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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 T₁ in a first heating zone such that (T_M−T₁ is in the range of from 5 to 30° C., and then raising the temperature of the film to a temperature T₂ in a second heating zone such that (T_M−T₂ is in the range of from 0 to 10° C., wherein T_M is the peak melting temperature of the polymeric film; wherein T₂ is greater than T₁; and wherein the times which a transverse section of the film spends in the first and second heating zones are defined by t₁ and t₂, respectively, such that the ratio of t₁ to t₂ 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/mm² in the machine direction and 2.5 to 17 kgf/mm² in the transverse direction.

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First Claim