Biaxially stretched polyester film with high cyclohexane dimethanol content and a secondary diol content and a primary and secondary dicarboxylic acid content and method for producing same and use of same

摘要

Biaxially stretched film (1) comprises polyester, whose diol component (at least 35 mole%) is made of 1,4-cyclohexanedimethanol and at least one further diol that is different from CHDM, and dicarboxylic acid component (at least 80 mole%) is made of benzene dicarboxylic acid and/or naphthalene dicarboxylic acid. The dicarboxylic acid component comprises main dicarboxylic acid component (at least 55 mole%) comprising 2,6-naphthalenedicarboxylic acid or terephthalic acid, and secondary dicarboxylic acid component (at least 5 mole%) that is different from main dicarboxylic acid component. Independent claims are also included for: (1) a biaxially oriented polyester film exhibiting (A) a modulus of elasticity of greater than 1500 N/mm 2>in each film direction, and a modulus of elasticity of greater than 7000 N/mm 2>in any film direction, (B) a F-5 value (force at 5% elongation) of greater than 40 N/mm 2>in each film direction, a force at 5% elongation of greater than 180 N/mm 2>in any film direction, (C) an elongation at break of greater than 20% in each film direction, (D) a shrinkage at 150[deg] C (15 minutes) of less than 3% in both film directions, and a shrinkage at 150[deg] C (15 minutes) of less than -1% (equivalent to 1% elongation) in any film direction, (E) a dielectric strength (at 50 Hz, 21[deg] C and relative humidity of 50 measured in air) of at least 40 V/mu and a partial discharge resistance (PDV) (measured in [V]) of x [V/mu m]x film thickness [mu m]+ y[v], where x is greater than 0.75 [V/mu m]and y is greater than 100 [V], and (F) a standard viscosity (SV) degradation rate of greater than -3 SV-E/hour, where SV-E is SV unit; and (2) producing the film, comprises extruding at least one identical or different polymer melts through a flat die, withdrawing and quenching for solidification on at least one roll of a substantially amorphous pre-film, reheating and biaxially stretching (orienting) the pre-film, and thermosetting and unrolling the biaxially stretched film.