ESPUMAS DE POLIOLEFINA DE CELULAS FINAS

LA INVENCION TRATA DE MATERIALES CELULARES FINOS DE POLIOLEFINA DE ELEVADA RIGIDEZ Y RESISTENCIA AL TERMOMOLDEO, CON DENSIDADES DE ESPUMA EN UN AMBITO DE ENTRE 10 Y 600 KG/M 3 , QUE ESTAN FORMADOS POR MEZCLAS DE POLIPROPILENO CON POLIETILENOS, QUE SE HICIERON REACCIONAR CON MONOMEROS BIFUNCIONALES INSATURADOS Y/O COMPOSICIONES DE ORGANOSILANO HIDROLIZABLES Y ETILENICAMENTE INSATURADAS, EN PRESENCIA DE FORMADORES DE RADICAL QUE SE DISGREGAN TERMICAMENTE, EN DOS PASOS REACTIVOS DEL PROCESO, Y, A CONTINUACION, SE ESPUMARON. LOS MATERIALES CELULARES FINOS DE POLIOLEFINA SON APTOS PARA SU EMPLEO EN EL SECTOR DE LA INDUSTRIA DEL ENVASADO, PREFERENTEMENTE PARA EL ENVASADO DE PRODUCTOS ALIMENTICIOS, PARA LAS PIEZAS EXTERIORES DE AUTOMOVILES Y LAS PIEZAS DE LOS ESPACIOS INTERIORES DE LOS AUTOMOVILES, ASI COMO PARA LOSCOMPONENTES DE APARATOS ELECTRICOS Y ELECTRONICOS. Fine-celled polyolefin foam with high heat distortion temperature and stiffness and a foam density of 10-600 kg/m consists of polypropylene (PP) and polyethylene (PE). It is made from mixtures of 10-90, preferably 60-80 wt.% PP and 90-10, preferably 40-20 wt.% PE in 2 reactive process stages (1, 2) and a foaming stage (3), as follows. (1) The PP-PE mixture is partly reacted with 0.05-2 wt.% bifunctional ethylenically unsaturated monomers (I) and/or 0.5-1 wt.% hydrolysable, ethylenically unsaturated organo-silane compounds (II) in the presence of 0.01-0.85 wt.% thermal free radical initiator (III), so that 5-35 wt.% of the (I) used and 10-40 wt.% of the (III) used are unreacted at the end of this stage. Reaction is carried out (1.a) with a powder mixture in the solid phase at 55-105 degrees C in a continuous screw mixer, using (III) based on acyl peroxides (IIIA), alkyl peroxides (IIIB), hydroperoxides (IIIC) and/or peresters (IIID) with a half life of 0.2-5 minutes at the reaction temperature; or (1.b) in the solid/melt transition phase at 105-190 degrees C in a twin screw extruder, using (III) based on (IIIA), (IIIB), (IIIC), peroxycarbonates, (IIID), ketone peroxides, peroxyketals and/or azo compounds with a half life of 0.2-2 minutes at the reaction temperature. (2) The unreacted components in the mixture are coupled at 195-270 degrees C in a twin screw extruder, with addition of 0.3-8 wt.% blowing agent and, if necessary, 0.01-0.35 wt.% peroxide with respect to the polyolefins. (3) The mixture is foamed by extrusion and hauled off as film, tube or profile or as a strand that is immediately cut into