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

A method of producing a polyethylene terephthalate, comprising performing a heat treatment of a polyethylene terephthalate prepolymer having an intrinsic viscosity of 0.18 dL/g or more and 0.40 dL/g or less in a solid state to provide an intrinsic viscosity of 0.70 dL/g or more,

• wherein the heat treatment in the solid state comprises a first-stage solid-phase polycondensation step, a temperature increase step, and a second-stage solid-phase polycondensation step in the stated order, and the respective steps satisfy the following conditions (1) to (3):
• (1) the first-stage solid-phase polycondensation step is a step of treating the polyethylene terephthalate prepolymer with heat under an inert gas atmosphere or reduced pressure, and a temperature (T1c) of the heat treatment is 190° C. or higher and 225° C. or lower;
• (2) the temperature increase step is a step of increasing a temperature of the polyethylene terephthalate prepolymer after the first-stage solid-phase polycondensation step under an inert gas atmosphere or reduced pressure from a temperature equal to or lower than the temperature (T1c) of the heat treatment of the first-stage solid-phase polycondensation step to a temperature (T2c), the temperature of the polyethylene terephthalate prepolymer is increased from the temperature T1c (° C.) to (T1c+15)° C. within 30 minutes, and the temperatures T1c (° C.) and T2c (° C.) satisfy the following (Eq. 1c) and (Eq. 2c):
• T1c+15≦T2c (Eq. 1c), and
• 205° C.≦T2c≦240° C. (Eq. 2c);
• and
• (3) the second-stage solid-phase polycondensation step is a step of treating the polyethylene terephthalate prepolymer after the first-stage solid-phase polycondensation step and the temperature increase step with heat under an inert gas atmosphere or reduced pressure, and a temperature (T3c) of the heat treatment is 190° C. or higher and 240° C. or lower.