Effect of perforations on the loss of corrugated cardboard bending stiffness

Bending stiffness of corrugated cardboard is a structural property that gives rigidity and strength. It depends on macroscopic structure of cardboard, different layers and thickness. The structure of corrugated cardboard used for secondary Shelf Ready Packaging (SRP) is weakened by perforations. Perforations serve as separation line used for converting SRP into the shelf-ready tray. The aim of this paper is to analyse the change of corrugated cardboard bending stiffness under the influence of perforations. The focus is on determining which of the explanatory variables affect the corrugated cardboard bending stiffness the most. The explanatory variables are: Type of perforation, Angle of perforation position and Quality of perforated corrugated cardboard. They are used to explain the variability in a measured property. The specimens with and without perforations were prepared using die cutter with machine-made knives. Three types of perforations (labelled: 1/1, 2/1 and 3/1 with the differences in the ratio of cut to uncut part) were positioned in five defined angles (0°, 20°, 45°, 70°, and 90°, where 0° represents Machine Direction, MD) and tested on three different quality of three-layer Eflute corrugated cardboard. Three-point bending tests were carried out using Instron tensile tester in order to observe the behavior of perforated specimens. Statistical analysis was performed to quantify the effect of perforation variables on the change of corrugated cardboard bending stiffness. The analysis showed that the explanatory variable Angle of perforation position was the most influential and provided the most significant information to explain the variability on the loss of corrugated cardboard bending stiffness. The trend in the measured values between all qualities of corrugated cardboard was obvious: the values decrease as the angle of perforation position increases; therefore, the highest values were for angle 0° and the lowest for angle 90°. A quantitative but not qualitative interaction between Quality and Perforation variables appeared. Hence, the “non-perforation – perforation” relationship was qualitatively always the same, although numerically it appeared somewhat different at different cardboard quality. The lowest loss of bending stiffness in the measured values was observed for the perforation type with the same ratio of cut and uncut part (labelled 1/1).