| 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 T 1 in a first heating zone such that (T M -T 1 ) is in the range of from 5 to 30° C., and then raising the temperature of the film to a temperature T 2 in a second heating zone such that (T M -T 2 is in the range of from 0 to 10° C., wherein T M is the peak melting temperature of the polymeric film; wherein T 2 is greater than T 1 ; and wherein the times which a transverse section of the film spends in the first and second heating zones are defined by t 1 and t 2 , respectively, such that the ratio of t 1 to t 2 is 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/mm 2 in the machine direction and 2.5 to 17 kgf/mm 2 in the transverse direction. |