Patent ID: 7115320

Claim:
A polyester film comprising a polyester resin containing an ethylene terephthalate component, a butylene terephthalate component, and a polyoxyalkylene glycol component, wherein the polyester resin comprises a polyester mainly composed of a repeating unit comprising ethylene terephthalate; a polyester mainly composed of a repeating unit comprising butylene terephthalate; and a block copolymer constituted of poly(ethylene terephthalate) or poly (butylene terephthalate) and a polyester of the polyoxyalkylene glycol and a dicarboxylic acid component; and wherein the content of the ethylene terephthalate component is in the range of 60% to 90% by weight relative to the total amount of the ethylene terephthalate component, the butylene terephthalate component, and the polyoxyalkylene glycol component, the content of the butylene terephthalate component is in the range of 10% to 40% by weight relative to the total amount of the ethylene terephthalate component, the butylene terephthalate component, and the polyoxyalkylene glycol component, and the content of the polyoxyalkylene glycol component is in the range of 0.1% to 5% by weight relative to of the total amount of the ethylene terephthalate component, the butylene terephthalate component, and the polyoxyalkylene glycol component.