BIAXIALLY STRETCHING TUBULAR POLYETHYLENE TEREPHTHALATE FILMS

摘要

An improved simultaneous biaxial stretching process for polyethylene terephthalate is provided by observing the following factors: the nonstretched film has a crystallinity of below 18%; the length of the stretching zone is 1 to 1.5 times the maximum expansion diameter; the film in the initial one-third of the stretching zone is kept at 83 DEG - 108 DEG C; and the temperature is smoothly and continuously lowered over the remaining two-thirds of the stretching zone so the film temperature at the stretching end point is at 70 DEG - 78 DEG C.