FR2822836A1 - Production of intumescent composition for power or telecommunications cables comprises dynamically crosslinking mixture of nonhalogenated thermoplastic polymer, carbonizable material, ammonium polyphosphate and mineral filler - Google Patents

Abstract

Production of an intumescent composition comprises preparing a mixture of a nonhalogenated thermoplastic polymer, a carbonizable material, ammonium polyphosphate and a mineral filler, and dynamically crosslinking the mixture in the presence of a silane and a crosslinking agent.

Description

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PROCESS FOR PREPARING INTUMESCENT COMPOSITION
The present invention relates to a new process for the preparation of intumescent compositions, and in particular for their application in the sheaths of energy or telecommunication cables.

 The materials used for cable cladding must meet a number of requirements. They must be non-polluting and non-toxic. They must withstand fire and retard the flame. Their combustion must not result in high smoke emissions. It is also desirable that these fumes are low opacity, low toxicity and little corrosive.

 In addition, the sheathing materials must have good mechanical resistance to deformation when s are exposed to heat. In particular, when the materials melt under the effect of heat, the drops formed during the fusion generate risks of burns and can furthermore lead to the spread of fire by generating new foci.

 Currently, it is sought to replace PVC or polymers containing halogenated additives which have been widely used until now for cladding and cable insulation. Indeed, the standards tend to prohibit the use of such additives not only because of the toxicity and corrosivity of the products released during their combustion, but also because of possible health risks during their manufacture and incineration. PVC is already excluded in certain energy or telecommunication cables, particularly for particular applications of certain administrations such as SNCF, RATP or EDF. Moreover, we tend today to favor the implementation of easily degradable products or even recyclable. These halogen-free materials delaying the spread of flame and fire are often also referred to as HFFR, the acronym for halogen free fire retardant.

 A known solution for making polymer cable sheaths more resistant to fire is to add metal hydroxides such as AI (OH) 3 or Mg (OH) 2. However, it is necessary to introduce a significant amount (about 150 200 phr) of these fillers to provide sufficient flame protection. There is then a degradation of the mechanical properties and

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 electrical material. In addition, these compositions have a high viscosity and are therefore difficult to implement. This is particularly noticeable at the time of extrusion, which requires more energy and whose speed is significantly reduced. A lower extrusion rate makes sheaths more expensive to produce.

 Intumescent paints and varnishes are known to protect the materials against degradation due to the sudden rise in temperature. They have particular that they swell when they are exposed to fire. They thus form an expanded carbon layer that acts as a heat shield on the surface of the material, this will protect it by: limiting the energy input of the flame to the material and preventing the diffusion of combustion gases . The combustion cycle thus interrupted, avoids the supply of the flame degradation products and stop the spread of fire.

 Also known from US 4,728,574 is cable insulation based on ethylene vinyl alcohol copolymer (EVOH) and ammonium polyphosphate. Formulations made with EVOH as an additive have shown that this polymer considerably increases the rigidity of the material.

 Many other additives causing the intumescence of a polymer are known, but also have drawbacks. For example, the pentaerythritol that is often used starts to decompose at temperatures above 200oC, which may cause problems during extrusion. Melamine, also used as a carbonizing agent, significantly increases the concentration of cyanide ions in the degradation products, as was shown by Mr A. Perichaud in his article "Evidence of cyanide in gases produced by inflammation of fire retardant polystyrene ": FRPM 97 6th European Congress on fireproofing of polymeric materials, Lille, 24-26 September 1997 (Pagel80).

 It is also known from EP-A-1,026,700 a cable sheath made of a halogen-free material composed of a polymer, a component causing the intumescence of the material and a flux. This crosslinkable composition further comprises, as crosslinking agent, silanes or peroxides. The static crosslinking of the extruded sheaths is carried out after the extrusion of the cable in a separate step, either by immersion in water or by exposure to water vapor

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(réticulation silane), soit sous pression de vapeur d'eau surchauffée ou de gaz inerte (réticulation peroxydique). Par ces procédés, on obtient une réticulation complète et un matériau difficilement recyclable. En outre, la fabrication de ces câbles s'effectue en 2 étapes ce qui augmente son prix.

(silane crosslinking), either under pressure superheated steam or inert gas (peroxide crosslinking). By these methods, complete crosslinking is obtained and a material that is difficult to recycle. In addition, the manufacture of these cables is done in 2 steps which increases its price.

 The object of the invention is therefore to provide a process for the rapid and easy preparation of an intumescent composition which is inexpensive, easily recyclable, compatible with the environment and which does not have the disadvantages mentioned.

 The invention proposes as a solution a process for preparing an intumescent composition comprising the steps of mixing a composition comprising a non-halogenated thermoplastic polymer, a char source, ammonium polyphosphate and a mineral filler, and dynamic crosslinking. in the presence of a silane compound and a crosslinking agent.

 According to a preferred embodiment, the non-halogenated thermoplastic polymer is a copolymer of ethylene and vinyl acetate (EVA).

 Preferably, the composition comprises 25 to 95 parts of non-halogenated thermoplastic polymer.

 The preferred carbon source is polyamide 6.

Advantageously, the composition comprises 2 to 20 parts of carbon source.

 Advantageously, the composition comprises 10 to 60 parts by weight of ammonium polyphosphate.

 The mineral filler is preferably selected from Kaolin, talc, magnesia, and other fillers used in the cabling. According to a particular embodiment, the composition contains catalysts, fluxes or fillers with a laminated structure or comprising pseudo-sheets or a large specific surface area. Advantageously, the composition comprises 2 to 30 parts by weight of mineral filler.

 The crosslinking agent is preferably a peroxide. According to one embodiment, the silane and / or the crosslinking agent are incorporated into the composition during the mixing step. According to another embodiment, the silane and / or the crosslinking agent are incorporated in the composition during the extrusion.

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 Advantageously, the dynamic crosslinking is carried out at a temperature above 1500C and under a shear greater than 20 s-1, for example in a twin-screw extruder.

 Another subject of the invention is the intumescent composition that can be obtained according to the process according to the invention.

 Yet another object of the invention is the use of this composition as a flame retardant, particularly in energy cables or telecommunication cables.

 Another object of the invention is a cable comprising a core 2, a sheath 3 and a protective coating 4, the sheath and / or the protective coating comprising this intumescent composition.

 A final object of the invention is finally a method of manufacturing a cable, comprising the step of extruding this composition around the core to form a sheath.

 According to a particularly advantageous embodiment, the extrusion step serves both the dynamic crosslinking and the shaping of the composition.

Other characteristics and advantages of the invention will appear on reading the following description of embodiments of the invention, given by way of example only, and with reference to the appended drawings which show: FIG. 1: a representation schematic cross section of a power cable according to one embodiment of the invention; and FIG. 2 is a schematic cross-sectional representation of an energy cable according to another embodiment of the invention;
The intumescent compositions generally comprise four constituents: a polymer matrix; - a source of charcoal; a carbon promoter; and - a source of gas. The different constituents and their functions are explained below.

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 As non-halogenated polymer matrix may be used for example polyethylene, polypropylene, and copolymers thereof, elastomers, thermoplastic elastomers, silicones or a mixture of these polymers. Among the ethylene copolymers, it is possible to choose the copolymers of ethylene and of vinyl acetate (EVA), the copolymers of ethylene and of propylene, the copolymers of ethylene and of alkyl acrylate, the copolymers of ethylene and of ethylene and acrylic acid, the ethylene terpolymers or the same polymers having specific groups such as acid or epoxy groups. Preferably, the polymer is a thermoplastic polymer, and the copolymer of ethylene and vinyl acetate (EVA) has been found to be particularly advantageous. An EVA containing up to 80% by weight of vinyl acetate and most preferably an EVA containing between 10 and 70% of vinyl acetate is preferably used. The particularly preferred polymer matrix in the context of the present invention is EVA 260 containing 28% vinyl acetate.

 The intumescent composition generally comprises from 25 to 95 parts by weight and preferably from 30 to 85 parts by weight of polymer matrix.

 As a carbon source can be used organic compounds rich in carbon which contain functional groups forming a char when they are exposed to heat alone or in the presence of a char promoter. Thus, it is possible to use, for example, polymers such as a polyamide (for example PA6) or ethylene vinyl alcohol (EV (OH)), PA6 being preferred.

 In the composition in general, from 2 to 20, preferably from 2 to 10, parts by weight of carbon source are used.

 The anthrax promoter is generally selected from compounds releasing an inorganic acid at high temperature. According to the invention, ammonium polyphosphate (APP), which forms polyphosphoric acid, is used as the carbon promoter.

 The gas source is responsible for gas generation during coal mining. The gas formed upon exposure of the composition at elevated temperatures then leads to the formation of a foam.

Advantageously, the ammonium polyphosphate (APP) can be used as

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 gas source in the intumescent composition. Thus, it is a single compound that plays both the role of carbon promoter and that of gas source.

 The composition generally comprises from 10 to 60 parts by weight and preferably from 20 to 35 parts by weight of APP.

 The composition also contains one or more mineral fillers such as kaolin, talc, magnesia or others. The addition of mineral fillers with a particular structure such as fillers with a laminated structure (graphite, mica) or comprising pseudo-sheets (fibrous clay, sepiolite) or a large specific surface area (molecular sieve zeolites) will make it possible to improve the properties of held in the fire.

 The mineral fillers are added in an amount of 2 to 50, preferably 5 to 40 and more preferably 10 to 30 parts by weight of the composition.

 As crosslinking agents, it is possible to use high temperature decomposing free radical generators such as organic peroxides, for example dicumyl peroxide, di-tert-butylperoxide, or 2,5-dimethylhexine (3) -2,5 -di-tert-butyl-peroxide.

 The composition generally contains from 0.5 to 7 parts by weight and preferably from 0.5 to 3 parts by weight of crosslinking agent.

 As silanes, aminosilanes or vinylsilanes will preferably be used. The silane is hydrolyzable and carries functional groups capable of reacting with the functional groups of the polymer matrix and optionally with the superficial OH groups of the filler (kaolin, talc, magnesia, etc.). An example of such a silane is a trialkoxysilane. Preferably, a silane having an amine function, such as aminotrialkoxysilane, is used.

As an example of such a silane, mention may be made of aminopropyltriethoxysilane.

 Preferably, the composition comprises from 0.2 to 10 parts and preferably from 0.5 to 5 parts by weight of silane compound.

 Usually, an antioxidant is also added to the composition. Such antioxidants are known, exemplified by Santonox TBMC (Flexsys).

 The amount of antioxidant in the composition is preferably from 0.05 to 2 parts by weight and in particular from 0.1 to 1 parts by weight.

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 Furthermore, the composition may contain other additives such as catalysts, fluxes.

 The process according to the invention is explained in more detail below.

 The dynamic crosslinking process is described in detail in application FR 00 05 775 in the name of the applicant.

 According to one embodiment, the dynamically crosslinked composition is obtained in one step. The resulting mixture which is implemented as a thermoplastic, is then extruded during the manufacture of the cable. The dynamic crosslinking of the mixture can be carried out in an internal mixer or in a twin screw extruder.

 The base polymer and the various additives of the composition excluding the crosslinking agents are kneaded at an elevated temperature so as to obtain a homogeneous mixture, when the mixture is homogeneous, the free radical generator is added. The temperature at which the free radical generator is added is preferably slightly less than the decomposition temperature thereof so that it is well dispersed in the mixture before reacting. The mixture is then strongly kneaded at a temperature above the decomposition temperature of the free radical generator and the mixture is strongly kneaded so as to obtain an effective dynamic crosslinking. The silane can be added either after this step, in this case we have a ready-to-use mixture which is used as a thermoplastic. In another alternative, the silane can be added during the manufacture of the cable, whatever the case envisaged, the cable does not require any subsequent crosslinking treatment unlike conventional static crosslinking. preparation of the mixture either during the initiation of the dynamic crosslinking.

 Preferably, the dynamic crosslinking is initiated at a temperature above 1500C and preferably between 170 and 2300C and under significant shear, that is to say greater than 5-1 and preferably between 50 and 250 s -1.

 In the process as just described, the mixture is first produced which has the properties of implementation of a thermoplastic polymer, this mixture is then extruded during the manufacture of the cable. The resulting cable has good fire resistance properties without the need for further crosslinking.

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 One can also consider with a sufficiently long and well adapted extruder to develop and manufacture the cable in one step which saves time and cost.

 It is noted that for these dynamically crosslinked materials as previously described, the crosslinking is generally not complete. However, it turns out that in the desired application this is an advantage since the viscosity of the intumescent composition is high enough not to drip under the effect of heat. At the same time, the low viscosity of the intumescent composition facilitates the implementation, for example the extrusion of cable sheaths.

 The composition obtained according to the invention charbonne under the effect of heat forming a foam but does not drip. The composition thus obtained thus provides effective protection against the flame with a low level of charge due to swelling and charcoal of the intumescent composition. In addition, the fumes of decomposition products are low in toxicity and therefore better compatible with the environment. Moreover, this intumescent composition is easy to implement, for example for the manufacture of cable ducts. The partial crosslinking obtained in general makes it possible to retain the thermoplastic character of the composition and in particular also allows recycling.

 The extrusion of the composition obtained according to the invention can advantageously be carried out in an appropriate manner to produce various products having the mechanical properties and flame resistance that the composition obtained has.

 As examples of such products, mention may be made of the energy or telecommunication cables whose insulator and / or cladding consist or comprise the composition obtained according to the invention.

 The invention relates to an energy cable 1 comprising a core 2 of conductive material surrounded by a sheath 3. The term energy cable means any electrical conductor for transporting electrical energy and comprising at least one sheath. Such a cable comprises a core of conductive material, generally surrounded by different layers including a sheath. This sheath preferably provides fire protection.

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 According to one embodiment, the sheath 3 is at least partially composed of the intumescent composition according to the invention. The electrical wire thus isolated has a significantly improved fire resistance.

 In order to manufacture such sheaths, it is possible for example to proceed as follows. The components are mixed in a continuous or batch mixer, then the composition is carried out by extrusion, a technique that allows the transformation of granules or strips of compound into product in the form of cable coating. The material is transported with a screw from the feeding area to the die. The material plasticizes under the action of the mixing induced by the rotation of the screw and the heat brought from the outside. The pressure increases progressively along the screw thus forcing the material to pass through the die to give it a frozen shape at the outlet of the latter. This technique makes it possible, thanks to the adaptation of a suitable die head, to cover copper wires or previously insulated wires.

 The fire resistance of the cables thus obtained is evaluated using the IEC 332 standard. The principle consists in measuring the length of the burn of the sheath after exposure to a flame. This standard has three components, the IEC 332/1 and / 2 standards which relate to the fire resistance of sheathed copper wires and IEC 332/3 which concerns the cable layers. This standard is more severe insofar as it takes into account all the materials constituting a sheet of cables.

 The cables whose sheath comprise the composition pass the test according to IEC 332/1 and 2. Furthermore, the cables according to the invention have been subjected to the UL94 test established to highlight the dripping behavior of paints and varnishes. . The cables are rated VO, ie they do not burn or drip when exposed to test conditions.

 According to the embodiment shown in FIG. 2, the sheath 3 comprises, in addition to the layer of insulating material, an outer protective coating 4. The insulating sheath 3 and / or the coating 4 may consist of or comprise an intumescent composition obtained according to FIG. the invention.

 The embodiment of Figure 2 is typical of low voltage AC cables. The integration of the composition obtained according to the invention in the layer 4 of cladding material allows a significant increase in mechanical characteristics, withstand and spread to fire.

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 In addition, the material forming the sheath of the cable can then be reworked, that is to say, extruded again to form a new sheath, after use of the cable. The sheath made with the recycled material retains good properties.

 Although the invention has been described in detail for application in power cable sleeves, the invention may be similarly applied to provide fire protection for telecommunication cables or other cables.

 The invention is described in more detail by means of the following examples.

EXAMPLE 1 (Comparative)
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 1800C, 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) is added, the mixture is again kneaded. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

EXAMPLE 2 (Comparative)
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 1800C, 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) and 40 parts by weight of kaolin are added, and the mixture is again kneaded.

The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

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EXAMPLE 3 (Comparative) 100 parts by weight of ethylene vinyl acetate (EVA) copolymer (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0, 5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 1800C, 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) and 40 parts by weight of kaolin are added, the mixture is kneaded. After homogenization of the mixture and cooling to a temperature of 120 ° C., 2 parts by weight of peroxide are added and the mixture is kneaded again. The mixture is statically cross-linked in press. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

EXAMPLE 4
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 1800C, 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) are added, the mixture is kneaded. After homogenization of the mixture and cooling to a temperature of 120 ° C., 2 parts by weight of peroxide are added and the mixture is kneaded again. The mixture is statically cross-linked in press. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

EXAMPLE 5
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in a mixer

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interne avec 7 parties en poids de polyamide 6 et 0, 5 parties en poids d'antioxydant (Santonox/TBMC) à une température de 230 C.

internally with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 180 ° C., 2 parts by weight of aminosilan (AllOO) and one part by weight of peroxide (Trigonox B50) are added, the mixture is again strongly kneaded so as to obtain dynamic crosslinking. then 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) are added, the mixture is again kneaded. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

EXAMPLE 6
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

 After homogenization of the mixture and cooling to a temperature of 180 ° C., 2 parts by weight of aminosilan (AllOO) and one part by weight of peroxide (Trigonox B50) are added, the mixture is again strongly kneaded so as to obtain dynamic crosslinking. then 50 parts by weight of ammonium polyphosphate PPA (Exolite AP422) and 40 parts by weight of kaolin are added, the mixture is again kneaded. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties.

EXAMPLE 7
100 parts by weight of ethylene vinyl acetate copolymer (EVA) (Elvax 260 from Dupont de Nemours 28% VA, melt index 6) are kneaded in an internal mixer with 7 parts by weight of polyamide 6 and 0.5 parts by weight of antioxidant (Santonox / TBMC) at a temperature of 230 C.

de 180 C, ajoute 2 parties en poids d'aminosilan (A1100) et une partie en poids de peroxyde (Trigonox B50), le mélange est à nouveau fortement malaxé de façon à obtenir une réticulation dynamique puis on ajoute 50 parties en poids de After homogenization of the mixture and cooling to a temperature

of 180 C, add 2 parts by weight of aminosilan (A1100) and one part by weight of peroxide (Trigonox B50), the mixture is again strongly kneaded so as to obtain a dynamic crosslinking and then 50 parts by weight of

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ammonium polyphosphate PPA (Exolite AP422), 40 parts by weight of kaolin and 5 parts by weight of talc is again kneaded. The mixture thus obtained is shaped in the form of a plate for the determination of the characteristics of fire resistance and mechanical properties. Table 1

<Tb>
<tb> 1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7
<tb> EVA <SEP> 260 <SEP> 100 <SEP> 100 <SEP> 100 <SEP> 100 <SEP> 100 <SEP> 100 <SEP> 100
<tb> PA <SEP> 6 <SEP> 7 <SEP> 7 <SEP> 7 <SEP> 7 <SEP> 7 <SEP> 7 <SEP> 7
<tb> SantonoxTBMC <SEP> 0.5
<tb> Kaolin-40 <SEP> 40--40 <SEP> 40
<tb> Talc ------ 5
<tb> APP <SEP> 50 <SEP> 50 <SEP> 50 <SEP> 50 <SEP> 50 <SEP> 50 <SEP> 50
<tb> Aminosilane ---- 2 <SEP> 2 <SEP> 2
<tb> Trigonox <SEP> B50--2 <SEP> 2 <SEP> 1 <SEP> 1 <SEP> 1
<Tb>

The mixtures thus obtained are then shaped in press to obtain plates of desired thickness (3 mm for the characterization according to UL94 or 1 mm for the determination of the mechanical characteristics). Part of the mixture is then extruded on an already insulated wire with a non-fireproof mixture (the thickness of the insulation = 0.5 mm and the thickness of the sheath = 0.5) and the cable thus obtained is tested according to the standard IEC 332 / 2. 2. The results are shown in Table 2.

 The mixtures obtained according to Examples 1 and 2 contain neither peroxide nor silane and are therefore not crosslinked. The mixtures according to Example 3 and 4 are crosslinked by a conventional crosslinking process (static crosslinking in a press at 200 ° C.). They therefore constitute examples of comparison. The mixture is crosslinked according to the process of the invention (dynamic crosslinking under high shear) but does not contain a mineral filler. Blends 6 and 7 are crosslinked according to the process of the invention and contain a mineral filler.

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Tableau 2

Table 2

<Tb>
<tb> Example <SEP> UL <SEP> 94 <SEP> UL <SEP> 94 <SEP> IEC <SEP> 332/1 <SEP> Constraint <SEP> to <SEP> Elongation <SEP> to
<tb> Burn <SEP> Drop <SEP> Class-and <SEP> 2 <SEP><SEP> break <SEP><SEP> break <SEP> [%]
<tb> Expands <SEP><SEP> [Mpa]
<tb> 1 <SEP> Yes <SEP> Yes <SEP> No <SEP> V2 <SEP> No <SEP> n. <SEP> d. <SEP> n. <SEP> d.
<tb> satisfactory
<tb> 2 <SEP> Yes <SEP> Yes <SEP> No <SEP> V2 <SEP> No <SEP> n. <SEP> d. <SEP> n. <SEP> d.
<tb> satisfactory
<tb> 3 <SEP> Yes <SEP> No <SEP> Yes <SEP> V2 <SEP> n. <SEP> d. <SEP> n. <SEP> d. <SEP> n. <SEP> d.
<Tb>

4 <SEP> No <SEP> Yes <SEP> No <SEP> V2 <SEP> n. <SEP> d. <SEP> n. <SEP> d. <SEP> n. <SEP> d.
<Tb>

5 <SEP> No <SEP> Yes <SEP> No <SEP> V2 <SEP> n. <SEP> d. <SEP> n. <SEP> d. <SEP> n. <SEP> d.
<Tb>

G <SEP> No <SEP> No <SEP> Yes <SEP> VO <SEP> Satisfactory <SEP> 13, <SEP> 7 <SEP> 170
<tb> t <SEP> IEC / 1 <SEP> and
<tb> 2
<tb> 7 <SEP> No <SEP> No <SEP> Yes <SEP> VO <SEP> Satisfactory <SEP> 12, <SEP> 4 <SEP> 170
<tb> tIEC / 1 <SEP> and
<tb> 2
<tb> n. <SEP> d. <SEP> = <SEP> no <SEP> determined
<Tb>

It is clear from the results that the dynamically crosslinked compositions (Examples 6 and 7) exhibit significantly improved fire behavior compared to other similar non-crosslinked or crosslinked compositions according to a conventional method. In particular, the process according to the invention makes it possible to obtain intumescent compositions which, when exposed to heat, expand without drip or burn.

 In particular, these compositions comply with the IEC 332/1 and / 2 and UL 94 standards.

Claims (19)

1. A process for preparing an intumescent composition comprising the steps of: - mixing a composition comprising a non-halogenated thermoplastic polymer, a carbon source, ammonium polyphosphate and a mineral filler; and dynamic crosslinking in the presence of a silane compound and a crosslinking agent. The method of claim 1, wherein the non-halogenated thermoplastic polymer is a copolymer of ethylene and vinyl acetate (EVA). 3. Method according to one of the preceding claims, wherein the composition comprises 25 to 95 parts of non-halogenated thermoplastic polymer. 4. Method according to one of the preceding claims, wherein the carbon source is a polyamide 6. 5. Method according to one of the preceding claims, wherein the composition comprises 2 to 20 parts of carbon source. 6. Method according to one of the preceding claims, wherein the composition comprises 10 to 60 parts by weight of ammonium polyphosphate. 7. Method according to one of the preceding claims, wherein the inorganic filler is selected from Kaolin, talc, magnesia, and other fillers used in the cabling. <Desc / Clms Page number 16> 8. Method according to one of the preceding claims, wherein the composition may contain catalysts, fluxes or fillers with a laminated structure or comprising pseudo-sheets or a large specific surface area. 9. Method according to one of the preceding claims, wherein the composition comprises 2 to 30 parts by weight of inorganic filler. 10. Method according to one of the preceding claims, wherein the crosslinking agent is a peroxide.  11. Method according to one of the preceding claims, wherein the silane and / or the crosslinking agent are incorporated in the composition during the mixing step. 12. Method according to one of claims 1 to 11, wherein the silane and / or the crosslinking agent are incorporated in the composition during extrusion. 13. Method according to one of the preceding claims, wherein the dynamic crosslinking is carried out at a temperature above 1500C and under a shear greater than 20 s-1. 14. Method according to one of the preceding claims, wherein the dynamic crosslinking is carried out in a twin screw extruder. 15. Intumescent composition obtainable by the method according to one of claims 1 to 14. 16. Use of the composition according to claim 15 as a flame retardant, in particular in energy cables or telecommunication cables. 17. Cable comprising a core (2), a sheath (3) and a protective coating (4), the sheath and / or the protective coating comprising an intumescent composition according to claim 16. <Desc / Clms Page number 17>  The method of manufacturing a cable according to claim 19, comprising the step of extruding a composition of claim 15 around the core to form a sheath. The method of claim 19, wherein the extruding step serves both the dynamic crosslinking and the shaping of the composition.