Effects of pitch length of perforation on the crease bending characteristics of a polypropylene sheet subjected to indentation of a perforation blade

This study reveals the bending formability of a polypropylene (PP) sheet indented by a perforation blade when changing the pitch of the dashed-ruled line and the indentation depth. Creasing is a folding method of a carton sheet in which a score (called as a ruled line) is made at the bent portion. When making a creased line on a resin sheet, the scored sheet thickness decreases by applying half cutting or creasing (pressing) at the bent portion to make it easier to fold. To smoothly process a folding line on the resin sheet, a dashed line using a perforation blade is sometimes considered. The pitch length of the dashed line, and its nicked (uncut) length, affect the crease bending characteristics of the resin sheet scored by the perforation blade. However, only a limited number of studies have analyzed the dashed line bending moment response. In this study, to clarify the bending formability of a 0.5-mm-thick PP sheet indented by a developed perforation blade, first, the influence of the perforation pitch length on the crease bending characteristics of a scored PP sheet was investigated from a 0.5-mm fine pitch up to an 8-mm commercially sold pitch with a cutting-to-pitch length ratio of 50%. Second, the nicked zone depth against the cutting tip was set as 50% of the 0.5-mm thickness of the PP sheet. Furthermore, it was revealed that burrs (wedged bottom) in the cut part of the perforated (dashed) line affected the bending moment resistance in the folding process of the scored PP sheet, when changing the indentation depth of the perforation blade.