Polyester resin particle and method for producing the same

1. A method for producing a polyester resin, comprising carrying out a hot-water treatment and a heat treatment, in this order, of polyester prepolymer particles obtained by melt polycondensation of a dicarboxylic acid component and a diol component,

wherein the hot-water treatment comprises bringing the polyester prepolymer particles with an intrinsic viscosity of from at least 0.10 dL/g to at most 1.0 dL/g and with a density of at most 1.36 g/cm 3 into contact with hot water having a temperature higher than the glass transition temperature of the polyester prepolymer particles and less than 100° C., under the condition satisfying the following formula (1):

40≦( T−Tg ) t≦ 6000  (1)

wherein t is a hot-water treatment time (second), T is the temperature of the hot water (° C.) and Tg is the glass transition temperature (° C.) of the polyester prepolymer particles

wherein the hot-water treatment time t (second) is from 30 to 80 seconds and

wherein said polyester resin is a polyethylene terephthalate.

2. The method for producing the polyester resin according to claim 1 , wherein the polyester prepolymer particles are those obtained by the melt polycondensation in the presence of a polycondensation catalyst containing a titanium compound and/or a germanium compound.

3. The method for producing the polyester resin according to claim 1 , wherein the polyester prepolymer particles are particles with an average particle size of from at least 0.5 mm to at most 10 mm.

4. The method for producing the polyester resin according to claim 1 , wherein the heat treatment is conducted at a temperature of from at least 120° C. to at most 245° C.

5. The method for producing the polyester resin according to claim 1 , wherein the heat treatment comprises a crystallization step, thereby yielding crystallized polyester prepolymer particles with a surface-crystallized layer having a thickness of from at least 15 μm to at most 110 μm and with an intrinsic viscosity of from at least 0.10 dL/g to at most 1.0 dL/g.

6. The method for producing the polyester resin according to claim 1 , wherein the heat treatment comprises a solid-phase polycondensation step, thereby yielding polyester resin particles with a surface-crystallized layer having a thickness of from at least 15 μm to at most 110 μm and with an intrinsic viscosity of from at least 0.60 dL/g to at most 1.5 dL/g.

7. The method for producing the polyester resin according to claim 1 , wherein the heat treatment comprises a crystallization step and a solidphase polycondensation step in this order.

8. The method for producing the polyester resin according to claim 7 , wherein the crystallization step yields crystallized polyester prepolymer particles with a surface-crystallized layer having a thickness of from at least 15 μm to at most 110 μm and with an intrinsic viscosity of from at least 0.10 dL/g to at most 0.40 dL/g, and wherein the solid-phase polycondensation step yields polyester resin particles with a surface-crystallized layer having a thickness of from at least 15 μm to at most 110 μm and with an intrinsic viscosity of from at least 0.60 dL/g to at most 1.5 dL/g.

9. The method for producing the polyester resin according to claim 8 , wherein a terminal carboxyl group concentration of the polyester prepolymer particles is at most 50 eq/ton.