Patent ID: 8512833

Claim:
A heat-shrinkable polyester film having a heat-shrinkage of 20% or more in both the longitudinal and transverse directions when treated with 80° C. water for 30 seconds, and a bidirectional balance parameter A of formula (I) in the range 1.16 to 1.19: A =( M D −M S )/( T D −T S ) (1) in which, A is the bidirectional balance parameter; M D and T D are elongations (%) at break in the longitudinal and transverse directions, respectively; M S and T S are strengths (kg/mm 2 ) at break in the longitudinal and transverse directions, respectively, A being calculated with the numerical values of M D , M S , T D , and T S as defined above, disregarding the units thereof, wherein the heat-shrinkable polyester film is drawn in both the longitudinal and transverse directions at a drawing ratio of 2.5 to 4.5, the difference of the drawing ratios in the longitudinal and transverse directions is 1.0 or less, and the heat-shrinkable polyester film is (i) drawn in the longitudinal direction, (ii) drawn in the transverse direction, and (iii) further drawn in the transverse direction after being passed through a neutral section.