Process for the continuous polymerization of polyethylene terephthalate in the solid phase

Claim 1

In a process for the continuous production of high molecular weight polyethylene terephthalate by polycondensation in the solid phase from a dried granulated polyethylene terephthalate in which the granulated polyethylene terephthalate is first at least partially crystallized following which the partially crystallized material is subjected to polycondensation, the improvement which comprises: (A) first preheating said polymer under forced motion to a temperature in the range of about 180° C. to 200° C. without substantial increase in the intrinsic viscosity of said polymer and while maintaining the crystallinity below about 40%; (B) at least partially crystallizing said preheated polymer in a fixed bed crystallizer by feeding said polymer into said fixed bed at a temperature in the range of about 180° to 200° C., maintaining it in said bed for a time sufficient to raise the crystallization to a value in the range of 40 to 60% while maintaining the intrinsic viscosity of the polymer below about 0.75, and thereafter removing it from said bed at a temperature in the range of about 195° to 215° C.; and (C) effecting said polycondensation under forced motion in an agitated reactor by introducing the product of step (B) into said agitator reactor and raising the temperature thereof to a value in the range of about 220° to 245° for a period of time sufficient to raise the intrinsic viscosity of the polymer to a value of at least 0.70 up to about 1.4, steps (B) and (C) being conducted under a non-reactive gas atmosphere.