Patent ID: 7122241

Claim:
A biaxially oriented polyester film having (i) a Young's modulus in a longitudinal direction of 8 to 12 GPa, (ii) a Young's modulus in a transverse direction of 6.5 to 9 GPa, (iii) a temperature expansion coefficient in the transverse direction (αt) of −5×10 −6 /° C. to +12×10 −6 /° C., (iv) a humidity expansion coefficient in the transverse direction (αh) of +6×10 −6 /% RH to +12×10 −6 /% RH and (v) a thermal shrinkage factor at 105° C. in the transverse direction of 0 to +1.5% and comprising (vi) ethylene-2,6-naphthalene dicarboxylate in an amount of at least 95 mol % of the total of all the recurring units.