STUDY ON ROUGH-SURFACE BIAXIALLY ORIENTED POLYPROPYLENE FILM .6. ROUGHENING BY LAMINATED CAST SHEET

When the roughening of biaxially oriented polypropylene film (BOP) is performed by forming beta crystals in a monolayer cast sheet, occasionally voids are formed in the BOP. In order to prevent this and to roughen both sides of the BOP, rough-surface BOPs were obtained by casting two-resin, three-layer sheets consisting of two surface layers with a high-melt flow index (MFI) polypropylene (PP) and a core layer with a low-MFI PP, by stretching the cast sheets five times in the machine direction (MD) with a roll-type stretching machine, and by stretching the MD-stretched sheets 10 times in the transverse direction (TD) with a pantograph-type stretching machine.