PURPOSE: To prevent mutual gluing of granules that appear at the drying time and the solid state polymerizing time of the granules by a method wherein a crystallized layer with a thickness 20ω or more is prepared only on the surface area of the granules composed of polyester having alkilene terephthalate as the main recurring unit and treated under a condition satisfying the specific relation formula by heated steam of 110°C or higher.
CONSTITUTION: The specific relation formula in the heated steam treatment is as follows: 300≥H≥A/T (wherein H: treating time in sec, T: temperaure in °C, A: coefficient about crystal layer thickness t, indicated by formula A=exp(at+b) wherein a is 0.01W0.05 and b is 1.0W5.0). Dimethyl terephthalate and ethylene glycol are molten polymer to obtain granules of polyethlene terephthalate. They are exposed to the atmosphere of heated steam for a short time under the above-mentioned relational condition. Then, they are heated and dried from 180°C to 230°C for three hours under reduced pressure and polymerized in solid state to obtain polyester chips the hang-up rate thereof is almost zero.
YAMAUCHI SHINICHI
SOGA AKIRA
Next Patent: STORING OF POLYESTER GRNULE