U.S. patent number 3,904,541 [Application Number 05/379,153] was granted by the patent office on 1975-09-09 for transmission cable filling compound.
This patent grant is currently assigned to Hexcel Corporation. Invention is credited to John R. Charlton.
United States Patent |
3,904,541 |
Charlton |
September 9, 1975 |
Transmission cable filling compound
Abstract
Communication transmission cable, method of protecting a
transmission cable, and composition for such method are provided,
whereby a cable filling composition for transmission cable is
employed which is a combination of a low molecular weight
polymerization product of a C.sub.4 1-olefin and an insoluble,
substantially inert powdered resin, which is either naturally
occurring or synthetic cellulosic material, an addition polymer
which is hydrocarbon or substituted hydrocarbon, or a condensation
polymer. The product has good rheological properties, low
dielectric constant, and low dissipation factor, while having no
detrimental effect on the other materials present in the
transmission cable.
Inventors: |
Charlton; John R. (Scarborough,
CA) |
Assignee: |
Hexcel Corporation (Dublin,
CA)
|
Family
ID: |
23496036 |
Appl.
No.: |
05/379,153 |
Filed: |
July 13, 1973 |
Current U.S.
Class: |
174/25C; 174/23C;
252/572; 156/48; 174/110PM; 585/6.3 |
Current CPC
Class: |
H01B
7/285 (20130101); H01B 3/441 (20130101) |
Current International
Class: |
H01B
7/285 (20060101); H01B 3/44 (20060101); H01B
7/17 (20060101); H01B 003/00 () |
Field of
Search: |
;252/63.2,64,65,66
;156/48 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Blum; T. M.
Claims
What is claimed is:
1. In a communication transmission cable, having a plurality of
conducting wires and an outer sheath,
the improvement which comprises having the voids between the
conducting wires and the outer sheath filled with a composition
having 10 to 50 parts by weight of a polybutene polymer having a
viscosity at 20.degree.C in the range of 500-20,000 S.U.S. and from
90 to 50 parts by weight of an inert, polybutene insoluble
polymeric powder having a dielectric constant of less than 5 and a
softening temperature above about 150.degree.F, wherein said
insoluble polymeric powder is selected from the group consisting of
cellulosic materials and addition polymers of ethylene, propylene,
vinyl acetate and vinyl chloride.
2. In a transmission cable, according to claim 1, wherein said
composition has from about 20 to 50 parts by weight of said
polybutene resin and from 80 to 50 parts by weight of said powder,
and wherein said powder is of an average size in the range of 5 to
100 microns.
3. In a transmission cable according to claim 1, wherein said
powder is an addition polymer of ethylene, propylene, vinyl
acetate, vinyl chloride or copolymers thereof having a particle
size in the range of 10 to 50 microns.
4. In a transmission cable according to claim 1, wherein said
powder is a cellulosic material having a particle size in the range
of 10 to 50 microns.
5. A composition useful as a filler in communication transmission
cables comprising from 10 to 50 parts of a polybutene resin having
a viscosity in the range of 500-20,000 S.U.S. at 20.degree.C and
from 50 to 90 parts by weight of an inert polymeric powder of from
5 to 100 microns mesh size having a softening temperature above
150.degree.F and a dielectric constant below about 5, wherein said
polymeric powder is selected from the group consisting of
cellulosic materials and addition polymers of ethylene, propylene,
vinyl acetate and vinyl chloride.
6. A composition according to claim 5, wherein said powder is of a
size in the range of 10 to 50 microns and is an addition polymer of
ethylene, propylene, vinyl chloride or vinyl acetate and copolymers
thereof.
7. A composition according to claim 5, wherein said powder is of a
size in the range of 10 to 50 microns and is a cellulosic
material.
8. A method for protecting a communications transmission cable from
internal corrosion which comprises:
introducing into said cable so as to substantially fill all the
voids in said cable, a composition according to claim 5.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
In the manufacture of transmission cables for communication, it is
customary to enclose insulated metal conductors within an outer
sheath to provide protection to the conductors. The conductors
which are usually copper wires insulated with polyethylene,
polyvinyl chloride, impregnated paper or other insulating material
are encompassed in an outer sheath which is usually a metal-plastic
composite structure, where the metal is most commonly aluminum, but
steel and copper are also employed.
An outer protective layer is then applied to the composite sheath,
to protect the composite sheath from the corrosive effect of ground
waters as well as other agents with which the sheath may come in
contact. The outer protective layer is commonly polyethylene, but
polyvinyl chloride also finds use.
Because the conductors are round, when a plurality of conductors
are bound together and enclosed in the sheath, voids inherently
exist. Where the voids are filled with moisture containing air,
internal corrosion of the cable may occur with reduced
effectiveness of the insulated conductor wires. A number of
different ways have been devised in order to minimize or eliminate
the potential internal corrosion.
2. Description of the Prior Art
One method of inhibiting internal corrosion from moisture-laden air
is to fill the cable with a dry inert gas under pressure. However,
this method is costly, since the entire cable must be maintained
under pressure and a source for the inert gas is necessary
throughout the length of the installed cable. When the cables are
broken or when connections must be made, the cable must be
repressurized each time and constant monitoring for leaks is
essential.
An alternative method which may be employed is the use of a filler
composition which fills the voids between the conductor wires and
the sheath, eliminating the presence of water. Materials commonly
employed today include low molecular weight polyethylene resins
combined with waxes. A typical formulation includes 85% paraffin
wax, microcrystalline waxes and petrolatum and 15% of a
polyethylene resin e.g. Union Carbide polyethylene resin DYLP. In
addition to the above composition, anti-oxidants may be included as
well as isobutylene resins to improve the rheological properties of
the composition and enhance flexibility at room temperature.
The filling compounds based on wax show poor flexibility at low
temperatures and at 20.degree.F or below, transmission cable laying
becomes difficult and uneconomic.
SUMMARY OF THE INVENTION
An improved transmission cable for communications and transmission
cable filler composition are provided. The improved communication
transmission cable is filled, so as to substantially remove any
voids or gas pockets. The filler composition contains a significant
amount of a low molecular weight C.sub.4 1-olefin polymer and a
powdered substantially insoluble low dielectric constant resin
powder. The resin will usually be a natural or synthetic cellulosic
material, an addition polymer which is hydrocarbon or alternately
substituted along the backbone of the polymer with a chloro or
acetoxy group, or a cured condensation polymer employing
formaldehyde in combination with urea or phenol. The resulting
compositions have good rheological properties, low dielectric
constants, acceptable dissipation factors and are substantially
inert to the other materials commonly employed in communication
transmission cables.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Transmission cables are provided having new filler compositions to
fill the voids between the conductor and the outer sheath. The
filler compositions comprise a low molecular weight polybutene
polymer and a substantially inert polybutene insoluble polymeric
powder, either naturally occurring or synthetic. The polybutene
will be present in from about 10-50 parts by weight, while the
insoluble powder will be present in from about 50-90 parts by
weight. Usually, the polybutene will be employed in 20-50 parts to
50-80 parts of the powdered resin. Normally, the parts by weight of
the two major components will add up to 100 parts. Other materials
may also be present in minor amount, such as conventional
anti-oxidants, colorants, stabilizers, and the like.
The individual materials will now be considered. The first material
is the polybutene, which is a 4 carbon atom 1-olefin, i.e. 1-butene
or isobutylene polymer. The polymer may have a broad or narrow
range molecular weight profile and will normally have a viscosity
in the range of 500-20,000 S.U.S. (Saybolt Universal Seconds) at
20.degree.C. The viscosity can be achieved by using mixtures of
polybutene polymers having various viscosity ranges, preferably at
least 60%, more usually at least 80% by weight of the polymer
fractions being within the range indicated.
The polymeric powdered material employed is a stable, inert solid
polymer which is substantially insoluble in the polybutene. The
material will have a dielectric constant, when measured at 1,000 hz
at 20.degree.C, of less than about 5, preferably less than about 4,
and particularly preferred, less than about 3. When combined with
the polybutene resin, it is preferred that the final composition
have a dielectric constant of less than about 4, and preferably
less than about 3.
The final product should have a dissipation factor (ASTM Method D
9-4) of less than about 0.05 per cent at 100.degree.C.
The materials which find use fall into three categories:
cellulosic, natural and synthetic; addition polymers; and
formaldehyde condensation polymers. These materials are employed as
powders, generally from about 5 to 100 microns average mesh size
more usually of from about 10 to 50 microns average mesh size. The
mesh size will vary in accordance with the desired flow
characteristics and melting properties of the final composition,
with the smaller particles providing greater reduction of the flow
of the final composition. Therefore, smaller particles would
generally be employed with the lower viscosity polybutene.
The first resin material to be considered will be the cellulosic
powders. These cellulosic powders include synthetic cellulose, such
as cellulose ethers having alkyl groups of from 1 to 3 carbon
atoms, e.g. methyl cellulose, ethyl cellulose and propyl cellulose;
and cellulose esters, wherein the carboxcylic acid group is of from
2 to 3 carbon atoms, e.g. cellulose acetate and cellulose
propionate. The naturally occurring cellulose sources include such
materials as wood flour and ground nut shells, such as walnut
flour, pecan flour, and the like.
The addition polymers are polymers of monomers of from 2 to 4
carbon atoms and may be hydrocarbon or have halogen or acetate
groups. The polymers will be of the following formula: ##EQU1##
wherein n is the number of monomeric groups in the polymer, X is
hydrogen, methyl, chloro, or acetoxy, and the X's in the polymer
may be the same or different; and Y and Z are end groups depending
on the method of polymerization.
The hydrocarbon polymers, i.e., polyethylene and polypropylene or
copolymers thereof will have melt points greater than 150.degree.F.
The non-hydrocarbon polymers, polyvinyl chloride, polyvinyl
acetate, and copolymers thereof may have the vinyl chloride or
vinyl acetate in any proportion.
Finally, the formaldehyde condensation polymer will be a cured
polymer employing phenol-formaldehyde or urea-formaldehyde.
The subject compositions can be readily prepared by combining the
polybutene resin with the inert powder and mixing the material
until homogeneity is achieved. These compositions are then
introduced into the cable to at least substantially fill all voids
in the cable so as to minimize or eliminate the presence of any
moisture containing gas.
A composition was prepared employing Indopol polybutylene H100, 100
parts by weight (35,944 S.U.S. at 100.degree.F) and polyethylene,
Union Carbide resin DKPQ, 100 parts. To this mixture was added
Indopol polybutene L50 (107 S.U.S. at 100.degree.F) 10 parts by
weight, to adjust the mixture to the desired viscosity. The
polyethylene powder could be replaced by the other powders to
obtain the desired filler composition.
The subject compositions are found to retain the desired
flexibility at temperatures as low as -40.degree.F. Furthermore,
the compositions retain flexibility properties and mechanical
properties as high as 150.degree.F, so that filler composition is
not lost by flowing out of the ends of the cable and the filler
composition protects the cable by retaining sufficient
rigidity.
Furthermore, relatively constant rheological properties are
maintained in the temperature range -40.degree.F to +150.degree.F.
The dielectric constant of the subject compositions are less than
about 3, have satisfactory insulation constants, acceptable
dissipation factors and are unreactive or inert toward the
insulation materials customly employed on the conductor wire and in
the outer sheath.
Although the foregoing invention has been described in some detail
by way of illustration and example for purposes of clarity of
understanding, it will be obvious that certain changes and
modifications may be practiced within the scope of the appended
claims.
* * * * *