Note: Descriptions are shown in the official language in which they were submitted.
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ETHYLENE POLYMER COMPOSITION FOR CABLE APPLICATIONS
The present invention relates to cable applications, such as a coating on a
fiber optical
cable, coaxial cable, or telecommunications cable, comprising a layer of a
specific
polyethylene composition. More specifically, the polyethylene composition used
in the cable
of the present invention comprises a particular type of ethylene /a-olefin
interpolymer,
especially a homogeneously branched ethylene/a olefin interpolymer, and most
preferably a
homogeneously branched substantially linear ethylene/a-olefin interpolymer;
and a
heterogeneously branched ethylene/a-olefin interpoiymer (or linear ethylene
homopolymer).
The cable of the present invention may have good mechanical properties such as
abrasion
resistance and flexibility, and good processability, moreover, may be less
environmentally
harmful (as compared with polyvinyl-chloride (PVC) based cables) when
disposed.
Various types of thermoplastic polymer have been used for wire and cable
jacketing
applications. Especially, polymer compositions based on ethylene homopolymer
via high
pressure polymerization processes (low density polyethylene (LDPE)), and
polyvinyl-chloride
(PVC) have been used conventionally.
Various mechanical properties are desired for the cable jacketing application,
for
example, mechanical properties such as abrasion resistance, flexibility and
reduced notch
sensitivity are highly required. Moreover, good processability is also
required for production
efficiency and good appearance or quality of produced cable.
However, the above resins { that is LDPE, PVC) have several deficiencies. For
example, LDPE may be acceptably flexible ( that is low stiffness) but very
often has low
abuse resistance; moreover, since PVC contains chlorine, PVC-based cables
release
environmentally harmful gas such as hydrochloride gas when combusted.
Furthermore,
considering environmental adaptability, polymers such as PVC, especially those
containing
lead stabilizers, tend to release environmental harmful materials (for
example, lead leached
into ground water) when combusted or landfilled and should be avoided for this
application.
In addition, when the plasticizers leach out of a PVC formulation, the cable
becomes brittle
which leads to premature failure.
Linear polyethylene has also been used as a layer in a cable application, but
these
linear polyethylene polymers do not have adequate abuse resistance in
combination with the
necessary flexibility; that is, to increase abuse resistance in a linear
polyethylene, one merely
has to increase the density of the polyethylene, however raising the density
reduces the
flexibility. Reduced flexibility hampers installation of the cable, especially
where the cable
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must be routed through numerous bends and twists/turns. Jacket or sheath
damage resulting
from poor flexibility usually results in cable failure.
In view of the above deficiencies, a resin composition which satisfies the
above
various mechanical properties, processability and environmental adaptability
has been long
awaited.
One aspect of the present invention is a cable comprising a layer of a
polyethylene
composition characterized in that the polyethylene composition comprises:
(A) from 5 percent (by weight of the total composition) to 95 percent (by
weight of
the total composition) of at least one first polymer which is an ethylene/a-
olefin interpolymer
having:
(i) a density from 0.865 g/cm3 to 0.95 g/cm3,
(ii) a molecular weight distribution (MW/M") less than 3.5, especially from
1.8
to 2.8,
(iii) a melt index (I2) from 0.001 g/lOmin. to 10 g/lOmin.,
(iv) a CDBI of greater than 50 percent; and
(B) from 5 percent (by weight of the total composition) to about 95 percent
(by
weight of the total composition) of at least one second polymer which is a
heterogeneously
branched ethylene/a-olefin interpolymer or a homogeneously ethylene
homopolymer having a
density from 0.9 g/cm3, preferably from 0.93 g/cm3 to 0.965 g/cm3.
Most preferably, the cable comprises a layer of a polyethylene composition
characterized in that the polyethylene composition comprises about 40 percent
(by weight of
the total composition) of the at least one first polymer which is
characterized as having:
(i) a density from 0.91 to 0.92 g/cm3,
(ii) a molecular weight distribution {MW/M") of about 2,
{iii) a melt index (I2) of about 0.1 g/10 min., and
(iv) a CBDI greater than 50 percent; and
about 60 percent (by weight of the total composition) of the at least one
second polymer
which is characterized as having heterogeneously branched ethylene/a-olefin
interpolymer:
(i) a density of about 0.96 g/cm3,
(ii) a melt index (I2) of about 6 g/10 min., and
(iii) a CDBI less than 50 percent.
Another aspect of the present invention is a cable jacket comprising the
polyethylene
composition of the invention which has at least 10 percent, preferably at
least 20 percent,
more flexibility than a cable made using conventional heterogeneous linear
ethylene polymer
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having about the same density as the inventive polyethylene composition.
Yet another aspect of the invention is a cable comprising a thermoplastic
cable jacket
having a thickness from 80 to 90 mils (2.0 to 2.3 mm) in contact with a metal
shield creating a
notch in said jacket, wherein a sample of said notched jacket taken in a
circumferential
direction, in accordance with ASTM D 638, has less than 55 percent loss of
elongation than
an un-notched cable jacket sample from said cable.
Still another aspect of the invention is a cable comprising a thermoplastic
ethylene
polymer cable jacket composition, wherein a plaque having a single notch, a
thickness from
70 to 80 mils (1.8 to 2.0 mm) made from said jacket composition has at least
100 percent,
preferably at least 200 percent, more preferably at least 300 percent,
especially at least 400
percent, and most especially at least 500 percent, ultimate tensile
elongation, wherein the
notch has a depth of at least 10 mils (0.25 mm), a radius from 0.275 mm to
0.55 mm,
preferably 0.3 mm to 0.525 mm, and especially from 0.38 mm to 0.51 mm, and
wherein said
ethylene polymer composition has a density of at least 0.945 g/cm~.
In still another aspect, the invention is a cable comprising at least one
layer of a
thermoplastic polymer, especially a polyethylene polymer composition of the
invention,
wherein the thermoplastic polymer has a strain hardening modulus, Gp, greater
than 1.6 MPa,
preferably greater than 1.7 MPa, especially greater than 1.8 MPa, and can be
as high as 2
MPa, wherein Gp is calculated according to the following equations:
(I) Qr - BEng
(II) ~jn - 6dr~ Cdr
1
(III) Gn = PRT
Me
The strain hardening modulus (Gp) is calculated from the conventional tensile
stress-strain
curve using the theory of rubber elasticity. More specifically, the true
stress, 6,, is calculated
from the engineering stress, 6s"e, and draw ratio, ~" as shown in Equation
(I). For cable jacket
resins. Equation (II) was used to calculate the strain hardening modulus,
where 7~," and 6dr
represent the natural draw ratio and engineering draw stress, respectively.
The natural draw
ratio was determined by measuring the elongation of a grid pattern which was
printed on the
tensile dogbones. As shown in Equation (III), the strain hardening modulus is
inversely
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related to the molecular weight between entanglements, M~, that is, the
molecular weight of
the tie-molecules between crystalline domains and p is the density of the
resin.
Figure 4, for example, shows strain hardening modulus as a function of density
of the
ethylene polymer composition. For examples E, En, A, and An, the strain
hardening modulus
relationship can be approximated by the following equation:
(IV) Gp = -98.57 + (208.89)(p) - ( 108.73)(p)'
where p = density of the ethylene polymer composition (including carbon black
in the density
calculation if appropriate) and Gp is the strain hardening modulus. Note that
polymers B and
Bn fall above the line, which is believed to be attributed to higher levels of
long chain
branching ( that is, the I,o/Iz melt flow ratio is higher for the homogeneous
component for
resin Bn than for the homogeneous component of resins En and/or An.
For comparative polymers 1, D, I and G, the strain hardening modulus follows a
different relationship described by equation (V):
(V) Gp = -438.03 + (92I .96)(p) - (483.46)(p)2.
IS Note that the line for the comparative polymers is much lower than that for
the polymer
compositions of the invention.
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According to one aspect of the present invention,
there is provided a cable of category 1, 2 or 3 as defined
by ASTM D 1248, comprising a jacket layer comprising a
polyethylene composition, wherein the polyethylene
composition comprises: (A) from 25 to 45 percent by weight
of the total composition of at least one homogeneously
branched ethylene/a-olefin interpolymer having: (i) a
density from 0.89 g/cm3 to 0.94 g/cm3, (ii) a molecular
weight distribution (Mw/Mn) from 1.8 to 3.5, (iii) a melt
index (I2) from 0.001 g/10 min. to less than 0.5 g/10 min.,
and (iv) a CBDI greater than 50 percent, (B) from 5 to 75
percent by weight of the total composition of at least one
heterogeneously branched ethylene interpolymer or linear
ethylene homopolymer having a density from 0.9 g/cm3 to 0.965
g/cm3, wherein the final melt index, I2, of the polyethylene
composition in the cable jacket is in the range of 1 to
50 g/10 minutes, the polyethylene composition has a density
of 0.945 g/cm3 or more, and the cable jacket has a strain
hardening modulus, Gp, greater than 1.6 MPA wherein Gp is
calculated according to the following equation:
- ~dr~'n Cdr
I
n n'n
where ~n and Qdr represent the natural draw ratio and
engineering draw stress, respectively, and a reduced notch
sensitivity as indicated for a notched cable jacket
comprising a polyethylene composition and having a thickness
from 2.03 to 2.29 mm (80-90 mil) taken in a circumferential
direction by less than 55s loss of elongation compared to an
unnotched cable jacket sample from said cable, as measured
in accordance with ASTM D 638 at 23.9° using a die V (5)
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with a 2.5 cm jaw separation and pulling at a rate of 5.08
cm per minute.
Preferably, the polyethylene composition used in
the cable of the present invention is prepared by a process
comprising the steps of:
(i) reacting by contacting ethylene and at least
one a-olefin under solution polymerization conditions in at
least one reactor to produce a solution of the at least one
first polymer which is a homogeneously branched
ethylene/a-olefin interpolymer, preferably a substantially
linear ethylene/a-olefin interpolymer,
(ii) reacting by contacting ethylene and at least
one a-olefin under solution polymerization conditions in at
least one other reactor to produce a solution of the at
least one second polymer which is a heterogeneously branched
ethylene polymer,
(iii) combining the solution prepared in steps (i)
and (ii), and
(iv) removing the solvent from the polymer
solution of step (iii) and recovering the polyethylene
composition.
The cables of the present invention have good
flexibility, mechanical properties and good processability,
furthermore, are environmentally less harmful when disposed
relative to cables comprising conventional PVC. An
important aspect of the present invention is the fact that
cables, where the outer cable jacket comprises the
compositions disclosed in this invention, have improved
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flexibility relative to comparative cables where the jacket
is produced from conventional heterogeneous linear low
density polyethylenes (LLDPE). Cable
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flexibility is an important performance criteria, since more flexible cables
are easier to install
and bend around corners. Cable flexibility was measured by clamping a piece of
cable
horizontally in an Instron tensile machine and measuring the force required to
deflect the
cable in the upward direction. Lower deflection forces demonstrate improved
flexibility, as
shown in Figure 1. Cable jackets produced from the copolymers of this
invention are
preferably 10 percent more flexible, and more preferably 20 percent more
flexible than
comparative cables made using conventional heterogeneous linear low density
ethylene
polymers having about the same density ( that is, the density of each polymer
is within IO
percent of the other).
These and other embodiments are more fully described below, and in conjunction
with the Figures, wherein:
FIG. 1 is a plot of deflection force (kg) versus cable deflection (mm) for
example A
and comparative example G;
FIG. 2 is a plot of ultimate tensile elongation (percent) versus notch number
in the test
sample for example B and for comparative example G;
FIG. 3 is a plot of change in the relative tensile elongation versus
temperature for
example A and comparative example G;
FIG. 4 is a plot of strain hardening modules (MPa) versus polymer and
composition
density for example polymers A, An, B, Bn, E, and En, and for comparative
examples D, G, I
and J;
FIG. 5 is a surface roughness scan of a cable jacket made from example B;
FIG. 6 is a surface roughness scan of a cable jacket made from comparative
example
G; and
FIG. 7 is a schematic representation, in perspective and party broken away,
showing
one cable of the present invention.
The "substantially linear" ethylene/a-olefin interpolymers useful in the
present
invention are not "linear" polymers in the traditional sense of the term, as
used to describe
linear low density polyethylene (Ziegler polymerized linear low density
polyethylene
(LLDPE)), nor are they highly branched polymers, as used to describe low
density
polyethylene (LDPE). The "substantially linear" ethylene/a-olefin
interpolymers have long
chain branching, wherein the backbone is substituted with 0.01 long chain
branches/1000
carbons to 3 long chain branches/1000 carbons, more preferably from 0.01 long
chain
branches/1000 carbons to 1 long chain branches/1000 carbons, and especially
from 0.05 long
chain branches/1000 carbons to 1 long chain branches/1000 carbons. Note that
the long chain
branches are not the same as the short chain branches resulting from
incorporation of the
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comonomer. Thus, for an ethylene/1-octene copolymer, the short chain branches
are six
carbons in length, while the long chain branches for such a substantially
linear ethylene/1-
octene copolymer are at least seven carbons in length, but usually much longer
than seven
carbons.
The substantially linear ethylene/a-olefin interpolymers of the present
invention are
herein defined as in U.S. patent 5,272,236 (Lai et al.) and 5,278,272 (Lai et
al.). Long chain
branching is defined herein as a chain length of at least 7 carbons, above
which the length
cannot be distinguished using I 3C nuclear magnetic resonance (NMR)
spectroscopy. The
long chain branch can be as long as the length of the polymer backbone.
For ethylene homopolymers and ethylene/C~-C, alpha-olefin copolymers, long
chain
branching can be determined by '3C NMR spectroscopy and can be quantified
using the
method of Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p. 285-297). Union
Carbide, in
EP 0659773 A1, used a 1990 paper (Mirabella et al.) to quantify long chain
branching. Exxon
used "viscous energy of activation" to quantify long chain branching in PCT
Publication WO
94/07930.
Both the homogeneous linear and the substantially linear ethylene/a-olefin
interpolymers useful for forming the compositions of the present invention are
those in which
the comonomer is randomly distributed within a given interpolymer molecule and
wherein
substantially all of the interpolymer molecules have the same ethylene /
comonomer ratio
within that interpolymer, as described in USP 3,b45,992 (Elston). The
homogeneity of the
interpolymers is typically described by the SCBDI (Short Chain Branching
Distribution
Index) or CDBI (Composition Distribution Branch/Breadth Index) and is defined
as the
weight percent of the polymer molecules having a comonomer content within 50
percent of
the median total molar comonomer content. The CDBI of a polymer is readily
calculated
from data obtained from techniques known in the art, such as, for example,
temperature rising
elution fractionation (abbreviated herein as "TREF") as described, for
example, in Wild et al,
Journal of Polymer Science, Poly. Phys. Ed., Vol. 20, p 41 (1982), in U.S.
patent 4,798,081
(Hazlitt et al.}, or in U.S. patent 5,089,321 (Chum et al.). The SCBDI or CDBI
for the
homogeneous ethylene/a-olefin interpolymer used in the present invention is
greater than 50
percent, more preferably greater than about 70 percent, and especially greater
than about 90
percent. The homogeneous ethyiene/a-olefin interpolymers used in the present
invention
essentially lack a linear polymer fraction which is measurable as "high
density" fraction by
the TREF technique ( that is homogeneously branched ethylene/a-olefin
interpolymers do not
contain a polymer fraction with a degree of branching less than or equal to I
methyl/1000
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carbons). For homogeneous linear or substantially linear ethylene/a-olefin
interpolymers,
especially ethylene/1-octene copolymers, having a density from about 0.88
g/cmj and higher,
these interpolymers also do not contain any highly short chain branched
fraction ( that is the
homogeneously branched ethylene/a-olefin polymers do not contain a polymer
fraction with a
degree of branching equal to or more than about 30 methyls/1000 carbons).
The homogeneous linear or substantially linear ethylene/a-olefin interpolymer
for use
in the present invention typically are interpolymers of ethylene and at least
one C3-C20 a-
olefin and/or C4-Clg diolefin, preferably interpolymers of ethylene and C3-C20
a-olefins,
more preferably a copolymer of ethylene and a C4-Cg a-olefin, most preferably
a copolymer
of ethylene and 1-octene. The term interpolymer is used herein to indicate a
copolymer, or a
terpolymer, or the like. That is, at least one other comonomer is polymerized
with ethylene to
make the interpoiymer. Ethylene polymerized with two or more comonomers can
also be
used to make the homogeneously branched substantially linear interpolymers
useful in this
invention. Preferred comonomers include the C3-C20 a-olefins, especially
propene,
isobutylene, 1-butene, 1-hexene, 4-methyl-1-pentene, I-heptene, 1-octene, 1-
nonene, and I-
decene, more preferably I-butene, I-hexene, 4-methyl-1-pentene and I-octene.
The homogeneously branched linear and substantially linear ethylenela-olefin
interpolymers used in the present invention have a single melting peak, as
determined using
differential scanning calorimetry (DSC) using a second heat and a scanning
range from -30°C
to 140°C at 10°C/minute, as opposed to traditional
heterogeneously branched Ziegler
polymerized ethylenela-olefin copolymers having two or more melting peaks, as
determined
using DSC.
The density of the homogeneously branched linear or substantially linear
ethylene/a-
olefin interpolymers (as measured in accordance with ASTM D-792) for use in
the present
invention is generally from 0.865 g/cm3 to 0.95 g/cm3, preferably from 0.89
g/cm3 to 0.94
g/cm3, and more preferably from 0.9 g/cm3 to 0.935 g/cm3.
The amount of the homogeneously branched linear or substantially linear
ethylene/a-
olefin interpolymer incorporated into the composition used in the cable of the
present
invention varies depending upon the heterogeneously branched ethylene polymer
to which it
is combined. However, preferably from 5 to 95 percent, more preferably from 20
to 80
percent, most preferably from 25 to 45 percent (by weight of the total
composition ) of the
homogeneous linear or substantially linear ethylene/a-olefin polymer may be
incorporated in
the polyethylene composition for use in the cable of the present invention.
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The molecular weight of the homogeneously branched linear or substantially
linear
ethylene/a-olefin polymer for use in the present invention is conveniently
indicated using
melt index measurement according to ASTM D-1238, condition 190°C/2.16
kg (formerly
known as "condition (E)", and also known as I2). Melt index is inversely
proportional to the
molecular weight of the polymer; although, the relationship is not linear. The
homogeneously branched linear or substantially linear ethylene/a-olefin
interpolymers useful
herein will generally have a melt index of at least 0.001 grams/10 minutes
(g/10 min.), and
preferably at least 0.03 g/10 min. The homogeneously branched linear or
substantially linear
ethylene/a-olefin interpolymer will have a melt index of no more than 10g/10
min., preferably
less than about 1 g /10 min., and especially less than 0.5 g/10 min.
Another measurement useful in characterizing the molecular weight of the
homogeneously branched substantially linear ethylene/a-olefin intecpolymers is
conveniently
indicated in melt index measurement according to ASTM D-1238, condition
190°C/10 kg
(formerly know as "Condition (N)" and also known as I10). The ratio of the I10
and I2 melt
index is the melt flow ratio and is designated as Ilp/I2. Generally, the
Ilp/I2 ratio for the
homogeneously branched linear ethyiene/a-olefin interpolymers is about 5.6.
For the
homogeneously branched substantially linear ethylene/a-olefin interpolymers
used in the
polyethylene composition of the present invention, the Ilp/I2 ratio indicates
the degree of
long chain branching, that is, the higher the Ilp/I2 ratio, the more long
chain branching in the
interpolymer. Generally, the Ilp/I2 ratio of the homogeneously branched
substantially linear
ethylene/a-olefin interpolymers is at least 6, preferably at least 7,
especially at least 8 or
above, and can be as high as 20. For the homogeneously branched substantially
linear
ethylene/a-olefin interpolymers, the higher the Ilp/I2 ratio, the better the
processability.
The molecular weight distribution of the substantially linear ethylene
interpoiymer in
the present invention may be analyzed by gel permeation chromatography (GPC)
on a Waters
150°C high temperature chromatographic unit equipped with three mixed
porosity columns
(Polymer Laboratories 103, 104, 105 and 106), operating at a system
temperature of 140°C.
The solvent is 1,2,4-trichlorobenzene, from which 0.3 percent by weight
solutions of the
samples are prepared for injection. The flow rate is 1.0 mL/minutes and the
injection size is
100 microliters. A differential refractometer is being used as the detector.
The molecular weight determination is deducted by using narrow molecular
weight
distribution polystyrene standards (from Polymer Laboratories) in conjunction
with their
elution columns. The equivalent polyethylene molecular weights are determined
by using
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appropriate Mark-Houwink coefficient for polyethylene and polystyrene ( as
described by
Williams and Ward in lournal of Polymer ScienceLPolymer Letters, Vol. 6, (621)
1968)
to derive the following equation:
Mpolyethylene=a*(Mpolystyrene)b~
In this equation, a=0.4316 and b=1Ø Weight average molecular weight, Mw, is
calculated in~the usual manner according to the following formula: Mw=E wi*Mi,
where wi
and Mi are the weight fraction and molecular weight, respectively, of the ith
fraction eluting
from the GPC column.
For the homogeneously branched linear and substantially linear ethylenela-
olefin
interpolymers, the molecular weight distribution (M,w/M") is less than 3.5,
preferably from 1.8
to 2.8, more preferably from 1.89 to 2.2 and especially about 2.
The ethylene polymer to be combined with the homogeneously branched linear or
substantially linear ethylene/a-olefin interpolymer is a heterogeneously
branched ethylene
polymer, preferably a heterogeneously branched (for example, Ziegler
polymerized)
I S interpolymer of ethylene with at least one C3-C20 a-olefin (for example,
linear low density
polyethylene (LLDPE)).
Heterogeneously branched ethylene/a-olefin interpolymers differ from the
homogeneously branched ethylene/a-olefin intecpolymers primarily in their
branching
distrilaution. For example, heterogeneously branched LLDPE polymers have a
distribution of
branching, including a highly short chain branched portion (similar to a very
low density
polyethylene), a medium short chain branched portion (similar to linear low
density
polyethylene) and often a linear ( that is, non-short chaitr branched)
portion. The amount of
each of these fractions varies depending upon the whole polymer properties
desired_ For
example, linear homopolymer polyethylene has no short chain branching. A very
low density
heterogeneous polyethylene having a density from 0.89 g/cm3 to 0.915 g/cm3
(such as
AttaneT''' copolymers, sold by The Dow Chemical Company and FlexomerTM sold by
Union
Carbide Corporation) has a higher percentage of the highly short chain
branched fraction, thus
lowering the density of the whole polymer.
Preferably, the heterogeneously branched ethylene polymer is a heterogeneously
branched ethylene/a-olefin interpolymer, most preferably Ziegler polymerized
ethylene/a-
olefin copolymer. The a-olefin for such ethylene interpolymer may include a-
olefin having 3
to 30 carbon atoms, more preferably an a-olefin having 4 to 8 carbon atoms,
most preferably
1-octene.
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More preferably, the heterogeneously branched ethylene polymer is a copolymer
of
ethylene with a C3-C20 a-olefin, wherein the copolymer has:
(l) a density from 0.9 g/cm3 to 0.965 g/cm3,
(ii) a melt index (h) from about 0.1 g/10 min. to about 500 g/IOmin.
The heterogeneously branched ethylene/a-olefin interpolymers and/or
copolymers,
especially those having a density of less than 0.95 g/cm', (excluding, of
course, ethylene
homopolymers having a single melting peak) also have at least two melting
peaks as
determined using Differential Scanning Calorimetry (DSC), using the same
scanning rate and
temperature range described earlier herein.
The compositions disclosed herein can be formed by any convenient method,
including dry blending the individual components and subsequently melt mixing
or by pre-
melt mixing in a separate extruder (for example, a Banbury mixer, a Haake
mixer, A
Brabender internal mixer, or a twin screw extruder).
Another technique for making the compositions in-situ is disclosed in PCT
applications WO 92/11269 and WO 94/01052. PCT applications WO 92/11269 and WO
94/01052 describe, inter alia, interpolymerizations of ethylene and C3-C20 a-
olefins using a
homogeneous catalyst in at least one reactor and a heterogeneous catalyst in
at least one other
reactor. The reactors can be operated in series or in parallel.
A preferred density of the polyethylene composition used for the cable of the
present
invention may depend upon desired stiffness of the finished cable. However,
typical densities
will preferably be from 0.91 to 0.96 g/cm3, more preferably from 0.92 to 0.96
g/cm3.
A preferred melt index ( that is I2) of the polyethylene composition disclosed
herein
may depend upon process conditions and desired physical properties. However,
generally,
the melt index of the polyethylene composition disclosed herein may be from
0.1 to 50 g/10
minutes for all categories of cable, preferably not greater than 0.4 g/10
minute for category
five (5), preferably from 0.4 to 1 g/10 minutes for category four (4),
preferably greater than 1
to 10 g/10 minutes for category three (3), and preferably greater than 10 to
25 g/10 minutes
for category two (2), and greater than 25 g/10 minutes for category one ( 1 ).
These general
categories are found in ASTM D 1248, and are also included in the Standard
Specifications
for Plastic, Molding and Extrusion. However, if the I2 of the polyethylene
composition
disclosed herein is lower than about 0.1 g/10 minutes, the polyethylene
composition is often
difficult to extrude and may cause melt fracture on the surface of the
finished cable.
Likewise, if the I2 of the polyethylene composition disclosed herein is higher
than the above
ranges, the molten polymer tends to have a low melt viscosity and melt
tension, thus may be
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difficult to fabricate into the desired cable.
The Ilp/I2 of the polyethylene composition disclosed herein may be preferably
from 7
to 16, more preferably from 9 to 14, most preferably from 10 to 13. If the
Ilp/I2 of the
polyethylene polymer disclosed herein is lower than the above range, surface
quality of the
finished cable tends to be deteriorated, and processability of the cable may
become
unacceptably low.
The resin composition of the present invention may comprise any known
additives
and/or fillers to the extent that they do not interfere with the enhanced
formulation properties
discovered by Applicants. Any additives commonly employed in polyolefin
compositions, for
example, cross-linking agents, antioxidants (for example, hindered phenolics
(for example,
IrganoxTT' 1010 made by Ciba Geigy Corp.), phosphites (for example, IrgafosTM
168 also by
Ciba Geigy Corp.), flame retardants, heat stabilizers, ultra-violet
absorbents, anti-static agents,
slip agents, process aids, foaming agents, plasticizers, dyes, miscellaneous
fillers such as clay
and pigments can be included in the formulation. A preferable additive of the
present
invention may include, for example, carbon black, and an antioxidant such as
IrganoxTM 1010
and IrgafosTM 168.
The composition of the present invention may be further fabricated into
desired cable
of the present invention by using any known fabrication method. The
composition of the
present invention may be used not only for cable jacketing, but also cable
insulation or any
layer of a cable. For example, the composition described herein may be heated,
melted,
kneaded and extruded by a mono- or bi-axial extruder through an extrusion die
such as a
cross-head die so as to be applied onto a core substrate, and then it may be
subjected to a
cooling step, or the next coating step if desired. Multiple layers of polymers
may be applied
onto the core substrate if desired. The core substrate may comprise any known
materials in
the art; for example, control cables comprising any conductive material such
as copper, and
aluminum, insulating material such as low density polyethylene, polyvinyl-
chloride,
polyethylene compositions including compositions described herein, conductive
or
semiconductive shields such as aluminum, copper, and steel, usually in form of
tape, foil,
screen, net or any combinations thereof, and any reinforcement material.
Various cables and cable designs may include, as at least one layer, the
polyethylene
compositions disclosed herein. For example, USP 3,638.306 (Padowicz) shows a
communications cable which has a water proof core of conductors and a sheath
including an
unsoldered steel layer. Figure 7 herein shows such a structure: the steel
layer ( 1 ) is stretch-
formed to attain a tightly registered longitudinal seam which eliminates the
necessity of
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soldering or other means of mechanically joining the seam.
A cable 101 includes a plurality of conductors or conductor pairs 4 within a
cable core 2. The conductors 4 are surrounded by and the interstitial spaces
therebetween are
filled with a waterproof filler material 6.
About core 2 is a core wrap 8 which may be a suitable plastic or other
material. A binder can be placed around core wrap 8 to hold it in position
about core 2, a
layer of conductive metal is placed about the core. A thin aluminum layer 10
having a
longitudinal seam 14 therein advantageously can be used for lightning
protection and
shielding. Longitudinal seam 14 is not required to be soldered or otherwise
mechanically
joined, a steel layer 20 having unsoldered overlapping edges 16 and 18 forming
a longitudinal
seam 17 is longitudinally wrapped about aluminum layer 10 to provide
protection from
mechanical forces such as abrasion. The use of an unsoldered seam 17 for steel
layer 20 is
possible, since the cable core 2 is waterproof. Steel layer 20 and aluminum
layer 10
advantageously can be transversely corrugated and meshed with each other to
provide a more
flexible sheath. Steel layer 20 is stretch-formed and cold-worked as it is
wrapped about
aluminum layer 10 and edges 16 and 18 are closely meshed to provide a tightly
registered
overlapping seam 17. The stretch-forming and cold-working insure that edges 16
and 18
retain their respective positions without the necessity for external holding
forces after the
forming forces have been removed. Thus, the tightly registered seam 17 is
maintained. Edges
16 and 18 will retain their positions and maintain the tightly registered seam
17 even when
cable 101 is would on a reel. The outer or overlying edge 16 of steel layer 20
advantageously
can be turned slightly inward toward core 2 to insure that no sharp edges are
presented by
steel layer 20.
Corrosion protection for steel layer 20 and added protection against water
penetration are provided by hot-melt flooding each side of steel layer 20 with
respective
coatings 12 and 22 of a corrosionproof, waterproof material (such as a
PrimacorT"' Adhesive
Polymer made by The Dow Chemical Company). This readily can be accomplished by
drawing cable 101 through a bath of appropriate material as layer 20 is being
applied.
Coatings 12 and 22 advantageously might be the same material as is utilized
for filler material
6. Protection against water penetration is obtained since coatings 12 and 22,
respectively, fill
all spaces between steel layer 20 and the adjacent layers 10 and jacket 24 of
the cable sheath.
Jacket 24 is desirably made using the ethylene polymer compositions disclosed
herein. Seam
17 is also sealed against water ingress by coatings 12 and 22 being drawn into
seam 17 by
capillary action of the tightly registered seam. Added mechanical strength is
also obtained
from the adhesive forces of coatings 12 and 22 which tend to adhere steel
layer 20 to adjacent
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layers 10 and jacket 24.
For added corrosion protection of layer 20 and for additional mechanical and
moisture protection, an exterior ethylene polymer composition jacket 24
advantageously is
extruded around the exterior surface of layer 20. Thus, the cable sheath
comprising an
aluminum layer 10, an unsoldered steel layer 20 and a thermoplastic layer or
jacket 24 joined
by corrosion coatings 12 and 22 provides mechanical, rodent, and waterproof
protection at a
cost substantially less than the sheaths of prior art cables. In Figure 7,
various layers may
comprise the ethylene polymer compositions disclosed herein, including jacket
24, layers 22,
12 and 8; further any or all of these layers may comprise the ethylene polymer
compositions
disclosed herein.
Other United States Patents disclosing useful cable structures enhanced by use
of a
layer comprising the polyethylene compositions layer of the present invention
include US
Patent 4,439,632 (Aloisio, Jr. et al.), US Patent 4,563,540 (Bohannon, Jr. et
al.), US Patent
3,717,716 (Biskeborn et al.), and US Patent 3,681,515 (Mildner).
The present invention will be more clearly understood with reference to the
following
examples.
Cable Example 1
A cable was produced by using polymer A which was an in-situ blend made
according to PCT Publications WO 92/11269 and WO 94/01052, wherein 36 weight
percent
of the total composition of a homogeneously branched substantially linear
ethylene/l-octene
copolymer having a density of 0.915 g/cm3 was made in a first reactor, and 64
weight percent
of the total composition of a heterogeneously branched linear ethylene/1-
octene copolymer
having a density of 0.955 g/cm3 was made in a second reactor. Polymer A had a
melt index
(I2) of 0.78 g/10 minutes, Ilp/I2 of 11.9, a density of 0.958 g/cm3 (note that
polymer A
contained 2.6 weight percent carbon black and 400 ppm of a fluoroelastomer)
and 0.039 long
chain branches/10,000 carbons (0.39 long chain branches/1000 carbons) as
determined using
a kinetic model, and a MW/M~ of 7.5. The polymer was extruded onto a cable by
using a cable
manufacturing line equipped with an extruder having a diameter of 6.35 cm,
length to
diameter ratio of 20 to 1 with a 5 turn metering screw having a compression
ratio of 3.66 to l,
with a crosshead die having a die diameter of 2.04 cm, die-tip inside diameter
of 1.73 cm, a
die gap of 0.318 cm, and 0 cm land length. The cable was produced by forming
corrugated
steel over a polyvinylchloride jacketed control cable and extruding the
polymeric jacket over
the steel sheath. The extruder speed was approximately 55 rpm and the cable
line speed was
held constant at 760 cm/minutes. The melt temperature was 232°C to
240°C using the
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following temperature profile: zone 1, 166°C; zone 2, 171°C;
zone 3, 188°C; zone 4, 205°C;
cross head, 219°C; die, 227°C. Pressure, amps, melt temperature
and cable melt strength were
evaluated subjectively (for example, the cable jackets did or did not have the
required melt
strength during extrusion as reported in Table 1). The surfaces of the cable
jackets were
evaluated visually and assigned a numerical surface rating, where the highest
quality surface
was given a rating of 100. The results are also reported in Table 1. The
finished cable was
subjected to physical properties test described below.
Cable Example 2
A cable was produced by using polymer B which was an in-situ blend made
according to PCT Publications WO 92/11269 and WO 94/01052, wherein 41 weight
percent
of the total composition of a homogeneously branched substantially linear
ethylene//-octene
copolymer having a density of 0.915 glcm3 was made in a first reactor, and 59
weight percent
of the total composition of a heterogeneously branched linear polymer
ethylene/1-octene
copolymer having a density of 0.955 g/cm3 was made in a second reactor. The
polymer B had
a melt index of 0.89 g/lOminutes, Ilp/I2 of 11.3, density of 0.957 g/cm3 (note
that polymer B
contained 2.6 weight percent carbon black and 400 ppm of a fluoroelastomer),
0.18 Long
chain branches/10,000 carbon atoms (1.8 long chain branches/1000 carbon atoms)
as
calculated using a kinetic model, and molecular weight distribution ( that is
MW/M") of 5.01.
The polymer was extruded onto cable as described in Example 1. The finished
cable was
subjected to the physical property tests described below. Melt tension and
cable surface
rating were measured by the methods described in Example 1, and are reported
in Table 1.
Cable Example 3
An cable is produced by using polymer C which was an in-situ blend ethylene/1-
octeneLOpoiymer produced by the same process described in Example 1, having a
melt index
of 0.87 g/lOminutes, Ilp/I2 of 10.47 and density of 0.952 g/cm3(note that
polymer C
contained 2.6 weight percent carbon black and 400 ppm of a fluoroelastomer)
and a MW/M" of
5.22. The polymer was extruded onto cable as described in Example 1. Surface
rating is
reported in Table 1. The finished cable was subjected to physical properties
tests described
below.
Comparative Cable Examgle 4
A cable was produced by using polymer D, which is a currently available
polyethylene (for example UCC 8864 by Union Carbide) having melt index of 0.76
g/ l Ominutes, I l p/I2 of 12.3, density of 0.942 g/cm', and MW/M" of 3.7, and
no long chain
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branching. Polymer D also contained 2.6 weight percent carbon black and about
400 ppm of a
fluoroelastomer. The polymer was extruded onto cable as described in Example
1. Melt
tension data and cable surface rating are reported in Table 1.
Cable Example 5
A cable was produced by using polymer E which was an in-situ blend ethylene/1-
octene copolymer produced by the same process described in Example 1, having a
melt index
of 0.58 g/lOminutes, Ilp/I2 of 1 I.03, and density of 0.944 g/cm3, and MW/M"
of 5.1. Polymer
E also contained 2.6 weight percent carbon black and 400 ppm of a
fluoroelastomer. The
polymer was extruded onto cable as described in Example 1. Melt tension and
surface rating
are reported in Table 1. The finished cable was subjected to physical
properties test described
below.
Cable Example 6.
A cable was produced by using polymer F which was an in-situ blend ethylene/ I-
octene copolymer produced by the same process described in Example 1, having a
melt index
I5 of 0.88 g/lOminutes, I10/I2 of 10.13, density of 0.94 g/cm3, and a MW/M" of
about 4.6.
Polymer F contained 2.6 weight percent carbon black and 400 ppm of a
fluoroelastomer. The
polymer was extruded onto cable as described in Example 1 and subjected to
physical
properties tests described below. Melt tension and surface rating are reported
in Table 1.
ComQarative Cable Example 7
A cable was produced by using polymer G, which is a currently available
polyethylene (for example UCC 3479 by Union Carbide) having melt index of 0.12
g/lOminutes, Ilp/I2 of 29.4, density of 0.958 g/cm3, MW/M" of 5.6, and no long
chain
branching. Polymer G contained 2.6 weight percent carbon black and about 400
ppm of a
fluoroelastomer. The polymer was extruded onto cable as described in Example I
and
subjected to physical properties tests described below. Melt tension and
surface rating are
reported in Table 1.
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Table 1
Visual Melt Strength
Used h (g/lOmin.) Density Surface (cN)
esin* to ,o/h(g/cm') Rating
Make
Cable
Polymer Example 0.78 11.90.958 90 -
A 1
Polymer Example 0.89 11.30.957 100 3.69
B 2
Polymer Example 0.87 10.470.952 75 -
C 3
Polymer Comp. 0.76 12.260.942 95 6.57
D Ex 4
Polymer Example 0.58 11.030.948 65 4.5
E 5
Polymer Example 0.88 10.130.940 70 4.2
F 6
Polymer Comp. 0.12 29.40.958 80 7.1
G Ex 7
All of these resins contamea 1,.b wt percent carbon black and 400 ppm
tluoroelastomer
Surface Profilometrv
The surface roughness of Example 2 and comparative Example 7 was quantified
using
surface profilometry. More specifically, the average surface roughness of
theses cables was
measured using a Surftest 402 Surface Roughness Tester, produced by Mitutoyo.
This
analyzer computes various surface roughness parameters given a scan of the
cable surface
with a diamond tipped stylus. Surface roughness is quantified by the
statistical parameter, R~,
known as the average roughness. This quantity is the arithmetic mean of all
departures of the
roughness profile from the average mean line as in Equation (V),
Ra - ~ ~n--I IJ lxll
where N is the number of digitized data points within the length of cable used
for the
measurement and f~'x) is the vertical departure from the mean surface line at
each data point.
The average roughness of Example 2 was 28.0 ~ 1.4 p in. (0.71 ~ 0.036
microns),
while the average roughness of comparative example 7 was 60.5 ~ 2.1 p. in
(1.54 ~ 0.053
microns). The surface roughness of the copolymers described in this invention
is less than
half the roughness of the comparative sample. Typical profilometer traces from
the surface of
cable Example 2 and Example 7 are shown in Figures 5 and 6.
This surface roughness data is surprising, given the I,o/IZ values, for
example, 11.3 for
Example 2 and 29.4 for comparative Example 7. More specifically, it is well
known that
processability improves and surface roughness (melt fracture) decreases as
I,o/h increases. In
other words, the very smooth cables produced by the copolymers of this
invention were
surprising, given their relatively low Ilo/h values.
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Circumferential and Longitudinal Tensile Tests
Circumferential tensile samples were cut from the finished cables
perpendicular to the
cable axis with no metal seam impressions within gauge length. Longitudinal
tensile samples
were cut parallel to the cable axis with no metal seam impressions within
gauge length. The
tensile test was carned out according to ASTM D 638, using Die V (5) (for
example
microtensile), with a 2.54 cm jaw separation and pulling at 1.27 cm/minutes.
The tensile
strength data are reported in Table 2.
Table 2
Circumferential Longitudinal
Tensiles Tensiles
Ultimate Ultimate
Yield Stress ElongationYield Stress Elongation
Resin (k /cm2)(k /cm2)(percent)(k (k cm2)(percent)
cm2)
Polymer 125 144 380 127 178 510
A
Polymer 117 158 450 122 186 525
B
Polymer 134 201 540 137 204 565
C
Polymer 169 111 460 157 214 670
G*
Polymer 89 123 385 89 176 530
E
Polymer 91 162 480 95 190 530
F
*Comparative Example
Notched circumferential tensile tests
Circumferential tensile samples were cut perpendicular to the cable axis from
the
finished cables prepared as described above, and the notch (due to the metal
overlap) was
centered within the gauge length. The test was carried out as described in
ASTM D638 using
Die V (5) (for example microtensile), with a 2.54 cm jaw separation and puling
at 5.08
cm/minute. The results are reported in Table 3.
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Table 3
Notched Notched
Tensile Tensile
at at
23.9C -32.2C
Ultimate Ultimate
Yield Stress ElongationYield Stress Elongation
Resin (k /cm2)(k /cm2)(percent)(k /cm2)(k /cm2)(percent)
Polymer 145 88 280 221 75 24
A
Polymer 125 63 220 *a *a *a
B
Polymer 96 79 250 21 I 80 180
C
Polymer 138 49 40 238 90 24
G*
Polymer 73 70 190 199 90 95
E
Polymer 82 42 61 197 98 116
F
*comparative Example
*a : Sample Cracked
Reduced Notch Sensitivity (Cables)
An important aspect of the present invention is the fact that cables, where
the outer
cable jacket is composed of the compositions disclosed in this invention, have
reduced notch
sensitivity relative to comparative cable jackets. It is well known that the
tensile properties of
polyethylenes are sensitive to notches or surface imperfections. During the
cable jacketing
process, notches are generally produced at the shield overlap. In the case of
poor or
incomplete shield overlap, severe notches are produced in the jacket which can
result in
failures under relatively mild impact or tensile forces. The reduced notch
sensitivity of the
cable jackets of this invention is shown in Table 4. For example, due to the
notch, the cable
jackets of this invention lost 26 to 54 percent of their tensile elongation,
that is, the tensile
I S elongation with no notch present. In contrast, 90 percent of the tensile
elongation was lost for
cable jackets produced from a comparative polyethylene (Example G). Thus,
cable jackets
produced from the copolymers of this invention have reduced notch sensitivity.
Reduced
notch sensitivity means the cables are easier to install, for example, the
cables do not fail
(split) during the bending and/or twisting which occurs during the
installation .process.
Table 4
Percent (%)
Cable Jacket Cable Jacket Loss of
Sample CircumferentialNotched Elongation.
Tensile Elon Circumferentialdue
ation Tensile Elon to Notch
ation
Exam 1e A 380 280 26
Exam 1e B 450 220 51
Exam 1e C 540 250 54
Comparative 400 40 90
Exam 1e G
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Cable Flexibility
Cable flexibility of the final cable jacket bonded to corrugated steel was
determined
by measuring the amount of force required to deflect the cable. A cable having
a length of 33
cm was cut, the cable core was discarded, and each end, approximately 3 cm in
length, was
flattened. The cable was inserted through the upper grip assembly of the
Instron tensile
machine and the flattened ends were clamped to the frame of the Instron
tensile machine. The
cable samples were deflected at a rate of 12.7 cmlminutes, and the force
required to deflect
the cable 5, 10, 15 and 20 mm was recorded and reported in Table 5. Lower
force indicates
greater flexibility. This test is described in detail in "Chemical/Moisture
Barrier Cable for
Underground Systems" by K.E. Bow and Joseph H. Snow, presented at IEEE1PCIC
Conference, held Sept. 1981 in Minneapolis, MN, pp. 1-20, especially pages 8-
10.
Table 5
Force
(Kg)
at Deflection
of
Cable SamplePolymer 5mm lOmm l5mm 20mm
density
( cm3)
Polymer 0.958 7.3 I 1.5 14.6 17.2
A
Polymer 0.957 6.8 11.5 14.6 16.8
B
Polymer 0.952 6.3 10.4 13.5 16.8
C
Polymer 0.958 8.0 12.7 16.4 19.7
G*
Polymer 0.948 5.2 9.4 12.5 14.8
E
Polymer 0.94 6.5 10.0 12.9 15.7
F
*C;omparatwe Example
The cables made from polymer A (density: 0.958 g/cm3), polymer B (density:
0.957
g/cm3) and polymer C (density: 0.952 g/cm3) showed greater flexibility ( that
is lower force
at deflection) than cable made from Polymer G (density: 0.958 g/cm~), where
these samples
are of similar density. Especially, the cable made from polymer A showed
superior flexibility
than the cable made from polymer G, despite the density of the both polymers
being about the
same. The results for these two trials are also shown graphically in FIG. 1.
The results shown
in Table 5 indicate the cables of the present invention have superior
flexibility than the cable
made from the current polymer. For example, the data show that it takes less
force to deflect
a cable of the invention for a given distance (for example, 5, 10, 15 or 20 mm
as shown in the
table), than for a cable made from currently commercially available
polyethylene, even at
similar densities.
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Shrinkback
Samples of jacket were removed from the finished cable prepared above, and the
shrinkback was measured in accordance with ASTM D 4565. As an exception to
ASTM D
4565. 4 specimens having 5.1 cm length parallel to the cable axis and 6.4 mm
width were cut
from the cable. One of the specimens was cut from a portion of the cable lying
directly over
the outer shield overlap and the other three were cut at successive 90 degree
increments to the
overlap. Cables should not shrink back more than 5 percent, preferably not
more than 2
percent, after 4 hours in an oven at 100°C. The results are reported in
Table 6.
Table 6
Resin percent
Shrinkback
Polymer 1.5
A
Polymer 0.5
B
Polymer 0.5
C
Polymer 1.0
G*
Polymer 1.0
E
Polymer 1.0
F
*Comparative Example
Melt Index Drift
The melt index of the cable jacket, after extrusion, was determined according
to
ASTM D 1238. The percent drift in melt index ( that is, the change in melt
index as a result
of extrusion) (percent M drift) was determined using the following equation:
percent MIdrift _ (Mlcable _Mlinitial) / Mlinitial
wherein MImitial represents a melt index of the resin prior to extrusion, and
MIcable represents a melt index after extrusion. The change in melt index as a
result of
extrusion indicates the amount of crosslinking that may take place during
extrusion; normally,
minimal change is desired. The results are reported in Table 7.
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Table 7
Resin MlcableMiinitialpercent
MIdrift
Polymer 0.83 0.78 6.4
A
Polymer 0.94 0.89 5.6
B
Polymer 0.96 0.87 10.3
C
Polymer 0.16 0.12 33.3
G*
Polymer 0.75 0.58 29.3
E
Polymer 0.96 0.88 9.1
F
*Comparative Example
The results shown in Table 7 indicate that the melt index drift of the resin
used in the
present invention was generally lower than that of commercially available
currently used resin
G*.
Jacket Bond Test
The jacket bond test was conducted according to ASTM D 4565 for cables with a
bonded steel sheath. A section of the cable jackets prepared as described
above was removed
by slitting the jacket longitudinally along the shield overlap. The cable was
ringed
circumferentantially with a knife, flexed at the cut point to break the steel
shield at the ring.
The metal sheath was opened, flattened, and the cable core was discarded. The
specimen strip
was cut in the circumferential direction. Three strips having a width of 13 mm
were cut for
each strip. For each specimen, the jacket was separated from the shield or
armor only of a
length sufficient to permit forming a tab of each sheath component. Three
specimens were
tested for each cable sample at a crosshead speed of 50 mm / minute. The
results are reported
in Table 8.
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Table 8
Circumferential Longitudinal Overlap
Bond Bond Bond
StrengthFailureStrength FailureStrength
Resin (N/m) Mode (N/m) Mode (N/m)
Polymer 4,136 Jacket6,110 Metal 6,366
A /
Jacket
Polymer 10,246Jacket7,299 Metal 3,929
B /
Metal
Polymer 6,523 Jacket7,721 Metal 1,160
G /
Jacket
Polymer 5,963 Metal 5,825 Metal 4,224
E
Polymer 6,601 Jacket6, I 10 Metal 6,091
D /
Metal
Bend Tests: Hot, Room Temperature and Cold
A cold bend test was conducted according to ILEA specification S-84-608-1988
which calls out ASTM 4565 for the specifics on the test procedure. Samples
were
equilibrated in a cold room at - 30°C for 4 hours, prior to the
testing. A cable sample having
length of 91.4 cm was bent in a 180° arc around a mandrel having a
diameter of 8 times the
cable diameter, then the sample was straightened, rotated 180°, and
then bent again 180°.
Upon completion of the second bend, the cable was straightened, rotated
90° and bent in a
180° arc. Upon completion of the third bend, the cable was
straightened, rotated 180° and
then bent for the fourth time.
A room temperature bend test was conducted in a manner similar to ASTM 4565.
The cable samples were conditioned at 20°C for 4 hours prior to
testing. A cable sample was
bent in the same manner as the cold bend test as described above, except the
sample was bent
around a mandrel having a diameter of 20 times the cable diameter.
A hot bend test was conducted in a manner similar to ASTM 4565. The cable
samples were conditioned at 60°C for 4 hours prior to testing. A cable
sample was bent in the
same manner as the cold bend test as described above, except the sample was
bent around a
mandrel having a diameter of 10 times that of the cable diameter.
After bending each cable sample, the surface area of the samples were
inspected for
cracks in the bent area using normal or corrected to normal vision. Results of
the cold, room
temperature and hot bend test are reported in Table 9.
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Table 9
Resin -30C bend 20C bend 60C bend
Polymer no visual no visual no visual
A change change change
Polymer no visual no visual no visual
B change change change
Polymer no visual no visual no visual
D* change change change
Polymer no visual no visual no visual
E change change change
Polymer no visual no visual no visual
G* change change change
~LOmparatme l;xample
Cold impact test.
According to ASTM D-4565, the cable samples were conditioned at -20°C
for 4 hours
and tested for impact resistance. A 0.45 kg weight was dropped onto the cable
samples from a
height of 0.9 m, and inner and outer surfaces of the cable samples were
inspected with normal
or corrected to normal vision. The results are reported in Table 10.
Table 10
Resin -20C bend
Polymer no visual
A change
Polymer no visual
B change
Polymer no visual
D* change
Polymer no visual
E change
Polymer no visual
G* change
* Comparative Example
Cable Torsion
Cable samples having length of 152 cm were conditioned more than 24 hours at a
temperature of 18 to 27°C. One end of the straight sample was fixed in
a vise and the other
end was rotated in a direction opposite to the overlap in the steel sheath
without bending
during the test, by an angle ~ defined below in Equation (IV),
- (IV) ~=540-3.5(OD)
wherein OD is an outer diameter of the cable in mm. The results are reported
in Table 11.
Table 11
Resin Torsion Result
Polymer no visual
A change
Polymer no visual
B change
Polymer no visual
D* change
Polymer cable zippered
E
Polymer no visual
G* change
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Example 8. 9, 10, 12 and 14, and Comparative Example 11 and 13 Abrasion
Resistance
The abrasion resistance of Polymers A, B, C and F (which are the same polymers
used in Examples 1, 2, 3 and 6), and Polymer H which is an in-situ blend
produced by the
same process described in Example 1 (polymer H is an ethylene/I-octene
copolymer blend),
are summarized in Table 13. Examples 8, 9 and 10 are summarized in Table 12.
The Taber
abrasion data is detailed in Table 13, which measurements were determined
using abrading
wheel H 18 with a 1000 g load and 1000 cycles on molded plaques.
Table 12
IZ Density
Example Resin (g/lOmin.)I,o/IZ (g/cm~)
No.
Example Polymer 0.92 11.87 0.94
8 An*
Example Polymer 0.89 11.35 0.94
9 Bn*
Example Polymer 0.82 11.45 0.952
14 H**
* "n" denotes natural version of these polymers, that is, no carbon black or
fluoroelastomer
* *Sample contains 2.6 wt percent carbon black and 400 ppm of fluoroeiastomer
Table 13
Taber Abrasion
Example No. Resin* (g
lost / 1000
revolutions)
Example 8 Polymer 0.033
An
Example 9 Polymer 0.031
Bn
Example 10 Polymer 0.033
C
Comparative ExamplePolymer 0.029
I 1 G
Example 12 Polymer 0.039
F
Comparative ExamplePolymer 0.031
12 D
Example 14 Polymer 0.029
H
* "n" denotes natural version of these polymers, that is, no carbon black or
fluoroelastomer
As the data of Table 13 indicate, the polymer compositions disclosed in the
present
invention have similar abrasion resistance relative to the currently available
polymers.
Examples 15, 16, 18 and 19, and Comparative Examples 17 and 20, Notch
Sensitivi~
Plaque samples for standard microtensile test according to ASTM D-1708, Die V
(5)
were prepared using a special mold containing four ridges with the dimensions
described in
Table 14. These ridges produced well defined notches in the final plaques.
Microtensile
dogbone samples were cut from the plaque, with the notch centered within the
gauge length.
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The tensile test was conducted according to ASTM D 638 at 25.4 cm/minutes
cross-head
speed (pull rate) with 2.5 cm jaw separation at three temperatures, for
example -30°C, 0°C
and 25°C, using each notched sample and control samples having no
notch. The results are
reported in Table 15.
Table 14
Notch Notch Radius/Depth
Depth Radius Ratio
(mm) (mm)
Notch 0.251 0.508 2.02
1
Notch 0.249 0.381 1.53
2
Notch 0.254 0.254 1.00
3
Notch 0.257 O.I27 0.50
4
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Table 15
Polymer
/ Elongation Stress
Density at at
Break Break
(percent) (kg/cm2)
Example glcm') Notch 20C 0C -30C 20C 0C -30C
No. (
Example Polymer Control546 452 279 229.8237.3 231.8
15 B /
0.957 Notch 529 180 32 212.6157.1 232.3
1
Notch 230 41 24 138.7173.9 242.6
2
Notch 44 24 17 55.9 176.8 220.8
3
Notch 34 20 13 52.9 150.0 220.4
4
Example Polymer Control627 458 150 236.0216.3 224.2
16 C /
0.952 Notch 439 392 26 195.0191.0 203.8
I
Notch 452 53 21 203.0182.0 203.3
2
Notch 48 26 20 75.5 183.5 211.1
3
Notch 38 29 17 41.3 54.1 163.6
4
ComparativePolymer Control637 304 128 173.3197.1 224.1
G /
Example 0.958 Notch 53 25 16 109.973.9 276.1
17 1
Notch 29 22 52 156.2128.9 211.6
2
Notch 20 18 52 179.464.8 211.4
3
Notch 22 19 12 104.955.5 394.5
4
Example Polymer Control624 505 472 252.1284.9 299.9
18 E /
0.948 Notch 543 497 310 210.7281.1 276.0
1
Notch 508 471 30 190.6265.9 223.5
2
Notch 218 43 23 140.4104.7 223.2
3
Notch 44 35 16 53.5 67.2 241.6
4
Example Polymer Control671 573 452 261.0215.1 270.8
19 F /
- 0.940 Notch 574 524 326 208.4281.2 253.4
1
Notch 542 493 33 196.0262.7 210.7
2
Notch 273 45 22 128.8127.3 216.1
3
Notch 47 35 26 57.1 64.7 79.2
4
ComparativePolymer Control923 739 372 259.7297.6 230.1
D /
Example 0.942 Notch 759 683 405 216.1285.8 225.4
20 I
Notch 736 653 454 209.5277.3 242.4
2
Notch 689 438 28 202.8205.9 199.0
3
Notch 71 47 19 83.2 84.1 207.1
4
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WO 97/38424 PCT/US97/05297
As shown in Table I5, the polymers used in the cable of the present invention
(for
example polymer B, C. E and F) were less notch sensitive than the polymers
currently
available in the industry (for example Polymer D and G), comparing at about
same density,
for example, Polymers B and C have the higher elongation at break than Polymer
G, and
polymers E and F have the higher elongation at break than Polymer D, at almost
all
temperatures.
Reduced Notch Sensitivity (Compression Molded Plagues)
Improved notch sensitivity of the copolymers of this invention was also
demonstrated
by the tensile properties of compression molded plaques, as described in
"Notched Tensile
Low-Temperature Brittleness Test for Cable Jacketing Polyethylene" by R.
Bernie McAda, as
appeared in the May 1983 issue of Wire Journal International Magazine. Well
defined notches
were produced in compression molded plaques using a special "notched" mold. In
general, as
shown in Figure 2, tensile elongation decreased as the severity of the notch
increased (for
example, Notch 2 was more severe than Notch 1, etc.). Figure 2 also shows that
the copolymer
described in this invention (Example B) is much less notch sensitive than
comparative
Example G. In fact, Notch 1 had no effect on the ultimate tensile elongation
of Example B
(within experimental error), while comparative Example G failed
catastrophically at all four
notches.
Imeroved Low Temperature Tensiles (Compression Molded Plaques)
The copolymers useful in this invention also have improved low temperature
tensile
properties. For example, as shown in Figure 3, the reduction in tensile
elongation for Example
A was 18 percent at 0°C and 56 percent at -30°C. In contrast,
the reduction in tensile
elongation for comparative Example G was 52 percent at 0°C and 80
percent at -30°C. Thus,
relative to comparative samples, the copolymers of this invention have
improved tensile
properties at low temperature. As a result, the cables of this invention are
easier to install at
low temperatures, for example, less susceptible to failures (splitting) at low
temperatures.
