| 摘要 |
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 (TM-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 (TM-T2 is in the range of from 0 to 10° C., wherein TM 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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