EP0203129A1 - Fire-proof flexible insulating coating for conduits, wires, electric cables and optical fibres. - Google Patents

Abstract

This coating consists, according to one embodiment of a first inner layer (2), of glass fibers comprising mica particles surrounding the conductor, the pipe or the pipe (1) of a second layer (3), of the same nature as the previous one, but crossed with it, a third layer (4), consisting of a polymer loaded with inorganic compounds of the refractory type, a fourth layer (5), consisting of a braid resin coated glass fiber, and a fifth layer (6), thermostable polymer loaded with an inorganic refractory material. When this coating is subjected to a temperature higher than 950o C, the organic parts decompose and the inorganic parts melt to give a foam which vitrifies and makes it possible to maintain the sealing and the electrical insulation.

Description

Flexible fire-resistant insulating coating for pipes, electric cables and optical fibers

The invention relates to a flexible fire-resistant insulating coating, based on mica, thermostable polymer and glass fibers, which provides its insulating properties at temperatures of the order of

I 000 ° C, consisting of one or more layers of mica, a layer of thermostable polymer or a mixture of ther¬ mostable polymer and refractory inorganic particles, a layer of glass fibers impregnated with a thermostable polymer or a thermostable polymer charged with refractory inorganic particles, and a layer of thermostable polymer or thermostable polymer charged with refractory inorganic particles.

Safety requirements require that, in certain use cases such as those encountered in the nuclear, petroleum, aeronautical, space, naval, chemical, etc. industries, circuits transporting energy or transmitting signals of control or command, can withstand for a sufficient time the high temperatures due, for example, to a fire or, for electrical circuits, to an abnormal rise in the intensity of the current flowing through them, so as to allow the evacuation of personnel and rescue of equipment. In the case of short circuits or overcurrent, it is desired that the significant increase in the temperature of the conductor, or even the melting of the latter, not cause a fire by combustion of the coating.

Many attempts have been made to solve this type of problem and some have given rise to patent applications.

For soft coverings, these are patents:

- US-A 2,427,183 which describes an insulating coating, for metallic conductor, comprising a layer of polytetrafluoroethylene inserted between two layers of mica or asbestos or fiberglass. The insulation is carried out by winding tapes around a conductor.

- US-A 2,459,653 which describes a method of insulating conductors by double helical winding of a polytetrafluoroethylene ribbon and glass strands impregnated with a silicone resin.

- US-A 2,606,134 which describes an insulating coating consisting of a successive helical roll, one or more layers of a ru-

5. polytetrafluoroethylene strip, followed by one or more layers of a glass fabric ribbon and a possible coating with a polytetrafluoroethylene dispersion.

- US-A 2,691,694 which describes an insulating coating identical to that which is the subject of the previous patent, but in which the final layer 0 of polytetrafluoroethylene is replaced by a helical winding of a glass fiber impregnated with polytetrafluoroethylene.

- FR-A 2.257.555 which. describes a coating composed of a needle-punched sheet of glass fibers impregnated with a polymeric binder loaded with asbestos, alumina, silica, carbon, quartz or talc, and containing flame retardants (halogenated hydrocarbons, etc.) and combustion inhibitors (antimony trioxide, etc.). In these compositions, the binder may be polyvinyl acetate, chlorinated or natural rubber or t pe 0 GRS, polymethyl methacrylate, poly methyl acrylate, polyurethane elastomer, polyvinyl chloride, polychloride of polyvinyl chloride. vinylidene, an epoxy resin, polystyrene or, alternatively, an acrylonitrile - butadiene - styrene terpolymer.

- FR-A 2,482,769 which describes an insulating, flexible and heat-resistant coating, composed of a knitted fabric of glass fibers impregnated with a binder based on acrylic latex loaded with coloidal silica, d alumina, zirconia or calcium silicate.

- US-A 3,602,636 which describes a coating consisting of a helical winding, a glass fabric carrying a coating of flame resistant synthetic rubber and protected by a sheath of polyvinyl chloride.

- EUROPEAN 80.107.217.4 which describes an insulating coating made of polyimide and mica.

5 It should however be noted that the techniques developed in these patents do not make it possible to solve the problems brought by one or more cables placed under fire conditions (resistance to temperatures of the order of 1000 ° C without fusion of the conductor or propagation of the fire, resistant to shocks or possible vibrations and to splashes of water or extinguishing fluids and toxic gas or smoke emissions ...) while ensuring the electrical continuity of the circuits.

In fact, cable insulators made of non-flammable plastic materials, such as those made of polyvinyl chloride, polyvinylidene chloride, chlorinated rubber _f cannot withstand fires for a prolonged period. When such cables are exposed to fire, the insulation decomposes and the chlorine which is released combines with the humidity of the air or with the water which is used for extinguishing the fire, forming hydrochloric acid which is highly corrosive with respect to neighboring conductors or metalli¬ cal structures.

Likewise, vinyl or rubber compositions exposed to flame temperatures above 370 ° C. propagate the fire by giving off toxic fumes.

For all these reasons, those skilled in the art have every interest, if they want to improve the fire resistance of insulating coatings, to limit the percentage of organic materials in the compositions and this, in favor of non-flammable mineral materials.

However, most of the inorganic materials used so far, alone or in combination, have drawbacks. Fiberglass loses its mechanical strength around 550 ° C and asbestos around 650 ° C. This latter product is, moreover, now known to be carcinogenic, and efforts are being made to eliminate its use.

In order to solve the various problems that we have just mentioned, various rigid coatings containing little or no organic elements have been developed and have been the subject of patents:

- FR-A 2,381,377 which describes a coating of electric wire made up of a copper tube concentric with the conductor and stuffed with magnesia.

- FR-A 2,462,771 which describes a coating of conductor similar to that which is the subject of the previous patent, but in which the problems due to the presence of moisture during connections are resolved by adding magnesia d '' a silicone oil resistant to 600 ° C.

These coatings, which are very efficient at high temperature or in the presence of flames and which meet a certain number of the requirements previously exposed, however still have a certain number of drawbacks: Long and expensive wiring operations; difficulties in making fire-tight connections; rapid oxidation of the outer metal casing, especially when used in a relatively acidic environment (H.-S atmosphere of petroleum refineries _* for example), or when water is sprayed onto cables, fire fighting courses; cable stiffness.

There is already known a flexible, fire-resistant insulating coating, corresponding to the preamble of claim 1 (European patent application EP-A-0106708). It consists of the stack of a layer of mica, a glass cloth and a layer of poltetrafluoroethylene, in order to preserve its insulating, electrical and thermal properties up to 1000 ° C. This coating, although very efficient in terms of its resistance to fire., However, has the disadvantage of offering an insufficient seal against water and extinguishing liquids, giving off fluorinated vapors, especially in the case where the coating has an outer layer of polytétra¬ fluoroethylene; this release of fluorinated vapors which can, in certain cases, cause chemical attacks with respect to the surrounding inorganic or metallic materials. The object of the present invention is to remedy these drawbacks. This invention, as characterized in the claims, solves the problem of creating a flexible insulation coating capable of protecting wires, cables, conduits and optical fibers from inflammation. or dielectric or insulating ruptures when these are subjected to heating or to the direct action of fire, at temperatures of the order of 800 ° C to 1000 ° C, for periods greater than 15 min. Another object of the invention is to obtain a flexible insulation product protecting against fire, which is easy to manufacture and to apply, compared to the products which are currently part of the state of the art.

The coating according to the invention is mainly characterized in that the layer of thermostable polymer, which is superimposed on the layer or layers of mica, consists of polyimide, polyamide-imide of polysulfone, polyethersulfone, phenilene polysulfide, silicone or polytetrafluoroethylene deposited by coating, in that the thermostable polymer which impregnates the layer of glass fibers and which constitutes the final layer of the coating is a resin loaded or not loaded with refractory inorganic compounds or with polytetrafluoroethylene, in that the inorganic refractory compounds used are titanium dioxide, zirconium dioxide, magnesium oxide, silicon dioxide, aluminum trioxide (Al_ 0 „), magnesium, calcium or aluminum silicates, silicon and zirconium carbides, alumina (Al- 0 „), zirconia (Zr 0„), calcium silicate, or any mixture of these compounds, and in that q the thermostable polymer constituting the final coating of the coating is polytetrafluoroethylene. The mica and polytetrafluoroethylene ribbons are deposited so that their direction of rotation is successively alternated.

The advantages obtained, thanks to this invention, consist essentially in this, that the coating has good characteristics of reliability and resistance to weathering, under normal conditions of use as under extreme conditions (environment of fire), is not a propagator of the fire, "-resistant to shocks, vibrations and splashes of water or extinguishing fluids and emits little or no toxic and / or corrosive fumes. Once exposed to the heat of the flame, the organic parts decompose, the parts inorganics melt to give a foam which vitrifies and ensures good sealing as well as excellent electrical insulation.

The invention is described below more _in detail with the help of drawings representing only two embodiments.

FIG. 1 represents a partial perspective view of an electric cable, a pipe or a pipe, surrounded by the covering according to a first embodiment.

2 shows a partial perspective view of an electric cable, a pipe or a pipe surrounded by the coating according to a second embodiment.

FIG. 3 represents a cross section along AA of FIG. 1.

FIG. 4 represents a cross section along BB of FIG. 2.

5 shows a cross section of an electrical cable comprising three primary elements as shown in Figure 1, surrounded by the coating according to the first embodiment.

Referring to Figures 1 and 3, we note that the coating according to the first embodiment comprises a first inner layer 2 surrounding the conductor, the pipe or the pipe 1. This first layer 2 can be coated with a layer 3 made of the same material. Then come two intermediate layers 4 and 5 and then an outer layer 6. Referring to Figures 2 and 4, we note that the coating se¬ lon the second embodiment comprises a first inner layer 8 surrounding the conductor, the pipe or the pipe 7. This first layer 8 can be coated with a layer 9 made of the same material. Next come two intermediate layers 10 and 11 and then an outer layer 12.

Referring to Figure 5, we note that a coating according to the first embodiment, consisting of an outer layer 18, two intermediate layers 16 and 17 and two inner layers 14 and 15, surrounds three primary conductors 1 coated in the same manner as described in FIG. 1. In this FIG. 5, the wires 13 constitute jams intended to fill the interstices in order to obtain a cylindrical assembly.

The inner layers 2 and 3 or 8 and 9 of the coating are preferably made of glass fibers in the form of a flexible fabric coated with a polymeric resin serving as an adhesive and supporting particles of mica. The material used is therefore in the form of a ribbon with a width between 6 mm and 25 mm or more and a thickness between 0.05 mm and 0.2 mm, consisting of a continuous layer of glitter of mica deposited on a support of glass fibers woven through an adhesive binder. In such ribbons, the mica can be of muscovite or phlogopite type and the binder of silicone elastomer, polyimide, polyamide-imide or any other thermostable polymer.

The intermediate layer 4 of the coating described in FIG. 1 _{/ as} well as the intermediate layers 4 and 16 of the cable described in FIG. 5, consist of a polymer which can optionally be loaded with inorganic compounds of refractory types. Among the polymers which can be used for the manufacture of this layer, mention may be made of: - Polyimides: polyarylamide, polyamino-bis-maleimide, polyether-imide, polyimidine, polyimidazopyrrolone. - Polysulfones: polyarylsulfone, polyphenylene ether sulfone, polyethersulfone bisphenol A polysulfone.

- Fluoropolymers: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride. - Fluorinated copolymers: tetrafluoroethylene - perfluoropropene, ethylene - tetrafluoroethylene, ethylene - chlorotrifluoroethylene, tetrafluoroethylene - perfluoroalkoxy and other thermostable polymers such as: polyparabanic acid, polybenzoxazole, polybenzimidazole -3-4 oxadiazole, polyquinolines, polyquinoxalines, polypyrrones, polyphenanthroline, polycarboranes, polyphosphazenes, polystyrylpyridine, polysilastyrene, polyaryletherketone, polyphenylene oxide modified or polyphenylene oxide, phenylene or silicone resins.

The preferred resins for making layers 4 and 16 of the coating are: polyimides, polyamide-imides, polysulfones and polyethersulfones, phenylene polysulfide, silicone resins and polytetrafluoroethylene.

These resins are preferably applied to the inner layers 2 or 3 corresponding to the coating shown in Figure 1 and to the inner layers 2 or 3 and 14 or 15 of the cable shown in Figure 5, using a technique of coating well known to those skilled in the art. In this case, the resin can be dissolved in an appropriate solvent or dispersed in water.

In order to improve the thermal properties of the intermediate layers 4 or 16, the polymer resins can be loaded with refractory inorganic compounds. These refractory materials are in a finely divided form so that they can merge with the glass fabric making up layers 2 or 3 and 14 or 15 and with the glass fibers making up layers 5, 11 and 17 when they are subjected to temperatures above 950 ° C. These refractory materials can be oxides of titanium, of zinc, of magnesium, of silicon, of aluminum or of calcium, of magnesium, of calcium or of aluminum, of carbides of silicon or of zirconium, etc.

The resins composing the binder used to adhere the refractory materials to the fabrics and glass fibers located in the surrounding layers, must decompose at high temperatures without giving a flame. At temperatures above 950 ° C the refractory materials melt on the surface of the glass fibers to give a refractory type structure resistant to temperatures much higher than that of the melting temperature of the base glass.

The intermediate layer 10, corresponding to the coating shown in Figure 2 _χ consists of a polytetrafluoroethylene tape whose thickness and width are adapted to the diameter of the element to be protected.

The intermediate layers 5 and 17 of the coatings represented in FIGS. 1 and 5 consist of a braiding of glass fibers coated with the resin making up the intermediate layers 4 or 16, or, possibly, of a different resin such as those evo¬ before. As we have seen above, these thermostable resins can optionally be loaded with inorganic refractory materials, of the same nature as those making up the layers 4 and 16.

The outer layers 6 and 18 of the coatings represented in FIGS. 1 and 5 are of the same nature as those described for the intermediate layers 4 and 16, namely that they consist of a thermostable polymer possibly loaded with an inorganic material. refractory of the type described above.

The outer layer 12, corresponding to the coating shown in FIG. 2 and to the second embodiment of the invention, is made up of polytetrafluoroethylene deposited on the layer 11 by coating by means of a dispersion. The complete manufacture of a coating according to the first embodiment is carried out as follows:

- The first layer of mica tape is wound helically around the element to be protected, using a conventional tape machine, so that the layer of mica particles is turned towards the element to protect. The ribbon is wound with a covering, for example of 50% or 66%, so as to ensure a good heat seal.

- When a second layer of mica tape is superimposed on the first, the face covered with mica is always turned towards the inside, but the direction of rotation of the tape is reversed compared to that of the previous tape.

- A thin layer, on the order of 2 to 10 hundredths of a millimeter, is then deposited by coating on the previous layer with a binder based on thermostable polymeric resin. This coating is carried out by dipping in a solution containing the polymer, when the latter is soluble in a solvent, or by dipping in an aqueous dispersion of the polymer when the latter is insoluble in all organic solvents.

Generally, the solutions contain between 10 and 50% _# by weight, and polymer dispersions between 10 and 40% by weight of polymer.

In this coating process, which is carried out continuously, the solvents or the dispersing agents are first evaporated by passage through an oven, then the resins can be optionally crosslinked in another oven at a higher temperature.

It is also possible, in the case where improved thermal behavior is required, to add to the solutions or dispersions of refractory mineral fillers such as those described above.

In the case of solutions, the following compositions are preferably used: - binder: thermostable polymer 10 to 45%, refractory mineral fillers 5 to 25%, solvent 30 to 85%.

In the case of dispersions, the following compositions are preferably used:

- binder: thermostable polymer 10 to 35%, refractory mineral fillers 5 to 25%, water 40 to 85%.

In addition to the binder, mineral fillers and water, the dispersions used for coating may optionally contain a thickening agent, the role of which is to adjust the viscosity so as to facilitate coating. The thickener used is generally an aqueous dispersion at 50%, by weight, of an acrylate-vinyl-pyrrolidone copolymer.

A braid of glass fibers coated with the same thermostable or refractory mixture as for the previous layer is then applied to the layer of thermostable or refractory resin.

To do this, we proceed as follows:

- the glass fiber is coated with the same mixture as that used previously to coat the pipe, the pipe or the cable and this according to the same process.

- the coated glass fiber is packaged on small spools specially adapted for a shielding machine.

the shielding is carried out, in a conventional manner for those skilled in the art, on shielding machines having a number of spindles adapted to the diameter of the pipe, the pipe or the cable to be coated.

The last operation consists in coating the braided coating described above with a layer of thermostable polymer or a layer of refractory binder, identical to that already described, in the same way.

The complete manufacture of a coating according to the second embodiment of the invention is carried out as follows: - The first, and possibly the second layer of mica tape, are obtained in the same manner as in the first embodiment.

- Then, by helical winding around the mica layer (s), a ribbon, preferably made of polytetrafluoroethylene ^, the thickness of which can vary, for example, between 7/100 th of a mm and 25/100 th of a mm and the width between 3 and 50 mm. This tape is applied with a conventional tape machine, so that the direction of rotation is reversed with respect to the direction of rotation of the mica tape constituting the lower layer. This PTFE tape is generally applied with an overlap of 50% or 66%.

- Then apply a braid of glass fiber coated with PTFE on the PTFE layer. These glass fibers are commercially available, but they can also be prepared by coating glass fibers previously sized with an aqueous dispersion of PTFE at 33%, by weight, of polymer. The braiding of the fibers is carried out in an identical manner to. that described above for the first method.

- The last operation consists in coating the coating described above with a layer of PTFE. In this case, an aqueous dispersion of 33% by weight of PTFE is used and a process identical to that described in the first process.

The coatings of thermostable polymers, possibly loaded with refractory mineral materials are intended to confine and securely maintain all the inorganic materials present in the coating.

When this coating is subjected to a flame, or to the intense heat of a flame, the polymer coating present on the surface decomposes without igniting and therefore without propagating the fire. If exposure to heat and / or flame continues, two cases may arise depending on the type of coating used:

- In the case of a coating without refractory inorganic material, there is, after the decomposition of the maintenance polymer, an in¬ candescence of the inorganic protective compound _^ constituted by glass fibers. Above 430 ° C, a temperature which corresponds to exposure to the direct flame or to the heat of the flame at least equal to _L 10 min, the glass fibers begin to lose their tensile strength. From 730 ° C, temperature which corresponds to an exposure to the direct flame or to the heat of the flame at least equal to 20 min, the glass fibers soften and a pasty melting. A kind of aerated glass foam is then formed, which contributes to improving the thermal barrier formed by the protective coating. After lowering the temperature, this protective barrier, of high viscosity, vitrifies to form, with the mica particles, a dielectric and waterproof insulating coating.

- In the case of a coating comprising refractory inorganic materials, we witness, as before, after the decomposition of the thermostable polymer, an incandescence of the inorganic products and then a partial melting, above 800 ° C., of the com ¬ placed refractory minerals with glass. This fusion is only partial, and only a small part of the mineral matter mixes with the glass. In fact, most of them have continuous operating temperatures above 1,250 ° C and melting points above 1,800 ° C. The majority of these mineral particles are inserted into the interstices existing between the glass fibers, thus forming a composite structure resistant to high temperatures and thermal shocks, having excellent dielectric strength and great insulating and heat-reflecting power.

In addition, whatever the manufacturing process used, the protective re¬ clothing according to the invention, subjected to heat or to the direct action of a flame, are resistant to impact and vi¬ bration as well as very large temperature variations.

It can therefore be seen that the invention allows the production of protective coatings against heat, very resistant to flames and suitable for insulating pipes, conduits, wires or electric cables. More particularly, in the case of electrical wires and cables, these coatings make it possible to transmit electrical energy, while being subjected to the intense heat of a fire while having the advantage of being flexible.

Claims

claims

1. Flexible fire-resistant insulating coating for pipes, wires, electric cables and optical fibers, based on mica, thermostable polymer and glass fibers retaining its insulating properties at temperatures of the order of 1000 ° C., consisting of one or more layers of mica, a layer of thermostable polymer or a mixture of thermostable polymer and refractory inorganic particles, a layer of glass fibers impregnated with a thermostable polymer or '' a thermostable polymer charged with refractory inorganic particles and a layer of ther¬ mostable polymer or thermostable polymer charged with refractory inorganic particles, characterized in that the layer of thermostable polymer, which is superimposed on the layers of mica, is made up of polyimide, polyamide-imide of polysulfone, polyethersulfone, phenilene polysulfide, silicone or polyté¬ trafluoroethylene, d coated by coating, in that the ther¬ mostable polymer which impregnates the layer of glass fibers and which constitutes the final layer of the coating, is a resin loaded or not loaded with refractory inorganic compounds or polytetrafluoroethylene, in that the compounds refractory inorganics used are titanium dioxide, zirconium dioxide, magnesium oxide, silicon dioxide, aluminum trioxide (Al_ 0 „), magnesium, calcium or aluminum silicates, silicon and zirconium carbides, alumina (Al „0 ~), zirconia (Zr 0„), calcium silicate, or any mixture of these compounds, and in that the thermostable polymer constituting the final layer of the coating is polytetrafluoroethylene.

2. Insulating coating according to claim 1, characterized in that the mica and polytetrafluoroethylene tapes are deposited so that their direction of rotation is successively altered.