Patent ID: 6890471
Filing Date: 2005-05-10
Classification: B29C,B29K,C08J,G11B,Y10S,Y10T

Abstract:
1. A process for producing a biaxially oriented polyester film, comprising the steps of: (1) stretching an unstretched film of a polyester which comprises ethylene-2,6-naphthalene dicarboxylate in an amount of at least 95 mol % of the total of all the recurring units to 4.5 to 7.0 times in a machine direction at a temperature of 100 to 190° C. to form a uniaxially oriented film; and (2) stretching this uniaxially oriented film to 3.0 to 6.0 times in a transverse direction at a temperature of 110 to 170° C. while raising the temperature in the traveling direction of the film and then stretching the film to 1.05 to 1.5 times in the transverse direction at a lower draw rate than the first stretching in the transverse direction at a temperature from the final temperature of the first transverse stretching to 240° C. while raising the temperature in the traveling direction of the film to form a biaxially oriented film having (i) a Young's modulus in the longitudinal direction of 8 GPa or more, (ii) a Young's modulus in the transverse direction of 6 GPa or more, (iii) a temperature expansion coefficient (αt) in the transverse direction of −5×10