Expanded styrene polymers having a reduced thermal conductivity
Expanded styrene polymers which have a density of less than 25 g/l and a thermal conductivity λ, determined at 10° C. in accordance with DIN 52612, of less than 32 mW/m*K, and also a process for producing them.
1. An expanded styrene polymer having a density in the range from 7 to 20 g/l and a thermal conductivity λ, determined at 10° C. in accordance with DIN 52612, in the range from 27 to 31 mW/m*K, which comprises from 1 to 4% by weight of natural graphite having a mean particle size in the range from 1 to 50 μm, and which has been obtained by pre-foaming, and welding of an expandable styrene polymer,
the expandable styrene polymer having been obtained by polymerization of styrene and, optionally, copolymerizable monomers and impregnation with a blowing agent,
wherein the polymerization is carried out in the presence of 0.01 to 2% of a nonionic surfactant.
2. The expanded styrene polymer according to claim 1 , wherein the expanded styrene polymer has from 2 to 15 cells/mm.
3. The expanded styrene polymer according to claim 1 , wherein the cells are tilled with a gas which comprises at least 90% by volume of an inorganic gas.
4. The expanded styrene polymer according to claim 1 , which comprises an organic bromine compound having a bromine content of at least 70% by weight and passes the burning test B2 in accordance with DIN 4102.
5. The expanded styrene polymer according to claim 2 , wherein the cells are filled with a gas which comprises at least 90% by volume of an inorganic gas.
6. The expanded styrene polymer according to claim 2 , which comprises an organic bromine compound having a bromine content of at least 70% by weight and passes the burning test B2 in accordance with DIN 4102.
7. The expanded styrene polymer according to claim 1 , wherein the nonionic surfactant is a maleic anhydride copolymer (MA), polyisobutylene anhydride (PIBSA) or a reaction product of one of these with hydroxypolyethylene glycol esters or amines.
8. The expanded styrene polymer according to claim 1 , wherein the molecular weight of the nonionic surfactant is in the range from 500 to 3000 g/mol.
9. The expanded styrene polymer according to claim 7 , wherein the molecular weight of the nonionic surfactant is in the range from 500 to 3000 g/mol.
10. A process for preparing expanded styrene polymers by polymerization of
styrene and. optionally, copolymerizable monomers in aqueous suspension and impregnation with a blowing agent, wherein tile polymerization is carried out in the presence of from 0.1 to 4% by weight of graphite particles having a mean particle size in the range from 1 to 50 μm, based on the styrene polymer, and 0.01 to 2% of a nonionic surfactant, and
obtaining an expanded styrene polymer by pre-foaming and welding the expandable styrene polymer,
the expanded styrene polymer having a density in the range, from 7 to 20 g/l and a thermal conductivity λ, determined at 10° C. in accordance with DIN 52612, in the range from 27 to 31 mW/m*K.
11. The process according to claim 10 , wherein the nonionic surfactant is a maleic anhydride copolymer (MA), polyisobutylene anhydride (PIBSA) or a reaction product of one of these with hydroxypolyethylene glycol esters or amines in amounts in the range from 0.01 to 2% by weight, based on the styrene polymer.
12. The process according to claim 10 , wherein the molecular weight of the nonionic surfactant is in the range from 500 to 3000 g/mol.
13. The process according claim 11 , wherein the molecular weight of the nonionic surlactant is in the range from 500 to 3000 g/mol.