U.S. patent number 3,735,025 [Application Number 05/167,741] was granted by the patent office on 1973-05-22 for semiconducting composition and cable jacketed therewith.
Invention is credited to Ting H. Ling, Marwick H. Solomon, Robert M. Wade.
United States Patent |
3,735,025 |
Ling , et al. |
May 22, 1973 |
SEMICONDUCTING COMPOSITION AND CABLE JACKETED THEREWITH
Abstract
Electrical cables are jacketed with a novel thermoplastic
semiconducting composition comprising chlorinated polyethylene,
ethylene ethyl acrylate and carbon black.
Inventors: |
Ling; Ting H. (Marion, IN),
Wade; Robert M. (Wabash, IN), Solomon; Marwick H.
(Muncie, IN) |
Family
ID: |
22608624 |
Appl.
No.: |
05/167,741 |
Filed: |
July 30, 1971 |
Current U.S.
Class: |
174/120SC;
174/105SC; 174/102SC; 174/110PM |
Current CPC
Class: |
H01B
1/24 (20130101); H01B 9/027 (20130101); H01B
3/004 (20130101) |
Current International
Class: |
H01B
9/02 (20060101); H01B 1/24 (20060101); H01B
3/00 (20060101); H01B 9/00 (20060101); H01b
005/16 (); H01b 009/02 () |
Field of
Search: |
;174/12SC,12SC,15SC,11PM,16SC,12C,12R,115,113R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Grimley; A. T.
Claims
We claim:
1. An electric cable comprising a conductor, a layer of polymeric
insulation surrounding said conductor, and a semiconducting
thermoplastic polymeric jacket directly surrounding said
insulation; said jacket comprising: 50-80 parts by weight of
chlorinated polyethylene, the difference to make 100 parts by
weight of ethylene ethyl acrylate, and 40-60 parts by weight of
semiconducting carbon black.
2. The cable of claim 1 wherein said jacket comprises 65-75 parts
by weight of chlorinated polyethylene and 45-55 parts by weight of
said carbon black.
3. The cable of claim 1 wherein said insulation is vulcanized.
4. The cable of claim 2 wherein said insulation is vulcanized.
5. The cable of claim 3 wherein said insulation comprises
polyethylene.
6. The cable of claim 4 wherein said insulation comprises
polyethylene.
Description
BACKGROUND OF THE INVENTION
Polymeric compositions that will conduct electricity have utility
for a number of purposes, varying from the discharge of
frictionally induced electrostatic charges on plastic surfaces
where such charges cause an accumulation of dust, to the
transmission of useful currents by the conductors of ignition
cables. The conductivity of polymeric compositions does not equal
that of metals since the composition resitivities usually vary from
about 1 to 10,000 ohm-centimeters. For this reason such
compositions are usually referred to as semiconducting as they
shall be in this application. A recent commercial interest in
electric cables with semiconducting jackets, particularly for
direct burial, has been stimulated by the development of cables of
a type described in U.S. Pat. No. 3,474,189. These cables have
drain wires embedded in a semiconducting outer jacket that provides
both electrical shielding and mechanical protection. Modern cables
for burial service employ vulcanized compositions such as
vulcanized polyethylene for insulation. This means that they have
higher temperature ratings than thermoplastic-insulated cables.
Fully to utilize the higher thermal ratings of vulcanized
insulation the jackets of the cables should be equally highly rated
and, what is even more exacting as a requirement for this modern
type of cable, the electrical conductivity of the cable jackets
should remain high through the whole service temperature range.
Attempts have been made to meet these requirements with vulcanized
semiconducting jackets. But vulcanized compounds, when used for
jacket stocks, have the serious disadvantage that they bond firmly
to the surface of the insulation and cannot be readily stripped
clean at splices and terminations. Further requirements for jacket
compositions for buried cables, which presently known materials do
not fully meet, include extrudability at high manufacturing speeds.
This has particular significance for the embedded drain wire cables
since the jackets can then be applied in tandem with the insulation
extrusion without slowing down the former. The composition must, in
addition, retain its properties in water and other commonly
encountered solvents, and resist burning. Significantly, since
cables are buried with a view to service for many years the jacket
composition must age exceptionally well, i.e. retain its good
characteristics after thousands of cycles of heating and cooling
and years of burial. No compositions are presently known fully to
satisfy all the enumerated requirements for cable jacketing.
SUMMARY
We have invented a composition which is thermoplastic and so will
not bond to cable insulation but is servicable at elevated
temperatures, retains its electrical conductivity under adverse
conditions, as shall be shown, and can be extruded at high speed.
Our composition comprises a homogenous blend of 10-90 or, more
preferably 50-80, or particularly 60-75 parts by weight of a
chlorinated polyolefin such, preferably, as polyethylene; the
difference to make up 100 parts by weight of ethylene ethyl
acrylate; and 30-75 or, more preferably 40--60, or particularly
45-55 parts by weight of semiconducting carbon black.
We have invented an electric cable comprising a conductor, a layer
of polymeric insulation such, preferably as vulcanized
polyethylene, surrounding the conductor, and a semiconducting
thermoplastic polymeric jacket directly surrounding the insulation.
The jacket comprises 50-80 or, preferably, 65-75 parts by weight of
chlorinated polyethylene, the difference to make 100 parts by
weight of ethylene ethyl acrylate, and 40-60 or, preferably, 45-55
parts by weight of semiconducting carbon black .
DESCRIPTION OF THE DRAWING
The FIGURE shows a pictorial lengthwise view of a cable of our
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the FIGURE a cable suitable for underground power service is
indicated generally by the numeral 10. In the cable 10 a conductor
11, which may be stranded, is covered in known manner by a layer 12
of semiconducting strand shielding composition. The conductor,
including the layer 12 is insulated with a surrounding layer 13 of
vulcanized polyethylene. Our invention has particular utility where
the insulation 13 is vulcanized because the cable can then make
most advantage of the high-temperature properties of the jacket, to
be described. Other vulcanized compositions, such as ethylene
propylene copolymers or diene terpolymers can also be employed
within the scope of our invention, and, of course, certain
advantages will still accrue where the insulation is thermoplastic,
such as thermoplastic polyolefin, although, generally, the
temperature rating will then be lower.
Over the insulation layer 13 there is directly extruded a
thermoplastic semiconducting jacket 14 into which drain wires have
been embedded during the extrusion operation. Since the jacket 14
is in direct surface contact with the insulation 13 it would bond
to the insulation if both were vulcanized. An advantage of our
cable resides in the fact that the thermoplastic jacket can always
be cleanly stripped, even from a vulcanized layer of
insulation.
EXAMPLE
Parts by weight chlorinated polyethylene 70 ethyl ethylene acrylate
30 semiconducting carbon black 50 lead phthalate 4 epoxy resin 2
lead stearate 1 antioxidant 0.5 flame retarder 5
The chlorinated polyethylene of the EXAMPLE was obtained from Dow
Chemical Company under the designation 2243.28, with a chlorine
content of 25 percent, crystallinity of 28 percent and specific
gravity of 1.08. Although we prefer to use chlorinated polyethylene
with chlorine contents of 20-30 percent our invention includes
chlorine contents of 15-70 percent.
The ethylene ethyl acrylate of the EXAMPLE was supplied by the
Union Carbide Plastics Company under the designation DPD-6169
having an ASTM D638 stiffness of 5000 psi, an ASTM D1505 density of
0.93 grams per cc and an ASTM D1238 melt index of 6.0 grams/10
minutes. The term ethylene ethyl acrylate, as used in this
application applies to copolymers of ethylene and ethyl acrylate,
which are commercially available with combined ethyl acrylate
contents of about 3-25 percent by weight.
The semiconducting carbon black of the EXAMPLE was supplied by
Godfrey L. Cabot, Inc. under the designation Vulcan XC-72.
Semiconducting carbon blacks suitable for the practice of our
invention are, however, commercially available from a number of
sources known to persons skilled in plastic compounding arts.
The lead phthalate and stearate serve as stabilizers and the epoxy
as an extrusion lubricant. For the additional flame retarder of the
EXAMPLE antimony oxide can be used or "Dechlorane" furnished by the
Hooker Electrochemical Company, and a suitable antioxidant is
polymerized 1,2-dihydro-2,2,4-trimethylquinoline. Other suitable
antioxidants, of which a number are well known to plastic
compounders can also be used within the scope of our invention.
Other suitable compounding agents are known that can be employed
within the scope of our invention which is not limited except as
hereinafter specifically claimed.
Resistivity tests of the composition of the EXAMPLE were conducted
over a period of five weeks in accordance with the following
schedule: specimens were aged in a 90.degree. C oven from 4:30 PM
to 8:30 AM each weekday and over the Friday to Monday weekend. From
8:30 AM to 11:30 AM each weekday they were aged in a 130.degree. C
oven. From 11:30 AM to 4:30 PM they were permitted to cool at room
temperature. Resistivity measurements were made each weekday at
8:05 AM while the samples were in the 90.degree. C oven, at 11:05
AM while they were in the 130.degree. C oven and at 4 PM at room
temperature.
Values of the resistivities obtained are shown in TABLE I.
TABLE I
Resistivity, Ohm-Cm Week Day 90.degree.C 130.degree.C Room Temp.
1st Mon. 935 2630 190 Fri. 840 2040 158 2nd Mon. 740 2130 171 Fri.
757 1750 167 3rd Mon. 610 1670 149 Fri. 650 1320 147 4th Mon. 528
1350 148 Fri. 612 1680 153 5th Mon. 510 1380 151 Fri. 493 1390
152
The data of Table I evidence an unexpected improvement in
conductivity of our composition with aging, over a wide range of
temperatures.
Specimens of cable jacketed with our composition made in accordance
with the EXAMPLE and specimens jacketed with semiconducting
polyethylene were tested for resistivity of the jacket at different
temperatures by holding the specimens in an air oven for two hours
at each temperature. The results are shown in Table II.
TABLE II
Ohm-Cm Temp. .degree.C Polyethylene Example 25 162 235 50 4,610 671
75 29,700 900 100 5,980,000 1,820 130 8,710 5,030 150 3,500
2,520
The resistivity of the composition of the EXAMPLE is seen not to
rise excessively upon hot water immersion by the data of Table III.
Measurements were made at room temperature.
TABLE III
Weeks water Resistivity immersion at 90.degree.C Ohm-Cm 0 185 1
2750 2 4710 4 6710
After 4 weeks immersion in different solutions and solvents the
resistivity of the composition of the EXAMPLE did not rise unduly,
as shown in Table IV.
TABLE IV
Solution or Solvent Resistivity Ohm-Cm 30% sulfuric acid 951 10%
nitric acid 967 10% hydrochloric acid 603 5% acetic acid 765 10%
sodium hydroxide 884 gasoline 525 acetone 253 ethylene dichloride
318 heptene 547 ASTM No. 2 oil 766 transformer oil 622
The resistance to heat deformation of the composition of the
EXAMPLE is shown in Table V to be superior at elevated temperatures
to that of semiconducting polyethylene or of polyvinyl chloride
jacket stock.
TABLE V
% Heat Deformation 70.degree.C 90.degree.C 121.degree.C
150.degree.C semiconducting polyethylene 0 2.63 100 polyvinyl
chloride 2.84 4.75 13.64 61.30 Example 2.80 4.88 5.58 53.30
We have invented a new and useful cable and composition of which
the foregoing description has been exemplary rather than definitive
and for which we desire an award of Letters Patent as defined in
the following claims.
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