EP0037611A1

EP0037611A1 - Foamed cable filler and cable containing such filler

Info

Publication number: EP0037611A1
Application number: EP81200373A
Authority: EP
Inventors: Johannis Doorn
Original assignee: Witco Chemical Corp
Current assignee: Witco Corp
Priority date: 1980-04-07
Filing date: 1981-04-03
Publication date: 1981-10-14
Also published as: JPS56156613A

Abstract

A filler for a telecommunication cable (1) comprising a foamed petrolatum (4) or petroleum jelly is disclosed. The cell structure is closed-cell and provides a light-weight cable filler with good electrical insulation properties, particularly a low dielectric constant. The foam exhibits a cup weight of about 60 to 135 gm/200 mls. The foamed petrolatum may be stabilized with a polymeric stabilizerto ensure integrity of the foam.

Description

FIELD OF USE OF THE INVENTION

This invention relates to telecommunication cables of the kind comprising a multiplicity of plastic-insulated conductors enclosed within a water-proof sheath. More specifically, this invention relates to a filler to be contained between the conductors within the sheath.

BACKGROUND AND DISCUSSION OF PRIOR ART

An electrical or communications cable is comprised of a great number of pairs of single conductive wires. Each of these singles is coated with a dielectric material to insulate them all individually from one another. A large number of these singles are then collected into a bundle which is the cable. The cable is coated on the outside within a sheath of a dielectric material to make an integral structure.
As is to be expected, collecting a plurality of round wires inta a cable results in a large volume of unoccupied space between wires. In the normal. course of things this. is simply "dead space" which becomes filled with air. In many applications this is satisfactory since air is an excellent dielectric. However, when the cable is intended to be installed underground, this type cable is usually not satisfactory. The reason for this is that an underground cable is frequently in contact with water. If a flaw develops in the outer sheath, water can leak into the dead space in the cable and this can eventually lead to trouble such as, e.g., shorting of a pair of wires.
In order to keep water out of these cables in underground installations, it has become common practice to fill the cable with an inexpensive liquid or low-melting solid dielectric.
It was known in the prior art to employ petrolatum or petroleum jelly as a filler. However, the use of petrolatums alone was not found to be entirely satisfactory and the prior art sought to chemically modify the petrolatum.
Eager et al, U. S. 3,745,231, granted July 10, 1973, disclosed a combination of petrolatum and polyethylene filler. Zinser et al, U. S. 3,775,548, granted November 27, 1973, disclosed adding polyethylene, polybutene -1 and polyisobutylene to the petroleum jelly filler. Woodland et al, U. S. 3,843,568, granted October 22, 1974, disclosed blending a petrolatum with a partially cross-linked polymer, in further combination with hollow particles of a synthetic thermoplastic polymer.
Other cable manufacturers were directed to using · thermoplastic foam in combination with a petrolatum. Wodike, U. S. 2,186,793, granted January 9, 1940, disclosed foamed rubber insulation with a minor percentage of petrolatum. Boult, U. S. 3,706,838, granted December 19, 1972, combined cellular polyethylene with petroleum jelly. Puckowski et _'al, U. S. 3,856,980, disclosed a cellular foam with a hydrocarbon wax. Reighter, U. S. 3,684,816, granted August 15, 1972, disclosed an open-cell foam with a liquid dielectric.
Thus, the prior art sought to limit the total amount of the petrolatum in the filler, and used principally foamed plastic materials in this regard. Such combinations were often difficult and costly to fabricate, and the industry is desirous of an improvement thereto.
It was also known, such as is disclosed in U. S. 3,060,136, granted October 23, 1962, to Nelson et al, that _. certain waxes could be foamed.
Now there is recognized by the present invention an acceptable cable filler which utilizes substantially all petrolatum or petroleum jelly but in a foamed condition.
It is a principal object of this invention to produce a low density filler for cables.
It is therefore a principal object of this invention to provide a foamed petrolatum as a cable filler.
It is another object of this invention to provide a cable filler with a low dielectric constant.
It is another object of this invention to provide a low materials cost cable filler.
It is another object of this invention to provide a readily fabricated filled cable, and yet one which is practical in commercial application.
The aforesaid as well as other objects and advantages as well become apparent in the following specification, and the adjoined claims, and the drawings, in which:

FIG. 1 is a perspective view of a filled cable of this invention; and
FIG. 2 is an enlarged sectional view 2-2 of the cable of FIG. 1.

The terms "petrolatum" or "petroleum jelly" as used hereinbefore and hereinafter shall be construed as being synonymous and includes hydrocarbons of about C₁₆ up to about C₅₀.
Broadly speaking the present invention comprises a cable and cable filler which comprises a foamed petrolatum or petroleum jelly. The foamed petrolatum exhibits excellent properties and characteristics particularly, low density, good dielectric, low cost, good stability, and improved flexibility in a cable.
It has surprisingly been found that a petrolatum when foamed provides a better cable filler material than petrolatums used heretofore. Furthermore, the bulk weight of the filler is reduced with a concommitant reduction in savings in cable costs.
Referring to FIGS. 1 and 2 there is shown the cable of this present invention generally designated as 1. Cable 1 comprises an outer sheath 2 containing a plurality of individual conductors 3; each of said conductors 3 comprises a wire 6 being covered with an insulator 5. The foamed petrolatum filler 4 of this present invention fills the interstices between the several conductors 3.. A metal core wrap 7, which is impervious to the petrolatum retains the conductors 3 and filler 4 in a fixed manner.
The filler 4 is shown with a plurality of closed celled voids 8, although in actuality the voids may be microscopic in nature, and therefore not necessarily visible to the naked eye.
It has also been found that to ensure and stabilize the structural integrity of the foamed petrolatum, hydrocarbon polymeric materials of a molecular weight of at least that within the wax range may be added to the petrolatum. Suitable hydrocarbon polymeric materials include the microcrystalline waxes; Fischer-Tropsch waxes; polyolefins (e.g. polyethylene, m.w.=2,000-15,000); polyisobutylene (m.w.=100,000-200,000) and the like. The molecular weight (m.w.) of the polymeric stabilizer may be from 2,000 to 200,000 and preferably 5,000 to 100,000. Other high molecular weight stabilizers are also within the contemplation of the invention.
One preferred stabilizer is a polyisobutylene-wax mixture of normal slack wax as obtained from medium neutral oil or bright stock oil, and a polyisobutylene in a m.w. range of 100,000 to 200,000. The polymeric stabilizer can be present effectively in amounts of as little as 0.01 to about 25 weight percent based on the weight of the unfoamed petrolatum. Although up to about 25 weight percent can be employed in the present composition, concentrations in the range of about 0.1 to 0.3 weight percent are generally sufficient and are preferred.
It is important to note that the presence of the limited measured proportions of the high polymeric stabilizers provides a structurally intact petrolatum or petroleum jelly foam which absent such stabilizers would not necessarily be the case.
The specifications for a typical petrolatum compound which can be foamed is as shown in Table I.
Certain specific petrolatums have been found to be useful pursuant to this invention and are set forth in Table I above.
The following examples illustrate the present invention.

EXAMPLE I

A petrolatum having the properties of Table I with a melting point of 78°C min., was subjected to foaming in an Oates Foaming Machine having the following settings:

Back pressure - 85 psi
Temperature - 88°C
Air - 6 psi
Line pressure - 100 psi
Rotor - 380
Pump - 380
Valve setting - 5 threads (approx.)
Hose Length - 19 feet, constructing valve to discharge.

In an operating period of 25 minutes, a consistent foam was produced having a cupweight of 96 grams (200 ml. cup, tare weight of 6 gm.), which converts into almost a 1:1 air/petrolatum ratio.
A second operating run at the same machine settings produced a foam with cup weights of 110 to 120 grams.
In operating the Oates Foaming Machine, the back pressure should be maintained in order to prevent "blow by", and the viscosity is maintained by cooling the material during foam formations.

EXAMPLE II

A petrolatum as in Example I was foamed in an Oates Foaming Machine having the following settings:

Back pressure - 15 psi
Temperature - 80°C
Air - 14-15 psi
Pump - 400 psi
Rotor - 250

The foam cup weight was 119 grams per 200 ml. cup (sp.gr. 0.6). The foam had a microscopic closed-cell structure.

EXAMPLE I_II

A petrolatum as in Table I having a melting point less than that of Examples I and II was foamed in the machine having the following settings:

Back pressure.- 15 psi
Temperature - 60°C initially (38°-40°C)
Air - 15 psi
Pump - 400 psi
Rotor - 250

The foam cup weight was relatively high at 150-165 gm/200 ml the foam had a microscopic closed-cell structure.

EXAMPLE IV

Example III was repeated except that 0.1% wax-polyisobutylene mixture was added to the petrolatum, and the back pressure increased to 36 psi.
The foamed product had a microscopic cell structure and a cup weight of 129 gms. per 200 ml.

EXAMPLE V

The foamed products of Examples II, III and IV were injection molded into a braided hose and allowed to set.

EXAMPLE VI

A petrolatum as in Example I was foamed in the aforedescribed manner (with assurance that the mixing head was cooled) both with and without a polymeric stabilizer as follows:
The foamed products of Samples 1 and 2 had densities of 520 kg/m³ respectively, and exhibited dielectric constants at 500 V as follows:
The composition of Example VI was filled into a multi-conductor cable as shown in FIGS. 1 and 2.
As mentioned hereinbefore, it is within the contemplation of this invention to include certain limited percentages of other materials in the petrolatum composition, such as polyolefins and waxes with melting points of up to 220°F, and greater, particularly, the microcrystalline waxes. Synthetic waxes are preferred and include Fischer-Tropsch waxes or polyethylene waxes, ester waxes and the like. Natural waxes such as Montan, cande- lilla, and carnauba, are also useful.
Other materials may be added to the foamed petrolatum, such as antioxidants, coloring agents, gelling agents, thickening agents and the like. The useful amounts of these latter said materials are readily known to one skilled in the art.
The composition of the present invention may be formed by one of several known foaming techniques to provide a foam having from about 10 to 40% or more by volume, and preferably 25 to 35% by volume, of a gas in a closed-cell configuration. It has been found that foam cup weight may be 60 gm/200 ml to 135 gm/200 ml and preferably 95 gm/200 ml; although cup weights less than 60 gm/200 ml and more than 135 gm/200 ml have been found useful. The resultant filler should have a dielectric constant of less than 5 and preferably less than 2.25, and the foam produced pursuant to this invention has been found to exhibit a dielectric constant less than 2.25. Particularly suited are those mechanical processes involving agitation and whipping action. Aerosol techniques are also within the contemplation of this invention.
Cables containing the foamed petrolatum as a filler can be fabricated by suitable techniques well known in the art. An examplary technique for fabricating a twisted, multi-pair communication cable includes the steps of passing a plurality of twisted pairs of insulated conductors into a forming zone to produce a bundle of the conductors and subsequently passing the bundle of the conductors through a stuffer box. The stuffer box is connected to an injection pump by means of a conduit which serves to inject the foamed petrolatum from the pump to the stuffer box. The foamed composition is passed through the side of the stuffer box under sufficient pressure to force it into the interstices between the several insulated conductors. The stuffer box can be adjusted to provide a layer of the petrolatum composition around the periphery of the bundle of conductors. The bundle of conductors including the foamed composition disposed within the bundle is passed from the stuffer box to a core wrapping machine which longitudinally folds first a strip of paper and then a strip of aluminum around the bundle. In a preferred embodiment, the strip of aluminum has an adhesive coating of a random copolymer of ethylene and acrylic acid on both sides for the purpose of achieving a bond between the overlapped edges of the strip. After the core wrap has been applied, the bundle having the core as its outer-most surface is passed through a crosshead die attached to an extruder which extrudes a sheath layer of polyethylene containing carbon black around the core wrap. The resulting cable is then collected on a take-up reel. While the several foregoing steps can be performed individually with interruptions between each step, it is generally preferred that the cable be fabricated on a continuous basis to avoid the necessity of using'storage reels between the several steps.
It is also within the contemplation of this invention, that in lower (below 100) pair cables, the improved di- elecetric properties will now make it possible to use less insulation thus resulting in further savings in material costs.
It is also within the contemplation of this invention to use the foamed petrolatum in combination with a cellular polyethylene to achieve desirable combination of advantages.
The present foamed material when replacing the prior art liquid fillers, minimizes cable draining now common with liquid-filled cables.
Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appended claims.

Claims

1. A cable filler comprising a petrolatum as a foam.

2. The cable filler of claim 1, wherein said foam is a closed-cell foam.

3. The cable filler of claim 2, wherein said filler has a dielectric constant of less than 2.25.

4. The cable filler of claim 3, wherein the foam contains 25 to 35% by volume of a gas.

5. The cable filler of claim 4, said foam having a cup-weight of from 60gm/200ml to about 135gm/200ml.

6. The cable filler of claim 1, wherein the petrolatum has a minimum melting point of about 49°C (ASTM D-127).

7. The cable filler of claim 5, wherein the cup- weight is from 95gm/200ml to about 120gm/200ml.

8. The cable filler of claim 1, said petrolatum comprising a polymeric stabilizer in about 0.01 to 25 weight percent of the petrolatum.

9. The cable filler of claim 8, said petrolatum comprising a polymeric stabilizer in about 0.1 to 0.3 weight percent of the petrolatum.

10. The cable filler of claim 8, wherein said stabilizer has a molecular weight of from 2,000 to 200,000.

11. The cable filler of claim 8, wherein the polymeric stabilizer is a wax-polyisobutylene mixture.

12. The cable filler of claim 1, said petrolatum comprising a polyethylene stabilizer.

13. The cable filler of claim 1, said petrolatum comprising a polyethylene-polyisobutylene stabilizer.

14. The cable filler of claim 10, wherein said filler has a dielectric constant of less than 2.25.

15. A cable comprising a plurality of insulated conductors and a sheath surrounding said conductors and being spacedly disposed therefrom, and a filler material filling the interstices between said conductors and said sheath, said filler comprising a foamed petrolatum.

16. The cable of claim 15, wherein said foam is a closed-cell foam.

17. The cable of claim 15, wherein said filler has a dielectric constant of less than 2.25.

18. The cable of claim 15, said foamed petrolatum comprising a polymeric stabilizer present in about 0.1 - 0.3 weight percent of the petrolatum.

19. The cable of claim 18, wherein the polymeric stabilizer is a wax-polyisobutylene mixture.