Shrinkable copolyester film

Claim 1

A shrinkable copolyester film comprising a copolyester derived from 50 to 99 mol %, based on the total mole of acids, of terephthalic acid, 1 to 25 mol %, based on the total mole of acids, of an aliphatic dicarboxylic acid selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and 1,10-decanedicarboxylic acid, 0 to 30 mol %, based on total mole of acids, of an aromatic dicarboxylic acid selected from the group consisting of phthalic acid, isophthalic acid, naphthalenedicarboxylic acid and diphenyl ether dicarboxylic acid, 70 to 100 mol %, based on the total mole of diols, of ethylene glycol and 0 to 30 mol % of a diol selected from the group consisting of neopentyl glycol, propylene glycol, 1,4-butanediol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, polyalkylene glycol and 1,4-cyclohexane dimethanol, the shrinkage of the film in the direction of either the machine direction or the transverse direction (main shrink direction) after 5 min treatment in an air oven at 100° C. being not less than 30%; the shrinkage of the film in the other direction perpendicular to said main shrink direction after 5 min treatment in an air oven at 100° C. being not more than 20%; the initial shrinkage stress (F 0 ) of the film in the main shrink direction being not more than 2000 g/mm 2 during the course of 5 sec after dipped in a silicone oil at 75° C.; the shrinkage stress (F 20 ) of the film in the main shrink direction after 20 sec dipping in a silicone oil at 75° C. being not less than (F 0 -100) g/mm 2 ; and the glass transition temperature of the film being 35° to 65° C.