Expandable olefin bead polymers

Abstract

The invention relates to expandable olefin bead polymers which comprise a blowing agent with a boiling point of from −5 to 150° C., selected from the group consisting of alkanes, alkanols, ketones, ethers and esters. The particles are unfoamed and have a bulk density above 500 g/l, and can be foamed to a bulk density below 200 g/l after storage for one hour at room temperature in free contact with the atmosphere. They are prepared by impregnating polyolefin pellets in suspension in a pressure vessel with the blowing agent, cooling the batch below 100° C., reducing the pressure and isolating the particles.

We claim:  
     
         1 . An expandable olefin bead polymer which may have been blended with up to 50% of a thermoplastic with a glass transition point below 180° C. and comprises from 1 to 40% by weight of an organic blowing agent with a boiling point of from −5 to 150° C., based in each case on the weight of the olefin polymer, wherein the unfoamed beads have a bulk density above 400 g/l and can be foamed to a bulk density below 200 g/l after storage for one hour at room temperature in free contact with the atmosphere by heating above 100° C.  
     
     
         2 . An expandable olefin polymer as claimed in    claim 1   , which comprises a halogen-free blowing agent.  
     
     
         3 . An expandable olefin polymer as claimed in    claim 1    which is a copolymer of propylene with up to 15% by weight of ethylene and/or 1-butene.  
     
     
         4 . An expandable olefin polymer as claimed in    claim 1   , which comprises from 0.001 to 10% by weight of a nucleating agent, based on the weight of the polymer.  
     
     
         5 . An expandable olefin polymer as claimed in    claim 1   , which comprises no admixed thermoplastics.  
     
     
         6 . An expandable olefin polymer as claimed in    claim 1    which has been blended with from 5 to 40% by weight of a polyamide.  
     
     
         7 . A process for preparing expandable olefin bead polymers by impregnating polyolefin pellets with from 2 to 50% by weight of an organic blowing agent with a boiling point of from −5 to 150° C. in suspension in a pressure vessel at elevated temperature, reducing the pressure on the batch and isolating and washing the impregnated pellets, wherein the batch is cooled below 100° C. before the pressure is reduced.  
     
     
         8 . A process as claimed in    claim 7   , wherein a halogen-free blowing agent is used.  
     
     
         9 . A process as claimed in    claim 7   , wherein the blowing agent is an alkane, an alkanol, a ketone, an ether, an ester or a mixture of these.  
     
     
         10 . A process as claimed in    claim 9   , wherein the blowing agent is a pentane, a hexane, a heptane, 3,3-dimethyl-2-butanone or 4-methyl-2-pentanone.  
     
     
         11 . A process as claimed in    claim 7   , wherein the polyolefin pellets comprise from 0.001 to 10% by weight of a nucleating agent.  
     
     
         12 . A process as claimed in    claim 11   , wherein the nucleating agent is a wax and/or talc.  
     
     
         13 . The use of expandable olefin bead polymers as claimed in    claim 1    for producing foams.