Improved Expandable Vinyl Aromatic Polymers

1 .- 10 . (canceled)

11 . Expandable vinyl aromatic polymers comprising at least one blowing agent and dispersed coke particles, said coke particles being characterized by an average stack height (Lc) of carbon crystallites less than 4 nm and a volume median particle diameter (D50) comprised between 0.8 and 4 μm as obtained from laser light scattering measurements according to ISO 13320.

12 . The expandable vinyl aromatic polymers according to claim 11 which comprise between 3 and 8% by weight of coke.

13 . The expandable vinyl aromatic polymers according to claim 11 , comprising between 2 and 10% by weight of a C3-C6 alkane.

14 . The expandable vinyl aromatic polymers according to claim 11 additionally comprising:

between 0.1 to 5% by weight of an halogenated polymer;

between 0.05 and 5% by weight of a flame retardant synergist; and

between 0.01 and 1.0% by weight of polyethylene wax characterized by a weight average molecular weight (Mw) comprised between 1500 and 5000 Da.

15 . A process for the preparation of beads or granules of an expandable vinyl aromatic polymer comprising the steps of:

a. producing a polymer melt stream of an expandable vinyl aromatic polymer, the expandable vinyl aromatic polymer comprising at least one blowing agent and dispersed coke particles, said coke particles being characterized by an average stack height (Lc) of carbon crystallites less than 4 nm and a volume median particle diameter (D50) comprised between 0.8 and 4 μm as obtained from laser light scattering measurements according to ISO 13320;

b. deriving a part of said polymer stream and creating main polymer melt stream ( 1 ) and a side loop with an additional polymer melt stream ( 2 );

c. dispersing the coke particles and the foam cell regulator into said additional polymer melt stream ( 2 );

d. joining the additional polymer stream ( 2 ) and the main stream ( 1 ) and forming a new polymer melt stream;

e. introducing a blowing agent into the new polymer melt stream;

f. cooling down the new polymer melt stream to a temperature of 200° C. or less;

g. introducing the flame retardant agent and the synergist into the new polymer melt stream;

h. discharging the melt stream through a die plate with holes and pelletizing the melt under water with a pressure above 3 bar.

16 . The process according to claim 15 , wherein the flame retardant synergist comprises a thermal free radical generator of the type comprising a C—C or C—O—O—C thermo-labile bond.

17 . The process according to claim 15 wherein between 5 and 30% of the main polymer stream is derived in step b) to form the additional polymer stream.

18 . The process according to claim 15 wherein, in step c), the coke particles and the foam cell regulator are dispersed in the additional polymer stream by means of an extruder.

19 . The process according to claim 15 wherein the dispersion in step c) is performed in the polymer melt at a temperature comprised between 180 and 250° C.

20 . The process according to claim 15 wherein, in step g), one or more thermal stabilizer(s) and anti-acid(s) are added.

21 . Polymer foams obtained from the molding of expanded vinyl aromatic polymers according to claim 11 , said foams being characterized by a thermal conductivity, (λ) measured according to ISO 8301, of:

32.5 mW/m·K or less at a foam density of 12.5 kg/m 3 or lower; or

31 mW/m·K or less at a foam density of 15 kg/m 3 or lower; or

31 mW/m·K or less at a foam density of 18 kg/m 3 or lower.