TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The half-value width of the crystallization temperature on cooling is 25-40 degrees C (preferably 30-37 degrees C). The crystallization temperature on cooling is 160-220 degrees C. The cooling involves cooling the melt-extruded polyester using a cooling cast drum and peeling the cooled polyester from the cooling cast drum when the surface temperature of the cooled polyester is a temperature satisfying the equation as given in the specification. The peeling of the cooled polyester from the cooling cast drum is carried out using a peeling roll which is disposed opposite to the cooling cast drum and has a roll diameter satisfying the equation (II) (where (II) is D1/D2 is less than 7, D1 represents a roll diameter of the cooling cast drum and D2 represents a roll diameter of the peeling roll). The melt-extruding involves adding at least one terminal sealing agent (0.1-5% mass) selected from an oxazoline compound, carbodiimide compound and an epoxide compound, with respect to a total mass of the polyester. Preferred Components: The polyester has an intrinsic viscosity of 0.7-0.9. The polyester comprises a polyfunctional monomer (0.005-2.5% mole) in which a total (a+b) of a carboxylic group number (a) and a hydroxyl group number (b) is greater than or equal to 3. The polyester comprises catalyst-derived titanium atoms (preferably organic chelated titanium complex). EXAMPLE - A polyester (titanium (Ti) catalyst-based polyethylene terephthalate (PET)) was prepared by reacting pure terephthalic acid (4.7 tons) with ethylene glycol (1.8 tons), followed by evaporation of water and esterification, and condensation polymerization under reduced pressure. The raw material polyester was dried to a moisture content of less than or equal to 20 parts per million (ppm) and introduced into a hopper of a monoaxial kneading extruder having a diameter of 50 mm. The raw material polyester was melted at 280 degrees C and extruded from a die through a gear pump and a filter (pore diameter: 20 mu m), under the following extrusion conditions. In addition, dimensions of slits of the die were adjusted such that the thickness of a polyester sheet was 4 mm. The extrusion conditions of a molten resin were: pressure change of 1% and a temperature distribution of a molten resin of 2%. The molten resin was extruded from a die. Specifically, a back pressure was pressurized 1% higher relative to an average pressure in the barrel of the extruder, and the piping temperature of the extruder was heated to a temperature 2% higher than an average temperature in the barrel of the extruder. A resin (10 mg) was sampled from the molten resin extruded from a die, and a crystallization temperature on cooling (Tc) and the half-value width of a crystallization temperature on cooling (Tc) were measured. The Tc was 180 degrees C and the half-value width of Tc was 35 degrees C. The molten resin was extruded on a cooling cast drum and was brought into close contact with the cooling cast drum using an electrostatic application method. For cooling of the molten resin, the temperature of the cooling cast drum was set to 25 degrees C, and cold air at 25 degrees C was ejected to the molten resin at an air velocity of 60 m/second from a cold air generator provided opposite to the cooling cast drum, and the surface temperature of polyester was lowered at a cooling rate of 450 degrees C/minute. When the cooled polyester reached the surface temperature (TL) of 70 degrees C, the polyester was peeled from the cooling cast drum, using a peeling roll disposed opposite to the cooling cast drum. The peeling roll used was a roll which had a dimension of D1/D2 of 6.3 when a roll diameter of the cooling cast drum was taken as D1 and a roll diameter of the peeling roll was taken as D2. In this manner, a polyester sheet having a thickness of 4 mm was obtained.