The invention deals with a fire-retardant composite composition comprising an original association of at least one specific thermoplastic polymer, of at least one specific particulate filler and of at least one specific fire-retardant agent, this composition complying with very favourable mechanical properties together with excellent fire-retardant properties.

Composite compositions based on at least one thermoplastic polymer are currently used in the electric industry due to the properties inherent with this type of polymers in terms of easily installation and shaping, of mechanical properties, of low density and small costs, with respect in particular to more traditional materials such as metal, wools, wood or glass.

However, the thermoplastic polymers, due to their organic nature, have a highly inflammable character, this requiring the use of fire-retardant agents, so that they can be used in environments subjected to high temperatures, such as electric apparatuses

In fact, the composite compositions used in electric apparatuses must satisfy severe standards in terms of fire resistance, which standards are in particular regulated by CEI standards applied in Europe, and in particular in France, like:

CEI 60695-2-11 standard for finished products, which defines the required flammability performance G FI ("Glow Wire Flammability Index"), that rises up to 850°C for continuous material without surveillance or to 960°C for material placed under more severe conditions; or

- CEI 60695-2-13 standard, which defines the flammability performance GWIT ("Glow Wire Ignition Temperature") which must be as a minimum at 775°C.

Some currently used and more efficient fire- retardant agents are the halogenated fire-retardant agents. However these agents risk to be shortly forbidden, since they have inconveniences regarding the environment, due to their highly toxic characters, in particular when they are subjected to a combustion.

Some frequently used non-halogenated fire- retardant agents are the fire-retardant agents that belong to the metal hydroxides family (such as aluminium hydroxide and magnesium hydroxide) , as in case of composite materials disclosed as examples in document ^' US 2008/0093107. With respect to halogenated fire-retardant agents, metal hydroxides free few fumes, when they are subjected to a combustion and are scarcely toxic. On the other hand, composite compositions comprising these agents have insufficient mechanical properties, in particular a low mechanical resistance and flexure module, these making them scarcely reliable to be used in the electric field.

Finally, the fire-retardant agents, in order to perform their function, are often embedded at very high contents in composite compositions, this contributing to degrade the mechanical properties of these latter ones, and also being capable of generating pollution problems induced by the bleed of the fire-retardant agent, when using the apparatus in which the compositions are embedded.

The problems encountered in environmental terms by the halogenated fire-retardant agents can also be found with the thermoplastic polymers that enter into the constitution of the composite compositions .

This is the case in particular encountered when the polymers belong to the family of the polystyrenes, of the poly (vinyl chloride) which, on one hand, are tributaries, due to their processing, of the relatively polluting oil chemistry and, n the other hand, have recycling difficulties, once they arrive at the end of their use.

Regarding the above mentioned problems, object of the inventors of the present invention is providing a composition that complies with the following specificities:

- fire-retardant properties without recurring to halogenated fire-retardant agents or to agents belonging to the family of metal hydroxides; mechanical properties which are not degraded with respect to the fire-retardant properties;

- absence of pollution connected to the bleed of the fire-retardant agent upon using the composition or the piece.

This object has been obtained with a fire- retardant composite composition comprising an original association of at least one specific ]_Q thermoplastic polymer, of at least one specific particulate filler and of at least one specific fire-retardant agent.

Consequently, the invention deals with a composite composition comprising a polymeric matrix

]_ comprising at least one polymer chosen among polyamides, polyterephtalates and polypropylenes in which a filler of the sepiolite type is dispersed, present in a content lower than 10% in weight with respect to the total weight of the composition and

20 a compound belonging to the family of melamine cyanurates, this latter one being included in the composition at a content ranging from 1% to 5% in weight with respect to the total weight of the composition .

The term polyamide means a polymer of the poly-condensate type in which the repeating units are linked through amide ground, this type of polymer being of the homopolymers (namely of the polymers comprising a single one and the same type of repeating units) or of the copolymers (namely of the polymers comprising several types of repeating units) .

Among the particularly useful polyamides for the invention, linear polyamides can be mentioned, which classically result from a poly-condensation of a dicarboxylic acid comprising from 4 to 12 carbon atoms with a diamine comprising from 4 to 14 carbon atoms or also resulting from a poly- condensation through cycle opening of lactamic compounds .

Polyamides complying with this definition can be, in particular: - polyamides 6, namely polyamides comprising a concatenation of repeating units of the following formula (I) :

(I)

polyamides 6/66, namely polyamides comprising a concatenation of repeating units of the following formula (I) :

(I)

and of repeating units of the following formula (II) :

(II)

The term polyterephtalate means a polymer of the poly-condensate type classically resulting from a poly-condensation of terephtalic acid and a polyol compound. In particular, polyterephtalates can be mentioned, which classically result from a poly- condensation of terephtalic acid with a diol comprising from 2 to 10 carbon atoms. Polyterephtalates complying with this definition can be, in particular, a poly(butylen terephtalate) (known with abbreviation PBT) characterised by a concatenation of repeating units of the following formula (III) :

(III)

Polypropylene means a polymer characterised by a concatenation of repeating units of the following formula (IV) :

(IV)

Being either polyamides, or polyterephtalates or polypropylenes, these polymers are particularly interesting for entering the composition of the invention, as far as they have the following features :

- they are thermoplastic, this making the composition comprising them particularly malleable and able to compose pieces with various shapes;

they are free from halogen atoms, this being compatible with environmental rules in force, and in particular with Reach European Directive;

they have good mechanical properties at high temperatures and with high stresses;

- they are easily available, since they are produced in tons, this making them particularly interesting in terms of costs, contrary to polymers of the polystyrene or vinyl polychloride type.

As mentioned above, the polymer (s) present in the composition compose a polymeric matrix, which means, in other terms, that they are present in a majority mass proportion with respect to other constituents of the composition which are sepiolite and the compound belonging to the family of melamine cyanurates .

Advantageously, the matrix is from 80% to 85% in weight with respect to the total weight of the composition . The sepiolite used as filler of the above polymeric matrix is a mineral belonging to the family of clays with fibrous structure, and from the point of view of the composition, to the family of hydrated magnesium silicates (of the ideal formula Sii ₂ Mg ₈ 0 ₃ o (OH) ₄ (OH ₂ ) .8H ₂ 0) appearing as needle-shaped particles. It is also characterised by a particularly high active surface, for example greater than 300 m ² /g and a very high density of silanol groups (-SiOH) , from which a very hydrophilic character results for this type of clays. Particles associate to form porous aggregates which have a wide capillary net, this explaining at the same time their important porosity and the light sepiolite mass. Finally, in contact with water or other liquids, the particles are not disrupted and form a suspension comprising a structure composed of said particles according to a compenetrated aleatory net, which works to trap liquids, this generating an increase of the suspension viscosity.

All their properties confer to the compositions of the invention comprising sepiolite, when this one is present at a content lower than 10% in weight, the following characteristics: - fire-retardant properties for viscous flame deletion;

- an improvement of barrier properties of the polymeric matrix, in particular due to the capability of sepiolites to be a solution for humidity recovery problems.

Sepiolite, within the invention, advantageously appears as nanoparticles which preferably have a mean particle diameter ranging from 0.1 to 0.2 micrometers and a fibre length ranging from 3 to 30 micrometers.

More specifically, sepiolite used in the invention can be a sepiolite marketed under the CD1 denomination by company Tolsa.

As previously mentioned, sepiolite is present in a content lower than 10% in weight with respect to the total weight of the composition and, preferably, is present in a content which ranges from 1% to 9%, still preferably, from 3% to 7% in weight with respect to the total weight of the composition, for example, 5% in weight with respect to the total weight of the composition.

In addition to the polymeric matrix and to sepiolite, the composition comprises a compound belonging to the family of melamine cyanurates at a weight content ranging from 1% to 5% in weight with respect to the total weight of the composition, for example, 1.5%, 2%, 3%, 4% or 5% in weight with respect to the total weight of the composition.

At such contents, the inventors were able to point out that this type of compounds embedded into a composition comprising a specific polymeric matrix (as defined above) and sepiolite (as defined above) , allows obtaining, in terms of fire extinguishing properties, similar properties to those obtained with other compositions in which this type of compound is embedded according to much greater contents (for example, on the order of 20% in weight or more) .

Consequently, the addition of this type of compounds at the above stated contents does not impair the mechanical properties of the composition, this allowing to avoid embedding glass fibres therein to give a remedy to the degrade of the mechanical properties due to the introduction of this same type of compounds at higher contents. Not having the need of recurring to glass fibres to improve the mechanical properties also allows accessing to an isotropic composition which, upon moulding, will have a homogeneous shrinkage, this improving the design of dies aimed to host this type of composition.

Moreover, this type of compounds does not comprise halogen atoms, this being important to comply with Reach European Directives which forbid the use of halogenated compounds.

A specific composition complying with the invention is a composition comprising:

- a polymeric matrix based on a polyamide, more specifically a polyamide 6;

- a sepiolite present in a content of 5% in weight with respect to the total weight of the composition;

- a compound of the melamine cyanurate type present in a content of 3% in weight with respect to the total weight of the composition.

The compositions of the invention can be produced by simply embedding, into a polymeric matrix complying with the invention, sepiolite and the compound of the melamine cyanurate type in he desired proportions.

The compositions are original in that they associate the three above specific ingredients, in particular in specific proportions, this conferring to these latter ones the following properties: fire-resistance properties within temperature ranges complying with the severe standard of electro-technical applications (the compositions of the invention favourably complying with the "Glow Wire Test" for temperatures ranging from 750°C to 960°C) ;

- mechanical properties which are not reduced due to the addition of a compound of the melamine cyanurate type and which do not require the addition of glass fibres;

- a low density;

chemical properties which satisfy the criteria imposed by Reach European Directive, in particular due to the fact that their ingredients do not comprise halogen atoms and consequently do not generate toxic gases.

As regards these properties, it is therefore natural that these compositions can be profited for producing pieces with fire-retardant properties.

The pieces of the invention can be produced through different processes of shaping plastic compositions, preferably with moulding processes.

In fact, as already mentioned, the compositions of the invention, due to the absence of glass fibres, are compositions that have a great isotropy, perfectly suitable for shaping through embedding in a die, shrinkage of the composition being perfectly homogeneous. Moreover, this shaping process is simple to operate, since it comprises^ a single step, this being also interesting in terms of production costs.

Other features and advantages of the invention will result from the following description of examples.

It is however clear that this description of examples is provided only as further clarification of the subject matter of the invention, and is not at all a limitation of this subject matter.

EXAMPLE

In this example, whose purpose is describing the intrinsic properties of the compositions of the invention in terms of behaviour to fires, Glow wire tests have been made, provided starting from a composition comprising a polymeric matrix in polyamide-6, which is available from company Rhodia, sepiolite available from company Tolsa (at 5% in weight with respect to the total weight of the composition) and melamine cyanurate available from company Budenheim (at 3% in weight with respect to the total weight of the composition) . These test consist in applying onto the composition a glow wire which respectively has a temperature of 750°C, 850°C and 960°C for 30 seconds. If, after the wire shrinkage, flames are extinguished in less than 30 seconds, the composition will be deemed as fire resistant.

Glow wire tests are successful for respective temperatures of 750°C, 850°C and 960°C.

As a comparison, for a specimen with the same size obtained with a composition comprising only, as polymeric matrix, polyamide 6 and sepiolite (at 5% in weight with respect to the total weight of the composition) , glow wire tests failed for a temperature of 750°C.

This demonstrates that the addition of melamine cyanurate in a limited content (as the case may be, 3% in weight, in our example) greatly improves the fire-retardant properties of the composition.

Specimens made starting from the composition of the invention has been also subjected to mechanical tests, from which the following properties resulted:

- a Young modulus (in MPa) of 4450 + 76; and

- an ultimate elongation (in %) of 6.6 ± 0.4. As a comparison, specimens with the same sizes made starting from a composition comprising only, as polymeric matrix, polyamide 6 and sepiolite (at 7% in weight with respect to the total weight of the composition) , have a Young modulus (in MPa) of 4714 ± 123 and an ultimate elongation (in %) of 5.4 ± 0.14.

It follows therefore that the addition of melamine cyanurate in the claimed proportions does not impair the mechanical properties of the composition, but instead improves them, this being assimilated to a synergic effect.