Apparatus for heat treatment of polyester particle and method of multistage solid-phase polycondensation of polyester particle

A multistage solid-phase polycondensation method for polyester particles, comprising:

• using an apparatus for a heat treatment of polyester particles for performing continuous solid-phase polycondensation of the polyester particles, comprising, in the stated order along a flow of the particles:
• (1) a first fluidized bed having a temperature of from 100 to 200° C., comprising:
• a porous plate, having an inclined part;
• an inert gas inlet;
• a continuous discharge in a constant amount;
• and
• optionally, a stirring mechanism;
• (2) a first moving bed having a temperature of from 190 to 230° C., comprising:
• an inert gas inlet;
• and
• a continuous discharge in a constant amount;
• (3) a second fluidized bed having a temperature of from 230 to 245° C., comprising:
• a porous plate;
• an inert gas inlet;
• a continuous discharge in a constant amount;
• and
• optionally, a stirring mechanism;
• and
• (4) a second moving bed having a temperature equal to or less than 250° C. and at least 15° C. higher than the temperature of the first moving bed, having an inert gas inlet and a gas exhaust outlet;
• wherein the second moving bed has a capacity twice or more as large as a capacity of the first moving bed;
• and
• performing solid-phase polycondensation of polyester particles having an intrinsic viscosity of 0.18 to 0.40 dL/g in the first moving bed of the apparatus for a heat treatment until the intrinsic viscosity increases by 0.03 to 0.10 dL/g;
• and
• performing additional solid-phase polycondensation of the polyester particles in the second moving bed of the apparatus until the intrinsic viscosity becomes equal to or larger than 0.70 dL/g.