Control of well‐defined crater structures on the surface of biaxially oriented polypropylene film by adding nucleators

While it is common to add anti‐blocking agents to biaxially oriented polypropylene (BOPP) films for general use in order to prevent blocking against each other, the technology of crater‐like film surface roughness formed on the BOPP films without any additives is well known in the industrial BOPP film areas. Numerous studies have been reported on the crater‐like film surface roughness on the BOPP films since the 1980s, but its formation mechanism and the controlling method of the crater‐like film surface roughness are yet to be clarified. In our previous reports, we presented a new hypothesis of crater formation mechanism from a new point of view on sheet morphology and crater shape on the BOPP film surface. It was strongly influenced by the crystal grain shape in the surface layer of PP sheet. In this report, it was clarified that a nucleator has a big influence on the formation of the crystal grains in the surface layer of PP sheets and on the formation of craters. In addition, craters did not form on the BOPP films stretched from the sheet of which the skin layer with crystal grain was shaved, even though β crystal still remained. It was clarified that the crystal grain is trans‐crystal from the observation using TEM. Therefore, it is concluded that the existence of β crystals in the surface layer of PP sheets is not essential in order to produce craters on BOPP films, but trans‐crystals are necessary to form the craters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3555–3564, 2013