DE2706809A1 - LOW CURRENT CABLE WITH SINGLE LAYER INSULATION - Google Patents

Description

PATENT ADVOCATE DR. HANS Ul.RICH MAY

D β MÖNCHEN 22, THIERSCHSTRASSE 27 TELEGRAMS: MAVPATENT MDNCHEN TELEX 02 4487 PATOP TELEPHONE CO80} 22SO01

G-7-P-5O / 1514-5f "Munich, February 17, 1977

G-7-G-5O / 1514a Dr.M / hs

File 15457

GENERAL CABLE CORPORATION, GREENWICH, CONNECT! CUT / USA

Low-voltage cable with single-layer insulation

Brief abstract of the invention

The invention relates to low-voltage cables, particularly telephone cables (lead-in wires) with improved single-layer insulation, which consists of a semi-crystalline, low molecular weight ethylene-propylene-diene terpolymer (EPDM). The insulation has better electrical properties, which has thinner insulation cross-sections allows, so that the overall cross-section of the low-voltage cable is smaller, the cable being lower in cost, higher Temperature resistance and moisture resistance and is suitable as a cable laid in the ground. The isolation is also tougher and therefore more abrasion-resistant.

Prior Art and Summary of the Invention

So-called single-layer insulation (unipass insulation) is known for low voltage cables, such as telephone cables. With such a Isolation, a connection or ground takes the place of both the isolation and the jacket, which used to be common Cable structure were used. In the case of the previously known low-voltage cables with single-layer insulation, however, polyvinyl chloride (PVC) the main component of insulation.

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The object of the invention is to improve the chemical and physical, especially electrical and mechanical properties of such low-voltage cables, especially telephone cables Single-layer insulation.

It has been found that ethylene-propylene-diene terpolymers (EPDM polymers) with a content of filler are used as single-layer insulation solve the task at hand for low-voltage cables. EPDM polymers with a filler content are known from US Pat. No. 3,148,169.

The low-voltage (telephone) cable according to the invention with single-layer insulation uses a semi-crystalline, low molecular weight ethylene-propylene diene terpolymer as the main component of the insulation (EPDM) with relatively small amounts of filler and preferably with flame retardant additives, as prescribed by the insurance companies. The composition of the Isolation is specified in more detail below.

Because of the improved electrical properties of the low-voltage cable according to the invention, the cross-section of a telephone cable

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(Strip conductor) of 4.06 mm χ 7 »62 mm (0.160 χ 0.300) for the known PVC single-layer insulation to 3.424 mm 5t842 mm

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(0.135 χ 0.230) can be reduced with the EPDM polymer used according to the invention, which saves costs and weight, and that The improved telephone cable according to the invention has further advantages, namely, inter alia, a better insulation resistance, a lower one Attenuation, higher temperature resistance »improved flexibility at low temperatures and excellent moisture resistance, making the cable suitable for underground installation suitable is.

The invention is further illustrated by the following description of an exemplary embodiment which refers to the attached Drawing refers to wherein corresponding parts are designated by like reference numerals in all figures. Show it: Fig. 1 is a view, mainly in section, of a telephone cable according to the invention;

2 schematically shows a device for applying the insulation in a single layer to the conductors of the cable.

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The invention is based on the discovery · that a substantially improved telephone cable with single-layer insulation (unipass telephone drop wire) with an ethylene-propylene diene terpolymer "hereinafter referred to as" EPDM ¹ * "can be produced as the main component of the insulation. The special · for purposes of the invention used EPDM polymer is semicrystalline and has a low molecular weight the invention suitable EPDM has a specific gravity of about Ot85;. is light amber in color and has a Mooney viscosity ML (1 + 4) at 121 ⁰ C (25O ° F ) from about 25.

An EPDM polymer with the specified properties is of the Du Pont Company · Wilmington · Delaware / USA under the trade name "NORDEL 2722" (e.Wz.). Possibly there is other semi-crystalline »low molecular weight polymers · which are chemically equivalent to the product" NORDEL 2722 ", but this is currently the case nothing known.

An essential advantage of the semi-crystalline · low molecular weight EPDM polymer is · that it has a low filler content can be processed e.g. about 47 parts of filler per 100 Parts of polymer · and this low filler content leads to significantly improved electrical properties in comparison with conventional EPDM compounds, where the filler content is around 110 per 100 parts of polymer. The diene content of the EPDM polymer according to the invention leads to a high crosslinking density in the vulcanized (hardened) insulation and thereby compensates for the low filler content.

Also, low density polyethylene can be used in an amount of about 18 parts per 100 parts of polymer instead of the usual Processing oil can be used at the low filler contents according to the invention. This modification leads to a high Module and high tensile strength · both properties that are required for a good low-voltage cable.

The use of a semi-crystalline EPDM polymer with low Molecular weight leads to an insulation material that is not only tough, but also easy to use when the filler content is low can be processed.

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The compression cut of the insulation according to the invention is around 47 parts clay per 100 parts polymer 60-90 % greater than in the case of insulations based on conventional amorphous polymers, such as the products ¹¹ NORDEL 1040 "or" NORDEL 1070 "(e.Wz.), Manufacturer Du Pont, build up.

Insurance company regulations, especially fire insurance, require that telephone cables have flame retardant insulation. Such an insulation burns when it is exposed to a flame, but the insulation no longer burns after removal of the flame within a short time, which is specified in the insurance regulations. The insulation according to the invention is made flame-retardant by adding a chlorine-containing additive and antimony oxide to the formulation. Suitable chlorine-containing additives include one from Hooker Specialty Chemicals Company, Niagara Falls, New York / USA, under the name "Dechlorane" (e.Wz.) or one from the Diamond Alkali Company, USA, under the trade name "Chlorovax 70 "(e.Wz.) product sold. The amount of chlorine-containing additive varies depending on the type used and can, for example, be between about 65 % and 77 % . In order to achieve adequate flame-retardant properties, about 1 to 2 % antimony oxide should be added to the chlorine-containing additive, the number given is only an example.

Fig. 1 shows a telephone cable 10 with conductors 12 and 14, which in the single-layer insulation16 are embedded from the described semi-crystalline, low molecular weight EPDM polymer is made. In the preferred cable construction, conductors 12 and 14 are included an adhesive 18 applied to conductors 12 and 14 before the insulation 16 was extruded over the conductors will.

The preferred cable construction uses an adhesive made by of the Dayton Chemical Products Division of Whittaker, West Alexandria, Ohio, under the trade name "Thixon XAP 1788" (e.Wz.) is sold.

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Other adhesives can be used, and one other a specific example is that from Hughson Chemical Lord Corporation, Erie, Pennsylvania / USA, under the trade name Adhesive sold "Chemlok B-2197-65" (e.Wz.).

Fig. 2 shows schematically an extruder 24 »through which the Insulation material 16 is extruded over conductors 12 and 14 in a single pass which applies the insulation required by the Takes place of both the insulation of conductors 12 and 14 and a jacket for the cable. The cable 10 comes from the extruder 24 to a customary continuous vulcanization apparatus, not shown, in which the insulation material is crosslinked, preferably to such an extent that it is thermoset.

In comparison with a conventional telephone cable with single-layer polyvinyl chloride insulation, the telephone cable according to the invention can be manufactured about 10% cheaper. The insulation resistance of this improved telephone cable is about 44,200 MΩ / km (14,500 MΩ / 1000 feet) versus 731.5 MÄ / km (240 MS / 1000 feet) for the polyvinyl chloride insulation. The dry capacitance of the conductors to each other is lower, 0.0559 pF / km (0.090 micromicrofarad per mile) compared to 0.08326 pF / km (0.134 x 10 ~ ¹² farad / mile) for the PVC. This leads to a lower attenuation.

The temperature resistance of the insulation on the cable according to the invention is about 90 ⁰ C, compared with 60 ⁰ C £ ÜR the PVC insulated cables. The electrical strength of the cable according to the invention is in a ratio of 20 kVolt to 11 kVolt higher than that of PVC-insulated telephone cables. This advantage reduces the possibility of terminal failure as a result of lightning strikes. The added flexibility it provides at low temperatures is a major benefit when installing telephone cables in cold weather.

All these advantages result from the use of the semi-crystalline, a low molecular weight ethylene-propylene diene terpolymer as the main component of single-layer insulation of the telephone cable according to the invention.

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As explained above, this terpolymer requires less filler, and it can be used with a low-density polyethylene, in order to improve the cutting ability of the ground and avoid the use of processing oil during _t be simultaneously improved the modulus and tensile strength. For 100 parts of the EPDM terpolymer, between 5 and 25 parts of low density polyethylene are preferably used. The low-current cable according to the invention is intended for use as a telephone cable (drop wire), but can also be used for other purposes where the same properties are desired.

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Claims (14)

Claims 1. Low-voltage cables, especially telephone cables, with at least one conductor and a single-layer insulation covering the conductor or conductors, characterized in that the main component of the insulation is a semi-crystalline ethylene-propylene-diene terpolymer with a low molecular weight and the insulation has a significantly lower than 110 parts 100 parts of polymer lying, but at least contains sufficient amount of a filler to give the insulation additional strength. 2. Low current cable according to claim 1, characterized in that the filler content is below about 75 parts per 100 parts of the polymer. 3. Low current cable according to claim 2, characterized in that the insulation compound is crosslinked and the diene content of the Terpolymers provides a high crosslinking density in the vulcanized insulation and thus the low filler content compensated. 4. Low current cable according to one of claims 1 to 3, characterized in that the insulation mass with about 47 parts treated clay and 18 parts low density polyethylene per 100 parts of the polymer. 5. Low-current cable according to one of claims 1 to 4, characterized in that the insulation has a sufficient amount of a chlorine-containing to impart flame-retardant properties Contains additive and antimony oxide. 6. low current cable according to claim 5 »characterized in that that the chlorine-containing additive contains about 65 to 77 % chlorine and the ratio of chlorine-containing additive to antimony oxide is at least about 2 to 1. 709835/0739 iNSPFCTED 7. Low current cable according to one of claims 1 to 6, characterized in that there are two at a distance from each other having parallel conductors, through a unitary section of the ethylene-propylene-diene terpolymer in one Are kept spaced from each other, wherein the insulation is a one-piece extrudate. 8. low current cable according to one of claims 1 to 7 »characterized in that the ethylene-propylene-diene terpolymer has a specific weight of about 0.85, is light amber, and a Mooney viscosity ML (1 + 4) at 121 ⁰ C ( 250 ⁰ F) of about 25. 9. Low current cable according to claim 8, characterized! that the insulation is crosslinked and thermoset. 10. A method for producing a low-voltage cable, especially telephone cable, wherein a plurality of electrical conductors are moved along parallel paths at a distance from each other and through guides in an extruder, characterized in that a semicrystalline ethylene-propylene- Low molecular weight diene terpolymer of the type set forth in claims 1 to 9 and passing the conductors with the coating extruded thereon through a continuous vulcanization apparatus to vulcanize and crosslink the polymer forming the extruded insulation to a thermoset state. .A method according to claim 10, characterized in that on An adhesive is applied to the ladder before the terpolymer is extruded over the ladder. 12. The method according to claim 11, characterized in that as Adhesive a product with the trade designation "Thixon XAP 1788" (e.Wz.) made by the Dayton Chemical Products Division by Whittaker, West Alexandria, Ohio / USA is used. 709835/0739 13. The method according to claim 11, characterized in »that as Adhesive a product that goes by the name of "Chemlock B-2197-65 "(e.Wz.) from Hughson Chemical Lord Corporation, Erie, Pennsylvania, USA. 14. Low voltage cables, especially telephone cables, according to one of the Claims 1 to 9 »characterized in that each of the conductors (12, 14) is coated with an adhesive (18), over which the terpolymer (16) is applied. 15 · Low-voltage cables, especially telephone cables, according to one of Claims 1 to 9 and 14 »characterized in that the ethylene-propylene-diene terpolymer has a specific weight of about 0.85, is light amber and has a Mooney viscosity ML (1 + 4) the cable has at 121 ° C (250 ⁰ F) of about 25, two mutually parallel spaced conductors (12, 14) which are held by a unit section of the insulation, which is a single extrudate at a distance from each other , wherein the insulation is compounded with about 47 parts of pretreated clay and 18 parts of low density polyethylene for every 100 parts of the polymer and the insulation is crosslinked and thermoset, the diene content of the terpolymer providing a high crosslink density in the vulcanized insulation and thereby the low filler content compensated, and wherein each of the conductors (12, 14) is coated with an adhesive (18) over which the insulation (16) is applied. 709835/0739