| abstract |
Provided is a polyester film excellent in productivity, capable of maintaining durability even under conditions of high temperature and high humidity, and capable of suppressing thickness defects, breakage, defects in the film, and the like in the film forming step, and a production method thereof. Wherein the polyester resin constituting the film has an intrinsic viscosity (IV) of 0.65 or more and 0.80 or less and a terminal carboxyl group amount of 20 equivalents / t or less, a diethylene glycol content of 0.9 mass% or more and 3.0 mass% or less, and an average ultrasonic wave velocity of the film of 2.20 km / sec or more. |