OIL RESISTANT CABLE

Abstract: The oil resistiviy of power and/or telecommunication cables to be used in petrochemical installations is improved by adding high density polyethylene, linear low density PE and/or a polyamide (nylon) to the filling sheath (4) and/or to the outer sheaths (5) of the cable in an amount in the range of 5-40 weight %.

Description: The present invention relates to power and/or telecommunication cables which will be exposed to oil in high fire risk areas like petrochemical and industrial installations. In order to obtain flame retardant properties cable sheaths usually contain inorganic fine particle filling materials like aluminium tri hydroxide (Al(OH)₃), magnesium hydroxide (Mg(OH)₂) MgCO₃, Zn borates or the like. As a rule increased amounts of filling materials of this kind will result in improved flame retardant properties. The oil resistivity of known cables is, however, not very good and when the cable from time to time is subjected to oil or other petrochemicals, the cable sheath and insulation material will be impaired so that the good flame retardant and electrical properties will be lost. The object of the present invention is to make a cable which is flame retardant and has improved oil resistivity as compared to known cables. The features of the invention are defined in claim 1. Tests have shown that cables made in accordance with the present invention withstand the IEC 332-3 category C fire retardence test. The materials also retain more than 60% of their original mechanical properties after ageing for 7 days at 90°C, in ASTM oil No. 2. Above mentioned and other features and objects of the present invention will clearly appear from the following detailed description of embodiments of the invention taken in conjunction with the drawings, where Figures 1 and 2 show the crossection of two cables having sheaths as defined. In Fig. 1 a cable core 1 may contain one or more electrical conductors 2 and/or optical fibers 3 included within an outer protective sheath 5 and possibly an outer protective sheath 4 which fills all interstices between the insulated conductors. The sheath 5 and preferably also the sheath 4 have improved oil resistivity. In Fig. 2 is illustrated a cable similar to that of Fig. 1 and having an outermost protective sheath 6 of nylon. The base material of the outer protective sheath 5 and possibly the sheath 4 should be chosen from the group of materials which are commonly known as ethylene copolymers and which includes ethylene vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene butyl acrylate (EBA), ethylene propylene polymer (EPR), ethylene propylene diene monomer (EPDM) or similar materials. In the sheaths 4 and 5 the amount of base material should be in the range of 40 to 90 weight %. In order to obtain the desired oil resistivity, the sheaths may contain polyethylene with high density (PEH) having a density between 0,941 and 0,960 and a melting index of 0,1 to 10,0, preferably 0,1 to 2,0. The sheaths may alternatively contain linear low density polyethylene (LLDPE), a polyamide or a combination of PEH, LLDPE and/or polyamide. The polyamide could be included in the form of nylon 11 or nylon 12 having a relative solubility viscosity (according to ISO 307) in the range of 1,0 to 3,0 preferably about 2,1. The polyamide may contain compatible plasticizers normally used in PA 11 & 12 like benzolsulfoneamide. The amount of PEH, LLDPE and/or polyamide in the sheaths should be in the range of 5 to 40 weight %. The polymers to be blended are not soluble and the PEH, LLDPE and/or polyamide portion will form small particles dispersed in the main polymer matrix. On extrusion the polymer additive forms fibrils. These are very oil resistant. This mixture of polymers used in a cable will have improved oil resistance because the oil will have a very long distance to travel in order to penetrate the sheath. The sheath material may be of the thermoplastic type or it may be crosslinked by adding crosslinking agents like silan or peroxide during the material mixing process or as an additive in the original materials. Crosslinking may also be obtained by subjecting the cable sheaths to radiation. Normal material handling agents like lubricating agents such as polymer waxes, stearic acid, hydrocarbon waxes, fatty acid amides and antioxidants, may also be added. The amounts of crosslinking and material handling agents in the final product constitute less than 7 weight %. The sheath material to be extruded over the cable conductors and cable core should preferably be made by starting out from melting polyethylene/polyamide material (the material with the highest melting point). Into this melted polymer it is advisable to blend a material with greater solubility, such as one or more of the base materials in the flame retardent halogene free sheathing material, in an amount of 10 to 50 weight %. This may as mentioned be chosen from the group of materials commonly known as ethylene copolymers and which includes: EVA, EEA, EBA, EPR, EPDM and similar materials. This blend or so called masterbatch (MB) can now be blended with the base sheathing compound in the range of 10 to 60 weight %. In Fig. 2 which includes an outer sheath 6 of nylon, experiments have shown that this nylon sheath adheres better to the lower sheath 5 when this sheath contains nylon, than to known sheath. The following test has been made: Bend test, 180°, on 12 times the cable diameter. Result: Less wrinkles on the inside bend with nylon in sheath 5. The above detailed description of embodiments of this invention must be taken as examples only and should not be considered as limitations on the scope of protection.

Claims: Oil resistant power and/or telecommunication cable containing a number of insulated conductors (2, 3) and/or optical fibers within one or more outer protective sheaths (4, 5), characterized in this that at least one of the outer protective sheaths (4, 5) contains an oil resistant material made up of a mixture of polyethylene and polyamide, in a base material of ethylene copolymers. Cable according to claim 2, wherein the amount of oil resistant material in said at least one of the outer protective sheaths is in the range of 5-40 weight %. Cable according to claim 1 or 2, wherein said polyethylene is a high density polyethylene of a density between 0,941 and 0,960 and of a melting index of 0,1 to 10, preferably 0,1 - 2,0. Cable according to claim 1 or 2, wherein said polyamide is nylon 11 or nylon 12 having a relative solubility viscosity, according to ISO 307, in the range of 1,0 to 3,0, preferably about 2,1. Cable according to claim 1, 2, 3, or 4, also comprising an outermost protective sheath (6) of 100% nylon and wherein the next-outer protective sheath (4, 5) contains nylon up to 40 weight %. Cable according to claim 1, 2, 3, 4, or 5, wherein one of said outer protective sheaths (4,5) fills all interstices between the insulated conductors.

Inventors: GRANHEIM, IVAR, PEDERSEN, JACK RAYMOND
Applicants: STANDARD TELEFON OG KABELFABRIK A/S
Application year: 1987
Main classification: H01B7
IPC codes: H01B7, H01B3, C08L23, G02B6, C08L77, C08K3