Development of a 4-point bending test to characterize creases on paperboard and packaging material

Abstract: During the manufacturing of a paperboard-based package, the material is in one step folded to obtain the desired shape of the end product. Prior to this step, the material undergoes another processing step, creasing, in which the material is damaged along the folding lines. The result of the creasing process is that the material delaminates which, in turn, causes the material to fold in smooth lines without any wrinkles or cracks along the edge. The strength of the crease can be measured to ensure the creasing has been done correct. This thesis will focus on developing a new method for evaluating creases using four-point bending, as the current method has flaws in that it is operator dependent and the bending is not taking place under ideal conditions. The first part of the thesis will focus on investigating the effect of different parameters and based on this suggest a new method for measuring the strength of the crease. The second part will focus on comparing the same suggested method to the current one and the first iteration of the four-point bending method used at Tetra Pak. Among the parameters tested, the parameters that significantly affected the maximum force registered during the bending was the different materials, the stiffness/thickness of the sample, MD or CD direction, if the bend was performed inside to inside or outside to outside and in the case of a thick material the position of the crease between the loading pins. The time it took to perform the measurements were fastest using the suggested method. The value of the strength of the crease was however significantly