Extruder and process for extruding a polymer

Abstract

The present invention relates to an extruder for a polymer, and a process for extruding a polymer using said extruder. In particular, the present invention provides an extruder comprising: (i) two or more barrel sections ( 1 a, 1 b, 1 c ) arranged sequentially from: (a) an upstream feed barrel section ( 1 a ) to which polymer feedstock to be extruded is fed, the upstream feed barrel section containing two or more screws each having a diameter of X; to (b) a downstream barrel section ( 1 c ) from which melted polymer is passed to a die and extruded; and (ii) one or more feed ports for feeding polymer feedstock to be extruded into the extruder at its upstream end, characterised in that the total area of the one or more feed ports through which polymer feedstock is introduced is greater than 4*X, and a process for extrusion of polymer comprising feeding a polymer feedstock to the feed port of such an extruder.

1 - 8 . (canceled) 
     
     
         9 . An extruder comprising:
 (i) two or more barrel sections arranged sequentially from:
 (a) an upstream feed barrel section to which polymer feedstock to be extruded is fed, the upstream feed barrel section containing two screws each having a diameter of X; to 
 (b) a downstream barrel section from which melted polymer is passed to a die and extruded; and 
   (ii) a feed port for feeding polymer feedstock to be extruded into the extruder at its upstream end,   characterised in that the feed port area is in the shape of a rectangle with rounded corners, the width of the feed port being limited by the width of the upstream feed barrel section to up to 2*X, the feed port length being greater than 2.5*X and the total area of the feed port through which polymer feedstock is introduced being greater than 5*X 2 .   
     
     
         10 . An extruder according to  claim 9  which comprises three of more barrel sections. 
     
     
         11 . An extruder according to  claim 9  which has a single feed port which has an area greater than 5*X 2 . 
     
     
         12 . An extruder according to  claim 9  in which the total area of the feed ports through which polymer is introduced is greater than 6*X 2 . 
     
     
         13 . An extruder according to  claim 9  in which the ratio of the screw pitch to screw diameter within the upstream feed barrel section is at least 1 and no greater than 2.5. 
     
     
         14 . An extruder according to  claim 9  in which the diameter of the screws in the feed port barrel section is 200 mm or greater. 
     
     
         15 . An extruder according to  claim 9  wherein the polymer feedstock is a polymer of ethylene or propylene and is in the form of a powder having a flowability ratio of from at least 1 to less than 6, said flowability ratio of the polymer powder being measured using the instantaneous shear test described in ASTM D 6773-02 at a consolidation pressure of 2000 Pa and at a temperature that is equal to the temperature of the polymer powder at the feed port during the extrusion process. 
     
     
         16 . An extruder according to  claim 15  wherein the polymer feedstock has a flowability ratio of less than 4. 
     
     
         17 . An extruder according to  claim 15  wherein the polymer feedstock has a flowability ratio of less than 2.