Note: Descriptions are shown in the official language in which they were submitted.
2~
This invention relates to new and useful
improvements for electrical cables adapted for use in
supplying electrical power and communications and,
more particularly, to an improved corrosion resistant
cable shielding tape forming a part of such cables.
More speci~ically, the present invention relates to
cable shielding tapes comprising a relatively thin
metal strip with one or more layers of polymeric resinous
material adhered to at least one side thereof~
In the art of designing and construating
electrical cables, especially telecommunication cables
such as telephone cables, it is known to assemble in-
sulated conductors in a core and surround it by shield
and jacket components. A well known telephone cable
design of such construction is referred to in the art
as an "Alpeth" cable. This type of cable is more fully
described in the F. W. Horn et al paper l'Bell System
Cable Sheaths Problems and Designs" in A. I. E. E.
Proceedings 1951, Volume 70~ The shielding tape of the
"Alpeth" cable is formed of a layer of bare aluminum
having a thickness of abou~ 8 mils which is usually
corrugated transversely prior to being wrapped about
the cable c~re. The corrugations impart greater flexi-
bility to the cable and permit bending of the cable
without wrinkling or ruptuxing of the shielding tape.
The term "shield, screen, or shielding tape"
as used herein means a relatively thin layer of any
metal, bare or coated, which can provide mechanical
protection and electrostatic and electromagnetic screening
for the conductors in the core of electrical power and
communication cables~
17,942-F
.,s~
When telephone cables are installed under-
ground by being buried directly in soil, the outer
jacket of such cables, which is ormed of a polymeric
resinous material such as polyethylene, may be subjected
to damage due to the rigors of installation; rocks;
rodents; lightning; frost; or dig-ins. The underlying
shielding tape can thus be exposed to sub-surface
water or brine and the attendant potential for corrosion.
Where ~he outer jacket of such cables is formed
from a polymeric resinous material, the jacket is
not well adhered to the shielding tape of bare metal.
The outer plastic jacket is known to slip over the
shielding tape and to fold up into shoulders as the
cables are pulled through ducts or placed into trenches.
The shielding tape is also known to kink, curl or twist
during installion causing fatigue in the tape and, in
extreme cases, rupture of the tape ~ecause of mechanical
bending stresses exerted thereon.
In order to improve the corrosion resistance of
a shielding tape of bare metal, a special adhesive poly-
ethylene f ilm may be applied to cover one or both sides
of the metallic strip as taught in U.S. Patent Nos~
3,233,036 and 3,795,540. Such shielding tapes are widely
used in the manufacture of electrical power and communi-
cations cables. The adhesive polyethylene used for this
film contains reactive carboxyl groups which have the
ability to develop firm adhesion to the metallic strip
and also to the overlying polyethylene jacket. The
metal component of such shielding tapes provide electro-
static screening and mechanical strength to the cable;
17,942-F -2-
~L~, ru~/lra~
the polymeric resinous material coating, e.g., ethylene
acrylic acid (EAA) copolymer coating, provides bondability,
sealability and corrosion protection to the metal component.
A metallic strip, such as aluminum, which is protected by
the adhesive polyethylene film normally has higher
resistance to corrosion.
When a polyethylene jacket is extruded over the
metallic strip coated with the adhesive polyethylene film,
the heat from the semi-molten polyethylene jacket bonds
the film coated metal strip to the jacket, forming a
unitized component which combines the strength of the
metal strip with the elongation and fatigue resistance of
the polyethylene jacket component. Such cable construc-
tion is referred to in the art as a "Bonded Jacket"
cable design. If the heat imparted to the jacket-foxming
polye~hylene is sufficiently high, the shielding tape
would become hot enough so that the overlapped portions
of the shielding tape bond together at the seam, thereby
forming a sealed tube or pipe around the core of the
cable. The "Bonded Jacket" cable with a sealed seam
has improved re~istance to moisture penetration into
the cable coxe. This cable construction also has been
shown to have greater mechanical strength necessary to
withstand repeated bending of the cable, i.e. kinking
and fatigue failures of the shielding tape, resulting
from bending stresses during installations. Further,
the stresses induced by the temperature cycles under
service conditions are reduced.
The plastic coating protects the metal to some
degree from coxrosion by limiting the area over which
17~942-F -3-
such corrosion can occur or by preventing contact between the metal and the
water or brine. The coating should be tightly bonded to the metal to resist
significant delamination therefrom during exposure to the cor~osive water
and the mechanical forces exerted by the formation of voluminous metal
corrosion products, thereby restricting the path of corrosive attack to the
exposed metal edges of the shielding tape.
Recently, examination of several commercial cables utilizing poly-
meric resinous material coated shielding tapes representative of the prior
art has revealed, however, that the coatings on such tapes are damaged during
cable manufacture exposing numerous corrodible bare spots on the surfaces of
the metal strip. More specifically, when a polyethylene jacket is extruded
over a plastic coated shielding tape, the h0at from the molten polyethylene
jacket softens or melts the polymeric resinous material coating making it
difficult or impossible to obtain a bond to the jacket and a sealed seam.
While the coating is in such softened or molten state, it is penetrated or
abraded by the smooth, corrugated or embossed core wraps, by the seams of
the tape, by the binder tapes, and/or by the weight of the core itself,
thereby exposing numerous corrodible bare spots on the surfaces of the metal
strip. As a result, the corrosion rate at the damaged spots is accelerated
due to an unfavorable ratio of the anodic and cathodic areas of bare and
coated metal. Furthermore, corrosion propagates between damaged spots and
prematurely destroys the longitudinal continui*y of the shielding tape which,
in turn, can render the
~, - ~1-
,
2~
cable inoperative. Since telephone cables are expected
to have a long service life, corrosion of shiélding
tapes which can lead' to premature cable failures is
indeed a serious technical and financial problem for the
wire and cable industry. The problem of coating damage
has not been recognized until the present invention because
of the industry's preoccupation with other major problems.
One of such problems was the need to develop thermal barrier
materials to protect the cable core from heat damage.
Another problem was associated with the introduction of
fully-filled telephone cable designs wherein the cable
core is filled with a grease-like compound to prevent
ingress and migration of water.
The corrodible bare spots may occur on either
side o~ the shielding tape but the problem is-parti-
cularly critical with the use,of corrugated metal1i~
strips where it'has been observed that the penetration
and/ox abrasLon damage exposing the bare metal is con-
centrated on the raised corrugated surfaces of the
shielding tape disposed toward,the core. A corrosive
attac~ on this type of circumferentially concentrated
damaged area of the corrugated metal strip will quickly
destroy the longitudinal electrical function of the
shielding tape. In order to maintain the prior art
criterion of restricting corrosion to the shielding tape
edges, it is now recognized that penetration and/or
abrasion resistance of the plastic coatings is required,
in addition to delamination resistance, to insure that
corrosion is generally confinec~ to the edges of the
shielding tape instead of being e~tended over the entire
,, surface theLeof'.
',
~ 2-F _5_
. .
,~
Although there is no known prior ~rt directly
concerned with overcoming the above identified problems,
the following prior patents speciically referred to
hereinbelo~ and in Table II illustrate the closest kno~;n
S prior art in the plasti~ coated shielding tape technology.
U.S. Patent No. 3,586,756 and U.S. Patent No.
3,950,605 (Example 3 and 6 - Table II) disclose shielding
tapes comprising a metal strip having an adhesive polymer
coating adhered to at least one side of the metal strip.
However, these prior patents do not provide for a de-
ormation resistant layer of a polymeric resinous material
composition having a deformation temperature of at least
130C as hereinafter described in this specification.
The coating on such tapes will be deformed during cable
manufacture exposing numerous corrodible bare spots
on the surfaces of the metal strip.
U.S. Patent No. 3,507,978 (Example 4 ~ Table II)
teaches a shielding tape comprising a metal foil having
layers of a copolymer such as ethylene/acrylic acid che~i-
cally bonded to both sides of t~e metal foil and an
additional layer of high density polyethylene bonded
to one of the copolymer layers~ However, there is no
teaching or suggestion in U.S. Patent No~ 3,507,~78
of the damage problem overcome by the present invention
2S and examination of commercial cables incorporating
such a shielding tape also illustrates that penetration
and/or abrasion of the hi~h density polyethylene la~er
occurs at current cable manufacturing and service use
conditions.
17,~42~
, i, .S
U.S. Patent No. 3,379,824 (E~ample 8 ~
Table II) teaches a shielding tape comprising a three
layer structure with an aluminum foil laminated between
two polypropylene layers or a polypropylene layer and
a polyethylene terephthalate layer. Again, there is
no teaching or suggestion of the damage problem over-
come by the present invention. In addition, although
these plastic layers will resist penetration and abrasion,
they do not provide corrosion protection when a corro-
sive environment is present in a cable since both
polypropylene and polyethylene terephthalate are highly
inert and can develop only a poor mechanical bond to
the metal strip based on friction adhesion. Therefore,
both the polypropylene and polyethylene terephthalate
layers will easily delaminate under exposure to corro
sive conditions and the mechanical forces exerted by
metal corrosion products.
U.S. Patent No. 3,325,589 (Example 9 to 11 -
Table II) discloses a plastic coated metal shielding
tape comprising a metal strip having an adhesive layer
immediately adjacent to the metal strip and an additional
Myla ~ or polypropylene layer adhered to one side of the
metal strip. Such a shielding tape was subjected to
simulated conditions of cable manufacture and a laboratory
corrosion test. It was found that the tape did not
provide satisfactory corrosion resistance to the metal,
i.e., the path of corrosive attack was not confined to
the exposed metal edges. The adhesive layer was deformed
from pressure exerted through the polypropylene or Myla
layer thereby exposing bare aluminum spots. Corrosion
~= Registered Trademark
17,942-F ~7~
h~ 2~
was taking place on these bare spots after subjecting -
the cable to a standard corrosion test with sodium hy-
droxide, as hereinafter defined in this specification,
due to the infiltration of the NaOH between the adhesive
layer and the polypropylene (PP) or Myla ~ layers.
U.S. Patent No. 3,7g0,694 (Example 8 - Table
II) discloses a polypropylene layer adhesively bonded
to a metal strip. The patent does not specify the use
of any particular adhesive. Since ethylene acrylic
acid (EAA) copolymex is the best known metal adhesive
in the industry today, the shielding tapes made according
to the teachings of that patent were found to give
similar results to those of U.S. Patent No. 3,325,589.
The patent teaches bonding of the jacket, a screen,
and composite tapes together during extrusion of the
cable jacket. Since the thermoplastic coatings on the
screen and composite tapes must be above its melting
point to effect bonding they were found to be damaged
a priori. Thus, this prior art patent also failed to
recognize the problem of coating damage on shielding
tapes. U.S. Patent Nos. 3,325,589 and 3,790,694, are
related to a heat resistant core wrap (thermal barrier)
and a fully filled cable, respectively.
U.S. Patent No. 3,321,572 (Example 13 - Table
II) and U.S. Patent No. 3,622,683 (Example 8 - Table II)
disclose, inter alia, shielding tapes comprising a metal
strip having a polymeric resinous material coating
adhered to at least one side thereof and capable of resis-
ting deformation at an elevated temperature. However,
these shielding tapas were found to fail the adhesion
17,942-F -8-
..~
requirement of the present invention. In these tapes,
it was found that the path of corrosive attack was not
confined to the exposed edges of the metal strip because
of the infiltration of corrosive element between the
polymex coating and the metal strip.
U.S. Patent No. 3,484,539 teaches the adhesion
of a heat sealable layerr such as, for example, poly-
vinyl chloride to a polymer layer capable of resisting
deformation at cable~forming temperatures. However, the
polymer layer of this patent, having adhered thereto
a heat sealable layer, is not "tightly bonded" to the
metal strip and is thus open to corrosive attack due to
the infiltration of corrosion causing liquids whan the
cable jacket is damagedO
None of the prior art patents hereinabove
discussed show or suggest that a deformation resistant
layer can be used in a shielding tape to prevent damage
to the protective coating during cable manufacture,
installation or service use~ Furthermore, none of the
polymer coatings on the shielding tapes disclosed in
the prior patents meet both the bonding or adhesion and
deformation resistance requirements of the present in-
vention to provide satisfactory corrosion resistance
to the shielding tapes by restricting the path of corro- ;
sive atkack to the exposed metal edges.
Although the "bonded jacket" cables have im-
proved resistance to moisture penetration into the
cable core and have greater mechanical strength necessary
to withstand repeated bending thereof, some problems have
also been encountered in terminating and splicing khe
17,942-F -9-
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cables., More specifically, it is cumbersome to separate
the jacket from the shielding tape for the purpose of
making electrical connections to the tape. ~hile it
is possible to terminate and splice the "bonded jacket"
cables without separating the jacket from the shielding
. tape, it has been shown that the quality of electrical
connections is not as good as that with the jacket
removed. More particularly, the electrical properties
of the connections to the shielding tape are known to
change less with time than the connections to the
shielding tape and bonded jacket of electrical cables
SUM~`5ARY AND DEFINITIONS
The present invention resides in an improved
corrosion resistant cable shielding tape comprising
(l) a metal strip having tightly and directly
adhered to one side thereof a first ad-
hesive layer composed of a copolymer of
ethylene and from about 2 to a~out 20
percent based on copolymer weight of an
ethylenically unsaturated carboxylic acid; and
(2) a first deformation resistant layer composed
of a polymeric resinous material tightly adhered
to said first adhesive layer, said first deforma-
tion resistant layer having a deformation tempera-
ture o at least about 270F.
The present invention also resides in an improved
cable adapted for use in sup?lying electrical power and
communications comprising a core of at least one insulated
~onductor, a shield surroundina saic core com?risina
17,942-~ -10
(1) a metal strip having tightly and directly adhered
to one side thereof a first adhesive layer
composed O r a copolymer of ethylene and from
about 2 to about 20 percent based on copolymer
weight of an ethylenically unsaturated carboxylic
acid; and
(2) a first deformation resistant layer composed of
a polymeric resinous material tightly adhered
to said first adhesive layer, said first deforma-
tion resistant layer having a deformation tempera-
ture of at least about 270F and positioned
inwardly in the direction of said core
and an outer plastic jacket surroundin~ said shield, wherein
the adhesive bond between said metal strip and said first
adhesive layer and between said first adhesive layer and said
first deformation resistant layer is at least 2.2 pounds
per inch of shielding tape width after aging for seven (7)
days in deionized water maintained at a temperature of 7~C.
In a preferred embodiment, the adhesive layer has
a deformation temperature of at least about 270F after
being irradiated with an effective amount o a high energy -`
ionizing radiation.
In another embodiment, a second deformation resis-
tant layer and/or other layers of polymeric resinous
materials is included in the shielding tape thereby
providing a multilayered structure having a combination
of desirable functional characteristics. For example,
deformation resistant layers of pol~eric resinous material
are tightly bonded to both sides of the metal strip,
if desired, to provide penetration and~or abrasion resis-
tance on both sides of the shielding ta~e.
17.~ -10~-
In a further embodiment, adhesive layers of
polymeric resinous materials having good bonding character-
istics to both the metal strip and the deformation resis-
tant layer or layers
l7,9~'t2-F ~lOb-
are used to tightly bond the deformation resistant layer to the metal strip
when direct adhesion of the same is insufficient to adequately provide
corrosion protection for the metal strip.
In another embodiment, heat seal layers of thermoplastic polymeric
resinous material are included in the shielding tape of this invention to
provide a hermetically sealable shield seam in the cable structure and to
provide a good bond between the cable shielding tape and outer plastic
jacket of the cable.
In a further embodiment, an adhesive/heat seal layer of thermo-
plastic polymeric resinous material having both good metal bonding and heat
seal characteristics is tightly bonded directly to one side or to opposite
sides of the metal strip.
The combined layers of polymeric resinous materials described
above have high electrical resistivity, high resistance to chemicals and
moisture and exceptionally good bonding to the metal strip thereby being
able to withstand the rigors of manufacturing processes as well as penetra-
tion and/or abrasion when in use without delamination in a corrosive environ- .-~
ment.
The shielding tape of this invention must meet both the adhesion
or bonding and deformation resistance requirements to provide satisfactory
corrosion protection to the shielding tape by restricting the path of
corrosive attack to the exposed metal edges of the metal strip.
Lamina~ed tapes of the present invention are readily fabricated
utilizing well known laminating or extrusion or coextrusion techniques such
as those described in United States patent 3,679,513 issued July 25, 1972
to Addinall et al, United States patent 3,402,086 issued September 17, 1968
to Smith et al, and United States patent 3,557,265 issued January 19, 1971
to Chisholm et al. When the laminating technique is used, the resinous
polymeric material is first converted into either a blown or a flat film
utili~ing a well known extrusion process. The resulting ~ilm is bonded to
,~, -11-
the metal strip by heat and pressure. Sometimes it is advantageous and/or
necessary to employ an adhesive inbetween the film and the substrate to
achieve a better adhesion therebetween.
The present invention-is not limited by either thc process used to
prepare the films from the resinous polymeric materials or the technique
used to fabricate the laminated tapes therefrom. However, as it is well
known in the art, the manner in which these films are prepared can induce
some differences in properties thereof. For example, the deformation
resistance of these films is, among other things, related to the degree of
molecular orientation imparted thereto: a film of a given polymeric com-
position having a relatively high degree of molecular orientation will
characteristically have a relatively high deformation resistance and vice
versa. For example, as it is seen in Examples 1 and 15 of Table 1 below,
a polymeric composition comprising 50 percent by weight of polypropylene
and 50 percent by weight of ethylene/acrylic acid copolymer has a deformation
temperature of 164C when the composition is converted into a film using a
blown film process (Example 15) and 1~4C when a flat film process ~Example
1) is employed. However, an additional degree of molecular orientation can
be imparted to blown or cast films by well known stretching techniques, e.g.
that described in United Stat~s patent 3,055,048 issued September 25, 1962
to H. P. Koppehele. These films can advantageously be stretched simultane-
ously in the machine and transverse directions.
When the laminated tapes of the present invention are prepared by
utilizing the well known extrusion coating technique, a molten polymeric
resinous material is forced through a slot in a flat die and is applied
directly onto the metal strip. The coating thus prepared is known to have
about the same degree of molecular orientation as the corresponding flat
film of the same polymeric composition.
When the laminated structures of the present invention comprise
a plurality of polymeric layers such as, for example, adhesive layer
-lla-
~76.~
deformation resistant layer and heat seal layer, it is most advantageous to
employ well known coextrusion techniques in preparing the blown or flat films
or in carrying out the e~trusion coating step.
The nccessary bond strength between the metal strip and an adjacent
layer of polymeric resinous material is obtained by the well known post heat-
ing step such as the one described in United States patent No. 3,~02,086.
Typically, the laminate is heated in an oven to a temperature of from 80 to
~50C
The present invention also provides a cable sh.ielding tape to
which an outer jacket is firmly bonded and wherein the jacket is easily
removed to
-llb-
2~
facilitate the splicing and grounding procedures and yet
provides corrosion protection in all areas of such shielding
tape by allowing removal of the jacket in such a manner that
a tightly bonded adhesive layer remains on the metal com-
ponent of the tape after stripping of the jacket.
More specifically, such a shielding tape has a
bond between a metal strip and an adhesive layer tightly
bonded thereto which bond is stronger than the interlayer
bond of other tightly bonded layers of polymeric resinous
material. By judicious selection of the types and propor-
tions of polymer composition for the deformation resistant
layer, the bond of the deformation resistant layer to the
adjacent layers of polymeric resinous material is made weaker
than that of the adhesive layer to the metal strip. The
interlayer bond must be capable of withstanding delamination
under conditions of normal use but which will separate prior
to delamination of the adhesive layer from the metal strip.
More specifically, as herein defined, "metal
strip" means a relatively thin layer of any metal whi~h
has good' electrical or mechanical properties useful in
electrical power and communications cablesO
As herein defined, the term "tightly bonded" means
restricting the path of corrosive attack -to the exposed
metal edges of the shielding tape by chemically and/or mechan-
ically bonding the deformation resistant layer to the metal
strip, either directly or indirectly with an adhesive layer,
or by bonding an adhesive/hea~ seal layer directly to the
meta~ strip, to prevent significant delamination of the defor-
mation resistant and adhesive/heat seal layers from the metal
strip under exposure to corrosive conditions and the resulting
mechanical forces exerted by the metal corrosion products.
17,9~2-F -12-
"Adhesive layer", as herein defined, means
a layer of polymeric resinous materials having good
bonding characteristics with the metal strip and defor-
mation resistant layer and the plastic jacket of the
electrical cable.
"Heat seal layer", as herein defined, means
a layer of thermoplastic polymeric resinous materials
having a sealing temperature of 121C or lower and, pre-
ferably, 110C or lower which will easily seal to
itself, or other polymeric resinous materials such as,
for example, those materials forming the outer plastic
jacket of a cable.
"Adhesive/heat seal layer", as herein de-
fined, means a layer of thermoplastic polymeric resinous
materials having both good metal bonding and heat seal
~haracteristics for the adhesive and heat ~eal layers
which will tightly adhere to the metal strip.
"Deformation resistant layer", 25 herein de-
fined, means a layer of polymeric resinous mat~rials
that substantially resist penetration and/or abrasion
at deformation temperatures of at least about 130C
and pressures normally associated ~ith cable manufacture,
installation and/or service use.
Improved cables adapted for use in supplying
electrical power or communications can be constructed
with the improved corrosion resistant cable shielding
tape described above~ Such cables comprise a core of
at least one insulated conductor, a shield of the im-
proved corrosion resistant cable shielding tape surrounding
the core, and an outer plastic jac~et surroundin~ the
... .
~ F -13-
tape. The deformation resistant layer of the shielding
tape may be positioned in the direction of the core,
in the direction of the outer jacket or in both direc-
tions to overcome penetration and/or abrasion damage
during manufacture and/or during service of the cable.
The invention is further understood by refer-
ence to the accompanying drawings in which like characters
of reference designate corresponding materials and parts
throughout the several views thereof, in which:
Figure 1 is a partial cross-sectional view
of a plastic coated metal shielding tape constructed
according to the principles o the present invention;
Figures 2-9 are partial cross-sectional views
illustrating modified plastic coated metal shielding
tapes constructed according to the principles of the
present invention;
Figure 10 is a cross-sectional view of a
typical power cable with three insulated conductors,
a plastic coated metal shield and an outer plastic
jacket; and
Figure 11 is a cut-away perspective view of
an end of a communications cable with multi-pair in-
sulated conductors in the core, plastic coated metal
shield and plastic outer jacket.
DETAILED DESCRIPTION OF THE PREEERRED EMBODIMENTS
_ _
Referring now to the drawings, Figure 1 illus-
trates an improved corrosion resistant cable shielding
tape 10 comprising a metal strip 12 having a deformation
resistant layer 1~ formed of a polymeric resinous
material such as a blend of 50 weiyht percent poly-
17,94Z-F -14-
7~
propylene and 50 weight percent ethylene/acrylic acid
copolymer tightly bonded to one side thereof. In
order to provide corrosion protection for the metal
strip 12, shielding tape 10 should be used in cable
constructions having a plastic outer jacket formed of
an adhesive composition which will tightly bond to
the metal strip 12 on the side opposite to that of
layer 14.
Figure 2 illustrates a modified cable shielding
tape 20 having a deformation resistant layer 24 like
layer 14 of Figure 1 tightly bonded to metal strip 12.
Layer 25 which is tight]y bonded to the opposite side
of strip 12 may be a deformation resistant layer like
layer 24 or may be an adhesive/heat seal layer formed
of an ethylene/acrylic acid copolymer.
Figure 3 illustrates another modified cable
shielding tape 30. The metal strip 12 may have a de-
formation resistant layer 34 like layer 14 of Figure 1
tightly bonded to one side thereof and a heat seal
layer 36 formed of low density polyethylene adhered to
layer 34O Alternatively, layer 36 may be a deformation
resistant layer formed o a material such as nylon which
will not tightly bond directly to the metal strip 12
with sufficient adhesion to provide corrosion protection
and layer 3~ may be an adhesive layer formed of a material
such as an ethylene/acrylic acid copolymer. ~ike
shielding tape lO of Figure 1, shielding tape 30 should
be used in cable constructions which have a plastic
outer jacket formed o~ an adhesive composition to insura
corrosion protection for the metal strip 12.
17,942-F -15-
~ ~ 7~2~
Figure 4 illustrates still another modified
cable shielding tape 40. There are four possible struc-
tures of shielding tape ~0 useful in accor~ance with
this invention. Layer 45 may ~e a deformation resistan~
layer like layer 14 of Figure 1 for two of the possible
structures or an adhesive/heat seal layer like layer 25
of Figure 2 for the other two structures. Layer 44 may
also be a deformation resistant layer like layer 14 of
Figure 1 when it will tightly bond directly to the
metal strip 12 or it may be an adhesi~e layer formed
of an ethylene/acrylic acid copolymer which in turn
is used to tightly bond a deformation resistant layer
46 like layex 36 of Figure 3 that will not tightly
bond directly to the metal strip 12. When layer 44
is a deformation resistant layer tightly bonded to
the metal strip 12, layer 46 is beneficially a heat
seal layer like layer 36 of Figure 3.
Figure 5 illus~rates still another modified
cable shielding tape 50. There are three possible
structures of tape 50 useful in accordance with this
invention. First, two deformation resistant layers 56
and 57 like layer 36 of Figure 3 which t~ill not kightly
bond directly to the metal strip 12 may be tiyhtly
bonded to the strip 12 with adhesive layers 54 and 55
like layer 34 of Figure 3. Second, the remaining two
possible structures may have a deformation resistant
layer 55 like layer 14 of Figure 1 tightly bonded to
the metal strip l2 a~d a heat seal layer 57 like layer
36 of Figure 3 bon~ed to layer 55. On the opposite
side of the metal strip 12 there may be a deformation
17,992-F
,
resistant layer 54 like layer 14 of Figure 1 tightly
bonded directly to the strip 12 and a heat seal layer
56 like layer 36 of Fiyure 3 bonded to layer 54 or,
in the alternative, there may be a deformation resistant
layer 56 like layer 36 o Figure 3 which will not tiyhtly
bond directly to the metal strip 12 that is tightly
bonded to ~he strip 12 with an adhesive layer 54 like
layer 34 of Figure 3.
Figure 6 illustrates a further modified cable
shielding tape 60. A deformation resistant layer 66 like
layer 36 of Figure 3 which will not tightly bond
directly to the metal strip 12 is tightly bonded to the
strip 12 with an adhesive layer 64 like layer 34 of
Figure 3. A heat seal layer 68 formed of an ethylene/-
acrylic copolymer is bonded to layer 66. Like shielding
tapes 10 and 30, shielding tape 60 should ba used in
cable constructions which have a plastic outer ~acket
formed of an adhesive composition ~o insure corrosion
protection for the metal strip 12.
Figure 7 illustrates a still further modified
cable shielding tape 70. The adhesive layer 74, defor-
mation resistant layer 76 and heat seal layer 78 are
the sam~ as the corresponding layers 64, 66 and 68 found
in Figure 6. Layer 75 may be a deformation resistant
layer like layer 14 of Figure 1 or, in the alternative,
an adhesive/heat seal layer like layer 25 of Figure 2
tightly bonded directly to the metal strip 12.
Figure 8 illustrates a still further modified
cable shielding tape 80. The adhesive layer 84, defor-
mation resistant layer 86 and the heat seal layer 88
17,942 F -17-
are the same as the corresponding layers 64, 66 and 68
found in Figure 6. On the opposite side of the metal
strip 12 there may be a deformation resistant layer 85
like layer 14 of Figure 1 tightly bonded directly to
the strip 12 and a heat seal layer 87 like layer 36 of
Figure 3 bonded to layer 85 or, in the alternative,
there may be a deformation resistant layer 87 like layer
36 of Figure 3 which will not tightly bond directly
to the metal strip 12 that is tightly bonded to the
strip 12 with an adhesive layer 85 like layer 34 of
Figure 3.
Figure 9 illustrates a final modified cable
shielding tape 90. The adhesive layers 94 and 95,
deformation resistant layers 96 and 97, and the heat
seal layers 98 and 99 are the same as the corresponding
layers 64, 66 and 68 found in Figure 6.
Referring now to Figures 10 and 11, a typical
three-conductor power cable 100 and multi-pair conductor
communications cable 110 are illustrated. The power
cable 100 has low resistance metal conductors 101, which
can be solid or stranded, usually of copper or aluminum,
which are each insulated, usually with an extruded
plastic cover 102 of, for example, polyvinyl chloride~
polyethylene or rubber. Space fillers 103 of, for
example, natural fibers or foamed plastic are used to
provide a substantially circular core assembly which is
enclosed in a shielding tape 104 formed from any one
of the shielding tape structures illustrated in Figures
1-9. The shielding tape 104 is preferably a longitudinally
folded tube with an overlapping seam that may be hermati-
17,942~F -18-
cally sealed by heat sealing the plastic coating of
the shielding tape together in the overlapping seam
during cable manufacture. An outer plastic jacket 105,
usually extruded polyeth~lene containing stabilizers and
carbon black, is beneficially bonded to the shielding
tape 104. The communications cable 110 includes an
inner core of many pairs of insulated conductors 111
(e.g. plastic coated copper wires) bundled in a plastic
core wrap 112 of, for example, polypropylene or poly-
ethylene terephthalate which is securely bound with a
binder tape 113. The bundle is enclosed in a shielding
tape 114 formed from any one of the shielding tape
structures illustrated in Figures 1-9. Like the
shielding tape 104 of power cable 100, shielding tape
114 is preferably a longitudinally folded tube with a
hermetically sealed overlapping seam. An outer plastic
jacket 115 preferably of polye~hylene is extruded
over the shielding tape 114 and is advantageously bonded
to the same.
The metal strip which is used in accordance
with this invention may have a thickness from 0 2 to
25 mils and, more preferably, from 2 to 15 mils. The
metal strip may be formed, for example, from al~ninum,
aluminum alloys, alloy-clad aluminum, surface modified
copper, bronze, steel, tin free steel, tin plate steel,
aluminized steel~ stainless steel, surface modified
copper-clad stainless steel, terneplate steel, gal-
vanized steel, chrome or chrome treated steel, lead,
magnesium or tin. These metals may also be surface
treated or have thereon surface conversion coatings.
17,9~2-F -19-
The deformation resistant layer which is used
in accordance with this invention may have a thickness
from 0.1 to 15 mils and, more preferably, from OOS to
2.0 mils. Beneficially, the deformation resistant layer
may be formed from any polymeric resinous material which
will provide a layer deformation temperature of at least
about 132~C such as, for example, polypropylene, carboxyl
modified polypropylene, polyamides, polyethylene
terephthalate, fluoropolymers, 1-4 di-methyl pentene
polymers, ethylene/propylene copolymers, stereo regular
polystyrene, flexible thermoset polymeric resinous
materials, Saran~, or irradiated carboxyl modified
olefin polymers. These polymeric resinous materials
may be blended with, for example, low or high density
polyethylene, ethylene/ethyl acrylate copolymers, ethy-
lene/vinyl acetate copolymers, carboxyl modified ethylene
polymers, ethylene/acrylic acid copolymers, ionic olefin
polymers, or chIorinated polyethylene, provided the
layer deformation temperature is at least about 132~C.
Flexible thermoset polymeric resinous materials such
as, ~or example, polyurethanes mav also be used provided
the 132C deformation temperature i5 achie~ed.
The adhesive layer may have a thickness from
0.1 to 10 mils, preferably from 0.3 -to 2.5 mils. Such
layer may be formed from any thermoplastic polymeric
resinous material which will tightly bond the de~ormation
resistant layer to the metal strip. Copol~mers of ethy-
lene and ethylenically unsaturated carboxylic acids
readily form a strong adhesive bond with aluminum and
are preferred in achieving beneficial results of the
17,~2-F -20-
present invention. The adhesive polymer which is bene-
ficially used in accordance with this invention is a
normally solid thermoplastic polymer of ethylene modified
by monomers having reactive carboxylic acid groups,
particularly a copolymer of a major proportion of ethy-
lene and a minor proportion, typically from 1 to 30,
preferably ~rom 2 to 20, percent by weight, of an ethy-
lenically unsaturated carboxylic acid. Specific examples
of such suitable ethylenically unsaturated carboxylic
acids (whieh term includes mono- and polybasic acids,
acid anhydrides, and partial esters of polybasic acids)
are acrylic acid, methacrylic acid, crotonic acid,
fumaric acid, maleic acid, itaconic acid, maleic anhydride,
monomethyl maleate, monoethyl maleate, monomethyl fumarate,
monoethyl fumarate, tripropylene glycol monomethyl ether
acid maleate, or ethylene glycol monophenyl ether acid
maleate. The carboxylie acid monomer is preferably
selected from ~ ethylenieally unsaturated mono- and
polycarboxylic acids and acid anhydrides having from
3 to 8 earbon atoms per molecule and partial esters
of such polycarboxylic acid wherein the acid moiety
has at least one carboxylic acid group and the alcohol
moiety has from 1 to 20 carbon atoms. The copolymer
may consist essentially of ethylene and one or more
of such ethylenically unsaturated acid comonomers or
can also contain small amounts of other monomers copoly
merizable with ethylene. Thus, the copolymer can
contain other copolymerizable monomers including an
ester of acrylic acid. The comonomers can be combined
in the copolymer in any way, e.g., as random copolymers,
17~942-F -21-
2~
as block or sequential copol~ners, or as graft copoly-
mers. Materials of these kinds and methods of making
them are readily kno~ln in the aL-t.
Beneficially, thc heat seal layer may have
a thickness from 0.1 mils to 10 mils and, preferably,
from 0.3 mils to l mil. The heat seal layer may be
formed from, for example, low or high density poly-
ethylene, ethylene/ethyl acrylate copolymers, ethylene/
vinyl acetate copolymers, carboxyl modified ethylene
polymers, or blends of the above.
The adhesive/heat seal layer may have a
thickness from 0.1 mils to 10 mils and, more preferably,
from 1 mil to 3 mils. The adhesive/heat seal layer may
be formed from, for example, carboxyl modified olefin
polymers, ionic olefin polymers, blends of carboxyl
modified oiefin polymers or biends of ion7c. olefin
polymers.
Deformation resistance of a layer of polymeric
resinous material is normally tested by means of a
penetrometer. However, kno-~n penetrometers are designed
for coatings (comprising one or more layers of synthetic
resinous material) 60 to 125 mils (1.52 to 3.17 mm) thic~
and data therefrom do not apply to the coating thic}cnesses
on cable shielding tapes or ter.lperatures and pressures
associated with the cable manufacture or use. There-
fore, a special penetrometer test was developed to
evaluate the ability of relatively thin coatings, i.~.,
coatings having a thicklless of 10 mils (0.254 N~l) OL-
less, on plastic clad metals to resist deformation
at elevated temperatures. The sl~ecial penetromcter
consists of a metal blocX weig]lin~ l.G~ ~;g onto whicl
'.
~ 17,g~l2-F -22-
... .
~76j~Z 3
a circular ring has been machined. The ring has an
outside diameter of 38.1 mm an~ a thickness of 25 mils,
The cutting edge of the rin~ in contact with the coated
shielding tape sample is rounded to a 0.79 ~m radius which
applies a pressure to the sample of 35 pounds per square
inch (24.6 gm/mm ). The testing procedure consists of
placing the sample of shielding tape on a base such as
a metal plate and then positioning the special penetrometer
on the sample with the ring in contact with the coating
thereon. An electrical circuit, open because
of the coating, is connected between the penetrometer
and the metal strip of the sample. Thereafter, the
entire assembly is placed in a circulating air oven
preheated to 218C which increases the temperature of the
shielding tape being tested at a rate of approximately
1~C per minute. ~hen Lhe ring peneLrates the coating
the electrical circuit is completed and the temperature
of the coating, determined by a thermocouple or other
' means, is recorded. This temperature is the deformation
temperature, for the coating be,ing tested~ It has
been found that the conditions of this test correlate
well with the temperatures and pressures associated
with cable manufacturing and/or service use. It has
been found that the deformation resistant l~yer should
have a deformation temperature of at least ab~ut 130C
and prefexably at least about 138C and above to
resist the temperatures and pressures normally asso-
ciated ~ith cable manu~acturing and/or service use.
The degree of adhesion between plastic layers,
and between a plastic layer and the metal strip of a
shielding tape o~ this inventi,on, which wi]l sa`tisy the
,~,, 17,9~2~~ -23-
1~7~
requirement for "tightly bonded" thereof, should represent
a value of at least about 1 kg/2.54 cm of tape width,
prefera~ly at least about 2 kg/2.~4 cm, after i~ersion
of a tape sample in deionized water maintained a~ a
temperature for a period of time of 7 days. The
degree of adhesion is determined by preparing a 6 inch
wide by 6 inch long by 60 mil (15.24 cm x 15.24 cm x 3.175 mm)
thick molding of a plastic jacketing material using
a procedure similar to that described in the U.S.D.A.*
Rural Electrification Administration (REA) specificatio~
PE-200. A sheet of shielding tape of the same dimen-
~ions (~ in. x 6 in.) was placed over the molding.
A strip of polyester film of 1 mil (0.254 mm~ thickness
was placed between the shielding tape and the molding
of the jacketing material to prevent bonding to one
end of the jacketing material to form a "tab'; for use
in a tensile strength testing machine. The shielding
tape was bonded to the molding using a compression
molding press and a molding temperature of 190C. The
molding pressure was 300 pounds per square inch
(0.2 };g/mm2). The heating cycle was as follows:
3 minutes to reach temperature Wit}l no pressure; ~
minutes under pressure; and 5 minutes to cool to room
temperature. After the shielding tape/jacketing material
laminate was prepared one inch (2.54 cm) wide samples
for bonding tests were cut on a sample cutter. The
samples were placed on a tellsile testing machine and
tested for bGnd strengt]l as ~ollows: the unbonded
portion of the shieldin~ tape was folded bac~ ~800r;
the sample was inserted inLo the tensile testin~ machine
*UIlited States ~epartr,;ent of ~g~ic~lture
'.
1~,942-1 -2q-
with the shielding tape in the upper jaw and the molding
of jacketing material in the lower jaw; a rigid metal
plate was placed behind the molding to maintain the
peeling angle at 180C; and the shielding tape was
then separated from the rigid molding of the jacketing
material at a crosshead speed of 5 inches per minute.
The required force to separate the shielding tape from
the molding was recorded as a measure of adhesive
strength~ The separation can occur at the metal strip/
plastic layer interface, or plastic layer/plastic layer
interface or plastic layer/jacketing material interface.
Several shielding tapes of plastic coated
aluminum were prepared and were tested for corrosion
resistance thereof. More specifically, test samples
of the shielding tapes having an area
of 5.08 cm x 5.08 cm were first subject to
a simulated jacketing test, as described hereinafter,
and were then immersed in one (1) normal sodium hy-
droxide (1~ NaOH) solution for 24 hours~ Bare aluminum
spots on the surfaces of the shielding tapes, which had
been exposed by damage to the plastic coatings thereon
during the simulated jacketing test, were thereby corro-
ded. The number of corroded spots, which were easily
identifiable in the test sample of shielding tape, were
counted and recorded as a corrosion damage index thereof.
An index of 0 indicates that no corrosion spots are
present while a given number indicates the number of
corrosion spots which can be counted on the sample.
Shielding tapes having poorly bonded plastic coatings
3~ thereon resulted in total dissipation of the metal
o~ten accompanied by delamination of the coatings.
17,9~2-F -25-
~L~7~2~ `
The simulated jacketing test was designed to
simulate temperature and pressure conditions normally
encoulltered inside a cable, during and following .hn
jacketing operation, in order to study the effects
thereof on cable components. The test is particularly
well suited to study the effect of the temperature and
pressure conditions on the plastic coating or plastic
coated shielding tapes. In order to conduct this test,
a cylindrical section of a cable having a length of
about 5~0 cm is converted into a rectangular configuration
having planar surfaces. The test is carried out using
the follo~ing procedure: A sample of molded jacketing
material of about 5.08 cm x 5.08 cm and weighing 13 grams
and having a thickness of 100 mil (2.54 mm) was heated in
an oven to a temperature of 218C; the jacketing
material was removed froltl the oven after 6 to 7 rninutes
and within a period of S seconds a sample of corrugated
shielding tape (5.08 cm x 5.08 cm) was placed on the
jacketing material; a corrugated core wrap of polyester
film, a section of a cable core having a generally rec-
tangular configuration and weighing 218 gramsr and a
2000 gram weight were then successively stacked on top
of the shielding tape; and finally, the entire assembly
was placed on a large aluminum bloc]c (weighing 95S
grarns) ~o cool while the temperature of the core wrap/-
shield int~rface was recorded through a thermocouple
placed tllerebetween. Thc al~ninum block provides a
heat sink and thereby simulates the cooling bath located
downstream of the extruder head.
17,9~2-~ -2G~
~7~
The temperature-time relationships fo~ the
shield obtained with this test correlate to those
obtained with cables containing a large number of con-
ductor pairs during extrusion of the jacket.l
Heat sealability was determined on film samples
of the coatings by means of a special seal test. Two
samples of film 50.8 mm wide are placed in contact with
each other in a heat sealer apparatus such as a Sentinel
Brand, Model 24AS, or equivalent. The temperature of
the sealer bar is increased in 5C increments from
88C to a temperature sufficient to seal the films
together. The temperature at which the films seal to
each other is recorded as the minimum seal temperature.
The dwell time in seconds for the sealer bar i5 equal
to 26.25 times the film thickness in mm. The air
pressure on the sealer bar is set to 28 g/mm2
The effect of "fillers" for the cable core was
tested with samples of plastic coated shielding tapes in
which coatings on both sides thereof were exposed to petro-
latum filling compounds (Witco 5B) and floodant (Witco 4)
at 115.5C for two seconds. A percent swell was calculat~d
based on the amount of filler picked up by the coating as
follows after the surface thereof is wiped clean of
any filler compound: The original weight of the coating
Z5 was subtracted from the weight of the coating after
exposure and this difference was divided by the original
weight. This number was mul~iplied by 100 to obtain percent
swell. The results of this test are listed in Table IX.
lR. C. Mildner, P. C. Woodland, H. A. Walters, and G. E.
Clock, entitled, "A Novel Form of Thermal Barrier for
Communication Cables," presented at the 14th International
Wire and Cable Symposium, Atlantic City, New Jersey, 1965.
17,942 F -27-
~76~
In a "connector stability" test, coated metal
samples approximately 50 mm x 150 mm were corrugated.
Then two Griplok~ connectors were attached to each longi-
tudinal end of the samples. The initial resistance in
milli-ohms was measured across the connectors using a
Kelvin Bridge. The samples were then given 50 temperature
cycles from -40C to +60C, with each cycle being of
an 8 hours duration, and the resistance was measured
again. The results of these tests are listed in Table X.
In a jacket bond strength and bend performance
test, a bonded jacket gas pipe was fabricated on a cable
jacketing line using lengths of corrugated laminates. The
laminates were oriented such that the multilayer coated
side contacted the extruded jacket. Samples of the pipe
were then collected for determination of jacket bond
strength and bend perfoxmance. The results of these
tests are listed in Table XII.
The following additional test methods were
used:
1. Physical properties of the coating were
determined by ASTM D-638.
2. Elmendorf Tear was determined by ASTM
D-1922.
3. Melt Index was determined by ~STM D-1238.
Representative examples of the presen~ inven-
tion along with deformation ternperatures and corrosion
index test results, are shown in Table I. The examples
were formed by extruding the plastic layers, each of
about one mil thickness, and then laminating them to
a hot metal strip having a temperature of about 190C.
17,942~F -28-
~7~2~
Bonded jac~et cables incorporating these
examples were fabricated on commercial cable manufac-
turin~ lines under norr~al proccssinc; conditions.
The penetrometer test for defor~a~tion resis-
tance was used to obtain the deormation temperature.
Examples 8-11 in Table I show the use of three
component blends as the deformation resistant layerO
Example 12 establishes the use of a four com-
ponent blend as the deformation resistant layer~
Example 13 establishes the lower limit for
deformation temperature of a blend of polyethylene with
polypropylene of about 130C.
Example 14 illustrates the use of an adhesive
- jacket to substantiate the utility of single side coated
metals according to Figures 1, 3 and 6.
Ex~mple 15 ilIust~a''es an embod~ment in ~7hich
polypropylene is used as a deformation resistant layer.
An EAA-PP blend is used as a second adhesive layer ~o bond
the deformation resistant layer to a first adhesive layer
of EAA. A second DAA-PP blend layer and a heat seal layer
o~ EAA can ~e successively applied to the PP layer to
obtain low temperature sealability.
~xamples 16~18 are comparative examples and were
prepared according to the procedure of this invention.
However, the composition of the blend in the deformation
resistant layex was selected where it was not sufficient to
provide a deformation temperature of at least 130C.
Example 19 illustrates a particular blend in the
deformation resistant layer which falls within the desir-
able range of deformation temperature and corrosion incle~.
17,9~2-~ -29-
~7~2~
Example 20 illustrates a functional ex~ple
with copper. Since copper degrades an EA~ coating in
the presence of moisturc, a copper stabilizer, OABH
(oxalic acid bis (benzylidene hydrazide)), has been
added to the EAA.
Example 21 illustrates a functional example
with ionomer (Surlyn~ 1652, 11% ~LA) as the metal adhesive
layer
Example 22 illustrates a functional example
with an EAA-polyethylene blend as the metal adhesive
layer.
Examples 23-25 illustrate functional examples
with crosslinked coatings which were unusual in that
they maintained their bondability, sealability, and
corrosion protection qualities after irradiation.
Examples 26-27 illustrate functional exarl~les
with Saran as the heat deformation resistant layer.
These structures are not illustrated in the drawings.
Like Example 15, a second adhesive layer consisting of a
blend or a suitab]e pol~ner is used to tightly bond a heat
deformation layer to metal. The basic structures would
be: 15etal/Adhesive layer/Second Adhesive layer/Deformation
layer; Metal/Aahesive layer/Second Adhesive layer/Defor-
mation Resistant layer/Heat Sealable layer (EVA); or
Metal/Adhesive layer/Second Adhesive layer (blend)/Defor-
ma~ion layer/Second ~dhesive layer (blend)/Sealable layer.
A comparative analysis of Tables I and II
demonstrates the damaye that occurs to the plastic
coated s~lielding tape of the prior art as measured ~y
- 30 the nur,lher o corrosion spots counted on a 25 cm2
'.
~ 17,9~2-~ -30
~,,a,,J7$~
sample. It also demonstrates the need for a deformation
resistant layer having a deformation temperature of
at least about 130C and tight bonding to prcvent the
occurance of ~are spots on the surface o~ the tal~e
and the attendant potential for corrosion thereon.
Examples 9-11 in Table II illustrate that
dama~e to lower melting point coatings on rnetal can
occur through a deformation resistant layer. Without
tight adherence between a deformation layer and a metal
adhesive layer, or with bonds between the two that are
water sensitive, corrosion can occur at the defects in
the adhesive coating on the r,letal.
Example 12 illustrates the non-functionality
of this patent construction for corrosion protection.
Example 13 illustrates the need for tight
adherence of coatings to metal.
Table III and IV illustrate the initial bond
strengths and bond strengths after aging for 7 days in
70C deionized water. Two sets of numbers are given
in Table III because multilayer coatings may not
necessarily fail at the irterface of the metal and an
immediately adjacent plastic layer during bond strength
tests. If the metal bond exceeds the bond of the various
plastic layers to each other r then bond failure occurs
at the weakest inter~ace thereof. (The example numhers
re~er to those in Table I ancl Tahle II where the detailed
shielding tape constructions are shown.) The mir.umum
- bond strength is 1.0 );~/2.5~ cm rec3ardless of whetller
the bond strcncJth refexs to a me~al/pol~eric layer
3~ ' bond or to a polymeric layer/pol~neric lay~r bond.
17,~2~F -31~
For -the former, corrosion rcsistance and mechanical
performance will be deficient below the minimum bond
strength. For the latter, the ability to withstand
handling without delamination will also be impaired
below this minimum bond strength.
From Table III, it can also be seen that the
judicious selection of the types and proportions of
pol~mer compositions will provide a bond between the
metal strip and adhesive layer which is stronger than
the interlayer bond of the other layers of polymeric
resinous materials while still providing a minimum
bond strength of 1.0 kg/2.54 cm between the polymeric
coating/polymeric coating bond.
Table V and VI show that the multilayer
coatings have improved ultimate tensile strength,
elongation, and tear strength when compared to coatings
of the presently known art. The example numbers refer
only to the improved coating structure shown in Table I
and not to the coated metal structure~
Tablec VII and VIII show actual cable data
wherein the cables are made using several shielding
tapes described in Tables I and II. The same example
numbers are used.
Table IX shows that the improved coatings of
this invention have increased resistance to adverse
effects of filling and flooding compounds. The attribute
is also of benefit in e~tending the service life of
filled cables.
17,~42-F -32-
Table X shows that the connector stability to
coated mctal is improved with the improved coati~g since
the increase in resistance over the initial value is
smaller.
Table XI shows that the electrical brea~do~,m
strength and resistance to permeation ls improved with
the new coating. The electrical strength of the new
coating may be used to advantage in filled cable designs
by elimination o, the standard electrical barrier which
is wrapped about the core. The reduced rates of
permeation may serve to improve corrosion resistance.
The bond strength figures of Table XII re-
flect the levels of interlayer bond of the multilayer
samples. These bond values are approximately 1/2 that
of the prior art example 5 of Table II~ However,
the interlayer failure provides a means ~or controlling
the level of bond between the polymer layers of the
shielding tape and the jacket, i.e. a bond strong enough
to provide g~od mechanical properties while allowing
easy stripping of the jacket for splicing. Moreover,
at least the adhesive layer of the multilayer coating
remains intact on the metal strip to provide continued
corrosion protectionO
~7,~4~
5 ~ ~
1~76~B
The bend performance values are sur~rising since
the multilayer samples, at half the bond strength,
exhibited bend performance equivalent to the control
sample. These rcsults tend to suggest that bend per-
formance requires a moderately high jacket bond strength
but perhaps even more important is the ability to relieve
stresses. The multilayer film provides a means of stress
relief via the lower interlayer adhesion.
17,'~12-F -3~1-
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17, 942-F 41-
7~f~ ,
T~BLE III. TIIIS INVE:I~TION
~ . .. . . __ . . . __
Table I Bond Stren~th in ~c3/25. 4 mrn
Example To ~l~tal 'ï'o Plastic
No.Ini.t;.~ftc~r f~CJinJIniti~lAft~r ~\y_
1 7.95 9.08 3.27 4.09
2 7.95 9.11 1.04 1.09
3* 7.95 9.08 .54 .68
4 7.90 8.99 2.60 2.59
7.95 9.09 4.63 2.95
6 2.77 2.93 2.81 2.92
7- 15.44 12.94 4.27 5.0g
8 6.45 6.04 1.05 1.00
9 6.36 6.1~ 1.34 1,36
6.36 6.68 2.36 2.13
11 6. ~5 6.59 3.13 3.0~
12 6.45 6.63 1.3~ 1.32
1~ 7.95 8.90 8.~0 ~.fl~
1~ 7.55 8.35 1.07 1.05
7.95 8~77 2.31 2.30
lÇ* 8.95 9.12 8.~8 9.54
17* 8.g5 9.17 7.45 6.13
18* 8.~0 9.13 8.72 7.13
19 8.92 9.15 ~.5~ ~.51
- 20 11.20 ~0.50 ~.26 4.28
21 7.8~ 7.90 1.43 1.45
22 8.29 g.l2 2.90 2.93 ;
23 9.64 10.05 8.~5 8.90
24 6.68 7.53 6.95 6.~3
~.07 9.50 ~.27 ~.31
26~ . ~0 9.15 1.81 1.78
~7~ . ~2 9.23 3. ~6 3.91
*Comparativc ,~xample~
17, ~ ~ 2 1' ~ ~ 2
` ~ ~7~2~
TABLE IV PRIOR ART
.
8Ond Stren~th in Lb/In of Width
Table II To Metal To Plastic
No. Init~alAft r Agin~, InitialAfter Aging
9.48 11.40 >9.48 >11.40
2 15.80 8.21 >15.80 -> 8.21
: - - 3 12 . 0013. 50 9. 39 10. 60
4 14.78 18.26 ->14.78>18.26
,5 17.60 19.49 >17.60>19.49
6 ~10.10 >14.59 10.10 14.59
- . 7 5.9 8.18 >5.9 > 8.1~ i
.8 0 0 0 0
9 17. 50 20. 10 0. 30 0
17 . 46 19 . 23 0 . 88 0
~,.11 I7. 43 18 . 96 ~0 0 45 0
12 1. 10 . ~ >1 . 10 > 0
13 0. 37 0 0
(PSTR side)
13 15.97 17.45>15.97 >17.45 3
~EAA side)
.
!
17, 942-F -43-
s
.~
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7~2
T~BL~ V. THIS INVENTION
Minimum
Table I . 2 Elmendorf Seal Tem-
EY~ampleTens~le (R~ ) Elonyation Tear perat-~re
No. Direction Yiel~ Ulti~ate (Percent) (~ms) _ C
1 MD~96 2~68 580 634 1
CD. 97 2~ 16 555 672 13
2 MD.99 2~ 57 605 525
CD. 95 2 ~ 22 656 717 113
4 MD1. 32 2~ 58 685 307 11
CD1.30 2. 36 685 442 3
MD1. 70 4~65 600 166 110
CD1.80 4 ~ 56 540 150
8 MD1. 38 2~ 82 770 480 104
CD1. 32 2 ~ 58 795 576
9 MD1. 37 2~ 64 775 295 104
CD1. 36 2 ~ 58 755 499
MD1. 41 2~65 695 262 107
CD1. 35 2049 750 486
11 MD1. 32 2~ 60 760 352
CD1. 29 2~ 50 800 538 110
12 MD1. 38 2~ 84 715 - 416 110
CD1. 27 2~ 47 740 589
- TABLE VI. PRIOR ART
Table II
Examyle
i~o.
1 MD1.13 lo90 300 170 110
CD1. 06 1.58 450 190
MDO 74 1~ 79 450 244 10
CD. 71 1~83 560 308 7
Tensile and Elongation: ASTM D~882
~D - l~achine Direction .
CD - Cross ~achine Direction
Elmendorf Tear: ASTM D-1922
17,9~2-F
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17, 942-F _47_
TABLE X. CONNECTOR STABILITY
Table I Resistance in Milliohms(l)
Example No. Initial After Cyclizing(
_ . . _ . .
2 0.6663 1.187
0.6912 1.702
18 0.7353 1.7825
5(3) 0.6750 2.727
Two connectors were attached to 50 mm by 140
mm sample of coated metal; the resistance of
the assembly was measured with a Kelvin
Bridge
2Resistance after 50 -40 to +60C temperature
cycles, each cycle of 8 hours duration
3Example No. 5 from Table II
17,942-F ~48~
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~7~
From the fore~oin~ detailed description, it
can be seen that the present invention pr~vides an
improved corrosion resistant cable shielding tapc for
use as a shield in electrical po~er and communications
cables.
! SpecifiCally, the present inventiOn resides
in an improved corrosion resistant cable shielding tape
comprising a metal strip having a deformation resis-
tant layer of polymeric resinous material tightly
bonded to at least one side thereof, the deformation
j resistant layer having a deformation temperature of at
; least about 130~C. The 5hielding tape must meet both
! the adhesion and deformation resistance requirements
simultaneously to provide satisfactory corrosion pro-
tection to the shieldin~ tapes by restricting the path
of corrosive attack to ~he exposed metal edges.
The deformation resistant layer of pol~eric
resinous material must therefore resist penetration
and/or abrasion exposing the metal strip at the tem-
peratures and pressures normally associated with cable
manu~acturing and/or service use.
The present invention also provides a plastic
coated cable shieldiny tape which includes layers of
polymeric resincus material other than the deformation
resis'ant layer thereby ~ormin~ a multilayered struc-
ture having a combination of desirable ~unctional
characteristics,
17,~ 51
, "~
