Hot-vulcanizable polyorganosiloxane compositions useful particularly for manufacturing electrical cables or wires

1. A polyorganosiloxane composition that can be vulcanized at high temperature to a silicone elastomer, useful in the field of the manufacture of electrical wires or cables having an improved fire performance, comprising:

a) at least one polyorganosiloxane polymer;

b) at least one reinforcing filler;

c) at least one organic peroxide;

d) mica;

e) zinc oxide;

f) optionally at least one additive customarily used in the field of high-temperature-vulcanizing polyorganosiloxane compositions;

g) platinum, a platinum compound and/or a platinum complex;

h) titanium oxide;

i) at least one bulking filler;

j) optionally at least one mineral species belonging to the wollastonite group; and

k) at least one semi-reinforcing filler k),

wherein that the semi-reinforcing filler k) is at least one selected from the group consisting of:

calcined kaolin powders;

talc; and

calcium carbonate that may or may not have been surface-treated.

2. The composition as claimed in claim 1 , wherein said composition comprises based on 100 parts by weight of polyorganosiloxane polymer(s) a):

15 to 100 parts of reinforcing filler(s) b);

0.2 to 8 parts of organic peroxide c);

0.5 to 30 parts of mica d);

0.2 to 10 parts of zinc oxide e);

0 to 15 parts of auxiliary additive(s) f);

0.0005 to 0.02 parts of ingredient g) expressed by weight of (elemental) platinum metal;

0.5 to 10 parts of titanium oxide h);

20 to 100 parts of bulking filler(s) i);

0 to 10 parts of one or more species j) belonging to the wollastonite group; and

1 to 100 parts of semi-reinforcing filler(s) k).

3. The composition as claimed in claim 1 , wherein ingredient a) comprises at least one polyorganosiloxane polymer containing from 0 to 4% by weight of vinyl groups and possessing a viscosity of greater than 1 million mPa·s at 25° C.

4. The composition as claimed in claim 1 , wherein ingredient i) comprises silica, alumina or a mixture thereof.

5. The composition as claimed in claim 1 , wherein ingredient i) consists of at least one aluminum trihydroxide treated with an organoalkoxysilane.

6. The compositions as claimed in claim 1 , wherein ingredient j is present and comprises at least one species selected from: calcium metasilicate (CaSiO 3 ) or wollastonite; mixed calcium sodium metasilicate (NaCa 2 HSi 3 O 9 ) or pectolite; and mixed calcium manganese metasilicate CaMn(Si 0 2 ) 2 or bustamite.

7. The composition as claimed in claim 1 , wherein optional ingredient f is present and comprises at least one antistructuring product f1); and/or at least one polysiloxane resin f2); and/or at least one stabilizing agent f3); and/or at least one colored pigment f4); and/or at least one boron-based compound f5).

8. A method for the production of the sheath or primary insulation of one or more single conductors used in the construction of fire-resistant electrical wires or cables, said method comprising: depositing a composition of claim 1 around each single conductor and then crosslinking to a silicone elastomer by heating to a material temperature ranging from 100° C. to 200° C.

9. A fire-resistant electrical wire or cable comprising a composition as claimed in claim 1 .

10. The electrical wire or cable as claimed in claim 9 , wherein said wire and/or cable comprises a

(1) a low smoke density which makes it possible to attain at least 80% light transmittance in accordance with the standard IEC 61 034, part 1; and/or

(2) said wire and/or cable meets the standard NFC 32-070 CR1 at 500 volts.

11. The composition as claimed in claim 1 , wherein ingredient b) comprises pyrogenic silica, precipitated silica, or a mixture of thereof.

12. The composition as claimed in claim 1 , wherein the semi-reinforcing filler k) is calcined kaolin powder.

13. the composition as claimed in claim 1 , wherein the semi-reinforcing filler k) is calcined kaolin powder that has undergone a chemical surface treatment.

14. The composition as claimed in claim 1 , wherein the semi-reinforcing filler k) is talc.

15. The composition as claimed in claim 1 , wherein the semi-reinforcing filler k) is calcium carbonate.

16. The composition as claimed in claim 1 , wherein the semi-reinforcing filler k) is calcium carbonate that has been surface-treated.

17. The composition as claimed in claim 16 , wherein the semi-reinforcing filler k) is calcium carbonate that has been surface-treated with vinylsilane, aminosilane, or (reactive or unreactive) silicone oils.

18. The composition as claimed in claim 1 , wherein said composition comprises based on 100 parts by weight of polyorganosiloxane polymer(s) a):

20 to 80 parts of semi-reinforcing filler(s) k).

19. The composition as claimed in claim 1 , wherein said composition comprises based on 100 parts by weight of polyorganosiloxane polymer(s) a):

40 to 70 parts of semi-reinforcing filler(s) k).