Process for the production of brittle polymeric film

Abstract

A process for the production of a polymeric film comprising a copolyester having an acid component and a diol component, said acid component comprising a dicarboxylic acid and a sulfomonomer containing a sulfonate group attached to the aromatic nucleus of an aromatic dicarboxylic acid, said process comprising the steps of: (i) melt-extruding a layer of said copolyester; (ii) stretching the extrudate in at least one direction; (iii) heat-setting the film by raising the temperature of the stretched film to a temperature Tin a first heating zone such that (T-T) is in the range of from 5 to 30° C., and then raising the temperature of the film to a temperature Tin a second heating zone such that (T-Tis in the range of from 0 to 10° C., wherein Tis the peak melting temperature of the polymeric film; wherein Tis greater than T; and wherein the times which a transverse section of the film spends in the first and second heating zones are defined by tand t, respectively, such that the ratio of tto tis at least 2:1; and a polymeric film obtainable thereby having an ultimate tensile strength at destruction in the range of 2 to 15 kgf/mmin the machine direction and 2.5 to 17 kgf/mmin the transverse direction.