Title of Invention

COAXIAL CABLE AND METHOD OF MANUFACTURING THE SAME

Abstract A coaxial cable (10) is provided with a specially prepared precoat layer (16) that facilitates removal of the precoat layer when the end of the cable is cored in preparation for receiving a connector. The cable (10) includes an inner conductor (12); a dielectric layer (14) surrounding the inner conductor; an outer conductor (18) surrounding said dielectric layer; and a precoat layer (16) disposed between the inner conductor (12) and the dielectric layer (14). The precoat layer (14) forms a first bond interface with the inner conductor (12) and a second bond interface with the dielectric layer (14), wherein the ratio of the axial shear strength of the first bond to the axial shear strength of the second bond is less than 1.
Full Text COAXIAL CABLE AND METHOD OF MANUFACTURING THE SAME
BACKGROUND OF THE INVENTION
Coaxial cables commonly used today for transmission of RF signals, such
as television signals, are typically constructed of a metallic inner conductor and a
metallic sheath "coaxially" surrounding the core and serving as an outer conductor.
A dielectric material surrounds the inner conductor and electrically insulates it
from the surrounding metallic sheath. In some types of coaxial cables, air is used
as the dielectric material, and electrically insulating spacers are provided at spaced
locations throughout the length of the cable for holding the inner conductor
coaxially within the surrounding sheath. In other known coaxial cable
constructions, an expanded foamed plastic dielectric surrounds the inner conductor
and fills the spaces between the inner conductor and the surrounding metallic
sheath.
Precoat layers are an integral part of most of these coaxial cable designs.
The precoat is a thin, solid or foamed polymer layer that is extruded or applied in
liquid emulsions over the surface of the inner conductor of the coaxial cable prior
to the application of subsequent expanded foam or solid dielectric insulation
layers. Precoats are usually made up of one or more of the following materials: a
polyolefin, a polyolefin copolymer adhesive, an anti-corrosion additive and fillers.
The precoat layer serves one or more of the following purposes: (1) It allows for a
more controlled surface to be prepared on which to deposit subsequent extruded
dielectric insulation layers. (2) It is used with or without added adhesive
components to promote adhesion of the dielectric material to the center conductor
in order to reduce movement of the center conductor in relation to the surrounding
insulation. Significant movement of this type can cause the center conductor to
pull back out of the grip of a field connector creating an open electrical circuit.
This phenomenon creates a field failure commonly known as a center conductor
"suck out". (3) It is used with or without added adhesive components to promote
adhesion of the precoat layer and subsequent dielectric insulation layers to prevent
dielectric shrink back. (4) It is used to reduce or eliminate water migration paths at
the dielectric/center conductor interface. Water migration into the dielectric of the
coaxial cable has obvious detrimental impacts such as increases in RF attenuation.
Unfortunately, a consequence of the design of currently available precoats
meeting the above criteria is that the precoat layer requires extra steps to remove it
from the center conductor prior to installation of the connector. During field
installation of the coaxial cable, the ends of the cable must be prepared for
receiving a connector that joins the cable to another cable or to a piece of network
electrical equipment, such as an amplifier. The preparation of the cable end is
typically performed using a commercially available coring tool sized to the
diameter of the cable. For coaxial cables having a foam dielectric, the coring tool
has an auger-like bit that drills out a portion of the foam dielectric to leave the
inner conductor and outer conductor exposed. After this "coring" step and just
prior to the installation of the connector, it has been necessary for the installer to
physically remove the precoat layer that remains adhered to the inner conductor.
The prescribed method employs a tool with a nonmetallic "blade" or scraper that
the technician uses to scrape or peel back the precoat layer, removing it from the
conductive metal surface of the inner conductor.
According to the procedures prescribed in the field installation manual
"Broadband Applications and Construction Manual", sections 9.1 and 9.2
published by coaxial cable manufacturer CommScope, Inc., the field technician is
instructed to use a non-metallic tool to clean the center (inner) conductor by
scoring the coating on the center conductor at the shield and scraping it toward the
end of the conductor. The conductor is considered to be properly cleaned if the
copper is bright and shiny. If this step is not properly performed or if this step is
completed with incorrect tools, such as knives or torches, the inner conductor or
other components can be damaged, reducing the electrical and/or mechanical
performance of the cable and reliability of the network.
From the foregoing, it should be evident that the need exists for a coaxial
cable in which the center conductor precoat layer can be more easily removed from
the center conductor, preferably during the coring step, when preparing the cable
for receiving a standard connector.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a coaxial cable with a precoat layer that
serves the important intended functions for standard precoats as described above,
but also allows for easy removal of the precoat during the initial step of cable end
preparation. Specially formulated precoat compositions and/or release agents
along with specialized process settings are used which can facilitate the removal of
the precoat layer during the initial step of end preparation using standard coring
tools. The removal of the precoat during the initial end preparation (coring) step
allows for more efficient connectorization and/or splicing operations in the field,
elimination of the need for any special precoat removal tools, and elimination of a
source of cable damage resulting from craftsmanship issues or improper end
preparation by field technicians.
Precoat components can be selected from homopolymers and copolymers
including, but not limited to: polyethylene homopolymers; amorphous and atactic
polypropylene homopolymers; polyolefin copolymers (including but not limited to
EVA, EAA, EEA, EMA, EMMA, EMAA), styrene copolymers, polyvinyl acetate
(PVAc); polyvinyl alcohol (PVOH); and paraffin waxes. These components may
be used singly or in any combination and proportion of two or more. The
components or mixtures of the components can fall in the class of hot melts,
thermoplastics or thermosets. The precoat layer, depending on chemistry, may be
applied neat, from a solvent carrier, or as an emulsion. Furthermore, an anti-
corrosive additive may be included.
The adhesive properties of the precoat layer may be defined in terms of an
"A" bond and a "B" bond. The "A" bond is the adhesive bond at the interface of
the center conductor and the precoat layer. The "B" bond is the adhesive bond at
the interface of the precoat layer and the surrounding dielectric material. The
chemical properties of the precoat must be such that equilibrium crystallinity
and/or "A" bond strength are rapidly achieved. This is necessary to prevent aging
effects of the precoat from developing a non-strippable bond prior to the use of the
cable. This can be achieved through proper selection of precoat components,
addition of nucleating agents and/or additives that migrate to the interface of the
"A" bond to limit its upper bond strength. A foamable polymer dielectric
composition is then applied over the precoat under conditions that produce a bond
("B" bond) between the precoat and the dielectric.
In achieving the objectives of the present invention, it is important that the
precoat composition has sufficient thickness and continuity so as to block axial
migration of moisture along the inner conductor. Preferably, the precoat
composition is applied to the inner conductor to yield a final thickness of from
0.0001 inch to 0.020 inch.
It is also important that the bond strength of the "A" bond interface and the
"B" bond interface be controlled in such a way that the precoat layer will be
removed completely and cleanly from the inner conductor as a result of the shear
forces applied to the precoat layer when a standard commercially available coaxial
cable coring tool is used to prepare the cable end for receiving a connector. More
particularly, it is important that the axial shear adhesion strength of the bond
interface between the inner conductor and the precoat layer, (i.e. the "A" bond) and
the axial shear adhesive strength of the interface between the precoat layer and the
dielectric, (i.e. the "B" bond), have a ratio less than 1. This will assure that when
the precoat is removed from the inner conductor, the bond failure will occur at the
precoat-inner conductor interface, i.e. the "A" bond, such that no residual precoat
is left on the inner conductor.
Additionally, it is important that the bond formed by the precoat layer
between the inner conductor and the dielectric should have a much lower bond
strength in a direction tangential to the surface of the inner conductor than in the
axial direction of the conductor. This will assure that the precoat "A" bond has
sufficient adhesion strength in the axial direction to perform its intended function
(reduction of movement of the inner conductor in relation to the surrounding
dielectric and elimination of water migration along the center conductor), while it
will still be readily removable from the inner conductor by the tangential peeling
forces that are exerted upon it during coring. In this regard, it is preferred that the
ratio of the axial shear adhesion strength of the bond between the inner conductor
and the precoat layer to the rotational shear adhesion strength of the bond is 5 or
greater, and more desirably 7 or greater.
These objectives are achieved by appropriate selection of the precoat
composition and process conditions as described herein. In one embodiment, the
precoat composition comprises a single polymer component, while in another
embodiment two or more components are compounded or blended into a precoat
composition. The precoat composition can include adhesives, fillers, anti-
corrosion additives, reactants, release agents, crosslinkers, with or without carriers,
solvents or emulsifiers. The precoat composition is then applied to the inner
conductor in a manner that produces a film that adheres to the center conductor
with a final thickness of from 0.0001 inch to 0.020 inch. An insulation compound
is then applied over the precoat resulting in a bond being produced ("B" bond)
between the precoat and the dielectric.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
Having thus described the invention in general terms, reference will now be
made to the accompanying drawings, which are not necessarily drawn to scale, and
wherein:
Figure 1 is a perspective view of a coaxial cable according to one
embodiment of the invention.
Figures 2 A and 2B schematically illustrate a method of making a coaxial
cable corresponding to the embodiment of the invention illustrated in Figure 1.
Figure 3 is schematic illustration of a tensile test apparatus useful for
testing the axial shear force needed to disrupt the adhesive bond between the
precoat and the center conductor.
Figure 4 is schematic illustration of a tensile test apparatus useful for
testing the rotational shear force needed to disrupt the adhesive bond between the
precoat and the center conductor.
DETAILED DESCRIPTION OF THE INVENTION
The present invention now will be described more fully hereinafter with
reference to the accompanying drawings, in which some, but not all embodiments
of the invention are shown. Indeed, the invention may be embodied in many
different forms and should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided so that this disclosure will satisfy
applicable legal requirements. Like numbers refer to like elements throughout.
In accordance with a preferred embodiment of the invention, Figure 1
illustrates a coaxial cable 10 of the type typically used as trunk and distribution
cable for the long distance transmission of RF signals such as cable television
signals, cellular telephone signals, internet, data and the like. Typically, the cable
10 illustrated in Figure 1 has a diameter of from about 0.3 and about 2.0 inches
when used as trunk and distribution cable.
As illustrated in Figure 1, the coaxial cable 10 comprises an inner
conductor 12 of a suitable electrically conductive material and a surrounding
dielectric layer 14. The inner conductor 12 is preferably formed of copper, copper-
clad aluminum, copper-clad steel, or aluminum. In addition, as illustrated in
Figure 1, the conductor 12 is typically a solid conductor. In the embodiment
illustrated in Figure 1, only a single inner conductor 12 is shown, located coaxially
in the center of the cable, as this is the most common arrangement for coaxial
cables of the type used for transmitting RF signals.
A dielectric layer 14 surrounds the center conductor 12. The dielectric
layer 14 is a low loss dielectric formed of a suitable plastic such as polyethylene,
polypropylene or polystyrene. Preferably, to reduce the mass of the dielectric per
unit length and thus the dielectric constant, the dielectric material is an expanded
cellular foam composition, and in particular, a closed cell foam composition is
preferred because of its resistance to moisture transmission. The dielectric layer 14
is preferably a continuous cylindrical wall of expanded foam plastic dielectric
material and is more preferably a foamed polyethylene, e.g., high-density
polyethylene. Although the dielectric layer 14 of the invention generally consists
of a foam material having a generally uniform density, the dielectric layer 14 may
have a gradient or graduated density such that the density of the dielectric increases
radially from the center conductor 12 to the outside surface of the dielectric layer,
either in a continuous or a step-wise fashion. For example, a foam-solid laminate
dielectric can be used wherein the dielectric 14 comprises a low-density foam
dielectric layer surrounded by a solid dielectric layer. These constructions can be
used to enhance the compressive strength and bending properties of the cable and
permit reduced densities as low as 0.10 g/cc along the center conductor 12. The
lower density of the foam dielectric 14 along the center conductor 12 enhances the
velocity of RF signal propagation and reduces signal attenuation.
A thin polymeric precoat layer 16 surrounds the center conductor 12 and
adheres the center conductor to the surrounding dielectric 14. The precoat layer 16
preferably has a thickness of from 0.0001 to 0.020 inches, more desirably from
0.0005 to 0.010 inches, and most desirably from 0.005 to 0.010 inches.
Closely surrounding the dielectric layer 14 is an outer conductor 18. In the
embodiment illustrated in Figure 1, the outer conductor 18 is a tubular metallic
sheath. The outer conductor 18 is formed of a suitable electrically conductive
metal, such as aluminum, an aluminum alloy, copper, or a copper alloy. In the
case of trunk and distribution cable, the outer conductor 18 is both mechanically
and electrically continuous to allow the outer conductor 18 to mechanically and
electrically seal the cable from outside influences as well as to prevent the leakage
of RF radiation. However, the outer conductor 18 or can be perforated to allow
controlled leakage of RF energy for certain specialized radiating cable
applications. In the embodiment illustrated in Figure 1, the outer conductor 18 is
made from a metallic strip that is formed into a tubular configuration with the
opposing side edges butted together, and with the butted edges continuously joined
by a continuous longitudinal weld, indicated at 20. While production of the outer
conductor 18 by longitudinal welding has been illustrated for this embodiment,
persons skilled in the art will recognize that other known methods could be
employed such as extruding a seamless tubular metallic sheath.
The inner surface of the outer conductor 18 is preferably continuously
bonded throughout its length and throughout its circumferential extent to the outer
surface of the dielectric layer 14 by a thin layer of adhesive 22. An optional
protective jacket (not shown) may surround the outer conductor 18. Suitable
compositions for the outer protective jacket include thermoplastic coating materials
such as polyethylene, polyvinyl chloride, polyurethane and rubbers.
Figures 2 A and 2B illustrate one method of making the cable 10 of the
invention illustrated in Figure 1. As illustrated in Figure 2 A, the center conductor
12 is directed from a suitable supply source, such as a reel 50, along a
predetermined path of travel (from left to right in Figure 2 A). The center
conductor 12 is preferably advanced first through a preheater 51, which heats the
conductor to an elevated temperature to remove moisture or other contaminants on
the surface of the conductor and to prepare the conductor for receiving the precoat
layer 16. The preheated conductor then passes through a cross-head extruder 52,
where the polymer precoat composition is extruded onto the surface of conductor
12. The precoat composition is a thermoplastic homopolymer or copolymer
composition selected from the group consisting of polyethylene homopolymer,
amorphous and atactic polypropylene homopolymer, polyolefin copolymers
(including but not limited to EVA, EAA, EEA, EM A, EMMA, EMAA), styrene
copolymers, polyvinyl acetate, polyvinyl alcohol, paraffin waxes, and blends of
two or more of the foregoing. In one exemplary composition, the precoat
composition contains at least 50% by weight of a polyethylene, and may
additionally include one or more copolymers of ethylene with a carboxylic acid,
for example an acrylic or methacrylic acid. When the polyethylene is blended with
one or more such copolymers, the copolymer content is preferably less than 25%
by weight. For example, the precoat composition may contain a blend of at least
50% by weight low density polyethylene, more desirably 75% or greater, with an
ethylene acrylic acid copolymer. The precoat composition may also include one or
more of fillers, anti-corrosion additives, reactants, release agents and crosslinking
agents. The polyethylene polymer component used in the precoat composition
preferably has a melt index (MI) of at least 35 g/10 min. and desirably at least 50
g/10 min. As is well known, the melt index is defined as the amount of a
thermoplastic resin, in grams, which can be forced through an extrusion rheometer
orifice of 0.0825 inch diameter in ten minutes under a force of 2.16 kilogram at
190°C. The high melt index results in the precoat layer having a relatively low tear
strength, which facilitates the peeling or tearing of the precoat material away from
the center conductor during coring. The bond is more frictive or frictional in
nature than adhesive, which provides the needed axial bond strength while
facilitating peeling away from the center conductor. This characteristic is also
enhanced by the relatively low adhesive copolymer content (e.g. the EAA or EMA
copolymer), or absence of such copolymer in the precoat composition. This also
allows for preferential bonding of the precoat layer to the surrounding dielectric (B
bond) material rather than the metallic surface of the center conductor (A bond)
while maintaining the water blocking characteristics of the precoat layer. Some
further illustrative examples of precoat compositions include the following: a 50
MI low density polyethylene resin (LDPE); an 80/20 parts by weight blend of 80
MI LDPE and EMMA copolymer adhesive; 80/20 parts by weight blend of 80 MI
LDPE and EAA copolymer adhesive; a blend of one of the foregoing with up to
5% by weight of a microcrystalline wax.
The precoat layer is allowed to cool and solidify prior to being directed
through a second extruder apparatus 54 that continuously applies a foamable
polymer composition concentrically around the coated center conductor.
Preferably, high-density polyethylene and low-density polyethylene are combined
with nucleating agents in the extruder apparatus 54 to form the polymer melt.
Upon leaving the extruder 54, the foamable polymer composition foams and
expands to form a dielectric layer 14 around the center conductor 12.
In addition to the foamable polymer composition, an adhesive composition
is preferably coextruded with the foamable polymer composition around the foam
dielectric layer 14 to form adhesive layer 22. Extruder apparatus 54 continuously
extrudes the adhesive composition concentrically around the polymer melt to form
an adhesive coated core 56. Although coextrusion of the adhesive composition
with the foamable polymer composition is preferred, other suitable methods such
as spraying, immersion, or extrusion in a separate apparatus can also be used to
apply the adhesive layer 22 to the dielectric layer 14 to form the adhesive coated
core 56. Alternatively, the adhesive layer 22 can be provided on the inner surface
of the outer conductor 18.
After leaving the extruder apparatus 54, the adhesive coated core 56 is
preferably cooled and then collected on a suitable container, such as reel 58, prior
to being advanced to the manufacturing process illustrated in Figure 2B.
Alternatively, the adhesive coated core 56 can be continuously advanced to the
manufacturing process of Figure 2B without being collected on a reel 58.
As illustrated in Figure 2B, the adhesive coated core 56 can be drawn from
reel 58 and further processed to form the coaxial cable 10. A narrow elongate strip
S, preferably formed of aluminum, from a suitable supply source such as reel 60, is
directed around the advancing core 56 and bent into a generally cylindrical form by
guide rolls 62 so as to loosely encircle the core to form a tubular sheath 18.
Opposing longitudinal edges of the strip S can then be moved into abutting relation
and the strip advanced through a welding apparatus 64 that forms a longitudinal
weld 20 by joining the abutting edges of the strip S to form an electrically and
mechanically continuous sheath 18 loosely surrounding the core 56. Once the
sheath 18 is longitudinally welded, the sheath can be formed into an oval
configuration and weld flash scarfed from the sheath as set forth in U.S. Patent No.
5,959,245. Alternatively, or after the scarfing process, the core 56 and surrounding
sheath 18 advance directly through at least one sinking die 66 that sinks the sheath
onto the core 56, thereby causing compression of the dielectric 14. A lubricant is
preferably applied to the surface of the sheath 18 as it advances through the sinking
die 66. An optional outer polymer jacket can then be extruded over the sheath 18.
The thus produced cable 10 can then be collected on a suitable container, such as a
reel 72 for storage and shipment.
In achieving the controlled bond strengths that provide the strippable
properties to the precoat, it is preferable to preheat the inner conductor in preheater
51 to a surface temperature of 75°F to 300°F prior to application of the precoat so
as to promote adhesion between the precoat layer and the surface of the center
conductor 12. Preheat temperatures below this range may not sufficiently heat the
center conductor, thus leaving moisture, oil or other contaminants on its surface.
Such contamination can impede consistent adhesion at the conductor-precoat layer
interface (A bond) and allow moisture migration along the surface of the inner
conductor. Likewise, preheat temperatures above this range may also deter
adhesion by degrading the precoat polymer in contact with the surface of the center
conductor causing the precoat layer to bubble or otherwise lose its consistency.
Between precoat and dielectric applications, it is also important to control
reheating of the center conductor and precoat layer prior to application of the
dielectric. If the coated conductor is reheated at all, reheating temperatures of less
than 200°F should be applied to promote a suitable B bond between these layers.
Heating the precoat and conductor above this temperature prior to application of
the dielectric layer may inhibit the adhesion of the two layers. Overheating at this
stage of the process can degrade the dielectric layer in contact with the precoat by
exposing the dielectric polymer to temperatures above its processing range. Such
resulting degradation and/or voids in the dielectric layer can reduce the B bond
strength and create paths for moisture migration between the precoat and dielectric
layers.
The controlled bond adhesion properties between the A bond interface and
the B bond interface are such that the precoat layer is removed completely and
cleanly from the inner conductor as a result of the shear forces applied to the
precoat layer during preparation of the cable end for receiving a connector using a
standard commercially available coaxial cable coring tool. Examples of
commercially available coaxial cable coring tools include the Cableprep SCT
Series coring tools from CablePrep Inc. of Chester CT, the Cablematic CST series
coring tools from Ripley Company, Cromwell CT, and the Corstrip series of coring
tools from Lemco Tool Corporation of Cogan Station, PA.
These coring tools include cutting edges that exert a combination of
rotational shear and axial shear on the cable core as the tool is rotated relative to
the cable. The coring tool typically comprises a housing having an axially
extending open end adapted for receiving the coaxial cable and a cutting tool
mounted to the housing and extending coaxially toward the opening. The cutting
tool typically includes an auger-like cylindrical coring portion having an outside
diameter sized to be received within the outer conductor of the coaxial cable, an
axially extending bore for receiving the inner conductor of the coaxial cable, and at
least one cutting edge at the end of the coring portion which removes a portion of
the dielectric material as the coring tool enters the end of the cable. In addition to
using standard commercially available coring tools, excellent results can be
observed by using coring tools in which the cutting edges have been specially
configured to promote tearing, rather than slicing, of the dielectric and precoat
layer.
The controlled bond adhesion force properties achieved pursuant to the
present invention can be measured by subjecting coaxial cable test specimens to
standard test methods. For example, the axial and rotational shear adhesion force
of the precoat bond interfaces, i.e. the "A" bond interface and the "B" bond
interface, are measured using a modified test procedure based upon ANSI/SCTE
test method 12 2001 as follows:
TEST FOR DETERMINING THE SHEAR FORCE NEEDED TO DISRUPT
THE ADHESIVE BOND BETWEEN PRECOAT AND CENTER
CONDUCTOR OF TRUNK AND DISTRIBUTION COAXIAL CABLES
1.0 Scope
1.1 This test is used to determine the shear force needed to disrupt the
adhesive bond between a coaxial cable center conductor and the
dielectric or precoat layer for Trunk and Distribution cables with
solid tubular outer conductors. The shear force of bond disruption
is determined in both axial (translational) and rotational modes.
2.0 Equipment
2.1 Tubing cutter.
2.2 Utility knife or other sharp knife.
2.3 Saw capable of cutting through outer conductor in the linear
direction without damage to the center conductor (Dremel tool,
etc.).
2.4 Ruler marked in at least 1/32"" gradations.
2.5 Tensile tester (Instron 446Xseries or Sintech 5Xor equivalent).
2.6 Center conductor/precoat bond pull out fixture as illustrated in
Figure 3 and described in ANSI/SCTE 12 2001.
2.7 Center conductor/precoat rotational bond tester fixture as illustrated
in Figure 4. Instruments such as Pharmatron TM-200 and Vibrac
Torqo 1502 or their functional equivalent are acceptable.
3.0 Sample Preparation
3.1 Obtain cable samples of 10-12 inches in length.
3.2 Remove outer j acket if present.
3.3 Measuring from one end, mark the sample on the outer conductor at
1 and 2 inches.
3.4 Using the tubing cutter, cut through the outer shield to a depth of no
more than 1/16 inch at each mark.
3.5 Cut through the remaining dielectric at the above cuts taking care
not to score or damage the center conductor.
3.6 Cut through the outer conductor along the axis of the center
conductor on the entire sample length except for the section
between 1 and 2 inches. Remove the outer conductor and dielectric
from either side of the 1 inch long test sample without disturbing or
damaging the test sample or center conductor.
4.0 Test Method
4.1 Axial test
4.1.1 Attach the center conductor bond pull out fixture to the
tensile tester.
4.1.2 Select a center conductor insert 3.0 ±1.0 mils larger than the
center conductor diameter and slide it onto the long stripped
portion of the test sample, larger OD end first.
4.1.3 Place sample and insert into the test fixture and fasten the
long end of the center conductor to the tensile tester.
4.1.4 Set the tensile tester to run at a rate of 2.0 inches/minute and
begin the test.
4.1.5 Continue the test until the bond to the center conductor has
been broken and record the maximum load (in pounds)
observed during the test.
4.1.6 Repeat the test for a minimum of six specimens.
4.2 Rotational test
4.2.1 Insert the sample into the rotational bond tester using the
appropriate fixtures.
4.2.2 Set the tester to rotate at a rate of 1 rpm and begin the test.
4.2.3 Continue the test until the dielectric/precoat breaks free from
the center conductor or the center conductor fails.
4.2.4 Record the maximum torque in inch-pounds observed during
the test and note whether the bond or center conductor
failed.
4.2.5 Repeat the test for a minimum of six specimens.
5.0 Data analysis
5.1 Calculate and report the average load and standard deviation for
each sample and report these results along with the sample name,
description, outer conductor and center conductor dimensions and
any other special notes deemed pertinent.
The axial shear strength of the bond interface between the precoat layer and
the center conductor, i.e. the "A" bond, and the strength of the bond interface
between the precoat layer and the dielectric layer, i.e. the "B" bond, are measured
according to a modified ANSI/SCTE test method 12 2001 (formerly IPS-TP-102),
"Test method for Center Conductor Bond to Dielectric for Trunk, Feeder, and
Distribution Coaxial Cables, with the following modification. The fixture has a
hole for center conductor insertion that is a minimum of 25% larger than the outer
diameter of the combined center conductor and precoat layer. If the precoat layer
strips cleanly from the center conductor without leaving portions thereof adhered
to the center conductor, then it can be concluded that the ratio of the axial shear
strength of the first bond interface ("A") bond to the axial shear strength of the
second bond interface ("B") is less than 1. If the precoat layer remains adhered to
the center conductor, then it can be concluded that the shear strength ratio is
greater than 1. Likewise, if dielectric material remains adhered to the precoat
layer, it can be concluded that the shear strength ratio is greater than 1, and that
failure occurred in the dielectric and not at the precoat bond interface.
The rotational shear strength of the bond interface between the precoat
layer and the center conductor, i.e. the "A" bond, and the rotational shear strength
of the bond interface between the precoat layer and the dielectric layer, i.e. the "B"
bond, are measured using the rotational test procedure described above. The ratio
of the rotational shear strength of the "A" bond interface to that of the "B" bond
interface should also be less than 1 if the precoat layer is to strip cleanly from the
conductor under the rotational (or tangential) shear forces exerted by the coring
tool. This is verified by examining the condition of the test specimen after
performing the test. If the precoat layer strips cleanly from the center conductor
without leaving portions thereof adhered to the center conductor, then it can be
concluded that the ratio of the axial shear strength of the first bond interface ("A")
bond to the axial shear strength of the second bond interface ("B") is less than 1. If
the precoat layer remains adhered to the center conductor, then it can be concluded
that the shear strength ratio is greater than 1. If dielectric material remains adhered
to the precoat layer, it can be concluded that the shear strength ratio is greater than
1, and that failure occurred in the dielectric and not at the precoat bond interface.
It is also preferred that the bond adhesion forces be controlled so that when
failure occurs at the center conductor-precoat bond interface, i.e. the "A" bond, the
axial shear adhesion force is greater than the rotational shear adhesion force. The
ratio of the axial shear adhesion force of the "A" bond to the rotational shear
adhesion force of the "A" bond is determined by dividing mean value for the axial
shear adhesion force (in pounds) by the mean value of the rotational shear adhesion
torque force (in inch-pounds). Preferably, the ratio of the axial shear adhesion
force of the "A" bond formed by the precoat layer between the inner conductor to
the dielectric layer to the rotational shear adhesion force of the "A" bond is 5 or
greater, and more desirably 7 or greater. These values can be measured using the
test procedure described above for samples in which failure occurs at the "A" bond
interface, that is, samples with the requisite ratio of "A" bond strength to "B" bond
strength of less than 1.
The present invention will now be further described by the following non-
limiting example. All percentages are on a per weight basis unless otherwise
indicated.
EXAMPLE
A precoat composition was formulated by compounding the following
constituents:
97.5% of a 80 MI low density polyethylene
2.5% of a 5.5 MI ethylene acrylic acid copolymer (6.5% acrylic
acid content)
This composition was applied to copper-clad aluminum conductors of a
diameter ranging from 0.1085 to 0.2025 inch in accordance with the following
procedures and conditions: The center conductor was preheated to 125°F. The
composition was applied in a controlled thickness using a polymer extrusion
process. The thickness of the application was controlled to a nominal average
thickness of 0.008 inches. This structure allowed to cool to near ambient
temperature and was then passed through a foaming polymer extrusion process to
apply a closed cell foam polyethylene dielectric layer.
The specimens were tested by the test procedures described above to
determine the shear force needed to disrupt the bond in both the axial and
rotational modes, and the results are given in the following table.

Many modifications and other embodiments of the inventions set forth
herein will come to mind to one skilled in the art to which these inventions pertain
having the benefit of the teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is to be understood that the inventions are not to
be limited to the specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the appended claims.
Although specific terms are employed herein, they are used in a generic and
descriptive sense only and not for purposes of limitation.
WE CLAIM:
1. A coaxial cable (10) comprising: an inner conductor; a dielectric layer (14)
surrounding said inner conductor (12), an outer conductor (18) surrounding said
dielectric layer (14), and a precoat layer (16) disposed between said inner conductor
(12) and said dielectric layer (14), said precoat layer (16) forming a first bond interface
("A" bond) with the inner conductor (12) and a second bond interface ("B" bond) with
the dielectric layer (14), the precoat layer (16) being of sufficient thickness and
continuity as to block axial migration of moisture along the inner conductor (12), and
wherein the ratio of the axial shear strength of the first ("A") bond to the axial shear
strength of the second ("B") bond is less than 1 such that the precoat layer (16) is
removed completely and cleanly from the inner conductor (12) as a result of the shear
forces applied to the precoat layer (16) during preparation of the cable end for receiving
a connector using a standard commercially available coaxial cable (10) coring tool.
2. The coaxial cable as claimed in claim 1, wherein the precoat layer has a
thickness of from 0.0001 to 0.020 inch.
3. The coaxial cable as claimed in claim 1, wherein the ratio of the axial shear
adhesion force of the "A" bond to the rotational shear adhesion force of the "A" bond is
5 or greater.
4. The coaxial cable as claimed in claim 3, wherein the ratio of the axial shear
adhesion force of the "A" bond to the rotational shear adhesion force of the "A" bond is
7 or greater.
5. The coaxial cable as claimed in claim 1, wherein the dielectric layer comprises a
closed cell polyolefin foam, and the precoat layer is a polyethylene composition.
6. The coaxial cable as claimed in claim 1, wherein the precoat layer is a
homopolymer or copolymer composition selected from the group consisting of
polyethylene homopolymer, amorphous and atactic polypropylene homopolymer,
polyolefin copolymer, styrene copolymer, polyvinyl acetate, polyvinyl alcohol, paraffin
waxes, and blends of two or more of the foregoing.
7. The coaxial cable as claimed in claim 6, wherein the precoat layer additionally
comprises one or more of fillers, anti-corrosion additives, reactants, release agents and
crosslinking agents.
8. The coaxial-cable as claimed in claim 6, wherein the precoat layer comprises a
blend of low density polyethylene and ethylene acrylic acid copolymer.
9. The coaxial cable as claimed in claims 6, wherein the low density polyethylene
has a melt index of at least 50 g/10 minutes.
10. The coaxial cable as claimed in any preceding claim, wherein the dielectric layer
is a closed cell foam polyolefin and said precoat layer comprises a thermoplastic
polymer composition comprising a blend of low density polyethylene having a melt
index of at least 35 g/10 min. and ethylene acrylic acid copolymer, and wherein the ratio
of the rotational shear adhesive force of the first ("A") bond to the rotational shear force
of the second ('B") bond is less than 1.
11. A method of manufacturing a coaxial cable (10) comprising:
directing a conductor along a predetermined path of travel into and through a
preheater and preheating the conductor to a surface temperature of 75° F. to 300° F,
melting in a first extruder a thermoplastic polymer precoat composition
comprising a blend of low density polyethylene having a melt index of at least 50 g/10
min and ethylene acrylic acid copolymer,
directing the preheated conductor into and through the fist extruder and
extruding onto the surface of the center conductor a continuous coating layer of the
molten precoat composition with a thickness of from 0.0001 to 0.020 inch,
allowing the layer of precoat composition to cool and solidify forming a first bond
interface ("A" bond) with the inner conductor,
optionally reheating the conductor and layer of precoat composition to a
temperature of no more than 200°F.,
directing the conductor and layer of precoat composition into and through a
second extruder and extruding onto the coated conductor a foamable polyolefin polymer
composition,
allowing the foamable polymer composition to expand, cool and solidify to form a
closed cell polyolefin foam dielectric surrounding the conductor with a second bond
interface ("B" bond) between the layer of precoat composition and the dielectric,
surrounding the foam dielectric with a continuous metallic sheath forming the
outer conductor of the coaxial cable, and
controlling the bond adhesion forces at the first and second bond interfaces so that
the ratio of the axial shear strength of the first ("A") bond to the axial shear strength of the
second ("B") bond is less than 1.
12. The method as claimed in claim 11, which involves also controlling the bond
adhesion forces so that the ratio of the rotational shear strength of the first ("A") bond to
the rotational shear strength of the second ("B")bond is less than 1.
13. The method cable as claimed in claim 11, which involves also controlling the
bond adhesion forces so that the ratio of the axial shear adhesion force of the "A" bond to
the rotational shear adhesion force of the "A" bond is 5 or greater.

Documents:

00862-kolnp-2006-abstract.pdf

00862-kolnp-2006-assignment.pdf

00862-kolnp-2006-claims.pdf

00862-kolnp-2006-correspondence other.pdf

00862-kolnp-2006-description complete.pdf

00862-kolnp-2006-drawings.pdf

00862-kolnp-2006-form-1.pdf

00862-kolnp-2006-form-3.pdf

00862-kolnp-2006-form-5.pdf

00862-kolnp-2006-international publication.pdf

00862-kolnp-2006-international search authority report.pdf

00862-kolnp-2006-pct form.pdf

00862-kolnp-2006-priority document.pdf

862-KOLNP-2006-ABSTRACT-1.1.pdf

862-KOLNP-2006-AMENDED DOCUMENT-1.1.pdf

862-KOLNP-2006-AMENDED PAGES.pdf

862-KOLNP-2006-CANCELLED PAGES.pdf

862-KOLNP-2006-CLAIMS-1.1.pdf

862-KOLNP-2006-CORRESPONDENCE 1.1.pdf

862-kolnp-2006-correspondence 1.3.pdf

862-KOLNP-2006-CORRESPONDENCE-1.2.pdf

862-KOLNP-2006-DESCRIPTION (COMPLETE)-1.1.pdf

862-KOLNP-2006-DRAWINGS-1.1.pdf

862-kolnp-2006-examination report 1.1.pdf

862-KOLNP-2006-FORM 1-1.1.pdf

862-kolnp-2006-form 18 1.1.pdf

862-kolnp-2006-form 3 1.1.pdf

862-KOLNP-2006-FORM 3.1.pdf

862-kolnp-2006-form 5 1.2.pdf

862-kolnp-2006-gpa 1.1.pdf

862-kolnp-2006-granted-abstract.pdf

862-kolnp-2006-granted-claims.pdf

862-kolnp-2006-granted-description (complete).pdf

862-kolnp-2006-granted-drawings.pdf

862-kolnp-2006-granted-form 1.pdf

862-kolnp-2006-granted-specification.pdf

862-KOLNP-2006-OTHERS 1.1.pdf

862-kolnp-2006-others 1.2.pdf

862-KOLNP-2006-OTHERS-1.1.pdf

862-KOLNP-2006-OTHERS.pdf

862-KOLNP-2006-PETITION UNDER RULE 137.pdf

862-KOLNP-2006-REPLY F.E.R.pdf

862-kolnp-2006-reply to examination report 1.1.pdf

862-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

abstract-00862-kolnp-2006.jpg


Patent Number 246889
Indian Patent Application Number 862/KOLNP/2006
PG Journal Number 12/2011
Publication Date 25-Mar-2011
Grant Date 21-Mar-2011
Date of Filing 07-Apr-2006
Name of Patentee COMMSCOPE, INC. OF NORTH CAROLINA
Applicant Address P.O. BOX 339, 1100 COMMSCOPE PLACE, HICKORY, NC
Inventors:
# Inventor's Name Inventor's Address
1 GIALENIOS, MICHAEL, DAMON 4103 HALLAMCOURT, CHARLOTTE, NC 28269
2 MCDANIEL, DONALD, ROGER, II 8634 COOKSVILLE ROAD, VALE, NC 28168
3 MINTON, RANDY, JAMES 851 RIDGE DRIVE, NEWTON, NC 28658
PCT International Classification Number H01B 13/016
PCT International Application Number PCT/US2004/028441
PCT International Filing date 2004-09-01
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/503,384 2003-09-16 U.S.A.
2 60/524,980 2003-11-25 U.S.A.