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
  • H01B7/42—Insulated conductors or cables characterised by their form with arrangements for heat dissipation or conduction
• • 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
  • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
  • H01B3/04—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances mica
• • 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
  • H01B3/28—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances natural or synthetic rubbers
• • 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
  • H01B3/42—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 polyesters; polyethers; polyacetals
  • H01B3/421—Polyesters
• • 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
  • H01B3/46—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 silicones
• • 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
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/29—Protection against damage caused by extremes of temperature or by flame
  • H01B7/295—Protection against damage caused by extremes of temperature or by flame using material resistant to flame

Definitions

• This invention relates to electrical wire and cables .
• cables which are capable of func ⁇ tioning for a period of time during a fire without shorting or otherwise failing.
• These cables have been called circuit integrity cables or signal integrity cables depending on their use.
• the previously proposed cables have generally used the principle that the indi ⁇ vidual conductors should be separated from one another by mica tapes, by large volumes of packing materials, by relatively thick layers of silicone insulation or by combinations thereof in order to prevent the formation of short circuits during a fire. There is therefore a need for a cable that will retain its integrity for a period of time when subjected to a fire but which is relatively small and lightweight and which is relati ⁇ vely inexpensive to manufacture.
• an electrical wire which comprises a metallic electrical conductor, an insulating mineral layer electrolytically formed on the conductor from chemi ⁇ cally delaminated weathered mica, and a silicone polymer layer located on the mineral layer.
• weathered mica is used herein to describe the weathering products of natural mica and includes minerals comprising vermiculite or minerals of a mixed layer type containing vermiculite layers as a major constituent. It includes any hydratable, layer latticed, expandable silicate structure, and primarily the three layer micas .
• the layers usually have a thickness of about 10 Angstrom units with the main ele ⁇ mental constituents being magnesium, aluminium, silicon and oxygen. It may be formed by replacement of non- exchangeable cations, e.g. potassium ions, by exchangeable cations, e.g. sodium or magnesium ions, in mica. Such replacement will normally occur through weathering of mica, but the term includes materials formed by other methods of cation exchange, e.g.
• the term includes materials such as vermiculites and smectites in which there has been complete replacement of the non-exchangeable cations, and any intermediate materials such as formed by partial replacement of the non-exchangeable cations, provided, as explained below, that it is possible to form a colloidal dispersion from the material.
• the use of a weathered mica instead of unweathe-red mica has the advantage that the cohesion of the resulting mineral layer is much larger than that of a deposited mica layer with the result that it is then possible to handle the wire more easily during manufac ⁇ ture and use, and in addition, much higher electrolytic deposition rates can be achieved with lower deposition voltages .
• the weathered mica is a mineral of a mixed layer type that contains mica layers interspersed with other layers that are formed by weathering.
• the weathered layers may comprise any hydratable, layer latticed, expandable silicate structure, e.g. hydro- biotite and hydrophlogopite layers , and preferably hydrophlogopite II layers although other layers may instead be present.
• the hydratable layers may comprise a major part of the original mineral although it is preferred for the major part (by weight) to be formed from* unweathered mica layers.
• the mineral used according to the invention may be regarded as formed from platelets that have a micaceous, or predominantly micaceous interior, and a surface that is formed from a hydrated silicate layer.
• the platelets preferably have an average thickness of not more than 500 Angstroms, more preferably not more than 300 Angstroms, especially not more than 200 Angstroms and most especially not more than 100 Angstroms, but preferably at least 20 Angstroms, more preferably at least 40 and especially at least 60 Angstroms .
• the wire will normally be provided with an outer protective layer or jacket which will protect the weathered mica layer from mechanical abuse during handling and which is preferably also electrically insulating so that it can provide further electrical insulation during normal operation.
• the protecting and insulating layer will normally be a polymeric layer which is formed on the coated conductor by an extrusion process although in some cases it may be preferred to apply the insulation by a tape wrapping process for example in the case of polytetrafluoroethylene or cer ⁇ tain polyimides . In other cases however, for example in the case of electric motor windings or transformer windings, where very thin, high temperature wire is required, it is possible to dispense with the polymeric insulation altogether .
• the wire according to the invention may be manu ⁇ factured in a particularly simple manner by passing an elongate electrical conductor through a dispersion of chemically delaminated weathered mica and applying an electrical potential to the conductor in order to depo- sit reconstituted weathered mica (hereinafter referred to simply as the "mineral" ) onto the conductor and drying the conductor and the mineral layer so formed.
• the silicone layer may be formed on the coated conductor by any appropriate method, e.g. by extrusion or dip-coating, and then curing the silicone layer so formed.
• the weathered mica dispersion may be formed by treating the weathered mica ore consecutively with an aqueous solution of an alkali metal e.g. a sodium salt, and especially sodium chloride, and an aqueous solution of a further salt, e.g. an organo substituted ammonium salt such as an n-butyl ammonium salt, in order to swell the ore for example as described in British Patent No. 1,065,385, the disclosure of which is incor ⁇ porated herein by reference.
• an alkali metal e.g. a sodium salt, and especially sodium chloride
• a further salt e.g. an organo substituted ammonium salt such as an n-butyl ammonium salt
• the ore After the ore has been swelled to a number of times its original size in water, it is delaminated for example by means of a mill, a mixer, an ultrasonic agitator or other suitable device to form the majority of the expanded mineral into a colloidal dispersion.
• the colloidal dispersion so formed can be fractionated by sedimentation into several cuts .
• a mineral such as vermiculite or other very highly weathered systems, as one moves from the 'fines' to the more coarse fractions the degree of hydration decreases through successive layers, the K2O content increases and the x-ray diffraction pattern moves closer to resembling the parent mineral.
• the dispersion is permitted to stand for between 1 and 60 minutes, preferably 5 to 20 minutes, and the top fraction decanted to supply the working colloid.
• the top fraction decanted to supply the working colloid.
• the particle size range of the decanted fraction typically is between 1 and 250 um, preferably between 1 and 100 ⁇ m.
• the suspension has a concentration of at least 0.5 and especially at least 1% by weight although lower con ⁇ centrations may be used provided that the concentration is not so low that flocculation occurs .
• the maximum concentration is preferably 8% and especially 4% by weight, beyond which the relatively high viscosity of the suspension may lead to unreproduceable coatings .
• the conditions that are employed to form the suspension will depend among other things on the particular type of mineral that is employed.
• the preferred method of forming the weathered mica dispersion is described in our copending patent application entitled “Mineral” and filed on even date herewith (Agent's reference RK375), claiming priority from British application No. 8813574.
• the conductor In order to coat the conductor, it is passed con ⁇ tinuously through a bath containing the mineral suspen ⁇ sion while being electrically connected as an anode with respect to a cathode that is immersed in the suspension, so that the weathered mica platelets are reconstituted electrolytically on the conductor in the form of a gelatinous coating.
• the fact that the coating is gelatinous and therefore electrically con ⁇ ductive means that it is not self-limiting in terms of the coating thickness and therefore enables relatively thick coatings to be formed.
• the plating voltage will depend on a number of factors including the residence time of the conductor in the bath, the desired coating thickness, the electrode geometry, the bath con ⁇ centration and the presence or otherwise of other spe ⁇ cies, especially ionic species, in the bath.
• the plating voltage will normally be at least 5V, more pre ⁇ ferably at least 10V and especially at least 20V since lower voltages usually require very long residence times in the bath in order to achieve an acceptable coating thickness .
• the voltage employed is usually not more than 200V and especially not more than 100V since higher voltages may lead to the production of irregular coatings and poor concentricity of the coating layer, to oxidation of the anode or electrolysis of the bath water and hence a poorly adhered coating.
• Such plating voltages will usually correspond to a current density of 0.1 to 6 mA mm"'--.
• the coating is dried in order to remove residual water from the gel. This may be achieved by hauling the coated wire through a hot-air column or a column heated by infrared sources or hot filaments. Additional columns may be used if desired.
• the wire may then be hauled off for final use or to be provided with an outer protective insulation .
• the orientation of the platelets in a direction parallel to the underlying conductor means that relatively rapid drying methods can be used to collapse the gel to leave an integral, self-supporting inorganic layer.
• the silicone polymers used for forming the sili ⁇ cone polymer layer are preferably elastomeric and adapted for coating conductors by extrusion or dip- coating. It is preferred to use elastomers rather than solvent based resins because the resin will impregnate the mineral layer at least to some extent which will normally require a long drying period during manufac ⁇ ture of the wire. In addition it has been found that the use of a silicone elastomer layer will improve the fire performance of the wire as described below.
• Suitable forms of silicone polymer from which silicone elastomers may be derived include polymers of which at least some of the repeating units are derived from unsubstituted or substituted alkyl siloxanes, for example, dimethyl siloxane, methyl ethyl siloxane, methyl vinyl siloxane, 3,3 ,3-trifluoropropyl methyl siloxane, polydimethyl siloxane, dimethyl siloxane/- methyl vinyl siloxane co-polymers , fluoro silicones, e.g. those derived from 3 ,3, 3-trifluoropropyl siloxane.
• the silicone polymer may be, for example, a homopolymer or a copolymer of one or more of the above siloxanes, and is advantageously polydimethyl siloxane or a copo ⁇ lymer of dimethyl siloxane with up to 5% by weight of methyl vinyl siloxane.
• Silicone modified EPDM such as Royalther (available from Uniroyal) and room tem ⁇ perature vulcanising silicones are also suitable materials .
• the silicone elastomer may, if desired, contain fillers, for example reinforcing fillers, flame retar- dants, extending fillers, pigments, and mixtures thereof.
• suitable fillers include diato- maceous earth and iron oxide. It will be appreciated that such fillers may be used in addition to a rein ⁇ forcing filler such as silica that is added to silicone polymer to form the silicone elastomer.
• a binder is incorporated in the mineral coating which can improve processability of the mineral-clad conductor.
• a binder is incorporated in the mineral dispersion and is deposited on the conductor along with the mineral in order to improve the processability of the clad conduc ⁇ tor.
• the material chosen for the binder should be inert, i.e. it should not corrode the conductor metal or react with the mineral coating and preferably it improves the bonding of the mineral layer to the con ⁇ ductor metal. It should also be electrophoretically mobile and non-flocculating.
• the binder may be disper- sible in the medium that is used to form the mineral suspension (water), for example it may comprise a water-dispersed latex, e.g. a styrene/butadiene/car- boxylic acid latex, a vinyl pyridine/styrene/butadiene latex, a polyvinyl acetate emulsion, an acrylic copo ⁇ lymer emulsion or an aqueous silicone emulsion.
• a water-dispersed latex e.g. a styrene/butadiene/car- boxylic acid latex, a vinyl pyridine/styrene/butadiene latex, a polyvinyl acetate emulsion, an acrylic copo ⁇ lymer emulsion or an aqueous silicone emulsion.
• binders in the form of emulsions because they may be dried quickly with only a few seconds residence time in the drying tower, whereas with aqueous solutions much longer drying times are necessary, and, if drying is forced, bubbles may be formed in the mineral layer that will cause imperfec ⁇ tions in the resulting dried layer.
• binders that are hydrophobic have the advan ⁇ tage that they can prevent or reduce the uptake of moisture by the mineral layer after it has been dried. This is particularly useful where the weathered mica has a relatively high degree of cationic replacement, i.e.
• the binder is preferably non-curable since curable binders do not significantly improve the performance of the wire and will normally reduce the speed at which the wire can be manufactured.
• the detrimental effect on the resistance caused by most of the binders may usually be ameliorated by the presence of the thin silicone layer. It is believed that the silicone layer acts as some form of electrical and/or mechanical barrier which prevents the char from the binder forming an electrical short circuit. Thus, for the first minute or so of the test, the electrical performance of the wire is usually dominated by that of the silicone layer. By the time the silicone layer has ashed, the char from the binder will normally have completely oxi ⁇ dized away and will no longer have any effect on the wire performance.
• the invention provides a flame resistant electrical wire which comprises a metallic electrical conductor and electrical insulation which comprises an insulating mineral layer that is formed from weathered mica and contains an organic binder, and, located on the mineral layer, a layer of a material that will provide a tem ⁇ porary barrier when the wire is subjected to a fire which will reduce or eliminate the detrimental effect of char formed from the binder on the electrical resistance of the wire insulation.
• the binder is preferably used in quantities in the range of from 5 to 30%, and especially from 10 to 25% by weight based on the weight of the weathered mica.
• the use of smaller quantities may not sufficiently improve the processability of the conductor and/or may not improve the adhesion of the mineral layer to the metal conductor adequately while the use of larger quantities of binder may lead to the generation of too much char for the silicone layer to mask.
• the binder has a carbonaceous char residue of not more than 15%, more preferably not more than 10% and especially not more than 5%.
• the char residue can be measured by the method known as thermogravimetric analysis, or. TGA, in which a sample of the binder is heated in nitrogen or other inert atmosphere at a defined rate, e.g. 10°C per minute to a defined temperature and the residual weight, which is composed of char, is recorded.
• the char residue is simply the quantity of this residual char expressed as a percentage of the initial polymer after having taken into account any non polymeric vola ⁇ tile or non-volatile components.
• the char residue values quoted above are defined as having been measured at 850°C.
• an outer protective layer pre ⁇ ferably a polymeric insulating layer, may be provided in order to protect the underlying mineral layer from mechanical abuse and in order to provide the required insulating and dielectric properties during normal use.
• polymers that may be used to form the outer layer include olefin homopolymers and copolymers of olefins with other olefins and with other monomers e.g. vinyl esters , alkyl acrylates and alkyl alkacrylates , e.g.
• low, medium and high density polyethylene linear low density polyethylene and ethylene alpha-olefin copolymers, ethylene/propylene rubber, ethylene vinyl acetate, ethylene ethyl acrylate and ethylene acrylic acid copolymers, and styrene/butadiene/styrene, styrene/ ethylene/butadiene/styrene block copolymers and hydrogenated versions of these block copolymers.
• a particularly preferred class of low charring polymers is the polyamides .
• Preferred polyamides include the nylons e.g.
• nylon 46, nylon 6, nylon 7, nylon 66, nylon 610, nylon 611, nylon 612, nylon 11 and nylon 12 and aliphatic/aromatic polyamides polyamides based on the condensation of terephthalic acid with trimethylhexa- methylene diamine (preferably containing a mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diamine isomers ) , polyamides formed from the condensation of one or more bisami ⁇ omethylnorbornane isomers with one or more aliphatic, cycloaliphatic or aromatic dicarboxylic acids e.g. terephthalic acid and optionally including one or more amino acid or lactam e.g.
• Preferred aliphatic polymers include polyethylene, polybutylene terephthalate, ionomers based on metal salts of methacrylated polyethylene, acrylic elastomers e.g. those based on ethyl acrylate, n-butyl acrylate or alkoxy-substituted ethyl or n-butyl acrylate polymers containing a cure site monomer and optionally ethylene comonomer, and block copolymers having long chain ester units of the general formula:
• G is a divalent radical remaining after the removal of terminal hydroxyl groups from a polyalkylene oxide) glycol, preferably a poly (C2 to C4 alkylene oxide) having a molecular weight of about 600 to 6000;
• R is a divalent radical remaining after removal of carboxyl groups from at least one dicarboxylic acid having a molecular weight of less than about 300;
• D is a divalent radical remaining after removal of hydroxyl groups from at least one diol having a molecular weight less than 250.
• Preferred copolyesters are the polyether ester polymers derived from terephthalic acid, polytetramethylene ether glycol and 1,4-butane diol. These are random block copolymers having crystalline hard blocks with the repeating unit:
• n 6 to 40.
• polyether-ester amide block copolymers are preferred aliphatic polymers.
• polyether-ester amide block copolymers are so called a "polyether-ester amide block copolymers" of repeating unit:
• A represents a polyamide sequence of average molecular weight in the range of from 300 to 15,000, preferably from 800 to 5000; and B represents a linear or branched polyoxyalkylene sequence of average molecu ⁇ lar weight in the range of from 200 to 6000, preferably from 400 to 3000.
• the polyamide sequence is formed from alpha,omega-aminocarboxylic acids, la ⁇ tams or diamine/dicarboxylic acid combinations having C4 to C]_4 carbon chains, and the polyoxyalkylene sequence is based on ethylene glycol, propylene glycol and/or tetramethylene glycol, and the polyoxyalkylene sequence constitutes from 5 to 85%, especially from 10 to 50% of the total block copolymer by weight.
• these polymers and their preparation are described in UK Patent Specifications Nos. 1,473,972, 1,532,930, 1,555,644, 2,005,283A and 2,011,450A.
• the polymers may be used alone or in blends with one another or with other polymers and may contain fillers e.g. silica and metal oxides e.g. treated and untreated metal oxide flame retardants such as hydrated alumina and titania.
• the polymers may be used in single wall constructions or in multiple wall construc ⁇ tions e.g. as described in British Patent Application No. 2,128,394A the disclosure of which is incorporated herein by reference.
• the polymers may be uncrosslinked or may be crosslinked for example by chemical cross- linking agents or by electron or gamma irradiation, in order to improve their mechanical properties and to reduce flowing when heated. They may also contain other materials e.g.
• polymer insulation or at least the inner wall of the insulation may be substantially halogen- free.
• certain halogen-containing polymers may generate electrically conductive species during a fire and so cause the wire to fail prematurely.
• the insulation preferably contains not more than 5% by weight halo ⁇ gens, especially not more than 1% by weight halogens and most especially not more than 0.1% by weight halo ⁇ gens.
• halogenated polymer that is particularly useful is the fluorinated polymers, pre ⁇ ferably those containing at least 10%, more preferably at least 25% fluorine by weight.
• the fluorinated polymer may be a single fluorine containing polymer or a mixture of polymers one or more of which contains fluorine.
• the fluorinated polymers are usually homo-or copolymers of one or more fluorinated, often per- fluorinated, olefinically unsaturated monomers or copo ⁇ lymers of such a comonomer with a non-fluorinated olefin.
• the fluorinated polymer preferably has a melting point of at least 150°C, often at least 250°C and often up to 350°C, and a viscosity (before any crosslinking) of less than 10 ⁇ Pa.s at a temperature of not more than 60°C above its melting point.
• Preferred fluorinated polymers are homo- or copolymers of tetra ⁇ fluoroethylene, vinylidine fluoride or hexafluoro- ethylene, and especially ethylene/tetrafluoroethylene copolymers e.g.
• the polymeric insulation, or the inner layer of any polymeric insulation preferably has a carbonaceous char residue of not more than 15% by weight as determined by thermogravimetric analysis.
• Such wires are the subject of our copending British patent application entitled “Electrical Wire” filed on even date herewith (Agent's ref: RK341" the disclosure of which is incorporated herein by reference.
• the wire according to the invention may be formed using most commonly available electrical conductor materials such as unplated copper and copper that has been plated with tin, silver or chromium.
• the conductor may be coated with an electri ⁇ cally conductive refractory layer, for example as described in European Patent Application No. 190,888, the disclosure of which is incorporated herein by reference.
• Figure 1 is an isometric view of part of a wire in accordance with the invention with the thicknesses of the layers of insulation exaggerated for the sake of clarity; and
• Figure 2 is a schematic view of apparatus for forming the wire of figure 1;
• Figures 3a to c are graphical respresentations showing the effect of a binder and a silicone layer on the circuit integrity performance of the wires .
• an electrical wire 1 comprises a 22 AWG seven strand copper conductor 2 which has been coated with a 50 micrometre thick layer 3 of a partially weathered mica, a 50 micrometre thick silicone polymer layer 3* and followed by a 0.15mm thick extruded layer of polymeric insulation 4 based on a blend of polytetramethylene terephthalate and a polytetramethylene ether terephthalate/polytetramethylene terephthalate block copolymer.
• the wire may be formed by means of the apparatus shown schematically in figure 2.
• the conductor 2 is fed into a bath 5 that contains a colloidal suspension of the weathered mica and binder, the suspension being fed from a supply bath 5', and agitated in order to maintain uniform mixing of the dispersion.
• the conductor passes down into the bath, around a roller 6 and then vertically upwards as it leaves the bath.
• a hollow tube 7 is positioned around the part of the conductor that leaves the bath and a hollow electrode 8 is located inside the hollow tube 7 so that the weathered mica is deposited on the rising part of the conductor . This prevents the mineral coating so formed being damaged as the conductor is Dassed around roller 6.
• the coated conductor After the coated conductor leaves the bath it passes through a drying tower 8 about 1.5 metres in length that is heated by a counter current of warm air so that the top of the drying tower is at a temperature of about 200°C while the bottom is at about 160°C.
• the coated conduc ⁇ tor After the mineral coating has dried the coated conduc ⁇ tor is passed through a coating pot 10 that contains a silicone polymer. After a layer of silicone polymer is applied to the wire, it is passed through a further w-rm air drying tower 11 arranged to have a temperature of about 130°C at the top and 90°C at the bottom.
• the wire When the silicone layer has been applied and dried the wire may then be spooled to await the provision of an insulating top-coat or a top-coat may be provided in-line for example by means of an extruder 12.
• the eed rate of the conductor 2 to the coating apparatus will depend on the thickness of the intended coating, the electrophoresis potential and the con ⁇ centration of the weathered mica in the bath. Feed rates in the range of from 2 to 20, and especially 5 to 10 metres per minute are preferred although increases in the feed rate should be possible, for example by increasing the dimensions of the bath in order to main ⁇ tain the same residence time with higher conductor speeds .
• Figures 3a to 3c show the effect of both the binder and the silicone layer on the electrical perfor ⁇ mance of the wire insulation.
• a 1 metre long twisted pair of wires was heated to 900°C in a gas flame, and the electrical resistance between the wires was recorded, and is shown along the ordinate, as a function of time since the heating commenced, shown along the abscissa.
• Figure 3a shows the performance of wires insulated only by means of a 25 micrometre thick layer of weathered mica that contained no binder The resistance fell when the wire was heated to a value slightly below 10 7 ohms in about 60 seconds, and remained at that level until the end of the test. Although this insulating layer had satisfactory electrical performance, it had inadequate mechanical performance and could not be manufactured at economic wire and cable processing rates.
• Figure 3b shows the performance of wires in which the mineral layer contains 15% by weight of a styrene butadiene styrene block copolymer binder.
• the mechani ⁇ cal properties were excellent and the wire could easily be mechanically handled through wire and cable pro ⁇ cessing operations at rates of up to 50m minute--!-.
• the electrical resistance of the wire fell to a value of about 10-*- ohms after 30 seconds, whereupon the resistance rose slowly until it reached about 10 7 ohms after 150 to 200 seconds and remained at this level until the test was terminated.
• the resistance drop to 10 ⁇ -'ohms would greatly restrict the voltage range to which such a wire could be specified.
• Figure 3c shows the performance of the wires of figure 3b with an additional 50 micrometre layer of a silicone elastomer to give a total thickness of 75 micrometres .
• the resistance falls to slightly over 10 ' ohms at 100 seconds after commencement of the test and remains at that level until the test is terminated. Thus the deleterious effect of the organic binder is completely removed.
• the mechanical performance of the insulation was good, the limits being determined by the strength of the silicone layer.
• the wire could easily be provided with a further layer of polymeric insula ⁇ tion.
• the working colloid that was used for coating the conductor was formed as follows: 800 gramms of a weathered mica in accordance with our co-pending British patent application entitled "Wire” (Agents ref: RK342) filed on even date herewith, was washed with boiling water for about 30 minutes and the resulting liquid was decanted to remove the clay frac ⁇ tion. The mineral was then refluxed for 4 to 24 hours in saturated sodium chloride solution to replace the exchangeable cations with sodium ions . This was then washed with distilled or deionised water to remove excess sodium chloride until no further chloride ions could be observed by testing with silver nitrate. The material was then refluxed for 4 to 24 hours with molar n-butyl ammonium chloride solution followed by further washing with distilled or deionised water until no chloride ions could be detected with silver chloride.
• a 20 AWG wire was passed through a 40 cm long bath of the colloid at a speed of 5 metres minute"-!- while the weathered mica was electrophoretically deposited on the conductor at a 4.2V plating voltage and a 165 rtiA current.
• the coated wire was then passed through a drying tower as shown in the drawing to form a mineral layer of 30 micrometre dry thickness .
• the wire was then passed through a bath of a two part silicone (KE1204 ex Shinetsu) and cured again as * hown in the drawing to form a 50 micrometre thick silicone layer. Thereafter a 100 micrometre thick single wall insulation formed from low density polyethylene containing 8% by weight decabromodiphenyl ether and 4% antimony trioxide flame retardant was extruded onto the wire.
• a two part silicone KE1204 ex Shinetsu
• the wire was tested for circuit integrity by twisting three wires together and connecting each wire to one phase of a three phase power supply, and then heating the wire to 900°C for a test period of three hours in accordance I ⁇ C 331.
• the wire was able to sup ⁇ port 300V phase-to-phase for the entire test at 900°C without failing (i.e. without blowing a 3A fuse).
• Example 1 was repeated with the exception that the following binders were used:
• Example 2 polyvinyl acetate
• Example 3 acrylic copolymer emulsion
• Example 4 polyvinylidine chloride
• Example 5 vinylpyridine terminated styrene-butadiene-styrene rubber
• the wire was tested as described in Example 1 and in each case the wires were able to support 300V phase- to-phase at 900°C for 3 hours.
• Example 1 was repeated with the exception that the silicone layer was formed from an extended polydimethyl siloxane based formulation.
• the silicone composition was room-temperature extruded onto the coated conductor to give a 75 to 100 micrometre thick layer and was vulcanised in a tube furnace at 300°C (20.5 second residence time).
• Example 7 The wire was tested as described in Example 1 and supported 440V phase-to-phase for 3 hours at 900°C.
• Example 6 was repeated with the exception that the plating voltage of the deposition bath was 15.5V ( 300mA) which gave a mineral layer thickness of 40 micrometres .
• Example 1 was repeated with the exception that the silicone used was a dip-coated solventless silicone (sylgard 184) applied to a thickness of 70 micrometres.
• the wire supported 300V phase-to-phase for 3 hours at 900°C.
• Example 1 was repeated with the exception that the low density polyethylene insulation was replaced with a 100 micrometre thick layer comprising:
• Example 9 was repeated with the exception that the PBT/Surlyn layer contained no flame retardant (decabromodiphenyl ether/Sb2 ⁇ 3. and that an additional polymeric layer of thickness 100 micrometres was pro ⁇ vided on top of the PBT/Surlyn layer.
• the additi * - al layer had the composition:
• polybutylene terephthalate (PBT) 70 polybutylene terephthalate - 30 polybutylene ether tereph ⁇ thalate block copolymer ethylene bis-tetrabromo- 10 phthalimide antimony trioxide 4 magnesium hydroxide 20
• PBT polybutylene terephthalate
• 30 polybutylene ether tereph ⁇ thalate block copolymer ethylene bis-tetrabromo- 10 phthalimide antimony trioxide 4 magnesium hydroxide 20
• Example 7 was repeated with the exception that the low density polyethylene insulation was replaced by the additional layer of Example 10.
• the wire supported 440V phase-to-phase for 3 hours at 900°C.
• Example 6 was repeated with the exception that the low density polyethylene insulation was replaced with a 100 micrometre thick layer of un-flame retarded high density polyethylene.
• Example 1 was repeated with the exception that the binder used was a vinyl acetate/ethylene copolymer, the plating voltage was 12.5V and current 422 mA, the line speed was 10 metres minute " -*- and the silicone layer and polymer insulation had the compositions shown below: Silicone composition
• antioxidant (Irganox 1010) 1.9 magnesium hydroxide 18.8
• the silicone layer had a thickness of 100 um and the polymer layer had a thickness of 125 um.
• the wire was tested as described in Example 1 and was able to support 440V (3A) bhase-to-phase for the entire test at 900°C.
• Example 13 was repeated with the exception that the polymer insulation had the composition:
• antioxidant (Irganox 1010) 1.9 magnesium hydroxide 18.8
• the plating voltage was 11.5V and current was 365 mA.
• the mineral layer has a thickness of 25 um and the silicone layer had a thickness of 125 um.
• the wire was able to support 440V (3A) phase-to- phase for the entire test (3 hours) at 900°C.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Organic Insulating Materials (AREA)
• Insulated Conductors (AREA)

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Citations (3)

• 1987
  • 1987-07-10 GB GB878716303A patent/GB8716303D0/en active Pending
• 1988
  • 1988-07-08 JP JP63505731A patent/JPH02504199A/ja active Pending
  • 1988-07-08 AU AU19905/88A patent/AU606723B2/en not_active Ceased
  • 1988-07-08 KR KR1019890700441A patent/KR0131402B1/ko not_active IP Right Cessation
  • 1988-07-08 CA CA000571500A patent/CA1319401C/en not_active Expired - Fee Related
  • 1988-07-08 IL IL87045A patent/IL87045A/xx unknown
  • 1988-07-08 WO PCT/GB1988/000544 patent/WO1989000762A1/en not_active Application Discontinuation
  • 1988-07-08 EP EP88905960A patent/EP0370041A1/en not_active Withdrawn
  • 1988-07-08 BR BR888807604A patent/BR8807604A/pt not_active Application Discontinuation
• 1990
  • 1990-01-09 DK DK005690A patent/DK163849C/da not_active IP Right Cessation
  • 1990-01-09 FI FI900108A patent/FI900108A/fi not_active IP Right Cessation

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