Study on rough‐surface biaxially oriented polypropylene film. II. Influence of stretching conditions

The production of rough‐surface biaxially oriented polypropylene film (BOP) has been studied by means of casting a polypropylene which contained γ‐quinacridone, a β‐crystal nucleator, with a T‐die extruder into a sheet which has subsequently 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. For roughening of BOP using β‐form crystals in a successively stretching tenter method, it is preferable to roughen in the MD‐stretching process, with suppression of the recrystallization into the α crystals after melting of the β crystals being the most important objective. By rapid heating of a cast sheet in the MD‐stretching process, a rough‐surface BOP with a crater‐like roughness was obtained. Theoretical proof for the effectiveness of the rapid heating in the MD‐stretching process was obtained from experiments on the melt‐transformation of the β crystals by differential scanning calorimetry (DSC) measurements.