DK163849B - Electrical lead and cable with insulation which is fire-resistant, and method of manufacturing the lead - Google Patents

Description

in

DK 163849 B

This invention relates to electrical wires and cables.

In certain areas where wires and cables are used, e.g. in military use or in the transmission of many signals, it is desirable to use cables capable of operating for a certain time in the event of fire, without being short-circuited or otherwise faulty.

These cables have been called damage-free circuit or damage-free signal cables depending on their use. In connection with known cables, the principle has generally been that the individual conductors should be spaced apart by strips of mica, by large amounts of gasket materials, by relatively thick layers of silicone insulation or by their compositions, to prevent the formation of short circuits during fire, 15 U.S. Patent No. 4,576,674 discloses a method of producing an electrically insulated conductive article for electrical apparatus, wherein the conductive article is immersed in water, wherein mica and a water-dispersible lacquer, has been dispersed, with subsequent electro-liquid deposition of mica and varnish on the conductive workpiece.

The electrodeposited layer is then dried before being further immersed in a water-soluble resin solution containing a curing agent, after which the resin coating is dried by heat, and then the electrically insulated conductive blank is impregnated with resin, which then solidifies by heat.

It has been found as a new technical effect that an electrical wire isolated by a layer of electrolytically deposited chemically delaminated weathered mica covered with an outer polymeric layer of silocone retains its resistance 30 for a certain time when the wire is exposed to fire. This discovery has enabled a cheap manufacture of damage-free circuit cables or damage-free signal cables that are relatively thin and lightweight.

In the present invention, there is provided an electrical conduit including a metallic electrical conductor, an insulating mica layer which is electrolytically formed.

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2, which is characterized in that the glaze is chemically delaminated and weathered, and that a polymer layer of silicone is also placed on the mica layer.

It is known that several phyllosilicate minerals form 5 intermediate complex compounds with a wide variety of charged and uncharged substances of both organic and inorganic origin, for example alkylammonium ions, amino acids and amino acid cations. The placement of the interposed substances between the layers of macro crystals usually results in changes in the basal distance which can be measured by X-ray diffraction techniques. In some circumstances, a further swelling may occur, whereby additional insertions occur at a wide range of polar and non-polar solutions. In special cases, the degree of expansion may be so great that "gel-like" samples are provided. The use of a weak mechanical influence on these severely swollen systems can lead to the preparation of colloidal dispersions of the mineral in a dispersing solvent, which is known as "chemical delamination".

In particular, this effect may be present in a number of complex mica-type compounds containing n-alkylammonium ions, with water as a dispersing solvent. Whether additional extensions with inserts occur depends on the low-shift density whereby 25 subsequent layers are separated from the mineral and the length of the alkyl chain in the associated interlaced materials.

Minerals with a surface change density in the range of 0.5 to 0.9 saturated with certain short-chain n-alkylammonium ions, e.g. n-propyl, n-butyl and isoamyl, perform exceptionally well in exhibiting extensive swelling. between the layers of water. Crystals exhibiting this kind of effect may have a volume increase of up to, and sometimes more than, 30 times their original volume, and remain coherent and "gel-like". Intermediate-layer minerals containing mixed layers of interchangeable and non-interchangeable cations may be partially saturated with

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3 short-chain alkylammonium ions and upon subsequent treatment with water they can swell "macroscopically" for only part of the layered structure.

In each case, a limited mechanical displacement will delaminate the swollen crystals along the macroscopically swelled cleavage plane, where the forces between the layers are minimized. This effect can be used to produce a colloidal dispersion of thin small sheets with a large aspect ratio. In the case where the mineral used initially is homogeneous, the composition of the colloid will be resistant. However, if the minerals in the mixed layers are used, a large number of different plate compositions and characteristics in the colloidal dispersion can be provided. Fractionation techniques, including precipitation, can be used to isolate components of the dispersant exhibiting different chemical and physical properties, from each other, and from the original mineral.

The term "weathered mica" is used herein to describe the weathering products of naturally occurring mica, and includes minerals consisting of vermiculite or mixed-layer minerals containing vermiculite layers as the main constituent. It includes any hydrating expandable silicate build with lattice-shaped 25 layers, and especially the three-layer mica. The layers usually have a thickness of approx. An angular current, the principal constituents including magnesium, aluminum, silicon and oxygen. It can be formed by replacing non-replaceable cations in mica, e.g. potassium ions, with interchangeable cations, e.g. sodium ions or magnesium ions. Such a replacement process can normally occur by weathering mica, but the term also includes materials provided by other methods of replacing cations, for example, by hydrothermal effects or in association with synthetic mica materials. Also included are materials such as vermiculites and smectites, in which

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4 continuously replaces the non-replaceable cations, and any intermediate material, such as a material provided by partial replacement of the non-replaceable cations, provided, as explained later, that it is possible to provide a colloidal dispersion from the material. The use of weathered mica instead of non-weathered mica has the advantage that the cohesion in the resulting mineral layer is much greater than the cohesion of a precipitated mica layer, with the result that it is possible to handle the wire more easily through manufacture and by and, in addition, that much higher electrolytic precipitation rates can be obtained at lower precipitation voltages.

It is preferred that the weathered mica is a mineral of a mixed-layer species that contains mica layers placed between other layers provided by weathering.

The weathered layer may include any hydrating, expandable silicate structure with lattice-shaped layers, for example hydrobiotite and hydrophlogopite layers, and especially hydrophlogopite II layers, although other layers may be present instead. The hydrating layers may constitute the majority of the original mineral, although it is preferable that the bulk be provided from non-weathered mica layers.

Thus, the mineral used according to the invention can be considered as being formed from small sheets having a mica-containing, or predominantly mica-containing, interior and a surface provided from a hydrated silicate layer. The plates should preferably have an average thickness of no more than 500 Angstroms, preferably having a thickness of no more than 300 Angstroms, especially no more than 200 Angstroms, and even better not more than 100 Angstroms, but preferably at least 20 Angstroms, with at least 40 Angstroms being preferred and in particular the 35 plates must be not less than 60 Angstroms.

The cord will normally be provided with an exterior

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5, a protective layer or sheath which will protect the weathered rubber layer from mechanical impact during handling of the cable, the outer protection being preferably also electrically insulating, so that further electrical insulation can be provided during normal operation. The protected and insulating layer will normally be a polymeric layer which, in an extrusion process, is placed on the pre-coated conductor, although in some cases it may be preferable to apply the insulation in a band winding process, e.g. in association with polytetrafluoroethylene or certain polyimides. In other cases, e.g. in connection with the windings in electric motors or transformers, where a very thin wire is required which can withstand high temperatures, it is possible to avoid the polymeric insulation layer completely.

The conduit provided by the invention can be made in a particularly simple manner by passing a long electrical conductor through a dispersion of chemically delaminated, weathered mica and applying to the conductor an electric potential to precipitate recovered weathered mica (hereinafter referred to as "simple"). the mineral ") on the conductor and dry the conductor and the mineral layer thus formed. After the mineral layer has been dried, the silicon layer can be formed on the coated conductor by any suitable method, for example by extrusion or coating by dipping, after which the silicon layer thus formed is cured.

The weathered mica dispersion can be obtained by treating the material sequentially with an aqueous solution of an alkali metal, e.g. a sodium salt, and especially sodium chloride, and an aqueous solution of an additional salt, for example an ammonium salt substituted with an organic material such as an n-butylammonium salt, to cause the pea to swell, such as e.g. disclosed in British Patent Specification No. 1,065,385. After the ore has swelled up to several times its original size in water, it is delaminated, e.g. using a grinding device, a mixing means, an ultrasonic device or other suitable

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6, whereby most of the expanded mineral material occurs in a colloidal dispersion. The colloidal dispersion thus formed can be fractionated by precipitation in various sizes. With a mineral such as vermiculite 5 or other highly weathered mixtures, when transitioning from "finer" to coarser fractions, a decrease in hydrogenation through the successive layers will occur, while increasing the content of K20 and the X-ray diffraction pattern. approaching the original 10 minerals pattern. When partially weathered mica is used, a distinct increase in mica-containing components can be readily detected, and as the process approaches the coarse, non-treatable fraction of the mineral, the X-ray diffraction pattern, TGA trace and elemental composition 15 clearly indicate that it is pure mica. In the latter case, it is possible to provide a dispersion of preferably mica containing lamellae by identifying the appropriate fractions of the colloidal mixture, i.e. by separating the coarse mica fraction and the strongly hydrated fine constituents 20 of vermiculite. Therefore, it is possible to produce a dispersion of g im like small plates as can be detected by XRD, TGA and elemental analysis using the chemical interchangeability of the intermediate layers of vermiculite and partially weathered intermediate layers of minerals.

In a typical process, the dispersion rests between 1 and 60 minutes, preferably between 5 and 20 minutes, and the top fraction is decanted to provide the working colloid. In many cases where partially weathered mica is used, it will not be possible to suspend all the mineral substance 30 since the weathering process does not occur uniformly throughout the mineral material and the greater the degree of weathering or cation exchange, the greater the proportion of the mineral can be dispersed. . The particle size of the decanted fraction is typically between 1 and 250 μιη, preferably between 1 and 100 μια. It is preferred that the suspension has a concentration of at least 0.5, and especially at least

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7 1% by weight, although lower concentrations may be used, provided that the concentration is not so low as to form lint. The maximum concentration is particularly preferred to be 8% and especially 4% by weight, as concentrations in addition to the relatively high viscosity of the suspension can lead to unproductable coatings. The conditions for providing the suspension will depend, inter alia, on the particular kind of mineral used. The preferred method of providing the dispersion of weathered mica is explained in the parallel patent application, which is referred to as "mineral", which relies on priority from British Application No. 8,813,574.

For coating the conductor, it is passed continuously through a bath of mineral suspension, while conductor 15 is electrically connected as anode to a cathode immersed in the suspension, so that the small plates provided by weathered mica are electrolytically precipitated on the conductor as a gelatinous coating. The fact that the coating is gelatinous and therefore electrically conductive means that the coating is not by itself limited in terms of the thickness of the coating, thus making it possible to provide relatively thick coatings. The plating voltage depends on a number of factors including the time the conductor is placed in the bath, the desired coating thickness, the geometric shape of the electrode 25, the concentration in the bath and the presence or absence of other substances, especially ionic substances, in the bath. The plating voltage should normally be at least 5V, preferably being at least 10V and especially at least 20V, since lower voltage usually requires 30 long residence times in the bath to obtain an acceptable thickness of the coating. The voltage used is usually not greater than 200V and especially not greater than 100V since greater voltages can cause an irregular coating and poor concentricity of the coating layer, oxidation of the anode or electrolysis of the water content of the bath, and thus poor adhesion of the coating. -

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8 things. Such location voltages will usually correspond to a current density of 0.1 to 6 mA mm “2.

After the coating line has left the bath, and preferably before coming into contact with rollers or other parts of the machinery, the coating is dried to remove residual water from the gel. This can be achieved by pulling the coated wire through a hot air column or a column heated by infrared sources or hot filaments. Additional columns can be used if desired. Thereafter, the cord may be provided with outer protective insulation. The orientation of the small plates in a direction parallel to the underlying conductor means that relatively rapid drying methods can be used to cause the gel to collapse, leaving a coherent, self-supporting inorganic layer.

The polymeric silicon materials used to provide the polymeric silicon layer may advantageously be elastomeric and suitable for coating conductors by extrusion or by coating by immersing the conductor. It is preferred to use elastomers instead of solution-based resins, since the resin will penetrate the mineral layer at least to some extent, which would normally require a longer drying period during the preparation of the conduit. In addition, it has been found that the use of an elastomeric silicon layer will improve the performance of the cord during a fire, as explained below.

Suitable forms of polymeric silicon substances from which elastomeric silicon substances can be derived include polymers wherein at least some of the repeating units are derived from unsubstituted or substituted alkyl siloxanes, e.g. dimethylsiloxane, methylethylsiloxane, methylvinylsiloxane, 3,3,3-trifluoropropylmethylsiloxane, polydimethylsiloxane, dimethylsiloxane / methylvinylsiloxane copolymers, fluorosilicones, for example, those derived from 3,3,3-trifluoropropyl. Silicon polymers can e.g. be a homopolymer or a copolymer of one or more of the foregoing

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9, and may advantageously be polydimethylsiloxane or a copolymer of dimethylsiloxane with up to 5% by weight of methylvinylsiloxane. Silicon-modified EPDM, such as Royaltherm (provided by Uniroyl) and silicates which vulcanize at room temperatures, are also suitable materials.

The elastomeric silicon fabrics may, if desired, contain filler materials, e.g. reinforcing fillers, flame retardants, extensions, pigments, and mixtures thereof. For example, suitable fillers include diatomaceous earth and iron oxide. It will be appreciated that such filler materials may be used in conjunction with a reinforcing filler material, such as silicic acid, which is added to the silicon polymeric material to provide elastomeric silicon materials.

Other materials, such as antioxidants, ultraviolet stabilizers, silicone oils which act as extenders, plasticizers and cross-linking agents may also be included.

It has been found that improvements in the mechanical properties of a cable can be achieved if a binder is included in the mineral coating, which can improve the possibilities of machining the mineral coated conductor. Thus, according to a preferred embodiment of the invention, a binder is included in the mineral dispersion and placed on the conductor together with the mineral material to enhance the machining capabilities of the coated conductor. The material selected as binding material must be inactive, ie. it should not corrode the conductor metal or react with the mineral coating, and preferably enhance the bonding of the mineral layer to the conductor metal. It must also be electrophoretic mobile and not form lye. The binder may be dispersible in the medium used to form the mineral suspension (water), and e.g. it may include a water-dispersed latex, for example a styrene / butadiene / carboxylic acid latex, a vinyl pyridine / styrene / butadiene latex, a polyvinyl acetate emulsion, an acrylic copolymer emulsion or an aqueous

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Silicon emulsion. It is preferable to use binders in the form of emulsions, as they can be dried quickly with only a few seconds of residence time in the dryer, while with aqueous solutions much longer drying times are required, and if drying is accelerated, bubbles can form in the mineral layer. which will cause failure of the resulting dried layer. In addition, at least hydrophobic binders have the advantage that they can prevent or reduce the absorption of moisture in the mineral layer after it has dried. This is particularly useful where the weathered mica has a relatively high degree of cation exchange, i.e., where it contains a relatively high degree of vermiculite, so that unwanted peeling of the mineral layer when exposed to flames can be avoided. The binder 15 should preferably not be hardenable, as hardening binders do not substantially improve the properties of the cord and will usually decrease the rate at which the cord can be made.

It has been recorded that the presence of a polymeric binder usually has a devastating effect on the electrical resistance of the mineral layer, usually during the first 1 to 2 minutes, when the wire is exposed to fire, and the effect becomes negligible, resulting in that certain wires that have been tested for damage-free circuit operation at reasonably high voltages, such as 200 volts, either exhibit failure within the first minute or two, or will survive a number of hours at the sample temperature. It is believed that the reduction in resistance of the conduit is due to the carbonization of the binder at the increased temperature, and / or further the generation of gas-free conductive substances from the binder or other organic components in the cable, and that this effect quickly dies out. as the carbon thus formed is oxidized. However, the devastating effect on the resistance caused by most binders can usually be offset by the presence of the thin silicon layer. That

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11 it is assumed that the silicone layer acts as a form of electrical and / or mechanical barrier which prevents carbon from the binder from forming an electrical short circuit. Thus, in the first minute 5, the electrical conductivity of the wire is dominated by the testing of the silicon layer's performance. By the time the silicon layer is ashes, carbon from the binder will normally be completely oxidized and will no longer have any effect on the conduit.

The binder is preferably used in amounts in ranges 10 from 5 to 30%, and especially from 10 to 25% by weight, based on the weight of the weathered mica. The use of smaller amounts may not adequately improve the conductivity of the conductor, and / or may not sufficiently improve the mineral layer by adhering to the metallic conductor, while the use of larger amounts of binder may result in large amounts of carbon for the silicone layer to cover this. It is also preferable not to use binders, such as neoprene, which produce large amounts of carbon. It is preferred that the binder has a carbonaceous charred residue of not more than 15%, yet better not more than 10% and especially not more than 5%.

The charred residue may be measured by a method known as thermogravimetric analysis, or TGA, wherein a sample of the binder is heated in nitrogen or another inert atmosphere at a predetermined rate, e.g. minutes to a predetermined temperature and the residual amount consisting of coal is recorded. The charred residual is simply the size of this residual amount of coal expressed as a percent of the original polymeric product after any non-polymeric or non-volatile component is taken into account. The above mentioned charred sizes are determined from a measurement at 850 ° C.

As mentioned above, an outer protective layer may be provided, preferably a polymeric insulating layer.

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12 layers, to protect the underlying mineral layer from mechanical abuse, and to provide the required insulating and dielectric properties during normal use. Examples of polymeric materials which can be used to provide the outer layer include olefin homopolymers and copolymers of olefins with other olefins and with other monomers, for example, vinyl esters, alkyl acrylates and alkyl alkacrylates, e.g. low, medium or 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 the styrene / butadiene / styrene, styrene / ethylene / butadiene / styrene block copolymers and hydrogenated versions of these block copolymers.

A particularly preferred class of low carbon polymers is polyamides. Preferred polyamides include nylons, for example, 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 condensation of terephthalic acid with trimethylhexamethylenediamine (for -20 stepwise containing a mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine isomers), polyamides formed by condensation of one or more bisaminomethylnorbornan isomers with one or more aliphatic, cycloaliphatic or aromatic dicarboxylic acids, for example terephthalic acid choices including one or more amino acids or lactams, for example, e-caprolactam comonomers, polyamides based on units derived from laurine lactam, isophthalic acid and bis- (4-amino-3-methylcyclohexyl) methane, polyamides based on condensation of 2,2-bis- (p-aminocyclohexyl) propane with adipic acid and aceleic acid, and plyamides based on the condensation of transcyclohexane-1,4-dicarboxylic acid with trimethylhexamic acid. thylenediamine isomers, as mentioned above. Other aliphatic polymers which may be used include polyesters, for example, polyalkylene terephthalate and especially polytetramethylene terephthalate, and cycloaliphatic diol / terephthalic acid copolymers, for example copolymers of units of terephthalate and isophthalate.

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13 thai with 1,4-cyclohexanedimethyloxy units, polyethers, for example polybutylene ether copolymers, and especially polyether esters such as esters with polytetramethylene ether and poly (tetramethylene terephthalate) blocks, aliphatic ionomers, for example those based on metal salts of ethylene (meth) and sulfonated olefins such as sulfonated EPDM and the like. Preferred aliphatic polymers include polyethylene, polybutylene terephthalate, ionomers based on methacrylate polyethylene metal salts, acrylic elastomers, for example those based on ethyl acrylate, n-butyl acrylate or alkoxy-substituted ethyl or n-butyl acrylate polymer and ethylene comonomers and block copolymers with long chain ester units of the general formula: 0 o

1 II

-OGO-C-R-C- 20 and short chain ester units of formula O 0

II II

-ODO-C-R-C-25 wherein G is a divalent radical remaining after the removal of the end hydroxyl groups from a polyalkylene oxide glycol, preferably a poly (C2 to C4 alkylene oxide) having a molecular weight of approx. 600 to 6000, R is a divalent radical remaining after the removal of carboxyl groups from at least one carboxylic acid having a molecular weight of less than ca. 300, and D is a divalent radical remaining after the removal of hydroxyl groups from at least one diol having a molecular weight of less than 250.

Preferred copolyesters are polyether ester polymers derived from terephthalic acid, polytetramethylene ether glycol and 1,4-butanediol. These are random block copolymers with crystalline hard blocks with the repeating unit:

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14 - {CH 2) 4-O-C - + - > 5 and soft blocks of amorphous, elastomeric polytetramethylene ether terephthalate with the repeating unit 10 0 TV 0 11 / T \ 11-E 0 (CH 2) 0- C- y yC with a molecular weight of approx. 600 to 3000, i.e. n = 6 to 40.

Other preferred aliphatic polymers include those based on blocks of polyether and polyamide, in particular the so-called "polyether-ester amide block copolymers" having a repeating unit: 20 -C-A-C-O-B-O-

IN! II

o where A represents a polyamide sequence having an average molecular weight in the range of 300 to 15,000, preferably from 800 to 5000, and B representing a linear or branched polyoxyalkylene sequence having an average molecular weight in the range of 200 to 6000, preferably from 400 to 3000.

It is preferred that the polyamide sequence be formed from alpha, omega-aminocarboxylic acids, lactams or diamine / dicarboxylic acid compositions having C4 to (4 carbon chains) and that the polyoxyalkylene sequence is based on ethylene glycol, propylene glycol and / or tetramethylene glycol and / or tetramethylene glycol to 85%, especially from 10 to 50% 35 of the total block of copolymers by weight.These polymers and their preparations are disclosed in UK Pat.

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No. 15,473,972, No. 1,532,930, No. 1,555,644, No. 2,005,283A, and No. 2,011,450A.

The polymeric Jeans are used alone or in mixtures among themselves or with other polymers and may contain fillers, for example silicic acid and metal oxides, which may, for example, be treated and untreated flame-recessed metal oxides such as hydrated aluminum and titanium. The polymers can be used in the construction of a single wall or multiple walls, for example, as disclosed in UK Patent Application No. 2,128,394A, to which reference is made. The polymers may be provided as non-crosslinked or as crosslinked, e.g. by chemical cross-linking agents or by emitting electrons or by gamma radiation, to improve the mechanical properties and to reduce flow by heating.

They may also contain other materials, such as antioxidants, stabilizers, substances for promoting crosslinking, and substances for promoting processes and the like. In some cases, the polymeric insulation, or at least the inner wall of the insulation, may be substantially halogen free. In addition, it has been found that certain halogen-containing polymers can provide electrically conductive substances under fire and thus cause the conduction to fail prematurely. In these cases, the insulation should preferably contain not more than 5% by weight of halogens, especially not more than 1% by weight of halogens and in special cases not more than 0.1% by weight of halogens. In other cases, however, e.g. In connection with aircraft wiring harnesses where it is desirable that the wires have properties to withstand high temperatures, it may be advantageous for the outer wall or primary sheath of the insulation to include a polymeric material with halogens. A class of halogen-containing polymers which are particularly useful are fluorine-containing polymers, preferably those containing at least 10%, with preference being given to at least 25% of 35 fluorine by weight. The fluorine-containing polymer may be a single fluorine-containing polymer or a mixture of polymers

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16 substances, one or more of which contain fluorine. The fluorine-containing polymers are usually homo- or copolymers of one or more fluorine-containing, often perfluorine-containing, olefinically unsaturated monomers or copolymers of such a comorner, with a non-fluorine-containing olefin. The fluorine-containing 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 crosslinking) of at least 104 Pa at a temperature of not more than 60 ° C above the melting point. Preferred 10 fluorine-containing polymers are homo- or copolymers of tetrafluoroethylene, vinylidine fluoride or hexafluoroethylene, and especially ethylene / tetrafluoroethylene copolymers, for example containing 35 to 60% ethylene, 35 to 60% tetrafluoroethylene by molecular weight and up to 10% of molecular weight of , polyvinylidene fluoride, copolymers of vinylidine fluoride with hexafluoropropylene, tetrafluoroethylene and / or hexafluoroisobutylene, hexafluoropropylene and copolymers of hexafluoropropylene and tetrafluoroethylene. Alternatively, C ^-C ^ perfluoroalkoxy-substituted perfluoroethylene homopolymers and copolymers can be used together with the fluorine-containing polymers mentioned above.

In addition, the polymeric insulation, or the inner layer of any polymeric insulation, preferably has a carbonaceous carbon residue of not more than 15% by weight, as determined by thermogravimetric analysis. Such wires are disclosed in the parallel UK patent application referred to as "electrical wiring", to which reference is made.

The conduit provided by the invention may be formed using the commonly available electrical conductor material, such as plated copper, and copper which has been plated with tin, silver or chromium. In addition, if desired, the conductor may have a coating with an electrically conductive refractory layer, e.g. as disclosed in European Patent Application No. 190,888, to which reference is made.

An exemplary embodiment of a conduit according to the present invention, and a method of manufacturing

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17 position of the wire is explained in more detail below with reference to the drawing, in which: FIG. 1 is an isometric view of a portion of a conduit of the present invention with the low thickness of the insulation 5 exaggerated for the sake of clarity; FIG. 2 is a schematic representation of an apparatus for forming the apparatus of FIG. 1; FIG. 3a to 3c are graphs depicting the action of a binder and a silicone layer for the operation of the weld without errors.

In FIG. 1, an electrical wire 1 includes a copper wire 2, No. 22 according to American Wire Gaures (AWG) with seven wires, which has been coated with a 50 micron thick layer 3 of partially weathered mica, a 50 micron thick polymeric silicone layer 3 'and fully of a 0.15 mm thick extruded layer of polymer insulation 4, which is based on a mixture of polytetramethylene terephthalate and a copolymer block of polythetramethylene ether terephthalate / polytetramethylene terephthalate.

The conduit may be formed by the means shown in FIG. 2 schematically shown apparatus. In this apparatus, the conductor 2 is led into a bath 5 containing a colloidal suspension of the weathered mica and the binder, which suspension is transferred from a supply bath 5 ', the bath 5 being continuously moved to maintain a uniform mixture in the dispersion. . The conductor is brought down into the bath, around a roller 6, after which the conductor is moved vertically upward as it exits the bath. A hollow tube 7 is located around the portion of the conductor leaving the bath, and a hollow electrode 4 is placed within the hollow tube 7 so that the weathered mica precipitates 30 on the portion of the conductor which is directed upward.

After the coated conductor leaves the bath, it is passed through a drying tower 8 of a length of approx. 1.5 meters, which is heated by a countercurrent flow of hot air so that the upper part of the dryer has a temperature of approx. 200 ° C, while the temperature at the bottom of the dryer is approx. 160 ° C. After the mineral coating is

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18, the conductor with coating is passed through a coating container 10 containing a silicone polymer. After a layer of silicone polymer is placed on the conduit, it is passed through a further hot air dryer 11, which is arranged 5 so that it has a temperature of approx. 130 ° C in the upper part and approx. 90'C at the bottom.

Once the silicone layer has been applied and dried, the conduit can then be wound onto a coil awaiting the provision of an outer insulating layer, or such outer layer may be provided in the present production line, e.g. by means of an extruder 12.

The rate at which the conductor 2 advances to the coating apparatus will depend on the desired thickness of the coating, the electrophoresis potential and the concentration of pre-coated mica in the bath. Feed rates in the range from 2 to 20, especially from 5 to 10 meters per second. per minute is preferred, although it should be possible to increase the feed rate, e.g. by increasing the dimensions of the bath, so as to maintain the same time in the bath at higher conductor speeds.

FIG. Figures 3a to 3c show the effect of both the binder and the silicone layer on the electrical properties of the wire insulation. In each case, 1 meter of a twisted batch line was heated to 900 ° C in a gas flame and the electrical resistance between the lines was recorded and shown along the ordinate as a function of the elapsed time since the beginning of the heating shown abscissa.

FIG. 3a shows the properties of the wires when they are only 30 insulated by a 25 micron thick layer of weathered mica which contains no binder. The resistance decreases when the wire is heated to a size which is slightly below 107 ohms of approx. 60 seconds, and remains at this level until the end of the test. Although this insulating layer had satisfactory electrical properties, the mechanical properties of the layer are insufficient and the wire

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19 could not be manufactured at economical wiring and cable manufacturing rates.

FIG. 3b shows the properties of conduits in which the mineral layer contains 15% by weight of a styrene butadiene styrene block of copolymer binder. The mechanical properties were excellent and the wire could be easily treated mechanically in the wire and cable manufacturing operations at speeds of up to 50 meters per meter. minute. In this case, the electrical resistance of the insulation layer dropped to a value of approx.

10 105 ohms after 30 seconds, at which time the resistance slowly increased until it reached approx. 107 ohms after 150 to 200 seconds, and the resistance remained at this level until the test was completed. The resistance to 10 ^ ohms will greatly limit the range of voltage to which such a wire could be used.

FIG. 3c shows the properties of the 3b, for which a 50 micron layer of a silicone elastomer is further positioned so as to obtain a total thickness of 75 microns. The insulation layer resistance 20 drops to just over 107 ohms through approx. 100 seconds after the start of the test and the resistance remains at this level until the test is completed. It will be seen that the destructive effect of the organic binder is thus completely removed. The mechanical performance of the insulation was good, as the restriction was determined by the strength of the silicone layer. The wire could easily be provided with a further layer of polymer insulation.

The invention is illustrated by the following examples: In all examples, the working colloid used for coating the conductor was formed as follows: 800 grams of weathered mica in accordance with the parallel UK patent application referred to as "wire" was washed with boiling water for approx. 30 minutes and the liquid 35 thus obtained was decanted to remove clay fractions. The mineral was refluxed for 4 to 24 hours in a saturated one

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20 sodium chloride solution so that the exchangeable cations were replaced with sodium ions. Then, the material was washed again with distilled or deionized 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 a molar n-butylammonium chloride solution, then further washed with distilled or deionized water until no further 10 chloride ions could be detected by silver wire precipitation.

The swollen material was then processed in a Greaves mixer for 20 minutes to displace the mineral and then stood for 20 minutes to precipitate the untreated mineral. The upper fraction was used as the working carbon loaded.

Example 1

A colloid with 4% by weight weathered mica and 15% by weight carboxylated styrene-butadiene-styrene rubber 20 based on the weight of the weathered mica was used as a coating bath. A 20 AWG line was passed through a 40 cm bath of the colloid at a rate of 5 meters per second. per minute, while the weathered mica was precipitated by electrophoresis on the conductor at a plating voltage of 4.2V 25 and a current of 165 mA. The coated conduit was then passed through a drying tower, as shown in the drawing, so as to provide a 30m thick thickness mineral layer. The conduit was then passed through a 2-part silicone bath (KE1204 ex Shinetsu) and cured again, as shown in the drawing, to provide a 50 micron thick silicone layer. Then, a 100 micrometer thick single insulating wall made from a flame retardant provided by low density polyethylene was extruded with 8% by weight of decabromide diphenyl ether and 4% antimony trioxide on the conduit.

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The wire was tested for flawless operation, with three wires twisted together and each of these wires connected to a phase from a three-phase power supply, after which the wire was heated to 900 ° C for a trial period of 5 hours in accordance with IEC 331. able to carry a voltage of 300 volts between phases throughout the test run at 900 ° C without failure (ie without burning a 3A fuse over).

Examples 2 to 5

Example 1 was repeated except that the following binders were used:

Example 2 polyvinyl acetate

Example 3 acrylic copolymer emulsion Example 4 polyvinylidine chloride

Example 5 styrene-butadiene-styrene rubber terminated with vinyl pyridine

The wire was tested as explained in Examples 1, 20 and in each case the wires could carry a voltage of 300V between the phases at 900 * 0 for 3 hours.

Example 6

Example 1 was repeated with the exception that the silicon layer was based on polydimethylsiloxane with an extensor.

The silicone composition was extruded at room temperature on the conductor coating to provide a 75 to 100 micron thick layer, after which it was cured in a tube oven at 300 ° C (residence time 20.5 seconds).

The wire was tested as explained in Example 1 and applied a voltage of 440V between the phases for 3 hours at 900 ° C.

Example 7

Example 6 was repeated with the exception that

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The curing voltage in the deposition bath was 15.5V (300mA), thereby providing a thickness of the 40 microns mineral layer.

The wire was applied at 440V between the phases for 3 hours 5 at 900 ° C.

Example 8

Example 1 was repeated except that the silicone used was a solution-free silicone used in deep coating and applied with a layer thickness of 70 microns. The wire was applied to a voltage of 300V between the phases for 3 hours at 900 ° C.

Example 9 Example 1 was repeated except that the low density polyethylene insulation was replaced with a 100 micron thick layer which consisted of:

Parts by weight 20 Polybutylene terephthalate (PBT) 80

Surlyn ionomer 20

Decabromodiphenyl ether 8

Antimony Trioxide 4

Irganox 1010 2 25 Triallylisocyanurate to promote crosslinking 5

The wire was applied to a voltage of 300V between the phases for 3 hours at 900 ° C.

30

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Example 10

Example 9 was repeated except that the OBT / Surlyn layer did not contain any flame retardant (decarbromodiphenyl ether (Sb203)) and that an additional polymeric layer having a thickness of 100 microns was provided on top of the PBT / Surlyn-5 layer. additional layers had the following composition:

Parts by weight 10 Polybutylene terephthalate (PBT) 70

Polybutylene terephthalate-polybutylene ether terephthalate block copolymer 30

Ethylene bis-tetrabromophthalimide 10

Antimony Trioxide 4 Magnesium Hydroxide 20

The wire was applied to a voltage of 300V between the phases for 3 hours at 900 ° C.

Example 11

Example 7 was repeated except that the low density polyethylene insulation was replaced with the additional layer of Example 10. The line was applied at 440V between the phases for 3 hours at 900 ° C.

25

Example 12

Example 6 was repeated except that the low density polyethylene insulation was replaced with a 100 micron thick layer of high density flame retardant polyethylene. The wire was applied 300V between the phases for 3 hours at 9000C.

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Example 13

Example 1 was repeated except that the binder used was a vinyl acetate / ethylene copolymer, that the plating voltage was 12.5V and the current 422 mA, and 5 that the feed rate of the wire was 10 meters per second.

The silicone layer and polymeric insulation were composed as follows:

Silicone Composition Parts by weight 10

Polydimethylsiloxane 61.2

Burnt silica 22.3

Painted silica 6.8

Burnt Titanium 3.4 15 Iron Oxide 3.4

Peroxide 2.4

Heat stabilizer (cerium hydrate) 0.5

Platinum as element 0.005 20

Insulation Parts by weight

Polybutylene terephthalate 43.5

Butylene terephthalate / polybutylene oxide terephthalate copolymer 15.8 Polycarbodimide 2.8

Decabromodiphenyl ether 9.5

Antimony Trioxide 3.8 244-26 3.9

Antioxidant (Irganox 1010) 1.9 Magnesium Hydroxide 18.8

The silicone layer had a thickness of 100 μπι and the polymeric layer had a thickness of 125 µm. The line was tested as explained in Example 1 and could carry a voltage of 440V (3A) between the phases throughout the test run at 900 ° C.

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Example 14

Example 13 was repeated except that the polymeric insulation had the following composition:

Polybutylene terephthalate 43.5

Butylene terephthalate / polybutylene oxide terephthalate copolymer 15.8

Polycarbodimide 2.8 Decabromodiphenyl Ether 9.5

Antimony Trioxide 3.8 244-26 3.9

Antioxidant (Irganox 1010) 1.9

Magnesium hydroxide 18.8 15

The plating voltage was 11.5V and the current was 365 mA. The mineral layer had a thickness of 25 µm and the silicone layer had a thickness of 125 μιη.

The line could carry a voltage of 440V (3A) between the 20 phases throughout the test run (3 hours) at 900 ° C.

Claims (10)

An electrical wire, which includes a metallic electrical conductor having an insulating mica layer formed electrolytically on the conductor, characterized in that the mica is chemically delaminated and weathered, and there is also a silicone polymer layer located on the mica layer. Electric wire according to claim 1, characterized by including an outer protective sheath 10 located on top of the silicone layer. Electrical wire according to claim 2, characterized in that the protective sheath is an electrically insulating sheath provided from an organic polymer. Electric wire according to claim 2 or claim 3, 15, characterized in that the protective sheath includes an inner and an outer layer, the inner layer being substantially halogen free. An electrical wire according to claims 1-4, characterized in that the mineral layer includes a binder. 6. Electrical wire according to claim 5, characterized in that the binder has a carbonaceous carbon residue of not more than 15% by weight. Electric conduit according to claims 5-6, characterized in that the binder has been included in the mineral layer in the form of an organic latex. 8. Electrical wire according to claims 1-7, characterized in that the silicone polymer material is an elastomer. An electric cable, characterized in that it comprises a plurality of wires according to claims 1-8, which are included in a cable sheath. A method of generating an electrical conduit, characterized by including the following steps: guiding a long electrical conductor through a suspension of chemically delaminated, weathered mica and applying an electrical potential to the conductor to provide deposition thereof. weathered mica on the conductor, drying the layer of weathered mica thus obtained, applying a layer of a polymeric silicone material to the surface of the weathered mica, drying the polymeric silicone layer.