Effects of folding numbers, scoring depth and bending velocity on bending-moment relaxation of creased paperboard

Abstract

This work deals with the time-dependent creasing characteristics of coated paperboard. The correlation between the bending strength (resistance) and time-dependent problems on the actual processing phenomenon has not been sufficiently discussed in the past. In this study, therefore, a prototype testing apparatus has been applied to investigate about the dynamic relaxation of bending moment. In order to reveal the relaxation characteristics of the bending resistance during the folding motion from an initial position up to a specified tracking angle, a white-coated paperboard of 0.3 mm thickness was scored with a creasing rule and then the bending test was carried out by varying the number of folding repetitions. Through this work, the followings were obtained: (1) The relaxation of the bending resistance was characterized by an exponential coefficient which was independent to the nominal shear strain while it varied with respect to the number of folding repetitions; (2) The relaxation coefficients of logarithmic approximation with the elapsed time are linearly characterized by the nominal shear strain and the number of folding repetitions; (3) The relaxation depends on the bending velocity.