Expandable vinyl aromatic polymers

Abstract

The present invention is an expandable vinyl aromatic polymer which comprises: a) a matrix of a vinyl aromatic polymer, b) 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix, c) 0.1 to 5% by weight calculated with respect to the polymer (a), of PiB (polyisobutene), homogeneously distributed in the polymeric matrix, d) 0-20% by weight, calculated with respect to the polymer (a), of one or more fillers, other than PiB, homogeneously distributed in the polymeric matrix, Wherein the proportion of PiB is adjusted to increase the Melt Flow Index (MFI) from an initial index to a final index such as the 10% compression strength of the foam made with said expandable vinyl aromatic polymer of the final index is essentially the same or higher than the foam made with said expandable vinyl aromatic polymer of the initial index. The expandable vinyl aromatic polymer of the invention is produced in the form of beads or granules. In an embodiment the expandable vinyl aromatic polymer comprises carbon black in a proportion sufficient for the foamed material obtained from the expandable vinyl aromatic polymer to have a thermal conductivity λ of about 34 mW/m° K or lower.

1 . Expandable vinyl aromatic polymer which comprises:
 a) a matrix of a vinyl aromatic polymer,   b) 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix,   c) 0,1 to 5% by weight calculated with respect to the polymer (a), of PiB (polyisobutene), homogeneously distributed in the polymeric matrix,   d) 0-20% by weight, calculated with respect to the polymer (a), of one or more fillers, other than PiB, homogeneously distributed in the polymeric matrix,   Wherein the proportion of PiB is adjusted to increase the Melt Flow Index (MFI) from an initial index to a final, index such as the 10% compression strength of the foam made with said expandable vinyl aromatic polymer of the final index is essentially the same or higher than the foam made with said expandable vinyl aromatic polymer of the initial index.   
     
     
         2 . Expandable vinyl aromatic polymer according to  claim 1  wherein it is in the form of beads or granules. 
     
     
         3 . Expandable vinyl aromatic polymer according to  claim 1  wherein it comprises carbon black in a proportion sufficient for the foamed material obtained from the expandable vinyl aromatic polymer to have a thermal conductivity λ of about 34 mW/m° K or lower. 
     
     
         4 . Expandable vinyl aromatic polymer according to  claim 1  wherein the thermal conductivity λ of the foamed material obtained from the expandable vinyl aromatic polymer is between about 33 and 34 mW/m° K. 
     
     
         5 . Expandable vinyl aromatic polymer according to  claim 1  wherein the thermal conductivity λ of the foamed material obtained from the expandable vinyl aromatic polymer is between about 32 and 33 mW/m° K. 
     
     
         6 . Expandable vinyl aromatic polymer according to  claim 1  wherein the thermal conductivity λ of the foamed material obtained from the expandable vinyl aromatic polymer is between about 30 and 31 mW/m° K. 
     
     
         7 . Expandable vinyl aromatic polymer according to  claim 1  wherein the PiB are those having a molecular weight (number average) of between about 500 and 5000. 
     
     
         8 . Expandable according to  claim 1  wherein the molecular weight ranges between about 900 and 3000. 
     
     
         9 . Expandable vinyl aromatic polymer according to  claim 1  wherein the vinyl aromatic polymer is polystyrene such as crystal polystyrene and HiPS. 
     
     
         10 . Use of the expandable vinyl aromatic polymer according to  claim 1  to make expanded articles, in particular insulation boards. 
     
     
         11 . Process to increase the Melt Flow Index of an expandable vinyl aromatic polymer while maintaining the same or a higher 10% compression resistance, comprising,
 a) providing a vinyl aromatic polymer in the molten state,   b) introducing 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix,   c) introducing 0.1 to 5% by weight calculated with respect to the polymer (a), of PiB (polyisobutene), homogeneously distributed in the polymeric matrix,   d) introducing 0-20% by weight, calculated with respect to the polymer (a), of one or more fillers, other than PiB, homogeneously distributed in the polymeric matrix,   Wherein the proportion of PiB is adjusted to increase the Melt Flow Index (MFI) from an initial index to a final index such as the 10% compression strength of the foam made with said expandable vinyl aromatic polymer of the final index is essentially the same or higher than the foam made with said expandable vinyl aromatic polymer of the initial index.   
     
     
         12 . Process according to  claim 11  wherein the PiB are those having a molecular weight (number average) of between about 500 and 5000. 
     
     
         13 . Process according to  claim 11  wherein the molecular weight ranges between about 900 and 3000. 
     
     
         14 . Process according to any one of  claim 11  wherein the vinyl aromatic polymer is polystyrene such as crystal polystyrene and HiPS.