Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

Sheets were cast by extruding polypropylenes (PP) which contained γ‐quinacridone, a β‐crystal nucleator, at levels of 0–10 ppm using a 30 mm ϕ extruder with a T‐die at extrusion temperatures of 200–260°C and chill roll temperatures of 30–90°C. The influences of raw resin characteristics such as γ‐quinacridone content and MFI of the base PP and casting conditions such as extrusion temperature and chill roll temperature on the amount of β‐crystals formed in the sheet were studied. The amount of the β‐crystals formed was larger as the γ‐quinacridone content was higher and the extrusion temperature was lower and almost independent of the chill roll temperature. As for the influence of MFI of the base PP, the amount of the β‐crystals formed was maximum at MFI ≑ 8 dg/min.