| abstract |
The film showing a heat shrinkage of 0 to 2.0% at 100 to 220 DEG C, useful as a base layer for magnetic tape, comprises a paraphenylene sulfide block copolymer essentially composed of recurring units (A): <IMAGE> and recurring units (B): the molar fraction of recurring units (A) being from 0.50 to 0.98, and having a melt viscosity (???*) of from 1,000 to 15,000 poises as measured at 310 DEG C and shear rate of 200 sec<-1>, a glass transition temperature (Tg) of from 20 to 80 DEG C, a crystalline melting point (Tm) of from 250 to 285 DEG C and a crystallization index (Ci) of from 15 to 45 (measured with non-stretched heat-treated polymer film). The film is produced by forming, cooling, stretching and heat setting at 250-275 DEG C as further defined by 200 + 15 log ??????THS???182.5 + 22.5 log ??? where THS is the heat setting temperature and ??? is the melt viscosity at 310 DEG C and a shear rate of 200 sec<-1>. |