STUDY ON ROUGH-SURFACE BIAXIALLY ORIENTED POLYPROPYLENE FILM .3. INFLUENCE OF MFI OF BASE RESIN

The influences of melt flow index (MFI) of base polypropylene (PP) and machine and transverse direction stretching conditions on the roughening of BOP have been studied. Rough-surface BOPs were obtained by casting homoisotactic PPs, having MFIs of 1. 3-9. 8 dg/min and containing no beta -crystal nucleator, with a T-die extruder into sheets which subsequently have been stretched successively in the machine direction (MD) and the transverse direction (TD) with a roll-type stretching machine and a pantograph-type stretching machine, respectively. The level of beta -crystal content in the cast sheet was maximum when a PP with MFI equals 8 dg/min was used as a raw material and the obtained roughness state of the BOP was the best.