US3733427A - Waterproof electrical cable - Google Patents

Abstract

A cable filling composition comprising polybutene, microcrystalline wax, polyethylene and an antioxidant is disclosed which exhibits desirable electrical performance while having good handling characteristics and compatability with polyethylene cable insulation. The composition prevents water ingress in a telephone cable.

Description

United States Patent [191 Clark et al. 5] May 15, 1973 [54] WATERPROOF ELECTRICAL CABLE [56] References Cited [75] Inventors: Michael Gordon Clark; Saleem UNITED STATES PATENTS Sabir Bhatty, both of Toronto 12, 3 6 87 7 k b 7 Rx lS e orn Canada 3,642,638 2/1972 Kitano ..252/63 [73] Assignee: Union Carbide Canada Limited, P i E i E. A G ldber Toronto, Ontario, Canada A ttorney- William George Hopley [22] Filed: May 11,1972 [57] ABSTRACT [21] APPLNO: 252496 A cable filling composition comprising polybutene, microcrystalline wax, polyethylene and an antioxidant is disclosed which exhibits desirable electrical per- [52] U 8 Cl 174/23 C 174/110 PM 252/63 formance while having good handling characteristics 252/64 and compatability with polyethylene cable insulation. The composition prevents water ingress in a telephone [51] Int. Cl. ..H01h 7/30 cable [58] Field of Search ..174/23 C, 23 R, 110 PM,

11 Claims, No Drawings WATERPROOF ELECTRICAL CABLE This invention relates to a composition for filling insulated electrical-type cable having a polyethylene insulated core. More particularly, it relates to a cable filling composition having polybutene as its major constituent.

Telephone cable of the Alpeth or PAP type when used for aerial installations or for burying in the ground consists of a number of copper conductors tightly packed, each insulated by a polyethylene covering.The combined packing of these polyethylene insulated conductors is usually referred to as the core of the cable. This core is normally covered with various layers of tape for a variety of mechanical and thermal purposes. A typical Alpeth cable consists of a core of packed polyethylene insulated conductors with a longitudinal covering of Mylar tape over which aluminum tape is applied. This is further protected by a jacket of extruded weather resistant polyethylene. PAP cable is similar to the Alpeth but includes an additional inner polyethylene jacket between the Mylar tape and the aluminum tape.

While these insulated cables give dependable service over long periods water may gain access to the cable core when the cable is damaged due to a break in the cable jacket or a poor connection at a splicing point. When water gains access to the core of the cable its location is difficult to pin point since the water may travel considerable distances within the cable once it has entered the jacket. When this happens telephone transmission through the wires is adversely affected due to signal loss, increased mutual capacitance of the wires and other factors.

In order to overcome this problem various compositions which have a dielectric characteristic compatible with the polyethylene insulation have been used to fill the air space between the insulated conductors. Such compositions serve to prevent water ingress when the cable sheath is damaged and helps to stabilize electrical transmission through the cable. Any such cable filling composition must be compatible with polyethylene which serves as the insulation for the conductor so that there is no significant degradation of the physical or electrical properties of such insulation. The permittivity of the composition must be sufficiently low to permit restoration of the mutual capacitance of the cable to its original value without significantly changing the cable thickness or reducing the insulation strength. The composition must also be effective over the working temperature range of the cable and must not be sufficiently fluid to drain from the cable at the highest temperatures likely to be encountered both during the initial manufacture of the cable and/or during any field operation such as splicing, termination, etc., where water proofing is advantageous. The temperature of the cable during and after the introduction of the filling compound will be significantly higher for the initial manufacturing phase and subsequent storage than for the field operation such as splicing. Thus, the filling composition will have different temperature requirements for the two cases. In addition, the composition must not become stiff at low temperatures to the point where it would affect the flexibility of the cable. For purpose of economy the filling composition must be capable of easy introduction into the cable at the appropriate stage of manufacture and it should be simple and reliable to keep testing and installation costs to a minimum. A cable containing such composition must remain easy to handle and cable lengths should be capable of joining or splicing by the standard methods. It must also of course not significantly degrade the electrical performance of the cable and should possess a high volume resistivity so that minor pin hole flaws in the composition are of no practical significance.

The most common type of cable filler compound presently in use is petroleum jelly and blends of polyethylene and petroleum jelly. These materials however have a tendency to separate into a liquid and solid phase which eventually affects the transmission performance of the cable and the cable life. The petroleum jelly also appears to adversely affect the tensile strength of the polyethylene insulation on the conductor wires thereby speeding up the aging process of the cable.

Another commonly used cable filler compound is polyethylene grease. This has the drawback that it has poor compatibility with the polyethylene insulation of the conductors and adversely affects the tensile strength and elongation of the conductor insulation. It was also found that the adhesion of the polyethylene insulation to the conductor increased greatly after prolonged contact with this type of filling material. Polyethylene grease also has a relatively high coefficient of thermal expansion which results in voids being formed in the cable when it is cooled.

Polyurethane foam has also been used as a cable filler and due to its cellular structure has' good electrical properties. However, polyurethane is difficult to introduce into a cable since it necessitates precise timing and control of the temperature during the filling operation. Furthermore, polyurethane foam is very difficult to remove from the insulated conductors for splicing.

It is therefore an object of this invention to produce a cable filling composition having good compatibility with polyethylene, low permittivity and desirable electrical performance over the working temperature range of the cable without adversely affecting the handling 1 characteristics of the cable or unduly complicating the method of splicing.

The above object is obtained by means of a cable filling composition consisting essentially of from 10 to 98 percent by weight of polybutene having a number average molecular weight of at least 400 and a viscosity at 210 F of at least 10 centistokes, from 1 to percent by weight of microcrystalline wax having a viscosity at 210 F of from 10 to 30 centistokes, from 0.1 to 10 percent weight of polyethylene having a melting point of about C or more and from 0.02 percent to 0.8 percent by weight of a suitable antioxidant.

The applicant has found that compositions consisting of polybutene, i'nicrocrystalline wax, polyethylene and an anti-oxidant provides greater compatibility with polyethylene insulation than filling compositions presently known in the art while at the same time retaining the desirable characteristics mentioned above. The polybutene used in the present invention preferably had a number average molecular weight of from 400 to 3,000, a specific gravity of from 0.860 to 0.920 at 20 C and a viscosity of greater than 10 centistokes at 210 F. While it is essential that the polybutene have a viscosity of at least 10 centistokes and a molecular weight of at least 400, the upper range of molecular weight need only be limited to polybutene having the desirable flow characteristics within the working temperature range of the cable.

The microcrystalline wax found suitable for the present invention has a viscosity at 210 F of from to 30 centistokes. The most suitable material used in the present invention was also found to have a drop melting point of from 155 F to 165 F, a congealing point of from 145 F to 155 F and a specific gravity at 73 F of from 0.916 to 0.920.

The polyethylene used in the compositions tested had a melting point of at least 90 C.

An antioxidant is also required in the composition to protect against oxidation of the filler at high temperatures encountered during the blending and filling of the cable as well as during the subsequent storage. Such oxidation would degrade the electrical properties of the filler. While any antioxidant known in the art for polyethylene can be used the material used in experimental trials was selected from 2,2'-thio bis(4-methyl-6-butyl phenol) and 2,6-di-t-butyl-4-methyl phenol.

The quantities of the individual components of this composition can be varied over a broad range without diverging from the invention. A surprising and unexpected feature of this composition is that while the major components of the composition, that is polybutene and microcrystalline wax are both stress cracking agents when used alone, it was found that the mixture did not have this adverse effect on polyethylene. In addition, the microcrystal line wax is not in itself suitable as a cable filler since it causes a drastic reduction in cable flexibility.

EXAMPLE I The applicant has found that compositions having a viscosity from about 100 to 250 centipoise provided the best flow characteristics for a cable filler. Compositions below this viscosity were too fluid to be properly before it completely cools ancl congeals. It was found that as little as 0.02 percent by weight of polyethylene gives an increase in the drop melting point. However, it is preferable to use 0.8 percent by weight of polyethylene for this purpose. The lower application temperature required for field operations permit the use of a filling composition having no polyethylene. However, the polyethylene may be used, if desired. The same argument applies to the use of an antioxidant where this may be eliminated in field operations, if desired.

It was found that bst r'e sults wre achieved by a composition consisting of from 50 percent to 95 percent by weight of polybutene, from 4 percent 49 percent by weight of microcrystalline wax, from 0.2 percent to 0.8 percent by weight of polyethylene and from 0.2 percent to 0.8 percent by weight of antioxidant. Such compositions provide best viscosity for handling during cable filling and operating conditions as well as high resistivity and low permittivity.

The compatibility of this type of composition with the polyethylene insulation of the conductor was found to be significantly better than other types of filler compositions known in the prior art.

EXAMPLE ll Polyethylene insulated wire samples were immersed in various types of filler compositions and placed in an air circulated oven at 70 C for a period of 2 weeks. The samples were then removed from the compositions, wiped clean and their tensile strength and elongation were measured. As can be seen in Table 11 given below, considerable degradation was observed in samples aged in other materials than the polybutene composition described in this application. Tests also indicated that the applicants polybutene based composition had superior electrical characteristics by virtue of its dielectric constant and lower dissipation factor.

Yield Tensile Elonga- Dissipastrength, strength, tion, Dielectric tion at Factor Filler (p.s.i.) (p.s.i.) percent const. 100 kc. at 1 me.

Petroleum jelly. 1, 500 1, 600 30 230 0.00152 0.00550 1, 450 1, 350 22B 0. 00107 0. 00211) 1, 500 1, 700 460 224 0. 00033 0. 00050 Polyethylene insulation before ageing 1,100 2, 000 550 230 0.00173 1 The polybutene filler consisted of 74.0% by weight of polybutene, 25.0% by weight 01 microcrystalline wax, 0.8% by weight of polyethylene and 0.2% by Weight of 2,2-thio-bis(imethyl-fi-butyl phenol).

handled and compositions above 2 50 we re in ucli tod thick for filling the'cable. Since polybutene and microcrystalline waxconstitute the overwhelming portion of the composition, various compositions of these two components were tested for the desired viscosity range. Various compositions within the desired viscosity range are shown in the table below. These viscosity readings were calculated at 1 10 C.

The polyethylene is required to increase the drop melting point of the mixture to prevent it from dripping from the cable conductors during initial manufacture We claim:

1. A filling composition for use in insulated electrical type cables having a polyethylene insulated core, said composition consisting essentially of from 10 percent to 98 percent by weight of polybutene having a number average molecular weight of at least 400 and a viscosity at 210 F of at least 10 centistokes, from 1 to percent by weight of microcrystalline wax having a viscosity at 210 F of from 10 to 30 centistokes, from 0.1 to 10 percent by weight of polyethylene having a melting point of at least C and from 0.02 percent to 0.8 percent by weight of a suitable antioxidant.

2. A composition as claimed in claim 1 wherein the polybutene has a number average molecular weight of at least 400, a specific gravity of from 0.860 to 0.920 at 20 C and a viscosity of at least 10 centistokes at 210 F.

3. A composition as claimed in claim 2 wherein the microcrystalline wax has a drop melting point of from F to F, a congealing point of from 145 F to 155 F and a specific gravity at 73 F of from 0.916 to 0.920.

4. A composition as claimed in claim 3 wherein the antioxidant is one selected from the group consisting of 2,2-thio-bis(4-methyl-6-butyl-phenol) and 2,6-di-tbutyl-4-methyl phenol.

5. A filling composition for use in insulated electrical type cable having a polyethylene insulated core, said composition consisting essentially of from 50 percent to 95 percent by weight of polybutene having a number average molecular weight of at least 500 and a viscosity at 210 F of from 13 to 18 centistokes, from 4 percent to 49 percent by weight of a microcrystalline wax having a viscosity at 210 F of from 13 to 18 centistokes, from 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90 C, and 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90 C, and 0.2 percent to 0.8 percent by weight of a suitable antioxidant.

6. A composition as claimed in claim 5 wherein from 65 percent to 85 percent by weight of said polybutene and from percent to 35 percent by weight of said microcrystalline wax is present in the composition.

7. A composition as claimed in claim 6 wherein the polybutene has a specific gravity of from 0.860 to 0.920 at C and the microcrystalline wax has a drop melting point of from 155 F to 165 F a congealing point of from 145 F to 155 F and a specific gravity of from 0.916 to 0.920.

8. A composition as claimed in claim 7 wherein the antioxidant is one selected from the group consisting of 2,2'-thio-bis(4-methyl-6-butyl phenol) and 2,6-di-tbutyl-4-methyl phenol.

9. An insulated electrical cable containing a filling composition consisting essentially of from 10 percent to 98 percent by weight of polybutene having a number average molecular weight of at least 400 and a viscosity at 210 F of at least 10 centistokes, from 1 percent to percent by weight of microcrystalline wax having a viscosity at 210 F of from 10 to 30 centistokes, from 0.1 percent to 10 percent by weight of polyethylene having a melting point of at least C and from 0.02 percent to 0.8 percent by weight of a suitable antioxidant.

10. An insulated electrical cable containing a filling composition consisting essentially of from 50 percent to percent by weight of polybutene having a number average molecular weight of at least 500 and a viscosity at 210 F of from 13 to 18 centistokes, from 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90 C and 0.2 percent to 0.8 percent by weight of a suitable antioxidant.

11. An insulated electrical cable as claimed in claim 10 wherein the antioxidant is one selected from the group consisting of 2,2-thio-bis (4-methyl-6-butyl phenol) and 2,6-di-t-butyl-4-methyl phenol.

Claims (10)

1. 2. A composition as claimed in claim 1 wherein the polybutene has a number average molecular weight of at least 400, a specific gravity of from 0.860 to 0.920 at 20* C and a viscosity of at least 10 centistokes at 210* F.
2. 3. A composition as claimed in claim 2 wherein the microcrystalline wax has a drop melting point of from 155* F to 165* F, a congealing point of from 145* F to 155* F and a specific gravity at 73* F of from 0.916 to 0.920.
3. 4. A composition as claimed in claim 3 wherein the antioxidant is one selected from the group consisting of 2,2''-thio-bis(4-methyl-6-butyl-phenol) and 2,6-di-t-butyl-4-methyl phenol.
4. 5. A filling composition for use in insulated electrical type cable having a polyethylene insulated core, said composition consisting essentially of from 50 percent to 95 percent by weight of polybutene having a number average molecular weight of at least 500 and a viscosity at 210* F of from 13 to 18 centistokes, from 4 percent to 49 percent by weight of a microcrystalline wax having a viscosity at 210* F of from 13 to 18 centistokes, from 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90* C, and 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90* C, and 0.2 percent to 0.8 percent by weight of a suitable antioxidant.
5. 6. A composition as claimed in claim 5 wherein from 65 percent to 85 percent by weight of said polybutene and from 15 percent to 35 percent by weight of said microcrystalline wax is present in the composition.
6. 7. A composition as claimed in claim 6 wherein the polybutene has a specific gravity of from 0.860 to 0.920 at 20* C and the microcrystalline wax has a drop melting point of from 155* F to 165* F a congealing point of from 145* F to 155* F and a specific gravity of from 0.916 to 0.920.
7. 8. A composition as claimed in claim 7 wherein the antioxidant is one selected from the group consisting of 2,2''-thio-bis(4-methyl-6-butyl phenol) and 2,6-di-t-butyl-4-methyl phenol.
8. 9. An insulated electrical cable containing a filling composition consisting essentially of from 10 percent to 98 percent by weight of polybutene having a number average molecular weight of at least 400 and a viscosity at 210* F of at least 10 centistokes, from 1 percent to 75 percent by weight of microcrystalline wax having a viscosity at 210* F of from 10 to 30 centistokes, from 0.1 percent to 10 percent by weight of polyethylene having a melting point of at least 90* C and from 0.02 percent to 0.8 percent by weight of a suitable antioxidant.
9. 10. An insulated electrical cable containing a filling composition consisting essentially of from 50 percent to 95 percent by weight of polybutene having a number average molecular weight of at least 500 and a viscosity at 210* F of from 13 to 18 centistokes, from 0.2 percent to 0.8 percent by weight of polyethylene having a melting point of at least 90* C and 0.2 percent to 0.8 percent by weight of a suitable antioxidant.
10. 11. An insulated electrical cable as claimed in claim 10 wherein the antioxidant is one selected from the group consisting of 2,2-thio-bis (4-methyl-6-butyl phenol) and 2,6-di-t-butyl-4-methyl phenol.