Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds

Definitions

• This invention relates to insulated electrical conductors.
• insulated wires include wires coated with a layer of a radiation crosslinked fluorocarbon polymer, particularly an ethylene/tetrafluoroethylene copolymer (often referred to as an ETFE polymer), which are extensively used for the wiring in aircraft.
• ETFE polymer ethylene/tetrafluoroethylene copolymer
• MIL-W-22759 sets various standards for such insulated wires. Reference may be made for example to U.S. Patents Nos. 3,763,222, 3,840,619, 3,894,118, 3,911,192, 3,970,770, 3,985,716, 3,995,091, 4,031,167, 4,155,823 and 4,353,961.
• Such wires have the significant disadvantage that if the outer surface of the insulation is damaged, subsequent flexing of the wire causes the damage to propagate through the insulation, at a rate which is highly unde­sirable. This disadvantage is especially serious when the insulated wire is to be used in an aircraft or in other high performance situations where the consequen­ces of insulation failure can be so serious. A quan­titative measure of this disadvantage can be obtained from a notch propagation test such as that described below.
• insulation which comprises an inner layer of a polymer which has little or no cross-linking and an outer layer of polymer which has a relatively high level of cross-linking. Furthermore, this improvement is obtained with little or no substan­tial deterioration of other important properties of the insulation, for example, resistance to scrape abrasion, resistance to crossed wire abrasion and resistance to cut-through.
• the present invention provides an insulated electrical conductor, especially a wire, which comprises
• a preferred method of making such an insulated conductor comprises
• the polymeric component in the polymeric com­positions used in the present invention preferably comprises, and more preferably consists essentially of, a melt-shapeable crystalline polymer having a melting point of at least 200°C, preferably at least 250°C, or a mixture of such polymers.
• melting point is used herein to denote the temperature above which no crystallinity exists in the polymer (or, when a mixture of crystalline polymers is used, in the major crystalline component of the mixture).
• Particularly preferred polymers are fluorocarbon polymers.
• fluorocarbon polymer is used herein to denote a polymer or mixture of polymers which contains more than 10%, preferably more than 25%, by weight of fluorine.
• the fluorocarbon polymer may be a single fluorine-­containing polymer, a mixture of two or more fluorine-­containing polymers, or a mixture of one or more fluorine-containing polymers with one or more polymers which do not contain fluorine.
• the fluoro­carbon polymer comprises at least 50%, particularly at least 75%, especially at least 85%, by weight of one or more thermoplastic crystalline polymers each containing at least 25% by weight of fluorine, a single such crystalline polymer being preferred.
• Such a fluorocar­bon polymer may contain, for example, a fluorine-­containing elastomer and/or a polyolefin, preferably a crystalline polyolefin, in addition to the crystalline fluorine-containing polymer or polymers.
• the fluorine-­containing polymers are generally homo- or co-polymers of one or more fluorine-containing olefinically unsaturated monomers, or copolymers of one or more such monomers with one or more olefins.
• the fluorocarbon polymer has a melting point of at least 200°C, and will often have a melting point of at least 250°C, e.g. up to 300°C.
• the polymeric composition has a viscosity of less than 105 poise at a temperature not more than 60°C above its melting point.
• a preferred fluorocarbon polymer is a copolymer of ethylene and tetrafluoroethylene and optionally one or more other comonomers, especially a copolymer comprising 35 to 60 mole percent of ethylene, 35 to 60 mole percent of tetrafluoroethylene and up to 10 mole percent of one or more other comonomers.
• polymers which can be used include copolymers of ethylene and chlorotrifluoroethylene; copolymers of vinylidene fluoride with one or both of hexafluoropropylene and tetrafluoroethylene, or with hexafluoroisobutylene; and copolymers of tetrafluoroethylene and hexafluoropropy­lene.
• the polymeric composition can optionally contain suitable additives such as pigments, antioxidants, thermal stabilisers, acid acceptors and processing aids.
• the first and second compositions preferably contain the same polymeric components, and more pre­ferably are substantially the same in all respects except for the level of cross-linking.
• the conductor is preferably a metal (e.g. cop­per) wire, which may be stranded or solid.
• the wire may be for example from 10 to 26 AWG in size.
• the first layer preferably contacts the conductor.
• the second member is preferably also in the form of a layer which has the same general shape as the first layer or which serves to join together a number of wires each of which is surrounded by a first layer, thus forming a ribbon cable.
• the layers are preferably in direct con­tact, but may be joined together by a layer of adhe­sive.
• the first and second members are preferably formed by melt-extrusion, particularly by sequential extrusion, which may be tubular or pressure extrusion, so that the layers are hot when first contacted, in order to promote migration of the cross-linking agent.
• the polymeric compositions should preferably be selected so that at least the outer layer has a tensile strength of at least 3,000 psi (210 kg/cm2); and since a higher tensile strength is usually desired in the cross-linked product and there is frequently a loss of tensile strength during the irradiation step, a higher initial tensile strength is preferred, e.g. greater than 6,000 psi (420 kg/cm2), preferably at least 7,000 psi (490 kg/cm2), particularly at least 8,000 psi (560 kg/cm2).
• the thickness of the inner layer is generally 0.0075 to 0.038 cm (0.003 to 0.015 inch), preferably 0.0075 to 0.0225 cm (0.003 to 0.009 inch).
• the thickness of the outer layer is generally 0.01 to 0.063 cm (0.004 to 0.025 inch), preferably 0.01 to 0.023 cm (0.005 to 0.009 inch).
• Preferred radiation cross-linking agents con­tain carbon-carbon unsaturated groups in a molar per­centage greater than 15, especially greater than 20, particularly greater than 25.
• the cross-­linking agent contains at least two ethylenic double bonds, which may be present, for example, in allyl, methallyl, propargyl or vinyl groups.
• cross-linking agents are triallyl cyanurate (TAC) and triallyl iso­cyanurate (TAIC); other specific cross-linking agents include triallyl trimellitate, triallyl trimesate, tetrallyl pyromellitate, the diallyl ester of 1,1,3-­trimethyl-5-carboxy-3-( p -carboxyphenyl) indan.
• TAC triallyl cyanurate
• TAIC triallyl iso­cyanurate
• Other cross-linking agents which are known for incorporation into fluorocarbon polymers prior to shaping, for example those disclosed in U.S. Patents referenced above, can also be used. Mixtures of cross-linking agents can be used.
• the first composition as extruded contains little or no cross-­linking agent (e.g. 0 to 2% by weight, preferably 0%), and the second composition as extruded contains more than is desired during the cross-linking step, e.g. at least 5%, preferably 5 to 25%, particularly 7 to 12%, by weight.
• the time for which the layers should be maintained in contact prior to cross-linking depends upon the extent of migration which is needed and the temperature during such contact, which is preferably 5 to 150°C below the melting point of the polymer (or the lower melting polymer if there are two or more polymers in the layers).
• the inner layer preferably contains 0 to 3% by weight of cross-­ linking agent and the outer layer preferably contains 3 to 10% by weight of crosslinking agent.
• the dosage employed in the irradiation step is generally below 50 Mrads to ensure that the polymer is not degraded by excessive irradiation, and the dosages preferably employed will of course depend upon the extent of cross-linking desired, balanced against the tendency of the polymer to be degraded by high doses of irradiation. Suitable dosages are generally in the range of 2 to 40 Mrads, for example 2 to 30 Mrads, pre­ferably 3 to 30 Mrads, especially 5 to 25 or 5 to 20 Mrads, particularly 5 to 15 Mrads.
• the ionising radiation can for example be in the form of accelerated electrons or gamma rays. Irradiation is generally carried out at about room temperature, but higher tem­peratures can also be used.
• the inner layer need not be cross-linked at all, but is preferably cross-linked so that it has an M100 value of 2.8 to 17.5 kg/cm2 (40 to 250 psi), par­ticularly 3.5 to 10.5 kg/cm2 (50 to 150 psi).
• the elongation of the inner layer is preferably at least 100%, particularly at least 125%, eg. at least 150%, especially 200 to 300%.
• the outer layer is preferably cross-linked so that it has an M100 value of at least 28 kg/cm2 (400 psi), particularly at least 31.5 kg/cm2 (450 psi), with yet higher values of at least 42 kg/cm2 (600 psi) being valuable in many cases.
• the elongation of the outer layer is preferably 40 to 150%, particularly 50 to 120%.
• the Notch Propagation Values are measured on a piece of insulated wire about 30 cm (12 inch) long.
• a notch is made in the insulation, about 5 cm (2 inch) from one end, by means of a razor blade at right angles to the axis of the wire.
• the depth of the notch is controlled by mounting the razor blade between two metal blocks so that it protrudes by a distance which is 0.01 cm (0.004) inch or, if the insulation comprises two layers and the outer layer has a thickness t which is less than 0.018 cm (0.007 inch) thick, by a distance which is (t-0.0051) cm [(t-0.002) inch].
• the end of the wire closer to the notch is secured to a horizontal mandrel whose diameter is three times the outer diameter of the insulation.
• a 0.675 kg (1.5 lb) weight is secured to the other end of the wire so that the wire hangs vertically.
• the mandrel is then rotated clockwise, at about 60 revolutions a minute, until most of the wires has wrapped around the mandrel.
• the mandrel is then rotated, counterclockwise, until the wire has unwrapped and most of the wire has again been wrapped around the mandrel.
• the mandrel is then rotated clockwise until the wire has unwrapped and most of the wire has again been wrapped around the mandrel. This sequence is continued until visual observation of the notched area shows the conductor to be exposed.
• the conductor is broken (or some or all of the strands of a stranded wire conductor are broken) then the failure is attributable to that breakage, not to propagation of the notch through the insulation.
• the number of cycles (half the number of times the rotation of the mandrel is reversed) is recorded.
• the M100 values are determined by a static modulus test as described in U.S. Patent No. 4,353,961 carried out at about 40°C above the melting point of the polymer, (e.g. at about 320°C for ETFE polymers).
• the tensile strengths and elongations are determined in accordance with ASTM D 638-72 (i.e. at 23°C) at a testing speed of 50 mm (2 inch) per minute.
• cross-wire abrasion values are measured by the tests described in U.S. Patent No. 4,353,961.
• Example 1 is a comparative Example.
• a 20 AWG (19/32) stranded tin-coated copper wire was insulated by melt-extruding over it, by sequential extrusion, an inner insulating layer 0.01 to 0.0125 cm (0.004 to 0.005 inch) thick and an outer insulating layer .018 to 0.020 cm (0.007 to 0.008 inch) thick.
• the layers were composed of the following compositions: The polymeric insulation was cross-linked by irra­diating it to a dosage of 14 Mrads.
• Example 1 The procedure of Example 1 was followed except that the composition of the inner layer was ETFE polymer 99.2 (Tefzel from duPont) Additives 0.8 Triallyl isocyanurate -

Landscapes

• Spectroscopy & Molecular Physics (AREA)
• Physics & Mathematics (AREA)
• Organic Insulating Materials (AREA)
• Processes Specially Adapted For Manufacturing Cables (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Insulated Conductors (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Laminated Bodies (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Connection Or Junction Boxes (AREA)
• Installation Of Indoor Wiring (AREA)
• Patch Boards (AREA)
• Dental Preparations (AREA)
• Materials For Medical Uses (AREA)

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Citations (5)

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• 1986
  • 1986-10-08 CA CA000520053A patent/CA1295574C/en not_active Expired - Lifetime
  • 1986-10-09 AT AT86307817T patent/ATE48720T1/de not_active IP Right Cessation
  • 1986-10-09 DE DE8686307817T patent/DE3667569D1/de not_active Expired - Lifetime
  • 1986-10-09 JP JP61241166A patent/JPH0679451B2/ja not_active Expired - Fee Related
  • 1986-10-09 ES ES86307817T patent/ES2012452B3/es not_active Expired - Lifetime
  • 1986-10-09 IL IL80269A patent/IL80269A/xx not_active IP Right Cessation
  • 1986-10-09 EP EP86307817A patent/EP0222507B1/de not_active Expired
  • 1986-10-10 KR KR1019860008497A patent/KR950007089B1/ko not_active IP Right Cessation
  • 1986-10-10 BR BR8604970A patent/BR8604970A/pt not_active IP Right Cessation

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