Extrusion blow molding apparatus for preparing polyester articles

An extrusion blowmolding apparatus for preparing articles from a thermoplastic polyester material, the apparatus comprising:

• an extrusion die having an upstream portion for receiving the thermoplastic polyester material and a downstream portion having a die head through which molten thermoplastic polyester material is flowed to form a parison suitable for extrusion blowmolding;
• wherein the extrusion die has extending therethrough a generally cylindrical barrel having a length to diameter (L/D) ratio of from about 20:1 to about 40:1, and an extrusion screw disposed within the barrel, wherein the extrusion screw comprises a shaft and a spiral flight extending radially from the screw shaft along at least a portion of the length of the shaft defining a feed section, a primary section, a secondary section, and a metering section, wherein the flight has an outer edge in sliding contact with an inner surface of the barrel;
• and wherein the cylindrical barrel has a radius R and the shaft has a radius S which satisfy the following relationship:
• about 0.10≦[(R−S)/R]≦about 0.40 throughout the feed section;
• and
• about 0.03≦[(R−S)/R]≦about 0.20 throughout the metering section.