| abstract |
A polyester film containing a polyester (A) mainly composed of polybutylene terephthalate and a polyester (B) mainly composed of polyethylene terephthalate, wherein the mass ratio (A / B) of the polyester (A) and (B) is 70. It is / 30 to 55/45, and the dry heat shrinkage rate (A) by heat treatment at 160 ° C. for 30 minutes in all four directions (0 °, 45 °, 90 °, 135 °) of the film surface is 20% or less. The difference between the maximum value and the minimum value of these dry heat shrinkage rates is 5% or less, and the dry heat shrinkage rate (B) by heat treatment at 200 ° C. for 15 minutes in the above four directions is 35% or less. The polyester film is characterized in that the difference between the maximum value and the minimum value of these dry heat shrinkage rates is 5% or less, and the thickness unevenness in the four directions is 10% or less. |