Study on rough-surface biaxially oriented polypropylene film. IV. Influence of addition of crystal nucleator

In the roughening of biaxially oriented polypropylene film (BOP) by utilizing β‐form crystals in a successively stretching tenter method, the influence of an α‐crystal or β‐crystal nucleator added to base polypropylene (PP) during roughening of BOP has been studied. Rough‐surface BOPs were made from homoisotactic PPs which had a melt flow index (MFI) of 8.5 dg/min and contained the α or β nucleator at levels of 0‐10 ppm. The β crystals formed in cast sheets and the roughness of the BOPs was analyzed. Degree of roughness and the diameter of craters on BOP decreased with increasing α‐ or β‐nucleator content. This stems from the fact that the diameter of the β spherulites formed in the cast sheet decreases with increasing nucleator content. In the cases of nucleator content below 1 ppm, the diameter of the β spherulites in the cast sheet did not change significantly, and the decrease in diameter of the BOP craters was small. On the other hand, the degree of roughness of the BOP dropped significantly when nucleator content was above 10 ppm. Accordingly, a nucleator content of about 1 ppm is suitable for the roughening of BOP for both the α and β nucleators.