Study on rough‐surface biaxially oriented polypropylene film. V. Analysis and control of roughness

In the previous papers, the roughening of biaxially oriented polypropylene film (BOP) by utilizing β‐form crystals in a successively stretching tenter method has been studied, and BOPs with various roughness have been obtained. In the present paper, the results obtained in the previous studies have been summarized. The roughness can quantitatively be represented by average roughness Ra (depth of roughness) and roughness period L (density of roughness). Ra and L can largely be changed by changing machine direction (MD)‐stretching temperature and the melt flow index (MFI) of base polypropylene (PP), respectively. Furthermore, a BOP with a low roughness period (high density of roughness) can be obtained by adding crystal nucleators to the base PP.