prop
erties, extruding molten polyethylene in an amorphous
6. A method for forming an intimate bond between
an electrostatic shield and polyethylene insulation sur
rounding an electrical conductor to protect the insulation
against the development of focal points at which corona
state about the coated conductor at a temperature of at
least 250° F. and at a pressure from 200 to 1200 pounds
per square inch to force molten polyethylene into! all of
the surface irregularities in the semiconductive ?lm, 35
discharge might occur which comprises coating a metal
thereby intimately bonding said ?lm to the inner face of
lic conductor with a continuous semiconductive ?lm
the polyethylene, and applying ‘to the outer face of the
polyethylene while it is still in a near-molten, amorphous
consisting essentially of 40 parts by weight of methylated
para?in, about 40 parts by weight of chlorinated par
state an outer layer of a semiconductive shielding com
position consisting essentially of from 25 to 50 percent 40 a?ins,‘ about 20 parts by weight of Wax, and from 10
to 20 parts by Weight of carbon-black particles uni
by weight of methylated paraf?n, ‘from 20 to ‘60 percent
formly dispersed throughout the ?lm coating to impart
by weight of polyvinyl acetate, and from 10‘ to 50 percent
thereto semiconductive properties, extruding molten
by weight of carbon~black particles uniformly dispersed
polyethylene in an amorphous state about the coated
throughout the composition to render it electrically con~
conductor at a temperature of at least 300° F. and at
ductive, thereby intimately bonding the outermost shield
a pressure from 600 to 1200 pounds per square inch to
ing‘ composition to the outer face of the polyethylene.
force molten polyethylene into all of the surface irregu~
4. A method for forming an intimate bond between
larities of the semiconductive ?lm, thereby intimately
an electrostatic shield and polyethylene insulation sur
bonding said ?lm to the inner face of the polyethylene,
rounding an electrical conductor to protect the insulation
against the development of focal points at which corona 50 and applying to the outer face of the polyethylene while
it is still in a near-molten, amorphous state an outer
discharge might occur which comprises coating a metallic
layer of a semiconductive shielding composition con
conductor with a continuous semiconductive ?lm con
sisting essentially of about 20 parts by weight of meth
sisting essentially of from 25 to 50 percent by weight of
ylated paramn, about 40 parts by Weight of polyvinyl
methylated paraf?n, from 20 to 60‘ percent by weight of
chlorinated para?ins, and from 10 to 50 percent by 55 acetate, and from 10 to 50 parts by Weight of carbon
black particles uniformly dispersed throughout the com
Weight of carbon-black particles uniformly dispersed
position to render it electrically conductive, thereby inti
throughout the ?lm coating to impart thereto semicon
mately bonding the outermost shielding composition to
ductive properties, extruding molten polyethylene in an
the outer face of the polyethylene.
amorphous state about the coated conductor at a tem
perature of at least 300° F. and at a pressure from 600 60
to 1200 pounds per square inch to force molten poly
ethylene into all of the surface irregularities in the semi
conductive ?lm, thereby intimately bonding said ?lm to
the inner face of the polyethylene, and applying to the
outer face of the polyethylene While it is still in a near
molten, amorphous state an outer layer of a semicon
65
ductive shielding composition consisting essentially of
from 25 to 50 percent by weight of methylated paraffin,
from 20 to ‘60 percent by Weight of polyvinyl acetate,
and from 10 to 50 percent by weight of carbon-black 70
particles uniformly dispersed throughout the composition
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,081,517
2,175,099
2,377,153
2,913,515
Hotfen ______________ __ May 25, 1937
Abbott ______________ _._ Oct. 3, 1939
Hunter et al. _________ __ May 29, 1945
Ebel et al. ___________ __ Nov. 17, 1959
OTHER REFERENCES
“Alathon,” Du Pont Information Bulletin No. X-70,
1956, 15 pages total, pages 10—13 relied upon.
“What’s With Polypropylene?” Modern Plastics, vol.
35, No. 7, March 1958, pages 89~92.
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