PROCESS FOR THE PRODUCTION OF FLAT THERMOPLASTIC SHEETS HAVING IMPROVED DIMENSIONAL STABILITY

摘要

ABSTRACT OF THE DISCLOSUREDisclosed is a process for the production ofbiaxially stretched flat sheets of thermoplastic materialof improved dimensional stability, comprising the stepsof: extruding the thermoplastic material from a slot dieto form a sheet; cooling the extruded sheet to form apre-film; heating the pre-film to an appropriate stretchingtemperature; stretching the heated pre-film in orthogonaldirections to form a stretched film; heat-setting thestretched film; cooling the heat-set film; and duringthe cooling step guiding the film in such a manner thatit converges in at least one of the transverse andlongitudinal directions.