US3525798A - Fully filled plaster sheathed telecommunication cables - Google Patents

Description

C. D. FORBER Aug. 25., 1970 FULLY FILLED PLASTIC SHEATHED TELECOMMUNICATION CABLES Filed March 21, 1968 PETROLEUM 8-P0L YETHYL ENE LOW DENSITY POL YE TH YL ENE POLYVl/VYL D/ETHYLENE COPOLYMER 5 HI/t.

CELLULAR POLYETHYLENE United States Patent Office 3,525,798 Patented Aug. 25, 1970 U.S. Cl. 174-26 9 Claims ABSTRACT OF THE DISCLOSURE In a fully filled plastic sheathed multi-conductor telecommunication cable there is provided between the conductors and the sheath a separating layer which will serve both as a heat barrier and a barrier to the passage through the sheath of the filling material and which will bond to the sheath at or below the temperature at which the sheath is extruded on the core.

This invention relates to telecommunication cables of the kind comprising a multiplicity of plastic insulated conductors enclosed within a waterproof sheath and, filling the interstices between the insulated conductors and between them and the waterproof sheath from end to end of the cable length, a water-impervious medium which will not drain under the influence of gravity or such hydrostatic pressure as may arise in the event of damage to the cable sheath but which will permit relative sliding movement of the plastic insulated conductors over one another during such bending of the cable as occurs during manufacture and installation of the cable.

The non-draining water-impermeable medium generally preferred is petroleum jelly. The material used for the sheath is generally polyethylene. However as polyethylene is pervious to petroleum jelly the possibility exists, especially when such fully-filled, plastic sheathed telecommunication cables are laid in the vicinity of heavy current power cables, of filling material migrating into and under certain conditions through the polyethylene sheath, thus creating an incompletely filled cable along which moisture may travel.

By the present invention there is provided an improved form of fully filled plastic sheathed telecommunication cable in which the risk of migration of the filling medium through the cable sheath is substantially eliminated.

The improved form of cable comprises a core comprising a multiplicity of plastic insulated conductors enclosed within a sheath of plastic material pervious to petroleum jelly and like mixtures of microcrystalline petroleum waxes and oils at certain ambient temperatures, the interstices between the individual conductors of the core and between the core and the sheath being filled with petroleum jelly or a like mixture of microcrystalline petroleum wax and oil, wherein there is present between the core and the sheath a separating layer which will serve both as a heat barrier and a barrier to the passage of the material with which the interstices are filled and which will bond to the sheath at or below the temperature at which the sheath is extruded on the core.

Where the cable sheath is of polyethylene the separating layer may consist of a layer or coating of polyvinyl diethylene copolymer on a carrier layer which will bond, or which carries a layer which will bond, to polyethylene at temperatures of about 200 C., which temperatures are the temperatures at which a polyethylene sheath is generally extruded on a cable core.

The separating layer is preferably a laminate consisting of a carrier layer of cellulose acetate carrying on one face a coating of polyvinyl diethylene copolymer and on the other face a coating of a low density polyethylene. The separating layer is preferably formed by longitudinally applying to, or helically lapping on, the cable core a tape of the laminate in such a way that the polyethylene layer is on the outside and contiguous margins of the tape overlap one another to form a complete envelope on to which the polyethylene sheath is extruded preferably at a temperature and under conditions which ensure that the exposed parts of the surface of the polyethylene layer become bonded to the polyethylene sheath.

Preferably the coating of polyvinyl diethylene copolymer on one face of the laminate itself carries an outer coating of a low density polyethylene, thereby providing a laminate having an outer coating of polyethylene on each of its faces. Use of a tape of the laminate of this latter form as the separating layer ensures that a bond is obtained between the overlapping margins of the tape when the polyethylene sheath is extruded on the core. Moreover, since the tape has a polyethylene coating on each of its faces, the tape can be applied to the cable core with either of its polyethylene layers on the outside and the necessity, present when employing a tape of laminate carrying on one face only a polyethylene coating of detecting which surface of the tape has the polyethylene coating is eliminated.

In both cases the tape of the laminate also serves as a thermal barrier enclosing the cable core and serving to prevent overheating of the conductor insulation during the operation of extruding the sheath.

The invention will now be more fully described, by way of example, with reference to the accompanying drawing which is a fragmental cross-sectional view, drawn to an enlarged scale, of a preferred form of telecommunication cable constructed according to the present invention.

The cable comprises a multiplicity of copper conductors 1 each having a dielectric 2 of cellular polyethylene. Helically lapped about the multiplicity of conductors in such a way that its contiguous margins overlap one another to form a complete separating envelope 3 is a tape of a laminate consisting of a carrier layer 4 of cellulose acetate carrying on one face a coating 5 of polyvinyl diethylene copolymer and carrying on its other face and on the polyvinyl diethylene copolymer coating 5, coatings 6 of a low density polyethylene. A polyethylene sheath 8 is extruded on and bonded to the outer polyethylene coating 6 of the separating envelope 3, the overlapping contiguous margins of the tape also being bonded together. The interstices between the individual cellular polyethylene insulated conductors 1 and between them and the separating envelope 3 are filled throughout the length of the cable with a water-impermeable medium consisting of petroleum jelly 7. If required, the cable may be provided with armouring (not shown) comprising galvanized steel wires laid helically over the sheathed cable and protected against corrosion by an extruded oversheath of polyvinyl chloride.

In some cases it may be necessary to lay telecommunication cables, such as pilot and telephone cables, underground alongside heavy current power cables designed for a continuous maximum conductor temperature of C. In such cases there is a tendency for moisture in the soil to be driven away from the vicinityof the feeder cables. This in itself may be conducive to the bleeding of petroleum jelly or other similar filling medium from the neighbouring fully filled pilot and telephone cable if of normal construction. This risk is avoided by constructing the pilot and telephone cable or cables in accordance with the invention.

What I claim is:

1. A telecommunication cable comprising a multiplicity of plastic insulated conductors forming a core enclosed within a sheath of plastic material pervious to petroleum jelly and like mixtures of microcrystalline petroleum waxes and oils at certain ambient temperatures, the interstices between the individual conductors of the core and between the core and the sheath being filled with one of said mixtures of microcrystalline petroleum waxes and oils, wherein there is present between the core and the sheath a separating layer which will serve both as a heat barrier and a barrier to the passage of the material with which the interstices are filled and which will bond to the sheath at or below the temperature at which the sheath is extruded on the core.

2. A telecommunication cable as claimed in claim 1, wherein the separating layer consists of a layer of polyvinyl diethylenc copolymer on a carrier layer which will bond to the sheath at or below the temperature at which the sheath is extruded on the core.

3. A telecommunication cable as claimed in claim 2, in which the sheath is of polyethylene, wherein the carrier layer of the separating layer will bond to polyethylene at temperatures of about 200 C.

4. A telecommunication cable as claimed in claim 1, wherein the separating layer consists of a layer of polyvinyl diethylene copolymer on a carrier layer which carries a layer which will bond to the sheath at or below the temperature at which the sheath is extruded on the core.

5. A telecommunication cable as claimed in claim 4, in which the sheath is of polyethylene, wherein the carrier layer of the separating layer carries a layer which will bond to polyethylene at temperatures of about 200 C.

6. A telecommunication cable comprising a multiplicity of plastics insulated conductors forming a core enclosed within a sheath of polyethylene pervious to petroleum jelly and like mixtures of microcrystalline petroleum waxes and oils at certain ambient temperatures, the interstices between the individual conductors of the core and between the core and the sheath being filled with petroleum jelly, wherein there is present between the core and the sheath a separating layer comprising a laminate consisting of a carrier layer of cellulose acetate carrying on its inner face a coating of polyvinyl diethylene copolymer and on its outer face a coating of a low density polyethylene which will bond to the polyethylene sheath at or below the temperature at which the polyethylene sheath is extruded on the core, which separating layer will serve both as a heat barrier and a barrier to the passage of the material with which the interstices are filled.

7. A telecommunication cable as claimed in claim 6, wherein the separating layer is formed by applying to the cable core a tape of the laminate in such a way that the polyethylene layer'is on the outside and contiguous margins of the tape overlap one another to form a complete envelope on to which the polyethylene sheath is extruded.

8. A telecommunication cable comprising a multiplicity of plastic insulated conductors forming a core enclosed within a sheath of polyethylene pervious to petroleum jelly and like mixtures of microcrystalline petroleum waxes and oils at certain ambient temperatures, the interstices between the individual conductors of the core and between the core and the sheath being filled with petroleum jelly, wherein there is present between the core and the sheath a separating layer comprising a laminate consisting of a carrier layer of cellulose acetate carrying on one face a coating of polyvinyl diethylene copolymer and carrying on its other face and on the coating of polyvinyl diethylene copolymer coatings of a low density polyethylene, the outermost of which polyethylene coatings will bond to the polyethylene sheath at or below the temperature at which the polyethylene sheath is extruded on the core, which separating layer will serve both as a heat barrier and a barrier to the passage of the material with which the interstices are filled.

9. A telecommunication cable as claimed in claim 8, wherein the separating layer is formed by applying to the cable core a tape of the laminate in such a way that contiguous margins of the tape overlap one another to form a complete envelope on to which the polyethylene sheath is extruded.

References Cited UNITED STATES PATENTS 3,445,324 5/1969 Curler et al. 161-165 2,345,229 3/1944 Barmack 15652 X 3,427,394 2/ 1969 McKean 17425 X 3,188,265 6/1965 Charbonneau et al. 161188 2,860,801 11/1958 Nielsen 117 -94 X 2,968,576 1/1961 Keller et al. 117-47 3,344,228 9/1967 Woodland et al. 174-107 3,098,113 7/1963 Brierley 174-26 FOREIGN PATENTS 776,174 6/ 1957 Great Britain.

LARAMIE E. ASKIN, Primary Examiner A. T. GRIMLEY, Assistant Examiner U.S. Cl. X.R. 174--110, 120

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