| abstract |
The copolyester in a copolyester film comprises, as dicarboxylic acid component, 80 to 97 mole percent of terephthalic acid and 3 to 20 mole percent of isophthalic acid' and, as diol component, 60 to 85 mole percent of 1, 4-butanediol and 15 to 40 mole percent of diethylene glycol. The copolyester has a reduced viscosity in the range of 0.8 to 1.4 dl/g and a melting point in the range 160to 200°C; and the film has a heat of crystal fusion in the range 5 to 10 cal/g, a haze value in the range 5 to 35 percent, and an initial Young's ; modulus in the range 3 x 10 3 kg/cm 2 to high-speed bonding characteristics, durability and high bond strength with respect to substrates. |