Process for continuously preparing extrudable, crosslinkable polyethylene compositions

Claim 1

IN A CONTINUOUS PROCESS FOR PRODUCING A CROSSLINKABLE POLYETHYLENE COMPOSITION IN THE FORM OF MOLDING GRANULES IN WHICH A POLYTHYLENE COMPOSITION IS CONTINUOUSLY FED INTO THE FEED ZONE OF A SCREW EXTRUDER, THEREIN COMPACTED, MELTED AND PASSED THROUGH A METERING ZONE TO A DISCHARGE DIE, AND IN WHICH A SOLUTION OF A PEROXY COMPOUND IS INJECTED INTO THE MOLTEN POLYETHYLENE COMPOSITION INSIDE THE EXTRUDOR PRIOR TO EXTRUSION OF THE MOLTEN POLYETHYLENE COMPOSITION THROUGH THE DIE, AND IN WHICH THE EXTRUDATE IS CUT INTO MOLDING GRANULES, THE IMPROVEMENT WHICH COMPRISES: A. SELECTING AS THE PEROXY COMPOUND ONE WHICH HAS A FLASH POINT OF AT LEAST 70*C, AND AN EQUIVALENT HALF-LIFE OF MORE THAN 1 HOUR, B. MODERATING THE PEROXY COMPOUND PRIOR TO INJECTION BY FORMING A MODERATED PEROXY COMPOSITION BY DISSOLUTION OR DISPERSION OF THE PEROXY COMPOUND IN AN INERT LIQUID CARRIER WHICH IS COMPATIBLE WITH THE POLYETHYLENE COMOSITION, SAID LIQUID CARRIER BEING SELECTED FROM THE GROUP CONSISTING OF LIGHT OIL AND MELTED WAX; C. CONTINUOUSLY INJECTING THE MODERATED PEROXY COMPOSITION THROUGH INJECTION PORTS INTO A MIXING ZONE NEAR THE DISCHARGE END OF THE EXTRUDER AT A RATE SUFFICIENT TO PRODUCE A CONCENTRATION OF FROM 0.1 TO 5.0 PERCENT BY WEIGHT OF SAID PEROXY COMPOUND IN THE MOLTEN POLYETHYLENE COMPOSITION IN SAID MIING ZONE, D. MAINTAINING THE TEMPERATURE IN SAID MIXING ZONE AT BETWEEN 130* AND 160*C, AND E. OPERATING THE EXTRUDER SCREW AT A RATE SUCH THAT THE METERING ZONE PROCESS THE MOLTEN POLYETHYLENE COMPOSITION THROUGH THE MIXING ZONE AND EXTRUSION DIE AT A RATE SUCH THAT THE AVERAGE HOLD-UP TIME IN THE MIXING ZONE IS LESS THAN 12 MINUTES.