Process for extruding foamed thermoplastics by utilizing an intermeshing co-rotating twin screw extruder

Claim 2

IN A PROCESS FOR EXTRUDING A THERMOPLASTIC POLYMER COMPRISING EXTRUDING A FOAMABLE THERMOPLASTIC POLYMER ON AN EXTRUDER WHILE INJECTING A BLOWING AGENT INTO THE EXTRUDER, UNIFORMLY DISTRIBUITING THE INJECTED BLOWING AGENT INTO THE POLYMER, AND ADDING HEAT TO SAID POLYMER, THE IMPROVEMENT COMPRISING PASSING SAID POLYMER DURING EXTRUSION BETWEEN INTERMESHING SCREW FLIGHTS OF A TWIN SCREW INTERMESHING COROTATING EXTRUDER WHILE LIMITING THE AMOUNT OF HEAT ADDED TO THE POLYMER DURING EXTRUSION SO THAT THE COOLING EFFECT OF THE BLOWING AGENT WHEN INJECTED INTO THE EXTRUDER AND UNIFORMLY DISTRIBUTED WITHIN THE POLYMER, WILL BRING THE POLYMER AND BLOWING AGENT MIXTURE TO SUBSTANTIALLY THE DISCHARGE TEMPERATURE.

Claim 3

A process as claimed in claim 1 wherein no heat is removed by external means from the polymer and blowing agent mixture prior to discharging said mixture from said extruder screws.

Claim 4

A process as claimed in claim 1 wherein heat is added to the polymer by working of the polymer between screws and by external heating means, and all heat from said external heating means is added to the polymer prior to injection of the blowing agent.

Claim 5

In a process for producing a thermoplastic comprising extruding foamable thermoplastic polymer on an extruder while injecting a blowing agent into the extruder, and discharging the polymer and blowing agent mixture from the extruder at a predetermined discharge temperature to form said foamed thermoplastic, the improvement comprising rotating two parallel extruder screws the flights of which intermesh in the same direction (co-rotating), passing said foamable thermoplastic polymers between said co-rotating screws while mixing said blowing agent into the polymer, adding heat to the polymer during passage between said screws by working the polymer with the screws and by external heating means, limiting the amount of heat added to the polymer by said external heating means so that the cooling effect of the blowing agent, when mixed into the polymer, will bring the polymer and blowing agent mixture to substantially the discharge temperature, whereby excessive heating, which would require subsequent removal by external cooling means of a substantial amount of excessive heat from the polymer and blowing agent mixture, is avoided.

Claim 6

In a process for producing a thermoplastic comprising extruding foamable thermoplastic polymer on an extruder while injecting a blowing agent into the extruder, and discharging the polymer and blowing agent mixture from the extruder at a predetermined discharge temperature to form said foamed thermoplastic, the improvement comprising rotating two parallel extruder screws the flights of which intermesh in the same direction (co-rotating), passing said foamable thermoplastic polymers between said co-rotating screws while mixing said blowing agent into the polymer, adding heat to the polymer during passage between said screws by working the polymer with the screws and by external heating means, limiting the amount of heat added to the polymer by said external heating means so that the cooling effect of the blowing agent, when mixed into the polymer, will bring the polymer and blowing agent mixture to substantially the discharge temperature, whereby excessive heating, which would require subsequent removal by external cooling means of a substantial amount of excessive heat from the polymer and blowing agent mixture, is avoided.

Claim 7

A process as claimed in claim 4, wherein all of the heat from the external heating means is added to the polymer prior to mixing said blowing agent therein.